Tim88

The purpose of the Lorentz ether was to model and understand electromagnetic phenomena, as a guide for theoretical development (which was extremely successful). Without it, the second postulate is pure magic; or, as Einstein phrased it in 1920: "space without ether is unthinkable; for in such space there [..] would be no propagation of light". Also, the name "Lorentz transformations" was introduced by Poincare in 1905, and they were first presented by him in their symmetric form. And I forgot to comment on another remark in your post #99: you wrote "Einstein showed a preferred frame is unnecessary". Well of course, no such assumption was needed for the derivation (from the second postulate!); but may I remind you, the starting point of this discussion happened to be the choice between either a 3D Absolute Space or a 4D Absolute Spacetime, so it's misleading to pretend that the 3D Space concept implies a superfluous entity compared to the alternative. I discovered thanks to these discussions that it's quite the inverse: as one cannot avoid a form of presentism (to be reasonable one must include the observation of present time, be it by means of "presentism" or by means of "evolving block"), one has with "evolving block" an additional metaphysical entity ("eternal time") that 3D Space can do without. But now the conversation is really drifting. I'll abstain from more if it doesn't further contribute to the topic.

Elaborating on the asymmetry: physically it is not the same if the traveler turns around, or if the Earth turns around. That explains that the situation is not symmetrical. For the standard Lorentz equations to be valid, one must relate them to a reference system that does not change velocity, a so-called "inertial reference system" as also used for classical physics. Then it's the other system that will clock "less time"; simply put, it has been "more in motion" according to all inertial reference systems. Of course, that explanation suffices for the calculation but does not explain the deeper "why", as in "what is really going on". For our intellectual satisfaction and in order to make sense of it, one can imagine models for what may be going on "under the hood". Historically there have been two models that explained the deeper "why" (thus going "beyond" the experimental physics), as discussed in detail in the appropriate forum. PS welcome to the forum nicktallguy

And so the discussion ended in an infinite loop: According to Lorentz no frame is preferred for the laws of physics, Einstein admitted that SR corresponds with the Lorentz ether, and neither you nor anyone else could show that presentism according to your definition (as I cited in post #93) is incompatible with SR. Note that an important feature of SR is that it is a pure theory of physics, free from metaphysics; that's why Lorentz, Einstein and Minkowski could agree on it, and why physicist hold that it's firmly established.

Yes that's right. And perhaps it's not related to what the OP had in mind anyway... let's see! (where is the OP?)

Not no, but yes. Elaborating on this brings us rather off-topic and It was already discussed before, but just for completeness: - Evidently you don't understand the meaning of the phrase "as it were". As a matter of fact, I referred to that same 1916 book (emphasis mine): This was recently discussed in Modern and Theoretical Physics, here and here. - Just in case in you didn't notice, the other dates are not even near 1916. At that time he and the others believed in 3D space plus time, and Mordred thought that it's inconsistent with SR which they promoted - just as I am doing today. Coincidentally I stumbled on a 1907 paper by Minkowski, with one chapter "The Fundamental Equations for Æther." Which makes me wonder, what his metaphysics really was, for I always assumed that he did not believe in such a thing. It may be worth to start a topic on the kind of ether concepts that Minkowski and Einstein had.

Blueyedlion gave a good answer, the object is perhaps best understood as field excitations in space. Thus no space is "pushed away", nor is space "formed inside the object". But in fact, according to GR it does vary radially depending on what is in it. [edit:] And of course proper, or "local" length does not depend on what is in it, but locally even a 1 metre rod will be found to be compressed in a gravitational field when the length is measured optically.

I'll start off with repeating my rather un-philosophical remark that time is a comparative measure of the progress of physical processes (or the "speed" of physical processes, or, as you say, of the changing property of matter); just as length is a comparative measure of the extension of physical bodies (pieces of matter). And as before, I disagree with the insertion of the word "just", because measurements of "time" and "length" are very much physical -despite the fact that they relate to human concepts.

Einstein objected to that analogy as it could lead to the misunderstanding that objects are somehow "curved" in a fourth dimension. In my opinion, the easiest way to think about it is the way he thought about it: rulers are shortened in radial direction by the Earths gravitational field, but they are not shortened when laid along the surface of the Earth. I never tried to simulate that, but if you don't need extreme precision, the equations are rather simple (see the link above). So it should be not too difficult to run such a simulation on a laptop.

The literature is full of errors, and empty claims without evidence are useless for discussions. In contrast, I demonstrated how "time" works with a 3D Space interpretation of relativity; and you failed to show any incompatibility between such a relativistic time, and presentism as defined in post #93 just above (basically your definition). For me that settled the question.

Mordred, I'm not open to word games. Everyone agrees that if you squeeze the meaning of the term "presentism" into the straitjacket of Newtonian mechanics, obviously presentism is not compatible with relativity. And by next forcing the possible interpretations to exclude the relativistic interpretation of some of the founders of relativity, you automatically find other options as the only possibilities. That's not serious. Ask the people who developed SR in the first place why presentism (without classical baggage) has no problem with SR - or just ask me! For sure you missed something in their and my arguments; but evidently you could not come up with an incompatibility yourself, as you didn't mention one, or at least, not a correct one. Let's try this. You write: Morderd, do you mean that those who believe in presentism don't acknowledge the past and the future? And didn't you ever hear of "local time"? Further, do you claim that the relativity interpretations that I gave are "eternalism" or "growing block"? According to you, my interpretation can't be "presentism". Maybe I'm without knowing it, a "growing block" defender? However, that is not possible, for I quite agree with "time" as in your definition of "presentism" (which differs from that in some sources given by Memammal): "Presentism follows the logic argument the view that it is only the present "here-now" (the three-dimensional world at the moment `now') that exists. 1) the universe exists only at the constantly changing present moment (past and future do not exist) 2) the universe is three-dimensional" Note that item 2) is also what Einstein explicitly believed and took as factual in 1916. What did he not understand according to you?

Without rulers and clocks, such models cannot be tested - that's outside of physics. And of course, that's also not what such theories mean. They are still meant to be valid for an almost empty universe.

No, that's a logical error. The counterpart of natural physical processes (from which we observe time) is objects or bodies (from which we observe length, not "space"). Then your full "So" sentence becomes: "So with no rulers (including natural bodies) length would still exist. And with no clocks (including natural physical processes) time would still exist." Without matter and physical processes, "length" and "time" as currently defined in physics would not exist. For physics we do need operational definitions, and if we don't even have natural "rulers" (e.g. 1 el) and "clocks" (e.g. 1 day), we cannot proceed.

Yes, and that's perhaps a pity. Perhaps, because in retro-perspective my comment looks a bit more doom and gloom than I feel about it. In recent days after his election Trump sounds more reasonable, and perhaps that's what many anti-establishment voters gambled on. It may turn out not too bad, maybe even less bad than another Bush. For the world population the worst effect could be less reduction of global warming (which is still bad), as he ignores the scientific facts.

When you put your clock away, physical processes don't stop progressing and clocks don't stop ticking.

I wrote: I should perhaps have added an illustration, which I already gave in an earlier discussion. One can plot the equation F=ma in a graph, with for example F on the x axis and ma on the y axis. That gives you, as it were, a force-acceleration "world". Force is perpendicular on acceleration in that graphical presentation of the equation. That should not be confounded with the physics. As a matter of fact, the force and the acceleration do have directions, but they are in the same direction. Exactly. It happens that by chance I agree with Einstein's remark there. "As it were": as if it were so: in a manner of speaking -http://www.merriam-webster.com

I agree that it's classless and the excesses are shameful, but it's hardly surprising - for example Hitler and Hamas were democratically elected, but not everyone was happy about those events either. And while comparisons with Hitler are much exaggerated, for me the related question remains: How could someone who calls for things like torture and murder remain eligible for president? Has the USA no rules to prevent such an incredible thing? In my eyes, THAT is most shameful. This isn't anything like earlier elections in the USA that I know of, it's more like like the Philippines where the people chose another lawless guy for their president earlier this year - and hardly surprising, that madman likes Trump, and Trump likes Putin.

Right - according to your own operational definition, time is not happening when all perfect clocks stopped ticking. Yes, you already gave a good answer early on - time is, just as length, a measure (a "meter"). And I would not say "just a meter", as the word "just" makes it sound as of little relevance.

I fully agree; note that it's essential to not overlook the clarifying words "as it were". The only paradox I can perceive here is a confusion between mathematics and physics. Here we discussed a graphical presentation of equation 12.

Why would a block paper use anti-block terminology?? Any label has been "made up" by someone; point in case, Einstein made up the label "special relativity". You can call things as you like, as long as you clearly define them in order to avoid mix-ups. Once more, just tell me what you find unclear, or what you think could be self contradictory, and I'll explain it in more detail. None of us would make such a claim. Once more, if one of my examples needs more elaboration concerning "time", don't hesitate to bring up exactly where or how you think that it doesn't work. By the way now the pdf on block advocacy (#81) works also for me. There some straw men are set up just for the purpose of shooting them down, but -not surprisingly- no incompatibility is demonstrated.

I think that it's rather well explained in Einstein's appendix on Minkowski space. Thus the "time" axis ct is perpendicular on the spatial axes purely for mathematical purpose (eq.12).

That's not what my physics textbooks say; moreover an operational tautology can hardly be "sufficient" but can be helpful for making the concept concrete. Do you say that length is "what a ruler measures", or that temperature is "what a thermometer measures"? Time is a measure of the relative progress (or "speed") of physical processes, and indeed we use clocks for precise comparisons of time, just as we use rulers for precise comparisons of length.

I'll elaborate a little on this. Time doesn't have a true direction, thus it's also not a real vector. For example if you have a car, it has a counter of miles or km traveled. That distance can only increase - even if you travel back home. The concept of "time" is similarly cumulative.

Here you are saying that atomic "processes slow down" in a gravitational field. The label "time" happens to refer to just that: it's a comparison of the "speed" of physical processes. And many clocks use the frequency of a resonator as time base. All our words are human inventions, but they relate to observations of nature. In other words, with this topic you fabricated an artificial contention.

My first impression was similar to yours; however, as Mordred here beautifully demonstrated, it is possible to give answers that are solid, non-controversial. Despite the disagreements between him and me about some aspects of "time" on the philosophy forum, I agree with his statements here above. I think that's very useful and constructive.

In view of : The following remark is just funny: Apparently none of the current participants here adheres to either classical presentism or Minkowski block universe; all of us acknowledge the necessity of including the fact that we live in the present. Now, I already injected some of the feedback of this thread back into the thread from which this is a spin-off; my explanations about how the Lorentzian space concept works now include some clarifications about what that concept means for "time". I hoped that it was clear as well as that the "eternal time" concept is superfluous. I'll be happy to elaborate here how "time" works for any of those 6 examples. Just tell me what is not clear about any of those examples, and I'll try to explain it with more clarity.