Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: jeffreyH on 20/01/2018 11:33:15
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Consider three frames labeled A, B and C containing objects a, b and c respectively. If we set our frame of observation to be A we can then define the motions of B and C. observations from A show that C is moving away with a constant velocity and B is maintaining an equal distance between both in straight line. Now we can determine that time dilation must be greater than that in A for both B and C. However, the inverse must also be considered possible if we take our observation point to be frame C. In both these situations the value of time dilation in A and B cannot be equal. If we now consider B to be our observation frame then the values in A and C MUST be equal. To state that this is because all things are relative misses the point. The absolute values of time dilation may be impossible for us to determine but that doesn't mean they do not exist. Opinions?
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There is no time dilation within a frame moving at constant velocity.
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You are talking about proper time so of course not. Proper time has a Lorentz factor of 1. That is no time dilation so that every measurement is taken with respect to the proper time in the observer's frame. Yes my language was poor. Can we discuss the topic now?
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I don't see what your point or problem is. There's nothing at all controversial about two or more inertial observers moving with respect to each other, at least once you understand the relativity of simultaneity.
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Well then you are missing the point entirely. The observations of A are different from B which are different again from C. They cannot all be right. The observations of A and C are inverses of each other. B sees no difference between A and C. So you are saying we can ignore this because of the relativity of simultaneity. Someone's clock must be the slowest. They have relative velocity differences.
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BTW This relates to the expansion of the universe.
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If we now consider B to be our observation frame then the values in A and C MUST be equal
VA(C) = v and VC(A) = -v. If only A and C are involved, each one measures the time passing slowly on the other.
If the distance A-B and B-C is kept constant, B has half of C velocity, as measured by A. VA(B) = v/2
But for C, the velocity of B has to be calculated: VC(B) = (-v +v/2))/(1+v.v/2) = (v/2) / (1+v2/2) (I take c=1).
And velocity of C measured by B is of course (-v/2) / (1+v2/2), and velocity of A measured by B is -v/2.
So B measures different velocities for A and C, and its calculations for time dilation are not the same.
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They cannot all be right
The shocking thing about Special Relativity (and it's expanded set of examples in General Relativity) is that they are all right/correct.
This is the point of the twin paradox (or at least the non-accelerated variants of it) - different observers don't agree.
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The twins paradox does not require acceleration. That is a fallacy.
Let's take this a step further. Let's have an infinite lattice of frames where the distance between any two of them is constant at any one time. So that they are all expanding away from each other at a constant rate. Which one has the slowest clock now?
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The situation described above is homogeneous and isotropic.
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Well then you are missing the point entirely. The observations of A are different from B which are different again from C. They cannot all be right. The observations of A and C are inverses of each other. B sees no difference between A and C. So you are saying we can ignore this because of the relativity of simultaneity. Someone's clock must be the slowest. They have relative velocity differences.
Your belief that one clock must be the slowest in an absolute manner comes from trying to apply a Newtonian notion of time to Relativity. In Relativity time is an aspect of of 4 dimensional space-time. The difference between this and the Newtonain notion of time is the in Relativity, the "direction" of time is not fixed, but is frame dependent.
An analogy would be that in Newtonian physics, you could treat time and space like the North-South and East-West directions, in that no matter what direction someone is facing, they would all agree on these directions. In Relativity, they behave more like the Left-Right and forward-backward directions which are entirely dependent on the direction you are facing.
Time dilation between relatively moving frames of references in this analogy would be like two people starting at a same point and walking in different directions at an equal pace. Each person measures forward progress as being in the direction that he is walking, and by this basis, the other person is always falling behind. There is no absolute meaning as to who is ahead of who, as the answer to this question depends on which way you are facing.
Relativity involves a whole new way of looking at the very nature of time and space.
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The directionality is important. Why does no one else mention it?
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The nub of the issue is exactly the absolute. In the infinite lattice none of the clocks can be the slowest. Otherwise the system cannot be isotropic. Any one position is indistinguishable from any other. That sounds a lot like our universe. Except that the universe does not have a uniform mass distribution. This has to have a bearing on our view of time dilation. If it is simply discarded then you are not missing but ignoring the point.
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The directionality is important. Why does no one else mention it?
The "directionality" that I was talking about was in reference to the Space and Time axes in Space-time, and not the relative motion as measured from any given frame.
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Motion perpendicular to the direction of travel is no longer a straight line but must become a diagonal. That is directional bias and preserves time dilation in all three spatial dimensions. In the direction of travel we have blue shift and against it red shift. If this is not directional then what is? To assume that this is limited to the spacetime diagram is again, missing the point. The spacetime diagram simply highlights the effect with non orthogonal axes.
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How would the situation on the following page change within the infinite expanding lattice?
http://galileo.phys.virginia.edu/classes/252/time_dil.html
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For information on the infinite lattice please see:
http://www.scholarpedia.org/article/Special_relativity:_kinematics
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Don't agree with B-C velocity
relative velocities:
A=0, B=v, c=2v, per A
ref A B C
A 0 v 2v
B -v 0 v/(1-2v2)
C -2v -v/(1-2v2) 0
Each pair should experience reciprocity.
Let's take this a step further. Let's have an infinite lattice of frames where the distance between any two of them is constant at any one time. So that they are all expanding away from each other at a constant rate. Which one has the slowest clock now?
If each is separating at a constant speed, the separation will not remain constant!
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I said nothing about speed. Just as you cannot assign a speed to receding galaxies. Since, eventually, you would have to assign a superluminal speed.
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If you take the absolute magnitude of the velocity you can get rid of the opposing signs altogether. Why confuse the issue?
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(https://upload.wikimedia.org/wikipedia/commons/thumb/8/8e/Time-dilation-002-mod.svg/660px-Time-dilation-002-mod.svg.png)
Consider this scenario:
The left picture is a light clock inside a space lab which we consider stationary. The right picture shows the same clock when observed by a space ship moving to the left at velocity v.
https://en.wikipedia.org/wiki/Time_dilation#Simple_inference
If another space ship is also observing the light clock at the same speed, but the direction is up, will they agree on the amount of time dilation?
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If another space ship is also observing the light clock at the same speed, but the direction is up, will they agree on the amount of time dilation?
Under SR conditions, dilation is a function of speed, so the direction makes no difference. It also makes no difference if it is a light clock, any other clock, or the rate of the paint peeling.
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let's say that the stationary observer measures that light takes 1 microsecond to travel from bottom mirror to top mirror. It also takes 1 microsecond to travel from top to bottom mirror. So the clock has 2 microseconds period.
How will the events appear to the observer moving horizontally to the light clock? Is it the same for the observer moving vertically?
If the space between the mirrors is filled with transparent medium which makes light travel at half of its speed in vacuum, what would be the difference?
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Re-read my prior reply, which applies to all these questions.
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Re-read my prior reply, which applies to all these questions.
That's an assumption. Can you prove it using equations? Is it compatible with Galilean, Lorentzian, or Einsteinean relativity?
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Re-read my prior reply, which applies to all these questions.
That's an assumption.
It's not an assumption, but rather something that follows directly from the two premises of SR (one of which is Galilean relativity). If you want to call something that has been repeatedly demonstrated 'assumptions', you can choose to do so.
Can you prove it using equations?
λ = 1/√(1-v²/c²)
There's nothing in that equation that changes with choice of direction of motion (λ is a scalar, not a vector, and v is a speed, not a velocity in any equation that squares it) or choice of process (paint peeling, light clock through material with high refractive index) to be dilated. Hence none of those factors effect the dilation due to motion of the process.
Is it compatible with Galilean, Lorentzian, or Einsteinean relativity?
Yes. Galileo never had reason to assume Einstein's second postulate. It didn't work with sound so he had no reason to suspect there was no speed-of-medium involved with light. Lorentz's and Einstein's relativity make the exact same empirical predictions, so yes to that part.
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λ = 1/√(1-v²/c²)
There's nothing in that equation that changes with choice of direction of motion
The commonly used symbol is gamma. One method to derive its value is using a light clock moving perpendicular to the light trajectory. The constraint to keep the light speed c leads to the conclusion that time has dilated by gamma factor.
The question is, do we get the same result if the clock is moving in the same direction as the light trajectory, while keeping the light speed at constant value c?
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λ = 1/√(1-v²/c²)
There's nothing in that equation that changes with choice of direction of motion
The commonly used symbol is gamma. One method to derive its value is using a light clock moving perpendicular to the light trajectory. The constraint to keep the light speed c leads to the conclusion that time has dilated by gamma factor.
The question is, do we get the same result if the clock is moving in the same direction as the light trajectory, while keeping the light speed at constant value c?
For the round trip, yes. The individual legs of the light trajectory will take different different amounts of time however. Going in one direction the light has to chase after a mirror going in the same direction, and going in the other direction the mirror is traveling in the opposite direction of the the light and they close in on each other. ( the total summed time of the two legs will be the same as in the typical light clock setup.
Basically: If you set up a spherical light clock (one where the light bounces back and forth between the center and inner wall of a sphere), all light paths, no matter what direction they are emitted, return to the center at the same time as long as they were emitted from the center at the same time.
This means that if you are only interested in time dilation, you have to deal with round trip time, as when you deal with just one leg, you also need to take Relativity of Simultaneity into account.
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(https://wikimedia.org/api/rest_v1/media/math/render/svg/7822076343669503d7c1d18a7943b8e861d32110)
https://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment#Light_path_analysis_and_consequences
(https://wikimedia.org/api/rest_v1/media/math/render/svg/706b597df878efffcb2eacd8c6c920b57ccd0626)
In the equations above, transversal time is dilated by gamma, while longitudinal time is dilated by gamma squared.
To make transversal time equals longitudinal time, the longitudinal path length must be contracted by gamma.
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(https://wikimedia.org/api/rest_v1/media/math/render/svg/7822076343669503d7c1d18a7943b8e861d32110)
https://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment#Light_path_analysis_and_consequences
(https://wikimedia.org/api/rest_v1/media/math/render/svg/706b597df878efffcb2eacd8c6c920b57ccd0626)
In the equations above, transversal time is dilated by gamma, while longitudinal time is dilated by gamma squared.
To make transversal time equals longitudinal time, the longitudinal path length must be contracted by gamma.
Which is is what Relativity predicts will happen.
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Which is is what Relativity predicts will happen.
Yes. So far looks good.
Let's take further test. There are two light clocks with exactly same length put side to side. In the first clock, the space between mirrors is kept at vacuum, while the second clock is filled with transparent medium which makes light travel at half of c.
The stationary observer sees that every 4 microseconds both clocks tick simultaneously by photons hitting their bottom mirrors. Does vertically moving observer sees the same phenomenon? What about the horizontally moving observer?
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Let's take further test. There are two light clocks with exactly same length put side to side. In the first clock, the space between mirrors is kept at vacuum, while the second clock is filled with transparent medium which makes light travel at half of c.
The stationary observer sees that every 4 microseconds both clocks tick simultaneously by photons hitting their bottom mirrors.
If one two otherwise identical light clocks has a high refractive index medium, then they're not both going to tick every 4 usec. The one is going to tick at half the rate of the other. Maybe the mirrors are closer if you want that?
If you're going to actually do the calculation of the time in each direction, you'll have to remember that the medium with the refractive index is moving in the alternate frames. That means that if the medium is moving fast enough, the light can actually make negative progress.
Does vertically moving observer sees the same phenomenon? What about the horizontally moving observer?
See reply 21, which says I don't need to compute the details to answer this question.
If the comoving clocks tick at the same rate for one observer, then they will for any observer. They may not tick simultaneously in most frames since they're not in the same location and thus relativity of simultaneity may have the tick events simultaneous in some frames and not in others.
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Which is is what Relativity predicts will happen.
Yes. So far looks good.
Let's take further test. There are two light clocks with exactly same length put side to side. In the first clock, the space between mirrors is kept at vacuum, while the second clock is filled with transparent medium which makes light travel at half of c.
The stationary observer sees that every 4 microseconds both clocks tick simultaneously by photons hitting their bottom mirrors. Does vertically moving observer sees the same phenomenon? What about the horizontally moving observer?
Like Halc said, you'd have to make the one set of mirrors closer to each other if you want the stationary observer to see the clocks tick in sync.
The fact that the light traveling through the medium doesn't travel at c relative to the stationary observer ( as measured by said observer will not alter the fact that our moving observer will measure the "slower" clock as having the same time dilation as the vacuum clock, no matter which direction he is moving relative to it. You need to apply relativistic velocity addition to the light passing through the medium. So, for example in the case where the light path is parallel to the relative motion of v, then: Our observer will measure the light traveling at (0.5c+v)/(1+0.5c(v)/c^2) relative to himself in one direction, and (0.5c-v)/(1-0.5c(v)/c^2). For an observer traveling perpendicular to this, you have to use the orthographic version of this equation.
While the math is a bit more involved, If the "stationary" observer measures the clocks as ticking at the same rate, so will the moving observer, just time dilated.
Do not get sidetracked by the fact that c = the speed of light ( in a vacuum). Is the value c that is important and what determines the value of time dilation etc, not whether or not light itself in actually traveling at c. In those scenarios where the light doesn't travel at c, you still need to use c in the equations.
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If one two otherwise identical light clocks has a high refractive index medium, then they're not both going to tick every 4 usec. The one is going to tick at half the rate of the other. Maybe the mirrors are closer if you want that?
No. Every 4 microsecond, vacuum clock ticks twice, while filled clock only ticks once
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If one two otherwise identical light clocks has a high refractive index medium, then they're not both going to tick every 4 usec. The one is going to tick at half the rate of the other. Maybe the mirrors are closer if you want that?
No. Every 4 microsecond, vacuum clock ticks twice, while filled clock only ticks once
This is a minor detail that has no significance tin terms of the larger picture of whether or not an observer with relative motion with respect to the clocks measure them as undergoing the same time dilation.
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We have seen that constant c implies that transversal clock experiences time dilation. Since longitudinal clock must have equal time dilation, it must also experience length contraction.
For speed less than c, vectorial addition formula can be derived by above constraints, which says that if the transversal clocks tick simultaneously at certain interval, the longitudinal clocks must also tick simultaneously at the same interval.
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Clock A is considered stationary. clock B moves to the right at speed half c. According to A, clock B ticks slower. But according to B, clock A ticks slower.
Add clock C, which moves to the right at a quarter of c relative to A. According to C, clock A and B tick equally slower than clock C.
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Nice question Jeffrey. You're getting good at them.
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philosophically I don't have one answer. It depends on your frame of reference.
But logically, you have to expect the universe to have a mean of joining them. The reason why that is is that without a logic our whole idea of how it works falls apart.
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Btw: Questions are so much better than answers :)
I'll tell you one thing. Had this dream, was on a shore at twilight, getting dark. It's was mysterious, and I heard and saw people acting out of their own necessities and needs. I stopped looking at them, instead looking up, because it was all unknown to me. And I saw the constellations, didn't recognize them but they were so beautiful. I lost myself in them.
Don't read this as something questioning any answer made here. I don't really know, I wish I did. It would make my life worthwhile.
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There is one other thing to define it from. What we call proper time, your wrist watch. It doesn't lie to you. If we accept that and then define the universe from it it becomes splintered. It's dependent on your frame of reference. so that is one definition, but then we have the one in where you talk to your friend over your smartphone, asking him if he sees the same as you. That's the universe, and you will agree assuming you're in a 'similar' frame of reference. Without it you will have to look for something more and that is where Lorentz transformations come in. Those are are more or less metaphysical, based on equation. Never the less they give you a logic.
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The end result is a logic very close to magic. Isn't it?
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But not really, it will give you a origin of a event. Then you will need to translate it into your own, or more correctly others. frame of reference. Don't remember the name we use for that but it works. Been a long time since I looked at this, and its all your fault Jeffrey :). It doesn't tell you what 'time' is globally, everything included, so you can't use it to define one frame of reference as being 'before' or 'after', at least I don't think you can do it that way, because the only definition I know of is 'proper time' and the Lorenz transformations of the same.
thinking some more of it. you will be able to define a logic and a origin, but that's all. and that is your question if I got it right?
Damn, there is something called the Andromeda paradox if I remember right.
https://medium.com/mathadam/the-andromeda-paradox-b4bb30a0e372
It doesn't state that the logic is wrong, that's what you need to see, but it does question what time is. Globally.
The point there is that you won't back up time, from any of those frames of reference. Assuming you and your friend meets up, 'Bob and Alice' you will be in a same frame of reference, with the 'invasion' or whatever event you looked at being in both of your past. Another name for time is 'entropy' and what may differ that from time is that it is specific to any frame of reference. Everything has a entropy. As far as I get it.
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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.
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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
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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?
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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). "
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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 effectsWould 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.
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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.
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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.
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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.
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Sorry, those posts by me that got deleted doesn't belong here.
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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.
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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
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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.