vuquta Posted January 17, 2010 Posted January 17, 2010 The success of modern physics seems to me to be quite a lot of indirect evidence supporting special and general relativity. For instance 1) Particle colliders and the discovery of the Z and W bosons. The framework of the standard model is a relativistic quantum field theory. 2) The GPS system requires that effects due to general relativity be taken into account. 3) Observations of muons in cosmic rays shows that time-dilations effects are real. 4) The perihelion of Mercury is very well explained in general relativity as is gravitational lensing. 5) The success of Maxwell's equations to explain classical electrodynamics. and I am sure people can add lots to this list. All support the view that relativity is quite well observed in nature. I am confused. Where in th above have you shown light has been measured at c in all directions and in different frames. In order to claim light is measured at c, you must actually be able to produce one way light transfer timing experiments. Do you have any?
Klaynos Posted January 17, 2010 Posted January 17, 2010 Does the Michelson–Morley experiment not fit for measuring the speed of light in different directions?
vuquta Posted January 17, 2010 Author Posted January 17, 2010 Does the Michelson–Morley experiment not fit for measuring the speed of light in different directions? No, common error. Modern Physics/Michelson-Morley Experiment Walter Ritz's emitter theory (or ballistic theory), was also consistent with the results of the experiment http://en.wikibooks.org/wiki/Modern_Physics:Michelson-Morley_Experiment Ironically, the original Michelson-Morley experiment was consistent with the ballistic theory http://www.mathpages.com/rr/s2-07/2-07.htm One such attempt is known as the Emission Hypothesis (or the ballistic theory of light), and was developed partly by Walther Ritz (C&N p.353). According to this theory, light behaves like bullets shot from a gun, its speed with respect to the source being a universal constant and independent of any ether. This idea is consistent with the null results of the Michelson-Morley experiment and many others. http://laser.phys.ualberta.ca/~egerton/specrel3.htm
swansont Posted January 17, 2010 Posted January 17, 2010 But Ritz's theory is falsified by other experiments, like the Sagnac effect.
vuquta Posted January 17, 2010 Author Posted January 17, 2010 But Ritz's theory is falsified by other experiments, like the Sagnac effect. correct. but the poster I responded to suggsted MMX as the standard for proving a measured c. I fixed that. Now, while you are on Sagnac, it does not prove the measured speed of light is always c in all directions. Though it does prove light travels at one speed regardless of source speed. So, where is your measured at c experiments with clocks? I want to see them.
swansont Posted January 17, 2010 Posted January 17, 2010 You mean like GPS, which doesn't work if relativity is wrong, already mentioned by ajb?
ajb Posted January 17, 2010 Posted January 17, 2010 I am confused. Where in th above have you shown light has been measured at c in all directions and in different frames. In order to claim light is measured at c, you must actually be able to produce one way light transfer timing experiments. Do you have any? All the examples I have given require that the speed of light be constant (with our already stated conditions) in their mathematical formulations. Thus, as they agree with experiments very well, I conclude that in nature the speed of light is (almost certainly very nearly) constant. It is possible that we have small distance (large energy) violations of Lorentz invariance. I don't know much about these. Search the literature and I am sure we could find experimental bounds on this. What one must note is that in the standard formulations of quantum field theory (on Minkowski space-time) global Lorentz invariants means we have a well defined inertial observer independent vacuum state. This is lost on curved space-times (though global hyperbolicity means not all is lost). I have no idea what violations of global (or local) Lorentz invariants would do to quantum field theory. I expect "serious violations" would be very problematic. Anyway, something to read about at some point.
vuquta Posted January 17, 2010 Author Posted January 17, 2010 You mean like GPS, which doesn't work if relativity is wrong, already mentioned by ajb? Not quite. Given, t' = ( t - vx/c² )λ t' = tλ - vxλ/c² The term tλ is the compensation for time dilation which is in GPS. The term vxλ/c² is the simultaneity shift which is not in GPS. If this term is correct, then the further a ground based clock is from the GPS clock, the more out of sync. That is SR. Thus, this crucial part of SR is disproven by GPS. Why is this so crucial? Because it is the artificial factor used to force two frames in different motions to measure the speed of light at the same speed. In partiicular, this term forces the light path to be exactly the path between the light emission point in the frame and the light receiver. Logically, the receiver will be moving in some unknown way while light proceeds toward because we live in a universe of motion. Yet, SR claims not. GPS confirms the receiver actually moves and thus that is why the clocks remain in sync. Merged post follows: Consecutive posts mergedAll the examples I have given require that the speed of light be constant (with our already stated conditions) in their mathematical formulations. Thus, as they agree with experiments very well, I conclude that in nature the speed of light is (almost certainly very nearly) constant. It is possible that we have small distance (large energy) violations of Lorentz invariance. I don't know much about these. Search the literature and I am sure we could find experimental bounds on this. What one must note is that in the standard formulations of quantum field theory (on Minkowski space-time) global Lorentz invariants means we have a well defined inertial observer independent vacuum state. This is lost on curved space-times (though global hyperbolicity means not all is lost). I have no idea what violations of global (or local) Lorentz invariants would do to quantum field theory. I expect "serious violations" would be very problematic. Anyway, something to read about at some point. I am a firm believer in a constant speed of light. Sure, at the smallest quantum levels, things are discreet and so it may break down, but that does not matter at the galactic levels. So, there is plenty of evidence that light moves through space at one speed c. But, that is a completely different issue from setting up a valid experiment to measure it. We must remember, as light moves, the frame moves but no one knows how. In other words, when you shoot a laser at a target, that target is moving through space just like light does. For example, consider two satellites. One wants to shoot at the other. Now, light is very fast compared to the satellites, but, as light moves toward the satellite, will the satellite sit still in space as light proceeds toward it? Clearly, no. So, even if they are in the same frame for a small period of time, as light proceeds toward the satellite, the satellite moves through space and most likely, it will be missed.
ajb Posted January 17, 2010 Posted January 17, 2010 But, that is a completely different issue from setting up a valid experiment to measure it. We must remember, as light moves, the frame moves but no one knows how. In other words, when you shoot a laser at a target, that target is moving through space just like light does. You can think of a frame as a coordinate system. You will need to explain to me further what you mean by movement of a frame? (Active Lorentz transformation?)
michel123456 Posted January 17, 2010 Posted January 17, 2010 _I was not aware of the Sagnac effect. Quite interesting BTW that the effect was interpretated by Sagnac as a proval for the existence of the luminiferous aether. (conclusion in which I disagree completely but that is another subject) _Obviously, the difference between "constant" and "absolute" is not clear. Vuquta understands, because he talked about the ballistic theory, and I thank him a lot for that. I am really happy when i learn something. _"constant" means the measurement is the same. The same as a horizon. If you stand at rest at sea level the horizon on Earth is at about 11km from you. If you walk toward the horizon, it is still at 11 km. If you take your car or a train, the measurement is the same. And it will be the same for all the observators around the globe (at sea level, it is only an analogy). The distance from the observator to the horizon is something that the observator carries with him, it depends from the observator (its height) in relation with the curvature of the globe. Physically, and astronomically, the distance 11km means nothing. In this case it is not an absolute, it is just a constant. _"absolute" would mean the horizon for each observator is at 11km. When the observator takes a car to get to the horizon , the speed of the car influences space, which expands, and the car will never reach the horizon. And of course, it is impossible to get to the horizon. In this last case, 11km is an absolute of the universe and means something very important both physically ans astronomically. That was only a silly analogy. Meaning to explain the difference between "constant" & "absolute".
ydoaPs Posted January 17, 2010 Posted January 17, 2010 _"constant" means the measurement is the same. The same as a horizon. If you stand at rest at sea level the horizon on Earth is at about 11km from you. If you walk toward the horizon, it is still at 11 km. 'constant' means that it is unchanging in a frame of reference. 'invariant' means it is unchanging between frames of reference. The speed of light it both constant and invariant.
vuquta Posted January 17, 2010 Author Posted January 17, 2010 You can think of a frame as a coordinate system. You will need to explain to me further what you mean by movement of a frame? (Active Lorentz transformation?) You will need to explain to me further what you mean by movement of a frame Agreed, since I opended the door, it is up to me. I do not have a precise definition. It is the unknown motion i guess folks call absolute motion. What I do know is that objects moves through space just like light does. Light moves through empty space at one speed c. Obviously, this does not apply to objects. But, I simply cannot logically conclude is while light moves through space, a light receiver will sit still in space waiting for light to strike it. For example, it is widely accepted that the dominant motion of the earth through space is about 18.55 miles per second. Now, the milky way is somehow moving and that motion is not known. So, if two satellites are lined up in the direction of the earth's orbit and are say 30,000 miles apart and assume one shoots in the direction of the orbit toward thje other. So, SR assumes the light path is eactly d or 30,000. But, light moves, at ≈ 186,000 for the ease of the math. Then, if t = d/c then t = 30,000/186000 = 0.161 seconds. But, in .161 seconds, the satellite moves in the direction of the earth's orbit and thus, 18.55 * 0.161 ≈ 3 miles. Therefore, the light path is longer than d. But, since it is not known exactly how the earth is moving this is guess work. But, the main point is that the light path may or may not be d and therefore, it is not logically decidable. That is my main point. SR hides a postulate that this light path is always d but this is not part of the light postulate since that postulate only addresses the motion of light that is constant in speed regardless of the motion of the light source. Any ray of light moves in the ``stationary'' system of co-ordinates with the determined velocity c, whether the ray be emitted by a stationary or by a moving body http://www.fourmilab.ch/etexts/einstein/specrel/www/ Merged post follows: Consecutive posts merged'constant' means that it is unchanging in a frame of reference. 'invariant' means it is unchanging between frames of reference. The speed of light it both constant and invariant. Experimentally, light has been proven only to be constant ie that it cannot be speed injected. Invariance actually, under the context of SR, means that the light path is exactly equal to the path between the light emission point in the frame and receiver. This has not been experimentally proven and is crucial to verify the simultaneity shift between two observers in relative motion. GPS has proven the time dilation but not the simultaneity shift which is this light path issue. Here is what I mean. GPS1 GPS2 ->v | | | | | | | Ground Clock 1 Ground Clock 2 When GPS1 is vertical with ground clock 1, it shoots a laser at GPS2. GPS1 and GPS2 are d apart. GPS1-----------------------------------------------GPS2 ->v | | | | | | | Ground Clock 1 Ground Clock 2 When the laser strikes GPS2, GPS2 is vertical with ground clock 2. Also all clocks are in sync. The ground concludes the light path is the distance d2 from ground 1 to ground 2. The satellites conclude the light path distance is d < d2. GPS2 then beams the light travel time to the geound clock 1 and it measures a slower speed of light compared to the GPS frame. Time dilation is part of GPS, so that needs to be backed out. But, that is insufficient to explain the measuring difference since the simultaneity shift term is not in the calculation for synching the ground and satellite clocks. Thus, they will measure a different speed of light, though light moves at a constant c.
Klaynos Posted January 17, 2010 Posted January 17, 2010 I have an experiment that requires the speed of light is constant in all directions, I have a delay line and I fire 100fs laser pulses and vary the time they take to pass through the system. I see no difference whether I set up the delay line one way or orthogonal to that direction. The time resolved measurements are identical in both cases.
vuquta Posted January 17, 2010 Author Posted January 17, 2010 I have an experiment that requires the speed of light is constant in all directions, I have a delay line and I fire 100fs laser pulses and vary the time they take to pass through the system. I see no difference whether I set up the delay line one way or orthogonal to that direction. The time resolved measurements are identical in both cases. You mean you have an experiment that measures the same value c in all directions. Light moves through space as a constant c. I am aware of one way frequency based experiments. These just prove the frequency is constant in all directions in a frame. Frequency is a funciton of speed and wavelength. This is why frequency cannot be used to decision a measured speed. Furthermore, it has been shown that the frequency would be a constant in Ritz's theory of light in all directions. The experiment must use clocks and no such experiment exists. At one mile, these clocks must be accurate at 10-13 seconds to even consider the experiment. To further this analysis, The Kennedy-Thorndike Experiment R.J. Kennedy and E.M. Thorndike, “Experimental Establishment of the Relativity of Time”, Phys. Rev. 42 400–418 (1932). This uses an interferometer similar to Michelson's, except that its arms are of different length, and are not at right angles to each other. They used a spectacular technique to keep the apparatus temperature constant to 0.001°C, which gave them sufficient stability to permit observations during several seasons. They also used photographs of their fringes (rather than observing them in real time as in most other interferometer experiments). Their apparatus was fixed to the Earth and could only rotate with it. Their null result is consistent with SR. http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html#round-trip_tests Note the armature lengths are different. If MMX or any frequency based experiment actually measured speed, then a null result would be impossible. That is obviously because the timing along a shorter path and longer path should be different with a constant speed of light. This experiment is sufficient to exclude frequency based experiments as timing instruments for measuring the constant speed of light.
ajb Posted January 17, 2010 Posted January 17, 2010 You will need to explain to me further what you mean by movement of a frameAgreed, since I opended the door, it is up to me. Ok, thanks. I do not have a precise definition. It is the unknown motion i guess folks call absolute motion. This sounds very "unrelativistic". You need to think about what the motion is relative to. What I do know is that objects moves through space just like light does. Their motion is very similar, that is right. Massive objects move along timelike geodesics and light moves along null geodesics. Light moves through empty space at one speed c. Obviously, this does not apply to objects. Yes, given what we have said before about coordinates etc. But, I simply cannot logically conclude is while light moves through space, a light receiver will sit still in space waiting for light to strike it. You can have a target moving with respect to the source. This is fine. We could even consider a target that is accelerating. That is my main point. SR hides a postulate that this light path is always d but this is not part of the light postulate since that postulate only addresses the motion of light that is constant in speed regardless of the motion of the light source. In any inertial frame, the speed of light is c. This is independent of the co-velocity of the inertial frame of the source and the inertial fame of the observer.
Klaynos Posted January 17, 2010 Posted January 17, 2010 We measure decay times in semiconductors, these can be calculated physically. The measurements are time resolved and use 100fs light pulses, these light pulses are delayed so we can scan in time. Now if we set up the delay orthogonal to it's original state we would expect the results to alter for the same distance moved if c was not constant in all directions, this does not happen.
vuquta Posted January 17, 2010 Author Posted January 17, 2010 (edited) Ok, thanks. This sounds very "unrelativistic". You need to think about what the motion is relative to. Yes, that implies we need to know what the motion of light is relative to. The motion of objects is relative to the same thing the motion of light is relative to. In any inertial frame, the speed of light is c. This is independent of the co-velocity of the inertial frame of the source and the inertial fame of the observer. Actually, to be more accurate, light moves through any frame at c. That is what the light postulate says and nothing more. Now, it becomes a question on how to measure it in a universe of motion. So, given that light moves though empty space at a constant c, how do we measure it? Merged post follows: Consecutive posts mergedWe measure decay times in semiconductors, these can be calculated physically. The measurements are time resolved and use 100fs light pulses, these light pulses are delayed so we can scan in time. Now if we set up the delay orthogonal to it's original state we would expect the results to alter for the same distance moved if c was not constant in all directions, this does not happen. Delay times validate that light speed cannot be speed injected with the source. I completely agree and would cite that as well. But, please let me see this experiment. Again, I do not argue that light is not constant in speed. I do agree it moves through empty space at one speed. It is now a question of measuring it. That is whst we are discussing. Further, if someone proved it did not measure c, that does not at all imply it does not travel at c. Logically, do you believe when light takes off toward a receiver that the receiver sits still in space as light moves toward it? Edited January 17, 2010 by vuquta Consecutive posts merged.
Klaynos Posted January 17, 2010 Posted January 17, 2010 It's two identical femptosecond pump probe experiments that just happen to be at right angles to each other, the basic set up can be found in any paper on femptosecond pump probe experiments.
ajb Posted January 17, 2010 Posted January 17, 2010 Actually, to be more accurate, light moves through any frame at c. That is what the light postulate says and nothing more. Any inertial frame. I am not sure how our statements (with inertial inserted) are not equivalent. Anyway, the speed of light c, is with respect to the motion of light as defined in any inertial reference frame. An inertial frame you can take to mean an inertial observer, though mathematically it is a choice of coordinates.
vuquta Posted January 17, 2010 Author Posted January 17, 2010 Any inertial frame. I am not sure how our statements (with inertial inserted) are not equivalent. Anyway, the speed of light c, is with respect to the motion of light as defined in any inertial reference frame. An inertial frame you can take to mean an inertial observer, though mathematically it is a choice of coordinates. Anyway, the speed of light c, is with respect to the motion of light as defined in any inertial reference frame. The light postulate says the motion of light is independent of the frame's motion "source motion". Then, its motion is defined by the frame. That is circular. Also, the issue is how to measure it. And light does not move relative to a frame. The is light emossion theory. It moves through space whether a frame is around or not. So what is light moving relative to? Merged post follows: Consecutive posts mergedIt's two identical femptosecond pump probe experiments that just happen to be at right angles to each other, the basic set up can be found in any paper on femptosecond pump probe experiments. Found a source. As the pulse energies for femtosecond pulses are usually small, the measured signal has to be obtained from the overlap region of two focused laser beams. Signal is frequency. http://spie.org/x648.html?product_id=723954 Frequency is very good for these applications because it is constant in all directions in a frame and has been validated as such.
ajb Posted January 17, 2010 Posted January 17, 2010 Just ripped off from wiki, the second postulate. "As measured in any inertial frame of reference, light is always propagated in empty space with a definite velocity c that is independent of the state of motion of the emitting body." All references to the second postulate sound similar. Note as measured in any inertial reference frame. The mathematical statement is that the free parameter in the Lorentz transformations is numerically equal to the speed of propagation of light as measured in an inertial reference frame.
Klaynos Posted January 17, 2010 Posted January 17, 2010 Anyway, the speed of light c, is with respect to the motion of light as defined in any inertial reference frame. The light postulate says the motion of light is independent of the frame's motion "source motion". Then, its motion is defined by the frame. That is circular. Also, the issue is how to measure it. And light does not move relative to a frame. The is light emossion theory. It moves through space whether a frame is around or not. So what is light moving relative to? Merged post follows: Consecutive posts merged Found a source. As the pulse energies for femtosecond pulses are usually small, the measured signal has to be obtained from the overlap region of two focused laser beams. Signal is frequency. http://spie.org/x648.html?product_id=723954 Frequency is very good for these applications because it is constant in all directions in a frame and has been validated as such. Signal is frequency, not sure what that means? i can tell you our signal is massive, not sure quite what their setup is, we use the overlap to excite (pump) and then measure the relaxation time but varying a probe delay to look how the signal changes for time after the pump pulse.
vuquta Posted January 17, 2010 Author Posted January 17, 2010 Signal is frequency, not sure what that means? i can tell you our signal is massive, not sure quite what their setup is, we use the overlap to excite (pump) and then measure the relaxation time but varying a probe delay to look how the signal changes for time after the pump pulse. Yes, but this is measuring frequency. It is reliable because the frequency is constant in all directions and all distances in a frame. But, this is not measuring the speed of light.
mooeypoo Posted January 17, 2010 Posted January 17, 2010 Light is a wave. Frequency is a property of the wave. I don't understand what the problem is, vuquta. It's like saying knowing mass of the object is not related to measuring its weight on earth. They're related.
Klaynos Posted January 17, 2010 Posted January 17, 2010 Yes, but this is measuring frequency. It is reliable because the frequency is constant in all directions and all distances in a frame.But, this is not measuring the speed of light. My experiments don't measure frequency, the detectors are simply photodiodes. They have no (well very limited) frequency dependence, and certainly none over the laser frequency range. it is not directly measuring the speed of light but if the speed was different in different directions the two orthogonal delay set ups would produce different results. Which they do not.
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