Tim88

I implied with that the exact contrary of what you read in it. As you may have clarified yourself, physical models such as for example virtual photons cannot be directly observed, they are part of metaphysics as defined in wikipedia (not everyone groups metaphysics the same, but let's not quibble about words). In contrast, QM and SR are founded on mathematical models which in turn are directly based on observed phenomena. Yes, absolutely! Most revealing is next the derivation of time dilation and length contraction, which is one way or the inverse depending on which time interval is put to zero. That simple, basic mathematical understanding cannot be compensated by innumerous space-time diagrams or hundreds of words. In the new General philosophy thread I intended to discuss two competing (and very different) models for making sense of, among other things, your topic no.1. Coincidentally, someone else introduced the topic of energies in there, and so we'll likely also discuss that mystery.

On your question: I doubt that "mechanical" is a fitting term for either Lorentz ether or Minkowski block universe. And on your comment: much more has been said already in the thread from which this is a continuation in part. Please discuss that there, and not here. - http://www.scienceforums.net/topic/97105-is-space-time-a-physical-entity-or-a-mathematical-model/ PS. I see that you participated there in the beginning, and I fully agree with your remark that "it becomes confusing very quickly, this is the nature of metaphysics". You may have overlooked the last part of my sentence: "we are condemned to "shut up and calculate"." I'm not aware that such equations are paradoxical or mind-boggling in nature; and as I explained, this discussion is not about mathematical ability. But perhaps you can (qualitatively) explain why nature imposes a "relativistic" mass term [math]\gamma m[/math] instead of a "Newtonian" mass term m, and how nature does it, physically.

Dear Michel, the key to the confusion is what I warned you about several times: VandD is -mostly- not discussing the ("simultaneous") distance measurement of the ground by the car. Instead, after the first two lines he is discussing a completely different measurement: the simultaneous measurement (for example with laser pulses) of the length of the car by the ground! In fact he also warned you about that, as follows (emphasis mine: "For the length contraction of the car the scenario is different (see my previous sketches)." As for that part: Yes indeed!

Bold face emphasis mine: Perhaps I should have summarized the thread from which this is a spin-off, in order to prevent such misunderstandings... I use here "physical" in contrast to your "mathematical". [edit:] I now added a short clarification to the first post - thanks! If you deem that the phenomena can be reasonably explained without a physical space or spacetime, then your comments are welcome in the thread from which this is a continuation in part. In contrast, this thread is meant for those who do believe that there must be more to spacetime than a mathematical framework, as well as for those who are looking for more than mathematical understanding.

I wrote "until"; you read "after". Once more, Mach did not believe in atoms. Atoms were a conceptual model for many centuries, but only last century we could really observe them. And I'm not labeling SR as metaphysics; it's unclear why you would think so. SR is a theory based on postulates which were presented as principles instead of physical models.

That's a somewhat different clock operation principle than the ones that I read and heard about - interesting! Please reference a paper that discusses its operation.

I now started that spin-off topic here: http://www.scienceforums.net/topic/98845-models-for-making-sense-of-relativity-physical-space-vs-physical-spacetime/

-- This is a spin-off of the thread "is space-time a physical entity [..]" -- A lot of people think that special relativity doesn't make sense and that it's hopeless to try to understand it; we are condemned to "shut up and calculate". However, I know of two physical models that can be used to explain the theoretical predictions, and possibly there is another model that I don't know of. [edit]: To be perfectly clear, with "physical models" I here mean two competing hypothetical physical entities that have been proposed to make sense of the phenomena as described by relativity theory. Right from the start it was perfectly possible to make sense of relativity by means of Lorentz's ether model. That model is quite different from the preceding material ether theories; one may just as well call it physical space. Einstein hoped to get rid of it for philosophical reasons, but others such as Langevin still made use of it[1] and in 1920 Einstein even expanded on the Lorentz ether for general relativity[2]. But in the meantime Minkowski had introduced a new interpretation of the Lorentz transformations, according to which "only a certain union of space and time shall retain substantiality". He even replaced the first postulate with a stronger one, the "Postulate of the absolute world"[3]. In the beginning his radical interpretation was mostly ignored (as in [1]), but in later years this physical spacetime interpretation became popular, and it is commonly called "block universe". It will be useful to discuss these models and their implications here, and in particular the explanatory features of each model, as each answers questions such as "what is really happening" slightly differently. Other things worth mentioning, are presentism vs eternalism and true symmetry vs. phenomenological symmetry. I may start off with discussing the different explanations of mutual time dilation; but if there is a more urgent aspect of interest, we can go with the flow. I can imagine that this topic will generate several child topics. Note: Once more, this is a spin-off of several current threads in the relativity forum as well as in this forum, such as http://www.scienceforums.net/topic/97105-is-space-time-a-physical-entity-or-a-mathematical-model/ [edit:] please don't comment on the general question "is space-time a physical entity [..]" in this thread but in that "mother"thread! This thread is for discussing two competing physical entities that can be used for explanations. Also, there were short discussions of more limited scope in 2010 and 2012: http://www.scienceforums.net/topic/44388-the-block-universe-concept-pros-and-cons/ http://www.scienceforums.net/topic/69780-the-block-universe/ [1] https://en.wikisource.org/wiki/Translation:The_Evolution_of_Space_and_Time [2] https://en.wikisource.org/wiki/Ether_and_the_Theory_of_Relativity [3] https://en.wikisource.org/wiki/Space_and_Time

Proper length is not a label that is reserved for one observer, excluding other observers; each observer has his own proper lengths. Possibly you misunderstood "proper" - that would explain a lot of the confusion! And probably additional confusion occurred because the example in the other thread about observing the length contraction of a moving car involves the inverse measurement of the example using Langevin's car with dropping balls, since the corresponding length contraction measurement is here the contraction of the distance on the ground. I'll retake your above statements and add precisions in bold; if you agree with the result, then you probably understand the meaning of that sentence now: I forgot to reply on this one, and I think nobody did. As I mentioned earlier, in this drawing is a glitch, but it's not essential for your question. Yes indeed: * Dground is the measurement of the ground taken in the FOR of the ground. * Dcar is the measurement of the moving ground taken in the FOR of the car. * Dground is longer than Dcar. * Dcar is shorter than Dground

You no doubt disagreed with a misunderstanding of what I said: it's hard to believe that you deem physical models useless for understanding! For example the atomic model could not be proven until the last century and was therefore still metaphysics; Mach did not believe it. But it facilitated physical understanding. As a matter of fact, many of your questions here fit Wikipedia's introduction description of metaphysics.

I do think that the topic of this thread is a matter of contention, so that I'm surprised to hear no counter arguments! By way illustration, we can think of a road with a strongly enforced speed limit. We see the cars on that road passing at varying speed, but (ideally) none surpassing a certain speed. Effectively that speed is not a property of the cars, but of the road. Similarly there is good reason to regard the maximum speed in nature c as a property, not of particles and radiation, but of the space through which they pass. For latecomers to this thread I'll now complete the list. 3. Einstein next discusses the fact that rotation affects the mechanical properties of rotating objects; again one should conclude that this is a characteristic, not of the object, but of the space in which it rotates - as Newton did. He omits there the reference to Newton's illustration (or experiment), which I'll add here for those who are not familiar with it: https://en.wikipedia.org/wiki/Bucket_argument#The_argument Then Einstein goes on to refer to Mach, as he included (somewhat) Mach's principle in GR; and Mach intended a purely relational theory, in which rotation is purely relative. However, in GR the effect of distant stars acts locally and not instantly at a distance; thus one arrives again at the concept of an ether. However, this GR ether is itself conditioned by masses. I also referred to Langevin: 4. First he mentioned the fact that acceleration is responsible for the creation of electromagnetic waves; if there is no physical space that corresponds to mathematical space, then there is nothing with respect to which such waves can be created. I can think of for example Brehmstrahlung as a good example. 5. As we know, the clock retardation in Langevin's "twin" example is absolute; it is a function of relative velocity, caused by the changes in velocity due to the non-inertial motion of the traveler. Thus he argued that in order to make physical sense of it, we should admit that these velocity changes must be happening with respect to something physical (the "ether"). I consider all of these good arguments for the claim that spacetime implies more than only mathematical space. However, probably most participants will agree with that generic conclusion, and the main contention is then what feasible physical interpretations are available. The main contenders that I know are the Lorentz ether (as enhanced by GR) and Minkowski block universe (again as enhanced by GR). The title of this thread doesn't give visibility to that subtopic, so I will later start the discussion of that topic in its own thread.

It appears that you claim that the explanations in the references that I know and rely on, are wrong. According to the cited references, atomic clocks are based on electromagnetic radiation. As I did not personally built such a clock, it is possible that I misunderstood something, basing myself on those explanations; however it is for me a self contradiction to speak of "oscillations" that do not involve "motion"! Maybe you overlooked the clarification that the word "conceive" in the OP could be misunderstood; it appears that is exactly what is happening here. [edit: precision:] the question was rephrased as: "What do current physical observations tell us about this connection?" PS. modern definition of second: "The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of cesium 133". In other words, I'm not mistaken about this. Observations involve EM radiation.

In post #37 I applied that sentence to the well illustrated example with the car. In that example, the car observers assume to be in rest (as observers in SR commonly do) so that the ground is moving fast under them. They drop balls on the ground, and the distance between the balls is constant from the time that they both hit the ground. In my variant of that example, the car observers measure the distance between the two balls on the ground as 1 m; and they think that these events are simultaneous. In contrast, the ground observers think that the balls land one after the other, and they measure the distance between the balls on the ground as 1.5m. As 1m is shorter than 1.5m, I agreed with Langevin: The spatial distance of two events that are simultaneous for the car observers, is shorter for them than for ground observers in motion relative to them.

Michael, it's unclear if you stopped replying to answers on your own question because: 1. you now understand it and simply forgot to tell us 2. you still don't understand it and gave up on it 3. you need more time to ponder over some of the answers, before you'll be back to this thread Which is it?

Robin I perfectly understood that you want to stick to a case in which all observers can agree that the travelling clock "lost time" compared to the stay at home clock. In my simplified version with only one acceleration step, that is the case. As several of us clarified earlier, acceleration matters for arriving at a different velocity (so that the traveler is not continuously at rest in an inertial reference system), as well for being able to return to the stay-at-home. And note that, in order to make it even clearer that the Lorentz transformations relate to velocity, there is also a version without acceleration: Instead of turning around, the traveler may send a time signal to another traveler passing nearby and who travels in opposite direction. If that other traveler adopts the time of the first traveler at the instant of passing, the SR prediction is just the same for the predicted clock difference when that last traveler passes the Earth clock. PS: Probably that is what Celeritas meant with "the all-inertial time-handoff scenario". Hi Michael, after "knowing" SR for a long time (that is , knowing how to calculate), I was confronted with the same issues some 15 years ago and in my opinion this is due to the purposeful lack of a physical model in SR so that models automatically are "metaphysics". Happily Scienceforums has a philosophy forum on which currently already a thread is open on a related topic. If nobody else does it then I'll soon start a spin-off topic that should be helpful for you (and probably also Robin), discussing two possible models to "make sense" of SR.

bold emphasis mine: Are you not complicating things unnecessarily? I'm just asking, as I don't really know what you have in mind, but the simplest case is a traveling clock that is passing the Earth's clock at high speed and later turns around and passes the Earth's clock again. Only one acceleration step involved, and roughly the same prediction about the difference in clock times between the two events.

It's unclear to me if your "not really" refers to the subject matter or to an imperfection in my phrasing... and "superposition of states" is agnostic about the physical mechanism. While we cannot know (yet) the internal mechanism of the creation of EM waves inside atomic clock atoms, we can find plausible explanations on the web, such for example http://science.howstuffworks.com/atomic-clock1.htm As a matter of fact, we understand the creation of EM waves at radio frequencies rather well - and that works by means of electron acceleration (e.g. https://en.wikipedia.org/wiki/Electromagnetic_radiation ). So, if with your remark you meant that you know how to create EM waves without electron motion then please explain. I'm looking forward to hear it.

With a little correction by me: At a first glance that's quite correct I would say (not nitpicking on "loosing time" but making the shown correction). In particular your last statement shows improved understanding in accordance with SR, as it's easy to identify a group of reference frames according to which in a part of the journey the traveling clock was advancing on the stay-at-home clock.

I was just in the process of rephrasing my clarification to swansont which you already cited, I'll make sure to keep it practical. In fact you simplify my rephrasing. Apparently we both read the question upside down! Thanks, that's reassuring to me. I will elaborate my corrected reply. Thus, can there be motion without time? The point of contention is if motion implies time. In logical deduction it often helps to test with less abstract examples, such as: Can there be a bicycle without wheels? -> The claim for discussion: a bicycle implies wheels. The contention is NOT if wheels imply a bicycle! Similarly: Can there be motion without time? -> The claim for discussion: motion implies time. I now think that you meant it the way I first understood it, which is the inverse of what you actually said (or else I'm too tired now). Maybe you managed to confuse everyone. Atomic transitions can be understood as a kind of movement, as it relates to the creation of an EM wave by means of an electron jump. - https://en.wikipedia.org/wiki/Atomic_clock [edit: slight rephrasing; better link]

[edit: removed other answer that I'll rephrase later] I'm pretty sure that the topic here concerns the physics of motion; it may be useful if geordief clarifies this point. I can imagine that you were not aware of hijacking and strawmanning; thus my negative impression may have been unwarranted. A limit is not a disconnect. Time on a light-like path corresponds to the progress of physical processes in a physical entity going at the speed of light. We all know that no massive clock can go at the speed of light and no valid reference frame can be set up at that speed. I could stop there and simply conclude that your reasoning is therefore invalid: http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/headlights.html Nevertheless in my opinion Gibbs made it too easy on himself, so I'll join you in your Einsteinian ride on a light wave, without fear of paradoxes. Clock rate is indeed zero in the limit: the wavefront of a light wave in vacuum is unaltered over its trajectory, just like a "frozen" clock. But contrary to what you suggested, a photon "experiences" no time nor distance. However from our perspective it can travel a great distance in a short time and in zero proper time, or as first phrased by Einstein (who was a physicist, not a mathematician): PS §4 of http://fourmilab.ch/etexts/einstein/specrel/www/

In philosophical discussions there is an increased risk of misunderstandings due to a variety of possible meanings of words, but regretfully, what happened here doesn't look like an innocent misunderstanding. The topic here as I interpreted, is not about math but about physics; and my understanding of the topic could not reasonably have been misunderstood, in view of how I defined time in the post to which you responded. Logically I had to assume that you were still talking about a physical wave of the kind that I mentioned and even you also mentioned just before: Once more, such standing waves consists, according to standard physics, of propagating waves - as you seem to acknowledge yourself. See also https://en.wikipedia.org/wiki/Wave. Nevertheless, looking back at the discussion I notice a glitch in my answer to the first post, I phrased it the wrong way round (thanks Strange for pointing that out!): In my mind it is not possible to conceive of motion without the concept of time, as time is a measure of the progress of physical processes. Thus motion implies time.

Yes indeed! I'm now finally ready to leave this thread, thanks for the interesting discussion.

I agree, only it's generally assumed that such decisions are the result of a multiple causes - such as don't have any ice and you are too tired to go to the shop, or the shops are closed, and so on. A bit like with the weather, which is assumed to be causal but still difficult to predict, with many input variables. I'm not sure if a predestined future is the same as a fully causal future.... Can't block universerists assume predestined random processes?

Bold face emphasis mine: That commentary on the Didache is interesting indeed, although it doesn't add much to what one immediately understands when reading it the first time. And I found it striking in the context of this discussion that it pretends that parousia means "return", while according to dictionaries it basically means "presence" or "coming" . Bible translations and commentaries are full of such manipulations. That early Christians expected his return is pure speculation. I stated effectively the opposite of what you thought, sorry that it was a bit ambiguous. I did not realize that 'That does not leave much for a historical Jesus' (and followed a few lines later by '"Historical Jesus" (or, what is left of him by "mainstream")'), can be read as "that does not leave much room for a historical Jesus". I meant that the historical Jesus in the mainstream account according to you is left with very little - and I implied that this leaves much leeway for the historical Jesus. You could therefore have saved yourself the effort to convince me that with just a little fantasy one can put a historical Jesus in that context. The "smaller" a reconstructed historical Jesus gets, the more the reconstructed puzzle by "historical Jesus people" resembles the reconstructed puzzle by "mythical Jesus people" - with many pieces even at exactly the same place. The Talmud doesn't add anything in my opinion, especially in view of your insight that it has some strong resemblances to the one of the gospels. One can use that as evidence that Jesus was historical as well as that Jesus was not historical, depending on one's reasoning. Further, if we assume that some of Paul's letters are mostly authentic, the hellinisation of Christians was already going on in the first half of the first century, by means of Paul himself. And finally, I forgot to add to my earlier message the possibility of a combination, merger or compromise between the "historians" and "mythians", but you reminded me of that by pointing in that direction with "One may very well argue why a historical Essene preacher, who might had nothing to do with what later became the Pauline and Johannine inspired Christianity, is of any significance other than him being used (post mortem) as the symbol for said religion." It is possible to come up with a reconstruction that would be at more or less at the limit, where Jesus is so much reduced that he serves as little more than a coat hanger for the concept "historical Jesus". Then some people would still speak of a historical Jesus theory while others would call the same reconstruction a non-historical Jesus theory. As a matter of fact already one "mythicist", Robert Price, wrote a book "The Incredible Shrinking Son of Man" and is said to have stated "There may have been a real figure there, but there is simply no longer any way of being sure." - https://en.wikipedia.org/wiki/Christ_myth_theory#Robert_M._Price I think that we have sketched the outlines of the debate rather well by now; if any onlooker would hope to find a straightforward answer here, then we must disappoint that person, as it's very much left to personal opinion, which, I dare say, cannot be reasonably formed without spending several months of serious study effort on it.

Sorry, I cannot understand how you could think so from my clarification that "stationary waves [..] are fundamentally built up from traveling waves" and "without time traveling waves cannot be created - even if one neglects that physical fact in the mathematical equation". Thus I have to ask in turn: are you suggesting that you can create a standing wave without time??