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cosmological time dilation
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fringuello giulivo
Nov 26, 2011, 7:20:19 AM11/26/11
to
Hi to you all,
in the FAQ of the "Ned Wright's Cosmology Tutorial ",
I find the following question:
"" Has the time dilation of distant sources light curves
previded by the Big Bang been observed? ""
The answer mentions some papers, e.g.:
arXiv:astro-ph/9602124v1
by G. Goldhaber et al.
title: " observation of cosmological time dilation
using type Ia supernovae as clocks "
23 Feb 1996.
Please can you explain how time dilation can arise
in a FLRW metric ? I don' t understand how time
dilation can be compatible with a constant time-time
component of the metric tensor.
My research on Google and on my general relativity textbooks
(graduate level) is unsuccessful.
Thank you in advance.
FG
in the FAQ of the "Ned Wright's Cosmology Tutorial ",
I find the following question:
"" Has the time dilation of distant sources light curves
previded by the Big Bang been observed? ""
The answer mentions some papers, e.g.:
arXiv:astro-ph/9602124v1
by G. Goldhaber et al.
title: " observation of cosmological time dilation
using type Ia supernovae as clocks "
23 Feb 1996.
Please can you explain how time dilation can arise
in a FLRW metric ? I don' t understand how time
dilation can be compatible with a constant time-time
component of the metric tensor.
My research on Google and on my general relativity textbooks
(graduate level) is unsuccessful.
Thank you in advance.
FG
eric gisse
Nov 27, 2011, 5:15:27 PM11/27/11
to
"fringuello giulivo" <Wl'Xconl'1dedrioel'uslincal...@rintintin.it>
wrote in news:4ed00db9$0$1379$4faf...@reader2.news.tin.it:
> Hi to you all,
>
> in the FAQ of the "Ned Wright's Cosmology Tutorial ",
> I find the following question:
>
> "" Has the time dilation of distant sources light curves
> previded by the Big Bang been observed? ""
>
> The answer mentions some papers, e.g.:
>
> arXiv:astro-ph/9602124v1
>
> by G. Goldhaber et al.
> title: " observation of cosmological time dilation
> using type Ia supernovae as clocks "
> 23 Feb 1996.
>
> Please can you explain how time dilation can arise
> in a FLRW metric ? I don' t understand how time
> dilation can be compatible with a constant time-time
> component of the metric tensor.
The time component may be static but the space component is not.
Two points on the expanding hypersurface will grow further apart in
time, thus time dilation / redshift.
Work it out with the FRW metric.
wrote in news:4ed00db9$0$1379$4faf...@reader2.news.tin.it:
> Hi to you all,
>
> in the FAQ of the "Ned Wright's Cosmology Tutorial ",
> I find the following question:
>
> "" Has the time dilation of distant sources light curves
> previded by the Big Bang been observed? ""
>
> The answer mentions some papers, e.g.:
>
> arXiv:astro-ph/9602124v1
>
> by G. Goldhaber et al.
> title: " observation of cosmological time dilation
> using type Ia supernovae as clocks "
> 23 Feb 1996.
>
> Please can you explain how time dilation can arise
> in a FLRW metric ? I don' t understand how time
> dilation can be compatible with a constant time-time
> component of the metric tensor.
Two points on the expanding hypersurface will grow further apart in
time, thus time dilation / redshift.
Work it out with the FRW metric.
Phillip Helbig---undress to reply
Nov 28, 2011, 3:13:55 AM11/28/11
to
In article <4ed00db9$0$1379$4faf...@reader2.news.tin.it>, "fringuello
of clock which emits pulses will seem slower. Basically, this is due to
the fact that the expansion of the universe causes the cosmological
redshift. (There is a huge amount of literature on this.) One can
think of the peaks in a wave of light as a clock. However, the same
argument applies to ANY sort of clock, not just a wave train. Observing
it, of course, means having some sort of standard clock. This has been
done for a long time with light, since the wavelength of certain
spectral lines on Earth is well known, and they are observed with
redshift. However, various people have, for various reasons, tried to
come up with other explanations for the cosmological redshift. Usually,
these would cause a redshift but NOT a time dilation in other cases,
which is why observing it is interesting. If one has some absolute time
scale, e.g. as given by the lightcurve of a supernova, then one should
see this timescale stretched with redshift.
giulivo" <Wl'Xconl'1dedrioel'uslincal...@rintintin.it> writes:
> in the FAQ of the "Ned Wright's Cosmology Tutorial ",
> I find the following question:
>
> "" Has the time dilation of distant sources light curves
> previded by the Big Bang been observed? ""
>
> The answer mentions some papers, e.g.:
>
> arXiv:astro-ph/9602124v1
>
> by G. Goldhaber et al.
> title: " observation of cosmological time dilation
> using type Ia supernovae as clocks "
> 23 Feb 1996.
>
> Please can you explain how time dilation can arise
> in a FLRW metric ? I don' t understand how time
> dilation can be compatible with a constant time-time
> component of the metric tensor.
Maybe you misunderstood. Due to the expansion of the universe, any sort
> in the FAQ of the "Ned Wright's Cosmology Tutorial ",
> I find the following question:
>
> "" Has the time dilation of distant sources light curves
> previded by the Big Bang been observed? ""
>
> The answer mentions some papers, e.g.:
>
> arXiv:astro-ph/9602124v1
>
> by G. Goldhaber et al.
> title: " observation of cosmological time dilation
> using type Ia supernovae as clocks "
> 23 Feb 1996.
>
> Please can you explain how time dilation can arise
> in a FLRW metric ? I don' t understand how time
> dilation can be compatible with a constant time-time
> component of the metric tensor.
of clock which emits pulses will seem slower. Basically, this is due to
the fact that the expansion of the universe causes the cosmological
redshift. (There is a huge amount of literature on this.) One can
think of the peaks in a wave of light as a clock. However, the same
argument applies to ANY sort of clock, not just a wave train. Observing
it, of course, means having some sort of standard clock. This has been
done for a long time with light, since the wavelength of certain
spectral lines on Earth is well known, and they are observed with
redshift. However, various people have, for various reasons, tried to
come up with other explanations for the cosmological redshift. Usually,
these would cause a redshift but NOT a time dilation in other cases,
which is why observing it is interesting. If one has some absolute time
scale, e.g. as given by the lightcurve of a supernova, then one should
see this timescale stretched with redshift.
Tom Roberts
Dec 8, 2011, 8:26:07 PM12/8/11
to
On 11/26/11 11/26/11 - 6:20 AM, fringuello giulivo wrote:
> "" Has the time dilation of distant sources light curves
> previded by the Big Bang been observed? ""
> "" Has the time dilation of distant sources light curves
> previded by the Big Bang been observed? ""
> Please can you explain how time dilation can arise
> in a FLRW metric ?
I think you attempt to make a distinction without a difference -- the measuring
> in a FLRW metric ?
of redshift is modeled THE SAME as measuring "time dilation". That is, the
modeling of redshift in signals from distant objects includes all relativistic
effects.
Stated differently, "time dilation" is measured between
OVERLAPPING coordinate systems, and that cannot occur for
distant astronomical objects. But that's OK, as GR models
this without any coordinates at all:
Remember how the measurement of redshift is modeled in GR: to determine the
measured interval between tick signals from a source, take the 4-vector interval
between source ticks, parallel transport it along the null geodesic of the
signal to the detector, and dot the result into the detector's 4-velocity.
This assumes that the interval between ticks is very small
compared to any time scales of changes in the geometry.
This procedure applies in both GR and SR, for any measurement of red-shift or
blue-shift of signals from a distant source (i.e. it handles all types of
red-/blue-shift: Doppler, gravitational, cosmological, ...). This also applies
to measuring "time dilation", except there is no EM signal and the source's
interval 4-vector is dotted directly into the detector's 4-velocity.
The redshift of signals from distant astronomical objects in an FLRW manifold
comes from the fact that the 4-velocities of the different "dust grains"
(galaxies) are not "parallel" [@]. I see no good way to apply the term "time
dilation" to this.
[@] meaning they are not parallel after parallel-transporting
one to the location of the other, along the signal path.
Tom Roberts
holog
Dec 8, 2011, 8:34:52 PM12/8/11
to
[[Mod. note -- I apologise to the author and to newsgroup readers for
the long delay in my processing this article, which was originally
submitted on 2 Dec 2011.]]
[[Mod. note -- 44 excessively-quoted lines snipped here. -- jt]]
how is the density of the universe effected by its expansion?
holog
Phillip Helbig---undress to reply
Dec 9, 2011, 9:00:55 PM12/9/11
to
In article
<e5ef231f-0dd5-4d0f...@l19g2000yqc.googlegroups.com>,
I assume you mean "affected".
Just as one might expect: the density is inversely proportional to the
cube of the scale factor. This holds for "ordinary" matter.
(Cosmologists often refer to this as "dust", but keep in mind that this
includes entire galaxies. (There is a reason for this. Also, for
astronomers every element except hydrogen and helium is a "metal".))
There is a different relationship for radiation, but this can be
neglected in our universe. The density corresponding to the
cosmological constant (which it now seems accounts for about 70%, as
opposed to 30% "ordinary matter" (though most of that probably consists
of some sort of matter we are not familiar with), on the other hand,
doesn't change with the expansion of the universe (which is why it is
called the cosmological "constant"). (Don't be confused by the fact
that the Hubble constant changes with time; it is called "constant" for
a different mathematical reason.)
One often speaks of a density PARAMETER Omega, which is essentially the
density divided by the square of the Hubble constant, as well as a
normalized cosmological constant lambda (written with a lower-case
rather than upper-case Greek lambda; the upper-case being the
cosmological constant mentioned above) (sometimes these are referred to
as Omega_matter and Omega_lambda, respectively). Here, the dependence
is more complicated, since as mentioned above the Hubble constant
changes with time in a rather complicated fashion. However, the ratio
|lambda|/Omega is proportional to the scale factor.
<e5ef231f-0dd5-4d0f...@l19g2000yqc.googlegroups.com>,
I assume you mean "affected".
Just as one might expect: the density is inversely proportional to the
cube of the scale factor. This holds for "ordinary" matter.
(Cosmologists often refer to this as "dust", but keep in mind that this
includes entire galaxies. (There is a reason for this. Also, for
astronomers every element except hydrogen and helium is a "metal".))
There is a different relationship for radiation, but this can be
neglected in our universe. The density corresponding to the
cosmological constant (which it now seems accounts for about 70%, as
opposed to 30% "ordinary matter" (though most of that probably consists
of some sort of matter we are not familiar with), on the other hand,
doesn't change with the expansion of the universe (which is why it is
called the cosmological "constant"). (Don't be confused by the fact
that the Hubble constant changes with time; it is called "constant" for
a different mathematical reason.)
One often speaks of a density PARAMETER Omega, which is essentially the
density divided by the square of the Hubble constant, as well as a
normalized cosmological constant lambda (written with a lower-case
rather than upper-case Greek lambda; the upper-case being the
cosmological constant mentioned above) (sometimes these are referred to
as Omega_matter and Omega_lambda, respectively). Here, the dependence
is more complicated, since as mentioned above the Hubble constant
changes with time in a rather complicated fashion. However, the ratio
|lambda|/Omega is proportional to the scale factor.
Phillip Helbig---undress to reply
Dec 9, 2011, 9:02:11 PM12/9/11
to
In article <e4-dnUIVi7j...@giganews.com>, Tom Roberts
be caused by some other mechanism. Many people have suggested this:
tired light etc. What we observe is simply a redshift; we don't know,
without further evidence, where it comes from. By measuring a
non-redshift time dilation, our confidence that the cosmological
redshift is caused by the same mechanism is increased.
<tjro...@sbcglobal.net> writes:
> On 11/26/11 11/26/11 - 6:20 AM, fringuello giulivo wrote:
> > "" Has the time dilation of distant sources light curves
> > previded by the Big Bang been observed? ""
> > Please can you explain how time dilation can arise
> > in a FLRW metric ?
>
> I think you attempt to make a distinction without a difference -- the measuring
> of redshift is modeled THE SAME as measuring "time dilation". That is, the
> modeling of redshift in signals from distant objects includes all relativistic
> effects.
While what you say is true, conceivably the cosmological redshift could
> On 11/26/11 11/26/11 - 6:20 AM, fringuello giulivo wrote:
> > "" Has the time dilation of distant sources light curves
> > previded by the Big Bang been observed? ""
> > Please can you explain how time dilation can arise
> > in a FLRW metric ?
>
> I think you attempt to make a distinction without a difference -- the measuring
> of redshift is modeled THE SAME as measuring "time dilation". That is, the
> modeling of redshift in signals from distant objects includes all relativistic
> effects.
be caused by some other mechanism. Many people have suggested this:
tired light etc. What we observe is simply a redshift; we don't know,
without further evidence, where it comes from. By measuring a
non-redshift time dilation, our confidence that the cosmological
redshift is caused by the same mechanism is increased.
Eric Flesch
Dec 11, 2011, 12:27:03 PM12/11/11
to
On Fri, 09 Dec 2011 21:02:11 EST, p helbig wrote:
> By measuring a
>non-redshift time dilation, our confidence that the cosmological
>redshift is caused by the same mechanism is increased.
However, GRBs actually show the opposite relationship, where the pulse
> By measuring a
>non-redshift time dilation, our confidence that the cosmological
>redshift is caused by the same mechanism is increased.
widths *decrease* with increasing redshift. Paper in-submission
astro-ph/1110.6175 "On the lack of time dilation in GRBs" by Kocevski
D & Petrosian V, tries to address this with the Malmquist effect but I
find their approach unsatisfactory because they don't model how the
Malmquist effect would truncate the GRB profile to match observation.
So I expect it won't be accepted. Which leaves the question of why
this is happening, if cosmological time dilation is true.
[[Mod. note -- It's worth noting that cosmological time dialation
*is* clearly seen in other data sets. I described one example in
this newsgroup in Feb 2009; that thread is archived at
http://www.spacebanter.com/showthread.php?t=133675
-- jt]]
Phillip Helbig---undress to reply
Dec 11, 2011, 12:27:16 PM12/11/11
to
In article <jbuard$ubm$1...@online.de>, hel...@astro.multiCLOTHESvax.de
(Phillip Helbig---undress to reply) writes:
> In article
> <e5ef231f-0dd5-4d0f...@l19g2000yqc.googlegroups.com>,
> holog <ho...@bellsouth.net> writes:
>
> > how is the density of the universe effected by its expansion?
> In article
> <e5ef231f-0dd5-4d0f...@l19g2000yqc.googlegroups.com>,
> holog <ho...@bellsouth.net> writes:
>
> > how is the density of the universe effected by its expansion?
> One often speaks of a density PARAMETER Omega, which is essentially the
> density divided by the square of the Hubble constant, as well as a
> normalized cosmological constant lambda (written with a lower-case
> rather than upper-case Greek lambda; the upper-case being the
> cosmological constant mentioned above) (sometimes these are referred to
> as Omega_matter and Omega_lambda, respectively). Here, the dependence
> is more complicated, since as mentioned above the Hubble constant
> changes with time in a rather complicated fashion. However, the ratio
> |lambda|/Omega is proportional to the scale factor.
Correction: proportional to the CUBE of the scale factor.
> density divided by the square of the Hubble constant, as well as a
> normalized cosmological constant lambda (written with a lower-case
> rather than upper-case Greek lambda; the upper-case being the
> cosmological constant mentioned above) (sometimes these are referred to
> as Omega_matter and Omega_lambda, respectively). Here, the dependence
> is more complicated, since as mentioned above the Hubble constant
> changes with time in a rather complicated fashion. However, the ratio
> |lambda|/Omega is proportional to the scale factor.
Eric Flesch
Dec 12, 2011, 4:15:08 AM12/12/11
to
>[[Mod. note -- It's worth noting that cosmological time dialation
>*is* clearly seen in other data sets. I described one example in
>this newsgroup in Feb 2009; that thread is archived at
>http://www.spacebanter.com/showthread.php?t=133675
Thank you for annotating my post with the contrary view. The paper
>*is* clearly seen in other data sets. I described one example in
>this newsgroup in Feb 2009; that thread is archived at
>http://www.spacebanter.com/showthread.php?t=133675
you cite is indeed interesting but contestable in that the possiblity
of Malmquist effect + high-luminosity profiles is given lip service
only and not fully explored.
But I don't have a stance on it. It is just that the history of
science shows us how far we can go to delude ourselves, before the
breakthrough comes to take us in a new direction.
Over the entrance of the University of Colorado library is written "He
who knows only his own generation remains always a child". A salutory
lesson even for scientists who, in the words of Michael Disney
(astro-ph/0009020), make the "fortunate epoch" assumption that we live
in the privileged time in which we tease out the crucial observations.
Disney: "Don't be impressed by our complex machines or our arcane
mathematics. They have been used to build plausible cosmic stories
before - which we have had to discard afterwards in the face of
improving evidence. The likelihood must be that such revisions will
have to occur again and again and again."
holog
Jan 6, 2012, 1:34:22 AM1/6/12
to
>
> Correction: proportional to the CUBE of the scale factor.
has more than 3 dimensions would this affect your calculations?
holog
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