Tim88

Bold emphasis mine: What we are discussing here is "the elephant in the room" that you don't see. Your words "spacetime affected" imply your adherence to the block universe (spacetime as a physical entity), which you reject.

The complication of two variants of block universe is useful input; probably it's most useful to keep it generic here without elaborating on variants, in order not to fall in distractions, as you say. However, I'm very sorry, most of your otherwise very interesting mathematical discussion is really besides the point for the discussion here. [edit:] I doubt that you mean that you really don't understand why Einstein can't see the stress tensor involvement in the Einstein field equations! Please check out his arguments as summarized in the discussion of which this is a fork, and see if you can offer an alternative to the physical interpretations that are discussed in more detail in this thread. http://www.scienceforums.net/topic/97105-is-space-time-a-physical-entity-or-a-mathematical-model/page-11#entry944692 http://www.scienceforums.net/topic/97105-is-space-time-a-physical-entity-or-a-mathematical-model/page-11#entry945982

With new emphasis: What to make of that?

A geometric method for solving such applied mathematical questions would likely be of interest in either the relativity forum or in the homework forum. It will be of no interest here, except if that method provides a different explanation for the car example than the two models of reality already under discussion. Thanks, that's interesting input. I'm not sure if it is valid though... Maybe someone would like to come to the defense? Apart of that, regretfully: Those comments are a bit off topic here but certainly belong in the thread from which this one is a fork, for further discussion there: http://www.sciencefo...ematical-model/ I find that rather puzzling; I have to assume that you propose "the intergalactic medium of standard model particles" as an alternative explanation to either Absolute Space or Absolute Spacetime. Certainly such particles can't do all the things that are required, as discussed in the "mother" thread linked here above! I could access it, and if no one else does, then tomorrow I'll play the devil's advocate and I'll do my best to apply that view of reality to the car example.

Nice! For the benefit of the discussion I'll later give a matching sketch that is applied to the car example.

I could not follow your reasoning which seems to be based on a misunderstanding that I already clarified twice (and did you actually read studiots one page explanation?) but it's immaterial for this discussion. Either you know of a third "model of reality" for SR (and if so, please present it!), or you can watch the "fight" between two known models, and hopefully inject some more stimulating questions!

After a hasty read I see that you made a quantitative beginner mistake, which you can easily spot if you plug in 0.5c for "0.5s" in your symmetrical point of view, and then transform back to your first view, using your calculus: you will find that clocks are supposed to move at the speed of light! Transformations of relative velocities are more complex in SR than in classical mechanics. If you won't use the exact numbers then it's an irrelevant glitch, but else it needs correcting.

Yes indeed! Radioactive decay is a similar "black box". Science teaches us to be agnostic. I assumed that time involves motion for the same reason that I find it plausible that if aliens exist, they are made from matter - merely based on experience. I cannot prove that spirits don't exist or that, contrary to macroscopic experience, motionless physical processes could exist that we cannot observe.

So, picking up where the competitive explanation was left (still almost at the start!) Basic fact: similar to classical mechanics, you are free to choose the landscape as pretended "rest frame" (neglecting rotation), in which case your car is "moving". I will borrow from a recent thread a pictorial presentation of a fast car (original by bvr and improved by me): Different from common practice, we assume here that the car conductor has set up an inertial reference system according to the assumption that the car is in rest and the ground is moving under it. Moreover the car happens to be driving at the crazy speed of 0.86c. Let's say that there are clocks c1 and c2 above two openings in the car, and these clocks have been "Einstein synced". Now the car driver drops two balls, presumably simultaneously, so that from his perspective : _________________________ | | | |_ | ___ c1 c2 ___| / \--- ----1m---- ---/ \ _______\___/___o__________o___\___/_________ <- v According to the car the balls were dropped simultaneously at 1 m distance, so that they also hit the moving ground at 1 m distance. According to the ground however the car is length contracted, and the balls are not dropped at the same time so that they hit the ground at different times: _____________ | | | | | | v ----> / \- -----o-/ \ ____________\_/___o_____\_/_____________________________________ ______________ | | | | | | v -----> / \- ----- -/ \ __________________o________\_/2m_____o_\_/____________________________ Distance between the corresponding events as measured with a ruler on Earth in blue. Now the differing worldviews: 1. Stationary ether (Absolute Space model): When you are driving your car, in general both your car and the landscape are in motion, resulting in what may be figuratively called different perspectives of the same reality. This is an essential point to keep in mind before reading on. Only for simplicity of explanation we'll first pretend in this introduction that the landscape is, by pure chance, in "absolute rest". 1a. The car is then Lorentz contracted due to the car's motion through space, as would be expected if fundamentally all matter consists of some kind of waves. In this example one could (in principle) measure that the car is half its proper length. 1b. The car's synchronization is in this case also messed up due to the car's motion, as can be easily understood by working out the timing errors from the light pulses as they propagate through space (we may ignore the air). 1c. As per the relativity principle these effects combine so that according to the car conductor it seems as if the ground is length contracted. Moreover, just as was the case in Newtonian mechanics, the same relationships occur between two reference systems in uniform translational motion. In other words, both inertial reference systems provide in general a somewhat "distorted" perspective on reality. Note that these combined effects are not a "conspiracy", as the PoR follows from the conservation laws. 2. Block universe (Absolute Spacetime model): When you are driving your car, you are selecting or experiencing a slice out of Spacetime; motion is a perception caused by your Spacetime trajectory. "Time-out" for me; maybe a block universe adept will be so kind to complete the explanation by means of Spacetime trajectories that traverse the block universe at different angles, resulting in different perspectives of the same reality, and so on. It's essentially what is understood by "space" in studiot's reference in post #34 - thanks again studiot, for finding such a neat one-page summary.

It sounds as if you think that the block universe philosophy was the basis for relativity theory, or as if you think that relativity is not based on facts of observation; if so, please check out the first post (incl. the "mother" thread) and study the references.

What really triggered this topic were endless discussions in the relativity forum with members who either want to know "what really is going on", or who question the physical self consistency of relativity theory because "apparent" or "relative" effects can have "absolute" consequences, and they want to know how that can work. Relativity theory doesn't fully answer such questions because it's solidly founded on laws about phenomena that are based on observation: it's "shut up and calculate" on purpose. We know that we can do much better, and this thread is meant to satisfy their intellectual need to understand how it can be understood to work "in reality". And yes, for this thread to remain manageable I intend to limit it to basic stuff such as mutual length contraction, time dilation and kinetic energy. We may spin off threads on related topics.

Hi you seem to be an adept of block universe. I would appreciate it if you help explaining possible physical interpretations here: http://www.scienceforums.net/topic/98845-models-for-making-sense-of-relativity-physical-space-vs-physical-spacetime/

That's what happens when philosophy and hard science are mixed up. The "standing waves do not involve motion" mistake was already corrected in this thread and your model is an abstraction because atoms are black boxes to us. Sure I cannot prove that motion is involved; instead, I was looking for examples of which we are really certain that no motion is involved. But none of us could find one. And here we come to the heart of the matter: where Mach was agnostic about atoms because they were not observed, you go one step further and positively state that oscillations and energy transfer happen without motion because you don't see it and quantum mechanics is agnostic about it. In conclusion, observations don't tell us that your hunch is wrong; we can only provide examples of physical observations in which we do not (and perhaps cannot) know if motion is involved. Studiot you are mistaken: I am not the OP who appears to have already left the room - and I'm not going to waste my time over words either.

He certainly did not. Traffic lights don't even oscillate.

I was merely referring to bvr's "theoretical rest frame". Concerning Lorentz's ether concept, that's contained in many of his papers. Not so. It will be better that I continue the elaboration of the example with both models, then it will become clear without wasting words. You did not agree because your history is incorrect on two accounts... History is not the topic here, but it can be the topic of a spin-off thread if you know which forum to put it on (just let me know and I'll join the conversation). Ah yes, very good! We must cover that aspect in the comparative description. In both models it has a physical sense. [edit:] removed a remark about words Nice one! Indeed, the Lorentz "ether" may be a kind of misnomer from that philosophical perspective. But enough background information I think, it's essential to continue the competing explanations with the car example that bvr started, else this thread will not fulfill its goal. I'll do that tomorrow.

That's exactly what I meant with my Ferrari engineer example. And that's what the topic is here: you claim something that you did not prove and even doesn't make any sense to me; oscillation without motion is a contradiction in terms. I therefore insist: please explain how to create such oscillations without electron motion. I know of no such model, be it emission or absorption. PS. technically it's impossible to prove what really goes on inside an atom, but it will be interesting to understand your motionless oscillation model.

That's probably right, in view of this paper by Stokes: https://en.wikisource.org/wiki/On_Fresnel%27s_Theory_of_the_Aberration_of_Light Anyway, such a model is not compatible with SR. Your statement about physicists is not generally true. Historically ether theory was advanced by physicists, and block universe by a mathematician. I suspect that mathematicians and those with mostly mathematical skills prefer the block universe idea because "time", "speed of light" and "distance" are for them just symbols and variables. And for sure the mathematically difficult field of GR (at full precision) is practiced by mathematical physicists. Note that your "theoretical rest frame" is another word for "Lorentz ether". And indeed, the main purpose of this thread is to make relativistic effects fully understandable for skilled laymen and practicing physicists. For me also, ether theory makes more sense than block universe; but it is arguably uglier (at least, I disliked the idea) and for some people block universe is just what they need to make sense of relativity. [edit:] just one little correction: no matter which of the two models for SR you use, "when I'm driving my car, I know I am in motion, not the landscape" is imprecise. Perhaps this is a good point to start explaining by means of the 3D and 4D views of reality. Basic fact: similar to classical mechanics, you are free to choose the landscape as pretended "rest frame" (neglecting rotation). 1. Stationary ether (Absolute Space model): When you are driving your car, in general both your car and the landscape are in motion. 2. Block universe (Absolute Spacetime model): When you are driving your car, you are selecting a slice out of Spacetime; motion is a perception caused by your Spacetime trajectory. I'm not sure if I introduced the block universe model altogether correctly as I don't find it intuitive; please correct if needed. Maybe my intuition for that model will be improved after the discussion here.

Obviously my illustration of atoms was clear for you, as you did not ask about that. Let's not deviate here from the topic which already has a wide scope. [edit:] But I now recall that I summarized Einstein's reference to Newton in the mother thread, maybe you would like to challenge their argument there. It is clear that you did not even look at the references that form the basis of this discussion, nor the summary of some of those references that I gave in two posts in the "mother" of this thread. As for mathematical elegance, there can be no difference between the same mathematics - that is just nonsense! See: https://en.wikisource.org/wiki/Translation:On_the_Dynamics_of_the_Electron_(June)and https://en.wikisource.org/wiki/Translation:On_the_Dynamics_of_the_Electron_(July) Anyway, nature can't care less about our taste of elegance and the discussion here focuses on physical understanding. That is somewhat mixed up, I would say. Decomposing: The Newtonian notion of space is not very different from the Lorentzian notion of "ether" (perhaps he should have used another word?); no additional "medium" is required. Minkowski's notion of space-time is 4 dimensional spacetime, as expressed by him in the reference I gave; it's nowadays called "block universe". What you call "the 3+1 dimensional notion of Minkowski space-time" is probably the 3+1 dimensional notion of Poincare space-time; you can read about it in the link I provided. That's also the notion of Langevin, who explained in great detail Minkowski space-time equations and the effects on our conceptual understanding of space and time. And he explained, as I summarized already in the other thread, how they have a bearing on the ether (perhaps you would say space or space-time). I agree that Poincare's invariant space-time interval can be nicely illustrated by means of Minkowski space-time diagrams. You probably did not know that in 1907 Einstein published a paper in which he presented the preceding work of Lorentz and his own as one and the same theory; and that was so because he considered the mathematical predictions, and not differences in philosophy. His own philosophy changed several times anyway. PS.a historical discussion is not the aim of this thread; nevertheless providing a bit more context was perhaps useful.

"The existence of tangible space": "No such thread found" [edit:] do you mean that it was a comment hidden inside another topic? However I just started a thread related to the debate between 3D+1 and 4D, as linked in the post just before yours. And what follows sounds rather inconsistent to me: I just summarized Einstein's explanations of why GR implies some kind of ether, see my preceding posts # 212-215. I agree that it's not "tangible" in the sense of "material", indeed it cannot be measured like that. But there are other physical measurements of space, some of which already mentioned.

Thanks for the precision! The next sentence clarifies: "The resulting detected beam current goes through a maximum when the frequency of the radiation field is swept through the resonant frequency of the cesium transition". I can understand that someone who builds Ferrari's may be annoyed when an average car user states that of course cars use roads to drive on, because the engine turns the front wheels which in turn push on the road; he may say no "not at all", high performance cars don't do that, "you are totally wrong". However that doesn't matter for the question if cars use roads to drive on.

Perhaps the clearest is to relate to the conceptual model of atoms, see http://link.springer.com/article/10.1007/s10838-009-9109-x : Even without hard positive evidence, atoms had explanatory power as to the "why" of certain mathematical predictions. Perhaps you can agree that such a concept can be useful to make for example sense of the mathematical formula's of vacuum pumps. The references I provided tell me a very different story than you give here [edit: what else happened in 1911?], and I'm hardly an expert on the history but I did a lot of reading after I discovered that it's a mistake to trust textbooks. Lorentz was not a philosopher, as far as I recall he merely assumed, following Maxwell, the existence of a medium that serves as reference for EM wave propagation - but by extension, also the existence and motion of matter. Such an ether model can itself not be material. If you wish, I can first present for example mutual time dilation as explained with the Lorentz ether, and next I or someone else can do the same with the block universe. However it may be interesting to first follow up on the subtopic started by Sensei in post #6, as an elaboration of that includes mass, energy as well as the magnetic field concept. And I'm afraid that different people may understand different things with understanding the Universe as 3+1 dimensional; but block universe strongly suggests "4 dimensional". Maybe that's the starting point of the Great Debate.

There is kind of fools play going on in these circles in which a big dose of philosophy is "packaged" inside physics, and then sold as experimentally confirmed physics - a bit like the sub-primes affair. But as far as SR is concerned this is merely a presentation of the mathematical relationships of the Lorentz transformations. It's up to you what view of the "world" you adopt as plausible working hypothesis.

That's even more wrong than I suspected: as clarified in the cited reference, Lorentz's ether is not mechanical in that sense as it does not propose a material ether; and I I'm pretty sure that also Minkowski's block universe doesn't match that description. [edit:] Note that, if one wants to make any sense of the popular odometer illustration, a block universe does require something that can be compared to the "ground" that is required for the odometer to function. But it would be a mistake to think that the block universe therefore is made of some kind of rigid fluid!

You are indeed hijacking this thread with off-topic comments. However, you raised the interesting subtopic of understanding the reality of kinetic energy, and which I intend to clarify. One may ask if red is better than sweet; the scientific jury will hand it over to the philosophical jury. Emphasis in bold mine: Indeed physics is, ultimately, just math. Except for die-hard mathematicians, most people like to understand the "why" of mathematical relationships in physics. For example Newton's theory did not only improve the mathematical predictions, it also increased physical understanding. Similar atomic models no doubt improved physical understanding long before atoms could be observed.

As too all often in philosophy, it depends a bit on what associations are triggered by a word. Dictionary: "having to do with machinery". Surely not! And note: your second comment was again in the wrong thread...