
#1
Feb2712, 10:08 AM

P: 32

The other day, I was calculating the age of universe dominated by vacuum energy and it turned out to be infinity. What does age of the universe being infinite mean? On explanation I thought of is that may be this implies that such a universe has no beginning. Is it a proper explanation?




#2
Feb2712, 12:43 PM

Sci Advisor
P: 2,194

No, it simply means the universe will never experience a big crunch, i.e. recollapse. Simply put, the scale factor never returns to zero. It is of course possible to have a universe which starts with a=0, but then persists indefinitely (as is the case with our own).




#3
Feb2712, 01:26 PM

P: 32

Hmm, isn't that more like the fate of the universe. What I was trying to calculate was what would be the present age of the universe in standard Friedman cosmology for a flat universe(sorry i didn't mention that before), as a function of the observed CMB redshift and Hubble. But what I got was that for vacuum dominated universe, the age would turn out to be infinity (irrespective of value of redshift and H), and the only meaningful explanation I could think of was universe with no beginning




#4
Feb2712, 05:05 PM

Emeritus
Sci Advisor
PF Gold
P: 5,198

Age of a vaccum energy dominated universehttp://www.astro.ucla.edu/~wright/CosmoCalc.html ...I get about 37 Gyr, not ∞. Also, what do you mean by, "as a function of the observed CMB redshift?" What does that have to do with anything? Isn't the only relevant value of z the value at which you want to compute the age of the universe (which would be z = 0 for the age at the present time)? 



#6
Feb2712, 08:48 PM

Emeritus
Sci Advisor
PF Gold
P: 5,198

I'm guessing that the OP tried to invert the differential equation and then integrate to solve for t(a), but obtained something proportional to [itex]\int_0^1 \frac{1}{a}\,da[/itex] which does not converge  which is another way of showing the same result. So I read that this is the de Sitter universe, and that it is also used as an approximation to inflationary models whose dynamics are similar. Is this idea of "no beginning" sort of the basis for "eternal inflation?" 



#7
Feb2812, 12:10 AM

Sci Advisor
P: 4,721





#8
Feb2812, 01:42 AM

P: 32




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