• Revise age of the universe?

    From root@21:1/5 to All on Sun Apr 28 22:06:40 2019
    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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  • From Phillip Helbig (undress to reply)@21:1/5 to All on Mon Apr 29 11:33:38 2019
    In article <q9vhb8$rr6$1@news.albasani.net>, root <NoEMail@home.org>
    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.

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  • From Thomas 'PointedEars' Lahn@21:1/5 to root on Mon Apr 29 21:41:56 2019
    [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_constant>

    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.

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  • From Richard D. Saam@21:1/5 to root on Wed May 1 19:25:18 2019
    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'.

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  • From Thomas 'PointedEars' Lahn@21:1/5 to Thomas 'PointedEars' Lahn on Thu May 2 21:21:46 2019
    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?

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  • From Phillip Helbig (undress to reply@21:1/5 to 'PointedEars' Lahn on Thu May 2 21:36:03 2019
    In article <20e47c4a-4e62-a49b-03c7-5394063fdb21@PointedEars.de>, Thomas 'PointedEars' Lahn <PointedEars@web.de> 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).

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  • From Phillip Helbig (undress to reply@21:1/5 to All on Sat May 4 11:37:14 2019
    In article <qafk5p$mqu$1@gioia.aioe.org>,
    helbig@asclothestro.multivax.de (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).

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  • From Steve Willner@21:1/5 to Richard D. Saam on Wed May 8 11:02:00 2019
    In article <u6mdnbzd2qfIWFTBnZ2dnUU7-YnNnZ2d@giganews.com>,
    "Richard D. Saam" <rdsaam@att.net> 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 swillner@cfa.harvard.edu Cambridge, MA 02138 USA

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  • From Phillip Helbig (undress to reply)@21:1/5 to willner@cfa.harvard.edu on Fri May 10 15:37:00 2019
    In article <qav5aq$3lo$1@dont-email.me>, Steve Willner <willner@cfa.harvard.edu> writes:=20

    In article <u6mdnbzd2qfIWFTBnZ2dnUU7-YnNnZ2d@giganews.com>,
    "Richard D. Saam" <rdsaam@att.net> 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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