[Galileo1564]

The twins paradox does not require acceleration. That is a fallacy.

Wrong. The twin paradox arises due to differing inertial frames. The turnaround twin changes frames which allows him to age less than the stay at home twin, and the turnaround twin can not change inertial frames without accelerating.

[yor_on]

And that is wrong Galileo :)

It's a old subject, if you could prove it to be correct you would prove SR wrong

http://alternativephysics.org/book/TimeDilationExperiments.htm
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Hmm, that one actually question it, doesn't it?'
Ah well, it states most of the experiments done, and then you have the ones done in the LHC.

If you define it from being unmoving at some common origin then there will need to be a acceleration differing between them to get to different speeds versus each other. If you define it from objects in relative motion without a common origin there will still be a time dilation as far as I know.

https://en.wikipedia.org/wiki/Relativistic_Doppler_effect

[Galileo1564]

The twin paradox arises due to differing inertial frames. The turnaround twin changes frames which allows him to age less than the stay at home twin, and the turnaround twin can not change inertial frames without accelerating

And that is wrong Galileo

Which part is wrong, that the twin paradox arises due to differing inertial frames, or that you can not change inertial frames without accelerating?

[yor_on]

Galileo, you're suggesting that a time dilation only belonging to GR, if I read you correct? Would that be true then relativistic Doppler effects shouldn't exist. There is no 'acceleration' to light, only a propagation at a set speed. You have emission and absorption, red and blueshifts, but no acceleration.There are other arguments and examples but that one should be sufficient.

" The relativistic Doppler effect is the change in frequency (and wavelength) of light, caused by the relative motion of the source and the observer (as in the classical Doppler effect), when taking into account effects described by the special theory of relativity. 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.

Astronomers know of three sources of redshift/blueshift: Doppler shifts; gravitational redshifts (due to light exiting a gravitational field); and cosmological expansion (where space itself stretches). "

[Janus]

Galileo, you're suggesting that a time dilation only belonging to GR, if I read you correct?

No, he isn't. It is a misconception that SR cannot deal with acceleration and you need to invoke GR to deal with it.  GR is only needed if you introduce gravitational effects

Would that be true then relativistic Doppler effects shouldn't exist. There is no 'acceleration' to light, only a propagation at a set speed. You have emission and absorption, red and blueshifts, but no acceleration.There are other arguments and examples but that one should be sufficient.

" The relativistic Doppler effect is the change in frequency (and wavelength) of light, caused by the relative motion of the source and the observer (as in the classical Doppler effect), when taking into account effects described by the special theory of relativity. 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.

Astronomers know of three sources of redshift/blueshift: Doppler shifts; gravitational redshifts (due to light exiting a gravitational field); and cosmological expansion (where space itself stretches). "

It is really important here to distinguish between "time dilation" which is the difference in clock rates measured between relatively moving frames of reference, and the "total difference in time accumulation" demonstrated at the end of the Twin Paradox scenario.
During the outbound and Inbound legs of the Trip, both observers measure the other observer as being time dilated. However, they both agree which one of them aged less during the period when they were separated then reunited.

And, as far as acceleration is concerned, it is required for the Twin paradox, as it is the only way under SR that the two twins can separate and then reunite* And which twin accelerates in order for them to reunite determines which twin will have accumulated less time upon their reuniting.

As far as acceleration and Doppler shift goes:   Like time dilation, Relativistic Doppler shift is a measurement made between an observer and a relatively moving source.  If we are moving apart, you see my light as being red-shifted and I see your light Red-shifted.  If we are moving together we see each other as blue-shifted.

But even here acceleration does matter with the Twin Paradox.
So for example: Twin A and Twin B separate at 0.6 c to a planet 6 light years away ( as measured by A), B then accelerates to return to A.
A starts off measuring a red-shift from B with a factor of 0.5  Now while it takes 10 years for B to get to the turn around point, A doesn't See this until  6 yr later.  In other words A sees that red-shift from B for 16 years, seeing B age 0.5x16 = 8 yrs
Then A sees B become blueshifted at a factor of 2.  Since B takes twenty years to make the round trip, this leaves just 4 years for A to see B blue-shifted, and see him age another 2*4 = 8 yrs for a total of 16 years during the 20 yrs he was gone.
B on the other hand see A red-shifted as they separate ( also at a factor of 0.5). It takes 8 yrs by his clock to get to the planet which is 4.8 light yrs from A ( length contraction) by his measure. During this time hes sees A age 0.5 x 8 = 4 yrs. 
He then accelerates to start the trip back ( assume negligible time spent accelerating).  He immediately sees the light from A go to blue-shift**  to a factor of 2.   It takes 8 yrs to meet up with A again, during which time he sees him age 2 x 8 = 16 years for a total of 20 years for his 16.

There is nothing contradictory between acceleration being required for the Twin paradox scenario and the observation of Doppler shift, and your criticisms of Galileo's statements are unfounded.   

* And they do have to reunite, as this is the only way that you can objectively say that one twin accumulated less total time.

** while A had to wait 6 years to  see the Doppler shift change due to B accelerating, this is because the change was the result of something happening 6 light years away.
B sees the change instantly because it is the result of what he himself is doing.

[yor_on]

Well, yes Janus. You have a point there but I still think Galileo wanted to relate a time dilation to the initial acceleration and turnaround. And I don't agree to that.
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actually I get a impression you do though?
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Or maybe you were thinking in terms of the twin paradox answering it, while I was thinking in general terms as a time dilation existing in both SR and GR, as exemplified by the muon thought experiment. You could argue that this too should have meant a acceleration somewhere along the line but I still don't think it matters for a time dilation existing?

That was the way I interpreted Jeffrey too btw, saying that time dilation's didn't needed to be locked down to just accelerations. Otherwise I don't find Galileo wrong. I totally agree on acceleration being necessary for the twin experiment to prove its point. That 'time dilation's' really exist.

[Halc]

Well, yes Janus. You have a point there but I still think Galileo wanted to relate a time dilation to the initial acceleration and turnaround. And I don't agree to that.
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actually I get a impression you do though?

Janus is correct. A pair of twins in a scenario that does not involve gravity cannot be separated and reunited without at least one of them undergoing proper acceleration at some point.  Acceleration is necessary for that particular scenario.

This does not imply that acceleration causes time dilation since I can have two clocks that stay in sync despite continuous acceleration of one that is a thousand times that of the other.

Or maybe you were thinking in terms of the twin paradox answering it, while I was thinking in general terms as a time dilation existing in both SR and GR, as exemplified by the muon thought experiment.

The muon experiment is not a thought experiment. It is real empirical evidence supporting SR. Gravity plays no significant role in it.  Acceleration plays no meaningful role in the scenario, so there's an example of dilation without the necessity of acceleration.

[yor_on]

With all respect, I'll wait for his answer. And I know about the twin experiment, and the muon experiment. even about NIST Halc, imagine.

[yor_on]

Sorry, those posts by me that got deleted doesn't belong here.

[Galileo1564]

Galileo, you're suggesting that a time dilation only belonging to GR, if I read you correct? Would that be true then relativistic Doppler effects shouldn't exist. There is no 'acceleration' to light, only a propagation at a set speed. You have emission and absorption, red and blueshifts, but no acceleration.There are other arguments and examples but that one should be sufficient.

" The relativistic Doppler effect is the change in frequency (and wavelength) of light, caused by the relative motion of the source and the observer (as in the classical Doppler effect), when taking into account effects described by the special theory of relativity. 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.

Astronomers know of three sources of redshift/blueshift: Doppler shifts; gravitational redshifts (due to light exiting a gravitational field); and cosmological expansion (where space itself stretches). "

No, I never suggested that time dilation only belongs to GR. I only suggested that to have the so called "twin paradox" where one twin ages differently than another, there has to be a change of reference frame, and there is no way to change reference frames other than by acceleration.

I think what you say about the doppler shift is correct. Personally I like Bondi's K calculus as the best way to understand it. Objects approaching each other read each other's clocks as fast, and receding observers read each other's clocks as slow.  In the twin paradox the traveling twin changes from a receding to an approaching frame of reference while the stay at home remains in the same frame and that is where the non-symmetry of time comes from. He must change reference frames, and there is no way to do that without accelerating. Tricks such as handing the clock to another approaching observer avoid this, but that changes the situation as the new traveler with the clock is in an approaching frame of reference, and that second (approaching) frame of reference must be taken into account from the start of the thought experiment when the first traveling twin started.

[Halc]

David Cooper's discussion is not accepted physics and was split into new-theories topic here:
https://www.thenakedscientists.com/forum/index.php?topic=81938.0

[David Cooper]

David Cooper's discussion is not accepted physics and was split into new-theories topic here:
https://www.thenakedscientists.com/forum/index.php?topic=81938.0

The "accepted physics" you talk of is not science. No science forum should be pandering to it.