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Revise age of the universe?



 
 
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  #1  
Old April 29th 19, 03:06 AM posted to sci.astro.research
root[_2_]
external usenet poster
 
Posts: 8
Default Revise age of the universe?

Can the recent findings of the Space Telescope Institute be used
to revise the age of the universe. What would the estimate
of 13.7E9 years become if the current rate of acceleration obtained
over the entire lifetime?
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  #2  
Old April 29th 19, 04:33 PM posted to sci.astro.research
Phillip Helbig (undress to reply)[_2_]
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Posts: 251
Default Revise age of the universe?

In article , root
writes:=20

Can the recent findings of the Space Telescope Institute be used
to revise the age of the universe. What would the estimate
of 13.7E9 years become if the current rate of acceleration obtained
over the entire lifetime?


If you are talking about changing only the Hubble constant (I think that=20
you are), then the age---all else assumed equal---is inversely=20
proportional to the hubble constant. However, keep in mind that we are=20
talking about a change of a few per cent (I am assuming that you are=20
comparing relatively local HST measurements to the value obtained from=20
CMB observations).

If the current rate of acceleration applied over the entire lifetime=20
(there is no reason to think that this is even remotely true), then the=20
size of the universe as a function of time would be an exponential=20
function and thus be infinitely old.
  #3  
Old April 29th 19, 09:41 PM posted to sci.astro.research
Thomas 'PointedEars' Lahn
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Posts: 75
Default Revise age of the universe?

[Moderator's note: I have tried to transform 8-bit characters to
something more legible. Please post only 7-bit printable ASCII
characters. -P.H.]

root wrote:
^^^^
Please post here using your real name.

Can the recent findings of the Space Telescope Institute be used
to revise the age of the universe.


Yes, if those findings were *conclusive*, i.e. would mean that the Hubble
constant *definitely* is greater, then that would mean that our universe
would be slightly younger than previously thought (see below).

However, different from the *wrong* popular-scientific accounts, the HST
estimate merely shows that there might be something fundamental that we do
not yet understand about the universal expansion because different *recent*
measurement methods produced so many different estimates for the Hubble
constant:

https://en.wikipedia.org/wiki/Hubble%27s_law#Observed_values_of_the_Hubble_const ant

Previously one could have thought (and IIUC it had been thought) that
the precision of the experiments were just not so good in the past, but
now we have for the Hubble constant e.g. 67.660.42 (km/s)/Mpc by
\_Planck_/ in 2018 (obtained from observing the CMB) and 74.031.42
(km/s)/Mpc by HST in 2019 (obtained from observing cepheids in the LMC).
At some point in time the estimates should converge to one value, but
apparently they do not.

These accounts should be a reliable description of what was really found
and concluded by the HST scientists:

https://www.nasa.gov/feature/goddard/2019/mystery-of-the-universe-s-expansion-rate-widens-with-new-hubble-data

https://www.spacetelescope.org/news/heic1908/

I think that the following much less hysterically written article sums
up and clarifies in laymen terms the
*misconceptions*/*misrepresentations* about the HST result as published
in the rest of the non-scientific media (Business Insider, CBC, Daily
Star, Digital Trends, Heise Newsticker, Science Alert, Sputnik News
etc.) pretty well:

https://gizmodo.com/hubble-measurements-confirm-theres-something-weird-abou-1834339830

What would the estimate of 13.7E9 years


The previous estimate was already 13.796p0.020 * 10^9 years (Planck
Collaboration 2018: TT,TE,EE+lowE+lensing+BA 68 % limits [1]), which is
"13.8E9 years" when properly rounded.

become if the current rate of acceleration obtained over the entire lifetime?


In that case I will leave the calculation to you, because you *can* do
it Because in that case the age of our universe is easily obtained as
the reciprocal of the Hubble constant:

t = 1/H_0.

[Moderator's note: True if the current RATE of expansion were constant,
but not if the current ACCELERATION were constant. -P.H.]

Note that the Hubble constant is a speed per distance, usually specified
in units of (km/s)/Mpc, which is a length over time over a length, and
therefore has dimensions of 1/[time]. [3]

However, this simple calculation definitely produces the wrong value
(sorry ;-)) because we know from observation that the speed of expansion
was and is not constant over time. Instead, the Hubble constant is
merely the value of the time-dependent Hubble *parameter*

H(t) = a'(t)/a(t)

*now*, at the *current* time:

H(t=t_0) = a'(t=t_0)/a(t=t_0) = H_0,

where a(t) is the scale factor of our universe at time t.

[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.

Therefore I think that obtaining the correct age is not trivial: you
would have to solve an integral of a function over time that involves
the Hubble parameter. That function needs to be designed such that it
fits the actual development of the past expansion speed as obtained from
theory and/or observation of distant objects:

https://en.wikipedia.org/wiki/Universe#/media/File:CMB_Timeline300_no_WMAP.jpg

[Moderator's note: It is an elliptic integral, so somewhat non-trivial
analytically, but well known, and can also be done numerically. -P.H.]

Note in this 2006 depiction of an inflationary LambdaCDM model (based on
WMAP data) the extreme expansion speed in the epoch of inflation (as per
the theory of cosmic inflation) in the first 10 years; then a
moderate, almost linear expansion until our universe was 13 =97 10
years old, followed by an accelerated expansion due to Dark Energy
(=9B) since about 770 =97 10 years ago.

[Moderator's note: Due to the non-ASCII characters, I'm not sure what
was meant, but in any case the age of the universe is essentially
independent of inflation since that lasted only a fraction of a second.
-P.H. There was deceleration until a few billion years ago and since
then acceleration.]

See also (highly recommended):

Tamara M. DAVIS & Charles H. LINEWEAVER (2003). Expanding Confusion:
common misconceptions of cosmological horizons and the superluminal
expansion of the Universe. https://arxiv.org/abs/astro-ph/0310808v2

_______
[1] https://en.wikipedia.org/wiki/Age_of_the_universe#Planck
[2] ESO (2018): Planck 2018 results. VI. Cosmological parameters.
https://arxiv.org/pdf/1807.06209.pdf
[3] Lawrence M. Krauss (2017): Physics Made Easy. Tomasa Terry.
https://youtu.be/bywYBtkfsWA?t=2636 (I recommend the entire talk)
--
PointedEars

Twitter: @PointedEars2
Please do not cc me. / Bitte keine Kopien per E-Mail.

  #4  
Old May 1st 19, 07:25 PM posted to sci.astro.research
Richard D. Saam
external usenet poster
 
Posts: 237
Default Revise age of the universe?

On 4/28/19 9:06:40 PM, root wrote:
Can the recent findings of the Space Telescope Institute be used
to revise the age of the universe. What would the estimate
of 13.7E9 years become if the current rate of acceleration obtained
over the entire lifetime?


The main point of the Space Telescope Institute work
https://arxiv.org/abs/1903.07603
is that 4.4 sigma discrepancy between Planck Ho and STI Ho 'is not
readily attributable to an error in any one source or measurement,
increasing the odds that it results from a cosmological feature beyond
LambdaCDM'.

  #5  
Old May 2nd 19, 09:21 PM posted to sci.astro.research
Thomas 'PointedEars' Lahn
external usenet poster
 
Posts: 75
Default Revise age of the universe?

Thomas 'PointedEars' Lahn wrote:
root wrote:
become if the current rate of acceleration obtained over the entire lifetime?


In that case I will leave the calculation to you, because you *can* do
it Because in that case the age of our universe is easily obtained as
the reciprocal of the Hubble constant:

t = 1/H_0.

| Moderator's note: True if the current RATE of expansion were constant,
| but not if the current ACCELERATION were constant. -P.H.


The OP was not even talking about the `current acceleration', but the
`current rate of acceleration'.

| 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".

Note in this 2006 depiction of an inflationary LambdaCDM model (based on
WMAP data) the extreme expansion speed in the epoch of inflation (as per
the theory of cosmic inflation) in the first 10^9 years; then a
moderate, almost linear expansion until our universe was 13 * 10^9
years old, followed by an accelerated expansion due to Dark Energy
(Lambda) since about 770 * 10^6 years ago.


| but in any case the age of the universe is essentially
| independent of inflation since that lasted only a fraction of a second.
| -P.H. There was deceleration until a few billion years ago and since
| then acceleration.


So the image I referred to is imprecise in that regard?

  #6  
Old May 2nd 19, 09:36 PM posted to sci.astro.research
Phillip Helbig
external usenet poster
 
Posts: 33
Default Revise age of the universe?

In article , Thomas
'PointedEars' Lahn writes:

Thomas 'PointedEars' Lahn wrote:
root wrote:
become if the current rate of acceleration obtained over the entire
lifetime?


In that case I will leave the calculation to you, because you *can* do
it Because in that case the age of our universe is easily obtained as
the reciprocal of the Hubble constant:

t = 1/H_0.

| Moderator's note: True if the current RATE of expansion were constant,
| but not if the current ACCELERATION were constant. -P.H.


The OP was not even talking about the `current acceleration', but the
`current rate of acceleration'.


Right, but what did he mean? There might be a language problem. I took
"current rate of acceleration" to mean "current value of the
acceleration". It certainly can't mean "current rate of expansion" (at
least without even bigger language problems). Richard Nixon once said
that while he was president, the rate of increase of inflation had gone
down. A journalist quipped that this was the only occasion when a
President of the United States made use of the third derivative.

| 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.

Note in this 2006 depiction of an inflationary LambdaCDM model (based on
WMAP data) the extreme expansion speed in the epoch of inflation (as per
the theory of cosmic inflation) in the first 10^9 years; then a
moderate, almost linear expansion until our universe was 13 * 10^9
years old, followed by an accelerated expansion due to Dark Energy
(Lambda) since about 770 * 10^6 years ago.


| but in any case the age of the universe is essentially
| independent of inflation since that lasted only a fraction of a second.
| -P.H. There was deceleration until a few billion years ago and since
| then acceleration.


So the image I referred to is imprecise in that regard?


Not imprecise; it's just that inflation is irrelevant. It happened
in much less than a second, so whether or not it happened doesn't much
affect the age of the universe today, which is based on the values of
lambda, Omega, and H measured today (from which their values at all
other times follow).

  #7  
Old May 4th 19, 11:37 AM posted to sci.astro.research
Phillip Helbig
external usenet poster
 
Posts: 33
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).

  #8  
Old May 8th 19, 07:02 PM posted to sci.astro.research
Steve Willner
external usenet poster
 
Posts: 1,161
Default Revise age of the universe?

In article ,
"Richard D. Saam" writes:
The main point of the Space Telescope Institute work
https://arxiv.org/abs/1903.07603
is that 4.4 sigma discrepancy between Planck Ho and STI Ho is not
readily attributable to an error in any one source or measurement,
increasing the odds that it results from a cosmological feature beyond
LambdaCDM'.


Indeed. Whatever it is, it doesn't seem to be statistics.

The preprint (linked above) gives references to other work on the CMB
and BAO, which methods give the Hubble-Lemaitre parameter at high
redshift, i.e., early in the history of the Universe. A simple
summary is that dark energy appears to have increased over
cosmological time. Fig 4 of the preprint gives some ideas of why
that might have happened. Another possibility, of course, is that
there is some unrecognized systematic error in one of the
measurements. The local H_0 looks pretty solid to me. I know less
about the early H but can't help wondering about the calculated
sound-wave distances, which depend on baryonic physics.

For calculating cosmological quantities, Ned Wright's calculator at
http://www.astro.ucla.edu/~wright/CosmoCalc.html
or the advanced calculator at
http://www.astro.ucla.edu/~wright/ACC.html
are terrific resources.

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA
  #9  
Old May 10th 19, 11:37 PM posted to sci.astro.research
Phillip Helbig (undress to reply)[_2_]
external usenet poster
 
Posts: 251
Default Revise age of the universe?

In article , Steve Willner
writes:=20

In article ,
"Richard D. Saam" writes:
The main point of the Space Telescope Institute work
https://arxiv.org/abs/1903.07603
is that 4.4 sigma discrepancy between Planck Ho and STI Ho is not=20
readily attributable to an error in any one source or measurement,=20
increasing the odds that it results from a cosmological feature beyond=

=20
LambdaCDM'.

=20
Indeed. Whatever it is, it doesn't seem to be statistics.


For historical reasons (remember the famous factor of 2?), people could=20
be forgiven for thinking that H_0 discrepancies would clear up---at=20
least for a while. This seems a real low-z vs. high-z issue, not an=20
issue with who is observing how and so on. It also doesn't seem to be=20
driven by prejudices. (I had the pleasure of hearing Allan Sandage=20
lecture at a Saas-Fee school back in 1993. The published version, in=20
The Deep Universe (together with contributions by the other two=20
lecturers, Malcolm Longair and Rich Kron), is an excellent introduction=20
to observational cosmology. In person, it was extremely clear that he=20
took the Einstein-de Sitter universe as given, due to inflation, which=20
of course means that H_0 has to be low to avoid the age problem. With=20
regard to observations, he was careful and critical (if sometimes=20
wrong), but here he drunk the inflation kool-aid hook, line, and sinker=20
(if I can be allowed to mix metaphors).

There is a workshop in Chicago in October on H_0 discrepancies.

The preprint (linked above) gives references to other work on the CMB
and BAO, which methods give the Hubble-Lemaitre parameter at high
redshift, i.e., early in the history of the Universe. A simple
summary is that dark energy appears to have increased over
cosmological time. =20


If dark energy can vary, then many things are possible, especially since=20
we have no idea why it should vary in a particular way (common=20
parameterizations are not based on any sort of theory).

Fig 4 of the preprint gives some ideas of why
that might have happened. Another possibility, of course, is that
there is some unrecognized systematic error in one of the
measurements. The local H_0 looks pretty solid to me. I know less
about the early H but can't help wondering about the calculated
sound-wave distances, which depend on baryonic physics.


I recently ran across this:

@ARTICLE { PFleuryDU13a ,
AUTHOR =3D "Pierre Fleury and H\'el\`ene Dupuy and"
Jean-Philippe Uzan,
TITLE =3D "Can All Cosmological Observations Be
Accurately Interpreted with a Unique
Geometry",
JOURNAL =3D PRL,
YEAR =3D "2013",
VOLUME =3D "111",
NUMBER =3D "9",
PAGES =3D "091302",
MONTH =3D aug
}

Here is my summary based on a quick glance:

They suggest that the well known `tension' between Planck and the m--z
relation for type Ia supernovae can be relieved if the calculations are
done with a Swiss-cheese model. This is because the CMB data have a
typical angular scale of 5 arcmin while the typical angular size of a
supernova is $10^{-7}$ arcsec. If the Swiss-cheese model is more
appropriate, but a homogeneous model assumed, then one will
underestimate H_0 and overestimate Omega_0.=20

Keep in mind that H_0 and Omega_0 are correlated in the CMB data.

The Swiss-cheese model takes a Friedmann-Lemaitre-Robertson-Walker
(FLRW) universe and removes some matter at certain places (creating the
holes), which is then placed in the center of the resulting hollow
spheres, either as a point mass, a spherical mass smaller than the hole,
or even something like an FLRW model inside the hole. This is not a=20
particularly accurate model for the universe, but it does have the=20
advantage of being an exact solution to the Einstein equations, so one=20
does not have to worry about the validity of approximations used in=20
other approaches (such as that used by Zeldovich, which is often known=20
as the Dyer-Roeder or ZKDR distance (the K being Kantowskii, who was=20
also one of the pioneers of this subject, and the D perhaps representing=20
Dashevskii instead, who was on two of the three early Soviet papers on=20
this topic (Zeldovich, Dashevskii & Zeldovich, Dashevskii and Slysh))).

There is a huge literature on such inhomogeneous models (and also on=20
more exotic inhomogeneous models), but I haven't notice that they have=20
been paid much attention in this context.
 




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