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According to the Big Bang model, space and everything in it was squeezed into a infinitely small point which subsequently expanded.

But if everything is squeezed into a point of zero size than there should be no distinguishing features. i.e. everything should be crushed into a perfectly homogeneous "thing" as there are no differences of features in a point since its size is zero.

How can we understand the subsequent differentiation?

Qmechanic
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good_ole_ray
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    The Big Bang didn't happen at a point. Your whole question is founded upon a misunderstanding of what the Big Bang was. – John Rennie Mar 16 '16 at 06:11
  • @JohnRennie actually i did see that answer. but we see the galaxies are moving further away from each other. ie their distance from each other is increasing. so at some time they were all squeezed together, right? – good_ole_ray Mar 16 '16 at 06:15
  • @good_ole_ray, arrow of time has been forward for the last 13.8 billion years since the singularity. However, from your explanation it seems that you are changing the direction of motion backward by trying to compress everything into a point. What happened is actually opposite to what you are describing. Saying "everything came out of nothing" is a better statement than "everything was compressed into a singularity." – Benjamin Mar 16 '16 at 06:19
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    @Benjamin not sure what you mean. are you saying we cannot infer from the galaxies moving further apart that they were not all squeezed together in the distant past? – good_ole_ray Mar 16 '16 at 06:25
  • @JohnRennie your grid answer seems to be referring to space whereas i am talking about the mass/energy in the space – good_ole_ray Mar 16 '16 at 06:27
  • The only thing you get by going backwards in cosmological time is an ever increasing density, but you can't extrapolate from that that everything was squeezed into one point. What you can get is a divergence in density, at which point, of course, you have learned nothing except that your theory breaks down. What really happened in the early universe is simply unknown. The divergent density is just another way of saying "unknown physics here". There are slight modifications of general relativity which don't have this problem, to begin with, they bounce at a finite density without divergence. – CuriousOne Mar 16 '16 at 06:30
  • @CuriousOne thanks. so you are saying all galaxies, energy, etc. were squeezed together to some ridiculously high density where all the laws of physics as we know them break down? – good_ole_ray Mar 16 '16 at 06:32
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    Yes, that's basically it. Physics is always based on observations on some scale, be that spatial, temporal, energy, temperature, pressure or any other scale. We then extrapolate from that scale to much larger and much smaller scales, hoping that things stay the same. There is no known example for the dynamics actually being the same all the way. At some point every extrapolation breaks down and new things are happening. The only way to know what those "new things" are is by performing new measurements closer to that new scale. That's what cosmology is trying to do, right now. – CuriousOne Mar 16 '16 at 06:35
  • @good_ole_ray: What I meant is exactly what CuriousOne said in a better wording. – Benjamin Mar 16 '16 at 06:38
  • @CuriousOne sounds like you have an answer there. just hard to imagine in any way how things could have any kind of difference when squeezed together to near zero size. – good_ole_ray Mar 16 '16 at 06:39
  • Oh, don't get us started on that... the theorists have hundreds of different possibilities how things could be different, I hinted at just one of them (it's called Einstein-Cartan theory and it's a minimal modification of general relativity, but there are many others). The imagination is not the hard part. The hard part is finding out which of the imaginative solutions is the one that nature likes! And sometimes it's none of them, at all... – CuriousOne Mar 16 '16 at 06:42
  • And I think John Renny's original response in the other post is comprehensive and informative. So, try to question statements argued in that post if you really want to be picky which is nice. Not all of us individually know everything. Each person has some expertise and we should all accept this. – Benjamin Mar 16 '16 at 06:43
  • @Benjamin thanks. didnt quite follow that post. i can hear how space can be scaled since it's not tangible but bringing matter closer together is a whole different story. – good_ole_ray Mar 16 '16 at 06:45
  • In defense of somewhat "testy" responses... there is a lot of false information about cosmology (and a lot of other stuff) out there. As a physicist you get asked the same tired questions based on the same false information, again and again and again. Physicists are human, they do have feeling about this stuff. Sometimes it's hard to distinguish the one hundredth's person with false ideas from the first... even though they are distinct people who are NOT required to know better. That's not an apology, but it is a fact of the case, for both sides. – CuriousOne Mar 16 '16 at 06:46
  • Quantum gravity as well as sting theorists, I think, have nice arguments too about the very moment of singularity. We know that all four fundamental forces of Nature were in fact united into a Single One just after this singularity. So between singularity and this moment is a mystery and leave it alone how singularity decided to expand? – Benjamin Mar 16 '16 at 06:48
  • @Banjamin: We don't know that. We suspect it and a lot of theoretical work is based on that assumption, including string theory. If you have watched the utter failure of string theory to pull this program out of the swamp, you may get an idea that it's 1) either not that simple or 2) that the basic idea of direct unification is false. That's a perfectly open possibility. Gravity, for instance, could be a thermodynamics remnant of an unseen fifth force that looks different from gravity itself, but that quantizes much better. Or there is no unification at any scale... or... or... or.. – CuriousOne Mar 16 '16 at 06:50

2 Answers2

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Singularities are an artefact of inadequate mathematical theories. There is no evidence they really exist. They are an indication our physical models have become inadequate at describing the physics involved.

  • so everything was squeezed together into slightly greater than zero size but not quite zero? – good_ole_ray Mar 16 '16 at 12:13
  • Nobody knows. Some people think BHs are stuffed full of "strings" with a very macroscopic size. We really need a quantum theory of gravity, and some experimental data before we can say anything –  Mar 16 '16 at 13:55
  • so perhaps could even be a singularity, no? – good_ole_ray Mar 16 '16 at 21:35
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Here is a possibility without any references, in fact there are no references available per my info on why/how big bang would have happened.

We know that singularities are formed when huge amount of matter comes together due to gravity.

It would not be unreasonable to think that the mother singularity would have formed same way - by accumulation of matter/energy due to gravity.

For big bang to happen, gravity must have somehow disappeared for just a moment. In that sense, gravity has to be self destructing given certain scenarios just like the mother singularity.

Disappearing of gravity would have resulted into the big bang. Like releasing a stretched cord.

Gravity must have re-appeared soon after big bang, but before it had time to act, inflation would have already taken place. And the expansion would have gained more momentum than what can be stopped by new appearance of gravity.

The structure formation can be attributed to the randomness in nature. There is nothing perfectly homogeneous. Things may appear to be homogeneous but at some level, they are not.

Universe is known to have gone through cycles of accelerated/slowed down expansion. Last switch from slowed expansion to accelerated expansion is believed to have happened 5 billion years ago. This cyclic observation may possibly be a hint towards an oscillating universe.

kpv
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