2 ms·
Yes to 1) and 2), however: > 3. The acceleration is actually slowing down, but it is not heading towards zero. It is approaching some steady state acceleration
by mr_mitm 3y ago
Yes to 1) and 2), however:
> 3. The acceleration is actually slowing down, but it is not heading towards zero. It is approaching some steady state acceleration.
No. The scale factor in LCDM (the current concordance model) is proportional to sinh^(2/3)(t/t_Lambda), which means it's asymptotically exponential. Acceleration will always increase.
(Edit: The expansion rate, so a'/a, will go to a constant value, though.)
Caveat: If the Hubble tension proves real, LCDM is wrong.
- bmitc 3y agoThanks! So the currently accepted model says the acceleration will grow indefinitely but our observations are saying that the acceleration levels out to a non-zero, positive constant?
- mr_mitm 3y agoNo, I think the confusion here is the difference between "acceleration" and "expansion rate". It's less ambigious when using math: https://en.wikipedia.org/wiki/Lambda-CDM_model#Cosmic_expansion_history https://en.wikipedia.org/wiki/Lambda-CDM_model#Cosmic_expans... a is the scale factor, which goes as sinh^(2/3). a' and a'' will always increase, but the _expansion rate_ a'/a will approach a constant value from above. Besides the Hubble tension discussed in the article, there is no real discrepancy between observations and theory.
- bmitc 3y ago> a is the scale factor, which goes as sinh^(2/3). a' and a'' will always increase, but the _expansion rate_ a'/a will approach a constant value from above. Thanks for that. I didn't realize there was such a definition of expansion rate and was going off the intuitive meaning of the terms. Thank you for the clarifications.