What Happens to the Universe if Omega Equals Exactly 1?

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Discussion Overview

The discussion revolves around the implications of the density parameter Omega (Ω) being exactly 1 for the fate of the universe. Participants explore theoretical scenarios regarding the universe's expansion, potential outcomes, and the role of dark energy, focusing on cosmological models and their interpretations.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant suggests that if Omega is exactly 1, the universe's fate cannot be definitively categorized as either a big crunch or a big freeze, proposing it as a paradox without a logical resolution.
  • Another participant argues that if Ω_m equals 1 without dark energy, the universe would asymptotically approach a stationary state, expanding forever but at a decreasing rate.
  • A different viewpoint indicates that current theories suggest Ω = 1, with Ω_m approximately 0.3 and Ω_Λ approximately 0.7, leading to expectations of perpetual expansion at an accelerated rate due to dark energy.
  • One participant humorously clarifies a misunderstanding regarding the values of lambda and omega, indicating a mix-up in their earlier statements.

Areas of Agreement / Disagreement

Participants express differing views on the implications of Omega being exactly 1, with no consensus reached on the final fate of the universe under this condition. Some propose that it leads to a stationary state, while others emphasize the role of dark energy in determining the universe's expansion.

Contextual Notes

There are unresolved assumptions regarding the role of dark energy and the definitions of Omega parameters, which influence the interpretations of the universe's fate.

cosmic time
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If Omega was exactly 1...

We know if the value of omega (the average mass of all matter int he universe was) was more than 1, the ultimate fate of our universe is the big crunch; also if omga was less than one, there wouldn't be enough gravitational pull to bring all matter back, however will expand forever, and will end in a big freeze.
I'm thinking if Omega was exactly 1, what's the final fate, it can't end in a crunch, or a freeze, or it can't be exactly one. It'll have to be a midway point between a freeze and a crunch, this can be used as a paradox, as there is no logical answer to my knowledge.
 
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If [itex]\Omega_m=1[/itex] and there's no dark energy or cosmological constant, then the universe asymptotically approaches stationarity as time approaches infinity. In other words, it expands forever, but at an ever slower rate. However, the most popular theory of the universe right now gives the following:

[tex]\Omega = 1[/tex]

[tex]\Omega_m \simeq 0.3[/tex]

[tex]\Omega_{\Lambda} \simeq 0.7[/tex]

That is, we think that [itex]\Omega = 1[/itex], but the dominant component has a negative pressure. In this scenario, we expect the universe to expand forever and at an accelerated rate.
 
So, for all practical purposes :wink: and ignoring Dark Energy, omega =1 and < 1 gives you the same end-of-universe scenario.

Welcome to Physics Forums!
 
o I am sorry I was referring to the value of lambda and omega as one...:smile:
 

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