Redshift z

[modest]

I agree that gravitational time dilation will cause redshift, but I would have issue with calling that space 'static' in the sense that things are not drawn away from the observer. My reasons are outlined in post 537.

Are you arguing that the earth is receding from the GPS satelites that have to account for gravity time dilation to accurately work? I think everybody would call the earth static in this context.

 

Post 537 answers this.

 

GPS satellites are not static—they are in orbit. The satellites are accelerated toward earth. The reason they maintain a fixed distance is because they have a tangent velocity. In Newtonian terms: they are accelerated toward the earth by the force of gravity and are accelerated away from the earth by the centrifugal force.

 

Gravitational redshift arises from a difference in gravitational potential. A difference in potential, dU, is proportional to gravitational force (gravitational force is the derivative of potential), so there is indeed a 'force' of gravity always present when an object is gravitationally redshifted.

 

Time dilation is considered a falsification of tired-light-type causes of redshift.

That is a strawman. I explicitly left out of my reasonin tired light mechanisms.

 

Huh? :(

 

Time dilation is supposed to rule out tired light cosmology. Reading your post:

 

Reading the Corredoira paper I see mentioned the Time dilation test, wich I didn't know previously and that he seems to find to be a valid test.

 

The Time dilation test of expansion with supernovae Ia lightcurves is supposed to validate expansion (well I haven't heard it mentioned in the last few years so maybe my criticism of it has already been discerned), but I see a problem with this test in that any mechanism that produces a redshift of the spectrum is gonna cause the time dilation effect too, for example gravitational redshift wich is static in space gives you the dilation. That can be seen too in that a redshift implies also a lower frequency on the receiver side of the electromagnetic wave and therefore a higher frequency of the source and that means (as the wave itself doesn't change unless one admits energy loss of the photon and thus interaction and scattering wich is not found) there is time dilation.

So provided one found a mechanism of redshifting in a static universe(that is the tough part) one would also have time dilation in the lightcurves.

Therefore the time dilation test proves redshifting, not expansion, and redshift is what we use to say there is expansion, that should invalidate the test to prove expansion.If you find a flaw in this reasoning, by all means point me to it.

 

Regards

Qtop

 

It doesn't look like you knew that, so I am pointing it out to you.

 

All the references I read like Leibundgut et al. 1996 talk about time dilation test as a way to prove expansion, if you have some more recent reference that says the Time dilation test refers only to falsification of tired light please show it.

 

If anyone said that time dilation proves expansion then I believe that would be in error. According to the modern scientific method popularized by Karl Popper, no theory can ever be proven, it can only be falsified. A test of a theory (like time dilation) can confirm the prediction and give credibility to the theory, or it can falsify the theory. No scientific theory is ever proven.

 

Do you know of any cosmological models that call for time dilation without expansion which have not been falsified?

 

Ultimately you haven't addressed what I asked, where is the flaw in my argument?

 

What argument?

 

~modest

[quantumtopology]

Do you know of any cosmological models that call for time dilation without expansion which have not been falsified?

Yes

 

What argument?

Think about it.

[modest]

Do you know of any cosmological models that call for time dilation without expansion which have not been falsified?

Yes

 

I'm curious what model this is.

 

What argument?

Think about it.

 

"Think about it" isn't really an argument.

 

As far as I understand, you are pointing out an observation (the time dilation of supernova) which was predicted by expanding relativistic cosmology and subsequently confirmed by observation. Your point would seem to be that this in and of itself does not prove the reality of expansion. In other words, there exists an observation consistent with expansion that doesn't prove it, being that observations of time dilation are necessary for expansion, but not sufficient to prove it.

 

I essentially agree with this, but I wouldn't so much call it an argument. I think most sources that talk about time dilation as a test for expansion would be either explicitly or implicitly comparing them with tired light or similar such non-geometric effects.

 

For example:

Has the time dilation of distant source light curves predicted by the Big Bang been observed?

 

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. The time dilation has been observed, with 5 different published measurements of this effect in supernova light curves. These papers are:

• Leibundgut etal, 1996, ApJL, 466, L21-L24
  
  
• Goldhaber etal, in Thermonuclear Supernovae (NATO ASI), eds. R. Canal, P. Ruiz-LaPuente, and J. Isern.
  
  
• Riess etal, 1997, AJ, 114, 722.
  
  
• Perlmutter etal, 1998, Nature, 391, 51.
  
  
• Goldhaber etal, ApJ in press.
  
  

These observations contradict tired light models of the redshift.

Frequently Asked Questions in Cosmology -- Has the time dilation of distant source light curves predicted by the Big Bang been observed?

 

On the other hand, the wording here is a bit odd:

 

1.4. Other Recent Proofs that the Expansion is Real

 

1.4.1. The Time Dilation Test

 

The Tolman (1930) surface brightness (1+z)4 effect was the only known test for the reality of the expansion untilWilson (1939) suggested that the shape of the light curves of Type Ia supernovae provides a clock. This supposition was based on the uniform shape of the light curve discovered by Baade (1938) and recalled as history by Minkowski (1964). Wilson reasoned that such clocks at different redshifts would measure the special relativity time dilation if the light curve shapes of SNe Ia at high redshifts could be observed. The stretching of the light curves, increasing with redshift, has now been observed. The data give a spectacular confirmation of the time dilation effect (Goldhaber et al. 1997, 2001).

http://arxiv.org/PS_cache/astro-ph/pdf/0106/0106566v1.pdf

 

And for using the word "proof", I might go as far as to call it rubbish :(

 

~modest

[quantumtopology]

I'm curious what model this is.

I'm working on it :(

 

"Think about it" isn't really an argument.

But it worked

 

And for using the word "proof", I might go as far as to call it rubbish :D

 

Now you're talking :(

[modest]

I'm working on it :(

 

In that case we can say that the time dilation of supernova falsifies all known working models of redshift that are alternatives to expansion.

 

It's a fair argument.

 

~modest

[coldcreation]

In that case we can say that the time dilation of supernova falsifies all known working models of redshift that are alternatives to expansion.

 

It's a fair argument.

 

~modest

 

 

Hey boys,

 

Time dilation is consistent with both ideas set out in the OP. The difference is that time dilation according to the standard model is primarily a special relativistic effect, due to radial motion. Whereas time dilation in a globally curved spacetime (of the type that would cause cosmological redshift z without radial motion) is entirely a general relativistic effect, due to the fact that electromagnetic radiation would propagate along geodesics (rather than Euclidean straight lines).

 

 

There are a number of things I have to do before posting Explanation 2, some technical and some personal. I've gone through fairly extensively the case for positive Gaussian curvature. The remainder of the work involves redshift and stability in a universe with constant negative Gaussian curvature. So instead of posting an incomplete model early, I'll wait until it's complete.

 

Thanks in advance for you patients.

 

 

CC (writing from the land of football, tennis and bulls :()

[quantumtopology]

The difference is that time dilation according to the standard model is primarily a special relativistic effect, due to radial motion.

Hmmm, Are you sure? For the standard model is explained by expansion I'd say.

 

 

 

Whereas time dilation in a globally curved spacetime (of the type that would cause cosmological redshift z without radial motion) is entirely a general relativistic effect, due to the fact that electromagnetic radiation would propagate along geodesics (rather than Euclidean straight lines).

Precisely what you need to get a redshift is geodesics that separate more the further away from a gravitational source (in other words that converge towards the center of mass), that simple fact stretches the wavelength of the ligth travelling along those geodesics.

 

Regards

QTop

[quantumtopology]

Hmmm, Are you sure? For the standard model is explained by expansion I'd say.

 

CC, I see now what you mean, that is exactly the reason why the time dilation test for expansion is tautological, it is just showing a Special relativistic effect for every EM wave that stretches its wavelength without the photons losing energy in their own frame of reference., That is when you discard "tired light" effects.

I thought you were refering to the official explanation.

 

Regards

QTop

[modest]

CC, I see now what you mean, that is exactly the reason why the time dilation test for expansion is tautological, it is just showing a Special relativistic effect for every EM wave that stretches its wavelength without the photons losing energy in their own frame of reference.

 

Stretched wavelengths are *not* an SR interpretation. SR redshift is completely derived and explained with aberration and time dilation.

 

The difference is that time dilation according to the standard model is primarily a special relativistic effect, due to radial motion. Whereas time dilation in a globally curved spacetime (of the type that would cause cosmological redshift z without radial motion) is entirely a general relativistic effect, due to the fact that electromagnetic radiation would propagate along geodesics (rather than Euclidean straight lines).

 

If you solve a null geodesic in FLRW then you get 1+z = a(now)/a(then) which can't be considered a "special relativistic effect". It is just what the physics is telling you happens to null geodesics in a homogeneous and isotropic spacetime. It is, in that sense, a general relativistic effect (as FLRW is a solution of GR).

 

In SR-coordinates redshift is 1+z = [(1+v/c)/(1-v/c)]^(1/2) which is the relativistic doppler effect for radial motion. You could consider that an approximation to the solution above and a valid interpretation of redshift, but it would be false to say redshift in standard cosmology is caused by such an effect to the exclusion of curved spacetime (it is, at most, an approximation and a valid interpretation).

 

~modest

[quantumtopology]

Stretched wavelengths are *not* an SR interpretation. SR redshift is completely derived and explained with aberration and time dilation.

The bold phrase might be close to what I'm sayng, but you have named a new redshift:SR redshift.I have the feeling I'm gonna use that new type often. I don't understand your first phrase, stretched wavelengths or what is the same slowed frequency waves are observations, not interpretations.

 

Perhaps going back to basics we can reach some agreement, I just ask you the effort to think for yourself.

 

Imagine an EM wave emitted from a distant source that is detected here on earth with a certain redshift, the photons travelling at c, in their proper time have not lost energy in their travel, and yet we observe them with a lower frequency at the detection point than the calculated frequency at the source. That is what redshifted means. Right so far?

 

Now if we apply what we know from SR in order to account for the change in frequency for this different frames we talk about time dilation (if we apply it to the spatial part, the stretching of the wave length we'd say length contraction). All this so far independently of whether or not the source is receding or not from us.

 

Do you agree up to this point?

[modest]

Imagine an EM wave emitted from a distant source that is detected here on earth with a certain redshift, the photons travelling at c, in their proper time have not lost energy in their travel, and yet we observe them with a lower frequency at the detection point than the calculated frequency at the source. That is what redshifted means. Right so far?

 

Now if we apply what we know from SR in order to account for the change in frequency for this different frames we talk about time dilation (if we apply it to the spatial part, the stretching of the wave length we'd say length contraction). All this so far independently of whether or not the source is receding or not from us.

 

Do you agree up to this point?

 

I don't follow what you're saying.

 

If someone is receding from you then according to SR you will observe the frequency of their light slower than they themselves emit it for two reasons (or, because of two factors). 1) Aberration—you can think of in terms of normal Newtonian doppler shift. and 2) time dilation. Their clocks run slow relative to yours.

 

When you combine these two effects you get the relativistic doppler effect formula.

 

Now if we apply what we know from SR in order to account for the change in frequency for this different frames we talk about time dilation (if we apply it to the spatial part, the stretching of the wave length we'd say length contraction).

 

Length contraction happens in a tangent direction. Something moving away from you is not length contracted. They are time dilated.

 

~modest

[modest]

Here's a good link:

What Causes the Hubble Redshift? Are the light waves "stretched" as the universe expands, or is the light doppler-shifted because distant galaxies are moving away from us?

 

And a good explanation of relativistic doppler effect with radial motion:

 

Twin paradox -- What it looks like: the relativistic Doppler shift

 

~modest

[quantumtopology]

I don't follow what you're saying.

Ok, I see why, you are assuming in advance that the source is moving away from us in my thought experiment. But it would work in this case too.

If someone is receding from you then according to SR you will observe the frequency of their light slower than they themselves emit it for two reasons (or, because of two factors). 1) Aberration—you can think of in terms of normal Newtonian doppler shift. and 2) time dilation. Their clocks run slow relative to yours.

 

When you combine these two effects you get the relativistic doppler effect formula.

 

Exactly, you have very cleverly separated the two factors, the component that you call aberration is the regular Doppler effect for sources of waves at non-relativistic speeds, is the one used in medicine for instance in echo-doppler ultrasonography. In an astronomical setting is what produces the blueshifting of Andromeda as it approaches us.

The second component you mention is the correction for time dilation as velocity between source and observer increases and approaches significantly big speeds in relation with lightspeed.

From the wikipedia:

"The relativistic Doppler effect is different from the non-relativistic Doppler effect as the equations include the time dilation effect of special relativity and do not involve the medium of propagation as a reference point. They describe the total difference in observed frequencies and possess the required Lorentz symmetry."

So far we perfectly agree, right?

Now I ask you to bear with me a little further in the thought experiment, if our source is set at fixed radial distance from us, if you think expansion would be acting then imagine the object has a powerful motor that propels it in our direction and cancels out the radial expansion, it would still show the second factor, the time dilation component, since the photons are traveling at c the frequency at the source is different from the frequency at the observer.

If source and observer were not receding from each other we would not have the first component, but we would still have time dilation component in Special Relativity,

that is derived from the hyperbolic structure of velocity space in Minkowski spacetime

 

Length contraction happens in a tangent direction. Something moving away from you is not length contracted. They are time dilated.

From the wikipedia:

"Length contraction is only in the direction parallel to the direction in which the observed body is travelling."

But let's leave aside for a moment length contraction.

[modest]

Ok, I see why, you are assuming in advance that the source is moving away from us in my thought experiment. But it would work in this case too.

 

 

Exactly, you have very cleverly separated the two factors, the component that you call aberration is the regular Doppler effect for sources of waves at non-relativistic speeds, is the one used in medicine for instance in echo-doppler ultrasonography. In an astronomical setting is what produces the blueshifting of Andromeda as it approaches us.

The second component you mention is the correction for time dilation as velocity between source and observer increases and approaches significantly big speeds in relation with lightspeed.

From the wikipedia:

"The relativistic Doppler effect is different from the non-relativistic Doppler effect as the equations include the time dilation effect of special relativity and do not involve the medium of propagation as a reference point. They describe the total difference in observed frequencies and possess the required Lorentz symmetry."

So far we perfectly agree, right?

 

Yup.

 

Now I ask you to bear with me a little further in the thought experiment, if our source is set at fixed radial distance from us, if you think expansion would be acting then imagine the object has a powerful motor that propels it in our direction and cancels out the radial expansion, it would still show the second factor, the time dilation component, since the photons are traveling at c the frequency at the source is different from the frequency at the observer.

If source and observer were not receding from each other we would not have the first component, but we would still have time dilation component in Special Relativity,

that is derived from the hyperbolic structure of velocity space in Minkowski spacetime

 

There are subtle caviates that have to do with coordinate choice, but the direct answer is no. There would be no time dilation. Something is time dilated in SR-coordinates (or in Minkowski spacetime if you like) if it is moving relative to you. If it is not moving then there is no time dilation. To prove this to yourself put v = 0 for time dilation:

[math]\Delta t' = \frac{\Delta t}{\sqrt{1-v^2/c^2}}[/math]

You'll get [math]\Delta t' = \Delta t[/math], no time dilation.

 

From the wikipedia:

"Length contraction is only in the direction parallel to the direction in which the observed body is travelling."

But let's leave aside for a moment length contraction.

 

Right, I meant tangent to the plane of observation. It appears we were talking past each other a bit there.

 

~modest

[quantumtopology]

Something is time dilated in SR-coordinates (or in Minkowski spacetime if you like) if it is moving relative to you. If it is not moving then there is no time dilation. To prove this to yourself put v = 0 for time dilation:

[math]\Delta t' = \frac{\Delta t}{\sqrt{1-v^2/c^2}}[/math]

You'll get [math]\Delta t' = \Delta t[/math], no time dilation.

 

You are right in that time dilation from not receding objects can not be explained with SR alone and therefore that equation is not the one that would apply,( although obviously is not the only equation to get time dilation,you have at least one more, the gravity time dilation ). So this short cut I tried is not viable, in anycase it is not why I proposed that the Time dilation test is tautological, what I meant is that if you have a redshift, whatever the mechanism you have time dilation.

To carry on with my thought experiment I have to introduce spacetime curvature ,wich is a different way of changing of inertial frames without the need of a relative motion.

 

 

Regards

Qtop

[modest]

You are right in that time dilation from not receding objects can not be explained with SR alone and therefore that equation is not the one that would apply,( although obviously is not the only equation to get time dilation,you have at least one more, the gravity time dilation ).

 

Yes, I agree.

 

That's why SR is only an approximation in any universe with mass or Lambda. GR is needed to solve exactly.

 

what I meant is that if you have a redshift, whatever the mechanism you have time dilation.

 

Yes. I agree.

 

~modest

[quantumtopology]

Hi, guys

 

Is this a real paradox or only apparent:

If one believes in a expanding universe that is also isotropic, one is forced to think that the universe provides us with a preferred velocity at our particular location. Why is this? If we were moving at a sufficiently higher velocity than the current one from this position, we should not get such isotropy because in front we would see less redshift for a given brightness and behind us much more. So here we have what seems a conflict between cosmology and the Principle of relativity from which so many things are deduced in modern physics, that tells us that there is not preferred velocity as far as laboratory physics goes, but if expansion really exists, the universe is giving us a preferred velocity, a kind of absolute velocity.

 

What do you think?

This paradox was formulated many years ago, now we have an added factor (the apparently accelerated expansion) but I don't think it changes the reasoning.

 

Regards

Happy 4th of july

 

QTop

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