md65536

Time is like distance. (They're both measures of lengths between events) You can walk from the door to the corner of the house and then back, and say, "I'm decreasing the distance that I walked," but you're not really. You're decreasing the displacement between you and the door. The total distance you've walked can only increase. Time as measured by clocks is like that, it's the total elapsed. The problem isn't that there's some hidden physical difference by what must be the "true physical meaning of time" and "true meaning of space", it is merely a difference between the measurements we're choosing to consider, and of choosing the wrong analogies to compare them. A temporal analogy to displacement might be the minimum communication time between two locations, which would be the length of a light-like path between them. This can be increased or decreased, but it's not a measure we call 'time'.

Looking at blogs.scienceforums.net/pengkuan/2019/05/ I hope I'm not violating the mod edit. This does not agree with SR. If Betty is inertial and the Earth changes inertial frames, Betty will age more. I haven't read the whole thing but I think you're making a mistake in section 2. You have the Earth and star S in an inertial frame, and they both change velocity by the composition of v and v, half way through the experiment. It looks like you're treating these two events as simultaneous in all frames, which you can't do. That will give you errors. It looks like you have the Earth travel a length-contracted distance away, and then travel a length-contracted distance back, but measure that in Betty's frame. If you'd done it completely, it should work out to the same as if the Earth traveled away, stopped, and then came back, and the full separation between Earth and Betty when stopped would be the rest distance, ie. the distance between Earth and S in their frame. I suspect that you're essentially having Earth teleport twice between its length-contracted distance and rest distance, in a time that Betty counts as zero. If it was accounted, she'd age more then. This is a guess, I haven't been thorough.

Yes, I misread your post as talking about a circular orbit centered on the observer's viewpoint, which is possible for larger orbits. It should be possible to completely negate the relativistic Doppler effect with such an orbit, leaving only negligible(?) gravitational Doppler shift including due to the observer's acceleration as the Earth rotates. In the case you're speaking of, where the orbit is not centered on the viewpoint, the spaceship approaches then recedes as it passes nearest the observer, and the Doppler shift from that would be much much greater than the shift due to the Earth's rotation. This is true even at normal "slow" satellite speeds. https://en.wikipedia.org/wiki/Doppler_effect#Satellite_communication --- Partial info and does not handle satellite at relativistic speeds.

This is incorrect. Unlike length contraction, time dilation doesn't depend on the direction, only the relative speed. There's no Doppler effect in this case, so you can "see" the true time dilation effect. You don't say if it's a spaceship year or Earth year, but the effects are the same regardless. Radio waves are light. You can describe it based on how it looks. The video below has some effects from the spaceship's perspective, including orbit at the end. Let's say we're talking one Earth year and one spaceship day. The spaceship would orbit about seven times a second in lowest orbits. It would appear slowed to 1/365 our time, so the one day of spaceship time would be seen over our year. Since the spaceship sends out a day's worth of signal and light, the light that it emits (not reflects) would appear very dark... 1/365th as bright. It would also be red-shifted by that factor. The spaceship would see blue-shifting and a year's worth of Earth's light/signals (and the sun's too) in a day, so it would be intensely lit, which is why it wouldn't necessarily appear darkly reflective. By the way, the relativistic Doppler ratio is \( \sqrt{\frac{1 + \beta}{1 - \beta}} \), where beta is the speed as a fraction of c. If you negate the speed, you get the inverse Doppler ratio. If you take the average of the Doppler ratio and its inverse, you get the Lorentz factor. So, if you have a spaceship traveling at constant speed through flat spacetime on a path that you can divide up into equal-length segments in one direction and the opposite, and have it arriving at its starting point in some inertial frame (eg. some point on an Earth orbit), you can see that the average rate of time seen passing in inertial frame is equal to the Lorentz factor. (Actually that's true for any constant-speed closed loop through flat space-time, but I can't think of how to see that intuitively.)

Based on the clues, they all did (except the original doesn't say Nick finished). You've never heard of the Millennium Falcon? It's the ship that made the Kessel run in less than twelve parsecs!

I've said about all I have to offer on the topic, and do not seem to have done anyone a stitch of good. So I'm bailing. Apologies for acting out of frustration.

I still think that this is consistent with Einstein's definition of simultaneity and with the convention used to define it. I don't see how it shows an improvement over Einstein. Einstein's definition of simultaneity is the standard definition still used today. Einstein used a convention in his definition, he did not claim the definition derived from experimental observation or from assumption. No one in history has provided a better definition, without a convention, that has replaced Einstein's as the accepted standard. No one has proven Einstein wrong or improved upon his definition. Unfortunately I'm deficient in maths to be able to express any of these statements in equations. If anyone has an equation that shows any of the statements are wrong, then I concede utter defeat.

Relativity of simultaneity and conventionality of simultaneity aren't the same thing. Your link's referring to the former. In SR you have eg. the embankment frame, with 2 Einstein-synchronized clocks. Those clocks aren't synchronized in the train frame (they might be according to some alternative convention, I'm not sure, but your link doesn't show that). In the train frame, some other pair of clocks will be synchronized. However, in SR they will be synchronized using the same convention (it is still Einstein-synchronization). The measure of simultaneity is relative, and different in the different frames. The definition of simultaneity used is the same in the different frames. Other definitions of simultaneity may work, but they're not needed or used in SR. We don't say that the embankment's clocks are "synchronized according to an alternative simultaneity convention" in the train frame, meaning that they read the same time according to some other set of rules, we say they are "not synchronized", meaning they are not reading the same time.

This seems rather ambiguous because they mention the issue but don't seem to address it. They mention the "problem of simultaneity", quote Einstein suggesting it is merely a convention, mention the "problem of clock synchronization" but no resolution, and cite a reference that says the one way speed of light can't be tested, except that it is phrased ambiguously as though suggesting it no longer applies: Regardless, it is generally agreed that the one-way speed of light is measurable given synchronized clocks, with respect to the particular sync convention. It's so hard to try to argue a mainstream position on a poorly understood issue around here without being called a dick, rude, and being accused of bashing. I'm not aware of the contradiction you're bringing up. I think it's based on a fundamental lack of understanding of SR. Sorry to say that, like I said I think your understanding of the philosophical, conventionality of simultaneity side of things is the best that I've seen, but your examples of alternative simultaneities, and claims that the Lorentz transformation require them, contradict SR. At best I think you'll have to show an alternative simultaneity is in agreement with experimentally verified predictions of SR. I don't think anyone has a hope of finding a contradiction in SR by using SR incorrectly, and with a decent understanding of SR it becomes hard to see any weakness where there is a possibility of contradiction. My position is that Einstein's convention has never been proven non-conventional. Personally I think it truly is conventional, and that physically meaningful simultaneity is merely a local measurement, something more like in general relativity, but I won't argue that because I'm not aware of anything to back it up.

It seems no one on the non-conventionality side is getting it so I'll try to explain. Einstein's definition of simultaneity and the clock synchronization method it enables, allow us to define whether two distant events are simultaneous in a given inertial frame. Yet, there is no way to say for sure that the two events really "are" simultaneous independent of the definitions. The answer to that is in the realm of metaphysics. There is no way to measure it without using some assumption that is equivalent to assuming the simultaneity definition. Even if multiple conventions give the same answer, that doesn't tell you that it truly "is". This doesn't matter in science, because Einstein's definition works perfectly fine, and the measurements are useful whether or not the events truly "are" simultaneous in some philosophical sense, while the answer to something that can't be measured isn't useful. If you argue that one of the related quantities (simultaneity, synchronization, speed, delay of light, etc) truly "is" the only possible physical reality, you can effectively derive that Einstein's simultaneity convention "is" in fact the only real one, even though such a fact can't be measured without effectively assuming it. That makes it a crackpot argument. I don't think anyone here arguing on the non-conventionality side is a crackpot, in the sense of knowingly promoting a position that contradicts science. I think the crackpot ideas on this side come from a lack of understanding.

Would some references suffice? I've cited a couple in support of my position.

As Andromacus mentioned, equivalent synchronization is achieved with the two methods. See https://en.wikipedia.org/wiki/Einstein_synchronisation: Yes. No citations. No statement on whether or not you accept that Einstein's definition of simultaneity is conventional (are you avoiding it because you don't know what that means?). Only "um"s and sarcasm and unrelenting deep-seated misunderstanding. https://en.wikipedia.org/wiki/One-way_speed_of_light: Do you refute this? Do you understand "all experimentally verifiable predictions of this theory do not depend on that convention"? As I understand it, that means that the experimentally verifiable predictions do not prove that Einstein's simultaneity definition is non-conventional, because if it was then the predictions of SR would depend on it.

As you say, "Slow clock transport gives the same result". This assumption holds only if the other does. Enough of this farce. Can you back up your crackpot claims with any citations at all? I'll start: https://en.wikipedia.org/wiki/One-way_speed_of_light 'The "one-way" speed of light from a source to a detector, cannot be measured independently of a convention as to how to synchronize the clocks at the source and the detector.' You refuse to say whether you accept that standard simultaneity is a convention, but you argue as if it is an empirical fact, seemingly not understanding the difference.

It still assumes that the transported clock's time is the same as the stationary clock's.

Is this about the one-way speed of light? Since when do members have to offer up substantive proof of accepted mainstream science? There is no known or accepted theoretical way to measure the one-way speed of light independent of some coordination of times at two locations. Unfortunately there is too much argument in this thread between people who don't understand conventionality of simultaneity, and one who doesn't understand special relativity. I don't see any common ground understanding.

Romer's measurement assumed universal time. It also works with standard simultaneity. Romer's measurement is based on changing delay of light as an observed object (Jupiter + Io) changes distance to the observer. This delay is not the same with standard simultaneity as it would be with other simultaneities. The one-way delay of light is not itself directly measured but is a consequence of standard simultaneity. Yes it's a one-way measure of the speed of light, but it is generally accepted that you can't measure a one-way speed of light without a notion of simultaneity. All of the arguments that standard simultaneity is not conventional, are based on things like "symmetry", not on experimental evidence.

This is Reichenbach's epsilon notation, I don't think it's been mentioned in the thread. A lot of "conventionality of simultaneity" work is done in the context of philosophy and I don't think it's up to par with scientific standards. Often, a writer will use an alternative definition of simultaneity, and implicitly redefine a bunch of quantities without making note of the redefinitions. So for example, if you have epsilon other than 1/2, the measure of "speed" that is different depending on direction is not exactly the same measurement of "speed" using Einstein's definition of simultaneity. Einstein did this first, and set the standard definitions for things like simultaneity and resulting definition of velocity, momentum, etc. Yet others will provide a different simultaneity definition, with a new measure of rate of motion, but they'll still call it "speed" even though it's not the same as the accepted definition in science. The quantity c is defined using the standard definition of speed; it makes no sense to me that it would change to fit some other new quantities that one might define. It is only some other measure, not the speed of light, that is different in different directions. The literature probably wouldn't agree with me on that, but I think they've generally been not nearly as careful as Einstein with their definitions and with hidden assumptions.

It's not magical. Einstein explains what is needed for measuring time in different places, provides it, and then can use it. That equation is beside the point anyway. It uses two times measured at A, and represents a two-way speed of light. It alone cannot be used to define simultaneity, or to measure the one-way speed of light. Simultaneity is defined just before that, without making reference to the speed of light. I incorrectly paraphrased Einstein as saying that given his definition of simultaneity, the one-way speed of light is measured as c. This is true, but it seems he didn't make that claim and didn't have to. Do you understand that Einstein defined simultaneity on its own, he did not derive it from an invariant speed of light? Do you accept that SR still maintains that definition of simultaneity, ie. that it is not certainly superfluous? This is important because a conversation about conventionality of simultaneity will not go very far if you refute that SR does make use of a convention.

No, that doesn't follow. In SR the respective signals from A and B travelled at the same speed, but were not emitted simultaneously in the train's frame (this is relativity of simultaneity, eg. the signals may have been emitted simultaneously in the track's frame). No, that's not right. You have the clocks synchronized in one frame. They're not synchronized in the other frame. Where they're not synchronized, they're simply not synchronized. That's not "synchronized using a different convention." I don't see an alternative convention that fits the definition of "synchronization", but if it's there I'd call that "different synchronization conventions that are consistent with the predictions of SR" or something like that. I should have said "I don't think it makes sense to look at it in way where one changes the definitions, but expects that the statements making use of them must still hold or else it's 'inconsistent'." But in Einstein's paper, he defines simultaneity and synchronization. If you provide alternative conventions, they don't use those definitions, and some statements that *do* use those definitions (such as the second postulate, I argue) do not apply to the alternative definitions, and that doesn't make them inconsistent. The statements are made with respect to the given definitions. But what is the meaning of t? Have you read the section "Definition of Simultaneity", in the 1905 paper? http://www.fourmilab.ch/etexts/einstein/specrel/www/ Einstein does NOT just assume d=vt has meaning independent of time (including simultaneity), instead he says that "speed" only makes sense with respect to the meaning of "time". That's surely why he avoids using speed in defining simultaneity (otherwise why mention it at all?). Paraphrasing, I think Einstein says, "Given this definition of simultaneity, we can define a one-way measure of the speed of light, which in agreement with experience we accept is always equal to c." How would you go about it the other way, given Einstein's quote above? Is this fair: "Without a definition of simultaneity, there is no means of measuring the one-way speed of light, but let us assume that it is equal to c, which then gives us a definition of simultaneity, which gives meaning to the one-way measure of speed that we've used." How do you avoid problems if you define time according to an assumption about speed, if the meaning of "speed of light" depends on how you define time? By the way, I'm sure this is true. You seem to have a better understanding of simultaneity and conventionality arguments than anyone I remember posting here, definitely better than mine and I've focussed on simultaneity more than anything else in science. But I haven't bothered with Malament etc much, because when I look into stuff like that I find too many people go off track, focussing on things like "symmetries" which add additional assumptions, and too often they lose sight of the core theory, so I've focussed on Einstein's stuff. Where I think you've made statements that contradict SR, I can't get past that to try to understand what you're saying.

I mean he makes no mention at all of any concept of speed in his definition of a common time at the two locations. Propagation time of light isn't the same as speed. No it doesn't follow from that protocol. Simultaneity is by definition, and invariance of speed of light by assumption. Indeed, after defining synchronization, Einstein specifically states (at least according to this translation), (emphasis mine) So I may be nitpicking, but when I went from my initial misunderstanding that Einstein assumes his definition of simultaneity describes reality (he doesn't, he simply makes use of it as a tool without commenting on its reality, which is what allows SR to be compatible with conventionality of simultaneity in the first place), to realizing what he has actually done, and how the way he did it is "bulletproof" (you can't prove a definition is "wrong", even if you could find it somehow doesn't conform to reality)... it gave me a sense that Einstein knew exactly what he was doing and was extremely careful, while so many others since have been too sloppy with their assumptions. Say on the other hand that Einstein didn't do it this way, but instead just assumed that the speed of light is equal to c, and from that concluded that events are simultaneous in accordance with Einstein-simultaneity. Then the definition of simultaneity is assumed to be true, and essentially that simultaneity is not conventional. This would be a mistake, I believe. Einstein truly seemed to grasp that we had not (still haven't) been able to measure whether two distant events are truly simultaneous or not, and it is only within the context of some assumptions that we can say they are. Equating equal timing and equal speed requires another assumption, that too many people make. Einstein's definition is free from problems or ambiguities in all of these intricate details that people could argue over.

I don't think that's true. I think you could make the case, but that might involve circular reasoning. I think at best you could start at either point and get to the other. In Einstein's 1905 paper, he doesn't use the speed of light in his definition of synchronization. http://www.fourmilab.ch/etexts/einstein/specrel/www/ It is only time, and not speed of light that is used here. Next, the travel times of light signals are used to define synchronization. THEN the quantity equal to the speed of light is assumed to be a universal constant. You can do it the other way around, but not without making some similar assumptions. A one-way speed between two points but measured by a single observer needs some way to relate the time at the different locations. If you define speed first such that the speed of light is invariant, and use that to synchronize clocks, I think that you have already implicitly defined simultaneity in your definition of speed.

This sounds like a misunderstanding of some basics that makes it difficult to make sense of the rest of what you're saying. In the famous experiment, all of the individual observers are inertial, and they all measure a one-way speed (using Einstein synchronization or Einstein's definition of simultaneity) of light that is equal to c. No different one way speeds of light are needed. The different observers measure time differently, but they also measure distance differently. There is no inconsistency in SR that you're speaking of. SR does not state whether or not Einstein's definition of simultaneity, and the resulting means of synchronizing clocks and measuring one-way speeds with a single observer, are conventional. SR is simply presented in a way that makes use of Einstein's definitions, so I think the second postulate must be read within the context of those definitions. If simultaneity is not conventional, and if Einstein's definitions are the only ones that truly "work" (eg. if we found evidence that ruled out other conventions), SR remains consistent because there is nothing in it that requires conventionality (I believe you're mistaken about that). If simultaneity truly is conventional, a formulation of SR that makes use of only one convention (as Einstein's) remains consistent. You have some definitions (eg. simultaneity). You have some quantities and measurements (eg. v) that use those definitions. You have some statements based on those measurements (eg. second postulate). I don't think it makes sense to look at it in way where you change the definitions, but expect that the statements making use of them must still hold or else it's "inconsistent".

Some types of compressed files can be compressed further, losslessly... http://www.fastcompany.com/3050180/tech-forecast/these-engineers-just-built-their-own-pied-piper-compression-algorithm yet it is known that there is no possible algorithm that can losslessly compress all possible input data. This puzzle's about that. ---- There is a type of data stream that is a fixed length N bits of binary data. The data is statistically random; every possible variation of 0s and 1s is as likely as any other. There is an optimal lossless compression algorithm that reduces the data size of as many of the possible data variations as is mathematically possible, and produces a variable-length output of M bits. The uncompress algorithm knows the value of N and the size of the compressed data stream. 1. How many of the possible data streams cannot be compressed, ie. where M >= N? 2. For large N, what's the average size savings achieved by the algorithm? 3. Describe or write pseudocode for such an algorithm (compress and uncompress). 4. The CEO of Hooli is offering $1M for your algorithm. Do you take it, or try to develop it with your own startup company?

Is rotation in higher dimensions also ruled out? This is purely speculation... Imagine a one-dimensional universe embedded on the equator of a rotating sphere. Different centrifugal force and preferred direction would be seen on the surface of the sphere, depending on phi coordinate or latitude. The center of rotation is on the r coordinate. In "flatland" style, the 1D beings seeing only the equator would see no preferred direction or center, and inertia/centrifugal force would appear as a homogeneous, isotropic expansion force. Is it possible that a rotation in 5D (or 4D?) could hide a center and preferred direction? Have you watched the Krauss "Universe from Nothing" video linked earlier? It explains how it is possible that a universe, consistent with measurements of our own, can exist with 0 net energy. I think it shows that questions like "what came before that, and what was its cause (ie. anything making or "wanting" the big bang to happen)?" don't need to have answers... or that the answers might just be "nothing."

Then the conclusion would be that there are places with nothing, and that gravity has no measurable effect on nothingness? I suspect everyone could agree on that (if little more than that). Measurements are consistent with a flat universe, but only "on the largest size scales." There is a lot in between "local" and "largest scale". It is not flat on scales of stars and galaxies etc. In areas where expansion dominates, measurements are consistent with both expansion and gravity being present. In areas where gravity dominates, measurements are consistent with both expansion and gravity being present. It's not like only one may occur in a single place. The facts as we observe them are consistent with accepted theoretical physics, if you're claiming otherwise (without the evidence) then you're talking about speculative theory.