Tim88

Yes, you got that right, but it seems that you missed the connection between what you want to know and what I told you: - Doppler is functionally not to be confounded with time dilation. That's indeed not directly a visual issue, but it's a conceptual one and you immediately are confronted with it visually if you include drawing the light waves in the picture of the set-up. Then you automatically distinguish between Doppler and time dilation, for Doppler is what happens due to reducing or increasing the number of waves "in flight" and has nothing to do with a difference in frequency standards, while time dilation is just the inverse. Time dilation is independent of direction, contrary to Doppler. It's even that difference of causal principle that is at the heart of the measurement. - There is nothing "transverse" going on in this set-up, as both directions of observation are approximately parallel to the direction of ion motion. Again it's essential to know that in order to make a correct sketch. Accurate labeling is therefore helpful for correct visualizing! More later.

I don't know such. However, the basic idea is fairly straightforward. What is called "transverse Doppler" is a misnomer, it's just time dilation. That effect comes on top of the Doppler effect. Wikipedia explains it rather well, the Doppler equations are given; only some info about the set-up is lacking. The basic idea was that one can accurately determine the forward and the backward Doppler shifts, and these relate to each other for a given particle that is going at a certain speed at a given time. But due to time dilation the short wavelengths (high f) are longer than classically expected, and the long wavelengths (low f) are also longer than classically expected. Compared to the Doppler shifted wavelength they are thus both redshifted. And that creates an asymmetry in the frequency shifts that can be measured, as discussed in Wikipedia. I'll now look up the details of the measurement set-up. From reading through their paper I got the following understanding of their set-up. Light coming out of the tube towards the detector consisted of: - light emitted in the forward direction (to the right in your drawing) - light emitted in the backward direction but next reflected by the mirror inside the tube. That mirror is an important element that is lacking in the Wikipedia drawing. - light from unaccelerated gas All that light went through the slit (shown in the Wikipedia drawing) and was next focused on the spectrometer's metal-glass grating which reflected the light onto a photographic plate (with again a focusing lens). Thanks to the grating, the image of the slit is split in different bands depending on the emission frequency. For classical theory there is only Doppler and for each rest frequency line there would be equal distance to the Doppler shifted lines. The deviation from that symmetry is a measure of the time dilation.

Yes, that question is much better. However, spacetime curvature concerns the mathematics; and accounting is again math. I can think of two possibilities: 1. you either deny or can't understand the need for the existence of a physical cause for the math 2. you believe in a physical Spacetime (a 4D metaphysical entity), but you dislike the term "ether" as a label for such a causal entity. Which is it? No, and again no! Once more, this thread is a continuation in part of the thread http://www.scienceforums.net/topic/97105-is-space-time-a-physical-entity-or-a-mathematical-model. In that thread I explained why Einstein argued that "According to the general theory of relativity space without ether is unthinkable; for in such space there [...] would be no propagation of light". This thread discussed two variant ether interpretations: 1) a "Lorentz" ether to which Einstein at that time adhered, and 2) a "Minkowski" "4D ether" to which he later tended, as it implies a form of immortality. Note however that it's not sure if that was really what Mnkowski had in mind. By now interpretation 1) has been sufficiently clarified, but interpretation 2) remained, regretfully, a bit obscure. And strangely, my question about one aspect of interpretation 2 (posts #234 and #238) was repeatedly hijacked for more discussion of interpretation 1 as well as for discussion of the topic "is space-time a physical entity or a mathematical model" - which is not the topic of this continuation-in-part. Once more: the speed of light is independent of the action of the source; in this thread we follow up on the insights of Einstein and consider that it's either a function of the properties of Space (interpretation 1) or of Spacetime (interpretation 2). If there is some constructive input about Spacetime as a physical entity and how it can be understood as governing the propagation of light, I will be interested. I'm not interested in more hijacking and I won't comment on such.

Hi Thales, I suspect that you think that it's like the Michelson set-up; but it is totally different. 1. the canal rays are explained in the Wikipedia article, inside the very text that accompanies the picture that you copied; and for a more elaborate explanation you should click with your mouse on the blue underlined "Canel rays" text. 2. These hydrogen ions emit light when they return (in flight) to a lower energy state.

You seem to think that neither Einstein or I ever thought about that. And again you bring it up in the wrong thread, as the error in your reasoning was already clarified in the mother thread (but even more elaborated in this thread, on p.12). Just one last question here to you: do you really pretend that the cause of the speed of the ball is the same as the cause of the speed of light?

You continue to confound mathematics with physics. You are mistaken: Einstein's relativity is characterized by the usage of common language. His writings are easy to understand, in my opinion (as I'm not a layman, I could of course overlook some parts that I think to be easy to understand for laymen while they are not!). Well seen! However, my point was merely that just because animals are living, that doesn't make them "4D objects". That's a misuse of language, a bit resembling of "Newspeak" - you know what I mean if you have read "1984". In fact, space-time is 4D because space is 3D; and if we add force, then objects would be 5D in a space-time-force sense! Instead of such Newspeak, I stick to normal language; and in normal language space is 3D - see also Einstein 1916. Philosophically everyone has a right to have his own opinion, but it's not acceptable that jargon resulting from weird ideas of a minority should be imposed on the majority. I won't further discuss such nonsense about nonstandard terminology here.

In other words, you would call clocks and animals "4 dimensional objects"?? To me that's highly uncommon use of language.

Your way of describing things risks to confuse people. Please understand that Newton's model also used x,y,z,t. Moreover Lorentz ether is an interpretation of SR, and block universe is another interpretation of SR. Regretfully it remained a bit unclear what exactly the block universe interpretation means, but that's because we could not find a true "block" believer to explain it to us.

I definitely explained Lorentz ether; you know very well that SR uses the math of Lorentz ether, and I explained in great detail how.

For completeness: I use the one way speed of light definition as in http://fourmilab.ch/etexts/einstein/specrel/www/ Thus the speed of light along x' of S' is c-v with respect to S' according to S.

I claim that their is no mathematical difference, and I elaborately demonstrated how the Lorentz ether works in not only creating a constant c for the return speed of light but also in obtaining invariance of c (note the continuing confusion between constant c and invariance; that's the origin of the lack of understanding). That's funny indeed! Maybe you don't see calculations when you read them, or maybe you forgot to click on hyperlinks. Consequently you even get your facts wrong, for everyone to see: This topic came to a dead end.

No I don't, for, once more, that question was elaborate in the mother thread: http://www.scienceforums.net/topic/97105-is-space-time-a-physical-entity-or-a-mathematical-model/ And if you can't explain light propagation that's also OK; it would just have helped to make block universe more convincing. Which just goes to show that you still don't understand my question; but we already knew that. Only this is worse, for it also means that you don't even understand that the speed of light is made isotropic by means of Einstein synchronization. Explaining that belongs not to this philosophy forum but to the physics forum (note that my calculation examples imply that fact and that Einstein specifically clarified that already in 1907; if you still have questions about it, start a topic in the relativity forum). It could be that that is the reason why you did not understand my question, as my question concerned the "true" one-way speed of light according to "block" in contrast to the "apparent" one-way speed of light as operationally defined in SR. And you suddenly asked me questions about the Lorentz ether of which I can't make any sense; in particular: To the contrary, this topic is based on the assumption that a theory cannot give results that differ from its mathematics, and my examples were meant to demonstrate that fact! Anyway, I have clarified as much as I could; and it appears that -currently- nobody else here is willing or capable of further explaining either the Lorentz ether interpretation or the block universe interpretation by means of clarifying examples. I thus consider this topic from here on to be "on standby". Thanks for the discussions, which made this topic not only more interesting for onlookers but also for me!

Thanks VanD, I see that you make a serious attempt to explain the block inverse. You are certainly right that I don't fully understand how the block universe can work as a substantial entity, as opposed to a mere mathematical tool. Now, by claiming that the 4D "block" is not some kind of a medium, you seem to deviate from other defenders of that interpretation and that you make it less substantial - for what is it then? If you claim that it is nothingness, then this is the wrong thread for you: the starting assumption or postulate of this thread is that there is something substantial (either "Space" or "Spacetime") that we assume in order to explain and make sense of it all, and this thread is discussing two of those interpretations that we can choose from. If you want to argue that neither Space nor Spacetime have substantial existence, then you should continue the discussion in the mother thread. Is there anyone who can explain with block universe interpretation how and relative to what, light truly isotropically propagates at speed c?

That's nonsense, as I demonstrated how the 3D + time interpretation perfectly matches the math and how it makes perfect sense metaphysically. I also explained how light propagation is understood with that interpretation; no need to repeat what I already elaborated one page back (page 12, post # 223). My demand for those who are promoting the 4D space interpretation (any variant of it), is to do the same, and ducking the issue doesn't bring anything.

In a way "time" is already there, as what we call "time" is based on the cyclic behaviour of the environment. However it's still our choice to call a certain aspect of what we see in nature "time". Taken without my elaboration here above, your two statements here are self contradictory - except if you think that nature doesn't exist outside of our fantasy!

The terminology of physics must be rooted in physics; and the issue I raised has nothing to do with geometry but the physical model behind the physics -thus metaphysics. If you are commenting physics terminology with geometric terminology, then indeed no useful discussion is possible. Here you confound invariance of reference systems with isotropic media! As I elaborated thrice already, if you are a ground observer and according to you light propagates isotropically at speed c relative to you, then according to you it propagates at c-v and c+v relative to the moving car. How do you explain light propagation? Let me phrase the issue differently, with a reminder with the starting point of this thread. The 3D Space and 4D Spacetime views of reality resulted, among other considerations, from the realisation (as earlier discussed here) that the speed c ("the speed of light in vacuum") must be a characteristic of some kind of medium - either 3D ("Lorentz ether") or 4D ("block universe"). It isn't a characteristic of the emitter or the receiver or of the state of motion of either, and it can't be a characteristic of the observer. However, "space" and "time" are definitely not substantially of the same nature. 4D Spacetime can therefore not provide a truly homogeneous medium for isotropic light propagation.

They do not; time dilation is a function of speed, as already explained by Einstein in 1905, here in section §4. The effect of acceleration is indirect, as it can change speed.

Mordred, I'm sorry as you clearly put time and effort in this, but it's hopeless as I'm not talking about anything that you discussed in your last two replies; but I'm hardly surprised, as metaphysics isn't really your thing. - No, I'm not asking about Lorentz ether - No, I'm not asking about symmetry of transformation equations - No, I'm not asking about the Doppler effect - No, I'm not asking about a "preferred frame" Instead, I am questioning a serious apparent defect of the block universe interpretation. Maybe someone else who adheres to the block universe interpretation and reads my posts #234 and 236, may be able to answer my question.

Science happens to be the averaging out of opinions of scientists. As you indicated, those are sometimes in error. Also a new paradigm may be revolutionary but still incorrect; science is just as much affected by fashion as scientists. In the long term of course much of that is ironed out, simply because generations of scientists die out and are replaced by new ones (that's a paraphrase, not originating with me, but I forgot who said that first). Better do so, for now the thread is freewheeling on its own, since we don't know which examples you find most interesting.

I think that you are confounding two different experiments by M-M; but sorry, I'm not talking about MM in particular, and neither am I talking about time transformations. Note also that a true one way test (i.e. revealing "true" one-way speed of light) cannot be done, as that would break the relativity principle. However that is not the topic of discussion here. If you don't believe me, please start it as a question in the relativity forum. I am talking about the physical interpretation of light propagation. If light propagates through a 3D ether, that is without conceptual problems, as I explained earlier on this page. Already with the car example, the speed of light relative to the car according to a ground observer (the "closing speed") is anisotropic. Thus I asked: how is propagation of light interpreted with the 4D Spacetime (block universe/evolving block) models? What are their "hidden reality" views? Surely the interpretation can't be that light propagation is both truly isotropic and anisotropic! Light can not be truly moving at c relative to an arbitrarily chosen 3D reference system, as that would be self contradictory. An obvious explanation attempt would be a literal 4D ether, made up of "space and "time". However, for light propagation to be truly isotropic, "time" and "length" should be of the same substance. And we know that this is not true; clocks measure time, and rulers measure length. Thus my question stands.

Mordred I suspect that such a discussion has more chance to take off when it is presented in the relativity forum, as more people are likely to see it. Meanwhile I suddenly thought of a rather basic issue that has not yet been discussed, and which is directly related to relativity of simultaneity: the isotropy of light propagation. With 3D Space (Lorentz ether) that's easy to picture: light propagates at c through the ether, the same in all directions. By means of a "local" reference system one can make it appear as if instead the light propagates at c relatively to that reference system. I explained this in detail in post #223 example 4. It may be useful to point out that the consequence of making light propagation appear to be isotropic relative to the chosen reference system (("closing velocity"), is that it then appears to be anistropic relative to other, "moving" reference systems, such as with for example a "moving" Michelson interferometer. From the perspective that the apparatus is moving, along an arm that is oriented along the direction of motion, the light appears to take more time to traverse it in one direction than in the opposite direction. How is propagation of light interpreted with the 4D Spacetime (block universe/evolving block) models? What is their "hidden reality" view? Surely the interpretation can't be that light propagation is both truly isotropic and anisotropic!

PS I had not seen your earlier comment which looks very wrong, and probably that's also what swansont referred to (I marked it in red): You are right that one should use the Huygens principle. If you do it correctly, you will find that the error is much smaller than you claim, and in the other direction. Correct use of that principle with a moving mirror implies that you account for the position of each point of the mirror at the time that the wavefront reaches that point. By the way, at first also Michelson got that one wrong in his first publication. If I correctly remember, he was corrected by Lorentz. As a matter of fact, indeed: https://en.wikisource.org/wiki/On_the_Relative_Motion_of_the_Earth_and_the_Luminiferous_Ether - As corrected by Lorentz, and also (without going in details):

Surely you know better than that! The MMX falsified Newton's mechanics, in particular the Galilean transformations; this was solidly established by Lorentz and Einstein. Maxwell and MM assumed their validity, which seemed at the time so natural that they didn't even mention that assumption. However, the point of the discussion is the calculations, which all of us (except Capiert) hold to be essentially correct, insofar as they were based on that faulty assumption. Sorry but it's unclear to me what error you perceive. There is a little issue with the reflection angle, and that was discussed in the literature of the time; is that perhaps what you mean? I can dig up one of the old publications next week if you like. For a null result one has to assume length contraction; that also fixes the issue with the reflection angles (that's a detail that is rarely mentioned). There is no cover-up; only a simplification. While MMX played a motivating role in the development of SR, it was just one of many experiments that led to it. From a modern perspective however, you can approach the question much more simply. The Kennedy-Thorndike experiment demonstrated the reality of Lorentz contraction in case of time dilation; and time dilation by the Lorentz factor has been established by means of a number of experiments since then. When you make a drawing taking that into account, you should find that you will predict a perfect null result for MMX. PS I see that now the Wikipedia article on this, while still flawed, is much improved, and the issue with the mirror is discussed as well: https://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment#Mirror_reflection

I have a number of those papers at work. I'll check next week; will message you if I find something! Note: I have no reprints, just copies of a number of his papers.

Apart of one detail, further answering to your points here would just continue the infinite loop, and some of what you try to make me understand happens to be what I already told you. But in a nutshell: SR contains no metaphysics, and physics is concerned with verifiable phenomena. The detail: I don't ignore what I actually verified myself. It's straightforward to verify the step from Lorentz-1904 (the transformations of Lorentz) to Poincare-1905 (the modern "Lorentz transformations"). If you don't know how, please start it as a topic in the physics section. We'll no doubt meet again in a future thread.