# Number of photons in universe? I'll take number from a star in unit time and extrapolate

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I'll take number per average star, multiple by appropriate numbers , star/Galaxy, galaxies/universe, 14 billion years, and try to figure their location.

I was looking for a rough number and a distribution function.

Extending Zephyrs comment as community wiki

See https://physics.stackexchange.com/questions/196366/number-density-of-cmb-photons

In this response, the number of photons per cubic meter is estimated as $n_lambda = 10^8$. Since the observable universe has a volume of the order $10^{80} m^3$, there are about $10^{88}$ photons in the observable universe.

## ASTR 160: Frontiers and Controversies in Astrophysics

### Overview

Class begins with a review of the mysterious nature of dark matter, which accounts for three quarters of the universe. Different models of the universe are graphed. The nature, frequency, and duration of supernovae are then addressed. Professor Bailyn presents data from the Supernova Cosmology Project and pictures of supernovae taken by the Hubble Space Telescope. The discovery of dark energy is revisited and the density of dark energy is calculated. The Big Rip is presented as an alternative hypothesis for the fate of the universe.

## First time stargazing (ever) with an XT10. Observations, thoughts, questions.

Re: tedious adapter switching — (along with just plain old tedious eyepiece switching) that’s why I just use a zoom.

It does make finding things a bit harder though as the field of view with a zoom is narrower than typical fixed length eyepieces on the longer focal length side of things.

Which brings up that M3, while a good target and hardly impossible to find, isn’t actually the easiest of targets to start on due to its being a bit far from any nearby bright star. M13, which comes up a bit later (but earlier and earlier as we progress into summer), is a better one to start on being that you really can see it in a finder scope and it is right near a defining star of "the keystone" in the Hercules constellation.

Moonlight definitely has a degrading effect on DSOs, and for now we’re heading towards a full Moon. You’ll learn to look forward to Moonless nights (or at least hours). Fortunately the planets Jupiter and Saturn (as well as Venus) will be coming around in the months ahead, and they don’t require such dark skies or avoidance of moonlight, so the situation will get better.

Keep at it — you already found M3 on your first go, it sounds like you’ve done your homework, and you already have some practical lessons learned (bug spray). You’re doing great!

I've done about 9 months of research!

I'll look for M13. I've read somewhere that Magnitude is not the end all be all of how easy something is to view. Surface Brightness is what you should really be looking at when exploring extended objects. I do lighting for a living so I'm familiar with the terminology, but am having trouble understanding how Magnitude and Surface Brightness relate. Is surface brightness also interchangeable with apparent magnitude?

What is contrast index? It's the next line down when looking at an object in Stellarium.

### #27 aram12

It takes time to learn the sky and all of the intricacies of astronomy. I was out last night in NJ as well in my B7-8 backyard. The moon definitely washes out the darkness, but the seeing was better last night than it has been in a while so it’s just good to get out to learn more. Where in NJ did you go for bortle 4? I know there are a few areas.

NW Jersey. All along the border. Specfically Stokes State Forest.

### #28 aram12

Your best views of deep sky objects will be in dark skies with dark adapted eyes. The light from the moon (or other nearby lights) will make it harder for your eyes to fully adapt and be able to see the faint objects in the sky. The moon also makes the background sky lighter so there won't be as much contrast between the black background of empty space and the stars/nebula, etc of the object you are looking at. Using averted vision will help see more since the rods in the periphery of your retina are able to detect faint light better than the cones in the center of your retina. When looking at globulars and nebulae I tend to look right, left, up, down around the object rather than directly at it and over time I'm able to see more and more detail. So best bet is to view those objects when the moon isn't out and you've given yourself time to dark adapt. You may also consider a zoom eyepiece. Field of view changes as you zoom in and out but if you are ok with tracking, you can quickly dial in the magnification without having change out an eyepiece, making it less likely that you will lose the object in the meantime.

Averted vision. Cool. Did not know about that.

It was certainly difficult to keep my eyes dark adapted, even with an eye patch.

I'll consider a zoom, for sure.

### #29 aram12

Don't give up on m3! I also recently got my first scope, 10" gso dob and have observed m3 several times from my front lawn (bortle 8ish soup). It will look like a fuzzy ball until you hit about 125x. Try it again from your house with the 10mm, it should start to resolve around that magnification. It will really start "popping" at about 150x with stars twinkling in & out of resolution like little diamonds. I also have a difficult time star hopping to this target and find it easier if I make the hop a few times through binoculars to get my path down. It sounds like you could also use a magnified finder scope because it's almost impossible for me to star hop with just a red dot in my extremely bright skies and it makes it a lot easier to re-center targets after changing eyepieces. I bought a dual finder bracket off Amazon to mount both a finder scope and red dot to my scope with no modifications. Also like others have said give m13 a shot as well it's a lot easier to hop to and seems to resolve a little easier than m3. Good luck and don't give up! The first time you get a glob to resolve you will be wowed.

You saw m3 in Bortle 8? One of the posters above seemed to imply that it was impossible without a 14" aperture in dark skies.

Considering adding a raci and a telrad, lol.

Can't wait to get out there again.

### #30 aeajr

A lot of info to get through so I'll be brief where I can. This will be a bit random.

Orion XT10 Dob with a 28mm 2" and a 10mm Plossl 1.25". Red dot finder.

After doing a ton of research, my Dad and I seem to have found a great place in NJ with Bortle 4 skies.

Last night was average seeing, average transparency, clear skies, almost waxing quarter moon.

This was our first time out in the field, actually paying attention to the sky.

Was surprised that it took so long for the stars to come out. Sunset was at around 8:10. Naked eye viewing didn't really get interesting until about 10:30p.

Spent most of my time trying to find M3. Found it very difficult to star hop. Need practice and more familiarity with the sky. Wondering if getting an even lower power eyepiece would help. The 28mm has a 2.3 degree. um, what do you call that? How much of the actual sky your eyepiece is describing? Also considering a Telrad.

I did eventually find it, I think. My first fuzzy. Didn't look like much. Just a smear. I was expecting a lot more, especially with, for example, descriptions like this.

"You’ll find it 6 degrees north-northeast of Beta Comae and it will show very easily in the finderscope. In binoculars of all sizes and even under urban lighting conditions, Messier 3 is very bright and will begin to show some signs of resolution with larger models, such as 10X50. Even small telescopes will see individual stars come to life and it will explode into a fine, pinpoint mass in telescopes as small as 6″."
-https://www.universe. 1110/messier-3/

Don't quite understand how much the moon degrades views. I've read a bunch of articles on the subject, and assumed that if I wasn't pointing "near" the moon, I'd be able to see the "easier" DSO's in Bortle 4 skies. Again, first time out, so my mileage will vary, obviously. Nothing to compare to, yet.

So I had the fuzzy in my eyepiece and tried to switch to my 10mm Plossl. Discovered that unthreading the 2" adapter and then threading the 1.25" took way longer than I expected. By the time I switched, M3 was gone and I couldn't find it. Went back to the 28mm and spent 10 minutes finding it again.

Congratulations on the new scope. Glad you recognize that you are just getting stared and there is a lot to learn.

It sounds like this is your first telescope and you selected a good one. As you gain experience and add eyepieces you will find your scope will become more effective.

The scope gathers light. It is the eyepieces that provide magnification so you need to learn more about eyepieces. This article is written for beginners so it will help you understand focal length, magnification, apparent field of view, field of view, the use of a Barlow lens and more.

Understanding Telescope Eyepieces- There are recommendations, based on budget,
but the meat of the article is about understanding the considerations and specifications
to know when selecting eyepieces.
https://telescopicwa. cope-eyepieces/

Understanding and using a Barlow Lens
https://telescopicwa. ens-and-how-to/

You say you have a 28 mm 2" and a 10 mm Plossl. I am guessing that the 28 mm is the Orion Deep View, this eyepiece:

The 28 mm Deep View has a 56 degree AFOV (read the article)

In that scope it provides 42.8X and about a 1.3 degree field of view.

You can go lower and wider using a different eyepiece. For example, I have a 38 mm / 70 degree Agena Astro Super Wide Angle eyepiece. This would be the same as the Orion Q70 38 mm but with a different label.

This will provide 31.5X and 2.2 degree field of view which is about as wide as you can go with this scope. The wider field of view will definitely help with finding things in the sky.

An adjustable height chair is extremely valuable and there are other accessories that will add to your enjoyment of your XT10

Understanding what targets to work under what conditions will help you be successful. The Moon is both a wonderful target to observe and a huge source of light pollution. I pick my targets according to conditions. A Bortel 4 rating only applies when there is no Moon.

I would not consider M3 a good first target. Start with things you can see visually and learn to aim the scope and the mechanics of changing eyepieces.

Have you aligned the finder to the telescope? This is best done during the day.

How to Use a Telescope: First Time User’s Guide
https://telescopicwa. ope-user-guide/

With how fast the sky moves, do y'all stick with one size set of eyepieces when viewing a particular target? Thinking of getting a mid power and high power 2". Does that make sense? Or a mid power and low power 1.25" to match with the Plossl?

Or is this 'tedious' adapter switching just something relevant to this scope? Curious.

Also must remember bug spray next time. Holy cow.

Bug spray is an essential astronomy tool.

Yes, you will want to get a variety of eyepieces. However, for first timers I usually recommend a low power wide view eyepiece that will maximize the field of view. That is what the 38 mm Q70 would do.

Then add a zoom eyepiece and a Barlow lens. Be sure to read the articles I posted above so you will understand the language and the use.

A good moderately priced zoom is the Celestron zoom - About \$90

The GSO 2X shorty Barlow teams well with the zoom and gives you 1.5X and 2X options at a low price.

Using these you can have 50X to 300X and every magnification in between. My zoom eyepieces are my most used eyepieces.

It is not unusual to spend more on eyepieces than you spent on the scope, but eyepieces are universal so you can use them in multiple telescopes. I have 6 scopes but I use the same eyepieces in all of them. I just use them differently depending on which scope I am using.

For example, this is the eyepiece set I built up over 4 years and the magnifications they provide in an Orion XT8i. This has the same focal length as your XT10 so the magnifications and field of view would be the same.

Orion XT8i – 8”/203 mm PushTo Dob/Newtonian, 1200 mm FL F5.9
Resolving power - .6 arc Seconds

AA SWA 70 38 mm 31.5 and 2.2 degrees FOV 2”
Meade 82 20 mm 60X and 1.37 degrees 2”

ES 82 14 mm 86X and .95 degrees
ES 82 8.8 mm 136X and .6 degrees
ES 82 6.7 mm 179X and .45 degrees
Meade 82 5.5 mm 218X and .37 degrees
ES 82 6.7+2XB 358X and .22 degrees
Meade 82 5.5+2XB 436X and .18 degrees

Baader Hyperion 8-24 zoom 50X to 150X
Baader Hyperion 8-24+1.5XB 75X to 225X (My most used 1.25” eyepiece in this scope)
Baader Hyperion 8-24+2XB 100X to 300X

You don't have to have this many eyepieces. The bolded ones are the ones I used most often in that scope. The magnifications would be different in my other scopes and the ones I use most would be different in other scopes.

Eyepatch seemed to work well, but the ones we bought have a bit of light leak. Need to be bigger. Also, really hard to train yourself to use them properly.

I feel like I need to make sure my Dob is leveled properly next time so the tilt properly aligns with Altitude and pan with Azimuth.

I really love Stellarium desktop and tried to use the Ios version in the field and it worked ok except that when you search, the keyboard is not red corrected. Ouch.
For next time (at the very least) I'm going to use the custom circle feature to make a ring at 2.3 degrees so I can better understand what I'm looking at through the eyepiece with the 28mm.

Paper maps seem awkward, but printing 'local' target charts seem to be the way many go. Something like what Turn Left does.

tldr: With a 10" reflector under Bortle 4 skies and a quarter moon, is this an expected view of M3?

What is this custom circle feature you mention? Are you talking about Stellarium or are you talking about some feature of a finder scope?

Edited by aeajr, 20 May 2021 - 08:46 AM.

### #31 wrvond

@aram12 - here's what you were seeing:

As you can see, a huge span between sunset, civil sunset, nautical sunset, and astronomical sunset. Ditto for sunrise.

*Information provided by AstroPlanner.

### #32 wrvond

<snip>

What is this custom circle feature you mention?

If you load your telescopes and eyepieces into Stellarium, choosing the ocular view will display a simulation of the view of a given target (in a circle).

### #33 aram12

That doesn't sound like M3 to me. That's one of the biggest and brightest globulars and a 10 inch scope easily resolves it. You will need to increase power to resolve it to stars but it is definitely more than a smudge even at low powers. There is a faint NGC globular close to M3 that would likely appear a faint smudge in a 10 inch. M3 is a showpiece object in a 10 inch scope. M13 and M5 are a little better but not by much.

Yes definitely get a telrad or a rigel quickfinder, It will make aiming the scope and finding objects much easier. The rigel qf will fit between the focuser and finderscope.

Just keep the 10mm in 2-1.25 adapter so it saves time when swapping out your 2" eyepiece. You will probably want to get wider angle eyepieces. They help greatly with a dob. I observed with just 2 eyepieces last Friday, APM 30 UFF for a low power finder and 13 APM XWA for medium/high power in my 16 inch. I was wearing a jacket so I just kept 1 eyepiece in the left pocket and the other in the right. The 13 has a 2 inch adapter already on it so it made switching quick and easy without the object drifting out of view. Are

Are you referring to the Snowglobe Cluster?

Looked at a comparison of telrad to rigel and thinking telrad.

What are your tFov's for those eyepieces? My 28mm gets me 1.3 degrees.

Edited by aram12, 20 May 2021 - 08:43 AM.

### #34 GGK

Definitely considering a Telrad or a Raci.

I really don't understand how a laser helps you. if the laser doesn't 'touch' the star you're trying to aim at, how is it so accurate? People who use Lasers talk about "no more neck strain" so they're obviously not looking down the length of the barrel, parallel with the beam. I can't picture how it helps. I mean, lol, it obviously does because people use them, I just can't wrap my head around it.

+1 for Telrad and RACI. I have both on my C8 SCT. Get close with the Telrad, then get on center with a 9x50 RACI, then move to the eyepiece. One thing I found I must do though is touch-up the RACI alignment before beginning the hunt. It shifts a little during breakdown and set up.

### #35 aram12

Getting use to magnification changes is a key. With Globulars, you want to get to a pretty high magnification to resolve them well. With the 10 inch I like something around 150x-200x. However, the 10mm should do OK at 120x. You may want to consider getting a 7mm with a wider field of view (since you have a manual scope). Doesn't have to be expensive, just a wider field of view around 7mm. Something like this would work: https://agenaastro.c. iece-93430.html

The best thing for finding objects is a 9x50mm finder scope (especially in light pollution). Telrad is good too if you have a pretty dark sky. If you get the Telrad consider getting Telrad charts like these: https://www.sky-spot.com/charts.htm . those will help quite a bit.

I'm still not good at finding objects so don't feel too bad. But the tools above can help quite a bit.

Those charts look great. Kind of a simpler, boiled down Turn Left at Orion.

Yeah, I think eyepiece recommendations should probably be in a separate topic, but that's a good place to start. Thank you!

I have yet to experience my chosen viewing location in true darkness but from what I saw with a quarter moon, I think the telrad will work best but am also considering a raci.

### #36 aeajr

There are many ways to find things in the sky. Star Hopping is only one approach

This is the method I use most of the time.

Using an angle gauge to help find targets – AltAz coordinates
https://www.cloudyni. y/#entry8120838

### #37 aram12

Also wanted to point out that you picked a very good size of scope. I personally find the 10 inch F4.7 newt to be an ideal mix of aperture, but still portable enough and manageable enough. I've had mine for probably 15 years and it's still my most capable scope. Once the Moon goes down, you'll have better luck with the globulars. It's easier to find M13 and it tends to be a better one for beginners.

Where do you view? Always curious when someone has the same scope.

EDIT: meaning quality of sky

Edited by aram12, 20 May 2021 - 08:53 AM.

### #38 aram12

Of course don't forget to look at the Moon with that scope. It's in my opinion the best object in the sky. Just know it will kill your dark adaption for a long timeframe.

And planets in a 10 inch dob are magical. Though a little hard to track at super high powers. I've had crazy good views of Saturn at 300-400x with the 10 inch. Especially when it's a steady and still night.

To get to that magnification, are you using a 3x Barlow?

### #39 aram12

Aram12,

No, if you were in Bortle 4 skies, that's not an expected view of M3 unless you were too early and the moon was close, transparency was bad, or you were pointing over a city.

I use an 8 inch SCT on a tracking GEM and view in Bortle 4 in southwest Florida. I don't know much about Dobs, but know that you have more light gathering capability that me.

Two nights ago I spent 1/2 hour viewing M3. The moon was more than 30 degrees away. At low magnification, M3 does look like a small grayish white fuzzy blob, but individual stars start to show on the outer edges with minor averted vision in my C8 at about 125 power. Seeing was excellent for me two nights ago and I was able to push magnification to 425 before the image started to degrade. I continued to use just slight averted vision, meaning that if I looked directly at a star, it would disappear, but all the stars around it would be in visible. At high magnification M3 has an apparent size in the eyepiece that's very easy to view and is quite a sight.

My location has the advantage with M3 because M3 passes within a few degrees of Zenith, which has the least amount of atmosphere to mess with my view. You might find M13 easier since it is higher in the sky for New Jersey compared to M3.

I star hop even with a C8 SCT and narrow field of view. It just takes practice. When panning, I see most faint objects first with averted vision, so practice helps you learn how to see things. I keep a large list (on paper) of all objects that I should be able to see with my C8 that includes RA and Dec coordinates. I use a Planisphere sometimes, but lately I've been using a phone app to help locate objects. Knowing my local sidereal time, which is simply the right ascension that's directly overhead, I can use RA and Dec coordinates to know where to look for an object. The app will identify the larger objects if I point on them, but at the minimum, I can point to the object RA and Dec location and know what else is in the area.

There are many apps available. I use SkyView. The attached pic is a screenshot from an hour ago showing the location of M3. SkyView will show the object path vs. time which allows me to judge the best viewing time. I use the Sidereal app to know my local sidereal time.

My mount today is GoTo, so some might think I'm odd for manually searching. I learned star hopping with a C8 using a non-GoTo GEM years ago and it was a valuable lesson. I often see other objects right near my target that I would never have know were there if I relied only on the computer to take me to the exact spot.

Regarding viewing time in a non-tracking telescope -- the earth spins 0.25 degrees per minute. When a star is in the middle of a 1 degree field of view, you only have 2 minutes before the star leaves the field.

I wear an eye patch so I can keep both eyes open, but I also wear a very light "bug" jacket with a hood. Keeps the skeeters off of me and blocks light around the eyepiece. This is a must for me when looking for less bright objects in a moonlit sky.

Have fun. It's a great lifelong hobby.

Gary

Close to zenith, not pointing towards moon. Trans was avg.

I must've not been looking at M3. With 10", I should've had a better view than your 8", as you said.

That's neat that SkyView shows the path. I'll have to check it out.

### #40 aram12

Lots of good information for you. I would just add that when the Moon is out. I look at the Moon. If you get a good zoom eyepiece, you can spend some time on it. It takes magnification really well most nights. Half phase or less!

The eyepiece choices are almost endless. Check out that forum and you will see what I mean. Once you get a few really good ones the plossls will likely get put away. Ed Ting of scopereviews.com recommends replacing the same focal lengths you received with the scope. For instance, if you got a cheap 28mm 2" e.p. with the scope, replace it with a 27mm Panoptic (Tele Vue) or a ES 28/68 (Explore Scientific) or another good brand. Build a collection from there. Some choose a high quality zoom to be their workhorse in a minimalist collection. As long as you buy quality it will be fine. You can always buy/sell on the classifieds here. Good luck with your new scope and enjoy your time with your father. Tempus fugit!

Thanks much! I will definitely post in a new topic if I'm looking for specific eyepiece recos. There's TOO much information about ep's!

### #41 therealdmt

I've done about 9 months of research!

I'll look for M13. I've read somewhere that Magnitude is not the end all be all of how easy something is to view. Surface Brightness is what you should really be looking at when exploring extended objects. I do lighting for a living so I'm familiar with the terminology, but am having trouble understanding how Magnitude and Surface Brightness relate. Is surface brightness also interchangeable with apparent magnitude?

Magnitude is basically how bright something is…if it were a single point like a star. Accordingly, it works great for describing how bright stars are! Works reasonably well for planets and moons, too, and also for globular and open clusters (even though they aren’t just points, they’re not so wide, and wide open clusters like say the Hyades are basically just seperate stars). However, "extended objects" (wider things like galaxies and some nebulae that are in no way just a single point) spread that same total magnitude out over a larger area and so any given point within that extended object isn’t as bright as the total integrated magnitude number. This is a bit of a complicated topic, but it perhaps mostly notoriously becomes an issue with galaxies.

"Apparent magnitude" is how bright something apparently is when viewed from Earth (our planet — so this is the one you mostly care about!)

"True magnitude" is how bright something would be if you were up relatively close to it, at some standard distance.

The basic idea is that a semi-bright star that is nearby can look as bright or brighter than a very bright star that is much farther away, so "true magnitude" takes distance into account to tell us how bright something really is. But for our amateur telescope using purposes, except that such things are nice to know/interesting, we don’t care about true magnitude. For star hopping, comparing objects, being prepared for how bright something might appear in the eyepiece, etc., we care about what we can actually see — apparent magnitude.

Well, except for extended objects. Then we might care more about "surface brightness" - how bright something is over a unit of area. Unfortunately, different areas of an extended object can be brighter or dimmer than other areas of the same object, so surface brightness, while useful and which works well for many objects, doesn’t always solve the problem of accurately describing how bright an extended object is. It can take a little knowledge of the object itself and studying reports from other observers to get a good idea of how bright an extended object should appear in your scope.

That said, you have a pretty good sized scope — you should be able to see many, many galaxies, star clusters and nebulae. Just understand that many of them won’t look like the fantastic objects captured by astrophotographers who leave their cameras open for hours in total gathering light, combine a selection of the best resulting images and apply various post processing techniques to enhance the final result. Your own eye only gets to take in photons for a brief period of time before it essentially refreshes — you can’t hold old photons in your eye while waiting for new photons to come in and build up an amazing total image. Nevertheless, the ability to see these objects at all that lie so far, far away in space and time with just a simple 10" mirror-in-a-tube that one can order online is pretty amazing

## The Three Meanings Of E=mc^2, Einstein's Most Famous Equation

Einstein deriving special relativity, for an audience, in 1934.

For hundreds of years, there was an immutable law of physics that was never challenged: that in any reaction occurring in the Universe, mass was conserved. That no matter what you put in, what reacted, and what came out, the sum of what you began with and the sum of what you ended with would be equal. But under the laws of special relativity, mass simply couldn't be the ultimate conserved quantity, since different observers would disagree about what the energy of a system was. Instead, Einstein was able to derive a law that we still use today, governed by one of the simplest but most powerful equations ever to be written down, E = mc 2 .

A nuclear-powered rocket engine, preparing for testing in 1967. This rocket is powered by . [+] Mass/Energy conversion, and E=mc^2.

ECF (Experimental Engine Cold Flow) experimental nuclear rocket engine, NASA, 1967

There are only three parts to Einstein's most famous statement:

1. E, or energy, which is the entirety of one side of the equation, and represents the total energy of the system.
2. m, or mass, which is related to energy by a conversion factor.
3. And c 2, which is the speed of light squared: the right factor we need to make mass and energy equivalent.

Niels Bohr and Albert Einstein, discussing a great many topics in the home of Paul Ehrenfest in . [+] 1925. The Bohr-Einstein debates were one of the most influential occurrences during the development of quantum mechanics. Today, Bohr is best known for his quantum contributions, but Einstein is better-known for his contributions to relativity and mass-energy equivalence.

What this equation means is thoroughly world-changing. As Einstein himself put it:

It followed from the special theory of relativity that mass and energy are both but different manifestations of the same thing — a somewhat unfamiliar conception for the average mind.

Here are the three biggest meanings of that simple equation.

The quarks, antiquarks, and gluons of the standard model have a color charge, in addition to all the . [+] other properties like mass and electric charge. Only the gluons and photons are massless everyone else, even the neutrinos, have a non-zero rest mass.

E. Siegel / Beyond The Galaxy

Even masses at rest have an energy inherent to them. You've learned about all types of energies, including mechanical energy, chemical energy, electrical energy, as well as kinetic energy. These are all energies inherent to moving or reacting objects, and these forms of energy can be used to do work, such as run an engine, power a light bulb, or grind grain into flour. But even plain, old, regular mass at rest has energy inherent to it: a tremendous amount of energy. This carries with it a tremendous implication: that gravitation, which works between any two masses in the Universe in Newton's picture, should also work based off of energy, which is equivalent to mass via E = mc 2 .

The production of matter/antimatter pairs (left) from pure energy is a completely reversible . [+] reaction (right), with matter/antimatter annihilating back to pure energy. This creation-and-annihilation process, which obeys E = mc^2, is the only known way to create and destroy matter or antimatter.

Dmitri Pogosyan / University of Alberta

Mass can be converted into pure energy. This is the second meaning of the equation, where E = mc 2 tells us exactly how much energy you get from converting mass. For every 1 kilogram of mass you turn into energy, you get 9 × 10 16 joules of energy out, which is the equivalent of 21 Megatons of TNT. When we experience a radioactive decay, or a nuclear fission or fusion reaction, the mass of what we started with is greater than the mass we wind up with the law of conservation of mass is invalid. But the amount of the difference is how much energy is released! That's true for everything from decaying uranium to fission bombs to nuclear fusion in the Sun to matter-antimatter annihilation. The amount of mass you destroy becomes energy, and the amount of energy you get is given by E = mc 2 .

The particle tracks emanating from a high energy collision at the LHC in 2014. Composite particles . [+] are broken up into their components and scattered, but new particles are also created from the available energy in the collision.

Energy can be used to make mass out of nothing. except pure energy. The final meaning is the most profound. If you take two billiard balls and smash them together, you get two billiard balls out. If you take a photon and and electron and smash them together, you get a photon and an electron out. But if you smash them together with enough energy, you'll get a photon, and electron, and a new matter-antimatter pair of particles out. In other words, you will have created two new massive particles:

• a matter particle, such as an electron, proton, neutron, etc.,
• and an antimatter particle, such as a positron, antiproton, antineutron, etc.,

whose existence can only arise if you put in enough energy to begin with. This is how particle accelerators, like the LHC at CERN, search for new, unstable, high-energy particles (like the Higgs boson or the top quark) in the first place: by making new particles out of pure energy. The mass you get out comes from the available energy: m = E/c 2 . It also means that if your particle has a finite lifetime, then due to Heisenberg uncertainty, there's an inherent unknowability to its mass, since ∆Et

ħ, and therefore there's a corresponding ∆m from Einstein's equation, too. When physicists talk about a particle's width, this inherent mass uncertainty is what they're talking about.

The warping of spacetime, in the General Relativistic picture, by gravitational masses.

The fact of mass-energy equivalence also led Einstein to his greatest achievement: General Relativity. Imagine that you've got a particle of matter and a particle of antimatter, each with the same rest mass. You can annihilate them, and they'll produce photons of a specific amount of energy, of the exact amount given by E = mc 2 . Now, imagine you had this particle/antiparticle pair moving rapidly, as though they had fallen from outer space, and then annihilated close to the surface of Earth. Those photons would now have extra energy: not just the E from E = mc 2 , but the additional E from the amount of kinetic energy they gained by falling.

If two objects of matter and antimatter at rest annihilate, they produce photons of an extremely . [+] specific energy. If they produce those photons after falling deeper into a gravitational field, the energy should be higher. This means there must be some sort of gravitational redshift/blueshift, the kind not predicted by Newton's gravity, otherwise energy wouldn't be conserved.

Ray Shapp / Mike Luciuk modified by E. Siegel

If we want to conserve energy, we have to understand that gravitational redshift (and blueshift) must be real. Newton's gravity has no way to account for this, but in Einstein's General Relativity, the curvature of space means that falling into a gravitational field makes you gain energy, and climbing out of a gravitational field makes you lose energy. The full and general relationship, then, for any moving object, isn't just E = mc 2 , but that E 2 = m 2 c 4 + p 2 c 2 . (Where p is momentum.) Only by generalizing things to include energy, momentum, and gravity can we truly describe the Universe.

When a quantum of radiation leaves a gravitational field, its frequency must be redshifted to . [+] conserve energy when it falls in, it must be blueshifted. Only if gravitation itself is linked to not only mass but energy, too, does this make sense.

Vlad2i and mapos / English Wikipedia

Einstein's greatest equation, E = mc 2 , is a triumph of the power and simplicity of fundamental physics. Matter has an inherent amount of energy to it, mass can be converted (under the right conditions) to pure energy, and energy can be used to create massive objects that did not exist previously. Thinking about problems in this way enabled us to discover the fundamental particles that make up our Universe, to invent nuclear power and nuclear weapons, and to discover the theory of gravity that describes how every object in the Universe interacts. And the key to figuring the equation out? A humble thought experiment, based on one simple notion: that energy and momentum are both conserved. The rest? It's just an inevitable consequence of the Universe working exactly as it does.

## Is there any universal unit for time that isn't based from our stellar perspective? I know caesium-133 and strontium are used to get extremely accurate measurements but it's only in reference to our solar system.

There is no indication that elements like caesium behave differently outside our solar system, nor is it expected that they are unique to our corner of space. So using this as a basis for the measurement of time should work anywhere and could be communicated with any hypothetical lifeforms weɽ encounter.

Perhaps the question was, is there a way to define time (or space, or velocity) without reference to an observer.

Thanks for answering my question! Would it though? If the aliens we communicate with are constantly moving faster through time, wouldn't our measuments of time vary?

I know this is a silly example but in the movie Interstellar, there is a scene where they visit a planet with such strong gravitational influence from the black hole it orbits that every hour they spend on the surface equates to 7 years I believe in earth time.

While this was a stretch by the director with respect to the scale of the effect, but the principal was correct (to my current and limited understanding of general relativity.)

Wouldn't our observation of the cesium on this imaginary planet be different from an observation made on cesium on earth?

## Talk:Big Bang/Archive 23

Someone should place the new book (published by Springer) Titled "Before the Big Bang" in the proper place near the end of the article. If it's not done by the time I know how, I'll do it.Julzes (talk) 07:48, 29 May 2009 (UTC)

why is "cannot and does not", and "describes and explains", in the second paragraph, in italics?

the emphasis is leaden, and surely redundant?

if this was a less important article, elsewhere, i wouldn't have thought twice about removing those italics, but i'd hate to tread on anyone's toes

Ok, this article is everything about theory except the THEORY ITSELF. I don't want to read through history, observations, or a bunch of Hubble Telescope related stuff. So what I suggest is (1) you smarten up, (2) create a section summarizing what the Big Bang Theory is, and to (3) don't make it over-complicated because as we all know, most of the people who are able to understand such complex words do not go to Wikipedia to look this up - people who look this up are mostly kids, teenagers, and the regular dumb person.--76.239.31.103 (talk) 09:02, 15 August 2009 (UTC)

From the very first paragraph in the article:

As used by cosmologists, the term Big Bang generally refers to the idea that the universe has expanded from a primordial hot and dense initial condition at some finite time in the past, and continues to expand to this day.

As far as I (a non-scientist) am aware, there is some controversy about the big bang theory. Some claim that the theory is dependant on speculation regarding the fabric of space, such as the existence of dark matter and dark energy. A section with the heading "Controversy" could sum up the current doubt that exists within the scientific community with regards to the big bang theory. A clear presentation of scepticism can only add to the credibility of the article. —Preceding unsigned comment added by 84.208.93.198 (talk) 00:27, 6 September 2009 (UTC)

I don't think there really is such a controversy: virtually every practising cosmologist accepts that the theory is 'true' (or rather that it's by far the best model of the universe we currently have, with no serious competitors). The problems of the nature of DM and DE, among others, are already discussed in the article but I wouldn't say the theory is dependant on them. It pre-dates both concepts, and even the more bizarre attempts to explain DM and DE are almost invariably refinements to the Big Bang model rather than alternatives to it. Olaf Davis (talk) 19:10, 6 September 2009 (UTC)

Reading about the development of the universe in the first 10-x seconds, I wonder what definition of "second" can be used in the absence of any structure or periodic events. Can anyone explain? Same holds for the diameters assigned to the unsiverse. Length = time span times velocity of light. 85.176.27.53 (talk) 20:17, 6 September 2009 (UTC) L.K. September 6th, 2009

The diameters assigned to the universe are just for the portion that expanded to be the region we can presently see this doen't imply any actual boundary. Regarding time and distance, the Planck length and Planck time could be considered natural units of distance and time, and do not require external events in order to be defined. I'm not sure why you'd consider time or distance to be undefined in the absence of something to measure, either spacetime itself is still parameterized by them even with nothing in it (and there's actually quite a lot in it, in the early universe). --Christopher Thomas (talk) 21:12, 6 September 2009 (UTC)

In the Article: Big Bang, Section: History, Line: 5 "in contrast to the static Universe model advocated by Einstein" People may be mistaken that Einstein was an advocate of the Static Model of the Universe but he in fact called it his "biggest blunder". Can this be Changed? Thank You Meste (talk) 13:11, 22 September 2009 (UTC) Meste

I have qualified the statement by adding "at that time". Einstein originally believed that any physically meaningful cosmological model must allow for a static universe, but later changed his position. Gandalf61 (talk) 13:34, 22 September 2009 (UTC)

This statement is direct from the article:

"Fred Hoyle is credited with coining the term Big Bang during a 1949 radio broadcast. It is popularly reported that Hoyle intended this to be pejorative, but Hoyle explicitly denied this and said it was just a striking image meant to emphasize the difference between the two theories for radio listeners.[8][9]"

I have examined both sources and nowhere does it validate this claim.

Those sources verify more than one claim in that grouping, but not all. I've added a third source for clarity. — . ^) Paine Ellsworth disscuss (^ `. 05:53, 23 September 2009 (UTC)

The sentence in the first paragraph "As used by cosmologists, the term Big Bang generally refers to the idea that the universe has expanded from a primordial hot and dense initial condition at some finite time in the past, and continues to expand to this day." gives the impression that the big bang was some sort of explosion of matter similar to the detonation of a nuclear weapon or a supernova.

However, the Big Bang was NOT an explosion of matter like a nuclear bomb. These types of explosions occur within space-time. The Big Bang on the other hand was an explosion of space-time itself. This means that the Big Bang cannot be an explosion at a single point that spews out matter from there (concentrically if you will). (Source and a more detailed explanation: http://www.scienceray.com/Philosophy-of-Science/The-Big-Bang.474317).

Could one of the senior members please rephrase this explanation? I would do it, but the article is currently protected for me. —Preceding unsigned comment added by Dasarp.mail (talk • contribs) 21:55, 17 May 2009 (UTC)

1. Adding some qualification to the lede, to give "As used by cosmologists, the term Big Bang generally refers to the idea that the universe has expanded from a primordial hot and dense initial condition at some finite time in the past, and continues to expand to this day (although not that the universe 'exploded' from a single point in the manner of a bomb)" or something similar
2. Making a section on "Popular misconceptions" or "Popular perception of the theory" or something - there we could treat the 'explosion', 'point of origin' and 'galaxies moving faster that light' ideas. Given my experiences I'd expect a reasonable proportion of traffic to this article being from people who're wondering about some of these questions.

I'm a first-time visiter to this page and was struck by the following sentence in the opening paragraphs: "Without any evidence associated with the earliest instant of the expansion, the Big Bang theory cannot and does not provide any explanation for such an initial condition rather, it describes and explains the general evolution of the universe since that instant." Firstly, I was struck by the fact that this sentence is central to defining the Big Bang, yet it's somewhat hidden in the middle of the second paragraph. But secondly, I hesitate to say that it should be put in the opening lines without some slight modification. It seems to me that the sentence is saying that the Big Bang cannot explain WHY the universe exists, since that would involve theological and philosophical questions about purpose, meaning, etc. This point--that the Big Bang theory cannot answer Leibnitz's question "Why is there something instead of nothing?"--could be made more explicitly, though, and since it is so crucial it really should be backed up with citations. (When I read it the first time I found myself thinking: Really? That's interesting. Who says so?) —Preceding unsigned comment added by 128.36.172.189 (talk) 02:53, 26 July 2009 (UTC)

Added "hypothetical", deleted "initial conditions and subsequent" in first sentence. In the second paragraph, as pointed out above, it is stated that the initial conditions cannot be explained by the theory. Hence, this is not part of the theory, just an assumption that the theory is based on. Due to the numerous issues (listed in the article), the model can only be hypothetical and not matter-of-fact, which the first sentence seems to imply. Petersburg (talk) 14:53, 1 October 2009 (UTC)

It is the model, not a hypothetical model. Restored along w/ init cond. Vsmith (talk) 14:56, 1 October 2009 (UTC) Agree with Vsmith. "Hypothetical" is redundant, as all models are, by definition, hypothetical this particular model happens to be a very good fit to reality (and I have no idea what a "matter-of-fact" model would be). "Initial conditions" (or, at least, "very, very early conditions") definitely are part of the model it just takes these as given and does not attempt to explain why those initial conditions were present. Let's put the first sentence back to how it was before. Gandalf61 (talk) 15:06, 1 October 2009 (UTC)

The image in this article under the paragraph heading "Galactic Evolution and Distribution" appears incorrect in both the small and large versions. It shows the distribution of Milky Way constellations in the Milky Way and not the distribution of Galaxies in the Universe. ----

Galaxy clusters are often named after the constellation in which they lie, but this only gives an indication of which area of the sky they are in - it does not mean that they are within the Milky Way. Objects on this image, such as the Virgo cluster and the Ursa Major cluster, are indeed far beyond our galaxy. Gandalf61 (talk) 13:01, 24 September 2009 (UTC)

The style of the section Features, issues and problems is irritating and supercilious. It is not in accord with scientific language that states facts, not moral attitudes declaring all opponents being idiots. The style is unencyclopedic. F.ex., the second paragraph:

The core ideas of the Big Bang—the expansion, the early hot state, the formation of helium, the formation of galaxies—are derived from many independent observations including abundance of light elements, the cosmic microwave background, large scale structure and Type Ia supernovae, and can hardly be doubted as important and real features of our Universe.

Answer: just because those "facts" (or rather: strong indications) are perceived as real, they're not as strong indication of the realness of Big Bang as indicated, since the facts listed requires logics mentioned elsewhere to actually support Big Bang. F.ex. the presence of large scale structures was often mentioned as a problem for Big Bang, since it requires an older Universe or some fundamental instability that only partially but very deficiently is provided by Dark Matter.

Of these features, dark energy and dark matter are considered the most secure: remaining issues, such as the cuspy halo problem and the dwarf galaxy problem of cold dark matter, are not considered to be fatal as it is anticipated that they can be solved through further refinements of the theory.

is extraordinarily weak logic. It requires citation after citation after citation. There are some indications supporting dark energy and dark matter somewhat, but there are no laboratory measurements on Earth supporting either of them. They simply are exotic physics, known only to cosmology. Such a degree of insecurity would be appropriate for the text too. Secondly:

remaining issues, such as the cuspy halo problem and the dwarf galaxy problem of cold dark matter, are not considered to be fatal as it is anticipated that they can be solved through further refinements of the theory.

signals an unfounded attitude that this will soon be solved. Actually I believe it won't. The neutrino problem will be solved, and so any standard model of physics will be replaced by a supersymmetric model, and many of the aforementioned problems will transform into new physics. The current theory won't survive, except possibly as crudely approximated special cases. Now, presenting my alternate divinations, in obvious opposition to the divinations of the text, I claim: neither the author nor me are prophets. A real scientific text shall just state the problems and point out possible solutions thereby citing some sources. . said: Rursus ( m bork³) 20:19, 5 October 2009 (UTC)

Rursus, you say "just because those "facts" (or rather: strong indications) are perceived as real, they're not as strong indication of the realness of Big Bang as indicated, since the facts listed requires logics mentioned elsewhere to actually support Big Bang." Yes, it's true the observations require interpretation to provide evidence of the BB. But those interpretations which are favourable to the theory are overwhelminlgy popular among cosmologists, and they're generally considered very strong evidence for it. I'm not quite sure what you're referring to about "some fundamental instability that only partially but very deficiently is provided by Dark Matter" - the primordial universe is generally accepted to have had Gaussian (or near-Gaussian) fluctuations which do a pretty good job of predicting current large-scale structure, and whether the matter was dark or baryonic is not directly related to their nature. The evolution of those perturbations over cosmic time requires a significant dark component to give the correct end result, but I don't see what's deficient about that. I agree with you that "dark energy . [is] considered [among] the most secure" is rather too confident given the state of DE I don't agree, though, with your assessment of dark matter. DM is more than "somewhat" supported it's the massively dominant paradigm and a large proportion of papers on the topic take its existence for granted, so strong is the evidence considered to be. It's correct that there are "no laboratory measurements on Earth" supporting it - but we can't present that as a major problem rather than a temporary inconvenience likely to be resolved, because most cosmologists do not and we're a tertiary source. Your final paragraph too is fair enough as your own opinion, but Wikipedia must report what the authorities say. If cosmologists are generally optimistic about the Big Bang theory then we must report that they are. "A real scientific text shall just state the problems and point out possible solutions" - but Wikipedia is not a scientific text it's an encyclopedia aimed at the general reader, and enough authors do say "the Big Bang is successful and robust" that we're justified, I believe, in echoing them. Olaf Davis (talk) 20:45, 5 October 2009 (UTC) OK, I'm irritated by the text explaining Big Bang as a truth, like it was a religion. We should require no "truths", only "attested theories" or "best available model", we should require no "the majority likes this", because Alfred Wegener was in minority, yet correct as we know it today. Personally I think Big Bang have serious flaws (see Shortcomings of the Standard Cosmology), but if I have to choose between models, my honesty requires me to choose Big Bang as being the least flawed. The language of the article describes Big Bang like a majority religion, but I would like it to be written as an act of science, a model that in comparison to other kinds of modelling is very weak, but yet the best available, considering the measurement hardships. It won't become a very good article if it is written like it being truth, instead it would profit very much from holding forth all the "holes" and the qualified efforts to fill those "holes", which still makes it a pretty viable theory. . said: Rursus ( m bork³) 15:07, 27 October 2009 (UTC) Rursurs was right that there was some peacock terms. I tried to edit them out. The only thing I simply removed instead of addressing in the text was the "fact" tag appended to the note regarding baryogenesis and inflation since this fact is easily found within the general reference list as described (it's simply a logical truism due to causality, actually). I provided two white paper citations to demonstrate the state-of-the-field wrt dark matter and dark energy investigations. If someone could format them properly, I'd greatly appreciate it. Thanks, Rursus for pointing out some of the problems in wording. ScienceApologist (talk) 22:06, 5 October 2009 (UTC)

The first sentence of Features, issues and problems, tells us:

While very few professional researchers now doubt the Big Bang occurred

is formulated like Big Bang was a matter of faith, where this or that supernatural power declared a "truth" and the true and only true adherents hailed the rightness of the supernatural. The real issues, religion aside, is whether Big Bang is tentatively accepted as a valid model, or not — not whether it is "true". What if there in fact is a lot of model agnostics that think: "Big Bang is posed with so many troubles, that I'll rather concentrate on observational astronomy. ", and what if there are a lot of Big Bang professionals that think: "OK, I'm working with this flawed model in preparation for novel LHC to occur and solve most of our problems!".

I can understand if the text tries to educate that this is the real creation, not that Creationist pseudoscience, but the scientific philosophies is not comparable to pseudoreligious pseudoscience by far, and so we shouldn't label science as "truth" but instead of "attested theory", as opposed to "weird ad-hoc-dogma". . said: Rursus ( m bork³) 14:34, 27 October 2009 (UTC)

Please forgive me the querulant tone, the article is pretty OK according to my taste. Many improvement since last time. . said: Rursus ( m bork³) 15:32, 27 October 2009 (UTC) I tried to fix it myself, pardon all inconveniences. . said: Rursus ( m bork³) 15:38, 27 October 2009 (UTC) I made a little tweak to the wording to avoid special pleading. Hope it's okay. ScienceApologist (talk) 15:41, 27 October 2009 (UTC) For what it's worth, Rursus, I can say with pretty high confidence from my own experience that the membership of those two groups you posit within cosmologists is essentially zero. Olaf Davis (talk) 17:40, 27 October 2009 (UTC)

These parts of the article don't make sense to me:

That space is undergoing metric expansion is shown by direct observational evidence of the Cosmological Principle and the Copernican Principle, which together with Hubble's law have no other explanation. Astronomical redshifts are extremely isotropic and homogenous,[4] supporting the Cosmological Principle that the Universe looks the same in all directions, along with much other evidence. If the redshifts were the result of an explosion from a center distant from us, they would not be so similar in different directions.

Why would not be the redshift same in all directions when observed from some random piece of an expanding cloud of galaxies (supposing we are far enough from the edge)? Whoever wrote this apparently meant that if you select a point in space outside the center of the explosion, the redshifts will not be symmetric. That is irrelevant, though: observers move with the stars which fly away from the center of explosion, and if you take that motion into account, you get symmetric redshifts from any point.

Explosions have a direction outward in the radial direction because they have a center. A "centerless explosion" is equivalent to a metric expansion". ScienceApologist (talk) 16:47, 25 October 2009 (UTC) You missed my point entirely, which was that an observer co-moving with the matter flying out from the explosion sees himself as the center from which everything moves away. There is no local feature which would allow differentiating between the center and other points assuming only objects within a finite distance are visible (thus we are unable to notice that the edge of the explosion is closer in one direction than in the other), Hubble's law fits just as well with sitting on any random object which was thrown out by the explosion than with sitting in the centre. You could say that the center is defined by the observer's frame of reference and not any inherent feature of the explosion. Also, a centerless explosion (which is pretty much what the steady-state model assumes) might be equivalent to a metric expansion in some abstract mathematical sense, but it is not the same thing physically, if we take relativistic effects into account. With metric expansion, you can observe redshifts which correspond to much higher relative speeds than the speed of light this would not be possible when the expansion would be nothing more than matter moving around. --Tgr (talk) 07:56, 26 October 2009 (UTC) an observer co-moving with the matter flying out from the explosion sees himself as the center from which everything moves away --> not at the same rate in all directions if there is a center. There is a preferred direction which corresponds to the radial direction and that is the one with the highest Hubble Constant. ScienceApologist (talk) 14:21, 26 October 2009 (UTC) Assume C is the center of the explosion, O is the observer sitting on a planet flying away from the center, X is some random other planet flying away. Since the explosion follows Hubble's law, the velocities of O and X relative to C are H 0 C O → >> and H 0 C X → >> , respectively. The velocity of X relative to O is then H 0 C X → − H 0 C O → >-H_<0>>> = H 0 O X → >> , thus from the point of view of O there is a linear relation between distance and speed of X (which is exactly the same relation an observer would see from C). --Tgr (talk) 01:56, 27 October 2009 (UTC) Since the explosion follows Hubble's law --> An explosion that follows Hubble's Law is not a normal explosion and the "center", C, is not really a "center". ScienceApologist (talk) 16:34, 29 October 2009 (UTC) Could you please sketch out the math showing how the observations would differ? I've been lurking in this thread, and I'm having trouble seeing how observable events in the two scenarios would be distinguished in the limit of an arbitrarily distant center of the explosion (i.e. far outside the observable universe). Providing this would also go a long way towards convincing Tgr of your viewpoint (right now, you're asking him to take "no, you're wrong" on faith). --Christopher Thomas (talk) 17:34, 29 October 2009 (UTC) Take Tgr's previous example and choose another point instead of C (call it Y, for example) and redo the analysis. You get exactly the same result if Hubble's Law applies universally. Y then acts exactly the same way as C and is therefore indistinguishable from C. For that reason, Y must either "also" be the center or there must be no center at all. There's really nothing more to it than that. A "center" implies a breaking of symmetry that is impossible in a Hubble's Law arrangement. ScienceApologist (talk) 17:08, 30 October 2009 (UTC) You get exactly the same answer, per his math above (just swap in Y instead of O the velocity of any X relative to Y ends up being H 0 Y X → >> , giving you Hubble's law with Y as the new centre). The only flaw I see in Tgr's argument is that you have to ignore relativity for it to work as-written ( | H 0 O X → | >|> can exceed C), and it's not obvious to me that this invalidates the argument (it might be possible to construct a deformed velocity/radius relationship such that these relations hold when using the SR velocity addition/subtraction formulae). I'm not saying the argument is _correct_ just that I don't think it's been properly refuted in this thread (important, because this should be cleaned up in the article if it's causing confusion). --Christopher Thomas (talk) 18:38, 30 October 2009 (UTC) I think you just proved my point. There can only be one center (by definition). You just proved that there exists another point (Y) indistiguishable from the proposed center (C). Ergo, there is no center. ScienceApologist (talk) 19:46, 30 October 2009 (UTC) You miss my point (and apparently Tgr's point, if I understand it correctly): that an "explosion" (expansion of some cloud of pointlike objects through space) is observationally indistinguishable from the metric expansion of space, provided that the edge of the cloud of expanding objects is outside the observation horizon. The appearance of Hubble's law recession does not itself demonstrate that the metric expansion exists, at least without arguments beyond those sketched above. Do you see what I'm getting at, here? --Christopher Thomas (talk) 21:38, 30 October 2009 (UTC) If the edge is unobservable then the center is unobservable and the explosion is indistinguishable from a metric expansion. Therefore it is a metric expansion. ScienceApologist (talk) 16:35, 31 October 2009 (UTC) I'm pretty sure the therefore it is a metric expansion doesn't follow. At minimum, you could construct an "explosion" scenario where there were the edge would eventually come into view. In an explosion scenario, you'd also be able to prove that an event horizon forms (roughly at the edge of the observable universe, if our density estimates are correct), whereas in a metric expansion scenario you have an observation horizon, but no event horizon in the black hole sense of the term. --Christopher Thomas (talk) 16:47, 31 October 2009 (UTC) An edge eventually coming into view is a meaningless thought-experiment in regards to the base assumptions we are considering here. The Copernican and Cosmological Principles are only applied to the universe in a space-like slice of spacetime (and that's why, for example, we avoid the perfect cosmological principle). Event horizons and future light cones are speculative based on universality. They do not affect cosmological models based on testable observational assumptions. ScienceApologist (talk) 16:55, 31 October 2009 (UTC) (deindent) I'm having a lot of trouble understanding this subthread, largely because I can't understand half the stuff that you (ScienceApologist) say. I'm not even sure if you disagree with Christopher Thomas or if this whole thread is just the result of a miscommunication. All experimental evidence is consistent with (for example) our being somewhere inside a very large spherical homogeneous ball of matter expanding into an infinite Schwarzschild vacuum. That setup is consistent with GR and it would look homogeneous and isotropic from any point not too close to the edge. It has a geometric center which needn't coincide with our location. One can argue against this on Occam's razor grounds, but it's not directly ruled out by the evidence. I dislike the term "metric expansion" because it suggests that the physics of the expansion of the universe is fundamentally different from the physics of an ordinary explosion, which is not the case, and also because I don't understand what it's supposed to be saying about the nature of the world. The FLRW metric, ds² = dt² − a(t)²dΣ², does "undergo metric expansion" in the sense that equal coordinate distances represent larger metric distances at later coordinate times, but that's merely a statement about the coordinates involved and not about the physical world. -- BenRG (talk) 18:35, 31 October 2009 (UTC) I agree with all you are saying, BenRG. I don't see why this is in contradiction to the article text. ScienceApologist (talk) 19:29, 31 October 2009 (UTC) BenRG: My understanding was that our experimental evidence was not consistent with our being inside a large spherical homogeneous ball of expanding matter, because any such model of the universe would run into the same problem as static universe models: no matter what density you assume, any sufficiently large volume ends up inside an event horizon, contradicting the assumptions made (i.e., that that volume is not undergoing collapse to a singularity). In virtually all descriptions of the big bang model that I've seen, metric expansion (or alternatively, a spacetime upon which drawing a coordinate system like that makes sense) is presented as being fundamentally different from an explosion through "non-expanding" space. This is consistent with the lede at metric expansion of space, among other places. If I'm wrong, fine, but I'm getting inconsistent messages here. --Christopher Thomas (talk) 21:38, 31 October 2009 (UTC) An event horizon outside our particle horizon does not affect the observations inside the particle horizon. You can have both metric expansion observed and an "exterior" event horizon and be perfectly consistent. ScienceApologist (talk) 14:26, 1 November 2009 (UTC) Measurements of the effects of the cosmic microwave background radiation on the dynamics of distant astrophysical systems in 2000 proved the Copernican Principle, that the Earth is not in a central position, on a cosmological scale.[notes 5] Radiation from the Big Bang was demonstrably warmer at earlier times throughout the Universe. Uniform cooling of the cosmic microwave background over billions of years is explainable only if the Universe is experiencing a metric expansion, and excludes the possibility that we are near the unique center of an explosion.

How does that have anything to do with the Copernican Principle? Sure, the cooling of the CMB (or the CMB itself in the first place) cannot be explained by an explosion, but that's irrespective of any symmetry considerations. Supposing we are in the center of an explosion does not give us any extra explaining power over supposing we are at some random point of an explosion. --Tgr (talk) 02:01, 25 October 2009 (UTC)

The Copernican Principle demands that every observer on a space-like slice of spacetime see the same cosmologically relevant phenomenon. However, it is not possible to actually observe what a distant observer sees since we are stuck in a very small part of spacetime. These observations enable us to "see" what a distant cosmologist sees and confirm the fact that there is nothing preferred about either observation. ScienceApologist (talk) 16:47, 25 October 2009 (UTC) I don't see how that is relevant to what I said. Maybe the CMB cooling differentiates between Copernican and non-Copernican models of the Big Bang, and it certainly differentiates between Big Bang and the explosion model (which has nothing to do with the Copernican principle since the explosion model is not necessarily non-Copernican), but it makes no sense to say that it differentiates between non-Copernican (sitting in the center) and non-Copernican (sitting in some random point) versions of the explosion model, since that model cannot explain the CMB in the first place. Thus, the claim of the article the the CMB cooling "excludes the possibility that we are near the unique center of an explosion" is wrong. --Tgr (talk) 07:56, 26 October 2009 (UTC) The source clearly indicates that the CMB has to be universal as opposed to local. ScienceApologist (talk) 14:21, 26 October 2009 (UTC) I don't think it's technically wrong, but it is misleading: the CMB does exclude our being near the 'unique centre' of an explosion because it excludes any type of explosion. However, phrasing it the current way does make it sound like it rules that out while leaving in the 'edge of an explosion' model, which as you say it doesn't, so I agree the wording should be changed. Olaf Davis (talk) 10:37, 26 October 2009 (UTC) I think this section of the article should be rewritten, because there really is no difference between "metric expansion" and a sufficiently symmetric explosion. In the zero-density case, when spacetime is flat, the FLRW metric is d s 2 = d τ 2 − τ 2 ( d ρ 2 1 + ρ 2 + ρ 2 d Ω 2 ) =d au ^<2>- au ^<2>left(><1+ ho ^<2>>>+ ho ^<2>dOmega ^<2> ight)> , which is literally just Minkowski space in different coordinates: substitute τ = t 2 − r 2 -r^<2>>>> and ρ = r / t 2 − r 2 -r^<2>>>> and you get d s 2 = d t 2 − d r 2 − r 2 d Ω 2 =dt^<2>-dr^<2>-r^<2>dOmega ^<2>!> . The "metric expansion" in FLRW coordinates is recessional velocity in Minkowski coordinates, the cosmological redshift in FLRW coordinates is special relativistic redshift in Minkowski coordinates, the larger-than-c comoving speeds in FLRW coordinates are lower-than-c special relativistic speeds in Minkowski coordinates, and so on. When you introduce enough matter that spacetime is noticeably curved then it gets harder to see what's going on, but nothing has fundamentally changed. The big bang was an explosion it was far more uniform than any other explosion in nature, but that's only a difference of degree, not of kind. The article repeatedly assumes that the astronomical data is only consistent with an explosion if we're at the center of it, which as Tgr points out isn't true: all that you can measure is relative distances and speeds, and those look the same whether or not you're at the center. -- BenRG (talk) 13:36, 26 October 2009 (UTC) The center of the explosion argument is fine for the null hypothesis associated with the Copernican Principle. As a general rule, all one needs to do to test the Copernican Principle is show that there is nothing preferred about our frame of reference. One could assume that Hubble's Law provided that we inhabit a preferred reference frame but the observations of higher temperature CMB at distant locations is evidence contrary to this assertion. ScienceApologist (talk) 14:21, 26 October 2009 (UTC) The reason we refer to the Copernican Principle is that, strictly, it is necessary to assume it to derive anything from cosmological observations. As noted elsewhere in the article, we can observe isotropy but we need CP to get to homogeneity. Specifically, we directly observe systematic changes with distance (e.g. lower clustering amplitude, higher CMB temperature, more quasars & star formation at high redshift than nearby). By assuming CP we infer that these are actually due to change with time rather than to our being located at the centre of the cosmic spheres. Of course, modern cosmology has been able to predict some of these changes (notable the CMB temperature) ahead of discovery, and such confirmed instances provide supporting evidence for the whole structure of cosmological theory, including the CP on which it rests, but (despite ESO press release) it is not a test of the CP specifically for that we would also need direct evidence that the T_CMB was higher in the past in our local region of the universe, and of course this would only confirm one small aspect of what the CP asserts. Furthermore, the first of these two paras is almost meaningless. In what sense are observed redshifts supposed to be "isotropic and homogeneous"? Strictly speaking they definitely are not, as this would mean that redshift (or at least statistical distribution of redshifts) was independent of distance! One could make a case that the Hubble expansion is isotropic (but not using Hubble's original data, as cited!), but this says nothing about homogeneity which is the crux for the CP. One could claim that the 3-D distribution of galaxies revealed by redshift surveys is homogeneous, but this claim is seriously disputed in the published literature: the large-scale structure extends to scales up to at least 100 Mpc, and some argue that fractal structure continues to arbitrarily large scales (in which case the CP is wrong as are all Friedman-based universe models). By the way, these two paras were inserted (after the last FA review) by banned sockpuppet user:Publicola, if that's relevant to anything. PaddyLeahy (talk) 19:13, 8 November 2009 (UTC)

Please, take a stab at rewriting it. I don't know if we really need those paragraphs at all, and will not object to their removal. ScienceApologist (talk) 21:11, 9 November 2009 (UTC)

It is stated in the article that the Universe has originated from a primordial hot and dense initial condition at some finite time.

I can’t comprehend how the universe cooled down. Was the cold medium (temperature) present around before big bang?68.147.38.24 (talk) 04:31, 8 November 2009 (UTC) khattak

This talk page is for improvements to the article not for tutorials on cosmology. But for what it is worth, space itself doesn't actually have a temperature, and the article does not speak of a temperature for space. The temperature of the background radiation that fills the universe is falling as the universe expands. This is described in the article. —Duae Quartunciae (talk · cont) 04:39, 8 November 2009 (UTC) The temperature given is the average temperature of the material within the universe. As the universe is a self-contained system, changing the volume of the universe (and density of the material within it) changes the average temperature (this is an "adiabatic expansion", described at adiabatic process#Ideal gas (reversible case only). The early universe was filled with a large number of photons and with a plasma of particles and antiparticles that were continually created and destroyed (the temperature being high enough for pair production. As it expanded, it cooled, with a number of effects occurring (as described in the article). If parts of the article are unclear, these can be improved. Were there any specific sentences or paragraphs that you felt should be changed to better describe the material? --Christopher Thomas (talk) 04:54, 8 November 2009 (UTC)

In the section about religion, it states that theologians "reject or ignore the evidence of the Big Bang". Well, how can they reject "evidence" that doesn't exist? Was anyone around to witness it? If anyone has please step forward. This article should present the Big Bang THEORY as what it is a THEORY. --The Great Fizack (talk) 23:11, 20 October 2009 (UTC)

You have quoted that phrase out of context - the full sentence is "Some [religious groups] accept the scientific evidence at face value, while others seek to reconcile the Big Bang with their religious tenets, and others completely reject or ignore the evidence for the Big Bang". Seems like a balanced statement to me. As the first sentence of the article says: "The Big Bang is the cosmological model of the initial conditions and subsequent development of the Universe that is supported by the most comprehensive and accurate explanations from current scientific evidence and observation". Model is just another word for theory. You are quite right to say that scientific evidence is not abslute proof - we cannot be certain about what happened 14 billion years ago, just as we cannot be certain about anything in the external world - see Descartes demon. Gandalf61 (talk) 09:48, 21 October 2009 (UTC) Fizack, theories in science carry a lot of weight, they are not just guesses the way the term is used in popular speech. The idea that direct observation is the only way to be confident about a historical event is lunacy. Abyssal (talk) 15:12, 21 October 2009 (UTC) Fizack, it sounds like you are confusing two very different uses of the word "theory". In colloquial use, "theory" means an uncertain guess which may or may not be true. In science, that is not called a theory, it's called a hypothesis. In science, a Theory (sometimes spelled with a capital T to denote the difference) is not just a hypothesis. It is something that has been extensively tested until it's so certain that it would be almost impossible to overturn it. It's closer to a fact than to a hypothesis, though scientists rarely use the word "fact" because there's always a teensy tiny possibility that they could learn something in the future that contradicts the current understanding. In a Theory, however, that possibility is ridiculously small. Consider that gravitation is also a Theory, but there's no way anyone would say "well, it's ONLY a theory. That means that gravity might not really exist!" --Icarus (Hi!) 19:12, 21 October 2009 (UTC) Except that "string theory" is also called a "theory". <g,d&rVF!> _ _ _ A. di M. 17:13, 2 November 2009 (UTC) True. But in every scientific discussion I've heard on the topic, one of the first things mentioned is that it really ought to be called the string hypothesis or the string model, since it is nowhere close to being an actual Theory right now. This appears to be an instance of the colloquial use bleeding over into a scientific context (it's understandable that this happens occasionally - scientists are human beings, after all, who grow up exposed to the colloquial meaning of as much as anyone else). String theory could be referred to as a "little t theory," but it is not a "bit T Theory." --Icarus (Hi!) 20:47, 2 November 2009 (UTC) Fizack, of course! Except remember the saying: "theories is the best we can get". . said: Rursus ( m bork³) 15:17, 27 October 2009 (UTC)

Related question: Why is there no page similar to Talk:Evolution/FAQ for the Big Bang? It seems that these concerns should be addressed at a centralized location. --Eunsung (talk) 21:27, 15 November 2009 (UTC)

Around 10-13 seconds after the Big Bang, things like the bottom quark and the tauon were stable particles (surviving as long as the Universe itself). Given their larger mass and the density of particles in the universe, could they have formed atom-like composites or produced interesting astronomic structures? Wnt (talk) 07:12, 21 November 2009 (UTC)

At 10 -13 seconds ABB, you are approaching the end of the electroweak epoch and the start of the quark epoch. At this stage the average energy of particle interactions is still too high to allow quarks to combine into mesons or baryons. The universe is filled with a sea of high-energy quarks, leptons and their antiparticles, with the quarks interacting via the strong force by exchanging gluons in a quark–gluon plasma. So the short answer is no, no composite structure could have survived at this time. Gandalf61 (talk) 14:17, 21 November 2009 (UTC) Thanks for responding! But let's look into some details, if I ask the question for a point solidly within the quark epoch, perhaps 10 -9 seconds ABB. If the average energy of particle interactions is too high to allow "quarks" to combine into "mesons or baryons", does that definitely mean that it is too high for bottom, charmed, and strange quarks to combine into exotic mesons or baryons? For example quark stars apparently can contain strange matter even though they consist of a quark-gluon plasma where regular quarks are concerned. I tried to look into this directly for a bit, but it is tough going for the uninitiated. Apparently bottom quarks have energy around 5 GeV, yet mesons with bottom-antibottom can have energies 26 keV to 110 MeV (. ) [1] In the unlikely instance that I'm not misinterpreting this, that would seem to mean that almost the entire 5 GeV mass of a bottom quark can be released as energy when it binds another quark, and would need to be returned in random collisions to recreate it. Since it has a mass 3000 times that of an up quark, I'd expect it to need 3000 times hotter a temperature and to become stable in mesons/baryons roughly 3000 times sooner than regular quarks i.e. at 10 -9 seconds ABB. I'm sure there are fallacies in what I just said, but it might be enlightening to see them corrected. ) Wnt (talk) 10:54, 22 November 2009 (UTC)

The article refers to the big bang as a singularity but it's not entirely clear that there is a consensus on this issue:

"So in the end our work became generally accepted and nowadays nearly everyone assumes that the universe started with a big bang singularity. It is perhaps ironic that, having changed my mind, I am now trying to convince other physicists that there was in fact no singularity at the beginning of the universe -- as we shall see later, it can disappear once quantum effects are taken into account." - Hawking, A Brief History of Time p. 50 —Preceding unsigned comment added by Craig Pemberton (talk • contribs)

This is mostly a case of the answer depending on what model we choose to apply when extrapolating back to the instant of the Big Bang. Using general relativity alone, it produces a gravitational singularity (using the same mathematical proof that shows that a black hole collapses to a gravitational singularity). However, most scientists expect that a theory of quantum gravity would produce different predictions (for both black holes and the Big Bang). We have no satisfactory theory of quantum gravity (or of unification of the fundamental forces, which is also expected to happen at those temperatures). Instead, different people have tried to use various different approximations to estimate how the system in question (universe or black hole, depending on who's doing it) would behave. Whether any of these answers is correct is debatable (and indeed, is being vigorously debated within the scientific community). There is general agreement, if I understand correctly, that you'd at least be starting with a plasma at or near the Planck temperature and with correspondingly high density, in the case of the early universe. Does this address your question? --Christopher Thomas (talk) 04:32, 3 December 2009 (UTC) Is the "singularity" real or only mathematical? We know that there are only 14 million years' worth of vibrations of a cesium atom possible in our past, but the point that makes is only that if you go back far enough in time, cesium atoms become increasingly unwieldy, until another physics takes over. We know that all sorts of cosmic things "happened" in miniscule fractions of a second at the beginning by this definition of time, but we could just as easily use the logarithm of time, or perhaps some other unit of spacetime defined by the assumption that a photon of light remains always the same color and always traverses the same number of wavelengths in a unit time (in which case space is exactly?? the same size at any time). Can we rule out that vast galactic empires played out in attoseconds of quark-gluon plasma, or that once 10^100 years is a tick of the clock our neutrinos and WIMPs will turn out to form interesting new patterns of life? Wnt (talk) 16:23, 6 December 2009 (UTC)

The article says that "Temperatures were so high that the random motions of particles were at relativistic speeds, and particle–antiparticle pairs of all kinds were being continuously created and destroyed in collisions." But isn't the first part true for most of the matter in the universe today, with neutrinos and dark matter moving so quickly they can only barely (if at all) stick to one galaxy? I'm not sure where those things stand regarding the antiparticle pairs. Wnt (talk) 16:03, 7 December 2009 (UTC)

The vast majority of dark matter is believed to be cold dark matter (CDM), with the 'cold' meaning that its motion is non-relativistic. It tends to stay bound to dark matter 'haloes' which are permanent structures often containing one or more galaxies, with a relatively small interchange of mass between haloes. Relativistic DM is called hot dark matter. You're right that massive neutrinos would qualify and they're a prime candidate for HDM, but their density in the universe is far lower than that of CDM. As for particle-antiparticle pairs, both neutrinos and CDM particles are thought to be extremely weakly interacting, so although they may be producing pairs (this is the mechanism through which people are searching for a direct DM detection), the interaction rate is far lower than it would have been for relativistic baryons. Olaf Davis (talk) 17:32, 7 December 2009 (UTC)

Since this is a theoretical model it should be noted in the first paragraph that, by definition, it is not fact and lacks certainty. Toneron2 (talk) 08:03, 12 December 2009 (UTC)

A recent edit on Dec 14 emphasizes "measurement" for inference of the age of the universe since the Big Bang. I think this is potentially misleading.

The age itself is not a measurement but an estimate based on best fit of parameters to measurements of supernovae, CMBR, and so on along with some theoretical assumptions about the model (six parameter ΛCDM). Hence measurements are used but the age itself really is an estimate, given by a best fit of parameters.

Furthermore, the value given (13.7 Gy) is already out of date, I think, given improved measurements of the Hubble constant by Reiss et al (2009) A Redetermination of the Hubble Constant with the Hubble Space Telescope from a Differential Distance Ladder, arXiv:0905.0695v1. The current reference in the article is to Komatsu et al (2008) Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Interpretation arXiv:0803.0547v2, which proposes a significantly smaller Hubble constant. Note that the new value for H0 is based more directly on measurement, whereas H0 from Komatsu et al is a secondary inference from other parameters. Although age of the universe has a lot of popular interest, it isn't actually one of the significant parameters of most interest to cosmologists, so it is often not given explicitly as part of recent results.

With more recent measurements, I think 13.2 Gy is probably closer except that this number is often not given explicitly. I'll hunt around in the mean time other suitable references would be good. However, I do think that "measurement" in the context of age of the universe is misleading. I appreciate that the current wording speaks of an age based on measurements but it is still a very indirect process going from measurements, to cosmological parameters, and then to derived parameters like age via reasonable assumptions about the model. —Duae Quartunciae (talk · cont) 07:17, 14 December 2009 (UTC)

Update. The value I suggested of 13.2 is not a good estimate merely my own off the cuff guess based on revisions to H0. I would suggest saying around 13.5 to 14 Gy (to be consistent with [Age of the Universe]) or 13.6 +/- 0.3 based on Menegoni, Eloisa et al. (2009), "New constraints on variations of the fine structure constant from CMB anisotropies", Physical Review D, 80 (8), doi:10.1103/PhysRevD.80.087302 An extract from Menegoni et al (2009) reads:

3 respect to the quoted standard constraint (see [2]). Including all CMB datasets improves the constraint to t0 = 14.3 ± 0.6 while combining with the HST prior yields t0 = 13.6 ± 0.3 Gyrs (all at 68% c.l..).

• (currently best measurements place initial conditions at a time approximately 13.7 billion years ago)
• (best available measurements in 2009 suggest that the initial conditions occurred around 13.3 to 13.9 billion years ago)

Hubble Deep Field give a Universe age for Baryon Matter about at least 40Gyrs. Since Einstein's Universe (1905 etc.) definition only includes Baryon Matter there is no place for 96% of Universe Energy in big bang theory. Using Hubble et al and the 1% sample of Universe Energy (galaxies), the sample is too small say the other 99% is expanding. More likely galaxies are dissipating in a Space many times larger than our technology. Also as many galaxies are in reverse, does this infer that portions are Universe is shrinking? The observed Universe is more like a Production Line creating the elements of the Peroidic table and some compounds. With a waste product 'furnace slag' of Dark Matter. The cooling of this Dark Matter radiating CMB. With this scenario, the ignition could be in many places at random time scales. No need for INFLATION THEORY as the process temp. would be the same wherever and whenever.

That is this bang needs an ignition theory!! Also conversion of Dark Energy to everything else.

GRAVITY Einstein's 'Matter causes curved space' theory of gravity and hence planetary orbiting. If the Universe is exanding to less density. Does this mean Earth's orbit will expand as density reduces?

58.161.199.130 (talk) 12:25, 2 January 2010 (UTC)John E. Miller

It says right now that the underlying assumptions are "Universality of Physical Laws" and "the Cosmoligical Principle"

But I thought I learned in my General Relativity course that a big bang must have occured at some time in the past in an FRW universe IF the cosmological constant is 0. If I remember correctly, there's an Einstein-de Sitter or Einstein Lemaitre (i don't remember the name) universe in which the cosmological constant is non-zero, and for some parameters you don't get a big bang.

When the cosmological constant is 0, I though I had learned that what made Penrose and Hawking famous was their proof that even in a non-FRW universe a big bang will occur (so the cosmological principle is not necessary in order for a big bang to happen).

Anyway, I think it should say "The occurence of the big bang is predicted in particular general relativity theories (for example, one in which the cosmological constant is 0)"

But I didn't want to change it if the experts say I'm incorrect. Please discuss. Dr. Universe (talk) 23:00, 5 January 2010 (UTC)

I'm not in a position to answer this, but I've left a note at WT:PHYS, where there are probably a few experts lurking. Thanks for bringing the concern up! --Christopher Thomas (talk) 04:05, 6 January 2010 (UTC) You're right in saying that not every FRW universe has an initial singularity. An obvious counter example is Einstein's steady state solution, which was his reason to include a cosmological constant in the first place, and as a (nongeneric) example of a solution both without a past and future singularity. On the other hand any FRW universe that conforms to the current observations (expansion, density, etc.) will have an initial singularity, which is what I think is meant in the article. TimothyRias (talk) 09:46, 6 January 2010 (UTC) Chaotic eternal inflation may not imply an initial singularity, according to Andrei Linde (although this seems to be a minority opinion).--Michael C. Price talk 11:28, 6 January 2010 (UTC) Even without homogeneity and isotropy, I think that one can infer that the Big-Bang occurred if one assumes that: (1) the universe is currently expanding (to a greater or lesser degree) everywhere today, and (2) pressure and energy are never negative so that the contravariant version of the Einstein tensor is non-negative definite everywhere at all times. JRSpriggs (talk) 09:08, 7 January 2010 (UTC)

These issues are subtle and perhaps sublime, but suffice to say that the two assumptions listed are the cleanest and most popular way to eliminate terms in the Einstein tensor that contribute some bizarre and counter-intuitive effects that eliminate the possibility of expanding space and therefore the Big Bang. This is the sense in which FRW depends on the cosmological principle. Granted, DeSitter spacetimes which can also be derived in this way are static, so it is important to assume that the physical relationships of "dust" and "matter" that dominate locally are also important globally or we would again end up with no singularity. Penrose and Hawking are actually irrelevant to this because they just proved that there is an inherent instability in non-FRW metrics that result in singularities and, if you like Penrose-matching techniques, a resumption of cosmological principle symmetries in the next go-round. ScienceApologist (talk) 16:52, 7 January 2010 (UTC)

See the notice at the top of this talk page. This discussion topic doesn't have to do with how to improve the article, but rather one individual's soapboxing for a beyond the fringe point of view. It is therefore not a proper use of this talk page. Let's end this discussion now.—Finell 23:35, 14 January 2010 (UTC)

• It is a "Belief" that it happened, though no evidence directly points to it
• Fuzzy logic: It states that matter just appeared, was collapsed into a singularity by exactly no force, then exploded. The theory is overwritten by the Scientific Law of Conservation of energy, as "the total amount of energy in an isolated system remains constant over time". Also, we may not be able to prove that the universe is expanding, as we have not reached the said "Edge of the universe".
• The wikipedia page for Religion describes the big bang: "A religion is a set of beliefs concerning the cause, nature, and purpose of the universe". Mevistoveles (talk) 18:45, 14 January 2010 (UTC)

Big Bang Theory does not attempt to define any purpose of the universe. Therefore it cannot be a religion even according to your definition. It does not seem to be on this list List_of_religions. However I do appreciate that there are numerous religous people interested in the theory. Chaosdruid (talk) 23:03, 14 January 2010 (UTC)

This is a very minor edit to the picture depicting an artist's impression of how the universe formed. I'm referring to the picture in the "Speculative physics beyond Big Bang theory" section. I think that if we add another line to the caption it will be perfect for the article. I'm having this in mind:"Please note that you cannot view the universe from outside the universe. Since the universe has no theoretical outside, you cannot have this picture. This is just an artist's impression.". I was thinking something on the borderlines of this. If anybody can change it accordingly, then I think it will become a great article. Thanks, Surya —Preceding unsigned comment added by Suryamp (talk • contribs) 15:18, 17 January 2010 (UTC)

I think the current caption for the picture makes it adequately clear, especially the part which says ". is represented at each time by the circular sections.". JRSpriggs (talk) 20:13, 17 January 2010 (UTC)

I have certain questions pertaining to singularity 1. if the universe was 'born' in a single point. how far are we from that location ??

2. is it (The Universe & the Big-Bang) Similar to a vacuum fluctuation wherein, particles & anti-particles are formed. but somehow got seperated before cancelling out. wouldn't this mean that the universe was created out of void or nothing Ap aravind (talk) 14:52, 6 January 2010 (UTC)

Regarding starting from a single point: Using a purely GR model, all parts of the universe would have come from the same arbitrarily-small region, so all parts could be considered the starting location. If I understand correctly, most scientists think that this purely-GR extrapolation stops working when the universe approaches the Planck temperature, or the volume being considered shrinks to the Planck size, so this should be considered an approximate picture of what happened (just a very good approximation once the universe cooled below the Planck temperature). Regarding vacuum fluctuations, it isn't so much that the matter and antimatter became separated, but that random processes in the matter/antimatter/photon plasma are expected to leave slightly more matter than antimatter through reactions that violate CP symmetry. We know of some reactions that do this, but not enough to explain the amount of extra matter present. Because we're pretty sure this is what happened, we conclude that there are more CP-violating reactions that only happen at higher temperatures (present after the Big Bang, but hard for us to duplicate in laboratories). This is discussed in greater length at baryon asymmetry. You could argue that this means the universe was created from nothing, but the energy required to create particle/antiparticle pairs had to come from somewhere (pairs literally created from nowhere vanish shortly after creation this is one way of describing virtual particles). Where the energy came from is a matter of speculation (could have been from an "inflationary field" or other exotic fields proposed to exist). The plan version of the Big Bang model mostly ignores this, and just says "if we rewind time, it looks like the universe started out full of very dense, very hot plasma, which cooled as space itself expanded". I hope these answers are useful to you! --Christopher Thomas (talk) 22:51, 7 January 2010 (UTC)

It seems difficult to appreciate that the beginning of the universe was really the beginning of everything, including space, matter,and time.All space and matter came into existence at the same time as time itself.Just as strange is the idea that 99.9999999999999 per cent of the volume of ordinary matter is empty space.Recent developments in physics are very close to the earliest moments of existence.The developments in dark energy and dark matter research reveal rewarding pieces of the big puzzle.Ern Malleyscrub (talk) 07:20, 23 January 2010 (UTC)

Why does a subtitle say Speculative physics beyond Big Bang? Isn't Big Bang one of possibilities being considered? If it fits some observations better than an another model, but does not fit other observations better than another model, why is Big Bang not speculative too, as everything else is? Or is this about some scientists trying to outmuscle some other scientists, like in climate thing? Goldor (talk) 02:21, 26 January 2010 (UTC)

The section is not talking about alternative theories to the Big Bang, thus implying that it is speculative. Rather the section is talking about the period of time prior to the well-understood expansion we call the "Big Bang". JRSpriggs (talk) 17:42, 26 January 2010 (UTC) Indeed, a proper understanding of the Big Bang model is that it was the origin of space and time itself, so speaking of a time "before" the Big Bang is self-contradictory: there may not be such a thing as "before", according to the model. CosineKitty (talk) 18:57, 26 January 2010 (UTC) According to the subsection Big Bang#Timeline of the Big Bang, "Extrapolation of the expansion of the Universe backwards in time using general relativity yields an infinite density and temperature at a finite time in the past. This singularity signals the breakdown of general relativity. How closely we can extrapolate towards the singularity is debated—certainly not earlier than the Planck epoch. The early hot, dense phase is itself referred to as 'the Big Bang', . ". Thus the Big Bang theory is not thought to reach past the Planck epoch to an initial singularity. JRSpriggs (talk) 19:29, 26 January 2010 (UTC) I think I may have gone off on a tangent. The original question was about other theories. Big Bang is the dominant mainstream cosmological theory, but there are still a few holdouts for the steady state universe, which is linked here. (I don't really know of any other major scientific theories for the origin, or lack of origin, of the universe. It would be interesting to find them and link from here.) Everything in science is "speculative", if you mean that we might change our mind later when other evidence comes to light. But it is not speculative in the sense that it is an arbitrary guess the Big Bang is a widely accepted theory because it explains thousands of astronomical observations made over the last 80 years. CosineKitty (talk) 23:38, 28 January 2010 (UTC)

Can I refer interested readers to a bookMarcus Chown "The Never-Ending Days of Being Dead".Yes,weird title,unfortunately,but the book covers recent developements in attempts to reconcile quantum physics with observed cosmology/astronomyParadox that the expansion of the Universe is speeding up due to "dark matter" and "dark energy".It's beyond me, but physists take it seriously.Is this worth adding to main article as reference book?ThanksErn Malleyscrub (talk) 02:31, 12 February 2010 (UTC)

It's a perfectly good popular science book, but it seems to me that it is probably better suited to a different topic than the big bang. ScienceApologist (talk) 17:32, 12 February 2010 (UTC)

Information that is in the public domain - especially information put out by a US Government Agency pertaining to the clenching evidence of Big Bang Cosmology - is something the readers of this article should justly be aware of. If the reader proceeds without this information, he may commit his integrity and his time to activities he may later regret. This is not an opinion or a discussion on the validity of Big Bang, but a reporting of an act of the Government Agency that contradicts the entire peer-reviewed literature evidence on which the Wikipedia article is based.

The said Agency is the primary authority on the science issue here. The peer-reviewed literature is secondary.

I am citing a blog post because it reports the facts in a concise and effective manner. The reader is then free to draw different conclusions. Please visit:

This post is made by Bibhas De. —Preceding unsigned comment added by 75.17.58.46 (talk) 18:07, 15 February 2010 (UTC)

You're going to need more than just a blog post as evidence if you're claiming that the COBE data was falsified. See WP:RS for guidelines on sources that are considered reliable. --Christopher Thomas (talk) 18:46, 15 February 2010 (UTC) It's worse than that. Someone is posting on a Wikipedia talk page a link explicitly accusing a living person of fraud. CosineKitty (talk) 19:25, 15 February 2010 (UTC) The public allegation of fraud (made on 5 April 2007) is now nearly three years old – and is known to John Mather's employers, and a host of other groups worldwide. Mather himself has responded to this twice in public: once in his University of Maryland commencement speech in December 2008, saying he would not cheat and again (about Nov/Dec 2009) in answer to a question in the "Ask a Nobel Laureate" program on the Nobel YouTube, saying that his detractors are just a few in number. A NASA attorney and legal advisor has said (in the 2009 Annual Meeting of the Mars Society) that Mather's acceptance of the Nobel Prize was procedurally correct from the viewpoint of the rules about a Federal employee accepting outside money. For nearly two years now, NASA has kept Mather confined to his pre-Nobel job. As to legitimate sources, the evidence of fatal instrument malfunction in orbit has been published in a peer-reviewed journal – it is in John Mather's very own discovery paper. http://www.bibhasde.com/Mather_text_1.jpg This malfunction grossly violated Mather's own stated stringent specifications for his own experiment in the very same paper, and thus made the experiment completely worthless - by his own criteria. Yet Mather proceeded to exatract from it a textbook perfect discovery – that which he had set out to make. For the reasons stated above, it is superfluous for anyone to write a critique in a peer-reviewed journal in order for this subject to be considered by the scientific community. – Bibhas De —Preceding unsigned comment added by 75.19.84.70 (talk) 21:33, 15 February 2010 (UTC)

Bibhas, we're not going to be including any of your insinuations, protestations, or conspiracy theories on this page. The fact that Mather has had many different roles within NASA is not relevant to this article in the least. That's all the evidence you have from reliable sources, so I suggest you move along. ScienceApologist (talk) 22:45, 15 February 2010 (UTC)

I moved the recent addition by Androstachys to a later section of the article since it seems odd to have it appear in the section about the early history of the theory. I also removed the sentence "This model does not invoke the logically awkward and seemingly magical appearance of Lemaître's Big Bang": whether you or I personally think it's awkward or seems magical, we can't claim that as fact in the article without a solid source to back it up. Olaf Davis (talk) 15:49, 18 February 2010 (UTC)

The entire idea for the big bang comes from the view that galaxies are flying apart from each other. However, we now know that that view is not entirely accurate, with galaxies as well as entire groups of galaxies actually drawing closer together. A much better theory than Big Bang is that there are anti-gravity bubbles within the structure of the universe, that these bubbles are growing, resulting in both a pushing apart as well as a pushing together of galaxies and groups of galaxies. The bubbles would be created by the same mechanism that creates matter, quantum fluctuations. Bob Mosurinjohn, aka Sputnick on APOD forum. —Preceding unsigned comment added by 173.34.148.124 (talk) 00:28, 19 February 2010 (UTC)

Of course, each star or galaxy has its own proper motion relative to the average motion of matter in that part of the universe. But this does not change the observationally supported fact that the average motion is proportional to one's position. See Hubble's law. Consequently the volume occupied by the matter currently in our observable universe is steadily increasing. JRSpriggs (talk) 02:46, 19 February 2010 (UTC)

New interpretation of cosmological red-shift showing that there was neither Big-Bang, nor the universe is expanding Put forward by: Hasmukh K. Tank, from Space Applications Centre of Indian Space Research Organization, 22/695 Krishna Dham-2, Ahmedabad-380051 India E-mail: [removed] Date:20th February,2010

Based on the strikingly matching values of decelerations of: Pioneer-10, Pioneer-11, Galileo and Ulysses space-probes with the deceleration of the cosmologically red-shifting photons, and the 'critical acceleration' of Modified Newtonian Dynamics [MOND], this letter proposes that all these decelerations are because of 'self-gravitational-pull' of the object's own gravity. So, every moving object has to continuously keep on spending a part of its kinetic energy. Newton's laws of motion s need a refinement, of taking into account this very-small deceleration, close to: 6.67 x 10^-10 meters per seconds squared. This refinement will: (i) help in understanding the relative strengths of gravitational and electric forces and (ii) lead to static model of the universe, i.e. there was neither any Big-Bang, nor the universe is expanding. The strikingly equal amounts of carefully measured1 anomalous decelerations of all the four space probes:For Pioneer-10, a = (8.09 +/- 0.2) x 10^-10 meters/sec^2 For Pioneer-11, a = (8.56 +/- 0.15) x 10^-10 meters/sec^2 For Ulysses,a = (12 +/- 3) x 10^-10 meters/sec^2 For Galileo,a = (8.0 +/- 3) x 10^-10 meters/sec^2 and their perfect matching with the deceleration of cosmologically red-shifting photons can not be an accidenta coincidence.For Cosmologically-red-shifted-photon a = 6.87 x 10^-10 meters/sec2 = H c. The reason why the deceleration of cosmologically red-shifting photon is slightly less is because: when the extra-galactic-photons enter our own milky-way-galaxy, they experience some gravitational blue-shift.So, the strikingly matching values of five different decelerations can not be ignored by a scientific mind. Moreover, this value of deceleration also matches with the ‘critical-acceleration’ of the Modified Newtonian Dynamics [MOND] devised to explain the ‘flattening of galaxies’ rotation-curves’.According to Hasmukh Tank, a scientist-engineer from ISRO, all these perfectly-matching-decelerations are because of ‘self-gravitational-pull’ experienced by the moving body itself. Because, every piece of matter, and every chunk of energy, produces a curvature of space-time around it, so when a body tries to move in any direction, it experiences a backward-pull, because of its own gravity. Space-time are bendable they are not perfectly rigid like the cement-road. So, moving through space-time is like walking on a sandy path so the moving object has to spend a part of its kinetic-energy, to keep moving. In the case of the cosmologically red-shifting-photons, the expense of energy can be expressed as follows:We can express the cosmological red-shift z in terms of de-acceleration experienced by the photon, as: z = H D / c i.e(h delta f / h f) = H D / c, and h delta f = (h f / c^2) (H c)D. So, the loss in energy of the photon is equal to its mass (h f / c^2) times the deceleration a = (H c) , times the luminosity-distance D traveled by it. Here, H is Hubble’s constant, and c is speed of light. And the acceleration a = 6.87 x 10-10 meters/sec^2. Based the previous paper^2 the acceleration a = H c can be expressed as a =H c = G M/ R = G 10^80 mp /(10^40re)^2 = G mp / re^2. Where M was total-mass of the universe, R was radius of the universe, G is Newton’s gravitational-constant, mp is mass of the proton, and re is classical-radius of the electron, as defined by Dirac re = e^2/me c^2.It means that the above acceleration a implies the ‘self-gravitational-pull’ at the level of the protons and neutrons contained in the nucleus of the atoms.A Gadanken-experiment to understand the ‘ self-gravitational-pull. Since the Sun is sure to expand in the future, and it is likely to swallow all the inner planets and our Earth, let us plan to shift the position of the earth. For this purpose, we will need a space-shuttle which can step-by-step transport the earth’s matter to a selected new position in the outer space. Supposing, in every trip, the shuttle is able to carry m kilograms of matter. As the shuttle starts its first trip, it will experience the earth’s gravitational-pull, and so, it will have to consume its kinetic-energy equal to say, m . g . h where: g is gravitational-acceleration, m is mass lifted by the shuttle, and h is height at which the mass is lifted. As the trips proceed, the earth’s mass will go on reducing, reducing the value of g . Also, the mass accumulated at the height h will pull the mass being lifted. Say, to lift half of the earth’s mass, total consumption of kinetic energy is K units. This amount of kinetic energy can either be re-obtained by bringing-back the lifted mass. Or, this amount of kinetic energy, which has got converted to gravitational-potential-energy, can be used to pull the remaining half portion of the earth’s matter to the heighth. It means, that we have to spend K units of energy to bring the earth to a new position. Supposing this new position is not sufficient for protecting the earth from the Sun’s expansion,then we will have to repeat this procedure. And we will have to consume K units of energy every-time. So, to keep a massive body moving, we have to continuously, keep on spending energy. It means that every piece of matter, and every chunk of energy, has to continuously spend a part of its kinetic energy to keep moving.Thus,we considered here a necessity of refinement of Newton’s laws of motion that: Every piece of matter, and every chunk of energy, has a ‘gravitational potential-well’, or ‘the curvature of space-time’ around it so when it tries to move in any direction, it has to climb its own potential-well so it experiences a backward-force, towards its previous position. This ‘self-gravitational-pull’ is proportional to its mass m, and acceleration H c. And the Force (F)= k . m ,where k = H c,and m is mass of the body. In the case of cosmologically red-shifting photon, its mass is m =(h f/c^2). This ‘self-gravitational-pull’ can be experimentally verified by: (i) applying force smaller than the acceleration H c in the outer space where there is no other gravitational force and(ii) we can send space-probes, like the Pioneer-10 and 11, in different directions, of different masses, and speeds.

This law of ‘self-gravitational-pull’ will lead to the static model of the universe, making the explanation for the relative strengths of gravitational and electric forces, proposed by Tank^2 , valid for all the history of the universe References 1.Anderson, J.D., Laing, P.A., Lau, E.L., Liu, A.S., Nieto M. M., and Turyshev.S.G.Indication, from Pioneer 10, 11, Galileo, and Ulysses Data, of an Apparent Anomalous, Weak, Long-Range Acceleration. Phys. Rev. Letters. 81 (1998) 2858-2861 [(Comment by Katz J.I.: Phys. Rev. Lett. 83, 1892 (1999) Reply: Phys. Rev. Lett. 83, 1893 (1999)].2,Tank H.K. “An Explanation for the Relative Strengths of ‘Gravitational’ and ‘Electric’ Forces Suggesting Equality of the ‘Electrostatic-potential-energy’, ‘Gravitational-potential-energy’ and ‘Energy of Mass’ of the Universe ” Science and Culture 75, No: 9-10, Sept-Oct 2009 p. 361-363 11:51, 3 March 2010 (UTC)

The acceleration in question seems to affect differently to(i) linearly moving objects, and (ii) to the orbiting objects. In the case of MOND the effective acceleration gets inceased from its expected value GM/r^2 to [GM/r^2xthe critical-acceleration]^1/2, where GM/r^2 is much lesser than the critical acceleration of MOND. So, we need to think more.11:22, 4 March 2010 (UTC) —Preceding unsigned comment added by 123.201.176.142 (talk) There are many papers on 'Gravitational self-force' accessable from www.google.co.in, which should help in understanding the 'self-gravitational-pull' in question.11:29, 4 March 2010 (UTC)

Oh, so "orbiting objects" are affected differently. Occam's razor says that it is always a bad sign when you have to add exceptions and special cases to your theory to sidetstep objections. I agree that you need to think more, but please do your thinking somewhere else. When you have published your theory in a peer-reviewed paper in a mainstream journal, then it is ready for Wikipedia - not before. Gandalf61 (talk) 12:55, 4 March 2010 (UTC)

While solving the most important problems, we need to do constructive critisism, and offer constructive suggestionsthis is not a quiz game played by collage students.Wikipedia's discussion-page should mean reader's reactions on the subject of the article. Peer-reviewed journals are commercial activities, so they bother very much for the impact-factor and mind-set of readers, they do not loose anything by not publishing a very-important paper. e.g. The paper on Bose-Einstein's statistics was rejected by NATURE, but later the subject turned out to be worth The Nobel Prize.Wikipedia will be helpful in the progress of science, if it helps in overcoming the problems associated with the present system of peer-reviewed journals.

I've taken the liberty of removing your email, since Wikipedia is a very visible site and is ripe for harvesting by spambots. Olaf Davis (talk) 12:47, 3 March 2010 (UTC). Thanks. (Sorry, I can't help myself.) I stopped taking this seriously when I got to "every moving object has to continuously keep on spending a part of its kinetic energy". This is a fundamental failure to understand Galilean invariance. An object is never "moving" in an absolute sense, but only relative to some observer in a non-accelerating frame of reference. If an object has to decelerate according to one observer, another observer will see that object start out at rest and spontaneously accelerate! That second observer measures an acceleration, and an increase of kinetic energy that is not caused by any force, which contradicts the starting proposition. The original assumption is inherently self-contradictory. CosineKitty (talk) 19:16, 3 March 2010 (UTC)

Dear friends, just think of a situation that every motion is relative. If every particle's motion is relative, then it would mean that no particle is actually,(i.e.absolutely)moving. So, in my opinion, there are two types of motions, (i) relative, and (ii) absolute, i.e. it moves with respect to its previous position. Einstein's relativity is correct with respect to the first,relative motion. But there is absolute motion as well, i.e. a change of co-ordinates of a particle with respect to its previous co-ordinates.The MOND's acceleration, and the deceleration experienced by the cosmologically red-shifted photon, are with respect to their absolute motion.11:11, 4 March 2010 (UTC) —Preceding unsigned comment added by 123.201.176.142 (talk) According to many physicists, Einstein's special relativity is correct only with respect to absolute frame of reference. Einstein's transformations have only one-way correctness. Google-search will show many papers showing mathematical-mistakes in the derivations of special-relativity's expressions. So, we need to keep an open mind.

Please insert <> or <> after the unnecessary discussion, otherwise all further additions to the talk will be hidden whether pertaining to that discussion or not. Rursus dixit. ( m bork 3 !) 21:14, 8 March 2010 (UTC)

The observed abundances of the light elements throughout the cosmos closely match the calculated predictions

No, not "closely", for Helium-3/4 the fitness is very good but for Lithium-7 the match is bad (see Big Bang nucleosynthesis). If we just adhoc grabs a auxilliary hypothesis, say that f.ex. heavier elements are spallated by cosmic radiation producing Li-7, this auxilliary hypothesis by itself isn't enough to justify the fitness to be good, we must have quite a few citations making this statement in the context of Big Bang nucleosynthesis, and in order to be NPOV, we must add something like are considered by scientists [whom, by the way?] to closely match. Rursus dixit. ( m bork 3 !) 21:14, 8 March 2010 (UTC)

The true details of nucleosynthesis arguments are actually statistically very significant if you take the priors correctly. What you need to do is look at all the species at once and take into account the errors on each and add appropriately. Lithium-7 is one of the least abundant species still around from the Big Bang and spallation is large enough to heavily pollute the sample (unlike, say, deuterium). So, it's not really a good idea to attribute this fact. The best nucleosynthesis papers show it to be nearly ironclad as a measurement. ScienceApologist (talk) 22:55, 17 March 2010 (UTC) Digging up a cite or two, especially ones that mention the spallation issue, and adding them to this article and to Big Bang nucleosynthesis might not be a bad idea? --Christopher Thomas (talk) 00:13, 18 March 2010 (UTC)

So dug: [2], [3], [4], and the seminal review of the "lithium problem" with the most likely solutions outlined: [5]. ScienceApologist (talk) 15:09, 19 March 2010 (UTC)

## The Mist of the Stars and the Great Void

T he Universe is permeated by a diffuse background formed by a very faint light called EBL (from Extr a galactic Background Light). This radiation, which covers a portion of the electromagnetic spectrum ranging from infrared to ultraviolet, is a cosmic fossil, consisting of the sum of the radiation emitted by all the stars and active galactic nuclei that have shone since the dawn of time. It is difficult to observe it directly, because its weak glow drowns in the overwhelming light of nearby galactic sources, first of all, the zodiacal light, a luminescence of the night sky produced by the scattering of sunlight by small dust grains dispersed in the solar system.

EBL is like a very faint mist. However, measuring its intensity and variations is of fundamental importance in understanding the evolutionary history of the Universe, in particular as regards the star formation rate and the density with which stars were and are distributed in the immensity of space. A study by many authors, published on November 1, 2012, in Science, provided an answer to the problem of measuring EBL.

The researchers used an indirect method to measure the intensity of EBL. First, they built a model of how the gamma rays emitted by 150 blazars placed at different distances from the Earth were filtered by the EBL “mist”, depending on their energy. Then they compared the quantity and energy of the gamma rays recorded by the Fermi space telescope with the distance of each blazar calculated through its redshift, to finally extrapolate the average density of the faint light formed by the EBL.

But let’s go on with some order. When an active supermassive black hole is present in the core of a galaxy, that is, a black hole engaged in engulfing large quantities of matter (stars, planets, interstellar gas), from the accretion disk that surrounds the black hole two mighty plasma jets are fired in opposite directions at very high speed. When one of the jets is oriented precisely towards the Earth, it appears to us as an extremely bright point source, a blazar. But blazars are also powerful gamma-ray sources. Fermi’s detectors identified over a thousand of them between 2008 and 2012, during the first four years since the launch of the satellite. Of all those blazars, the researchers selected 150 belonging to the BL Lacertae type, with gamma-ray emissions over 3 GeV, that is, with energies over a billion times higher than those carried by visible light photons.

A gamma photon emitted by a blazar in our direction traveled for billions of years before ending up intercepted by the detectors of the Fermi Large Area Telescope (LAT). But not all gamma rays emitted by a blazar towards Earth reach us. A percentage of them, varying according to the distance and the energy transported, disappear during the long journey, leaving the place to a couple of particles, an electron and its antimatter counterpart, a positron. The transformation occurs when a gamma photon collides with an ultraviolet or visible light photon, belonging to the EBL.

The result of these random annihilations of gamma photons due to EBL is that the detectors of the Fermi space telescope received more gamma rays from the nearest blazars and fewer gamma rays from the farthest ones, with a much more evident decrease the higher the energy transported, especially over 25 GeV. The analysis of the spectrum of gamma-ray energies from nearby and distant blazars thus enabled researchers to model gamma-ray attenuation curves, linked to the distance in space (and time) of the emitting blazars. Based on the three different curves obtained, they then calculated the average density of the “fog” of diffused starlight, through which the gamma rays from the blazars — similar to lighthouses that “pierce” a foggy night — had had to work their way up to us.

The results of the research gave important indications about the evolutionary history of the Universe. The first stars, extremely massive and brilliant, composed exclusively of hydrogen and helium, formed around 400 million years after the Big Bang, perhaps a little more slowly than had previously been assumed. The peak of star formation, however, seems to have taken place three billion years after the Big Bang. From that moment on, the star formation rate has always been declining.

Finally, the measurement of the thickness of the faint mist formed by the EBL provided a figure for the average stellar density in the Universe: just 1.4 stars per 100 billion cubic light-years. Such density equals an average distance between one star and the other of 4,150 light-years. Of course, within galaxies, the distance between stars is much less. The triple system of Alpha Centauri, for example, is about a thousand times less distant from the Sun. Furthermore, in some globular clusters and the galactic cores, the stars are so close to each other as to exceed the thousands per cubic parsec. But galaxies are like remote islands, scattered in an immensely large and, above all, immensely empty space.

To better understand how large this void is, it may be useful to transform the average distance between the stars given above in light-years into kilometers, a more common unit of measurement for us humans. Well, 4,150 light-years correspond to almost 40 million billion kilometers (3.926 × 10¹⁶ km, expressed in the most compact scientific notation). The enormity of such a distance becomes even more disconcerting if you reflect on the huge number of stars that have existed since the dawn of time to today. Hundreds of billions of stars per galaxy, billions of galaxies in the entire Universe, and innumerable generations of stars that existed and died in each galaxy, each of which left a trace in the fossil radiation of the EBL. Still, this indescribably large number of stars was and is utterly insufficient to fill the Universe. Only 1.4 stars per 100 billion cubic light-years. Practically almost absolute emptiness.

## Was the Big Bang a quantum mechanical vacuum fluctuation?

It has been proposed by Edward P. Tryon that the Universe may be a large scale quantum mechanical vacuum fluctuation where positive mass-energy is balanced by negative gravitational potential energy, as a consequence of the early inflationary launch of the expansion of the Universe, in which these quantum fluctuations particles got amplified, which would explain how our Universe could have inflated from these particles. But what particle(s) exactly? What initial particle is being referred to here?

It is known that light preceded matter, so bosonic energy, chronologically speaking, could have been the first elementary particle to give rise to all the other particles that formed from it later. The Big Bang theory is said to have started from one single point. If I’m understanding it correctly, this hypothesis referring to that 1 point as being only 1 particle. Of course, it seems more probable that the Universe started out with one particle, rather than a bunch of particles to start out with, but that does not mean that this hypothesis therefore has to be correct.

When a photon is scattering with matter or antimatter, part of energy from the photon is given to matter/antimatter, and a new photon with smaller energy is created. A particle which received energy from photon is accelerated. It can be repeated over and over again, and from an initial 511 KeV photon after millions of such interactions, you will have millions of photons with very low energies (e.g. visible spectrum, then infrared).

But wait a minute, a photon that preceded all other particles? To suggest that an electromagnetic particle such as the photon could have been the first particle before all the other particles, from which the strong and weak force came forth later, that has to be backed up with scientific facts, observations and maths. It has already been proven that the electroweak force once preceded electromagnetism and the weak force. Concerning the strong force, which is carried out between protons and neutrons, when for instance a neutron decays, electromagnetism does indeed “show up” (a neutron decays into proton, electron and antineutrino). Again, there seems to be electromagnetism involved. However, this does not mean that the strong force came after electromagnetism, and this hypothesis therefore has to be true. I’d like to know if anyone here could provide me with facts in favour of this hypothesis, or against this.

The law of conservation of energy forbids new energy to be added (because energy can neither be created nor destroyed), so the suggestion that a boson, like the photon, could have pair produced two matter/antimatter particles (a gamma photon is able to create a pair of electron-positron must have at least 1.022 MeV energy) seems to be the only remaining option to explain the vast amount of matter and energy in the Universe we have today, because this conservation law has to be satisfied, since new energy could not have been generated/added, therefore the existing energy could only have been changed/divided. The question how this first bosonic energy could have been in existence in the first place is the domain of philosophy, not science, so I won’t make any suggestions about that mystery, I’m only trying to find out the chronology of the Big Bang, and what happened after that first initial particle. If this hypothesis is true (which I’m not so sure about yet), taking inverse Compton scattering in account (in which a charged particle transfers part of its energy to a photon), it’s not quite clear to me how to get from an electron/positron pair to, well, more than an electron/positron pair, because they can’t divide any further, can they?

## Theory of Light to the 19th Century:

During the Scientific Revolution, scientists began moving away from Aristotelian scientific theories that had been seen as accepted canon for centuries. This included rejecting Aristotle’s theory of light, which viewed it as being a disturbance in the air (one of his four “elements” that composed matter), and embracing the more mechanistic view that light was composed of indivisible atoms.

In many ways, this theory had been previewed by atomists of Classical Antiquity – such as Democritus and Lucretius – both of whom viewed light as a unit of matter given off by the sun. By the 17th century, several scientists emerged who accepted this view, stating that light was made up of discrete particles (or “corpuscles”). This included Pierre Gassendi, a contemporary of René Descartes, Thomas Hobbes, Robert Boyle, and most famously, Sir Isaac Newton.

The first edition of Newton’s Opticks: or, a treatise of the reflexions, refractions, inflexions and colours of light (1704). Credit: Public Domain.

Newton’s corpuscular theory was an elaboration of his view of reality as an interaction of material points through forces. This theory would remain the accepted scientific view for more than 100 years, the principles of which were explained in his 1704 treatise “Opticks, or, a Treatise of the Reflections, Refractions, Inflections, and Colours of Light “. According to Newton, the principles of light could be summed as follows:

• Every source of light emits large numbers of tiny particles known as corpuscles in a medium surrounding the source.
• These corpuscles are perfectly elastic, rigid, and weightless.

This represented a challenge to “wave theory”, which had been advocated by 17th century Dutch astronomer Christiaan Huygens. . These theories were first communicated in 1678 to the Paris Academy of Sciences and were published in 1690 in his “Traité de la lumière“ (“Treatise on Light“). In it, he argued a revised version of Descartes views, in which the speed of light is infinite and propagated by means of spherical waves emitted along the wave front.

## How Just Three Stars Light Up a Stellar Nursery

Today I’m going to toss a little bit of math your way. If you’re an arithmophobe, never fear: It’s mostly just me throwing around some gee-whiz numbers, and I’ll help you swallow this medicine with the sweet, sweet eye candy above.

That image is from Robert Gendler, Roberto Colombari, and Martin Pugh, and it shows the young star cluster called NGC 6193 embedded in a vast cloud of gas and dust called NGC 6188. Both are very roughly 4,000 light-years away in the constellation of Ara. The image combines data from the huge 8.2 meter Very Large Telescope in Chile with some from a much smaller 32 cm telescope.

The cluster is young, only a few million years old. The brightest stars in it are massive, hot, luminous, and blue. They flood out light, illuminating and ionizing the gas in the cloud, which responds by glowing red.

I could go into details, but I already have in countless posts about emission nebulae, as well as in Crash Course: Nebulae. I’ll leave it up to you, Bad Readers, to determine how deeply you want to dive into those particulars by clicking those links.

But I want to point something out. Images like this are gorgeous, and always stop me in my tracks. The details, the colors, the structure of the gas … all of these combine to make such arresting images!

Still, it’s the science behind them that touches some atavistic part of my brain, giving me a chill that is both intellectual and visceral.

ESO/Gendler, Colombari, and Pugh

In many such nebulae, there are quite a few massive stars lighting them up, sometimes dozens of them. But in others, like NGC 6188, it’s only a few. In this case I mean that literally: The vast majority of energy pumped into the gas is being done by three stars.

In the center of the nebula you can see two stars, their cores blurred into a single smear, but their distinct presence revealed by the pair of X-shaped diffraction spikes coming out from them. Moreover, one of those two is itself a binary star, two stars in close orbit, so close they appear as one. So you’re actually seeing three stars there! One is a brutal O3 star, probably 50,000 times more energetic than the Sun, and the other two are O6, smaller but still beasts. All together they probably crank out 100,000 times as much light as the Sun does.

If you replaced the Sun with any of those three stars, the Earth wouldn’t last long. It’d be fried to a crisp.

But here’s the thing: The glowing part of that nebula, the gas energized by those stars, is roughly 20 light-years across. That’s 200 trillion kilometers! All that gas, probably several times the mass of the Sun, glowing due to the light of just three stars.

That made me wonder: How many photons are those stars emitting?

The math on that isn’t so bad. I won’t start from first physics principles, because that would take a lot of words. Instead, let me skip around a bit.

First, how many photons does the Sun emit? Well, the energy of a photon is defined by its wavelength or frequency. The Sun emits most strongly in the green portion of the spectrum, and that’s a wavelength of about 0.5 microns (or 500 nanometers if you prefer). The equation of the energy in a single photon is:

Energy = h x c / wavelength

Where h is Planck’s constant (just a number that has units of energy times time), and c is the speed of light. You can look those numbers up, but in the end the answer is that a single green photon has an energy of about 4 x 10 -19 Joules (a Joule is a unit of energy the energy stored in a single calorie of food is equivalent to more than 4,000 Joules).

The Sun emits about 4 x 10 26 Joules of energy every second. That’s spread out over many different colors, each with their own energy, but I’m being really rough here, so assume they’re all green for math purposes. Dividing that total energy by the energy per photon gives us the number of photons the Sun emits:

4 x 10 26 / 4 x 10 -19 = 10 45

Holy. WOW. That’s a lot of photons. Written out it’s:

1,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 photons!

And that’s every second. The Sun has been doing this for 4.6 billion years, so I’ll leave it to you to figure out how many photons total the Sun’s given off since it was born (but it’s roughly 10 62 , and yikes).

Mind you, those stars lighting up NGC 6188 are 100,000 times brighter than the Sun, so they emit 10 50 photons per second! They also tend to emit higher energy light, like ultraviolet. That kind of light is preferentially absorbed by the hydrogen in the gas cloud. That ionizes the gas, blasting the electrons off the atoms. When the electron recombines, it re-emits that energy as light, usually that characteristic red you see in the image.

That’s how (well, in part that’s how) just a few stars can light up gas for trillions of kilometers around.

Funny, too: As bright as those stars are, distance is more important. At 4,000 light-years away, they’re 250 million times farther away from the Sun * . So even though they blast out 100,000 as much energy, they’re just barely visible to the naked eye at that distance. I’m not sure what’s more unnerving: The energies involved, or the vast distances. Both are mind-numbing.

So in case you were wondering, when I see astronomical images, that’s the sort of stuff that goes through my mind. I’ve said it many times, but it bears repeating: There is great beauty in astronomy, but that’s dwarfed by what these cosmic artworks teach us about the Universe.

* Correction (Oct. 26, 2016): I originally wrote 250 billion here. Oops. Still, they’re a long ways off.