A critique of Mike Fontenot's CADO scheme

[ghwellsjr]

Mike Fontenot has a scheme he calls CADO for Current Age of a Distant Object. He has presented some of his ideas in this thread:

https://www.physicsforums.com/showthread.php?t=436131

But the complete description of his scheme is presented in a paper that costs $15 which I have a copy of. I believe the entire foundation of his claims is flawed and here's why:

Mike claims that one of Einstein's two assumptions is:

...ASSUME that the speed of any given light pulse is always measured to be the same by all inertial observers...

But this is decidedly not what Einstein presented as one of his two postulates that form the basis of Special Relativity. In his 1905 paper and in subsequent publications, he always maintained that although the average round-trip speed of light would be measured as c, the division of the time intervals for each direction of the trip was completely arbitrary and he chose to define the two portions to take an equal amount of time.

But Mike claims that the slow transport of clocks yields exactly the same result which raises time synchronization from an arbitrary (relative) definition to a "real" and "meaningful" quantity. He rejects the notion that only frame invariant quantities are legitimate and instead adopts the notion that measured quantities are expressions of reality.

So instead of recognizing that it is not possible to talk about the timing of two separated events in an absolute sense, Mike claims that if an observer can measure it, then it is of necessity the ONLY valid statement that can be made, thus his CADO.

Mike is offering a theory that is counter to Einstein's theory of special relativity. What he fails to realize is that the measurement using slow transport of clocks is just one of many different measurements that all appear to an inertial observer that he is stationary in the presumed ether. The problem is that these measurements cannot be reconciled between different observers having a relative motion or for a single observer who has accelerated between making the measurements. In other words, the fact that the slow transport of clocks appears to look just like Einstein's arbitrary definition of time synchronization of distant clocks is part of the problem, not part of the solution.

 

[Mentz114]

Although I don't agree with everything you've said, that's very interesting thank you.

I would not read a paper with the title Current Age of a Distant Object, because the word 'Current' is not uniquely defined in the context. 'Now' is a subjective experience not shared by observers moving relative to each other, so it seems futile from the outset for one observer to declare that a distant objects age is x 'now'.

 

[Dale]

"...ASSUME that the speed of any given light pulse is always measured to be the same by all inertial observers... " - Mike Fontenot (CADO)

"Any ray of light moves in the 'stationary' system of co-ordinates with the determined velocity c" - Einstein (OEMB)

But this is decidedly not what Einstein presented as one of his two postulates that form the basis of Special Relativity.

I don't know, they seem equivalent to me.

Mike claims that if an observer can measure it, then it is of necessity the ONLY valid statement that can be made, thus his CADO.

My primary objection is that by the principle of general covariance all coordinate systems will agree on every possible measurement. Mike has never provided a single example of any coordinate system disagreeing on the outcome of any measurement, and yet this is the supposed thing which makes his coordinate system unique and prefered. It is, in fact, not unique.

 

[grav-universe]

The only way to synchronize the clocks in inertial frames so that all observers agree upon the "nows" is to pick an arbitrary inertial reference frame and then set clocks in all other inertial frames to have no simultaneity difference along the line of travel when viewed from that frame of reference, so zero rather than d v / c^2 for SR. The other frames will now also measure no simultaneity differences for the reference frame or each other as well, and there would be no sudden time jump of the stay at home observer according to the traveling observer at the point of turnaround in the twin paradox, which does seem more natural.

There would still be the normal time dilation and length contraction of objects in other frames as viewed from the reference frame, but the other frames will view the inverse of that for the reference frame and the inverse for each other, rather than symmetrically. In other words, instead of measuring each other as length contracted, one frame will view the other as contracted while the other views the first as elongated by the same amount, as one would normally expect before being introduced to the simultaneity convention of SR, so seems somewhat more natural as well. The same goes for time dilation, one frame veiwing the clocks of another as slower while the other views the first frame's clocks as faster by the same amount. Observers traveling at the same speed relative to the reference frame will measure no time dilation or length contraction of each other.

Finally, inertial frames would still measure the same speed of each other, although a different speed than before, but light would only be measured to travel at c by the reference frame, while all other frames would measure it to travel at different speeds in different directions, although the two way speed would still be measured as c. This simultaneity convention does have its advantages, it makes more sense in some ways, and I personally have begun using it more to draw out some details better and perhaps even a little easier than using the symmetry of the Einstein simultaneity convention, although that doesn't make it any more "correct". In fact, by using this convention, we would then introduce a non-symmetry within individual frames, such as with a rotating wheel, now timed to rotate slower on one edge than the other due to the different simultaneity used, as well as for something like bouncing objects off of a wall, which otherwise might rebound with the same reflection speed as the incident speed, but now is measured to travel at different speeds before and after the rebound, as well as objects ejected in different directions by the same mechanism being measured at different speeds in different directions, and so on.

 

[jtbell]

In [Einstein's] 1905 paper and in subsequent publications, he always maintained that although the average round-trip speed of light would be measured as c, the division of the time intervals for each direction of the trip was completely arbitrary and he chose to define the two portions to take an equal amount of time.

But Mike claims that the slow transport of clocks yields exactly the same result which raises time synchronization from an arbitrary (relative) definition to a "real" and "meaningful" quantity.

Synchronization using "slow clock transport" does give the same result, in the limit as v --> 0, as Einstein's procedure which assumes that the speed of light is the same in both directions. You end up with the same laws of physics.

In Einstein's procedure, the "division of the time intervals for each direction of the trip [is] completely arbitrary" in the sense that you can decide on a different rule for the division, which leads to a different, but nevertheless consistent, set of laws of physics.

See for example, this thread, especially the last post which notes that if you use a non-standard clock-synchronization method you have to re-define the relationship between velocity and momentum.

 

[GrayGhost]

Although I don't agree with everything you've said, that's very interesting thank you.

I would not read a paper with the title Current Age of a Distant Object, because the word 'Current' is not uniquely defined in the context. 'Now' is a subjective experience not shared by observers moving relative to each other, so it seems futile from the outset for one observer to declare that a distant objects age is x 'now'.

If the CADO (current age of distant observer) is marked by an event, then all observers must agree, given his clock's date time signifies his age. IOWs, his clock would have to have been at birth, or we'd have to have confirmation of his/her age in relation to some prior clock readout he/she possessed (and the clock assumed always to tick perfectly). However, if there is no event used as a marker, then it's left to the personal opinion of the observer which completely depends upon his own sense-of-simultaneity (and thus relative velocity and range) and thus coordinate values ... and so observers of luminal relative v will disagree.

However, to say "CURRENT AGE OF DISTANT OBSERVER" in-and-of-itself does not suggest one-way-or-the-other as to whether every observer must agree. It could be "per POV". If I interpret Mike Fontenot's statements correctly, he is saying only that the twin B and co-located MSIRF observer agree on the CADO. yes?

GrayGhost

 

[GrayGhost]

"...ASSUME that the speed of any given light pulse is always measured to be the same by all inertial observers... " - Mike Fontenot (CADO)

"Any ray of light moves in the 'stationary' system of co-ordinates with the determined velocity c" - Einstein (OEMB)I don't know, they seem equivalent to me.

Me too.

My primary objection is that by the principle of general covariance all coordinate systems will agree on every possible measurement. Mike has never provided a single example of any coordinate system disagreeing on the outcome of any measurement, and yet this is the supposed thing which makes his coordinate system unique and prefered. It is, in fact, not unique.

EDIT: For clarity of point, I made a few edits (re-statements) which are highlighted ...

I think the issue is really this though ...

If we are to compare the differences between competing non-inertial spacetime transformation methods, then IMO the following must be considered in determining which is preferred ...

Twin B runs his transformation method for twin A ...

1) twin B calculates the current A-clock time readout, for some B-instant.
2) twin B calculates his own range from twin A per A, at that same B-instant.​

After the twin's flight test is completed, we determine the solns for the above 2 calculations ... using the twin A and twin B track and navigation data collected, using each competing method for spacetime transformation. So ...

If transformation methods determine a different current A-time-readout per B for any specific B-time, and they determine a different B-range (wrt A per A) at that A-time, then the ones that are correct should be the one's that match A's results for the same 2 calculations.

If transformation methods determine a different current A-time-readout per B for any specific B-time, yet they determine the same B-range (wrt A per A) at that corresponding A-time, then there would be a problem ... because twin A can agree with only one of them.

If transformations methods determine the same current A-time-readout per B for any specific B-time, yet they determine a different B-range (wrt A per A) at that A-time, then there would be a problem ... because twin A can agree with only one of them.​

Whichever non-inertial transformation method agrees with twin A's observations and LT results, would seem to be a correct method. It seems to me that the LTs are all we have as a tool for spacetime transformation (given we are not considering the general theory here, and considering only flat spacetime). I say this because twin A is always inertial, and the LTs apply from his POV. Also, because SR is an accepted theory of spacetime transformation. Now, no one disputes that twin A must do extra work over and above the effort involved in an all-inertial scenario, so that's not the issue here. It would seem that all observers must concur with the twin A data and LT spacetime transformations A made (of B), which are based on the accepted SR.

Now if all non-inertial transformation methods agree on everything, then I'd say they are all good. If not, then not all good.

GrayGhost

 

[GrayGhost]

Synchronization using "slow clock transport" does give the same result, in the limit as v --> 0, as Einstein's procedure which assumes that the speed of light is the same in both directions. You end up with the same laws of physics.

Agreed.

In Einstein's procedure, the "division of the time intervals for each direction of the trip [is] completely arbitrary" in the sense that you can decide on a different rule for the division, which leads to a different, but nevertheless consistent, set of laws of physics.

All you are saying here is that they can measure space and time differently, but the laws of physics are invariant under Lorentz rotations, yes?

GrayGhost

 

[jtbell]

With a different synchronization convention, the resulting "new" laws of physics would be invariant under Lorentz transformations. At least that's how I understand it.

 

[GrayGhost]

With a different synchronization convention, the resulting "new" laws of physics would be invariant under Lorentz transformations. At least that's how I understand it.

My understanding is that a synchronisation convention that differs with the Einstein/Poincare method cannot have an invariant 1-way speed of light. If not, wouldn't the 1st relativity postulate be violated?

GrayGhost

 

[pervect]

IT was mentioned that the CADO paper costs 15 dollars. Has it actually been published somewhere? And was this publication (assuming my guess is correct, but I don't see why else it would cost money) peer-reviewed? I've been assuming to date that it was NOT peer reviewed, based on what seems to me to be some fairly obvious inconsistencies between its claims and my textbooks.

I'm not going to rehash my comments in depth here.

see https://www.physicsforums.com/showpost.php?p=2961936&postcount=50

1) Any cado-like approach must either prefer one of the two observers over the other (i.e. when the worldlines cross, it throws out the inconsistent coordinates) or it must assign the same event in space-time two different time coordinates.

 

[JesseM]

With a different synchronization convention, the resulting "new" laws of physics would be invariant under Lorentz transformations. At least that's how I understand it.

It depends on what kind of different synchronization convention you have in mind, right? If you pick a preferred frame which uses Einstein's method and then have all other frames synchronize their clocks to agree with the preferred frame's definition of simultaneity, this would be a convention where the laws of physics would have different equations in different frames. I suppose if you could come up with a convention that could be enacted by an observer in a sealed compartment with no knowledge of the compartment's motion relative to other observers (as is possible with the Einstein synchronization convention), then by the principle of relativity all observers should see the same laws of physics when they write them down in a coordinate system based on this convention, but I wonder if it's even possible to come up with a non-Einstein convention that can be constructed by totally sealed observers this way, where different observers can't even communicate about things like which direction they consider to be the one of increasing x-coordinate (so they can't have rules saying that light is defined to be faster in the +x direction than the -x direction, for instance).

 

[JesseM]

IT was mentioned that the CADO paper costs 15 dollars. Has it actually been published somewhere? And was this publication (assuming my guess is correct, but I don't see why else it would cost money) peer-reviewed? I've been assuming to date that it was NOT peer reviewed, based on what seems to me to be some fairly obvious inconsistencies between its claims and my textbooks.

Mike said the paper was "Accelerated Observers in Special Relativity", published in "Physics Essays, December 1999, p. 629. Whether or not the papers are reviewed by the editors, the journal often publishes totally fringe papers, I see from looking at the list of 1999 issues that in March 1999 they published a paper by fellow physicsforums poster Gordon Watson about his "refutation" of Bell's theorem (see this thread for Gordon's continued efforts to push this refutation 12 years later) and if you look at the list of recent titles on their main page you see a lot of other fringe claims.

 

[ghwellsjr]

"...ASSUME that the speed of any given light pulse is always measured to be the same by all inertial observers... " - Mike Fontenot (CADO)

"Any ray of light moves in the 'stationary' system of co-ordinates with the determined velocity c" - Einstein (OEMB)

But this is decidedly not what Einstein presented as one of his two postulates that form the basis of Special Relativity.

I don't know, they seem equivalent to me.

The issue is whether the speed of the one-way "ray of light" is measured to be c (as Mike is claiming) or defined to be c (as Einstein is claiming).

Your quote from OEMB is taken out of context. Here is the entire quote:

The following reflexions are based on the principle of relativity and on the principle of the constancy of the velocity of light. These two principles we define as follows:--

1. The laws by which the states of physical systems undergo change are not affected, whether these changes of state be referred to the one or the other of two systems of co-ordinates in uniform translatory motion.​

2. Any ray of light moves in the "stationary'' system of co-ordinates with the determined velocity c, whether the ray be emitted by a stationary or by a moving body. Hence

velocity = (light path) / (time interval)​

where time interval is to be taken in the sense of the definition in § 1.​

And, of course, § 1 is where we read:

We have not defined a common "time'' for A and B, for the latter cannot be defined at all unless we establish by definition that the "time'' required by light to travel from A to B equals the "time'' it requires to travel from B to A. [Emphasis in original]​

So I'm really surprised that you can't see the difference between Mike's statement and Einstein's statement, especially after you have made so many statements in the past that you can't measure the one-way speed of light, such as:

There is NO WAY to measure the one-way speed of light, and there is no such thing as the one way speed of light "chosen by nature". The one way speed of light is something that a human being DEFINES by virtue of CHOOSING an arbitrary synchronization convention.

 

[Dale]

The issue is whether the speed of the one-way "ray of light" is measured to be c (as Mike is claiming) or defined to be c (as Einstein is claiming).

I do understand that difference, I just didn't notice it when reading it. Thanks for clarifying.

 

[JesseM]

The issue is whether the speed of the one-way "ray of light" is measured to be c (as Mike is claiming) or defined to be c (as Einstein is claiming).

What precisely defines the difference between "measured" and "defined"? It can't just be that measurements are coordinate-independent, since then you couldn't say that the two-way speed is "measured" either. And "defined" can't mean we could judge something to be true just by looking at the definitions even if we knew nothing about the laws of physics, since you treat both postulates as "definitions" yet it's a nontrivial fact about the laws of physics that it's possible to find a set of coordinate systems satisfying both postulates, we could easily imagine a universe with different laws where this wasn't possible.

 

[Dale]

If we are to compare the differences between competing non-inertial spacetime transformation methods, then IMO the following must be considered in determining which is preferred ...

Now if all non-inertial transformation methods agree on everything, then I'd say they are all good. If not, then not all good.

I didn't really follow your list of things that must be considered. Different coordinate systems will disagree on the labels assigned to many different things. This includes labels such as the coordinate numbers themselves, and more conceptual labels such as "simultaneous" or "velocity". There are a few conceptual labels that they will agree on, such as "proper time" and "spacetime interval", and those things are called invariants or scalars. The result of any possible measurement performed under any possible experiment is a scalar, so it is agreed on by all coordinate systems.

 

[ghwellsjr]

What precisely defines the difference between "measured" and "defined"? It can't just be that measurements are coordinate-independent, since then you couldn't say that the two-way speed is "measured" either. And "defined" can't mean we could judge something to be true just by looking at the definitions even if we knew nothing about the laws of physics, since you treat both postulates as "definitions" yet it's a nontrivial fact about the laws of physics that it's possible to find a set of coordinate systems satisfying both postulates, we could easily imagine a universe with different laws where this wasn't possible.

We normally treat our measurements as valid but according to Einstein, we run into a problem:

We might, of course, content ourselves with time values determined by an observer stationed together with the watch at the origin of the co-ordinates, and co-ordinating the corresponding positions of the hands with light signals, given out by every event to be timed, and reaching him through empty space. But this co-ordination has the disadvantage that it is not independent of the standpoint of the observer with the watch or clock, as we know from experience.​

It's because different observers get conflicting measurements that forces us to rethink our measurements and the one that Einstein settled on was the time for each portion of a round-trip speed of light measurement.

Keep in mind, this thread is about Mike Fontenot's CADO scheme and how he justifies it. Maybe I should have made the point stronger in my first post, but I'm really explaining his definitions of "elementary observations", "elementary measurements" and "elementary calculations". For example:

I don't think c being constant for all inertial observers IS derived ...

Of course it is?

Some people DO go to great lengths to avoid making that assumption. Even Einstein, in his Crown book, DID make a point of avoiding it, and instead showed that he could instead start with an arbitrary definition of simultaneity. But if you read essentially all of his other writings on special relativity, he usually just states that all inertial observers will measure any given light pulse to have exactly the same speed, and then just gets going with the stuff that really matters.

I think attempts to avoid starting with the speed-of-light assumption, while possible, result in a more arbitrary-seeming approach. Much more straightforward, in my opinion, is to start with the speed-of-light assumption, based purely on the experimental evidence, and then go from there. In practice, that's usually what's done, even if it's not talked about much.

It's the kind of thing that can be debated and argued about endlessly, but which doesn't amount to a hill-of-beans in practice.

Mike Fontenot

Here is a quote from the Crown book Mike referenced http://www.bartleby.com/173/8.html:

That light requires the same time to traverse the path A —> M as for the path B —> M is in reality neither a supposition nor a hypothesis about the physical nature of light, but a stipulation which I can make of my own freewill in order to arrive at a definition of simultaneity. [Emphasis in original]​

Mike claims that Einstein became lax on this point (without providing any reference) and discounts it as not amounting to a hill-of-beans but it is really fundamentally important to the theory of Special Relativity. It would be one thing if Mike would simply say that he's rejecting Einstein's theory and promoting his own new and different theory, but instead, he's claiming that he alone understands Einstein's theory and everyone else gets it wrong.

 

[JesseM]

We normally treat our measurements as valid but according to Einstein, we run into a problem:

We might, of course, content ourselves with time values determined by an observer stationed together with the watch at the origin of the co-ordinates, and co-ordinating the corresponding positions of the hands with light signals, given out by every event to be timed, and reaching him through empty space. But this co-ordination has the disadvantage that it is not independent of the standpoint of the observer with the watch or clock, as we know from experience.​

It's because different observers get conflicting measurements that forces us to rethink our measurements and the one that Einstein settled on was the time for each portion of a run-trip speed of light measurement.

By "run-trip" do you mean "round-trip"? The method "that Einstein settled on" does involve a two-way trip from A to B back to A, but it's based on making the one-way speed equal on both legs so the time the signal bounces off B is set to be halfway between the time it left A and the time it returned to A. In any case I see no connection between your comments and my original question about the difference between a "measurement" and a "definition", you haven't given any clear notion of what you mean by that distinction.

Keep in mind, this thread is about Mike Fontenot's CADO scheme and how he justifies it. Maybe I should have made the point stronger in my first post, but I'm really explaining his definitions of "elementary observations", "elementary measurements" and "elementary calculations".

I think the problem is that his terms are just ill-defined, and explaining them in terms of ill-defined notions like the measurement/definition distinction doesn't really help.

 

[ghwellsjr]

By "run-trip" do you mean "round-trip"?

Yes, thanks, I fixed it.

The method "that Einstein settled on" does involve a two-way trip from A to B back to A, but it's based on making the one-way speed equal on both legs so the time the signal bounces off B is set to be halfway between the time it left A and the time it returned to A.

Yes, that is what Einstein said, just as I described in my first post:

In his 1905 paper and in subsequent publications, he always maintained that although the average round-trip speed of light would be measured as c, the division of the time intervals for each direction of the trip was completely arbitrary and he chose to define the two portions to take an equal amount of time.

In any case I see no connection between your comments and my original question about the difference between a "measurement" and a "definition", you haven't given any clear notion of what you mean by that distinction.

This isn't my distinction--it's Einstein's. Do you agree with Mike that it doesn't amount to a hill of beans or do you agree with Einstein when he said:

That light requires the same time to traverse the path A —> M as for the path B —> M is in reality neither a supposition nor a hypothesis about the physical nature of light, but a stipulation which I can make of my own freewill in order to arrive at a definition of simultaneity.​

NOTE: here he is talking about M being the midpoint between A and B which amounts to the same thing as going from A to B and reflecting back to A

I think the problem is that his terms are just ill-defined, and explaining them in terms of ill-defined notions like the measurement/definition distinction doesn't really help.

I guess you are calling Einstein's distinction an "ill-defined notion". Are you sure you want to do that?

You and others have complained that Mike never defines what he means by "elementary measurements" but insists that you find out from his paper. I have done that and am reporting what Mike is saying.

I have already addressed the issue of why we cannot measure the one-way speed of light in this post:

There are several reasons that I keep saying that we cannot measure the one-way speed of light, not the least of which, it's what Einstein said in his 1905 paper and what he repeated in several explanations in the years following.

But beyond that, the one-way speed of light is the characteristic of an absolute ether rest frame. By that, I mean, only when you are at rest in the ether will the two halves of the measureable round-trip (from light source/detector to mirror and back to light source/detector) light time be equal. If you are moving with respect to the ether, then it will take longer for the light to get to the mirror than it will for the light to get back to the source/detector (or the other way around). Being able to identify the difference in these two times is identical to being able to identify the absolute ether rest frame.

When you attempt to make the measurement, you get a null result, just like MMX. What if the first time Michelson did his experiment and could not measure any ether wind, he stopped right there and wrote his paper declaring that he had discovered the absolute ether rest frame? What a co-incidence!

The same thing happens when you attempt to measure the one-way speed of light, you will measure that it is identical to c. Now you can claim that you have discovered the absolute ether rest frame. But you better not do it again after you have accelerated with respect to your first measurement or you will discover that nature had fooled you just like it would have fooled Michelson if he had done his experiment just one time.

There is another way to consider this problem. Suppose in your rest frame you measure the one way speed of light and get c. In other words, both halves of the round-trip speed of light take the same time. Then you observe someone else traveling at a high rate of speed. In your rest frame, that other person will measure the round trip speed of light to be c (keeping in mind time dilation and length contraction and relativity of simultaneity) but you will conclude that each half of the round trip will not take an equal time. However, as you observe him measuring the time for the two halves, you see that he also concludes that they are equal (again because of time dilation, length contraction and relativity of simultaneity). Keep in mind, I'm only considering one frame of reference here.

Now why does Einstein say that the assignment of equal times to both halves of the round trip speed of light measurement is an arbitrary definition, as opposed to anything that can be measured? It's because the alternative theory popular at the time, Lorentz Ether Theory, maintained that there was a single preferred absolute ether rest frame and that we on the Earth are also traveling with respect to this rest frame. We are like the other observer in my above example. We could use a single agreed upon rest frame as the absolute rest frame as our single definition from which to make all measurements. Then when we use that definition to assign the times of the two halves of the round trip light speed experiment, we will say that they are not equal, just like we will say that our lengths are contracted in the direction of the ether wind and our clocks are running slow and we have simultaneity issues but they are all consistently resolved by referring back to our arbitrarily agreed upon absolute rest frame.

If my words don't clarify the distinction between a measurement and a definition of the one-way speed of light, maybe you should study Einstein writings in 1905 and 1920. Like I said, this isn't my idea, I could never have thought this up on my own, I learned it from Einstein.

 

[JesseM]

Do you agree with Mike that it doesn't amount to a hill of beans or do you agree with Einstein when he said:

That light requires the same time to traverse the path A —> M as for the path B —> M is in reality neither a supposition nor a hypothesis about the physical nature of light, but a stipulation which I can make of my own freewill in order to arrive at a definition of simultaneity.​

NOTE: here he is talking about M being the midpoint between A and B which amounts to the same thing as going from A to B and reflecting back to A

I guess you are calling Einstein's distinction an "ill-defined notion". Are you sure you want to do that?

No, I'm calling your specific claim that the two-way speed is a "measurement" and the one-way speed is a "definition" an ill-defined notion. Also, if you specifically synchronize clocks using Einstein's method of light signals of course it is logically impossible that the one-way speed would fail to be equal in both directions, but that doesn't mean Einstein would also say that the one-way speed being the same in both directions would be "neither a supposition nor a hypothesis" if we used the slow transport method of synchronization, since even though these two methods are equivalent under our universe's laws of physics it would be logically possible to have a universe where they weren't.

 

[GrayGhost]

I didn't really follow your list of things that must be considered. Different coordinate systems will disagree on the labels assigned to many different things. This includes labels such as the coordinate numbers themselves, and more conceptual labels such as "simultaneous" or "velocity". There are a few conceptual labels that they will agree on, such as "proper time" and "spacetime interval", and those things are called invariants or scalars. The result of any possible measurement performed under any possible experiment is a scalar, so it is agreed on by all coordinate systems.

Yes. However, here's my point ...

Consider twin B in his vessel along with 2 other passengers. Each (of the 3) uses whatever method suits them to determine where twin A was when he did a flyby of an inertial boey (the event), and each uses whatever other method they wish to determine the following ...

1. what was the A-time-readout at said event?
2. what was the B-range per A at that A-time?​

Now, let's say all 3 fellows differed in their prediction. After the flight test is done, all the twin A track and navigation data is collected for analysis, and we ask ...

OK, at the flyby event ...

Q1. what did the A-clock actually then read per A himself?
Q2. what did twin A then hold for the current twin B range?​

We then look to see who (of the 3) got which answers right ...

There are a few possible outcomes here ...

1. Noone predicted Q1 correctly. Noone predicted Q2 correctly. This is no good.

2. One (or more) predicted Q1 correctly. Noone predicted Q2 correctly. This is no good.

3. One (or more) predicted Q1 correctly. One (or more) predicted Q2 correctly, and one (or more) of those got the first question correct too. This is great. At least one has a good process going.​

I fully understand the difference between invariants and coordinate values, but here's the thing ...

Let's say one fellow got Q1 wrong, but somehow came up with a B-range-per-A that agrees with twin A's data associated with that wrong time. I submit that his transformation method was no good, even if it was somehow in part correct. If the A-clock read 2:22 per A at the flyby event, and the B-range was then 0.25 lt-sec per A, then the fellows in twin B's vessel must predict both these values if their method is to be considered good.

You disagree? If so, why?

thanx,
GrayGhost

 

[GrayGhost]

No, I'm calling your specific claim that the two-way speed is a "measurement" and the one-way speed is a "definition" an ill-defined notion.

The 1-way speed of light has never been verified as invariant c by experiment, yes?

Also, if you specifically synchronize clocks using Einstein's method of light signals of course it is logically impossible that the one-way speed would fail to be equal in both directions, but that doesn't mean Einstein would also say that the one-way speed being the same in both directions would be "neither a supposition nor a hypothesis" if we used the slow transport method of synchronization, since even though these two methods are equivalent under our universe's laws of physics it would be logically possible to have a universe where they weren't.

I suggest we should run that slow transport test soon, see what happens :) I figure Paul Allen could fund it !

GrayGhost

 

[JesseM]

The 1-way speed of light has never been verified as invariant c by experiment, yes?

I think tests of the one-way speed using the slow transport method of synchronization have been done, see this abstract for example.

 

[ghwellsjr]

No, I'm calling your specific claim that the two-way speed is a "measurement" and the one-way speed is a "definition" an ill-defined notion.

JesseM, I have the highest regard for what you post on this forum as I have stated before, so now I find myself in this awkward position of contesting you. Is it that when you read Einstein's paper, you don't see that he affirmed the two-way speed of light to be measured as c and he defined the one-way speed of light to be an arbitrary definition? His paper and his book are very clear to me and I think it is unfair of you to say that this is my specific claim as if now I am called upon to defend it.

Here's what he said about the measurement of the two-way speed of light near the end of section 1 of OEMB:

In agreement with experience we further assume the quantity

(2AB)/(t'_A-t_A) = c​

to be a universal constant--the velocity of light in empty space.​

Are you suggesting that he was not affirming the measured two-way speed of light in this statement?

Here's what he said a little earlier in his paper about the two one-way portions of the round-trip measurement:

We have not defined a common "time" for A and B, for the latter cannot be defined at all unless we establish by definition that the "time" required by light to travel from A to B equals the "time" it requires to travel from B to A.​

Are you suggesting that he was not denying that the one-way times could not be measured?

Please try to help me understand why you think this claim is mine and not Einstein's.

Also, if you specifically synchronize clocks using Einstein's method of light signals of course it is logically impossible that the one-way speed would fail to be equal in both directions, but that doesn't mean Einstein would also say that the one-way speed being the same in both directions would be "neither a supposition nor a hypothesis" if we used the slow transport method of synchronization, since even though these two methods are equivalent under our universe's laws of physics it would be logically possible to have a universe where they weren't.

Are you suggesting that Einstein never heard of or thought of the slow transport method of synchronization and that if he had, he would have rescinded his 1905 paper and his 1920 book?

 

[ghwellsjr]

The 1-way speed of light has never been verified as invariant c by experiment, yes?

I suggest we should run that slow transport test soon, see what happens :) I figure Paul Allen could fund it !

GrayGhost

I think tests of the one-way speed using the slow transport method of synchronization have been done, see this abstract for example.

Didn't I cover all this in my long quote of myself in post #20?

 

[JesseM]

JesseM, I have the highest regard for what you post on this forum as I have stated before, so now I find myself in this awkward position of contesting you. Is it that when you read Einstein's paper, you don't see that he affirmed the two-way speed of light to be measured as c and he defined the one-way speed of light to be an arbitrary definition? His paper and his book are very clear to me and I think it is unfair of you to say that this is my specific claim as if now I am called upon to defend it.

Here's what he said about the measurement of the two-way speed of light near the end of section 1 of OEMB:

In agreement with experience we further assume the quantity

(2AB)/(t'_A-t_A) = c​

to be a universal constant--the velocity of light in empty space.​

Are you suggesting that he was not affirming the measured two-way speed of light in this statement?

Sure, I personally have no problem with talking about "measurement" of coordinate-dependent quantities (rest length would be another example), but it just shows that drawing some absolute dividing line between "definitions" and "measurements" is pretty questionable, at least if you aren't able to give clear criteria for what separates the two.

Here's what he said a little earlier in his paper about the two one-way portions of the round-trip measurement:

We have not defined a common "time" for A and B, for the latter cannot be defined at all unless we establish by definition that the "time" required by light to travel from A to B equals the "time" it requires to travel from B to A.​

Are you suggesting that he was not denying that the one-way times could not be measured?

"not denying that the one way-times could not be measured" is a triple negative which is a bit confusing, I guess you are asking if I am denying that he claimed the one-way times couldn't be measured, only defined? If so, I don't think he was making the very broad claim that no possible experiment could qualify as a measurement of one-way speed, instead it seems to me he was just saying that under the clock synchronization method he had proposed, it was true by definition that the time was the same in both directions.

Are you suggesting that Einstein never heard of or thought of the slow transport method of synchronization and that if he had, he would have rescinded his 1905 paper and his 1920 book?

That question is kind of over-the-top IMO, even if he decided his previous comments about the one-way speed being purely a matter of definition were wrong, they were a very minor part of his paper and book which wouldn't require "rescinding" them. But in any case, as I said I see his comments there as just stating that under the specific synchronization method he had discussed the isotropy of the one-way speed was just a matter of definition, so I don't think those comments of his are incorrect. And of course if we adopt the slow transport method then the method itself is just a definition/convention about what it means to by synchronized, but relative to this definition/convention I think we can talk about "measuring" the one-way speed.

 

[ghwellsjr]

Sure, I personally have no problem with talking about "measurement" of coordinate-dependent quantities (rest length would be another example), but it just shows that drawing some absolute dividing line between "definitions" and "measurements" is pretty questionable, at least if you aren't able to give clear criteria for what separates the two.

Well, since Einstein was establishing the definition of what the time coordinate of a frame of reference was, I don't see how we can require him to restrict "measurement" to coordinate-dependent quantities.

Besides, I still think you are missing the point that Einstein was making which is that as much as we would like to trust our measurement of the one-way speed of light, we run into a conflict with what two different observers would measure. That is the reason we have to look for another way to resolve the issue of the one-way speed of light. We don't have this problem with the round-trip speed of light because two different observers always get the same answer.

So the clear criteria, according to Einstein as I quoted him in post #18 is that different observers get different measurements for the same thing.

"not denying that the one way-times could not be measured" is a triple negative which is a bit confusing, I guess you are asking if I am denying that he claimed the one-way times couldn't be measured, only defined? If so, I don't think he was making the very broad claim that no possible experiment could qualify as a measurement of one-way speed, instead it seems to me he was just saying that under the clock synchronization method he had proposed, it was true by definition that the time was the same in both directions.

I don't see how Einstein could have been more clear when he said he could choose any definition, including a different one than he chose. Suppose he did choose a different one where the times were not necessarily equal but that it disagreed with experimental evidence, would he then be wrong? I don't think so. He would just be agreeing with one of the other observers who got a different measurement.

That question is kind of over-the-top IMO, even if he decided his previous comments about the one-way speed being purely a matter of definition were wrong, they were a very minor part of his paper and book which wouldn't require "rescinding" them. But in any case, as I said I see his comments there as just stating that under the specific synchronization method he had discussed the isotropy of the one-way speed was just a matter of definition, so I don't think those comments of his are incorrect. And of course if we adopt the slow transport method then the method itself is just a definition/convention about what it means to by synchronized, but relative to this definition/convention I think we can talk about "measuring" the one-way speed.

I can see how you would think that his comments were a minor part of his paper if you don't recognize the importance of the aspect of the requirement for the one way speed of light to be an arbitrary definition but I really think you need to read his 1920 book. Even Mike recognizes that Einstein argued his case strongly in that book, he just thinks that Einstein eventually lost interest in the issue after that.

 

[GrayGhost]

Didn't I cover all this in my long quote of myself in post #20?

Ahhh yes, I missed that. Probably got distracted at the time.

There was no proof that light's 1-way speed was c, but it's clear that Einstein believed it in 1905. I could be wrong, but I figure Einstein defined his convention as such because of a combination of a few things ... the assumed homogeneity of space and time, the knowledge that mediums support energy transfer at some set speed, and Maxwell's theory. Poincare eventually pointed out that Einstein's convention (which is his own as well) may well have been the result of an inherent desire for the simplest solns. Let's face it, Einstein fully recognized the benefit of defining a 1-way light speed of invariant c. The solns are much simpler, arrived at much easier, and the theory's more elogant. However, it's probably true that it all comes down to our desire for simplicity. I figure we desire simplicity because of experience, and so the 1-way speed of light is likely truly c. I for one won't be believing otherwise until someone proves otherwise.

That said, I figure Einstein's choice of a 1-way light speed of c was a convention which he believed in, driven (in part) by realizing how much uglier nature would have to be otherwise.

GrayGhost

 

[JesseM]

Well, since Einstein was establishing the definition of what the time coordinate of a frame of reference was, I don't see how we can require him to restrict "measurement" to coordinate-dependent quantities.

Well, I just said that I have no problem with the notion of "measuring" coordinate-dependent quantities.

Besides, I still think you are missing the point that Einstein was making which is that as much as we would like to trust our measurement of the one-way speed of light, we run into a conflict with what two different observers would measure.

Are you talking about this quote?

We might, of course, content ourselves with time values determined by an observer stationed together with the watch at the origin of the co-ordinates, and co-ordinating the corresponding positions of the hands with light signals, given out by every event to be timed, and reaching him through empty space. But this co-ordination has the disadvantage that it is not independent of the standpoint of the observer with the watch or clock, as we know from experience.

If so, he's just talking about one specific method of defining simultaneity, where each observer defines the time of the event by when they receive the light from that event. There's no broad statement here about other methods (like slow transport) automatically being observer-dependent, he specifically says "this co-ordination has the disadvantage that it is not independent of the standpoint of the observer."

So the clear criteria, according to Einstein as I quoted him in post #18 is that different observers get different measurements for the same thing.

"Clear criteria" for what? If you think this is some sort of general statement about the difference between "measurements" and "definitions" (which is what I asked you for) you're reading things into the quote that clearly aren't there, he's just bringing up a possible method and pointing out a problem with it, he doesn't even use the words "measurement" or "definition".

I guess you are asking if I am denying that he claimed the one-way times couldn't be measured, only defined? If so, I don't think he was making the very broad claim that no possible experiment could qualify as a measurement of one-way speed, instead it seems to me he was just saying that under the clock synchronization method he had proposed, it was true by definition that the time was the same in both directions.

I don't see how Einstein could have been more clear when he said he could choose any definition, including a different one than he chose.

Huh? Are we still talking about this quote?

We have not defined a common "time" for A and B, for the latter cannot be defined at all unless we establish by definition that the "time" required by light to travel from A to B equals the "time" it requires to travel from B to A.

Nothing there about being able to "choose any definition, including a different one than he chose". He just says that you need a simultaneity convention to define a common time for A and B, and explains that to do this he is adopting the definition light has the same one-way speed in both directions. (I actually agree with your statement that he could have chosen a different definition, but you're reading something that isn't there if you think he said this in that quote, and in any case the fact that he could have chosen a different definition doesn't contradict my claim that it is possible to measure the one-way speed relative to some definitions that don't directly involve light, such as slow transport.)

Suppose he did chose a different one where the times were not necessarily equal but that it disagreed with experimental evidence

I don't get it, if you choose a different definition of simultaneity, how could it possible disagree with "experimental evidence"? If I say "I define clock B to be synchronized with clock A if clock B's reading with the light hits it is 3/4 of the way between clock A's reading when the light departs and clock A's reading when the light returns", what possible form of experimental evidence could "disagree" with this?

I don't think so. He would just be agreeing with one of the other observers who got a different measurement.

What "other observers who got a different measurement"? When he talked about observers getting different measurements that was specifically about what would happen if each observer defined the time of an event by when the light from the event reached them.

I can see how you would think that his comments were a minor part of his paper if you don't recognize the importance of the aspect of the requirement for the one way speed of light to be an arbitrary definition but I really think you need to read his 1920 book.

Remember, I am not claiming there is any objective coordinate-independent truth about the one-way speed of light, just that it may be "measured" with regard to certain simultaneity conventions which would themselves be arbitrary definitions. So the basic point that simultaneity itself is a matter of arbitrary definition, and that the one-way speed depends on this arbitrary definition, is not one I disagree with.

I have read the 1920 book, and I guess when you refer to the thing about the one way speed of light being a matter of arbitrary definition you're referring to this chapter, but I think you completely misunderstand the argument if you think it would fall apart if he were to agree that the one way speed can be "measured" relative to a simultaneity convention which is itself an arbitrary choice. Just imagine replacing this:

After thinking the matter over for some time you then offer the following suggestion with which to test simultaneity. By measuring along the rails, the connecting line AB should be measured up and an observer placed at the mid-point M of the distance AB. This observer should be supplied with an arrangement (e.g. two mirrors inclined at 90°) which allows him visually to observe both places A and B at the same time. If the observer perceives the two flashes of lightning at the same time, then they are simultaneous.

I am very pleased with this suggestion, but for all that I cannot regard the matter as quite settled, because I feel constrained to raise the following objection: “Your definition would certainly be right, if I only knew that the light by means of which the observer at M perceives the lightning flashes travels along the length A —> M with the same velocity as along the length B —> M. But an examination of this supposition would only be possible if we already had at our disposal the means of measuring time. It would thus appear as though we were moving here in a logical circle.”

After further consideration you cast a somewhat disdainful glance at me—and rightly so—and you declare: “I maintain my previous definition nevertheless, because in reality it assumes absolutely nothing about light. There is only one demand to be made of the definition of simultaneity, namely, that in every real case it must supply us with an empirical decision as to whether or not the conception that has to be defined is fulfilled. That my definition satisfies this demand is indisputable. That light requires the same time to traverse the path A —> M as for the path B —> M is in reality neither a supposition nor a hypothesis about the physical nature of light, but a stipulation which I can make of my own freewill in order to arrive at a definition of simultaneity.”

With this:

After thinking the matter over for some time you then offer the following suggestion with which to test simultaneity. Two clocks should be synchronized at the location A, then one should be moved extremely slowly to the location of B. When we perform this experiment, and subsequently send light between the clocks, we do find that the time to go from the clock at A to the clock at B is the same as the time to go from the clock at B to the clock at A.

I am very pleased with this demonstration, but for all that I cannot regard the matter as quite settled, because I feel constrained to raise the following objection: “Your definition would certainly be right, if I only knew that clock moved to B did not tick significantly faster or slower than the one at A as it traveled, in which case they might become significantly out-of-sync. But an examination of this supposition would only be possible if we already had at our disposal the means of measuring time. It would thus appear as though we were moving here in a logical circle.”

After further consideration you cast a somewhat disdainful glance at me—and rightly so—and you declare: “I maintain my previous definition nevertheless, because in reality it assumes absolutely nothing about the rates of moving clocks. There is only one demand to be made of the definition of simultaneity, namely, that in every real case it must supply us with an empirical decision as to whether or not the conception that has to be defined is fulfilled. That my definition satisfies this demand is indisputable. That the two clocks remain synchronized is in reality neither a supposition nor a hypothesis about the physical nature of clocks, but a stipulation which I can make of my own freewill in order to arrive at a definition of simultaneity.”

This would result in no need for any but cosmetic changes to the rest of his arguments.