question: Given that the Schwarzchild radius of the mass of the universe is more than 13 light years, and the universe was once smaller than that, how did everything not instantly collapse into a singularity at the beginning of time?
comment: We aren't 100% sure on this yet. But whatever force (Dark Energy) that is causing the universe to expand is likely what overcame the force of gravity from collapsing the universe back into a singularity.
passages: 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 black hole. This may be explained by considering that commonly-used calculations and limits for 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.
  
  Section::::Timeline.:Inflation and baryogenesis.
   The initial state of the universe, at the beginning of the Big Bang, is also predicted by modern theories to have been a singularity. In this case the universe did not collapse into a black hole, because currently-known calculations and density limits for gravitational collapse are usually based upon objects of relatively constant size, such as stars, and do not necessarily apply in the same way to rapidly expanding space such as the Big Bang. Neither general relativity nor quantum mechanics can currently describe the earliest moments of the Big Bang, but in general, quantum mechanics does not permit particles to inhabit a space smaller than their wavelengths.
   Despite the early universe being extremely dense—far denser than is usually required to form a black hole—it did not re-collapse into a black hole during the Big Bang. Models for gravitational collapse of objects of relatively constant size, such as stars, do not necessarily apply in the same way to rapidly expanding space such as the Big Bang.
  
  Section::::Formation and evolution.:High-energy collisions.
   Mazur and Mottola suggest that the violent creation of a gravastar might be an explanation for the origin of our universe and many other universes, because all the matter from a collapsing star would implode "through" the central hole and explode into a new dimension and expand forever, which would be consistent with the current theories regarding the Big Bang. This "new dimension" exerts an outward pressure on the Bose–Einstein condensate layer and prevents it from collapsing further.
   Despite being extremely dense when very young and during part of its early expansion - far denser than is usually required to form a black hole - the universe did not re-collapse into a black hole. This is because commonly-used calculations for 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.
  
  Section::::Understanding the expansion of the universe.:Effects of expansion on small scales.
   Second, all solutions suggest that there was a gravitational singularity in the past, when "R" went to zero and matter and energy were infinitely dense. It may seem that this conclusion is uncertain because it is based on the questionable assumptions of perfect homogeneity and isotropy (the cosmological principle) and that only the gravitational interaction is significant. However, the Penrose–Hawking singularity theorems show that a singularity should exist for very general conditions. Hence, according to Einstein's field equations, "R" grew rapidly from an unimaginably hot, dense state that existed immediately following this singularity (when "R" had a small, finite value); this is the essence of the Big Bang model of the Universe. Understanding the singularity of the Big Bang likely requires a quantum theory of gravity, which has not yet been formulated.
   It might be thought that a sufficiently massive neutron star could exist within its Schwarzschild radius (1.0 SR) and appear like a black hole without having all the mass compressed to a singularity at the center; however, this is probably incorrect. Within the event horizon, matter would have to move outward faster than the speed of light in order to remain stable and avoid collapsing to the center. No physical force therefore can prevent a star smaller than 1.0 SR from collapsing to a singularity (at least within the currently accepted framework of general relativity; this does not hold for the Einstein–Yang–Mills–Dirac system). A model for nonspherical collapse in general relativity with emission of matter and gravitational waves has been presented.
   The size of the Local Void was calculated due to an isolated dwarf galaxy located inside it. The bigger and emptier the void, the weaker its gravity, and the faster the dwarf should be fleeing the void towards concentrations of matter, yet discrepancies give room for competing theories. Dark energy has been suggested as one alternative explanation for the speedy expulsion of the dwarf galaxy.
   The problem is that any small departure from the critical density grows with time, and yet the universe today remains very close to flat. Given that a natural timescale for departure from flatness might be the Planck time, 10 seconds, 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 of its critical value, or it would not exist as it does today.
   Gravitational collapse requires great density. In the current epoch of the universe these high densities are only found in stars, but in the early universe shortly after the Big Bang densities were much greater, possibly allowing for the creation of black holes. High density alone is not enough to allow black hole formation since a uniform mass distribution will not allow the mass to bunch up. In order for primordial black holes to have formed in such a dense medium, there must have been initial density perturbations that could then grow under their own gravity. Different models for the early universe vary widely in their predictions of the scale of these fluctuations. Various models predict the creation of primordial black holes ranging in size from a Planck mass to hundreds of thousands of solar masses.
   The more matter there is in the Universe, the stronger the mutual gravitational pull of the matter. If the Universe were "too" dense then it would re-collapse into a gravitational singularity. However, if the Universe contained too "little" matter then the self-gravity would be too weak for astronomical structures, like galaxies or planets, to form. Since the Big Bang, the universe has expanded monotonically. Perhaps unsurprisingly, our universe has just the right mass-energy density, equivalent to about 5 protons per cubic meter, which has allowed it to expand for the last 13.8 billion years, giving time to form the universe as observed today.
   In the case of a white dwarf, the restarted fusion reactions releases heat, but the outward pressure that exists in the star and supports it against further collapse is initially due almost entirely to degeneracy pressure, not fusion processes or heat. Therefore, even when fusion recommences the outward pressure that is key to the star's thermal balance does not increase much. One result is that the star does not expand much to balance its fusion and heat processes with gravity and electron pressure, as it did when burning hydrogen (until too late). This increase of heat production without a means of cooling by expansion raises the internal temperature dramatically, and therefore the rate of fusion also increases extremely fast as well, a form of positive feedback known as thermal runaway.
   As time passes and one goes away from the singularity, the effect of matter on metric evolution, which was insignificant at the early stages of evolution, gradually increases and eventually becomes dominant. It can be expected that this effect will lead to a gradual "isotropisation" of space as a result of which its characteristics come closer to the Friedman model which adequately describes the present state of the Universe.
   The coincidence problem asks why the acceleration of the Universe began when it did. If acceleration began earlier in the universe, structures such as galaxies would never have had time to form, and life, at least as we know it, would never have had a chance to exist. Proponents of the anthropic principle view this as support for their arguments. However, many models of quintessence have a so-called "tracker" behavior, which solves this problem. In these models, the quintessence field has a density which closely tracks (but is less than) the radiation density until matter-radiation equality, which triggers quintessence to start behaving as dark energy, eventually dominating the universe. This naturally sets the low energy scale of the dark energy.
   If the mass of the remnant exceeds about (the Tolman–Oppenheimer–Volkoff limit), either because the original star was very heavy or because the remnant collected additional mass through accretion of matter, even the degeneracy pressure of neutrons is insufficient to stop the collapse. No known mechanism (except possibly quark degeneracy pressure, see quark star) is powerful enough to stop the implosion and the object will inevitably collapse to form a black hole.
   General relativity is used to predict that at the beginning of the Universe, a body containing all mass, energy, and spacetime in the Universe would be compressed to an infinitely dense point somewhere between the size of a human head and a skyscraper-filled city block, according to today's best models on inflation. The use of only general relativity to predict what happened in the beginnings of the Universe has been heavily criticized, as quantum mechanics becomes a significant factor in the high-energy environment of the earliest Universe, and general relativity on its own fails to make accurate predictions. In response to the inaccuracy of considering only general relativity, as in the traditional model of the Big Bang, alternative theoretical formulations for the beginning of the Universe have been proposed, including a string theory-based model in which two branes, enormous membranes much larger than the Universe, collided, creating mass and energy.
   Gravitational singularities are mainly considered in the context of general relativity, where density apparently becomes infinite at the center of a black hole, and within astrophysics and cosmology as the earliest state of the universe during the Big Bang. Physicists are undecided whether the prediction of singularities means that they actually exist (or existed at the start of the Big Bang), or that current knowledge is insufficient to describe what happens at such extreme densities.
   This difficulty is avoided if one includes in the model only the major terms of the limiting (at "t" → 0) metric and writes into it a matter with arbitrary initial distribution of densities and velocities. Then the course of evolution of matter is determined by its general laws of movement and that result in . During each Kasner epoch, density increases by the law
  
  where "p" is, as above, the greatest of the numbers "p", "p", "p". Matter density increases monotonously during all evolution towards the singularity.
  
  Section::::Metric evolution.
  
  Very large "u" values correspond to Kasner powers
   Section::::Timeline.
  
  Section::::Timeline.: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. This 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 beyond the end of the Planck epoch.
   Graceful exit problem (cosmology)
  
  The graceful exit problem in cosmology was the need to explain how the universe slowed from its initial inflation to its later rate of expansion.
   Oppenheimer and his co-authors interpreted the singularity at the boundary of the Schwarzschild radius as indicating that this was the boundary of a bubble in which time stopped. This is a valid point of view for external observers, but not for infalling observers. Because of this property, the collapsed stars were called "frozen stars", because an outside observer would see the surface of the star frozen in time at the instant where its collapse takes it to the Schwarzschild radius.
  
  Section::::History.:General relativity.:Golden age.
   Initial singularity
  
  The initial singularity was a gravitational singularity of seemingly infinite density thought to have contained all the mass and space-time of the Universe before quantum fluctuations caused it to rapidly expand in the Big Bang and subsequent inflation, creating the present-day Universe. The instant immediately following the initial singularity is part of the Planck epoch, the earliest period of time in the history of the universe.
  
  Section::::Traditional models of the Universe.
   According to the Big Bang Model, during the first few moments after the Big Bang, pressure and temperature were extremely great. Under these conditions, simple fluctuations in the density of matter may have resulted in local regions dense enough to create black holes. Although most regions of high density would be quickly dispersed by the expansion of the universe, a primordial black hole would be stable, persisting to the present.
   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.
   This tiny value is the crux of the flatness problem. If the initial density of the universe could take any value, it would seem extremely surprising to find it so 'finely tuned' to the critical value formula_9. Indeed, a very small departure of Ω from 1 in the early universe would have been magnified during billions of years of expansion to create a current density very far from critical. In the case of an overdensity this would lead to a universe so dense it would cease expanding and collapse into a Big Crunch (an opposite to the Big Bang in which all matter and energy falls back into an extremely dense state) in a few years or less; in the case of an underdensity it would expand so quickly and become so sparse it would soon seem essentially empty, and gravity would not be strong enough by comparison to cause matter to collapse and form galaxies. In either case the universe would contain no complex structures such as galaxies, stars, planets and any form of life.
  
raw_presuppositions: The universe should have collapsed into a singularity at the beginning of time due to the mass of the universe.
raw_corrections: Whatever force caused the universe to expand likely overcame the force of gravity from collapsing the universe into a singularity.