Predicting Universe Collapse: Understanding the Forces at Work

  • Context: Graduate 
  • Thread starter Thread starter wolram
  • Start date Start date
  • Tags Tags
    Forces Universe
Click For Summary

Discussion Overview

The discussion revolves around predicting the potential gravitational collapse of the universe, focusing on the forces involved in cosmic expansion and contraction. Participants explore concepts related to the Hubble flow, gravity, and the implications of dark energy on the universe's fate.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant questions whether it is possible to predict when the universe will begin to gravitationally collapse based on certain forces.
  • Another participant seeks clarification on which specific forces are being referenced in the original question about gravitational collapse.
  • A participant suggests that the forces producing the Hubble flow and gravity are central to understanding the universe's expansion and potential contraction.
  • There is mention of inflation as a key factor in the universe's expansion, with a suggestion that some unexplained momentum may be responsible for the continuation of this expansion.
  • It is proposed that if the universe is slightly above critical density, it may stop expanding and begin contracting without a pause, although the transition would be extremely slow.
  • Concerns are raised about the role of dark energy or a cosmological constant, with one participant stating that if dark energy is strong enough, the universe will continue to expand indefinitely and never contract.

Areas of Agreement / Disagreement

Participants express differing views on the mechanisms behind cosmic expansion and the potential for gravitational collapse, indicating that multiple competing perspectives remain unresolved.

Contextual Notes

There are limitations in the discussion regarding the assumptions about dark energy, critical density, and the nature of cosmic expansion, which remain unresolved and open to interpretation.

wolram
Gold Member
Dearly Missed
Messages
4,411
Reaction score
551
Just from these forces can one predict when the universe will start to gravitationally collapse?

Edit

Would there be a (lag) from expansion to contraction.
 
Last edited:
Space news on Phys.org
wolram said:
Just from these forces can one predict when the universe will start to gravitationally collapse?

Hi Wolram,

I think something got lost in your question. Which forces in particular?

Jon
 
jonmtkisco said:
Hi Wolram,

I think something got lost in your question. Which forces in particular?

Jon

Silly me, Whatever it is that produces the Hubble flow and gravity, or may be i should ask,
can we predict when expansion will stop, will there be a lag before a re collapse.
 
Hi Wolram,

These are very broad questions. I am not aware of even an ATTEMPT to explain why expansion continues. As you know, the favored view at the moment is that inflation was the original motivation for expansion. Subsequently, some unexplained form of momentum is supposed to keep expansion going. But it is a strange form of momentum, because nothing actually "moves".

Objects continue to become further apart because they were already becoming further apart. They were already becoming further apart because of inflation. And inflation apparently caused objects to become further apart from each other at almost exactly the Newtonian escape velocity.

In the absence of Dark Energy or other cosmological constant, a flat universe (which ours approximates) will expand more and more slowly, but never at a zero expansion rate. In other words, the expansion will asymptotically approach zero.

If the universe is even slightly above critical density (say, by a total of 1 photon), then it will stop expanding at a certain point in time and begin contracting. There won't be a "pause" per se between expansion and contraction, it will be instantaneous. However, the expansion will be extreeeemely slow for a long time before it reaches zero and then begins contacting at an extreeeemely slow rate, which will accelerate over time.

If Lambda (Dark energy or cosmological constant) is sufficient to overcome the total force of gravity, then expansion will continue to accelerate at a geometrical rate. That is the current mainstream projection regarding Dark Energy. Such a universe will never contract.

Jon
 
Thanks jonmtkisco , it was a question that had me thinking.
 

Similar threads

  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 1 ·
Replies
1
Views
3K
  • · Replies 18 ·
Replies
18
Views
3K
  • · Replies 28 ·
Replies
28
Views
3K
  • · Replies 0 ·
Replies
0
Views
2K
  • · Replies 16 ·
Replies
16
Views
4K
  • · Replies 23 ·
Replies
23
Views
2K
  • · Replies 19 ·
Replies
19
Views
4K
  • · Replies 10 ·
Replies
10
Views
3K