Can the universe ever contract?

Question

I am currently going through this answer related to the Big Bang theory and from there a question arose in my mind:

Can the universe ever contract?
Can it ever contract to singularity?

I wonder, if it is possible, how it would happen? Is there any chance at all?

I am unaware about the physical reality of this question.

@G.smith thanks. I thought that the question was irrational but the topic is already aroused! — , Oct 08 '20 at 16:51
Does this answer your question? Is there a consensus on the fate of our universe? — John Rennie, Oct 08 '20 at 18:02
@ John Rennie , actually I was not focused on such a topic and I even don't know what was big crunch before this but now I think that it was unintentionally quite close to that. — , Oct 08 '20 at 18:35
One thing to say sir, I really enjoy your linked answer in this question. it was really informative and it helped me to break my long lasted doubted misconception . — , Oct 08 '20 at 18:38

Deschele Schilder · Answer 1 · 2020-10-11T15:31:12.663

Nobody knows for sure how the universe will evolve. It's accepted by almost all cosmologists that the universe is expanding at an increasingly accelerated rate.
Almost all. There are indeed convincing experimental facts (type IA supernovae, the CMBR), but there is also counter-evidence. I think this is not taken too seriously because there were already Nobel prizes awarded for the discovery that the universe is expanding at an accelerated rate.

See for example this paper, containing much math. The link to this paper is made in this article (many more links are included here).

So maybe dark energy (the Nature of which is completely unknown; it's supposed to become non-diluted by the expansion of space) is not necessary after all. The Dutchman Erik Verlinde (who received the Spinoza prize in 2011 for his in the Netherlands so-called revolutionary new theory of gravity, including a premium of 2 million euros...) proposes that dark energy, as well as dark matter, are emergent properties, though I think observations on the Bullet Cluster defuse his theory.

So the situation is far from settled. And who knows what the future in cosmology holds in store?

score 0 · Answer 2 · answered Oct 10 '20 at 15:30

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Whether it will or it won't, we don't know for sure. Unless we understand the dark energy and dark matter, only time will tell.

It was one of the earlier theories but current evidence seems to suggest that won't be the case. According to the most prominent contemporary physicists, everything in the universe will spread apart so far that it will result in a cold death of the universe where you won't be able to see any star in the night sky.

answered Oct 10 '20 at 15:30

LostCause

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Can you post a reference to your statement about prominent physicists and not seeing any star? I would like to suggest that the "cold death" makes all of a specific collection of gravitationally bound matter eventually end up in a black hole. During this process, there may be stars and planets and living beings, After there is nothing but black holes, there will not be any "you" to try to anything. – Buzz Nov 01 '20 at 19:27
@Buzz I dont think I need to provide a reference if I am writing something that is the current viewpoint or current working hypothesis. What you are suggesting requires the universe to eventually slow down its expansion and we don't have much evidence to support that since most of the evidence suggests just the opposite. – LostCause Nov 02 '20 at 20:46
I am wondering if you understand that the current consensus Friedmann model with $\Omega_{\Lambda}~=0.7$ eventually has H(t) asymtotically approach a constant. – Buzz Nov 03 '20 at 02:33
@Buzz Please give a full logical explanation on how from this constant you can reach your conclusion. – LostCause Nov 04 '20 at 03:32
I do not think the space allowed for a comment is sufficient for "a full logical explanation". It would help if I knew about what you already know. Are you familiar with the Friedmann equation? In particular see https://en.wikipedia.org/wiki/Friedmann_equations#Detailed_derivation. – Buzz Nov 04 '20 at 16:45
I don't think you are adding any value to the discussion. You need to do a lot more than just these Friedmann equations. Since his model suggests both steady-state and big bang equally. Just explain what is the implication of "H(t) asymptotically approach a constant" and what is the implication if that was not the case. You can just say random things to sound smart but at some point, you need to start explaining. – LostCause Nov 05 '20 at 19:21
@LosrCause I find that I don't get what your phrases mean. Can you provide some definitions? By "his model" do you refer to the Friedmann eqs (FE). If this is so, do you say that FE "suggests both steady state and big bang". FE does "support" the "big bang" since the solutions re time allow for any time t>0. Please explain what it means that FE supports steady state. Do you say that 4 values for $\Omega$s have a solution for a(t) where the value of a(t) does not change with time (t)? Do you also claim that both $da/dt$ and $d^2a/dt^2$ do not change for this value of t? – Buzz Nov 05 '20 at 21:50
I am not sure what kind of answer you are seeking.
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Are you seeking an answer about what seems to be a near consensus among cosmologists (based on a lot of cosmological/astronomical evidence) the most likely result?
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@user276504 Are you looking for the whether some cosmologist disagreeing with the majority might have a speculation about a possible collapse?
– Buzz Nov 05 '20 at 22:13

Can the universe ever contract?

2 Answers2