Unable to see how light's one-way speed can be c experimentally

[Dale]

As Einstein said, the clocks of classical physics were truly or absolutely synchronized, if only on paper. (That's how Einstein's observers got the results c and c - v for light's one-way speed.) http://www.bartleby.com/173/7.html

Einstein never mentioned anything about "truly or absolutely synchronized" clocks in the cited material. Furthermore, he never presented a competing method for synchronizing clocks. My original question to you remains completely unanswered:

How would you suggest synchronizing the clocks in your proposed "direct" experiment?

This is a key question. You are surprised that such an experiment has not been done. This is a key part of the experiment, and understanding why may help you understand why the experiment hasn't been done.

I noted that not all theories are indistinguishable from SR

That is true but irrelevant and non-responsive. The reference never claimed that ALL theories are indistinguishable from SR, only that there exists "a large class of theories in which the one-way speed of light is anisotropic" with some specified other characteristics and that "these theories ... are experimentally indistinguishable from SR".

This is important to your question. Think about it a bit. What does the existence of a theory in which the one way speed of light is not c and which is experimentally indistinguishable from SR imply about your desired experiment?

and you deleted my reply, which was the fact that Einstein said that a theory that contains the absolutely synchronous clocks of classical physics would yield c variance. (See above site.) Are you saying that Einstein was wrong here?

I deleted the rest of your reply because I didn't want my response to it to detract from the rest of the exchange, but since you continued to press the issue I will respond.

You must stop misquoting and misattributing statements from Einstein (or anyone else). In the references you have provided Einstein never says what you claim he says. Stop misrepresenting his comments. Such behavior is not tolerated on this forum.

But nature cannot be forced by man.

True, but not relevant. Clock synchronization is not part of nature, it is a purely man-made convention.

As Einstein said, it is not coordinates that we are talking about, but the simple law of the constancy of light's speed in space. (See above URL again.) This law is controlled by one fact, the fact of light's source independency, just as Einstein noted (when he mentioned De Sitter).

Also true but irrelevant. The source independency of the one way speed of light is an experimentally testable fact which does not require clock synchronization. It is a different physical question from the value of the one way speed or its isotropy. The fact that synchronization is not necessary to answer one question in no way implies that synchronization is unnecessary to answer the other.

The bottom line remains the question that I posed to you which you have not answered. You are surprised at the lack of a direct experiment, but you are not the first person to be interested in doing this type of experiment. All those before you abandoned the attempt. Why? Because of this one issue. If you want to resolve your surprise, then you must confront the issue of synchronization, not avoid it.

 

[ghwellsjr]

I have the 1966 edition which you can see http://www.eftaylor.com/pub/spacetime/STP1stEdThruP20.pdf.

I cannot find anything even remotely resembling your quote. Could you please find about where it got edited out?

Perhaps it would be best just to give you the quote.

Here is the quote from Wheeler & Taylor's book _Spacetime Physics_, 1963 edition, page 18:

[Wheeler's "latticework" = standard coordinate system]
"... We assume that every clock in the latticework, whatever its construction, has been calibrated in meters of light-travel time." "How are the different clocks in the lattice to be synchronized with one another? As follows: Pick one of the clocks in the lattice as the standard of time and take it to be the origin of an x, y, z coordinate system, Start this reference clock with its pointer at t = 0. At this instant let it send out a flash of light that spreads in all directions. Call this flash of light the reference flash. When the reference flash gets to a clock 5 meters away, we want that clock to read 5 meters of light-travel time. So an assistant sets that clock to 5 meters of time long before the experiment begins, holds it at 5 meters, and releases it only when the reference flash arrives. When [the] assistants at all the clocks in the lattice have followed this procedure (each setting his clock to a time in meters equal to his own distance from the reference clock and starting it when the light flash arrives), the clocks in the lattice are said to be synchronized."

That's it.

That's it? As I said before, there is nothing in there even remotely resembling 'clocks are simply set by definition to get the chosen value "c."'

As DaleSpam just said, "You must stop misquoting and misattributing statements from Einstein (or anyone else)."

 

[harrylin]

Please see my latest two replies to Nug. (especially the 2nd -- please try to show one-way invariance on paper)

Note that the prin of rel. does not call for light speed invariance, but only for law invariance.

Funny enough, you wrote the above in reaction on my clarification that according to SR, the principle of relativity is also valid for light propagation (=>invariance of the two-way speed of light). With that I meant Maxwell's law of light propagation. Obviously the relativity principle on its own is not SR!

One way invariance is perhaps most easy to understand by splitting up the actions of humans from those of nature. One-way invariance, as you now surely realize, is simply two-way invariance plus convenient clock synchronization (this was shown by means of the "Einstein" synchronization equations that I linked to you in post #13).
That leaves us with showing how Kennedy-Thorndike style two-way invariance is accomplished by nature. You can find how that works for example here:
https://en.wikipedia.org/wiki/Kennedy–Thorndike_experiment#Theory

In short, Lorentz contraction + time dilation maintain two-way invariance of the measured speed of light in all directions. Subsequent clock synchronization assures that the measured one-way speeds will equal the measured two-way speeds. Note that in SR, the measured speed of light is commonly called "the speed of light" - SR is void of metaphysics.

 

[ghwellsjr]

I don't understand why you say it cannot happen even on paper. I draw spacetime diagrams all the time that illustrate how light propagates at c in any Inertial Reference Frame (IRF) and how the coordinates of all the events can be transformed to any other IRF moving with respect to the original one and yet light still propagates at c and all observers continue to see and measure exactly the same things in all IRF's.

Is it that you have never seen how this happens on paper because you don't understand Special Relativity or is it that you thoroughly understand Special Relativity but still find fault with it?

To be honest and straightforward, the only way that you can see what I am talking about is to try to show even two frames' observers getting c via two clocks. You cannot simply use a spacetime diagram that has such stuff built in.

Here is a start:

Frame A
[0]-----------------------[?]
~~>light ray
[0]-----------------------[?]
Frame B

Given a light ray emitted at the origin clocks when both start on zero, please show (on paper) how both frames' observers can get c for the one-way speed of light.

Thanks!

I have seen what you are talking about from your very first post. As I said in the very first response to you in this thread "Light's one-way speed of exactly c ... cannot come from an experiment."

And that's what others have been saying in this thread.

We already know that.

Einstein knew that.

Why do you keep asking the same question over and over again when it has already been addressed over and over again?

And you didn't answer my question:

Is it that you have never seen how this happens on paper because you don't understand Special Relativity or is it that you thoroughly understand Special Relativity but still find fault with it?

 

[stevendaryl]

That's it? As I said before, there is nothing in there even remotely resembling 'clocks are simply set by definition to get the chosen value "c."'

I don't understand why you're objecting to BluMuun's characterization. In the passage he quotes, clocks are synchronized by light signals:

When the reference flash gets to a clock 5 meters away, we want that clock to read 5 meters of light-travel time. So an assistant sets that clock to 5 meters of time long before the experiment begins, holds it at 5 meters, and releases it only when the reference flash arrives.

This sure seems to me to be a matter of setting the clocks so that lightspeed has the chosen value. It's saying that at t=0, according to the reference clock, a light signal is sent toward a clock 5 meters away. When the signal reaches that clock, it is set to time t=5/c. With that setting, it's necessarily true that the computed speed of light for that signal will be:

speed = (Distance)/(Elapsed Time) = 5/(5/c) = c

I think BluMuun is missing that the REASON we can use lightsignals to synchronize clocks is because we already know that light has speed c, using pre-relativistic clock synchronization (slow clock transport).

 

[ghwellsjr]

You cannot falsify a definition because it is a given (given by man, not nature).

Suppose instead of Einstein's convention, we use one that says that the outbound propagation of light is twice as fast as the inbound. Don't you think that would easily be falsifiable?

Can you please answer my question?

 

[ghwellsjr]

That's it? As I said before, there is nothing in there even remotely resembling 'clocks are simply set by definition to get the chosen value "c."'

I don't understand why you're objecting to BluMuun's characterization. In the passage he quotes, clocks are synchronized by light signals:

When the reference flash gets to a clock 5 meters away, we want that clock to read 5 meters of light-travel time. So an assistant sets that clock to 5 meters of time long before the experiment begins, holds it at 5 meters, and releases it only when the reference flash arrives.

This sure seems to me to be a matter of setting the clocks so that lightspeed has the chosen value. It's saying that at t=0, according to the reference clock, a light signal is sent toward a clock 5 meters away. When the signal reaches that clock, it is set to time t=5/c. With that setting, it's necessarily true that the computed speed of light for that signal will be:

speed = (Distance)/(Elapsed Time) = 5/(5/c) = c

Wheeler & Taylor never used the phrase or any part of it that BluMuun attributed to them. If BluMuun had attributed that phrase to Einstein, I would have had no problem because he made the point very clear that his synchronization process is an arbitrary definition made of his own free will.

I think BluMuun is missing that the REASON we can use lightsignals to synchronize clocks is because we already know that light has speed c, using pre-relativistic clock synchronization (slow clock transport).

No, Einstein's second postulate doesn't have (or need) a reason and slow clock transport is just as much an arbitrary definition just like Einstein's. Neither one is the reason for the other.

Furthermore, you seem to think that slow clock transport is an experiment that does measure the one-way speed of light apart from an arbitrary convention of the type that BluMuun is asking for, correct?

 

[BluMuun]

What does synching a clock on paper mean? Are you serious?

Clocks were synchronized in the 1800s. It was done by slow clock transport, later by telegraph, with most people not giving it much thought (though, by the late 1800s at least, it was getting serious thought, e.g. by Poincare before Einstein).

History:

Quote by BluMuun
Oddly enough, given all the info at that site that you cited and I sighted, one would think that the direct experiment would be mentioned somewhere. By "direct" I mean using two mutually-at-rest clocks that are not rotating and have not been transported (because such clocks run slow).

Dalespam asked:
"How would you suggest synchronizing the clocks in such an experiment?"

BluMuun answered:
"The same way clock were set on paper for 100's of years prior to Einstein. Can you tell me why Einstein decided to get rid of such clocks?"

PAllen wrote:
That's a total non-answer. Again: how do you think this was done? Tell us how you think clocks were synchronized between e.g. London and Glasgow in the 1800s?

BluMuun answered:
Perhaps you overlooked my phrase "on paper." Clocks were absolutely synch'd on paper prior to SR. And Einstein used such clocks here: http://www.bartleby.com/173/7.html

PAllen changed the subject from a direct experiment to using slow clock transport, and then called my answer a "total non-answer." He paid no heed to the given that clock transport cannot be involved.

I was of course talking about absolutely synchronous clocks, and since we do not have absolute time, such clocks must necessarily be on paper. This applies to clocks between London and Glasgow as well as all other clocks in this universe.

{re my statement "As Einstein said, if the clocks of classical physics were used to measure light's one-way speed, then it would vary with observer velocity."}
Is this your only source? How do you misinterpret it so? I believe the part you must be referring to (you don't say) is describing not what would or could happen if clocks were somehow synchronized differently, but what people believed would happen before they had evidence that they were wrong. There is no 'classical clocks' that would allow measurement of varying one way speed of light. Can you tell a reductio ad absurdum argument when you see it?

Given your above, I believe that the word "misinterpret" has been gravely misapplied. Re your remark " but what people believed would happen before they had evidence that they were wrong," please be so kind as to tell us what is "wrong" with classical clocks. (I already asked this above by asking why Einstein decided to discard such clocks, but you totally ignored it.)

 

[BluMuun]

BluMuun said:
"I was interested in Nugatory's claim that "horrible complications" occur if we do not get c, so I asked him to list one."

One such problem is that we can calculate the speed of light from Maxwell's laws of electricity and magnetism, and Maxwell's equations make no allowance whatsoever for the velocity of the observer.

I fully explained why this is not a "horrible complication," and asked Nugatory for a real example, but he went on talking about Maxwell. What more can I do re this?

However, I would like to clear up the following:

BluMuun noted:
"As Einstein said, if the clocks of classical physics were used to measure light's one-way speed, then it would vary with observer velocity. And, again, he made no mention of this being a problem re Maxwell's equations."

You are misunderstanding that passage. Einstein is describing how things would work if we assume that the one-way speed of light were not constant for all observers, thus forcing us to choose between the principle of relativity and Maxwell's electrodynamics; his point in the subsequent discussion is that if if we instead assume that the one-way speed of light is c for all inertial observers we get both.

Please give me your opinion of
(i) what the principle of relativity says about light's one-way speed,
and
(ii) what Maxwell's equations say about light's one-way speed.

All I have so far is this:

Yes, but if we have a law that predicts a particular value of light speed, then law invariance applied to that law yields a prediction of light speed that is invariant. And that is exactly the situation that confronted physics between 1861 (Maxwell's electrodynamics) and 1905 (Einstein published).

How did Maxwell give us one-way c invariance? Which experiment gave us c invariance for light's one-way speed?

If c invariance had been a law prior to SR, then there would have been no need for SR.

But, as I said at the start, I cannot see how one-way c invariance can happen experimentally, so I do not see how it can be a law.

 

[BluMuun]

I wrote:
"Oddly enough, given all the info at that site that you cited and I sighted, one would think that the direct experiment would be mentioned somewhere. By "direct" I mean using two mutually-at-rest clocks that are not rotating and have not been transported (because such clocks run slow)."
(I was looking for a test of one-way, two-clock light speed invariance. DaleSpam had pointed me to a bunch of other stuff.)

How would you suggest synchronizing the clocks in your proposed "direct" experiment? [/quote]

I answered your question, as follows:
"The same way clocks were set on paper for 100's of years prior to Einstein. Can you tell me why Einstein decided to get rid of such clocks?"

What way was that? I am unaware of anyone addressing clock synchronization issues prior to Einstein.

"As Einstein said, the clocks of classical physics were truly or absolutely synchronized, if only on paper. (That's how Einstein's observers got the results c and c - v for light's one-way speed.) http://www.bartleby.com/173/7.html"

Einstein never mentioned anything about "truly or absolutely synchronized" clocks in the cited material. Furthermore, he never presented a competing method for synchronizing clocks. My original question to you remains completely unanswered:

He was talking about pre-SR physics, or classical physics. The only time that existed then was absolute time, and the only clock synchronization that existed then was absolute synchronization. Einstein even (elsewhere) defined absolute time as follows:
"The simultaneity of two definite events with reference to one inertial system involves the simultaneity of these events in reference to all inertial systems. This is what is meant when we say that the time of classical mechanics is absolute. According to the special theory of relativity it is otherwise." [Einstein's book on relativity, p. 149]

This is a key question. You are surprised that such an experiment has not been done. This is a key part of the experiment, and understanding why may help you understand why the experiment hasn't been done.

It was you who claimed that there exist tests of SR. You cited a site, but it contained no such tests. Please present a test of one-way two-clock light speed invariance. (SR does not give round-trip invariance, which was given experimentally prior to SR, and neither does SR give mechanical relativity, which also preceded SR.)

You must stop misquoting and misattributing statements from Einstein (or anyone else). In the references you have provided Einstein never says what you claim he says. Stop misrepresenting his comments. Such behavior is not tolerated on this forum.

How else could a pre-SR observer get c for light's one-way speed other than by using the absolutely synchronous clocks of classical physics?

How could any observer get c - v for light's one-way speed other than by using the absolutely synchronous clocks of classical physics?

Simply by giving us these one-way light speeds, Einstein was clearly talking about the use of the absolutely synchronous clocks of classical physics. This is so obvious that saw no need to provide the dreary details. (Please do not accuse me of misrepresenting anyone.)

Good, so you do, in fact, see how the one way speed of light can be c in a frame, you simply "manually force" it to be c.

Blumuun:
"But nature cannot be forced by man. As Einstein said, in nature light actually passes frames differently, and given truly synchronous clocks, this fact of nature would be reflected in the clock measurements because they are true measurement, not false one made by absolutely asynchronous clocks."

True, but not relevant. Clock synchronization is not part of nature, it is a purely man-made convention.

What I was saying is that light's one-way invariance cannot even be "manually forced" because it is physically impossible - it cannot exist given nature as-is.

But, as I have said, the only way to see this is by trying to show c invariance on paper, as follows:


Frame A
[0]-----------------------[?]
~~>light ray
[0]-----------------------[?]
Frame B

Given a light ray emitted at the origin clocks when both start on zero, please show (on paper) how both frames' observers can get c for the one-way speed of light.

 

[BluMuun]

I don't understand why you say it cannot happen even on paper.

I have seen what you are talking about from your very first post.

First, you say that you do not understand why I say that it cannot happen on paper, and then you say you fully understood it from the start. I have no idea what you are really trying to say. Sorry.

 

[BluMuun]

Can you please answer my question?

I have answered it. I said that given such stuff, it must happen.

 

[BluMuun]

Wheeler & Taylor never used the phrase or any part of it that BluMuun attributed to them. If BluMuun had attributed that phrase to Einstein, I would have had no problem because he made the point very clear that his synchronization process is an arbitrary definition made of his own free will.

As the guy said, it is clear from the context that Wheeler was forcing the value c, i.e., that clocks are simply set by definition to get that value. In fact, Wheeler was just giving his definition of Einstein's definition of synchronization (which Wheeler called "standard synchronization.")

Since Wheeler gave no justification for placing the time on the distant clock, he was clearly just arbitrarily doing so of his own free will.

No, Einstein's second postulate doesn't have (or need) a reason and slow clock transport is just as much an arbitrary definition just like Einstein's. Neither one is the reason for the other.

But Einstein's second postulate must say something about nature, or it is not a scientific postulate. What does it say about nature?

 

[PAllen]

I answered your question, as follows:
"The same way clocks were set on paper for 100's of years prior to Einstein. Can you tell me why Einstein decided to get rid of such clocks?"

They never existed. There was nothing to get rid of. Clocks were set and synchronized using physical procedures.

"As Einstein said, the clocks of classical physics were truly or absolutely synchronized, if only on paper. (That's how Einstein's observers got the results c and c - v for light's one-way speed.) http://www.bartleby.com/173/7.html"

This refers to the false prior belief that when setting and synchronizing clocks using procedures like slow clock transort, an absolute synchronization was achieved. People used real clocks, real procedures, but had in their heads false assumptions about the ideal they were approximating.

It was you who claimed that there exist tests of SR. You cited a site, but it contained no such tests. Please present a test of one-way two-clock light speed invariance. (SR does not give round-trip invariance, which was given experimentally prior to SR, and neither does SR give mechanical relativity, which also preceded SR.)

SR says such an experiment is meaningless. Meaningful is measuring source independence of light speed, and two way isotropy and invariance of lightspeed. Given that that is all that is meaningful, we can make a choice to have a more complex mathematical model (by assuming the right kind of one way anisotropy), or choose a simpler mathematical model by assuming one way isototropy. This is purely a choice. All sane physicists choose the simpler model, but there can' be measurements to select one over the other.

How else could a pre-SR observer get c for light's one-way speed other than by using the absolutely synchronous clocks of classical physics?

Pre-SR observers measured one way light speed all the time using procedures that amounted to slow clock transport. We could do the same today - only now we understand there is no point to it except as a check on how well our clocks are synchronized.

How could any observer get c - v for light's one-way speed other than by using the absolutely synchronous clocks of classical physics?

No one ever got this by measurement.

What I was saying is that light's one-way invariance cannot even be "manually forced" because it is physically impossible - it cannot exist given nature as-is.

But, as I have said, the only way to see this is by trying to show c invariance on paper, as follows:Frame A
[0]-----------------------[?]
~~>light ray
[0]-----------------------[?]
Frame B

Given a light ray emitted at the origin clocks when both start on zero, please show (on paper) how both frames' observers can get c for the one-way speed of light.

Simple:

Frame A sees light go 1 km in approx 1/(300000) seconds.
Frame B sees light go 1 km in approx 1/(300000) seconds.

Frame A sees B's measurement different from how B sees it. Per A, B's 1km is (say) .5 km. Per A, the light takes only 1/600000 seconds to cross B's km. However, per A, the end of B's kilometer is moving such that the the light travels 2 of A's km before reaching the end of B's km. So, per A, the time between B's source flashing, and B's km end receiving it is 2/300000 seconds. But, per A, B's clock is running at 1/2 speed. So it only advances 1/300000 seconds. Thus A sees how B gets a speed of c, just like A does. B sees their own measurement the same way A sees his own measurements. B sees A's measurement the same way A sees B's measurement.

 

[Dale]

He was talking about pre-SR physics, or classical physics. The only time that existed then was absolute time, and the only clock synchronization that existed then was absolute synchronization.

Sure, but my question to you which you continued to avoid rather than address was HOW to synchronize the clocks in your proposed experiment. Whether the synchronization procedure gives absolute or relative synchronization is not the question. The question is experimentally how to synchronize clocks.

You are the one asking for an experiment, so a reply about synchronization "on paper" is simply a transparent attempt to dodge the question.

It was you who claimed that there exist tests of SR.

There are many tests of SR, the "direct" test you are asking for is not one of them, and I never claimed it was.

How else could a pre-SR observer get c for light's one-way speed other than by using the absolutely synchronous clocks of classical physics?

By using clocks synchronized using the Einstein synchronization convention. For such clocks the one way speed of light is guaranteed to be c.

Simply by giving us these one-way light speeds, Einstein was clearly talking about the use of the absolutely synchronous clocks of classical physics. This is so obvious that saw no need to provide the dreary details. (Please do not accuse me of misrepresenting anyone.)

This is a misrepresentation. Einstein clearly defined what he meant by simultaneity in the beginning section of his 1905 paper. He most clearly and emphatically did not mean absolutely synchronous clocks. As I said earlier, such blatant misrepresentation is not permitted on this forum.

What I was saying is that light's one-way invariance cannot even be "manually forced" because it is physically impossible - it cannot exist given nature as-is.

Not only is it not impossible, it is guaranteed under Einsteins synchronization convention. You admitted that it could be done previously, calling it "manually forcing". I don't know why you are backtracking now.

Suppose I have two clocks 10 ft apart. When one clock reads 0 it sends a light pulse to the other which is received and reflected back when the other clock reads 10 ns (c=1 ft/ns), and then the reflection is received at the first clock at 20 ns, then they are synchronized according to Einsteins definition and the one way speed of light is guaranteed to be c. We can always adjust the time on the second clock so that this is true, and since the two way speed of light is c in all frames this process can be done in all frames.