yknot

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1. Does the train example show relative simultaneity?

swansont, on 17 Nov 2013 - 10:11 AM, said: >Synchronization requires clocks to run at the same rate. Clock frequencies vary by gamma from frame to frame, so clocks in different frames run at different rates. Q.E.D. No, clock synchronization does not call for equal clock rates across frames; it just requires that the clocks in each frame are related in some way, preferably correctly (i.e., absolutely synchronized). (In order to determine event order, all you need is a pair of synch'd clocks no matter what rate they have as long as both have the same rate, as they will if they are in the same frame.) >You're also wrong about proving a negative, because this is not a matter of data or evidence. The statement is a ramification of the theory, which means the prediction is mathematical and it is possible to prove a negative in mathematics. Math is not physics. And how would you prove that two clocks cannot be absolutely synchronized? This could happen purely accidentally or by the random thumpings of a herd of monkeys, so it is indeed physically possible. >It is observed not to agree with how nature behaves. It's also disagrees with electrodynamics, a very successful theory. Einstein said otherwise. He said that given the clocks of classical physics (and he never said that such clocks cannot exist, only that we should discard them and replace them with his asynchronous clocks), light's one-way speed will certainly vary with frame velocity. [Quoting Einstein:] "w is the required velocity of light with respect to the carriage, and we have w = c - v. The velocity of propagation of a ray of light relative to the carriage thus comes out smaller than c. But this result comes into conflict with the principle of relativity.... For, like every other general law of nature, the law of the transmission of light in vacuo must, according to the principle of relativity, be the same for the railway carriage as reference-body as when the rails are the body of reference." http://www.bartleby.com/173/7.html Actually, this does not come into conflict with the principle of relativity because that principle just calls for everyone to have the same general laws, and in this case the general law is w = c ± v. There was never even an apparent conflict, so there was never any need to invent a theory (SR) to "fix" it . >It agrees with how nature behaves, to within experimental error. It's also consistent with electrodynamics, a very successful theory. Here we have a major problem; there has never been any experiment showing light's invariance between two mutually-at-rest clocks; in fact, this cannot even be shown on paper (no matter how much math you use).
2. Does the train example show relative simultaneity?

Since a negative statement cannot be proved, I ask for evidence. You have a lot of nerve accusing someone of selective quoting without having even looked at the source. I think that you owe me an apology. And who better to learn SR from than the originator? And the whole point of E's work cannot be to show that absolute synch is impossible because such a negative cannot be proved. If you know of such a proof, then state it. I further resent being labeled close-minded this early in the game. See my last post for this "session." As for my statement that events are observer-independent, here is someone else who stated that: [Tom Roberts wrote:] This is a foundation of modern physics: all physical phenomena are completely independent of coordinates, because Nature quite clearly doesn't need or use coordinates. Coordinates are merely tools of description, and artifacts related to the choice of coordinates cannot affect physical phenomena, only the _description_ of them. There's no reasonable definition of "real" that makes _descriptions_ be "real". http://groups.google.com/group/sci.physics/browse_frm/thread/d4ac4d13086ac07e/a29b0e07db6f1f8b#a29b0e07db6f1f8b Maybe you would like to argue with Tom? What, specifically, is "wrong" with the Galilean trans. claim that light's speed from point A to point B varies per inertial frame? OTOH, what is "right" about relativity's claim that light's speed from point A to point B is c in all inertial frames? To whom it may concern: Einstein's embankment observer says that he was centered on the events when they occurred, and he also says that since he need not take into account any movement toward either light ray, he can safely conclude that the events occurred simultaneously simply because the rays from the events reached him simultaneously. Similarly, Einstein's train observer says that he also was centered on the events when they occurred, and he also says that since he need not take into account any movement toward either light ray, he can safely conclude that he events did not occur simultaneously simply because the rays from the events reached him at different times. After being adjacent (or side-by-side), the two observers separate. Since they are in different locations when the light rays arrive, they _cannot_ see the rays in the same way. (This was even hinted at by Einstein when he said "If an observer sitting in the position M’ in the train did not possess this velocity, then he would remain permanently at M, and the light rays emitted by the flashes of lightning A and B would reach him simultaneously, i.e. they would meet just where he is situated.") Clearly, this has nothing to do with how the lightning events occurred, but everything to do with the spatial separation of the two observers. Just as clearly, it is improper to use light signals from events to judge their time order if observer differences (such as spatial separation during the observation) are completely ignored. One way for Einstein's observers to validly use light rays from the events to judge their occurrence order would be if each observer knows how he moves in relation to the rays. For example, if the embankment observer knows that he remains centered on the approaching rays, then he can he validly claim that the events occurred simultaneously. Of course, the best way for observers to determine event order is simply by placing truly synchronous clocks at the events in question. Here is how Einstein described such clocks: "[in classical physics] [t]he simultaneity of two definite events with reference to one inertial system involves the simultaneity of these events in reference to all [other] inertial systems. This is what is meant when we say that the time of classical physics is absolute." [Einstein's book _Relativity_, p. 149] Yes, Einstein decided to discard such clocks (because he wrongly believed that they violated the principle of relativity), but he of course could not prove the negative that such clocks cannot exist. All that is needed is some method for truly synchronizing clocks. And after discarding truly synchronous clocks, Einstein replaced them with absolutely asynchronous clocks, but such clocks cannot possibly make correct measurements. As we all know, events are independent of coordinate systems, and two events can occur in only one way, and clocks should reflect this simple fact. For example, two people born on opposite sides of Earth will reflect the fact that they were born truly simultaneously by remaining practically the same age, so clocks should also reflect this.
3. Does the train example show relative simultaneity?

yknot said: Question: Would sim. be rel. given truly synch'd clocks* AT the events? Strange replied: >See Janus's answer above. He made no mention of truly synch'd clocks, but Einstein did, saying that simultaneity would not be relative given such clocks. Quoting Einstein: "[in classical physics] [t]he simultaneity of two definite events with reference to one inertial system involves the simultaneity of these events in reference to all [other] inertial systems. This is what is meant when we say that the time of classical physics is absolute." [Einstein's book _Relativity_, p. 149] If all it takes is a pair of (truly) synchronous clocks at the events to get rid of relative simultaneity, then it is clear that the latter is not given by nature but by man via his choice to use asynchronous clocks at the events or by improperly using light rays from the events. The only way that observers can properly use light signals from events to judge the simultaneity of them is if the observers know how they are actually moving in relation to these light signals. But neither observer in Einstein's train example knows this. In fact, it is utterly ignored. (More on this below.) But why go to the trouble of using observers and light signals; why not just place absolutely synchronous clocks at the events. As Einstein said, this eliminates relative simultaneity and gives all observers absolute time (for judging event time differences). Strange: >The relatively of simultaneity is about how the two observers see the relationship between two different events. Of course they will see them at different times. But one will consider the two events to have happened at the same time, and the other will consider the two events to have happened at different times. This is AFTER taking into account the arrival time of the light. But if the observers know that one is actually moving _toward_ one light signal and _away_ from the other, and that the other observer is _not_, then they will simply conclude (correctly) that the events happened in only one way (say truly simultaneously), and will say that they cannot properly use light signals from the events whilst they are moving helter-skelter wrt said signals. yknot said: Here is E's def. of abs. time: Strange replied: >Which he then goes on to demonstrate is incompatible with reality In exactly what way are truly synchronous clocks "incompatible with reality"? It seems to me that Einstein's clocks are the ones that are incompatible because they wrongly say that two events can be said to occur in many different ways (temporally) whereas anyone knows that events are independent of observer observations and events occur in only one way in reality. (Ironically, Einstein's above agrees.)

5. Does the train example show relative simultaneity?

Yes, of course it's because O2 is closer to the source, but how did he get closer? My answer is simply that he moved relative to the source or, more specifically, rel. to light's emission point, or even more specifically, he moved closer or toward the tip of the approaching ray. In other words, it's observer motion relative to the ray's tip that matters here, and not observer motions relative to each other. We can see this clearly by using a single observer and a light source. The closer this obs. is the the source, the quicker he will see the light that is emitted (toward him). Yes, this is too simple, but it is also critical to understanding E's train ex. which purportedly showed rel. simult. whereas all it really showed was the very simple fact that observer motion rel. to light makes diff. obs's see the light differently. We can say more: It is wrong to use light rays from events + differently-moving obs's to judge the events' occurrence times if you refuse to take into account the fact that the obs's move diff'ly wrt to the sources. (The best way to correctly time events is by placing correctly synch'd clocks at the events.)
6. Does the train example show relative simultaneity?

To show that relative observer motion is not really involved, we can eliminate it by placing both observers in the same inertial frame as follows: --------------------O1------------------------------O2---------------------A-Frame x axis--------------------<~~~~~~~~~~light ray Just as in E's train ex. and as in my half-****d version,, O2 sees the ray before O1. Why do they see the ray arrive differently? (Catch you in the am)
7. Does the train example show relative simultaneity?

Let's worry about the very simplest part of my example. Forget about length contractions and invariant light speed (because no one is measuring either lengths or speeds). Forget about points of view where one person looking at another (because there are none). Let me just ask this one simple question: Why do my observers see the light ray differently? (This cannot be due to "different relative motions" because neither observer is observing or recording the motion of other.) (And I can just as well ask the same question about E's version - why did his two observers see the two rays arrive differently?) There has to be some physical reason why the observers see things differently.
8. Does the train example show relative simultaneity?

I started (in order to simplify) with a single flash to show that the difference between the two observers in the single-flash case has everything to do with their different motions, and really nothing at all to do with event times. Then this conclusion can easily be extended to cover the entire train example by simply adding a second lite flash, but this is not really necessary is it? (I'm just saying that E's train ex. does not show that sim. is rel. but merely shows that observers moving differently will see events differently if they judge event times by light-rays-from-the-events and totally ignore the fact that they moved differently during the experiment, which is what really caused them to see the events diff'ly.)
9. Does the train example show relative simultaneity?

This was 1/2 of E's train ex. & he had his observers equidistant from both light-emitting events. (The lightning strikes could leave burn marks in each frame to verify this, as many have said.)
10. Does the train example show relative simultaneity?

To keep it as simple as possible, we will use only the right half of E’s train example. O1 -----------------------------------------------<~~~~~light O2--> A light ray starts equidistant from inertial observers O1 and O2, as shown. And yet O2 sees the ray before O1. (And this is absolutely before because these are light-like events.) Why this difference? I’m guessing that is has nothing to do with either the event or light’s speed, but that it has everything to do with the fact that the observers moved differently in relation to the approaching light ray. But this does not show that simultaneity is relative; it merely shows that observers moving differently will see events differently. It is wrong to ignore these different motions, and to then go on and say that the events occurred differently for the two train example observers.
11. What does the Doppler effect say about light's motion?

OK, I resent the blatant insult. From someone who cannot even spell invariant, I am receiving an insult? Please. This will be my final post in this forum. (Everybody clap loudly!) But I will leave a parting shot that cannot be denied. No one has every correctly measured any speed, much less light's speed. If you fail to grasp this, then consider the following simplefacts: (1) No one can prove that their clocks are not intrinsicallyslowed. (Intrinsic slowing is the same as twins and triplets aging differently. It is physical and not reciprocal.) (This alone makes all speed measurements invalid) (2) No one can prove that their rulers are not intrinsically contracted. (This adds to the above problem) (3) No one can prove that their clocks are correctly or absolutely synchronous. (This invalidates all one-way speed measurements, from the speed of a bug relative to a log to the speed of light.) If you cannot validly measure the speed of a freekin bug relative to a log, then your physics is totally screwed up. Face the facts. I'm serious, dudes. Very serious. PS> ACG52 presented zero proof of light's invariance one-way speed. He cannot because there is no proof. Tip: click inside this box to load the editor
12. What does the Doppler effect say about light's motion?

You must have forgotten about or somehow overlooked my fence analogy (given in my first post). Let's say that a picket fence is floating in space (inertially, no acceleration). Let's say that you and I see different frequencies for this fence. That is, we observe different numbers of fence posts passing us each second. Is not the only way that this can occur is for us to be moving at different speeds relative to said fence? And, as I said in my original post, since relative motion is reciprocal, we must say that the fence is moving at different speeds relative to each of us. Methinks that you fellows are (for some reason that I cannot yet fathom) fighting too strongly against the simple equation w = c - v. It's time to face the facts and get on with life.
13. What does the Doppler effect say about light's motion?

To Mr. Hyde: Let me for a minute return to my original post. What do you, Mr. Hyde, think causes observers to see different colors when viewing the same passing light ray? Since the light itself cannot and does not change color, we are left with only one answer, namely, the different speeds of the observers relative to the passing light. This simple experiment alone is enough to prove that light's speed relative to observers varies. But let me also return to Einstein's simple equation, w = c - v. Regardless of your statement that Einstein was in the process of "proving" that classical time was incorrect, he _did_ in fact derive the equation w = c - v. Can you show us how he derived it? And as for your statement that there were no Mars or Moon probes in Einstein's day, this is irrelevant because Einstein could have used a thought experiment, as he often did (even in the "important" case of his derivation of the relativity of simultaneity.) Perhaps if you just show how Einstein derived his equation w = c - v, you will see what I have been talking about (non-argumentatively). But I _will_ give you the following little hint: Einstein did not really prove that the clocks of classical physics were wrong, but simply discarded such clocks in lieu of the really wrong clocks (asynchronous clocks) of special relativity. As we know, he replaced good clocks with bad clocks (absolutely synchronous clocks with absolutely asynchronous clocks) in order to (try to) get all clocks to record "c" for the one-way speed of light. Of course, he very conveniently did _not_ show how this can be done experimentally. But you, Mr. Hyde, are welcome to try. Well, I have blabbered enough for now. (Oh, I almost forget to mention that you have yet to show how your probe experiment yields the value "c" for light's one-way speed.) Well, this is only about light's source independency, not its one-way speed. All clocks today are synchronized per Einstein's definition, and this definition assumes "c" for light's one-way speed. Obviously, truly or absolutely synchronous clocks would be better for GPS, but it can get by with Einstein's slightly-off clocks because of the following: On the satellite side, timing is almost perfect because they have incredibly precise atomic clocks on board. But what about our receivers here on the ground? Remember that both the satellite and the receiver need to be able to precisely synchronize their pseudo-random codes to make the system work. If our receivers needed atomic clocks (which cost upwards of $50K to$100K) GPS would be a lame duck technology. Nobody could afford it. Luckily the designers of GPS came up with a brilliant little trick that lets us get by with much less accurate clocks in our receivers. This trick is one of the key elements of GPS and as an added side benefit it means that every GPS receiver is essentially an atomic-accuracy clock. The secret to perfect timing is to make an extra satellite measurement. That's right, if three perfect measurements can locate a point in 3-dimensional space, then four imperfect measurements can do the same thing. By using an extra satellite range measurement and a little algebra a GPS receiver can eliminate any clock inaccuracies it might have. If you, Mr. Swan..., think that GPS clocks are absolutely synchronous, then please tell us how that was done. According to current theory, it cannot be done, and should not be done ("cause time is relative, not absolute per Albert E). What you all are overlooking here is the simple fact that Einstein himself said mathematically that the one-way light speed will vary given the clocks of classical physics, clocks which he was unable to obtain probably because he wanted to discard them.
14. What does the Doppler effect say about light's motion?

First of all, it is funny that Einstein did not mention your "one-way experiment," and second of all, it is not possible to measure light's one-way speed without using two clocks, and third of all, why did you ignore Einstein's simple equation saying that given the clocks of classical physics, light's one-way speed must vary with frame velocity? And please show the math (you said it was simple math) for your experiment to show how light's one-way speed can be c in any inertial frame. Your claim that my above was "totally false" is itself totally false, as you will soon discover by trying to do the math.
15. What does the Doppler effect say about light's motion?

To Hyde: Please point out my argumentative stuff; I do not intend to be so. To explain my "fixation" on light's one-way speed, and why and how it differs fundamentally from the round-trip speed, I turn to Einstein's own words, since you seem to think that mine are somehow "argumentative." (I really should not have to use Einstein's words to explain SR because they have been readily available to everyone for decades, but since you asked....) The one-way and round-trip cases are different. One-way light speed "invariance" had to be given by definition, whereas round-trip speed invariance was given prior to special relativity via experiment, as Einstein said in his 1905 paper
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