Astronomy

How is the gravitational effect of galaxies outside of the visible universe on galaxies within the visible universe currently modeled?

How is the gravitational effect of galaxies outside of the visible universe on galaxies within the visible universe currently modeled?


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Given currently accepted models of the universe,

  • How much mass is outside of the visible universe?

  • What is the gravitational effect of that mass on the visible universe?

The question How strong is the gravitational stretch we experience from the edge of the universe? is possibly related, but it's focused on some stretching effect which I'm not familiar with.

One answer to the related question How much of the Universe is invisible to us, and how does it affect our theories? states:

there does not seem to be any large mass concentrations outside the observable universe, since these would be seen as bias for movement of galaxies and galaxy groups, which also supports that the rest of universe is at least very close to what we can observe directly

But this talks about the absence of large mass concentrations, while I'm asking more generically how mass outside the visible universe is reflected in current models.


We don't know…

We don't know how much Universe there is outside our observable Universe.

The observable Universe seems to have a "flat" geometry (in the 3D sense, not in 2D). If it really is globally flat, then it just goes on and on forever, i.e. there is infinite mass. However, just as Earth looks flat on small scales, it might very well be that the Universe has another geometry on scales larger than we can observe.

A recent paper (Di Valentino et al. 2019) claimed evidence for a "positively curved" geometry, implying that the Universe is only (very roughly and with high uncertainties) three times bigger than what we see (see this answer and comments for the calculation). However, the authors sort of cherry-picked one out several of the data sets of Planck Collaboration (2018), and the evidence is not convincing.

… and we don't care

However, no matter if the Universe is finite or infinite, we do not take into account the mass outside the observable Universe in any calculations. This mass does not affect us in any way. Gravity travels at the speed of light, and hence hasn't had time to reach us yet. More importantly, due to the inverse square-law, gravity on any object is by far dominated by nearby sources.

Well, we care a little

There is a sense in which you can say that the gravity is taken into account, though: So-called "cosmological simulations" aim to simulate the formation and evolution of the large-scale structure and the galaxies of the entire Universe. Of course, we cannot simulate the entire Universe, so instead we simulate a large chunk of it; large enough that another similarly-sized chunk would not be statistically different from it (preferably several hundred million light-years on each side).

A galaxy close to the edge of the computational box, say its left side, doesn't only feel the gravity of the galaxies on the right. This would make the simulated universe "implode". Rather, we use a computational trick called "periodic boundary conditions" which means that a particle that happens to travel through the left side of the box enters immediately through the right side. And a galaxy close to the left side feels the gravity of matter lying close to the right side.

Snapshot from the Virgo simulations (Jenkins et al. 1998), where I've tiled the box in several copies, emphasizing the periodic boundaries.


You don't need to model it if you assume the universe is homogeneous and isotropic. If it is, then any uniform shell of material has absolutely no gravitational effect on anything inside the shell. This is true in Newtonian physics and in GR.

https://physics.stackexchange.com/a/43640/43351

It is still not known whether the universe is infinite, but it is almost certainly at least several times larger than the observable universe (assuming homegeneity). So the anwer to how much mass is beyond the observable universe could be anything from $sim 10$ times what is in the observable universe to infinite.


Spiral galaxy

Spiral galaxies form a class of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae [1] and, as such, form part of the Hubble sequence. Most spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as the bulge. These are often surrounded by a much fainter halo of stars, many of which reside in globular clusters.

Spiral galaxies are named by their spiral structures that extend from the center into the galactic disc. The spiral arms are sites of ongoing star formation and are brighter than the surrounding disc because of the young, hot OB stars that inhabit them.

Roughly two-thirds of all spirals are observed to have an additional component in the form of a bar-like structure, [2] extending from the central bulge, at the ends of which the spiral arms begin. The proportion of barred spirals relative to barless spirals has likely changed over the history of the universe, with only about 10% containing bars about 8 billion years ago, to roughly a quarter 2.5 billion years ago, until present, where over two-thirds of the galaxies in the visible universe (Hubble volume) have bars. [3]

The Milky Way is a barred spiral, although the bar itself is difficult to observe from Earth's current position within the galactic disc. [4] The most convincing evidence for the stars forming a bar in the galactic center comes from several recent surveys, including the Spitzer Space Telescope. [5]

Together with irregular galaxies, spiral galaxies make up approximately 60% of galaxies in today's universe. [6] They are mostly found in low-density regions and are rare in the centers of galaxy clusters. [7]


The universe versus the observable universe

Both popular and professional research articles in cosmology often use the term "universe" to mean "observable universe". This can be justified on the grounds that we can never know anything by direct experimentation about any part of the universe that is causally disconnected from us, although many credible theories, such as cosmic inflation require a universe much larger than the observable universe. No evidence exists to suggest that the boundary of the observable universe corresponds precisely to the physical boundary of the universe (if such a boundary exists) this is exceedingly unlikely in that it would imply that Earth is exactly at the centre of the universe, in violation of the cosmological principle. It is likely that the galaxies within our visible universe represent only a minuscule fraction of the galaxies in the universe.

It is also possible that the universe is smaller than the observable universe. In this case, what we take to be very distant galaxies may actually be duplicate images of nearby galaxies, formed by light that has circumnavigated the universe. It is difficult to test this hypothesis experimentally because different images of a galaxy would show different eras in its history, and consequently might appear quite different. A 2004 paper claims to establish a lower bound of 24 giga parsecs (78 billion light-years) on the diameter of the universe, based on matching-circle analysis of the WMAP data.

The comoving distance from Earth to the edge of the visible universe (also called cosmic light horizon) is about 14 billion parsecs (46 billion light-years) in any direction. This defines a lower limit on the comoving radius of the observable universe, although as noted in the introduction, it's expected that the visible universe is somewhat smaller than the observable universe since we only see light from the cosmic microwave background radiation that was emitted after the time of recombination, giving us the spherical surface of last scattering (gravitational waves could theoretically allow us to observe events that occurred earlier than the time of recombination, from regions of space outside this sphere). The visible universe is thus a sphere with a diameter of about 28 billion parsecs (about 92 billion light-years). Since space is roughly flat, this size corresponds to a comoving volume of about

or about 3×10 80 cubic meters.

The figures quoted above are distances now (in cosmological time), not distances at the time the light was emitted. For example, the cosmic microwave background radiation that we see right now was emitted at the time of recombination, 379,000 years after the Big Bang, which occurred around 13.7 billion years ago. This radiation was emitted by matter that has, in the intervening time, mostly condensed into galaxies, and those galaxies are now calculated to be about 46 billion light-years from us. To estimate the distance to that matter at the time the light was emitted, a mathematical model of the expansion must be chosen and the scale factor, a(t), calculated for the selected time since the Big Bang, t. For the observationally-favoured Lambda-CDM model, using data from the WMAP satellite, such a calculation yields a scale factor change of approximately 1292. This means the universe has expanded to 1292 times the size it was when the CMBR photons were released. Hence, the most distant matter that is observable at present, 46 billion light-years away, was only 36 million light-years away from the matter that would eventually become Earth when the microwaves we are currently receiving were emitted.

Misconceptions

Many secondary sources have reported a wide variety of incorrect figures for the size of the visible universe. Some of these are listed below.

  • 13.7 billion light-years. The age of the universe is about 13.7 billion years. While it is commonly understood that nothing travels faster than light, it is a common misconception that the radius of the observable universe must therefore amount to only 13.7 billion light-years. This reasoning only makes sense if the universe is the flat spacetime of special relativity in the real universe, spacetime is highly curved on cosmological scales, which means that 3-space (which is roughly flat) is expanding, as evidenced by Hubble's law. Distances obtained as the speed of light multiplied by a cosmological time interval have no direct physical significance.
  • 15.8 billion light-years. This is obtained in the same way as the 13.7 billion light year figure, but starting from an incorrect age of the universe which was reported in the popular press in mid-2006 . For an analysis of this claim and the paper that prompted it, see .
  • 27 billion light-years. This is a diameter obtained from the (incorrect) radius of 13.7 billion light-years.
  • 156 billion light-years. This figure was obtained by doubling 78 billion light-years on the assumption that it is a radius. Since 78 billion light-years is already a diameter, the doubled figure is incorrect. This figure was very widely reported.
  • 180 billion light-years. This estimate accompanied the age estimate of 15.8 billion years in some sources it was obtained by incorrectly adding 15 percent to the incorrect figure of 156 billion light years.

How is the gravitational effect of galaxies outside of the visible universe on galaxies within the visible universe currently modeled? - Astronomy

Copyright © 2014 by author and Scientific Research Publishing Inc.

This work is licensed under the Creative Commons Attribution International License (CC BY).

Received 2 October 2014 revised 1 November 2014 accepted 28 November 2014

Static cosmology has been abandoned almost a century ago because of phenomena which were unexplained at those times. However, that scenario can be revived with the modern findings of gravitational forces, coming from outside of the “luminous world”, tugging on our universe. These unexplained phenomena were: the redshift, the CMB, and Olbers’ paradox. All these can now be explained, as done in the present manuscript. 1) The observed redshift, which is commonly attributed to the Doppler effect, can also be explained as a gravitational redshift. Thus, the universe is not expanding, as has also been described in recent publications, thereby, making the “Big Bang” hypothesis unnecessary. 2) Gravitation is induced by matter, and at least some of the distant matter is expected to be luminous. That electro-magnetic emission is extremely redshifted, and thus perceived by us as CMB. CMB is not necessarily a historic remnant related to the “Big Bang”, rather it is the redshifted light, coming from extremely distant luminous matter. 3) According to Olbers’ paradox, the night sky is expected to be bright. The sky looks dark because the light coming from extremely faraway light sources, out of our visible universe, is extremely redshifted. Therefore it is perceived by us as CMB. As in the cosmological literature many problems with the “Big Bang” hypothesis have been described, where as the problems with the static universe model are resolved in the present manuscript, the static state scenario should be renovated.

Big Bang Never Happened, CMB Is Redshifted Light, Gravitational Redshift, Dark Sky Illusion, Einstein, Static Universe

Albert Einstein proposed a homogeneous isotropic static, temporally infinite model of the universe in 1917 [1] , but then came the clamor for an expanding universe. Therefore he forwarded in 1931 a steady-state dynamic universe in expansion [2] [3] . This expanding model requires a mechanism to recreate matter and it has also been abandoned [4] . To Einstein, a static universe required a force equal, but opposite to the gravity, produced by the matter of the universe to avoid total collapse. He named this repelling force the “cosmological constant”.

Years thereafter, the static and expanding steady state cosmological models were considered obsolete. The prevailing cosmological model became the Big Bang hypothesis. However, there are many flaws with this scenario [5] [6] . Therefore, other models must also be considered.

Since those times, at the beginning of the 20 th century, many new cosmological findings have been observed. Among those are the description of the dark matter and the pulling of extra-universal forces on our universe, including the description of parallel universes. Parallel worlds, termed multiverse, or in other words―an infinite, endless universe with indefinite matter―will exert gravity all around us. This endless, infinite gravitational force pulls on our universe in all directions. The universe is tugged by this gravity coming from outside the observable universe [7] - [9] . It is indicative that observed tilt exerted across the entire horizon of our universe comes from a faraway source [10] . Problems exist with the Big Bang hypothesis, however, new cosmological findings were discovered since Einstein’s days, hence, the static world must be reconsidered.

In order to verify Einstein’s static cosmological model of 1917, the three following observations must be explained:

1) It must explain the intergalactic redshift.

2) It must explain the source of the cosmic microwave background.

3) It must explain why the night sky appears black between stars and galaxies.

Herewith are explanations to all these three cosmological observations by which the static universe model can be renovated.

2. Explaining the Intergalactic Redshift

The first observation that must be explained is the redshift theme. The mainstream explanation is the Doppler shift, and therefore, the hypothesis of an expanding universe. However, many other cosmological explanations have been described. Even Hubble, who discovered this redshift, warned about jumping to conclusions that this universe was actually expanding.

One of the oldest and prominent alternative theories is the gravitational inspired redshift. The influence of gravity on light has been proposed by Albert Einstein already in 1911 [11] . Another interpretation of gravitational redshift is by quantum celestial mechanics in which no space expansion is necessary [12] . Gravitational redshift has been described as the electromagnetic influence from gravity on photons. Energy is transferred from the light wave when it propagates from the gravitational body ensuing in the light’s redshift [13] .

As light moves out of a gravitational field, it must lose energy because it works against that gravitational field. As photons always travel at the speed of light, the only way this energy loss can show up is in the increase of wavelength (or decrease in frequency). Distant objects, like those tugging at our universe [7] - [10] , have a gravitational effect, as has dark matter. These tremendous gravitational forces can cause light to be redshifted.

Although it is generally accepted that the mass of dark matter is over 95% of the mass of the universe, its gravitational redshift effect on light is considered to be too weak to account for the observed redshift. However, if the gravitational force coming from outside the “luminous matter” is infinite and immense, it becomes evident that it is able to produce the observed redshift. The notion that gravitational forces that tug on our universe exist outside the observable universe, is already well accepted in the cosmological community [7] - [10] .

If one includes the matter of an infinite universe (multiverse), the “luminous matter” comes to be only a fraction of the total mass, so the visible universe is less than the usually described 4.9% of all matter.

The redshift can be approximated by the binominal expansion to become:

where Ζ is the redshift, G is Newton’s gravitational constant, M is the mass exerting the gravity and R is the distance between the peak of the gravitational effect to the photons source. When M becomes almost indefinite (∞), it obviously is able to redshift any light. Therefore it can account for the observed redshift.

The galaxies which are farther away from the Milky Way are more affected by the redshift caused by the parallel worlds, because their distance (R) to those out-of-the-visible-world forces, is shorter. The galaxies nearer to the Milky Way will appear less redshifted, as their distance (R) from the main gravitational field is larger, so their redshifting effect diminishes.

In an isotropic, infinite, endless cosmos the gravitational forces coming from all directions are expected to be similar. It turns out that the gravitational effect of our own vicinity is extremely minor and negligible in comparison to that of the endless multiverse. The gravitational influence coming from any direction is countered by the pull coming from the opposite direction. The redshift effect vanishes altogether due to the pull coming from the opposite direction, and that location is close to our universe.

The evidence that the average gravitational force coming from the extra-celestial gravitation is stronger than that of our universe is the observation that it pulls on clusters within our universe [10] . In other words, the magnitude of the redshift decreases as the distance (R) of the photons from the peak of the gravitational force which tugs on our universe, increases. That is, that its distance from us decreases. This explains Hubble’s finding that the redshift increases in proportion to the increase of distance of the light source from us.

Photons approaching the Milky Way might balance, or even outweigh this redshift effect. Therefore they are even blueshifted, as is the case with the Virgo cluster including the Andromeda galaxy. Photons departing from a gravitational field are redshifted whereas those approaching such fields are blueshifted. These blueshifted galaxies cast doubts on the expanding universe theory. Therefore gravitational red and blue shifts must be reconsidered [14] . The observed redshifts give the illusion that an object is receding away, when in fact an extremely immense mass is causing that redshift.

Summing up the redshift issue, there exist several alternatives to the Doppler shift. Another alternative is the gravitational redshift from a tremendously immense gravitational force induced by endless matter, much greater than the observable matter.

3. Explaining the Source of CMB

The second observation that must be explained is the CMB topic. The prevailing cosmological explanation of the CMB is that it is a historic remnant of the “light emitted by the Big Bang” and is assumed to be its thermal residue. CMB is an electromagnetic radiation with its brightest wavelength of about 1.9 mm. Therefore it is possibly an extremely redshifted light, coming from parallel worlds.

Considering that a multitude of innumerable, endless universes exist all around our universe, and their electromagnetic emission includes light like that emitted by our universe, and that light is extremely redshifted, it will be perceived by us as CMB. This very extreme redshift may be the result of the departure of the photons from the tremendously strong gravitational force caused by the countless, infinite parallel worlds all around our universe.

The light emitted by parallel worlds will have a wavelength like that of any star. As said, that light will be extremely redshifted by gravity of those parallel worlds, so it will reach us in the CMB wavelength. To calculate this redshift the sun was chosen arbitrarily, but any star could be chosen.

The peak wavelength emitted by the sun is considered to be λ source = 483 nm. The peak wavelength of the CMB is about λobs = 1.9 mm . So the redshift, which is commonly denoted by “Z” is:

CMB is a key prediction of the hot Big Bang theory and an important observation that discriminates between the “Big Bang” and the static world scenario. The recently detected ripples in the CMB, attributed to gravitational waves, also lend credence to the idea of a multiverse [15] . Gravitational waves coming from outside the visible universe can easily produce ripples. Therefore the conception of a static, endless, infinite universe must be revived.

4. Explaining the Dark Night Sky

The third observation that must be explained is the “dark night sky paradox”. The sky appears black between the stars and galaxies. It is said that if the universe is static, homogeneous at a large scale, and populated by an infinite number of stars, any sightline from earth must end at the surface of a star. So the sky at night should appear completely bright, not black. This paradox was described by the astronomer Heinrich Wilhelm Olbers (1758- 1840). This unexplained paradox is one of the evidences for a non-static universe and supports the hypothesis of an expanding universe. However, the dark sky is a completely false impression. The night sky is not dark at all, most of the light perceived by us is just out of the visual spectrum. The light emitted from very distant sources is extremely redshifted and reaches us as CMB, so we cannot see it. Therefore, we get the erroneous impression that the sky is dark. The extreme redshift of the light is the solution of Olbers’ paradox.

The Big Bang theory, in spite of being the mainstream hypothesis, is very problematic [5] [6] . Hence, other models should also be considered. These include the old Einstein’s 1917 static world scenario. In order to revive this static state model of the universe, its old problems must be resolved. This is done in this manuscript and has the consequent implications:

¾ The redshift has been explained by gravitational forces which tug on our universe [10] . It has already been reported that observational evidence favors a static universe and that the universe is not expanding [16] [17] .

¾ The CMB is redshifted light emitted by sources out of the observable universe, and Olber’s paradox is just an illusion.

¾ The light emitted from distant light sources is extremely redshifted. Therefore it is perceived on earth as CMB which is out of our visible wavelength.

In conclusion, alternative explanations for the redshift, CMB and Olbers’ paradox, which are the cornerstones of the “Big Bang” hypothesis, are presented in this paper. By solving the problems with the static state model of the universe, this model can be renovated. Therefore the “Big Bang” may never have happened.

The static state model does not require the creation of a singularity from nothing, and does not have the many problems described with the Big Bang hypothesis. So the static world model again becomes a credible belief as it was in 1917. Although much evidence accumulated against the Big Bang hypothesis, it is still widely accepted. Therefore, the significance of the present paper is in solving the problems with the alternative model, the static scenario.


Contents

The Big Bang theory offers a comprehensive explanation for a broad range of observed phenomena, including the abundances of the light elements, the CMB, large-scale structure, and Hubble's law. [10] The theory depends on two major assumptions: the universality of physical laws and the cosmological principle. The universality of physical laws is one of the underlying principles of the theory of relativity. The cosmological principle states that on large scales the universe is homogeneous and isotropic – appearing the same in all directions regardless of location. [11]

These ideas were initially taken as postulates, but later efforts were made to test each of them. For example, the first assumption has been tested by observations showing that largest possible deviation of the fine-structure constant over much of the age of the universe is of order 10 −5 . [12] Also, general relativity has passed stringent tests on the scale of the Solar System and binary stars. [13] [14] [notes 1]

The large-scale universe appears isotropic as viewed from Earth. If it is indeed isotropic, the cosmological principle can be derived from the simpler Copernican principle, which states that there is no preferred (or special) observer or vantage point. To this end, the cosmological principle has been confirmed to a level of 10 −5 via observations of the temperature of the CMB. At the scale of the CMB horizon, the universe has been measured to be homogeneous with an upper bound on the order of 10% inhomogeneity, as of 1995. [15]

Expansion of space

The expansion of the Universe was inferred from early twentieth century astronomical observations and is an essential ingredient of the Big Bang theory. Mathematically, general relativity describes spacetime by a metric, which determines the distances that separate nearby points. The points, which can be galaxies, stars, or other objects, are specified using a coordinate chart or "grid" that is laid down over all spacetime. The cosmological principle implies that the metric should be homogeneous and isotropic on large scales, which uniquely singles out the Friedmann–Lemaître–Robertson–Walker (FLRW) metric. This metric contains a scale factor, which describes how the size of the universe changes with time. This enables a convenient choice of a coordinate system to be made, called comoving coordinates. In this coordinate system, the grid expands along with the universe, and objects that are moving only because of the expansion of the universe, remain at fixed points on the grid. While their coordinate distance (comoving distance) remains constant, the physical distance between two such co-moving points expands proportionally with the scale factor of the universe. [16]

The Big Bang is not an explosion of matter moving outward to fill an empty universe. Instead, space itself expands with time everywhere and increases the physical distances between comoving points. In other words, the Big Bang is not an explosion in space, but rather an expansion of space. [4] Because the FLRW metric assumes a uniform distribution of mass and energy, it applies to our universe only on large scales—local concentrations of matter such as our galaxy do not necessarily expand with the same speed as the whole Universe. [17]

Horizons

An important feature of the Big Bang spacetime is the presence of particle horizons. Since the universe has a finite age, and light travels at a finite speed, there may be events in the past whose light has not yet had time to reach us. This places a limit or a past horizon on the most distant objects that can be observed. Conversely, because space is expanding, and more distant objects are receding ever more quickly, light emitted by us today may never "catch up" to very distant objects. This defines a future horizon, which limits the events in the future that we will be able to influence. The presence of either type of horizon depends on the details of the FLRW model that describes our universe. [18]

Our understanding of the universe back to very early times suggests that there is a past horizon, though in practice our view is also limited by the opacity of the universe at early times. So our view cannot extend further backward in time, though the horizon recedes in space. If the expansion of the universe continues to accelerate, there is a future horizon as well. [18]

Thermalisation

Some processes in the early universe occurred too slowly, compared to the expansion rate of the universe, to reach approximate thermodynamic equilibrium. Others were fast enough to reach thermalisation. The parameter usually used to find out whether a process in the very early universe has reached thermal equilibrium is the ratio between the rate of the process (usually rate of collisions between particles) and the Hubble parameter. The larger the ratio, the more time particles had to thermalise before they were too far away from each other. [19]

According to the Big Bang theory, the universe at the beginning was very hot and very compact, and since then it has been expanding and cooling down.

Singularity

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. [20] This irregular behavior, known as the gravitational singularity, indicates that general relativity is not an adequate description of the laws of physics in this regime. Models based on general relativity alone can not extrapolate toward the singularity—before the end of the so-called Planck epoch. [5]

This primordial singularity is itself sometimes called "the Big Bang", [21] but the term can also refer to a more generic early hot, dense phase [22] [notes 2] of the universe. In either case, "the Big Bang" as an event is also colloquially referred to as the "birth" of our universe since it represents the point in history where the universe can be verified to have entered into a regime where the laws of physics as we understand them (specifically general relativity and the Standard Model of particle physics) work. Based on measurements of the expansion using Type Ia supernovae and measurements of temperature fluctuations in the cosmic microwave background, the time that has passed since that event—known as the "age of the universe"—is 13.799 ± 0.021 billion years. [23]

Despite being extremely dense at this time—far denser than is usually required to form a black hole—the universe did not re-collapse into a singularity. Commonly used calculations and limits for explaining gravitational collapse are usually based upon objects of relatively constant size, such as stars, and do not apply to rapidly expanding space such as the Big Bang. Since the early universe did not immediately collapse into a multitude of black holes, matter at that time must have been very evenly distributed with a negligible density gradient. [24]

Inflation and baryogenesis

The earliest phases of the Big Bang are subject to much speculation, since astronomical data about them are not available. In the most common models the universe was filled homogeneously and isotropically with a very high energy density and huge temperatures and pressures, and was very rapidly expanding and cooling. The period from 0 to 10 −43 seconds into the expansion, the Planck epoch, was a phase in which the four fundamental forces — the electromagnetic force, the strong nuclear force, the weak nuclear force, and the gravitational force, were unified as one. [25] In this stage, the characteristic scale length of the universe was the Planck length, 1.6 × 10 −35 m , and consequently had a temperature of approximately 10 32 degrees Celsius. Even the very concept of a particle breaks down in these conditions. A proper understanding of this period awaits the development of a theory of quantum gravity. [26] [27] The Planck epoch was succeeded by the grand unification epoch beginning at 10 −43 seconds, where gravitation separated from the other forces as the universe's temperature fell. [25]

At approximately 10 −37 seconds into the expansion, a phase transition caused a cosmic inflation, during which the universe grew exponentially, unconstrained by the light speed invariance, and temperatures dropped by a factor of 100,000. Microscopic quantum fluctuations that occurred because of Heisenberg's uncertainty principle were amplified into the seeds that would later form the large-scale structure of the universe. [28] At a time around 10 −36 seconds, the electroweak epoch begins when the strong nuclear force separates from the other forces, with only the electromagnetic force and weak nuclear force remaining unified. [29]

Inflation stopped at around the 10 −33 to 10 −32 seconds mark, with the universe's volume having increased by a factor of at least 10 78 . Reheating occurred until the universe obtained the temperatures required for the production of a quark–gluon plasma as well as all other elementary particles. [30] [31] 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. [4] At some point, an unknown reaction called baryogenesis violated the conservation of baryon number, leading to a very small excess of quarks and leptons over antiquarks and antileptons—of the order of one part in 30 million. This resulted in the predominance of matter over antimatter in the present universe. [32]

Cooling

The universe continued to decrease in density and fall in temperature, hence the typical energy of each particle was decreasing. Symmetry-breaking phase transitions put the fundamental forces of physics and the parameters of elementary particles into their present form, with the electromagnetic force and weak nuclear force separating at about 10 −12 seconds. [29] [33] After about 10 −11 seconds, the picture becomes less speculative, since particle energies drop to values that can be attained in particle accelerators. At about 10 −6 seconds, quarks and gluons combined to form baryons such as protons and neutrons. The small excess of quarks over antiquarks led to a small excess of baryons over antibaryons. The temperature was now no longer high enough to create new proton–antiproton pairs (similarly for neutrons–antineutrons), so a mass annihilation immediately followed, leaving just one in 10 8 of the original matter particles and none of their antiparticles. [34] A similar process happened at about 1 second for electrons and positrons. After these annihilations, the remaining protons, neutrons and electrons were no longer moving relativistically and the energy density of the universe was dominated by photons (with a minor contribution from neutrinos).

A few minutes into the expansion, when the temperature was about a billion kelvin and the density of matter in the universe was comparable to the current density of Earth's atmosphere, neutrons combined with protons to form the universe's deuterium and helium nuclei in a process called Big Bang nucleosynthesis (BBN). [35] Most protons remained uncombined as hydrogen nuclei. [36]

As the universe cooled, the rest energy density of matter came to gravitationally dominate that of the photon radiation. After about 379,000 years, the electrons and nuclei combined into atoms (mostly hydrogen), which were able to emit radiation. This relic radiation, which continued through space largely unimpeded, is known as the cosmic microwave background. [36]

Structure formation

Over a long period of time, the slightly denser regions of the uniformly distributed matter gravitationally attracted nearby matter and thus grew even denser, forming gas clouds, stars, galaxies, and the other astronomical structures observable today. [4] The details of this process depend on the amount and type of matter in the universe. The four possible types of matter are known as cold dark matter, warm dark matter, hot dark matter, and baryonic matter. The best measurements available, from the Wilkinson Microwave Anisotropy Probe (WMAP), show that the data is well-fit by a Lambda-CDM model in which dark matter is assumed to be cold (warm dark matter is ruled out by early reionization), [38] and is estimated to make up about 23% of the matter/energy of the universe, while baryonic matter makes up about 4.6%. [39] In an "extended model" which includes hot dark matter in the form of neutrinos, [40] then if the "physical baryon density" Ω b h 2 >h^<2>> is estimated at about 0.023 (this is different from the 'baryon density' Ω b >> expressed as a fraction of the total matter/energy density, which is about 0.046), and the corresponding cold dark matter density Ω c h 2 >h^<2>> is about 0.11, the corresponding neutrino density Ω v h 2 >h^<2>> is estimated to be less than 0.0062. [39]

Cosmic acceleration

Independent lines of evidence from Type Ia supernovae and the CMB imply that the universe today is dominated by a mysterious form of energy known as dark energy, which apparently permeates all of space. The observations suggest 73% of the total energy density of today's universe is in this form. When the universe was very young, it was likely infused with dark energy, but with less space and everything closer together, gravity predominated, and it was slowly braking the expansion. But eventually, after numerous billion years of expansion, the declining density of matter relative to the density of dark energy caused the expansion of the universe to slowly begin to accelerate. [7]

Dark energy in its simplest formulation takes the form of the cosmological constant term in Einstein field equations of general relativity, but its composition and mechanism are unknown and, more generally, the details of its equation of state and relationship with the Standard Model of particle physics continue to be investigated both through observation and theoretically. [7]

All of this cosmic evolution after the inflationary epoch can be rigorously described and modeled by the ΛCDM model of cosmology, which uses the independent frameworks of quantum mechanics and general relativity. There are no easily testable models that would describe the situation prior to approximately 10 −15 seconds. [41] Understanding this earliest of eras in the history of the universe is currently one of the greatest unsolved problems in physics.

Etymology

English astronomer Fred Hoyle is credited with coining the term "Big Bang" during a talk for a March 1949 BBC Radio broadcast, [42] saying: "These theories were based on the hypothesis that all the matter in the universe was created in one big bang at a particular time in the remote past." [43] [44]

It is popularly reported that Hoyle, who favored an alternative "steady-state" cosmological model, intended this to be pejorative, [45] but Hoyle explicitly denied this and said it was just a striking image meant to highlight the difference between the two models. [46] [47]

Development

The Big Bang theory developed from observations of the structure of the universe and from theoretical considerations. In 1912, Vesto Slipher measured the first Doppler shift of a "spiral nebula" (spiral nebula is the obsolete term for spiral galaxies), and soon discovered that almost all such nebulae were receding from Earth. He did not grasp the cosmological implications of this fact, and indeed at the time it was highly controversial whether or not these nebulae were "island universes" outside our Milky Way. [49] [50] Ten years later, Alexander Friedmann, a Russian cosmologist and mathematician, derived the Friedmann equations from Einstein field equations, showing that the universe might be expanding in contrast to the static universe model advocated by Albert Einstein at that time. [51]

In 1924, American astronomer Edwin Hubble's measurement of the great distance to the nearest spiral nebulae showed that these systems were indeed other galaxies. Starting that same year, Hubble painstakingly developed a series of distance indicators, the forerunner of the cosmic distance ladder, using the 100-inch (2.5 m) Hooker telescope at Mount Wilson Observatory. This allowed him to estimate distances to galaxies whose redshifts had already been measured, mostly by Slipher. In 1929, Hubble discovered a correlation between distance and recessional velocity—now known as Hubble's law. [52] [53] By that time, Lemaître had already shown that this was expected, given the cosmological principle. [7]

Independently deriving Friedmann's equations in 1927, Georges Lemaître, a Belgian physicist and Roman Catholic priest, proposed that the inferred recession of the nebulae was due to the expansion of the universe. [54] In 1931, Lemaître went further and suggested that the evident expansion of the universe, if projected back in time, meant that the further in the past the smaller the universe was, until at some finite time in the past all the mass of the universe was concentrated into a single point, a "primeval atom" where and when the fabric of time and space came into existence. [55]

In the 1920s and 1930s, almost every major cosmologist preferred an eternal steady-state universe, and several complained that the beginning of time implied by the Big Bang imported religious concepts into physics this objection was later repeated by supporters of the steady-state theory. [56] This perception was enhanced by the fact that the originator of the Big Bang theory, Lemaître, was a Roman Catholic priest. [57] Arthur Eddington agreed with Aristotle that the universe did not have a beginning in time, viz., that matter is eternal. A beginning in time was "repugnant" to him. [58] [59] Lemaître, however, disagreed:

If the world has begun with a single quantum, the notions of space and time would altogether fail to have any meaning at the beginning they would only begin to have a sensible meaning when the original quantum had been divided into a sufficient number of quanta. If this suggestion is correct, the beginning of the world happened a little before the beginning of space and time. [60]

During the 1930s, other ideas were proposed as non-standard cosmologies to explain Hubble's observations, including the Milne model, [61] the oscillatory universe (originally suggested by Friedmann, but advocated by Albert Einstein and Richard C. Tolman) [62] and Fritz Zwicky's tired light hypothesis. [63]

After World War II, two distinct possibilities emerged. One was Fred Hoyle's steady-state model, whereby new matter would be created as the universe seemed to expand. In this model the universe is roughly the same at any point in time. [64] The other was Lemaître's Big Bang theory, advocated and developed by George Gamow, who introduced BBN [65] and whose associates, Ralph Alpher and Robert Herman, predicted the CMB. [66] Ironically, it was Hoyle who coined the phrase that came to be applied to Lemaître's theory, referring to it as "this big bang idea" during a BBC Radio broadcast in March 1949. [47] [44] [notes 3] For a while, support was split between these two theories. Eventually, the observational evidence, most notably from radio source counts, began to favor Big Bang over steady state. The discovery and confirmation of the CMB in 1964 secured the Big Bang as the best theory of the origin and evolution of the universe. [67] Much of the current work in cosmology includes understanding how galaxies form in the context of the Big Bang, understanding the physics of the universe at earlier and earlier times, and reconciling observations with the basic theory. [ citation needed ]

In 1968 and 1970, Roger Penrose, Stephen Hawking, and George F. R. Ellis published papers where they showed that mathematical singularities were an inevitable initial condition of relativistic models of the Big Bang. [68] [69] Then, from the 1970s to the 1990s, cosmologists worked on characterizing the features of the Big Bang universe and resolving outstanding problems. In 1981, Alan Guth made a breakthrough in theoretical work on resolving certain outstanding theoretical problems in the Big Bang theory with the introduction of an epoch of rapid expansion in the early universe he called "inflation". [70] Meanwhile, during these decades, two questions in observational cosmology that generated much discussion and disagreement were over the precise values of the Hubble Constant [71] and the matter-density of the universe (before the discovery of dark energy, thought to be the key predictor for the eventual fate of the universe). [72]

In the mid-1990s, observations of certain globular clusters appeared to indicate that they were about 15 billion years old, which conflicted with most then-current estimates of the age of the universe (and indeed with the age measured today). This issue was later resolved when new computer simulations, which included the effects of mass loss due to stellar winds, indicated a much younger age for globular clusters. [73] While there still remain some questions as to how accurately the ages of the clusters are measured, globular clusters are of interest to cosmology as some of the oldest objects in the universe. [ citation needed ]

Significant progress in Big Bang cosmology has been made since the late 1990s as a result of advances in telescope technology as well as the analysis of data from satellites such as the Cosmic Background Explorer (COBE), [74] the Hubble Space Telescope and WMAP. [75] Cosmologists now have fairly precise and accurate measurements of many of the parameters of the Big Bang model, and have made the unexpected discovery that the expansion of the universe appears to be accelerating. [76] [77]

The earliest and most direct observational evidence of the validity of the theory are the expansion of the universe according to Hubble's law (as indicated by the redshifts of galaxies), discovery and measurement of the cosmic microwave background and the relative abundances of light elements produced by Big Bang nucleosynthesis (BBN). More recent evidence includes observations of galaxy formation and evolution, and the distribution of large-scale cosmic structures, [79] These are sometimes called the "four pillars" of the Big Bang theory. [80]

Precise modern models of the Big Bang appeal to various exotic physical phenomena that have not been observed in terrestrial laboratory experiments or incorporated into the Standard Model of particle physics. Of these features, dark matter is currently the subject of most active laboratory investigations. [81] Remaining issues include the cuspy halo problem [82] and the dwarf galaxy problem [83] of cold dark matter. Dark energy is also an area of intense interest for scientists, but it is not clear whether direct detection of dark energy will be possible. [84] Inflation and baryogenesis remain more speculative features of current Big Bang models. Viable, quantitative explanations for such phenomena are still being sought. These are currently unsolved problems in physics.

Hubble's law and the expansion of space

Observations of distant galaxies and quasars show that these objects are redshifted: the light emitted from them has been shifted to longer wavelengths. This can be seen by taking a frequency spectrum of an object and matching the spectroscopic pattern of emission or absorption lines corresponding to atoms of the chemical elements interacting with the light. These redshifts are uniformly isotropic, distributed evenly among the observed objects in all directions. If the redshift is interpreted as a Doppler shift, the recessional velocity of the object can be calculated. For some galaxies, it is possible to estimate distances via the cosmic distance ladder. When the recessional velocities are plotted against these distances, a linear relationship known as Hubble's law is observed: [52] v = H 0 D D> where

Hubble's law has two possible explanations. Either we are at the center of an explosion of galaxies—which is untenable under the assumption of the Copernican principle—or the universe is uniformly expanding everywhere. This universal expansion was predicted from general relativity by Friedmann in 1922 [51] and Lemaître in 1927, [54] well before Hubble made his 1929 analysis and observations, and it remains the cornerstone of the Big Bang theory as developed by Friedmann, Lemaître, Robertson, and Walker.

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 homogeneous, [52] 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.

Measurements of the effects of the cosmic microwave background radiation on the dynamics of distant astrophysical systems in 2000 proved the Copernican principle, that, on a cosmological scale, the Earth is not in a central position. [86] Radiation from the Big Bang was demonstrably warmer at earlier times throughout the universe. Uniform cooling of the CMB 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.

Cosmic microwave background radiation

In 1964, Arno Penzias and Robert Wilson serendipitously discovered the cosmic background radiation, an omnidirectional signal in the microwave band. [67] Their discovery provided substantial confirmation of the big-bang predictions by Alpher, Herman and Gamow around 1950. Through the 1970s, the radiation was found to be approximately consistent with a blackbody spectrum in all directions this spectrum has been redshifted by the expansion of the universe, and today corresponds to approximately 2.725 K. This tipped the balance of evidence in favor of the Big Bang model, and Penzias and Wilson were awarded the 1978 Nobel Prize in Physics.

The surface of last scattering corresponding to emission of the CMB occurs shortly after recombination, the epoch when neutral hydrogen becomes stable. Prior to this, the universe comprised a hot dense photon-baryon plasma sea where photons were quickly scattered from free charged particles. Peaking at around 372 ± 14 kyr , [38] the mean free path for a photon becomes long enough to reach the present day and the universe becomes transparent.

In 1989, NASA launched COBE, which made two major advances: in 1990, high-precision spectrum measurements showed that the CMB frequency spectrum is an almost perfect blackbody with no deviations at a level of 1 part in 10 4 , and measured a residual temperature of 2.726 K (more recent measurements have revised this figure down slightly to 2.7255 K) then in 1992, further COBE measurements discovered tiny fluctuations (anisotropies) in the CMB temperature across the sky, at a level of about one part in 10 5 . [74] John C. Mather and George Smoot were awarded the 2006 Nobel Prize in Physics for their leadership in these results.

During the following decade, CMB anisotropies were further investigated by a large number of ground-based and balloon experiments. In 2000–2001, several experiments, most notably BOOMERanG, found the shape of the universe to be spatially almost flat by measuring the typical angular size (the size on the sky) of the anisotropies. [91] [92] [93]

In early 2003, the first results of the Wilkinson Microwave Anisotropy Probe were released, yielding what were at the time the most accurate values for some of the cosmological parameters. The results disproved several specific cosmic inflation models, but are consistent with the inflation theory in general. [75] The Planck space probe was launched in May 2009. Other ground and balloon-based cosmic microwave background experiments are ongoing.

Abundance of primordial elements

Using the Big Bang model, it is possible to calculate the concentration of helium-4, helium-3, deuterium, and lithium-7 in the universe as ratios to the amount of ordinary hydrogen. [35] The relative abundances depend on a single parameter, the ratio of photons to baryons. This value can be calculated independently from the detailed structure of CMB fluctuations. The ratios predicted (by mass, not by number) are about 0.25 for He 4 / H >> , about 10 −3 for H 2 / H >> , about 10 −4 for He 3 / H >> and about 10 −9 for Li 7 / H >> . [35]

The measured abundances all agree at least roughly with those predicted from a single value of the baryon-to-photon ratio. The agreement is excellent for deuterium, close but formally discrepant for He 4 >> , and off by a factor of two for Li 7 >> (this anomaly is known as the cosmological lithium problem) in the latter two cases, there are substantial systematic uncertainties. Nonetheless, the general consistency with abundances predicted by BBN is strong evidence for the Big Bang, as the theory is the only known explanation for the relative abundances of light elements, and it is virtually impossible to "tune" the Big Bang to produce much more or less than 20–30% helium. [94] Indeed, there is no obvious reason outside of the Big Bang that, for example, the young universe (i.e., before star formation, as determined by studying matter supposedly free of stellar nucleosynthesis products) should have more helium than deuterium or more deuterium than He 3 >> , and in constant ratios, too. [95] : 182–185

Galactic evolution and distribution

Detailed observations of the morphology and distribution of galaxies and quasars are in agreement with the current state of the Big Bang theory. A combination of observations and theory suggest that the first quasars and galaxies formed about a billion years after the Big Bang, and since then, larger structures have been forming, such as galaxy clusters and superclusters. [96]

Populations of stars have been aging and evolving, so that distant galaxies (which are observed as they were in the early universe) appear very different from nearby galaxies (observed in a more recent state). Moreover, galaxies that formed relatively recently, appear markedly different from galaxies formed at similar distances but shortly after the Big Bang. These observations are strong arguments against the steady-state model. Observations of star formation, galaxy and quasar distributions and larger structures, agree well with Big Bang simulations of the formation of structure in the universe, and are helping to complete details of the theory. [96] [97]

Primordial gas clouds

In 2011, astronomers found what they believe to be pristine clouds of primordial gas by analyzing absorption lines in the spectra of distant quasars. Before this discovery, all other astronomical objects have been observed to contain heavy elements that are formed in stars. These two clouds of gas contain no elements heavier than hydrogen and deuterium. [102] [103] Since the clouds of gas have no heavy elements, they likely formed in the first few minutes after the Big Bang, during BBN.

Other lines of evidence

The age of the universe as estimated from the Hubble expansion and the CMB is now in good agreement with other estimates using the ages of the oldest stars, both as measured by applying the theory of stellar evolution to globular clusters and through radiometric dating of individual Population II stars. [104] It is also in good agreement with age estimates based on measurements of the expansion using Type Ia supernovae and measurements of temperature fluctuations in the cosmic microwave background. [23] The agreement of independent measurements of this age supports the Lambda-CDM (ΛCDM) model, since the model is used to relate some of the measurements to an age estimate, and all estimates turn out to agree. Still, some observations of objects from the relatively early universe (in particular quasar APM 08279+5255) raise concern as to whether these objects had enough time to form so early in the ΛCDM model. [105] [106]

The prediction that the CMB temperature was higher in the past has been experimentally supported by observations of very low temperature absorption lines in gas clouds at high redshift. [107] This prediction also implies that the amplitude of the Sunyaev–Zel'dovich effect in clusters of galaxies does not depend directly on redshift. Observations have found this to be roughly true, but this effect depends on cluster properties that do change with cosmic time, making precise measurements difficult. [108] [109]

Future observations

Future gravitational-wave observatories might be able to detect primordial gravitational waves, relics of the early universe, up to less than a second after the Big Bang. [110] [111]

As with any theory, a number of mysteries and problems have arisen as a result of the development of the Big Bang theory. Some of these mysteries and problems have been resolved while others are still outstanding. Proposed solutions to some of the problems in the Big Bang model have revealed new mysteries of their own. For example, the horizon problem, the magnetic monopole problem, and the flatness problem are most commonly resolved with inflationary theory, but the details of the inflationary universe are still left unresolved and many, including some founders of the theory, say it has been disproven. [112] [113] [114] [115] What follows are a list of the mysterious aspects of the Big Bang theory still under intense investigation by cosmologists and astrophysicists.

Baryon asymmetry

It is not yet understood why the universe has more matter than antimatter. [32] It is generally assumed that when the universe was young and very hot it was in statistical equilibrium and contained equal numbers of baryons and antibaryons. However, observations suggest that the universe, including its most distant parts, is made almost entirely of matter. A process called baryogenesis was hypothesized to account for the asymmetry. For baryogenesis to occur, the Sakharov conditions must be satisfied. These require that baryon number is not conserved, that C-symmetry and CP-symmetry are violated and that the universe depart from thermodynamic equilibrium. [116] All these conditions occur in the Standard Model, but the effects are not strong enough to explain the present baryon asymmetry.

Dark energy

Measurements of the redshift–magnitude relation for type Ia supernovae indicate that the expansion of the universe has been accelerating since the universe was about half its present age. To explain this acceleration, general relativity requires that much of the energy in the universe consists of a component with large negative pressure, dubbed "dark energy". [7]

Dark energy, though speculative, solves numerous problems. Measurements of the cosmic microwave background indicate that the universe is very nearly spatially flat, and therefore according to general relativity the universe must have almost exactly the critical density of mass/energy. But the mass density of the universe can be measured from its gravitational clustering, and is found to have only about 30% of the critical density. [7] Since theory suggests that dark energy does not cluster in the usual way it is the best explanation for the "missing" energy density. Dark energy also helps to explain two geometrical measures of the overall curvature of the universe, one using the frequency of gravitational lenses, [117] and the other using the characteristic pattern of the large-scale structure as a cosmic ruler.

Negative pressure is believed to be a property of vacuum energy, but the exact nature and existence of dark energy remains one of the great mysteries of the Big Bang. Results from the WMAP team in 2008 are in accordance with a universe that consists of 73% dark energy, 23% dark matter, 4.6% regular matter and less than 1% neutrinos. [39] According to theory, the energy density in matter decreases with the expansion of the universe, but the dark energy density remains constant (or nearly so) as the universe expands. Therefore, matter made up a larger fraction of the total energy of the universe in the past than it does today, but its fractional contribution will fall in the far future as dark energy becomes even more dominant.

The dark energy component of the universe has been explained by theorists using a variety of competing theories including Einstein's cosmological constant but also extending to more exotic forms of quintessence or other modified gravity schemes. [118] A cosmological constant problem, sometimes called the "most embarrassing problem in physics", results from the apparent discrepancy between the measured energy density of dark energy, and the one naively predicted from Planck units. [119]

Dark matter

During the 1970s and the 1980s, various observations showed that there is not sufficient visible matter in the universe to account for the apparent strength of gravitational forces within and between galaxies. This led to the idea that up to 90% of the matter in the universe is dark matter that does not emit light or interact with normal baryonic matter. In addition, the assumption that the universe is mostly normal matter led to predictions that were strongly inconsistent with observations. In particular, the universe today is far more lumpy and contains far less deuterium than can be accounted for without dark matter. While dark matter has always been controversial, it is inferred by various observations: the anisotropies in the CMB, galaxy cluster velocity dispersions, large-scale structure distributions, gravitational lensing studies, and X-ray measurements of galaxy clusters. [120]

Indirect evidence for dark matter comes from its gravitational influence on other matter, as no dark matter particles have been observed in laboratories. Many particle physics candidates for dark matter have been proposed, and several projects to detect them directly are underway. [121]

Additionally, there are outstanding problems associated with the currently favored cold dark matter model which include the dwarf galaxy problem [83] and the cuspy halo problem. [82] Alternative theories have been proposed that do not require a large amount of undetected matter, but instead modify the laws of gravity established by Newton and Einstein yet no alternative theory has been as successful as the cold dark matter proposal in explaining all extant observations. [122]

Horizon problem

The horizon problem results from the premise that information cannot travel faster than light. In a universe of finite age this sets a limit—the particle horizon—on the separation of any two regions of space that are in causal contact. [123] The observed isotropy of the CMB is problematic in this regard: if the universe had been dominated by radiation or matter at all times up to the epoch of last scattering, the particle horizon at that time would correspond to about 2 degrees on the sky. There would then be no mechanism to cause wider regions to have the same temperature. [95] : 191–202

A resolution to this apparent inconsistency is offered by inflationary theory in which a homogeneous and isotropic scalar energy field dominates the universe at some very early period (before baryogenesis). During inflation, the universe undergoes exponential expansion, and the particle horizon expands much more rapidly than previously assumed, so that regions presently on opposite sides of the observable universe are well inside each other's particle horizon. The observed isotropy of the CMB then follows from the fact that this larger region was in causal contact before the beginning of inflation. [28] : 180–186

Heisenberg's uncertainty principle predicts that during the inflationary phase there would be quantum thermal fluctuations, which would be magnified to a cosmic scale. These fluctuations served as the seeds for all the current structures in the universe. [95] : 207 Inflation predicts that the primordial fluctuations are nearly scale invariant and Gaussian, which has been accurately confirmed by measurements of the CMB. [75] : sec 6

If inflation occurred, exponential expansion would push large regions of space well beyond our observable horizon. [28] : 180–186

A related issue to the classic horizon problem arises because in most standard cosmological inflation models, inflation ceases well before electroweak symmetry breaking occurs, so inflation should not be able to prevent large-scale discontinuities in the electroweak vacuum since distant parts of the observable universe were causally separate when the electroweak epoch ended. [124]

Magnetic monopoles

The magnetic monopole objection was raised in the late 1970s. Grand Unified theories (GUTs) predicted topological defects in space that would manifest as magnetic monopoles. These objects would be produced efficiently in the hot early universe, resulting in a density much higher than is consistent with observations, given that no monopoles have been found. This problem is resolved by cosmic inflation, which removes all point defects from the observable universe, in the same way that it drives the geometry to flatness. [123]

Flatness problem

The flatness problem (also known as the oldness problem) is an observational problem associated with a FLRW. [123] The universe may have positive, negative, or zero spatial curvature depending on its total energy density. Curvature is negative if its density is less than the critical density positive if greater and zero at the critical density, in which case space is said to be flat. Observations indicate the universe is consistent with being flat. [125] [126]

The problem is that any small departure from the critical density grows with time, and yet the universe today remains very close to flat. [notes 4] Given that a natural timescale for departure from flatness might be the Planck time, 10 −43 seconds, [4] the fact that the universe has reached neither a heat death nor a Big Crunch after billions of years requires an explanation. For instance, even at the relatively late age of a few minutes (the time of nucleosynthesis), the density of the universe must have been within one part in 10 14 of its critical value, or it would not exist as it does today. [127]

Before observations of dark energy, cosmologists considered two scenarios for the future of the universe. If the mass density of the universe were greater than the critical density, then the universe would reach a maximum size and then begin to collapse. It would become denser and hotter again, ending with a state similar to that in which it started—a Big Crunch. [18]

Alternatively, if the density in the universe were equal to or below the critical density, the expansion would slow down but never stop. Star formation would cease with the consumption of interstellar gas in each galaxy stars would burn out, leaving white dwarfs, neutron stars, and black holes. Collisions between these would result in mass accumulating into larger and larger black holes. The average temperature of the universe would very gradually asymptotically approach absolute zero—a Big Freeze. [128] Moreover, if protons are unstable, then baryonic matter would disappear, leaving only radiation and black holes. Eventually, black holes would evaporate by emitting Hawking radiation. The entropy of the universe would increase to the point where no organized form of energy could be extracted from it, a scenario known as heat death. [129]

Modern observations of accelerating expansion imply that more and more of the currently visible universe will pass beyond our event horizon and out of contact with us. The eventual result is not known. The ΛCDM model of the universe contains dark energy in the form of a cosmological constant. This theory suggests that only gravitationally bound systems, such as galaxies, will remain together, and they too will be subject to heat death as the universe expands and cools. Other explanations of dark energy, called phantom energy theories, suggest that ultimately galaxy clusters, stars, planets, atoms, nuclei, and matter itself will be torn apart by the ever-increasing expansion in a so-called Big Rip. [130]

One of the common misconceptions about the Big Bang model is that it fully explains the origin of the universe. However, the Big Bang model does not describe how energy, time, and space were caused, but rather it describes the emergence of the present universe from an ultra-dense and high-temperature initial state. [131] It is misleading to visualize the Big Bang by comparing its size to everyday objects. When the size of the universe at Big Bang is described, it refers to the size of the observable universe, and not the entire universe. [17]

Hubble's law predicts that galaxies that are beyond Hubble distance recede faster than the speed of light. However, special relativity does not apply beyond motion through space. Hubble's law describes velocity that results from expansion of space, rather than through space. [17]

Astronomers often refer to the cosmological redshift as a Doppler shift which can lead to a misconception. [17] Although similar, the cosmological redshift is not identical to the classically derived Doppler redshift because most elementary derivations of the Doppler redshift do not accommodate the expansion of space. Accurate derivation of the cosmological redshift requires the use of general relativity, and while a treatment using simpler Doppler effect arguments gives nearly identical results for nearby galaxies, interpreting the redshift of more distant galaxies as due to the simplest Doppler redshift treatments can cause confusion. [17]

The Big Bang explains the evolution of the universe from a starting density and temperature that is well beyond humanity's capability to replicate, so extrapolations to the most extreme conditions and earliest times are necessarily more speculative. Lemaître called this initial state the "primeval atom" while Gamow called the material "ylem". How the initial state of the universe originated is still an open question, but the Big Bang model does constrain some of its characteristics. For example, specific laws of nature most likely came to existence in a random way, but as inflation models show, some combinations of these are far more probable. [132] A topologically flat universe implies a balance between gravitational potential energy and other energy forms, requiring no additional energy to be created. [125] [126]

The Big Bang theory, built upon the equations of classical general relativity, indicates a singularity at the origin of cosmic time, and such an infinite energy density may be a physical impossibility. However, the physical theories of general relativity and quantum mechanics as currently realized are not applicable before the Planck epoch, and correcting this will require the development of a correct treatment of quantum gravity. [20] Certain quantum gravity treatments, such as the Wheeler–DeWitt equation, imply that time itself could be an emergent property. [133] As such, physics may conclude that time did not exist before the Big Bang. [134] [135]

While it is not known what could have preceded the hot dense state of the early universe or how and why it originated, or even whether such questions are sensible, speculation abounds on the subject of "cosmogony".

Some speculative proposals in this regard, each of which entails untested hypotheses, are:

  • The simplest models, in which the Big Bang was caused by quantum fluctuations. That scenario had very little chance of happening, but, according to the totalitarian principle, even the most improbable event will eventually happen. It took place instantly, in our perspective, due to the absence of perceived time before the Big Bang. [136][137][138][139]
  • Models including the Hartle–Hawking no-boundary condition, in which the whole of spacetime is finite the Big Bang does represent the limit of time but without any singularity. [140] In such case, the universe is self-sufficient. [141] models, in which inflation is due to the movement of branes in string theory the pre-Big Bang model the ekpyrotic model, in which the Big Bang is the result of a collision between branes and the cyclic model, a variant of the ekpyrotic model in which collisions occur periodically. In the latter model the Big Bang was preceded by a Big Crunch and the universe cycles from one process to the other. [142][143][144][145] , in which universal inflation ends locally here and there in a random fashion, each end-point leading to a bubble universe, expanding from its own big bang. [146][147]

Proposals in the last two categories see the Big Bang as an event in either a much larger and older universe or in a multiverse.

As a description of the origin of the universe, the Big Bang has significant bearing on religion and philosophy. [148] [149] As a result, it has become one of the liveliest areas in the discourse between science and religion. [150] Some believe the Big Bang implies a creator, [151] [152] while others argue that Big Bang cosmology makes the notion of a creator superfluous. [149] [153]


How is the gravitational effect of galaxies outside of the visible universe on galaxies within the visible universe currently modeled? - Astronomy

A spiral galaxy resembles a pinwheel, with spiral arms coiling out from a central bulge. This galaxy, known as M100, looks much like our home galaxy, the Milky Way. However, the Milky Way has a bar of stars, dust, and gas across its center. Image credit: D. Hunter (Lowell Observatory) and Z. Levay (Space Telescope Science Institute)/NASA

Only three galaxies outside the Milky Way are visible with the unaided eye. People in the Northern Hemisphere can see the Andromeda Galaxy, which is about 2 million light-years away. People in the Southern Hemisphere can see the Large Magellanic Cloud, which is about 160,000 light-years from Earth, and the Small Magellanic Cloud, which is about 180,000 light-years away.

Galaxies are distributed unevenly in space. Some have no close neighbor. Others occur in pairs, with each orbiting the other. But most of them are found in groups called clusters. A cluster may contain from a few dozen to several thousand galaxies. It may have a diameter as large as 10 million light-years.

Clusters of galaxies, in turn, are grouped in larger structures called superclusters. On even larger scales, galaxies are arranged in huge networks. The networks consist of interconnected strings or filaments of galaxies surrounding relatively empty regions known as voids. One of the largest structures ever mapped is a network of galaxies known as the Great Wall. This structure is more than 500 million light-years long and 200 million light-years wide.

A globular cluster is a tightly grouped swarm of stars held together by gravity. This globular cluster is one of the densest of the 147 known clusters in the Milky Way galaxy. Image credit: NASA

New stars are constantly forming out of gas and dust in spiral galaxies. Smaller groups of stars called globular clusters often surround spiral galaxies. A typical globular cluster has about 1 million stars.

Elliptical galaxies range in shape from almost perfect spheres to flattened globes. The light from an elliptical galaxy is brightest in the center and gradually becomes fainter toward its outer regions. As far as astronomers can determine, elliptical galaxies rotate much more slowly than spiral galaxies or not at all. The stars within them appear to move in random orbits. Elliptical galaxies have much less dust and gas than spiral galaxies have, and few new stars appear to be forming in them.

An irregular galaxy, Sextans A does not have a simple shape like a spiral or elliptical galaxy. The bright, yellowish stars in the foreground are part of the Milky Way, Earth's "home" galaxy. Image credit: NASA

Galaxies move relative to one another, and occasionally two galaxies come so close to each other that the gravitational force of each changes the shape of the other. Galaxies can even collide. If two rapidly moving galaxies collide, they may pass right through each other with little or no effect. However, when slow-moving galaxies collide, they can merge into a single galaxy that is bigger than either of the original galaxies. Such mergers can produce spiral filaments of stars that can extend more than 100,000 light-years into space.

Emissions from galaxies

An image taken in 2001 with the Hubble Space Telescope reveals the irregular-shaped galaxy ESO 510-13, which astronomers theorize is twisted because of gravitational effects that occurred when it absorbed a smaller galaxy. Image credit: NASA and Hubble Heritage Team

The energy emitted by galaxies comes from various sources. Much of it is due to the heat of the stars and of clouds of dust and gas called nebulae. A variety of violent events also provide a great deal of the energy. These events include two kinds of stellar explosions: (1) nova explosions, in which one of the two members of a binary star system hurls dust and gas into space (2) much more violent supernova explosions, in which a star collapses, then throws off most of its matter. One supernova may leave behind a compact, invisible object called a black hole, which has such powerful gravitational force that not even light can escape it. Another supernova may leave behind a neutron star, which consists mostly of tightly packed neutrons, particles that ordinarily occur only in the nuclei of atoms. But some supernovae leave nothing behind.

The most distant galaxies yet observed appear as faint patches of light in this photograph taken by the Hubble Space Telescope. The brighter swirls are galaxies somewhat closer to Earth, and the bright orange object is a star in our own galaxy. The telescope photographed this tiny portion of the sky, called the Hubble Ultra Deep Field, in 2004. Image credit: NASA/ESA/S. Beckwith (STScl) and the HUDF Team

A small percentage of galaxies called active galaxies emit tremendous amounts of energy. This energy results from violent events occurring in objects at their center. The distribution of the wavelengths of the emissions does not resemble that of normal stars, and so the emissions are known as nonthermal radiation. The most powerful such object is a quasar, which emits a huge amount of radio, infrared, ultraviolet, X-ray, and gamma-ray energy. Some quasars emit 1,000 times as much energy as the entire Milky Way, yet look like stars in photographs. Quasar is short for quasi-stellar radio source. The name comes from the fact that the first quasars identified emit mostly radio energy and look much like stars. A radio galaxy is related to, but appears larger than, a quasar.

A Seyfert galaxy is a spiral galaxy that emits large amounts of infrared rays as well as large amounts of radio waves, X rays, or both radio waves and X rays. Seyfert galaxies get their name from American astronomer Carl K. Seyfert, who in 1943 became the first person to discover one.

Some active galaxies emit jets and blobs of highly energetic, electrically charged particles. These particles include positively charged protons and positrons and negatively charged electrons. Electrons and protons are forms of ordinary matter, but positrons are antimatter particles. They are the antimatter opposites of electrons -- that is, they have the same mass (amount of matter) as electrons, but they carry the opposite charge. See Antimatter.

The cause of the intense activity in active galaxies is thought to arise from a colossal black hole at the galactic center. The black hole can be as much as a billion times as massive as the sun. Because the black hole is so massive and compact, its gravitational force is powerful enough to tear apart nearby stars. The resulting dust and gas fall toward the black hole, adding their mass to a disk of matter called an accretion disk that orbits the black hole. At the same time, matter from the inner edge of the disk falls into the black hole. As the matter falls, it loses energy, thereby producing the radiation and jets that shoot out of the galaxy.

Galaxy M83 The galaxy M83 is shaped much like our home galaxy, the Milky Way. The diameter of the Milky Way is approximately 100,000 light-years -- roughly 700 billion times the sun's diameter. Image credit: noAO/AURA/NSF

Scientists have proposed two main kinds of theories of the origin of galaxies: (1) bottom-up theories and (2) top-down theories. The starting point for both kinds of theories is the big bang, the explosion with which the universe began 10 billion to 20 billion years ago. Shortly after the big bang, masses of gas began to gather together or collapse. Gravity then slowly compressed these masses into galaxies.

The two kinds of theories differ concerning how the galaxies evolved. Bottom-up theories state that much smaller objects such as globular clusters formed first. These objects then merged to form galaxies. According to top-down theories, large objects such as galaxies and clusters of galaxies formed first. The smaller groups of stars then formed within them. But all big bang theories of galaxy formation agree that no new galaxies -- or very few -- have formed since the earliest times.

Astronomers have found evidence of what conditions were like before the galaxies formed. In 1965, American physicists Arno Penzias and Robert Wilson detected faint radio waves throughout the sky. According to the big bang theory, the waves are radiation left over from the initial explosion. The strength of the radio waves appeared to be very nearly the same in every direction. But in 1992, a satellite called the Cosmic Background Explorer (COBE) detected tiny differences in the strength of radio waves coming from different directions. The differences in strength arise from tiny increases in the density of matter in the universe shortly after the big bang. The small regions of increased density had a stronger gravitational force than the surrounding matter. Clumps of matter therefore formed in these regions and the clumps eventually collapsed into galaxies.

Most astronomical observations made to date support big bang theories. According to these theories, the universe is still expanding. Two kinds of observations strongly support the idea of an expanding universe. These observations indicate that all galaxies are moving away from one another and that the galaxies farthest from the Milky Way are moving away most rapidly. This relationship between speed and distance is known as the Hubble law of recession (moving backward), or Hubble's law. The law was named after American astronomer Edwin P. Hubble, who reported it in 1929.

Redshift causes a displacement of lines in the spectrum (band of colors) sent out by a galaxy that is moving away from Earth. If the galaxy were motionless relative to Earth, those lines would appear in the positions shown in the upper diagram. The cause of the displacement is known as redshift because the lines are displaced toward the red end of the spectrum. Image credit: World Book diagram by Ernest Norcia

Scientists estimate the distance to galaxies by measuring the galaxies' overall brightness or the brightness of certain kinds of objects within them. These objects include variable stars as well as supernovae.

Evolution of spiral galaxies

Astronomers do not understand clearly how galactic spirals evolved and why they still exist. The mystery arises when one considers how a spiral galaxy rotates. The galaxy spins much like the cream on the surface of a cup of coffee. The inner part of the galaxy rotates somewhat like a solid wheel, and the arms trail behind. Suppose a spiral arm rotated around the center of its galaxy in about 250 million years -- as in the Milky Way. After a few rotations, taking perhaps 2 billion years, the arms would "wind up," producing a fairly continuous mass of stars. But almost all spiral galaxies are much older than 2 billion years.

According to one proposed solution to the mystery, differences in gravitational force throughout the galaxy push and pull at the stars, dust, and gas. This activity produces waves of compression. A familiar example of waves of compression are ordinary sound waves. Because the galaxy is rotating, the waves seem to travel in a spiral path, leading to the appearance of spiral arms of dense dust and gas. Stars then form in the arms.


4 Answers 4

Dark energy, dark matter, and gravity are intimately entwined concepts, certainly. The question seems to blur dark matter and dark energy together or use the terms interchangeably, but they are separate theories attempting to reconcile separate discrepancies.

One facet contributing to the majesty of Einstein's Equations for gravity (see http://en.wikipedia.org/wiki/Einstein_field_equations, particularly the form given just before "Sign convention") are that they are all-inclusive- curvature is mass-energy, mass-energy is curvature. The equation begs to be enlarged and expanded to include the entire universe, and thus it is the foundation of modern cosmology.

As such, Einstein's Equations describe how the Universe should expand, deform, warp, or contract (if it had enough mass) given its content of mass and energy. Dark energy is part of the nascent attempt by theorists to reconcile what matter we can see with the largest-scale behavior as observed. Gravity as we are traditionally familiar with it is always attractive, so any collection of objects moving apart from each other should at least be slowing down, if not actually turning around and colliding. What we see on the grandest scales, though, is an acceleration. Something fundamental has to be wrong with the traditional picture, and dark energy is a catch-all term for attempts at the modification of Einstein's Equations themselves.

Dark matter, on the other hand, is a catch-all term for attempts to reconcile smaller-scale discrepancies between the observed behavior of objects and the theoretical predictions of their behavior assuming that every object was visible. This is where the alternate term "Missing Matter" comes from. Smaller objects, like galaxies and clusters of galaxies, seen to behave as if there were extra, invisible matter holding them together. It is a less-ambitious correction, since there is no attempt to argue that Einstein's Equations themselves need correction, we merely need some extra matter that doesn't produce any light on the right hand side in order to account for the extra curvature of spacetime inferred from the behavior of observed objects on the left.

I'm sorry if that's not as neat or tidy an answer as you were looking for. Given the deep philosophical implications of both sides of Einstein's Equations being both cause and effect, it is impossible to draw the same kind of distinction between gravity, dark matter, and dark energy as you could between the influences of, say, sunshine and heat from the Earth's core on ground temperatures. Therefore, for instance, there is no "extra" spacetime. Einstein himself discouraged the use of "deformation" and "warping" as they lead to the notion that there is some natural condition for spacetime and matter just messes it all up. Spacetime and matter are like the first two cards of a house of cards- they have to be taken together because either one by itself will just collapse.


Cosmological Theories

So I’ve been doing a lot of reading and research (and thinking in general) about astronomy and the cosmos. In the course of my various research, especially in relation to questions of “origins,” as the beginning of the universe is often called in religious circles, this question has come up a few times. So for those a little rusty in their space science knowledge, there were two major theories proposed for the universe within a naturalistic framework, one was the “Steady State” theory, originally proposed by Sir James Jeans, and the other was the “Big Bang” theory, proposed first (without that title) by Belgian priest and astronomer Georges Lemaître. The term “big bang” actually came from British astrophysicist Sir Fred Hoyle, who was more a fan of the steady state theory, but that’s a different story.

As you probably know, the Big Bang theory, with continuing modifications and additions, ultimately won out, thanks in part to two important discoveries. The first discovery came between 1924 and 1929, when Edwin Hubble was able to confirm that the universe was expanding (using redshifts and other indicators like recession and distance velocity), which ultimately led to the creation of Hubble’s Law. The second discovery came in 1964 with something called cosmic microwave background radiation, or CMBR. This is basically microwave temperature signatures thought to be left over from the original expansion and inflation of spacetime following the Big Bang. That is the dominant theory in astronomy today about our cosmic origins. Below are two model depicting what this Big Bang process might have looked like.

NASA model showing the expansion of the universe and the CMBR.

Another model for the Big Bang.

Now there are lots of debates about the Big Bang versus a Christian God (and some other “Gods/gods”) creating the universe. The primary source of explanation from a creationist perspective is the Bible, and specifically the Book of Genesis (1:1-31), which lays out the basic creation by God of the universe as Christians understand it:

In the beginning God created the heaven and the earth 1 …And God said, Let there be lights in the firmament of the heaven to divide the day from the night and let them be for signs, and for seasons, and for days, and years: 15 and let them be for lights in the firmament of the heaven to give light upon the earth: and it was so. 16 And God made two great lights the greater light to rule the day, and the lesser light to rule the night: he made the stars also. 17 And God set them in the firmament of the heaven to give light upon the earth, 18 and to rule over the day and over the night, and to divide the light from the darkness…

Depending on whether a Christian prescribes to a conservative literal interpretation, as most Biblical creationists do, or a more liberal interpretation, which the majority of Christian scientists do, there is a good bit of wiggle room for reconciling the scientific theories with the Bible. For those serious students of science and theology I suggest checking out Gerald Rau’s book Mapping the Origins Debate: Six Models of the Beginning of Everything, which I just finished reading last week. In it he provides a helpful classificatory scheme for teasing out key differences in views between naturalism and supernaturalism within these origin debates.

Although this question is immensely fascinating, it is not the main focus of this post, so for some of these science-religion debates check out this link, this link, and specifically concerning the Big Bang here. The answer we choose has wider implications than you might at first think (here’s one example of how this impacts us all), since at root this is really a debate between two opposing worldviews, those of naturalism and supernaturalism. [In reality, this is a much bigger debate than just two worldviews, but that is another discussion that will have to wait for a different post. Suffice to say here that the question of interest to us–does the universe have an edge–will likely have a different answer depending on which of these ontological positions–naturalism or supernaturalism–you tend to find more personally compelling.]

So does the universe have an edge? Well, if it did, how would we know, and where should we look to find it? To answer that we need to first ask, just how big is our universe? Supposedly our universe has over 100 billion galaxies and so many stars that I can’t even comprehend the number used (10 sextillion ??). The European Space Agency says “something like 10 22 to 10 24 stars in the Universe.” And that doesn’t even get into the question of multiverses, which would require yet another entire post.

Fortunately for us PBS/NOVA has a great special dedicated to exactly how big the universe is here, and NASA has a great introductory page on the same question here. The answer is basically, we have no idea, since we can only see so far into space (or backwards into time). This little bit from the PBS page helps make this point:

There is an edge to what we are able to see and could ever possibly see in the universe. Light travels at 300,000 kilometers per second (186,000 miles per second). That’s top speed in this universe—nothing can go faster—but it’s relatively slow compared to the distances to be traveled. The nearest big galaxy to our Milky Way, the Andromeda galaxy, is two million light-years away. The most distant galaxies we can now see are 10 or 12 billion light-years away. We could never see a galaxy that is farther away in light travel time than the universe is old—an estimated 14 billion or so years. Thus, we are surrounded by a “horizon” that we cannot look beyond—a horizon set by the distance that light can travel over the age of the universe. This horizon describes the visible universe—a region some 28 billion light years in diameter.

If it still seems overwhelming try this cool little guide designed by the folks at Harvard’s Center for Astrophysics: “How big is our universe?” I spent a lot of time trying to find a helpful image to go with this question, but truth be told, there is just no way to even begin to capture how vast the known universe might be. But hey, we can’t let that stop us, right! So here is one take on our known universe, with the complexity and scale getting bigger and wider from top left to bottom right:

Diagram showing various scales of the universe.

Now don’t let these models fool you into thinking that there is some clear “edge” where the stars and cosmic debris all stops–that’s just an artifact of needing an end point for a graphic.


CornellCast

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Only 4 percent of our universe is made of ordinary matter like atoms and molecules. The other 96 percent is in entirely unfamiliar forms we know almost nothing about. About 25 percent is dark matter, which holds galaxies and larger-scale structures together another 70 percent is thought to be dark energy, an even more mysterious entity that appears to be driving the accelerated expansion of the universe.

In the Spring 2017 Hans Bethe Lecture at Cornell, physicist Joshua Frieman introduces the Dark Universe and describes new experiments and observatories that aim to illuminate its enigmas.

Frieman is a founder, and currently serves as director, of the Dark Energy Survey, a collaboration of more than 300 scientists from 25 institutions on three continents that is probing the origin of cosmic acceleration. His research centers on theoretical and observational cosmology, including studies of the nature of dark energy, the early universe, gravitational lensing, the large-scale structure of the universe, and supernovae as cosmological distance indicators.

The Hans Bethe Lectures, established by the Department of Physics and the College of Arts and Sciences, honor Bethe, Cornell professor of physics from 1936 until his death in 2005. Bethe won the Nobel Prize in physics in 1967 for his description of the nuclear processes that power the sun.


31 Replies to &ldquoWhat’s Outside the Universe?&rdquo

Hi PUNCHCARD4GTAC,
That question is what drives research, as well as natural human curiosity.
We have a long way to go to find the answers.
In other words, finding the cause of the distortion in the Cosmic Microwave Background Radiation arrears to me to be so difficult, that it will not be found in my lifetime.

I love this topic. I always try to think about what would “be” if our universe (or any universes as it may be), did not exist. What would “exist” if anything….and if nothing existed, how do we picture it..or, like a 4th or higher dimension, can we picture it? This is kinda the same questions as “what is out universe expanding into?”. For some reason this totally intrigues me……and for some crazy reason, if nothing existed, I picture infinite “yellow”.

Yes it is a multi-verse. In fact, an infinite multiverse. The individual universes emerge from the infinite stuff that surrounds them. Namely densely packed photons of all wavelengths and energies. Essentially the same stuff of black holes.

Our universe exists inside a cavitary bubble created by the shock wave of a singular event in a medium of significant density (non-particulate) that resulted from the resolution of a higher energy state to a lower energy state (an explosion as it were) in that medium not unlike Feynman’s solution for detonating the plutonium bomb (implosion/explosion ).

This medium? Densely packed photons, hnu, or energy The same stuff that not only makes up everything in our universe (all particles can eventually be reduced to their photons), but that which exists at the boundary of our cavitary bubble, and beyond, being responsible for the gravitational field into which everything is subsequently being drawn (calculate the resultant gravitational vectors inside of a hollow sphere in a large cube of very dense material). This material (densely packed photons), by the way, is the same stuff of black holes (particulate matter enters and is reduced to it’s constituent photons).

From electron positron interactions we know that only 2 511kev photons result. No particles. Electrons and positrons have mass and from the formula for conversion of mass and energy, Ta Da! so do photons (only while moving which is going to be a hard one to measure given their speed and linear orientation through the Higgs field, however in a circular course their mass should be measurable)!

Imagine, packing electrons as tight as one may, actually touching one another, into a 10cc cube. Summing their gravitational components from their masses using the gravitational equation we would arrive at some number for this 10cc cube.

Now, since the electron is quite voluminous (as it contains only one photon, no other particles), imagine if the volume of the electron were to be reduced to the volume of it’s constituent photon.

What we end up with would be the same amount of gravitational content in a volume significantly smaller (infinitely smaller?) than our 10cc cube. Conversely, if we created a 10cc cube of this condensed electron constituent, we might even call it a baby black hole with all of the gravitational attributes of something so dense and concentrated.

Now scale the whole shebang from infinite to infinitesimal.

Finally, all of the constituents of our universe are accelerating, via gravity, to the edges of our universe due to a large amount of gravitationally significant material that exists at it’s margins (and further).

At some point in time the cavitary bubble will cease to expand and will then contract (could be happening now…).

Yet, we will continue to accelerate to the margins, under the gravitational pull (in our hollow, cavitary sphere), and ultimately merge with and into the stuff (energy, photons, hnu, however you’d like to define it) that exists there (which may also be occurring and may actually be responsible for some of the information gathered by COBE as some of our particulate matter gets consumed by the margins.).

The complete collapse of the cavitary bubble with our continued acceleration towards the margins will eventually result in the consumption and ultimate reduction of all matter back into their constituent photons and dissipation of the bubble probably back into another high energy state singularity as the margins crash into one another that requires resolution into a lower energy state via another cavitary, shock wave explosion.

So we live in a kind of baked bread multi-verse with all of the holes in the baked dough representing the many universes and the dough representing the stuff that lies between them all (densely packed photons) from which everything is made.


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