The SR Question of the Century ================================= ================================= Why has no one simply used two clocks on a table to measure light's one-way speed? ================================= ================================= (Note: No, Roemer did not do it; he used slow clock transfer, where one clock spanned the Earth's orbit, and since moving clocks run slow, his clocks were asynchronous.) For those who may need it, here is a detailed version of my question: ================================= Given two new atomic clocks still in their shipping crates, how would anyone use these clocks to measure light's one-way speed in a way that is proved to be correct? ================================= Basically, I am speaking simply of the one-way version of the Michelson-Morley experiment. And if you happen to believe that the MMx round-trip experiment somehow even _implied_ one-way invariance, then you need to prove this via the critical case of a frame that moves wrt the light source. The given question is extremely important because an incorrect measurement of light's one-way speed means incorrect measurements of all one-way speeds and all time spans involving two or more clocks. The given question is also extremely important because special relativity (our current theory of time measurement) is based solely upon Einstein's light postulate, which claims light speed invariance in the one-way case.
How long must the table be and how accurate must the clocks be to satisfy an aether proponent? Also, since GPS uses one-way transmissions, doesn't it qualify as a good test of the invariance of the speed of light?
GPS good test? I don't know, so many effects are involved, I would hardly think it is "clean". Here's a "Living Review" of the many effects involved in designing and maintaining the GPS: relativity.livingreviews.gps I think you have to assume one-way light travel goes at c, because of the issues involved in keeping the clocks synchronized as you separate them. These issues are not important because in the solar system gravity is so weak and velocities so low, I guess.
'outandbeyond' is right; in the GPS case, as in all current 2-clock cases, scientists simply assume one-way invariance and isotropy. Since my question pertained to theoretical physics, it matters not how long the tables are, and the clocks are really ideal clocks. Let me put it to 'russ_watters' this way: Given two ideal unstarted spatially-separated clocks, show how they could be correctly related temporally - bearing in mind that proof is required, and also bearing in mind that no assumptions are allowed, and further bearing in mind that you must show this for a frame that moves wrt the light source if light signals are involved. I claim that so far no one has ever correctly related any two clocks in any frame. (Thus, no one has ever correctly measured any one-way speed, any momentum, or any two-clock time span.) (If Einstein had known how to correctly relate clocks, then he would have had absolute simultaneity instead of his merely relative simultaneity, and SR would never have been created.)
I can't even assume I can turn the clocks on? That they're at rest with respect to each other? That if I send light signals from one location at regular intervals that the destination receives the signals at regular intervals? That there's not a michevious devil between the two clocks that will intercept all communications and transmit fake data? Sounds like you've already decided SR is wrong; I doubt any argument or experiment, no matter how sound, could convince you otherwise.
Absolute simultaneity was assumed pre-Einstein's relativity theory. However, Einstein showed that this is something that has to be carefully defined in operational terms; say, partly by all observers agreeing that one and only one of them will be the arbitrator of which events are simultaneous and which not. He didn't acutally reject absolute simultaneity; just that it is something that has to be agreed on in operational terms beforehand, if it is to be used at all. SR does not always need absolute simultaneity. GR theorists often define hypersurfaces in space-time, each of which has a unique time: i.e., defined absolute simultaneity. However, the definition can change from treatment to treatment. I have been trying to think of a reason why it is necessary to specify that the clocks be unstarted. So far, i don't see that it is necessary.
The SR Question of the Century ================================================= ================================================= Why has no one simply used two clocks on a table to measure light's one-way speed? ================================================= ================================================= Good question Martin. Don't get fobbed of with the GPS stuff or synchronization issues. Scientists are spending a fortune sending probes to Mars to try and find water, life, etc, surely this simple low cost test should be done. I have no idea why nobody has done it, but I think the results will be surprising. Two similar tests were done around the 1990s 1. Roland DeWitte used an electrical pulse to measure one-way speeds and found SR at fault (he is an amateur and so was ignored). 2. Krisher et al (JPL) did a test but the results were too noisy to be conclusive. However, they claimed it supported SR! (They are the professionals and so their results were accepted as good). See http://www.kevin.harkess.btinternet.co.uk/oneway/oneway.html for more info and also go to "reasons Einstein was wrong"
Perhaps this should be explained: Either two events are simultaneous as seen by an observer, or they are not. Einstein's point is that events seen as simultaneous by one observer are not necessarily seen as simultaneous by any other observer. Is this what Martin Miller meant by mere "relative simultaneity"? If so, won't he please explain, contra Einstein, why all observers can see two events as simultaneous? Ordinary distance measurements require simultaneity. If one had a measuring stick, then we could just line up points on the stick with the endpoints of the interval whose distance we wish to measure. However, if a one-way light-speed measuring procedure requires a distant place, then we would have to transport a clock there, correct? Could table-top measurements of the one-way speed be made with today's technology? I guess not. But Martin Miller has made ideal clocks (and by definition? ideal measuring rods as well) available to us. So, let me see if I can ... Put a one-meter stick on the table top. Put one unstarted clock at one end and the other at the other end. Nah, won't do. We need to start the clocks and make sure they are well synchronized. Then put one clock at one end and the other clock at the other end. We can design read-outs so that any observer standing in front of the table and equidistant from the clocks can monitor them to ensure that they are synchronized throughout the measurement process. Release a light pulse at time = sometime and get the time = sometime + traveltime when the pulse arrives at the other end. One-way speed is then 1 meter/traveltime. Neat, huh? However, H.L. Mencken said something to the effect that every neat, obvious, simple solution is apt to be wrong.
People are trying to see if light speed varies from place to place; from time to time; from direction to direction (anti-isotropy). See this "Living Review" article on experimental tests of GR: relativity.livingreviews.experiments
--- 'outandbeyond2004' wrote: "Put a one-meter stick on the table top. Put one unstarted clock at one end and the other at the other end. Nah, won't do. We need to start the clocks and make sure they are well synchronized. Then put one clock at one end and the other clock at the other end. We can design read-outs so that any observer standing in front of the table and equidistant from the clocks can monitor them to ensure that they are synchronized throughout the measurement process." MM replies: You did not tell us how the clocks are to be synchronized, and your midpoint observer cannot verify correct synchronization unless he can prove that he is not moving either toward or away from the light rays from the clocks' readouts. (To see that he may be moving wrt the light signals, simply add a light source at each clock beside its readout, with the light sources' frame moving wrt the clocks' frame, and let each source emit light rays simultaneously with its nearby readout. This makes it clear that only one frame out of an infinity of frames will remain at rest relative to these sources, which in turn means that only one frame out of an infinity of frames will remain at rest in relation to the sources' light signals, which in turn means that only one frame out of an infinity of them will remain at rest in relation to the clock readouts' light signals. Bear in mind that light's source independency guarantees us that the light rays from a clock readout and a nearby light source will travel together as if they were one ray.) --- 'Hurkyl' noted: "Sounds like you've already decided SR is wrong; I doubt any argument or experiment, no matter how sound, could convince you otherwise." MM replies: Try me. --- 'outandbeyond2004' noted: "I have been trying to think of a reason why it is necessary to specify that the clocks be unstarted. So far, i don't see that it is necessary." MM replies: This was just an initial condition, not a final one. (I mentioned it only to make sure that the experiment started from scratch; the experimenter must of course start the clocks at some point, but how and when are parts of the given problem.) 'outandbeyond2004' also noted: "Perhaps this should be explained: Either two events are simultaneous as seen by an observer, or they are not. Einstein's point is that events seen as simultaneous by one observer are not necessarily seen as simultaneous by any other observer. Is this what Martin Miller meant by mere "relative simultaneity"? If so, won't he please explain, contra Einstein, why all observers can see two events as simultaneous?" MM replies: Yes, that is exactly what I meant by "relative simultaneity," but I can still see that a little more explanation is necessary here. The key questions here are (a) Since events are observer-independent, why should observers' mere _viewpoints_ of light rays from events be involved? and (b) What is physical cause of Einstein's relative simultaneity? To answer the last question first, the precise physical cause of the relativity of simultaneity is simply different frame movements in relation to the light rays from the events. No matter how two events may actually occur, observers in different frames who view light rays from the events _must_ see the rays arrive differently. For example, Frame A's observer may move toward the light from Event 1 but away from the light from Event 2, whereas Frame B's observer may move away from the light from Event 1 but toward the light from Event 2. (And it should be apparent that this answer also answers the first question.) Of course, simultaneity would not be relative if truly or absolutely synchronous clocks were used to time events. As I mentioned earlier, Einstein's clocks are not synchronous. In fact, he explicitly admitted this in his book _Relativity_. Here is how he put it: quote from Einstein's _Relativity_: " But an examination of this supposition would only be possible if we already had at our disposal the means of measuring time." [Ref.: http://www.bartleby.com/173/8.html] In this brief sentence, Einstein said a lot. Since the context was light's one-way, two-clock speed, he was admitting that he could not correctly measure this speed. Also, he was admitting that he could not correctly measure any other one-way speed because, as he said, he did not possess the means of (correctly) measuring time. Further, he was admitting that he could not correctly measure any two-clock times. In short, he was admitting that the clocks of special relativity are not truly synchronous. We do _not_ need a theory whose clocks are asynchronous. We _do_ need synchronous clocks. --- 'wisp' noted: "Good question Martin." MM replies: Thanks. And as soon as its full meaning has become apparent, you will see that it is the most important question re flat space-time physics that can be asked. See the following to see why no rotating clocks can yield anisotropy: http://www.geocities.com/antirelativity/Rotating_Clock_Analysis.html The only real test of Einstein's light postulate is a direct and simple measurement of light's one-way speed between two same-frame clocks which are correctly related temporally. (No rotating clocks; no transported clocks; no asynchronous {Einsteinian} clocks.) --- 'outandbeyond2004' further noted: "People _are_ trying to see if light speed varies from place to place; from time to time; from direction to direction (anti-isotropy)." "See this "Living Review" article on experimental tests of GR:" "relativity.livingreviews.experiments" MM replies: I saw nothing there about correctly synchronizing clocks or correctly measuring any one-way speeds. Here is what one must do to prove that one's two-clock time measurements are correct: [1] One must prove that one's clocks are correctly related. [2] One must prove that one's clocks are not slowed. [3] One must prove that the rod connecting the clocks is not contracted. So far, no one has presented a proof of any of the above; therefore, no one has presented a proof that even mere _relative_ speeds can be correctly measured, such as the speed of a bug relative to a log!
Martin Miller, have you studied the lunar laser ranging experiment? There should be time-varying components in the data making possible an analysis to determine the one-way speed of light. I admit a lack of familiarity with the state of art: I do not know if such an analysis is possible now.
To 'outandbeyond2004': Since LLR (Lunar Laser Ranging) is a one-clock measurement of the time taken by the light signal to travel to the moon and back, no synchronization is involved. To fully understand what it’s all about, we need a proper and simple example, such as the following one: [clock]---------[rod]---------[mirror] [source]~~>ray Imagine a rod in space which has been ruler-measured to be 1 LY long. (Ignore the hardships involved if this were actually done.) Picture a started-and-running atomic clock at one end of the rod, and a mirror at the other end. Imagine a light source that is moving relative to the clock-mirror frame. As this light source meets the clock in passing, the former emits a light ray toward the mirror. It is at this point that we must be careful; i.e., we must ask ourselves What are the consequences of the relative motion between the clock-mirror frame and the light source frame? Clearly, if the mirror moves away from the light source, then the light ray from the source should take longer to reach the mirror than otherwise. Similarly, it is clear that if the mirror moves toward the light source, then the light ray from the source should take less time to reach the mirror than otherwise. However, if the rod is physically contracted, and if the clock is physically slowed, then these two physical distortions will yield an incorrect result, namely, round-trip light speed invariance. Of course, this incorrectness could not be revealed by a ruler because the ruler would also be physically contracted. Therefore, an LLR measurement will always seem to obtain very accurate results of the ('instantaneous') distance between two objects, but this ignores the fact that (a) no one has taken into account the objects' movements in relation to the light signals, (b) no one has proved that the clock is unslowed, and (c) no one has proved that the rod is uncontracted. In other words, the Michelson-Morley experiment did not correctly measure light's round-trip speed, and the LLR cannot correctly measure the distance to the moon. (Given undistorted clocks and rods, we would find that light's round-trip, one-clock speed varies.) Here are the differences and similarities of the Michelson-Morley (MMx) round-trip case and the one-way case: Round-trip Case: The MMx null result is a law of nature; however, the MMx result was incorrect because Nature distorted the instruments. One-way Case: In the one-way case, there can be no law of nature because Nature cannot synchronize clocks; however, man can synchronize clocks, and if he synchronizes them _correctly_ (absolute synchronization), then he can obtain a _correct_ result. (Disclaimer: Of course, he would have to mathematically correct for clock slowing and rod shrinkage, but we have the formulas, so this is easy!)
Martin Miller, your response does not show that you know how useful time-varying data can be. For the benefit of other readers if not yours, let me give an example. A laser based on earth is shooting photons at a mirror that is orbiting earth. Let's pretend we do not know exactly what the speed of the photons are, so we can calculate only roughly the round-trip distance to and from the mirror. Nevertheless, we continue to gather data, and we notice that the round-trip time varies with time. There is a diurnal dependence, a monthly dependence and an annual one, among others. Theorists develop an elaborate theoretical model of the experiment with many adjustable mathematical parameters, including one for the speed of light. When we have many data points spread over a period of many years, we try to fit the model to the data, adjusting the model parameters as necessary to match the data with the predictions of the model. If the time-varying components of the data are not important, the fitting of the model to the data would not work, of course. One reason might be too much noise. However, if the quality of the data is good, then we may have an interesting or "tight" range of values for each parameter including the speed of light. Actually, every experiment with important time varying data is modeled that way. Other examples are the Shapiro round-trip radar time delay experiment and binary pulsars. Many other ongoing experiments depend on the speed of light, so I feel fairly confident that we do have a good grip on its one-way value even though we have not yet measured it directly. For details see the article I had linked to earlier and have relinked here for convenience: relativity.livingreviews.experiments
Martin, Such clocks' asynchronicity may realize the GR effect of the expanding universe on nearly local time, or even the curvilinear movement of the observer himself relative to each clock.
'outandbeyond2004' wrote: "Many other ongoing experiments depend on the speed of light, so I feel fairly confident that we do have a good grip on its one-way value even though we have not yet measured it directly." If we correctly word your above, then we have the following: "Many other ongoing round-trip experiments depend on the round-trip speed of light, so I feel fairly confident that we do have a good grip on its round-trip value." We certainly have a firm grip on light's round-trip speed - it is invariant and isotropic; however, as I will prove below, the round- trip speed has nothing to do with either light's one-way, two-clock speed or with clock synchronization. The conceptual keys behind the following experiment are two, namely, (i) a ban on Einstein's rigged clocks (which are _forced_ by a baseless definition from man to obtain one-way 'invariance'), and (ii) the use of two frames sharing one light source (something which is never done in relativity texts). The physical facts upon which the experiment is based are also two, viz., (i) the simple fact that light's motion through space is not infinitely rapid, and (ii) the corollary that light must always take a finite amount of time T to move between any two points. The Apparatus (2 tables, 4 clocks, 1 light bulb): [diagram given below] >>> There are two narrow, adjacent tables, each 30 meters long and 1 meter high (per a ruler at rest wrt each table). Table F is fixed relative to the lab, whereas Table R can roll relative to the lab. >>> There is an unstarted clock [C] each end of each table. >>> There is a light source (e.g., a light bulb, represented by the asterisk) aligned with the left end of Table F at table-top height. At the start, Table R's left end is to the left of Table F's left end, as shown: ...[C]=======Table R=======[C] ........ ........[C]=======Table F=======[C] In the 2nd scene, the source emits a light ray to the right just as the left clocks meet in passing and start on zero: ........[C]=======Table R=======[C] ........~~>ray ........[C]=======Table F=======[C] In the 3rd scene, the light ray reaches Table F's right-hand clock: .............[C]=======Table R=======[C] ........~~~~~~~~~~~~~~~~~~>ray ........[C]======Table F======[C] In the final scene, the light ray reaches Table R's right-hand clock: .................[C]=======Table R=======[C] ........~~~~~~~~~~~~~~~~~~~~~~~~>ray ........[C]======Table F======[C] Since not even a light ray can be in two places at once, and since (as was mentioned above) not even a light ray can move infinitely rapid), the ray must take a finite amount of time T to travel between the two right-hand clocks. Here is what the experiment tells us about light's one-way speed relative to each of the two frames: *************************** Light's one-way speed wrt Table F = 30m/100ns = c Light's one-way speed wrt Table R = 30m/(100+T)ns =/= c *************************** In other words, experiment shows that light's one-way speed varies with frame velocity. So how did Einstein obtain his one-way invariance? He did so by incorrectly placing the _same_ time x/c on both right-hand clocks when they were 'hit' by the light ray. Why did Einstein force clocks to obtain one-way invariance? He did this because he improperly extrapolated invariance from the round-trip case. Ironically, exactly none of the above has anything at all to do with the real problem which is How to correctly measure time? (And this problem was also ignored by outandbeyond's talk of "how useful time-varying data can be.") In other words, the real problem for today's space-time theorist is How can clocks be correctly synchronized? Here is a hint: Without using more than one clock, one must be able to guarantee that the clock-starting entities have truly equal speeds relative to the clocks. Let's quit talking about "how useful time-varying data can be," "how great the GPS system is," "how wonderful it is that we have atomic clocks," "how the MMx took away the aether," "how Einstein made time relative," "how wonderful special relativity is," "how the MMx proved round-trip invariance," etc., etc., etc., and let's concentrate on the real issue of absolute clock synchronization because as of now, we cannot even correctly measure the speed of a bug relative to a log.
Wow, Martin - what you suggest is a test of relativity that ignores the effects of relativity. You completely miss the point of SR by not applying it to your apparatus: the moving table experiences a tme dilation and as a result, it still takes 100ns (according to the moving clocks) and still measures C to be C. This is why I asked you before how big your apparatus had to be and how accurate the clocks had to be to test this. Add also how fast the apparatus has to move and how you synchronize clocks in different frames of reference. Try doing the calculation: I think you will find that for an apparatus like the one you suggest, time dilation (or your "T") is less than the precision of the experiment and thus outside its ablity to detect. But with a big enough (and fast enough) apparatus, you will detect a time dilation. And if you plan on arguing against time dilation, please remember that time dilation is no longer just an untested prediction of SR, but is in fact, experimental data.
Martin, I don't suppose you ever got caught speeding. You'd be put in an asylum for the insane if you tried to convince the patrolman with statements like this: \\ as of now, we cannot even correctly measure the speed of a bug relative to a log. // Good driving, Martin! Kidding aside, it wasn't Einstein's original idea that the speed of light is constant to every inertial observer. Rather it is a theoretical consequence of Maxwell's equations for electromagnetism. These equations in turn are based on the results of countless experiments that were done long before Einstein's birth. Einstein did have the original thought that the laws of mechanics should be recast to be based on the same speed of light constant as the laws of electromagnetism are. Martin, your problem may be that you are basing your theory on your everyday experience, instead of experiments done by others. It can be difficult to appreciate how every working GPS device is confirming the truth of GR and SR. It is indeed hard for people to accept that the speed of light is absolutely the same to every inertial observer. So very, very bizarre.
Note to russ_watters: Time dilation cancels out in the experiment because the two tables speeds through space are equal. outandbeyond2004 noted: "Kidding aside, it wasn't Einstein's original idea that the speed of light is constant to every inertial observer. Rather it is a theoretical consequence of Maxwell's equations for electromagnetism." You are mixing up light's propagational motion through space with Einstein's definition of clock synchronization. Maxwell's equations say nothing at all about light's one-way, two-clock speed, and Einstein's definition says nothing at all about Maxwell's equations. (If you believe otherwise, then tell us how Maxwell synchronized clocks.) Since you have claimed that light's one-way, two-clock speed is the same for all inertial observers, you have the burden to prove this, so let's see if you can. You have also claimed the "truth" of SR, so let's see if you can prove that its clocks are correctly synchronized. And I could not help but notice that you had no counter to my very simple and very direct experimental proof that Einstein's clocks are not correctly synchronized, and that light's one-way speed is not invariant. I have presented a simple and direct experiment, and you have (to put it bluntly, so pardon me!) presented absolutely nothing. To repeat, the burden of proof is on the claimer. (This means that I did not even need my experiment!) Let's please stop runnning around in circles, and let's see some 'meat on the table' for Einstein's case! Where's the beef??
In relativity, there is no such thing as "speed though space" - no absolute speed, only relative speed: the speed of each table relative to the other. And even if there were an absolute speed, since the tables are moving relative to each other, their absolute speeds would be different. Sorry, no, this is a classic time/length dilation problem. Hehe, no. That's called burden-of-proof-shifting. Einstein's relativity is the accepted explantion because it has met the scientific community's standard of proof. YOU are claiming it is false, and YOU must therefore provide positive evidence of that. It is clear to me, however, that your assertions are based soley on your flawed understanding of what the theory says.
russ_watters noted: "In relativity, there is no such thing as "speed though space" - no absolute speed, only relative speed: the speed of each table relative to the other. And even if there were an absolute speed, since the tables are moving relative to each other, their absolute speeds would be different." "Sorry, no, this is a classic time/length dilation problem." You can't have your cake and eat it, too. You were the one who mentioned time dilation. Were you speaking of intrinsic clock slowing or a mere point-of-view "slowing"? If it's the latter, then it has nothing to do with physics; if it's the former, then it must be due to clock motion through space. And, no, even using speeds through space does not mean that the tables speeds through space differ because I can specify that their speeds through space are equal. russ_watters noted: "Hehe, no. That's called burden-of-proof-shifting. Einstein's relativity is the accepted explantion because it has met the scientific community's standard of proof. YOU are claiming it is false, and YOU must therefore provide positive evidence of that. It is clear to me, however, that your assertions are based soley on your flawed understanding of what the theory says." To repeat, ad nauseam, where is your proof of one-way, two-clock invariance and isotropy? To also repeat ad nauseam, where is your proof that Einstein's cute little (hehe) clocks are correctly related temporally? And while you are at it, please present at least one scientific prediction made by special relativity. (That is, at least one prediction that does not directly depend upon clocks which have yet to be validated by you or anyone else.) And I did not merely claim that Einstein's clocks are incorrectly related, I proved it experimentally. I also proved that light's one-way speed varies with frame velocity. Re your claim that "Einstein's relativity is the accepted explantion because it has met the scientific community's standard of proof," who in that community has experimentally measured light's one-way speed and found it to be invariant and isotropic? Was this critical experiment performed under cover of darkness at the Antarctic? hehe! And please try to remember that Einstein himself explicitly admitted that he did not possess the means of measuring time! This is why no one has ever correctly measured even the relative speed of a bug wrt to log.