Accordingly to this article: https://medium.com/the-cosmic-companion/is-the-universe-younger-than-we-t=hought-e8a649a32ec8
"Is the Universe Younger than We Thought?", is the age of the universe,
not 13,8 billion years, but 11 billion years old.
This seems, to me, a rather big shift, specific because it is based on gravitational lensing.
Figure 6 of the /Science/ research article gives a nice comparison
of some of the recent Hubble-constant measurements, showing that the
choice of cosmological model (at least within the range of models
considered by the authors) makes rather little difference.
-- jt]]
Accordingly to this article: https://medium.com/the-cosmic-companion/is-the-universe-younger-than-we-thought-e8a649a32ec8
which in turn describes this research paper
"A measurement of the Hubble constant from angular diameter distances
to two gravitational lenses"
https://science.sciencemag.org/content/365/6458/1134
which in turn describes this research paper
"A measurement of the Hubble constant from angular diameter distances
to two gravitational lenses"
https://science.sciencemag.org/content/365/6458/1134
The paper is behind a paywall, but the Abstract, which is public,
summarizes the results. [[...]]
[[Mod. note -- I've now found the preprint -- it's arXiv:1906.06712.
Sorry for not including that in my original mod.note. -- jt]]
The preprint is 1909.06712
Two additional preprints are at
https://arxiv.org/abs/1907.04869 and
https://arxiv.org/abs/1910.06306
These report direct measurements of gravitational lens distances
rather than a recalibration of the standard distance ladder.
The upshot is that
the discrepancy between the local and the CMB measurements of H_0 is
between 4 and 5.7 sigma, depending on how conservative one wants to
be about assumptions.
"New physics" could be something as simple as
time-varying dark energy
In article <mt2.1.4-81115-1569549391@iron.bkis-orchard.net>,...
"Jonathan Thornburg [remove -animal to reply]"
<jthorn@astro.indiana-zebra.edu> writes:
The preprint is 1909.06712
Two additional preprints are at
https://arxiv.org/abs/1907.04869 and
https://arxiv.org/abs/1910.06306
One other note from the talk: it takes an expert modeler about 8 months
to a year to model a single lens system. Shajib and others are trying
to automate the modeling,
On 19/10/15 10:17 PM, Steve Willner wrote:
In article <mt2.1.4-81115-1569549391@iron.bkis-orchard.net>,
"Jonathan Thornburg [remove -animal to reply]"
<jthorn@astro.indiana-zebra.edu> writes:
The preprint is 1909.06712
Two additional preprints are at...
https://arxiv.org/abs/1907.04869 and
https://arxiv.org/abs/1910.06306
...
One other note from the talk: it takes an expert modeler about 8 months
to a year to model a single lens system. Shajib and others are trying
to automate the modeling,
You obviously do not mean that they do it by pencil and paper at this
moment.
So why is modeling labor-intensive? Isn't it just putting a
point mass in front of the observed object, which only requires fitting
the precise position and distance of the point mass using the observed
image?
(And if so, is the actual imaging with the point mass in some
place the difficult part?) Or is the problem that the lensing object
may be more extended than a point mass? (Or is it something worse!?)
[[Mod. note -- In these cases the lensing object is a galaxy (definitely
not a point mass!). For precise results a nontrivial model of the
galaxy's mass distribution (here parameterized by the (anisotropic)
velocity dispersion of stars in the lensing galaxy's central region)
is needed, which is the tricky (& hence labor-intensive) part.
-- jt]]
At this level of precision, it's probably not enough to simply
parameterize this, but rather one needs some model of the mass
distribution near the beams.
In article <qo67pc$csc$1@gioia.aioe.org>,
"Phillip Helbig (undress to reply)" <helbig@asclothestro.multivax.de> writes:
At this level of precision, it's probably not enough to simply
parameterize this, but rather one needs some model of the mass
distribution near the beams.
That's exactly right (at least to the extent I understood Shajib's
talk). In particular, one has to take into account the statistical distribution of mass all along and near the light path and also (as
others wrote) the mass distribution of the lensing galaxy
itself.
The upshot is that the discrepancy between the local and the CMB measurements of H_0 is between 4 and 5.7 sigma, depending on how
conservative one wants to be about assumptions.
......> 1. both the local ("direct") measurements
and the distant ("indirect") measurements are made by two
_independent_ methods, which agree in each case. That is, the two
direct methods (SNe, lensing) agree with each other, and the two
indirect methods (CMB, something complicated) agree with each other,
but the direct and indirect measurements disagree.
2. contrary to what I wrote earlier, even a non-physical change of
dark energy with time (say an abrupt increase at some fine-tuned
epoch) cannot fix the disagreement.
3. while there have been several suggestion for new physics to fix
the problem, none of them so far seems to work without disagreeing
with other data.
What fun!
3. while there have been several suggestion for new physics to fix
the problem, none of them so far seems to work without disagreeing
with other data. ... What fun!
Yes! So why are only 20 people attending?!
To the question in another message, I don't see why some local
perturbation -- presumably abnormally low matter density around our
location -- wouldn't solve the problem in principle, but if this were
a viable explanation, I expect the speaker would have mentioned it.
It's not as though no one has thought about the problem. The
difficulty is probably the magnitude of the effect. I don't work in
this area, though, so my opinion is not worth much.
In article <qo590f$c75$1@dont-email.me>, I wrote:
The upshot is that the discrepancy between the local and the CMB
measurements of H_0 is between 4 and 5.7 sigma, depending on how
conservative one wants to be about assumptions.
3. while there have been several suggestion for new physics to fix
the problem, none of them so far seems to work without disagreeing
with other data.
What fun!
On 11/2/19 3:50:25 AM, Steve Willner wrote:
In article <qo590f$c75$1@dont-email.me>, I wrote:
The upshot is that the discrepancy between the local and the CMB
measurements of H_0 is between 4 and 5.7 sigma, depending on how
conservative one wants to be about assumptions.
3. while there have been several suggestion for new physics to fix
the problem, none of them so far seems to work without disagreeing
with other data.
What fun!
The Ho data is tightening:
**
Testing Low-Redshift Cosmic Acceleration with Large-Scale Structure https://arxiv.org/abs/2001.11044
Seshadri Nadathur, Will J. Percival,
Florian Beutler, and Hans A. Winther
Phys. Rev. Lett. 124, 221301 - Published 2 June 2020
we measure the Hubble constant to be
Ho = 72.3 +/- 1.9 km/sec Mpc from BAO + voids
at z<2
and
Ho = 69.0 +/- 1.2 km/sec Mpc from BAO
when adding Lyman alpha at BAO at z=2.34
**
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