Re: SR time dilation on remote objects ?
From: Bjoern Feuerbacher (feuerbac_at_thphys.uni-heidelberg.de)
Date: 08/11/04
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Date: Wed, 11 Aug 2004 19:11:02 +0200
Marcel Luttgens wrote:
> Bjoern Feuerbacher <feuerbac@thphys.uni-heidelberg.de> wrote in message news:<cfardg$js9$1@news.urz.uni-heidelberg.de>...
>
>>Marcel Luttgens wrote:
>>
>>>Bjoern Feuerbacher <feuerbac@thphys.uni-heidelberg.de> wrote in message news:<cf7tar$6ab$1@news.urz.uni-heidelberg.de>...
>>>
>>>
>>>>Marcel Luttgens wrote:
>>>>
>>>>
>>>>>Bjoern Feuerbacher <feuerbac@thphys.uni-heidelberg.de> wrote in message news:<ceqahd$f84$1@news.urz.uni-heidelberg.de>...
>>
>>[snip]
>>
>>
>>
>>>>>In such universe, observers A and B separated by a distance d move
>>>>>*from each other* at a velocity v, which is a function of d.
>>>>
>>>>And of time, if you didn't notice.
>>>>
>>>
>>>
>>>Unless one assumes a steady state model. I know that such model is
>>>controversial, but it is however plausible.
>>
>>Why is that plausible? How would one explain all the evidence in
>>such a model?
>
>
> This has been done by the proponents of such model.
References, please.
[snip]
>>>>>Applying SR, observer A situated at a distance d from observer B
>>>>>will claim that tB = tA * sqrt(1-v^2/c^2), but, in his frame of
>>>>>reference, observer B is perfectly right (sic) to claim that
>>>>>tB = tA * sqrt(1-v^2/c^2)!
>>>>
>>>>Using tB and tA here makes no sense, because
>>>>1) time dilation applies to time *intervals*, so you should write
>>>>dt or delta t or something like that.
>>>>2) you *still* ignore the *crucial* difference between the time when
>>>>the light as emitted and the time when it was observed.
>>
>>Did you get it this time? I bet you didn't.
Apparently you really did not get it.
[snip]
>>>As v=HD, or D=v/H,
>>>
>>>v(now) = v(us to A) + v(A to B) + ... + v(X to Y) + v(Y to Z)
>>>
>>>According to SR, one should use the relativistic addition of
>>>those "sub-velocities", and get a global velocity which is less
>>>than c.
>>
>>How often do I need to tell you that the velocities in cosmology
>>are only apparent and hence are not subject to the rules of SR?
>>
>
>
> Apparent velocities leading to apparent redshifts?
No. Apparent velocities leading to a very real redshift.
[snip]
>>> as well as the following claims:
>>
>>>"...the worldlines of the galaxies get flatter and giving velocities
>>>v = dDnow/dt that are greater than c. But in special relativistic
>>>coordinates the velocities are less than c."
>>
>>See? This says *obviously* that in cosmology, one does *not* use
>>special relativistic coordinates and therefore also *not* the special
>>relativistic velocity addition!
>>
>
>
> The cosmologists contradict themselves.
No, not at all. Sorry for you that you are unable to understand
the stuff you quote.
> Using Wright's demonstration,
> I get v(now) = v(us to A) + v(A to B) + ... + v(X to Y) + v(Y to Z)
> In this *analytical* case, one *has* to use the relativistic addition
> of velocities.
No, one hasn't. One is even not allowed to do that, since, as Wright
explained, the "v" here is the change in the cosmology distance "D" -
which is *not* identical to the distance definitions used in SR!
BTW, what specifically do you mean by "analytical" here?
> This is different from *globally* claiming that "in cosmology, one does
> *not* use special relativistic coordinates and therefore also *not* the
> special relativistic velocity addition!"
This statement does indeed apply here. Try to understand that.
> The *analytical* approach, used by Wright himself, demonstrates that
> SR addition is pertinent, hence that galaxies that are far enough away
> from us necessarily *cannot* have velocities greater than the speed of
> light.
Where does he demonstrate that?
>>>"But the Hubble law distance Dnow, which is measured now, of these
>>>most distant galaxies is infinity (in this model). Furthermore,
>>>this galaxy with infinite Hubble law distance and hence infinite
>>>Hubble law velocity is visible to us, since in this model the
>>>observable Universe is the entire Universe. The relationships
>>>between the Hubble law distance and velocity (Dnow & v) and
>>>the redshift z are given below:
>>>v = HoDnow
>>>Dnow = (c/Ho)ln(1+z)
>>>1+z = exp(v/c)"
>>>
>>>Notice "in this model",
>>
>>Yes, I noticed that. Why did you feel the need to quote something
>>which is only true for one particular, rather unrealistic model?
>>
>
>
> If it is unrealistic, then why did Wright used it to demonstrate that
> Dnow and galaxies's velocity can be infinite?
He simply wanted to show that that can be true in some models. So what???
>>>and also "Furthermore,
>>>this galaxy with infinite Hubble law distance and hence infinite
>>>Hubble law velocity is visible to us, since in this model the
>>>observable Universe is the entire Universe."
>>>
>>>This wonderful conclusion suffices to falsify the whole reasoning.
>>
>>No! Why on earth do you think so?
>
>
> Simply because nothing can be seen at infinite distances (unless, of
> course, if the light speed is itself infinite).
I see that you *still* confuse different definitions of distance,
although Wright pointed out *several times* that one has to
be careful what one means when one uses that word, as also carefully
explained *which* distance here is infinitely large.
You are apparently *really* incapable of learning something, no matter
how clearly it is expressed.
>>>"The predicted curve relating one distance indicator to another
>>>depends on the cosmological model."
>>>"Here are the technical formulae for these distances. The graphs
>>>below show these distances vs. redshift for three models:
>>>the critical density matter dominated Einstein - de Sitter model
>>>(EdS), the empty model, and the accelerating Lambda-CDM model
>>>(LCDM) that is the current concensus model."
>>>
>>>Three different models giving different results!
>>
>>Err, and what's your problem with that??? That obviously has to
>>be expected!
>>
>
>
> The problem is that it is difficult to trust the results and conclusions
> of theories using different models, especially the one which lead to
> an accelerated expansion.
I have no clue what you mean here. The BBT uses exactly one
established model today. And Wright says that clearly in what you
quote above. Say, how severe *are* your reading comprehension problems?
>>>Which one will be the next?
>>
>>All evidence we have today points towards the LCDM.
Did you get that?
>>>2) From http://www.astro.ucla.edu/~wright/tiredlit.htm
>>>
>>>"Tired light models invoke a gradual energy loss by photons as
>>>they travel through the cosmos to produce the redshift-distance law."
>>>This has three main problems:
>>>
>>>There is no known interaction that can degrade a photon's energy
>>>without also changing its momentum, which leads to a blurring of
>>>distant objects which is not observed. The Compton shift in
>>>particular does not work."
>>>
>>>Not true, a cosmic negative acceleration cH doesn't change the
>>>photon's momentum.
>>
>>And what would be the mechanism for this negative acceleration?
>>*How* are the photons decelerated?
>>
>
>
> Assuming a stable (not expanding) universe with a cosmic negative
> acceleration cHo,
You ignored my question above. What would be the cause, the mechanism of
that negative acceleration?
> A light ray of wavelength lambda is sent from a point P.
> At a distance d from P, the energy loss of a photon of frequency Nu is
>
> (hNu/c^2) * cH0 * d = hNu * (H0/c) * d,
Why?
> where h is the Plank constant.
>
> Hence, the residual energy hNu(o) of the photon at the distance d is
>
> hNu(o) = hNu - hNu * (H0/c) * d = hNu (1 - H0*d/c), hence
> Nu(o) = Nu (1 - (H0*d/c), and
> lambda(o) = (1 - (H0*d/c) / lambda
>
> Let's notice that H0*d corresponds to the recession velocity
> v = H0*d assumed in an expanding universe.
>
> Hence,
>
> z = (lambda(o) - lambda) / lambda
> = (H0/c)d * (1+z), and
>
> d = (c/H0) * z/(1+z)
>
> Conclusively, the existence of a cosmic "deceleration" cH0
> suffices to explain the so-called tiring of light in a stable universe.
If you can explain from where you get your formula for the energy loss
above from...
>>You ignored the word "interaction" above!
>>
>
>
> Not at all,
Yes, you did.
> the energy loss of the photon should be globally recycled
> by the universe itself.
That's a totally vague statement and *still* says *nothing* about
the actual interaction.
>>>"The tired light model does not predict the observed time dilation
>>>of high redshift supernova light curves. This time dilation is
>>>a consequence of the standard interpretation of the redshift:
>>>a supernova that takes 20 days to decay will appear to take 40
>>>days to decay when observed at redshift z=1."
>>>
>>>Nobody knows what exactly happens on the SNe.
>>
>>We know enough for the measurements to be reliable.
>>
>
>
> Did you look at the error bars in
> http://www.astro.ucla.edu/~wright/tiredlit.htm ?
> The data spread is very big.
Yes. So what? The same graph shows that tired light is clearly ruled out.
If you have got another model which can produce results which agree
with the data presented in this graph, feel free to show your calculations.
>>>The apparent time dilation could be due to gravitational effects.
>>
>>Why would the observed time dilation then depend on the distance
>>to the SNs?
>>
>
>
> If there is such time dilation.
The error bars in the graph are not so large that one could reasonably
claim that there is no time dilation at all.
Also, in what you said above, you already assumed that there *is*
a time dilation, and then claimed that it could be due to
gravitational effects. So your reply here is merely an evasion. Answer
the question!
>>>"The tired light model can not produce a blackbody spectrum for
>>>the Cosmic Microwave Background without some incredible coincidences.
>>>The local Universe is transparent and has a wide range of
>>>temperatures, so it does not produce a blackbody, which requires
>>>an isothermal absorbing situation. So the CMB must have come from
>>>a far away part of the Universe, and its photons will thus lose
>>>energy by the tired light effect."
>>>
>>>>From the many discussions about tired light and the CMB, that
>>>took place on this or other NGs, one should be careful and not
>>>automatically claim that the blackbody spectrum is not compatible
>>>with a stable universe.
>>
>>I have so far seen no calculation in this newsgroup demonstrating
>>that one could have a blackbody CMBR in a stable, static universe.
>>
>>Care to present such a calculation?
>>
>
>
> Calculations have been done long ago, which then gave better results
> that those based on an expanding universe. But I didn't indeed see
> recent calculations.
References, please.
>>>"The tired light model fails the Tolman surface brightness test.
>>>This is essentially the same effect as the CMB prefactor test,
>>>but applied to the surface brightness of galaxies instead of
>>>to the emissivities of blackbodies".
>>>
>>>Same remark as just above.
>>
>>If you can explain this in a stable, static universe, feel free
>>to present your calculations.
Ignored. Big surprise.
Bye,
Bjoern
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