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  • Post #53

No Israel I cannot understand how the speed of light can be both variable, c'=c(1+2Q/c^2), and constant ("the SL is always the same in a gravitaional field"). But FQXi member Steve Carlip can, so you have a good chance of winning the essay contest:

http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/speed_of_light.html

Steve Carlip: "Einstein went on to discover a more general theory of relativity which explained gravity in terms of curved spacetime, and he talked about the speed of light changing in this new theory. In the 1920 book "Relativity: the special and general theory" he wrote: "...according to the general theory of relativity, the law of the constancy of the velocity of light in vacuo, which constitutes one of the two fundamental assumptions in the special theory of relativity [...] cannot claim any unlimited validity. A curvature of rays of light can only take place when the velocity of propagation of light varies with position." Since Einstein talks of velocity (a vector quantity: speed with direction) rather than speed alone, it is not clear that he meant the speed will change, but the reference to special relativity suggests that he did mean so. This interpretation is perfectly valid and makes good physical sense, but a more modern interpretation is that the speed of light is constant in general relativity. (...) Finally, we come to the conclusion that the speed of light is not only observed to be constant; in the light of well tested theories of physics, it does not even make any sense to say that it varies."

http://arxiv.org/pdf/gr-qc/9909014v1.pdf

Steve Carlip: "It is well known that the deflection of light is twice that predicted by Newtonian theory; in this sense, at least, light falls with twice the acceleration of ordinary "slow" matter."

Pentcho Valev pvalev@yahoo.com

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  • Post #54

Israel,

You should be aware of Jim's Roemer argument. Didn't he tell you here and yesterday that Roemer's observations of Jupiter moons led to the insight that light propagates with limited speed and these observations were no round-trip experiments?

What about your attempt to correct Einstein in excess of his own self-correction in 1920, I quote from his Leyden lecture: "... the whole change in the conception of the ether which the special theory of relativity brought about,

consisted in taking away from the ether its last mechanical quality,

namely, its immobility." If I understood your essay correctly, you are calling this immobility PSR. Einstein continued to know well that the PSR and his PR exclude each other. You seem to disagree. If you are correct then the proponents of Einstein's PR will perhaps be happy with you as their most brilliant PR manager. I regret that your essay is, with its only six pages, a bit too cryptic as to fully persuade me.

Eckard

Pentcho

Lets try again. It is very easy and very intuitive. Think again of the waves in a liquid. If we consider that the liquid has the same density, i.e. the liquid is homogeneous, the speed of the waves, say c, will always have the same magnitude in any region of the liquid. Do you agree in this? The speed of the waves is not defined by the source but by the liquid. Once a wave is generated the wave moves away from the observer at a given velocity. Ok?

Now let us make the next assumption that no ship and nothing moving through the liquid can move faster than the speed of the waves. The speed c is a limiting speed. No material object can go faster than c. ok? We can take advantage of the fact that the speed of the wave is maximum and constant in this homogenous liquid to determine the rapidity of other objects. I mean, we can take the motion of the wave as a basic unit of motion or speed, and refer all movements of physical entities (PE) to the speed of the wave. Ok? Conceive this as if it were a race between a wave and a PE. You will take as a criterion of motion the speed of a wave. Then you can evaluate the rapidity of something according to the fact that it moves slower, equal or faster than the wave.

Now, imagine that you wish to measure the speed of a (PE), say the speed v of a ship moving through the water. But you know that the ship cannot move faster than c. So, to determine the quantity of motion of the ship (i.e. how fast it moves relative to the motion of the wave). You place two buoys that will delimit a distance L. Then, you let the ship to travel the distance and measure the time it requires for the trip, say, t_s. Then you let a wave to travel the same distance and register the time, say t_l. Now keep in mind that you want to know what physical entity is faster, the wave or the ship. To make a quantitative estimate we can divide the speed of the ship by the speed of the wave. This is called beta, i.e. beta=v/c=(L/t_p)/(L/t_l). Since c is the maximum speed, beta for the particle will be less than or equal to 1. ok? This same result can be obtained if you divide only the times, i.e. beta=t_l/t_p. Do you understand my picture so far?

No, imagine that we have an inhomogeneous liquid. And this inhomogeneity is caused by the presence of a spherical source that changes the density of the liquid as function of the distance to the center of the sphere. In this case the speed of the waves will be no longer constant at given region of the liquid (do you agree?); the speed of the waves will vary, lets say, according to the expression c'=c(1+2Q/c^2). Then, imagine that you are in a given region of the liquid where the speed is not c but, lets say, 1.5c. But however in that region of the liquid, the speed of the wave is also the maximum speed that any PE can achieved. Nothing can travel faster than 1.5c. Therefore, if you would like to measure the speed of any PE according to the procedure above, you will obtain again that beta=v/1.5c is less than or equal to 1, but in this case v has as a limiting speed 1.5c and not c as in the case where the liquid is homogeneous. If you further go to another region, there you will find another absolute value for the speed of the wave, and again in that region the speed will be the maximum speed, in that region nothing can travel faster than the speed of the wave. Thus is you measure the speed of the wave, making reference to the speed of the wave you will get again 1.

Now translate these ideas into the case of the speed of light and keep in mind that light travels through the aether (free space or vacuum). In a homogeneous aether the speed of light will be always c. But under the influence of gravitational fields the aether is inhomogeneous and the speed of light is no longer c. Nevertheless, in a given region of space, it is the maximum speed any PE can attain, then, if you follow the experimental procedure outlined above to measure the speed of light, you will get a constant value, i.e. beta= 1. The same value is obtained both with a gravitational field or without it. This is so, because the speed of light at a given region of space is the maximum speed. Do you understand this? Do you understand why the speed of light is constant when it is measured although it is not in reality as it moves from region to region in a gravitational field?

Now, the next thing you have to do to fully understand these ideas is to read my reference 17. There I explain that the experimental techniques that we use to measure the speed of any PE are incapable of measuring the speed of any PE in one way. We can only measure average speeds, not instantaneous speeds. To the best of my knowledge, measurements of the one-way speed have not been possible so far.

I agree with the quote of Steve Carlip in your last post. But you should understand that theory and experiment are two different things.

I hope that this time I have elucidated this issue. Please let me know you got it.

Israel

Hi Eckard

Thank you for your comments. I am sorry, when I read your previous post I didn't realize that you were referring to James. I apologize for this.

As to the Roemer' argument I have exposed some arguments in reply to James. The Roemer's approach is controversial and I have analyzed a couple of reports who claim to have reproduced Roemer's measurement of the speed of light on a table top experiment. In my reference 17 I showed that this is not the case. I asked James for some references with explicit calculations of the experiments and he has not replied my last post. As well, I would appreciate if you have any references on this topic.

Another example of this is the Bradley's approach. Many people claim that the one-way speed of light can be determined from the classical aberration expression, i.e., tan (theta)=v/c. The problem here is, how we measure v? v is the speed of the earth relative to what? To simplify the calculations astronomers assume the speed of the earth around the sun or any other arbitrary reference system. Is this correct? If one determines v relative to jupiter one will get a different value. So, I ask: is not the expression suggesting that the speed v is the absolute speed?

On the other hand, I would like to add that Einstein denied the PRS because he thought there was a contradiction between the PR and the PSR. However, a universe deprived of a PRS only leads to a series of paradoxes. Once the PRS is restored the paradoxes fade away.

As to the extract, indeed I call the immobility (from a macroscopic viewpoint) the PSR. One can say, that this is the Lorentzian aether, an immovable and homogenous substance. But considering the action of massive objects, the aether is no longer homogenous and immovable. So, I appeal to Descartes's aether which Newton simplified as immovable. Even at the microscopic scale, quantum mechanics has shown that the vacuum is not immovable. Several other theories also hold that the vacuum can be assumed as a particular state of condensed matter. So many evidences from cosmology, to quantum mechanics, to condensed matter seem to suggest that PRS and the material fluid are the right assumptions.

In relation to the length of my essay I see no relevance in the discussion. Why do you point out this? The limit was 25 000 characters, they are compacted in 6 pages.

Finally, in relation to your comment "cryptic" I will be glad to elucidate any inquiry you may have. As far as I can see you seem to be in agreement with Einstein. So, I would appreciate if you could tell me if I am wrong and where I am wrong. I may be erred, but despite this, unquestionably, only the body of experimental observations will decide whether Einstein was wrong or not.

Israel

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  • Post #57

Hi Israel,

I hope you won't mind if I list the acronyms. Thanks.

PSR-preferred system of reference

AS-absolute space

GF-gravity field

GPR-Galillean princip relativity

ISR-inertial system of reference

LP-laws of physics

RT-relativity theory

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    • Post #58

    Israel, your story is not so difficult to understand - the problem is that it is irrelevant. You wrote:

    "Then, imagine that you are in a given region of the liquid where the speed is not c but, lets say, 1.5c. But however in that region of the liquid, the speed of the wave is also the maximum speed that any PE can achieved. Nothing can travel faster than 1.5c. Therefore, if you would like to measure the speed of any PE according to the procedure above, you will obtain again that beta=v/1.5c is less than or equal to 1, but in this case v has as a limiting speed 1.5c and not c as in the case where the liquid is homogeneous."

    The essential information here is that the wave speed is 1.5c, that is, greater than c. Your claim that no PE (physical entity) can move faster may be true but is of little significance. Let us go to the original case:

    The top of the tower emits light with frequency f, speed c and wavelength L (as measured by the emitter). The observer on the ground measures the frequency to be f'>f, the speed of light to be c'>c and the wavelength to be unchanged, L'=L. That is what both Newton's emission theory and Einstein's relativity predict. However c'>c is incompatible with Einstein's 1905 light postulate (this claim needs a proof of course) so Einstein's relativity turns out to be inconsistent. And this important conclusion cannot be affected by the assumption that a PE can or cannot move faster than light.

    THIS story is relevant, yours is not I am afraid.

    Pentcho Valev pvalev@yahoo.com

    Hi Pentcho

    I am sorry, you keep asking the same questions. My arguments were aim at explaining why experimentally the same value is obtained for the speed of light whether you are on the top or the bottom of the tower despite the fact that the speed of light is faster at the top and lower at the bottom.

    You say: However c'>c is incompatible with Einstein's 1905 light postulate (this claim needs a proof of course) so Einstein's relativity turns out to be inconsistent.

    Again you are mixing things. The second postulate is only true for inertial systems of reference, but it is no longer valid for non-inertial systems of reference (NIS). In virtue of the principle of equivalence, this mean that the second postulate is not valid for system of reference under the influence of gravitational fields. In such case the speed of light will be c'>c. Special relativity does not apply to study systems under the influence of gravitation. So, the fact that you found that there is a difference frequency which is different etc. is correct (to a first approximation) because your are considering the problem in a gravitational field of the earth.

    Israel

    Hi Jason

    I just wonder the purpose of listing the acronyms. Thanks

    Israel

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    • Post #61

    Pentcho

    Reading your posts (here and elsewhere) it seems as if you are trying to apply the popular frames of Special Relativity to gravitational fields. Well you cannot because there is no gravitational potential in SR.

    Assume you are floating in free space and Israel is near a black hole. You will measure the speed of light in your location to be 299792.458 km/s (c) however Israel will measure it in your location to be a zillion km/s. This does not mean that the speed of light changed in your location. This is just that Israel's clock slowed and his ruler shrunk. Now with his slower clock and a shrunken ruler he measures the speed of light in his location to be 299792.458 km/s (c); however according to your clock and ruler this is just a few meters/s (c').

    So in the presence of gravity you will measure c' (not c). Only in "local inertial frames" is the measured speed of light c. This does not mean that c changed; however it does mean that the MEASURED speed of light is not necessarily 299792.458 km/s.

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    • Post #62

    Israel, you wrote: "I am sorry, you keep asking the same questions. My arguments were aim at explaining why experimentally the same value is obtained for the speed of light whether you are on the top or the bottom of the tower despite the fact that the speed of light is faster at the top and lower at the bottom."

    Yes I keep asking the same questions but you keep giving contradictory answers. Below in this thread I asked you about the speed of light that the observer on the ground MEASURES:

    Pentcho: "The top of a tower of height h emits light with frequency f, speed c and wavelength L (as measured by the emitter):

    f = c/L

    An observer on the ground measures the frequency to be f'=f(1+gh/c^2), the speed of light to be c' and the wavelength to be L':

    f' = c'/L'

    The questions: c' = ? ; L' = ?

    My answers: c'=c(1+gh/c^2) ; L'=L "

    You answered:

    Israel: "To a certain degree, I agree with your result, namely

    c'=c(1+gh/c^2)

    but recall that it comes from an approximation."

    Israel, please confirm or reject the following statement:

    The observer on the ground MEASURES the speed of light to be greater than c (c'>c).

    Yes or no?

    Pentcho Valev pvalev@yahoo.com

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    • Post #63

    Hi Israel,

    I just wanted to have the list of acronyms to refer to as I read your paper. I like your paper. It is well written, clearly articulated and interesting to read. I am sympathetic to your view that there is a medium of some kind. But I have to take issue with you that a preferred system of reference exists. I assume that a PSR has an absolute clock and an absolute reference frame. A Galilean reference frame is philosophically appealing, but it turns out to be incorrect.

    I thought that your closed circuit argument was a clever way to undermine experimental evidence for RT. Unfortunately, the GPS satellite system, which works very well, uses and confirms GR and QM to a high degree of accuracy.

    Nevertheless, it was a good paper.

    Pentcho

    I have explained clearly to you that calculations and measurements are different things. Your approximation is correct but the measurement will always yield c. If you had understood my wave illustration you would not have seen any contradiction but you considered them irrelevant. So, what else can I do? You see a contradiction because you are disregarding the measurements procedures, because you are not paying attention to how the speed of something is in practice measured. This is not irrelevant. Keep in mind how in real life and in practice the observer on the bottom will measure the speed of light when he receives the signal from the observer at the top, this is not trivial as you may think. You need to have an experimental setup to measure the speed of light, you need to have a system of units to measure, this is why I asked you to consider the speed of the wave as a unit of motion. For all of this that you are overlooking, you do not understand why when we measure the speed of light you will always get c instead of c'>c. Please read again my wave illustration and my reference 17. Otherwise you will never get out of your perplexity.

    The answer to your question is no.

    Israel

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    • Post #65

    Israel, I do indeed disregard your "measurement procedures" but this is because in the following text you say everything I need to hear:

    You wrote above in this thread (Jul. 30, 2012 @ 06:50 GMT): "On the other hand, when we are under the influence of a gravitational field. The speed of light waves will vary according to the expression: c'=c(1+2Q/c^2), where Q is the gravitational potential, i.e. the instantaneous velocity of light will vary from point to point within the gravitational field. This can be reinterpreted in terms of frequency and this is the cause of the redshift or the blueshift."

    I think the equation c'=c(1+Q/c^2) is the correct one but this is a minor objection. The essential points are that the speed of light does vary, that "this can be reinterpreted in terms of frequency" and that "this is the cause of the redshift or the blueshift".

    Regards, Pentcho

    Hi Jason,

    "I assume that a PSR has an absolute clock and an absolute reference frame. A Galilean reference frame is philosophically appealing, but it turns out to be incorrect."

    An absolute time and an absolute reference frame does not necessarily mean Galilean relativity, which the argument I've given in my essay may help you to see. Furthermore, as Israel has correctly pointed out, relativity theory is not inconsistent with a preferred reference frame, which is therefore not an "incorrect" assumption to make---only Einstein argued that it should be superfluous from the point of view of relativity, since SRT *can* be derived without it. The problem is therefore to reconcile Newtonian intuition with relativity theory, and furthermore, to justify that upon the basis of scientific evidence.

    Cheers,

    Daryl

    Hi Jason,

    The PSR has no Galilean character, in this PSR relativistic laws apply instead. So, I do agree that relativity makes the correct quantitative predictions, although not the most cogent physical interpretations. On the other hand, I would like to mention, that I found no contradiction in Newton's famous schollium about relative and absolute motion. This remain valid and fresh despite relativity theory. From my view, the term RELATIVITY does not mean that absolute motion is pointless as Mach and Einstein insisted, but that something is referred to something else, this is really the all-inclusive PR. If one acknowledge this, one can refer all physical quantities to any reference system even if the system is the PSR.

    The close circuit argument was only aim at pointing out the importance of the experimental component of physics. I would not qualify it as "clever", I'm just underlining this well known fact that it seems to be unnoticed by most people. This fact does not undermine the theory but only states a clear distinction between experiment and theory. I do agree with the assumption that in an empty space (no gravitational fields) the one-way speed of light is isotropic despite that, to the best of my knowledge, it has not been measured. The reality is that one cannot get rid of gravity.

    Best wishes

    Israel

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    • Post #68

    Hi Israel, Hi Daryl,

    There could be some funky way to get a preferred reference frame. But you have to make some very progressive assumptions. You have to really use and abuse the laws of physics (which can be a very good thought experiment). But what is so intriguing about a PSR? What are you each looking for? Are you trying to satisfy a need for a philosophically pleasing set of laws of physics? I suspect that is the case for most physicists/physics enthusiasts. But what is the motivation for finding the holy grail of reference frames, the preferred frame?

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    • Post #69

    Dear Israel Perez,

    Your all-inclusive PR is not the only attempt to maintain Einsteinian PR while nonetheless questioning the fundamentals it was built on: Cahill, Christov, Jackson, ... You wrote to Jason: "Relativity makes the correct quantitative predictions, although not the most cogent physical interpretations." Neo-Lorentzians like Selleri and van Flandern claimed their theories furnishing the same quantitative results more easily. I do not share such views. I am just curious.

    The reason why I failed to be convinced and called your essay cryptic is on my side: Because you did not show illustrating Figures, my shaky command of English might have hampered me the more. Sometimes I did not even find words in my dictionary. What does schollium mean?

    You wrote: "Once the PRS is restored the paradoxes fade away." How about restoring simultaneity as does Phipps?

    So far I cannot see in what Einstein was wrong when he considered his PR based on his denial of a PSR.

    Last contest was won by a fictitious Newton who easily understood Einstein. Sorry, I am not a Newton. I rather trust in the possibility of human fallacies.

    Eckard

    Hi Jason,

    Those are the right questions to ask, I think. One could argue, for instance, that from the realist point-of-view a block universe logically follows from Einstein's interpretation of the relativity of simultaneity, and that this is a metaphysical dead end---but that argument isn't scientific, so it's only a starting point for questioning the validity of the interpretation; i.e., we can take arguments like Minkowski's and Putnam's as the first part of a reductio ad absurdum, really ensuring we understand why the implication *is* what logically follows, given the standard point-of-view on the meaning of relativity, so that we can move on from them to complete the reductio.

    In my opinion, Einstein's interpretation of the meaning of relativity is actually incompatible with cosmology and causal coherence, and therein lies the scientific evidence for a preferred reference frame. Furthermore, in my view the preferred frame can be reconciled with relativity in a way that does in fact make logical sense (i.e., isn't "funky") and doesn't really use and abuse the laws of physics, particularly with reference to the principle of relativity, beyond a clear distinction (as opposed to a fuzzy understanding) that the principle applies to the physical description of what is *perceived*, and not necessarily of *what is*.

    Of course, that's basically an ontological distinction---but I stress that I think there is very good reason, from the point-of-view of cosmology, that the demands of relativity can only go as far as a description of phenomena, and definitely can't be applied as such to the true simultaneity-relation between noumena. My argument for this is 24,996 characters long, not including spaces, and I do encourage you to read it.

    Regards,

    Daryl

    Hi Eckard,

    I hope you get a chance to read my essay. I've argued that both Newton and Einstein were wrong about the meaning of simultaneity in the coordination of phenomena.

    Best,

    Daryl

    Hi Janson

    I am going to be categoric, please do not take me wrong, this is not personal:

    You said: "You have to really use and abuse the laws of physics "

    What are the laws of physics? The laws of physics are a set of equations that are found and established by physics. However, the laws can be modified at will according to the experimental evidence. At the end, observations decide what the laws are. Today there is a crisis in physics, a puzzle that, as evidence accumulates, becomes more and more complex. As in the past, scientific revolutions demand radical solutions. So, this contest asks: Which of our BASIC assumptions are wrong? I am answering the question clearly: the PRS. I see that there is no experimental reason to reject it. It is not a matter of philosophical satisfaction. It's a matter of physics, of "reality", of simplicity, of intuition and of progress for physics. Like I said in my essay, assumptions are reconsider several times in several moments in the history of science in view of the fact that they are suitable to solve the problems that physics has, this is the case. Probably you do not see all of this and probably you do not care about all of this.

    Now I ask you: What is wrong with reconsidering the assumption? If you understood my essay then you understood that the current laws of physics are not affected by this assumption in the least and, what is more important, no experiment is in conflict with it but quite the contrary, the fact that experiments lead to the same physical laws in any reference system speak for it. Since no experiment force us to abandon it, one may conclude that its rejection is only a matter of either prejudice or parsimony. If you have no objection in these respects, my question is: Why are you so reluctant to accept it? What are your arguments to reject it?

    I argue in my essay that most of the problems in physics can be "easily" solved if one accepts both the PSR and the notion that "empty" space is not only composed of gravitational potentials (as relativity holds) but that space is a material fluid a la Descartes. This is the benefit for physics.

    Best wishes

    Israel