Is There a Center of Mass to the Universe?

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Discussion Overview

The discussion centers around the concept of whether the universe has a center of mass and the implications of this idea on cosmic phenomena such as the potential for a 'Big Crunch.' Participants explore theoretical models and analogies, particularly the balloon analogy, to understand the structure and dynamics of the universe.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants propose that, based on current theory, the universe likely does not have a center of mass, likening it to the surface of a balloon which lacks a central point.
  • Others question whether a center of mass is necessary for phenomena like the 'Big Crunch,' suggesting that if the universe were to contract, it would not be towards a central point.
  • One participant argues that gravity could eventually cause the universe to stop expanding and start contracting, using the analogy of a rock thrown upwards on Earth to illustrate this point.
  • Another participant mentions that the acceleration of the universe's expansion may be influenced by dark matter and radiation energy, which complicates the role of gravity in reversing expansion.
  • A later reply raises a question about the location of any potential contraction, specifically whether it would occur at the same point as the Big Bang.

Areas of Agreement / Disagreement

Participants express differing views on the existence of a center of mass in the universe and its implications for cosmic expansion and contraction. There is no consensus on these points, and the discussion remains unresolved.

Contextual Notes

Participants reference analogies and theoretical models that may depend on specific interpretations of cosmological principles. The discussion includes assumptions about gravity, dark matter, and the nature of cosmic expansion that are not fully explored.

mg0stisha
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I guess this is a relatively simple question, but depending on the answer can have complex
follow-up questions. So here goes with the first: is there a center of mass to the universe? Or is this not possible?

P.S. Is this site being weird for anyone? It only works on my phone's web browser as of about 3 hours ago...
 
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Based on current theory, the answer is probably not. I don't know it applies here, but an analogy often used to derscribe the universe is that it is like the surface of a balloon (in three dimensions, not two). Using the analogy, note that the surface of a balloon has no center.
 
Okay, now for a follow up. Wouldn't the universe have to have a center of mass to eventually pull everything in the universe back to said center of mass to create the 'Big Crunch' or whatever else it may be called?
 
mg0stisha said:
Okay, now for a follow up. Wouldn't the universe have to have a center of mass to eventually pull everything in the universe back to said center of mass to create the 'Big Crunch' or whatever else it may be called?

No. Going back to the balloon analogy, the balloon may deflate and eventually shrink to zero size, but to the people on the surface there wouldn't be any "center" that the balloon is shrinking towards. Every point on the surface would steadily get closer to every other point, and this applies to the entire surface.
 
Ah, I see! One last one now: What would cause the theoretical 'balloon' to stop expanding and start shrinking?
 
Gravity. Just think of it as throwing a rock up on the surface of the earth. Initially it is going up (expanding) but gravity is slowing down its speed until it goes to zero, then reverses its direction and it starts falling (shrinking). Note that it looks like there is another 'force' at work which actually accelerates the expansion so gravity may never be strong enough to actually reverse the expansion.
 
Cyosis said:
Gravity. Just think of it as throwing a rock up on the surface of the earth. Initially it is going up (expanding) but gravity is slowing down its speed until it goes to zero, then reverses its direction and it starts falling (shrinking). Note that it looks like there is another 'force' at work which actually accelerates the expansion so gravity may never be strong enough to actually reverse the expansion.

Yes, and this gravity mostly comes from dark matter, which comprises 90% of the matter in the universe. Some of it also comes from the energy in radiation.
 
Thanks everybody, and I got one more for you all. Where will the universe's contraction take place? Would it be at the same point where the big bang happened?
 

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