View Single Post
  #7  
Old May 4th 19, 11:37 AM posted to sci.astro.research
Phillip Helbig
external usenet poster
 
Posts: 38
Default Revise age of the universe?

In article ,
(Phillip Helbig (undress to reply))
writes:

| Moderator's note: Actually, the deceleration and acceleration almost
| balance so that the age of the universe is very close to the Hubble
| time. In our universe, this happens only near the present epoch. There
| have been a couple of papers addressing this coincidence. -P.H.

For example, if you use the Planck Collaboration's 2015 value of H_0 =
67.31 (km/s)/Mpc (TT+lowP) [1], with 1/H_9 = 14.5 Ga you do NOT obtain
Planck's corresponding t_0 = 13.813 Ga but something considerably
larger.


I think I have shown here that the moderator's statement is not true.
A difference of several hundred million years is NOT "very close".


There are at least two papers on arXiv on this topic, one by Geraint
Lewis, Pim van Orschok (not sure of the spelling), and possibly more
authors, and one by Bob Kirshner and a co-author. The degree of
coincidence is independent of the Hubble constant, but of course depends
on the values of lambda and Omega used. (The second paper has an
obvious title; the first is also about something else, but the title
isn't obvious.) I can't check now but they can probably be found at
arXiv.org in less than a minute.


The papers in question are at
https://arxiv.org/abs/1001.4795 (Pim van
Oirschot, Juliana Kwan, Geraint F. Lewis; MNRAS 404, 4, 1633--1638, 1
June 2010), who note that "the time averaged value of the deceleration
parameter over the age of the universe is nearly zero", which is
equivalent to saying that the age of the universe is equal to the Hubble
time (see the solid red line in their figure 1); and
https://arxiv.org/abs/1607.0002 (Arturo Avelino and Robert P. Kirshner;
ApJ 828, 1, 35, 25 August 2016), who point out that H_0t_0 = 0.96+/-0.01
(and also that this agrees well with other estimates of the age of the
universe).