[David Cooper]

If you're doing this on one planet and your cousin is doing the same thing on another planet moving relative to yours, both of you are making the same claim to be stationary, and at least one of you is being fooled.

No, I'm stationary from my PoV and he's stationary from his.
But, since these viewpoints are different there's no contradiction.
Nobody is being "fooled"

Of course someone is being fooled. Let's put your two experiments closer together so they're sharing the same space. We can call your clocks A and B and your cousin's clocks A' and B'. You've both separated them and are ready to time light moving from A to B (or A' to B'). Clock B' passes clock A before you send the light signal out that you want to time. Indeed, clock A' is right alongside clock A when the two signals are sent. Your signal reaches clock B a second later (if you're the one who's stationary). His signal has not reached clock B' yet and has to go a long way further before it can. So if he thinks his light signal took one second to go from A' to B', he's wrong. If he's right, then he must be stationary and you must be the one that's moving.

As I have pointed out before, I know that other people who are moving WRT me will see things differently- so it's no surprise that they will interpret the experiment I'm doing differently and will think the one-way speed of light I measure is different.
I know that.
But, as I pointed out before, they won't even agree with me about the speed of the bus into town, so I don't expect them to agree with me about the one way speed of light.
I'm only interested in measuring it in my frame of reference.

In which case, you must be aware that you almost certainly aren't measuring the real speed of light relative to you.

I was wrong about all these methods measuring light on a round trip though - you're certainly getting the same result as if you were measuring it on a round trip, but it might not quite be that. If you were to move your clock at the speed of light, for example, that would be the same as sending light from position A to B to synchronise the clocks and then sending light from A to B to see how long it takes to cover that course as judged by those clocks, which is practically the same thing as using a light signal to time itself over the course, so there is nothing two-way about it. If you move the clock at speeds a bit less than c, it's slightly different because some cycling is taking place in the clock (each tick involving something moving from one place to another and back - with the clock moving, the cycling thing won't move all the way back). The slower you move the clock, the closer these cycles are to being complete round trips. Infinitely-slow clock transport, if it was possible, would involve complete round trips for each cycle.

[Bored chemist]

It's not that anyone is wrong. it's a different point of view.
My cousin lives in France, I live in England.
If someone asks us "what's the name of the Capital city" we will give different answers- but nobody is being "fooled" are they?

[David Cooper]

It's not that anyone is wrong. it's a different point of view.
My cousin lives in France, I live in England.
If someone asks us "what's the name of the Capital city" we will give different answers- but nobody is being "fooled" are they?

They're answering different questions, just as they would if asked for the name of their mother. The issue with relativity is really very simple. If light is passing you at c relative to you and you then accelerate towards it, it cannot still be passing you at c relative to you. Anyone who believes it can be is buying into magic rather than science. The only model that can get round this issue is the eternal static block universe model where light has no speed as nothing moves at all, but that model also depends on magic for its existence because it can't account for how it was generated without switching to different laws of physics including an absolute frame of reference and Newtonian time.

[Bored chemist]

They're answering different questions,

Fine.
The two questions being asked are what's the one way speed of light as BC  determines it and what's the one way tipped of light as BC's cousin determines it.
Why would you expect the answers to always agree?

[jeffreyH]

Ok let's have a thought experiment. A ship 1 light second in length. A detector mid way that can detect in two directions, forward and backward. The ship is moving forward at 0.9999 etc the speed of light. We detect a photon from the forward direction at time t0 and another from the backward direction at time t1. Please give the time of emission of each photon with respect to the detector.

[David Cooper]

They're answering different questions,

Fine.
The two questions being asked are what's the one way speed of light as BC  determines it and what's the one way tipped of light as BC's cousin determines it.
Why would you expect the answers to always agree?

The questions being asked are, what's the apparent one-way speed of light relative to the apparatus as BC determines it based on the assumption that he isn't moving and setting up his apparatus to measure it as c, and what's the apparent one-way speed of light relative to the apparatus as BC's cousin determines it based on the assumption that he isn't moving and setting up his apparatus to measure it as c. Obviously they will both come up with the answer c, but at least one of them is not measuring the one-way speed of light relative to them.

[dutch]

If a clock runs slow because it's moved, it fails to record all the time that has passed for it, and that results in an error in its timing. The faster you move it, the bigger that error is.

The difference is in the rate the clocks tick. It's still not an error because the amount of time that passed for the clock is exactly the number the clock reads. All clocks work the same down to the subatomic scales (in every experiment ever done). I know exactly what you're trying to say but calling it an "error" is just wrong.

it fails to record all the time that has passed for it

The above is especially wrong. The time that's passed for it is exactly equal to what its clock reads (proper time). The clock is measuring the number of ticks that take place and there is no error for a moving clock. Clocks moving relative to an absolute rest frame would simply tick slower. This slower tick rate is no more invalid than the faster tick rate of "stationary" clocks.

 

E.g. IF the system is stationary, THEN a clock moving through the system runs slow. While we are discussing things under that condition ("IF the system is stationary"), everything said is governed by that condition. When we switch to a different condition such as "IF the system is moving at 8.866c", everything we then say is governed by that new condition. The fact that we can't tell which of the cases is true does not negate the truth (conditional truth) of what is said about that case on the basis that it's true if the condition is true and may not be true if the condition is false.

I tend not to believe the "block universe" model but it's still mathematically valid. Your logic is only true from the 3D LET perspective and is not true from a completely 4D "block" perspective. The reason why LET and SR still both remain valid is because we can't set ε absolutely to distinguish the two. The two certainly use a CONVENTION or an agreed upon set of rules to explain what ε is. This convention goes beyond simply setting a single reference frame. However, for the last 110 years countless geniuses arguing fiercely have not set ε in a theory beyond using a convention.

You keep pushing that LET or some version of it must be true and SR's 4D concept is wrong. I personally tend to not like the fully 4D conceptualization of SR but I don't need to choose between LET and SR here. All I need to do is show that ε is chosen arbitrarily. I've done this multiple times.

The Bored chemist keeps saying from his perspective he could measure c one-way. However, his perspective is chosen by assuming ε =1/2 then he makes his measurement (completely circular reasoning). He couldn't offer one shred of proof that ε =1/2 and he simply chooses it by CONVENTION. I could do the same thing while choosing ε =1/4.

Even the idea that ε ≠ 1/2 means that you're moving at velocity v is assumed via convention.

It's the choice of frame that selects a proposed one-way speed of light relative to the system.

OK. And theories like SR and LET simply set up ε and therefore "choice of frame" via convention. The entire way they view ε is through convention.

You choose a frame of reference and thereby conditionally assert that the speed of light is the same relative to that frame in all directions. That makes the speed of light not equal to c relative to objects moving through that frame in most directions and provides a different theory as to the reality of the situation to any of the theories based on using different frames (all of those theories being in contradiction of each other as only one of them can be true).

Yes, one (or at least one convention) is most definitely right and all others are probably wrong. However, we have no way to prove what ε is so we simply create theories that form an agreed upon way to choose ε. These agreements are called conventions. The agreements are not called reference frames.

You choose a frame of reference and thereby conditionally assert that the speed of light is the same relative to that frame in all directions. That makes the speed of light not equal to c relative to objects moving through that frame in most directions and provides a different theory as to the reality of the situation to any of the theories based on using different frames (all of those theories being in contradiction of each other as only one of them can be true).

In a completely 4D universe you can still have ε =1/2 for all frames and have them all right locally. In a 3D LET framework it can't work. I know you don't like the fully 4D concept and I don't like it either but I'm not going to argue against its math. However, Einstein still set ε to a certain value arbitrarily in his theories.

If you restrict yourself to ε=1/2, you are selecting the frame of reference in which the system is at rest, and that sheds no light on anything. It's only when you work things through using at least two different reference frames that you can gain a real understanding of what's going on.

Einstein locally chose ε=1/2 and reference frames moving at velocity v relative to any point are seen as "rotated" in a 4D structure in the fully 4D conceptualization. ε appears to be something other than 1/2 when using the Lorentz Transformation (which comes from LET) but it does not in the fully 4D structure. This is similar to how a car would look shorter when its going up a steep hill when viewed from above. However, the car is not truly shorter. Again you can choose to believe either SR or LET as both match every experiment ever done (either can extend to a general theory). SR is easier to work with because its just simpler to assume ε=1/2 as a convention.


You keep saying I'm obfuscating things. However, I'm simply not trying to get a simple question bogged down by a pro LET or pro SR sideshow.

The simple answer:

We can ONLY measure the one-way speed of light via an arbitrarily set convention because we arbitrarily set ε.

[David Cooper]

If a clock runs slow because it's moved, it fails to record all the time that has passed for it, and that results in an error in its timing. The faster you move it, the bigger that error is.

The difference is in the rate the clocks tick. It's still not an error because the amount of time that passed for the clock is exactly the number the clock reads. All clocks work the same down to the subatomic scales (in every experiment ever done). I know exactly what you're trying to say but calling it an "error" is just wrong.

It's what you've just said that's wrong because you're assuming that the amount of time that's passed for the clock is equal to the amount of time it's recorded. When a light clock is stationary, it ticks at maximum speed because the round trip distance is shortest. When you move it, the round trip distance increases, so the clock records fewer cycles in a given length of time. If you move a clock backwards and forwards at the right frequency and with the right timing, you can shorten the round trip for the light and make the clock tick faster than normal, but again it is not recording the amount of time that has passed for it as it is exaggerating the amount of time that has gone by. Move it backwards and forwards a different way and you can make it record less time passing than has actually passed. Any movement of a clock leads to an error in the amount of time it records. Why would anyone be fooled by one kind of failure for a clock to record the right amount of time that's passed for it while not being fooled by another? In all cases, the light is moving at the same speed through space without being slowed by any kind of slowing of time.

Here's another case that shows up the truth. Imagine a powerful distant source of gamma rays that damages DNA. Perpendicular to the direction these rays are coming, we run the twins "paradox" experiment, having one twin travel at very high speed and the other travel slowly. Both are exposed to the same amount of radiation, and the moving twin has interacted with it with greater intensity throughout. That twin can be "younger" but genetically more damaged. This business of him supposedly being younger is really no different from putting some food in the freezer while identical food rots outside the freezer and then claiming on defrosting the food from the freezer that it's younger. It isn't - it's merely had its functionality slowed and has decayed less.

it fails to record all the time that has passed for it

The above is especially wrong. The time that's passed for it is exactly equal to what its clock reads (proper time). The clock is measuring the number of ticks that take place and there is no error for a moving clock. Clocks moving relative to an absolute rest frame would simply tick slower. This slower tick rate is no more invalid than the faster tick rate of "stationary" clocks.

The light in the light clock which has recorded less time has travelled the same distance as the light in the clock that was stationary. Time wasn't slowed for the moving clock - it merely took more time for it to complete each tick due to the lengthened cycle distance. Why would you be taken in by slowed functionality? We understand exactly how the functionality is slowed, so it's daft to ignore that understanding and to assert instead that time has slowed for anything. All that has slowed is the rate of cycle completions.

tend not to believe the "block universe" model but it's still mathematically valid. Your logic is only true from the 3D LET perspective and is not true from a completely 4D "block" perspective.

There are eight different models worthy of mention, four of them being 3D and four being their 4D equivalents. (Other models are possible beyond the eight, but they are always either obfuscated versions of the eight which can be written off as a result or they are equivalent models with extra dimensions added for no relevant gain.) Two of the eight models are static eternal blocks which were never generated in past to future order because the future was always pre-existing, so all the apparent causation tied up in their content is rendered fake, meaning that they instead depend on so much luck to account for their state that they are actually relying on magic. The other six models can optionally involve block universes too, but, if they do, they are attempting to account for the generation of the block rather than doing imaginary physics inside the block after all the construction-phase has been completed. One pair of these models moves all objects through time in such a way that no clocks run slow, but that results in event-meshing failures which again disqualify these models (or require extra complexity to be brought in to tolerate and correct those failures, which requires a changing history of events at individual Spacetime locations under Newtonian time). The remaining four models come in two pairs, one pair producing infinite numbers of contradictions (which leaves them relying on magic for their functionality) and the other pair eliminating the contradictions by having an absolute frame. With this last pair, one of them has a time dimension which adds no useful functionality over the model that uses Newtonian time alone, but both are viable.

The reason why LET and SR still both remain valid is because we can't set ε absolutely to distinguish the two.

They do not both remain valid - all SR models have either been shown not to function in a viable manner, or in the case of the static block model have been shown to lack real causation because no effects have can have been caused by their apparent causes.

The two certainly use a CONVENTION or an agreed upon set of rules to explain what ε is. This convention goes beyond simply setting a single reference frame. However, for the last 110 years countless geniuses arguing fiercely have not set ε in a theory beyond using a convention.

How does it go beyond choosing a frame of reference?

You keep pushing that LET or some version of it must be true and SR's 4D concept is wrong. I personally tend to not like the fully 4D conceptualization of SR but I don't need to choose between LET and SR here. All I need to do is show that ε is chosen arbitrarily. I've done this multiple times.

I don't say that the 4D concept is wrong - I say that two versions of it are viable, but one of them has to be able to tolerate event-meshing failures and the other has to have an absolute frame whose Newtonian time coordinates the slowing of any clocks regarded as being at rest in other frames.

OK. And theories like SR and LET simply set up ε and therefore "choice of frame" via convention. The entire way they view ε is through convention.

Well, it's fine for you and others to call it a convention, but that isn't as clear in meaning as describing it as choosing a frame of reference to use as the base for the analysis.

Yes, one (or at least one convention) is most definitely right and all others are probably wrong.

That claim is not compatible with SR where there is asserted to be no absolute frame. If it was accepted by the SR camp, we wouldn't be arguing about anything.

However, we have no way to prove what ε is so we simply create theories that form an agreed upon way to choose ε. These agreements are called conventions. The agreements are not called reference frames.

They are selections of convenient reference frames.

In a completely 4D universe you can still have ε =1/2 for all frames and have them all right locally. In a 3D LET framework it can't work. I know you don't like the fully 4D concept and I don't like it either but I'm not going to argue against its math. However, Einstein still set ε to a certain value arbitrarily in his theories.

You can only do away with it in a model that is so broken that real causality is eliminated.

Einstein locally chose ε=1/2 and reference frames moving at velocity v relative to any point are seen as "rotated" in a 4D structure in the fully 4D conceptualization. ε appears to be something other than 1/2 when using the Lorentz Transformation (which comes from LET) but it does not in the fully 4D structure. This is similar to how a car would look shorter when its going up a steep hill when viewed from above. However, the car is not truly shorter. Again you can choose to believe either SR or LET as both match every experiment ever done (either can extend to a general theory). SR is easier to work with because its just simpler to assume ε=1/2 as a convention.

Any change in frame of reference involves changing the speed of light across objects relative to those objects, and this applies in the 4D models just as in the 3D ones. It's only in the static block that you have the illusion of it working because nothing is moving at all. Go to the construction phase instead and then look at the speed of light relative to objects and you find a different story.

You keep saying I'm obfuscating things. However, I'm simply not trying to get a simple question bogged down by a pro LET or pro SR sideshow.

The simple answer:

We can ONLY measure the one-way speed of light via an arbitrarily set convention because we arbitrarily set ε.

Which is no different from saying that you're selecting a frame of reference and then using the assumption that light moves relative to it at c as a basis for measuring the speed of light as c. Of course, if you move a clock very slowly, you hide from yourself the fact that you're choosing a specific frame of reference if you don't understand how the time it's recording is going out of sync with the time recorded by the other clock, and that's the important thing here that needed to be explained.

[dutch]

It's what you've just said that's wrong because you're assuming that the amount of time that's passed for the clock is equal to the amount of time it's recorded. When a light clock is stationary, it ticks at maximum speed because the round trip distance is shortest. When you move it, the round trip distance increases, so the clock records fewer cycles in a given length of time. If you move a clock backwards and forwards at the right frequency and with the right timing, you can shorten the round trip for the light and make the clock tick faster than normal, but again it is not recording the amount of time that has passed for it as it is exaggerating the amount of time that has gone by. Move it backwards and forwards a different way and you can make it record less time passing than has actually passed. Any movement of a clock leads to an error in the amount of time it records. Why would anyone be fooled by one kind of failure for a clock to record the right amount of time that's passed for it while not being fooled by another? In all cases, the light is moving at the same speed through space without being slowed by any kind of slowing of time.

The time a clock measures is due to its internal ticking. In LET moving reference frames are just as valid as stationary ones to those observers so moving clocks work just as well. Sure their ticking is slowed relative to the absolute rest frame in LET but they otherwise function the same. They measure the time as it shows on the clocks just like clocks in the "rest frame" do and they match every other comoving clock. The "rest frame" in LET could have a uniform gravitational field in the entire observable universe making the clocks tick slower in our corner of the greater universe. This would not negate the fact that the clocks we have do measure something very real. They measure the local time (proper time).

Here's another case that shows up the truth. Imagine a powerful distant source of gamma rays that damages DNA. Perpendicular to the direction these rays are coming, we run the twins "paradox" experiment, having one twin travel at very high speed and the other travel slowly. Both are exposed to the same amount of radiation, and the moving twin has interacted with it with greater intensity throughout. That twin can be "younger" but genetically more damaged. This business of him supposedly being younger is really no different from putting some food in the freezer while identical food rots outside the freezer and then claiming on defrosting the food from the freezer that it's younger. It isn't - it's merely had its functionality slowed and has decayed less.

Like I've shown a dozen times on this thread:

t'/t = f'/f = (1 - v/c) / γ = γ / (1 + v/c) =  (1 - a/c)  / (1 + b/c)  γb/γa  where  v = (a + b) / (1 + a b /c²)

The frequency f' is symmetric. The same thought experiment you have above must also work if most of the stuff in the universe was moving relative to the absolute rest frame while the twin was not. In this case everything in the universe except the twin would be younger but the twin would still be fried because f' would still be the same. Your thought experiment does not work because t', f', and energy are symmetric between reference frames. All observables are symmetric between reference frames so no thought experiment like this works. Your thought experiment shows that moving towards something blueshifts the light and away redshifts the light. This would be readily apparent to a 19th century physicist and anyone who studies the Classical or Relativistic Doppler Shift.

This business of him supposedly being younger is really no different from putting some food in the freezer while identical food rots outside the freezer and then claiming on defrosting the food from the freezer that it's younger. It isn't - it's merely had its functionality slowed and has decayed less.

Except if you were to go to bed and I would freeze you solid or even significantly lower you body temperature that would be very noticeable to everyone. If you were on a spacecraft and it accelerated slowly while you slept you would be able to act normally when you woke up.

All that has slowed is the rate of cycle completions.

If I take every kind of clock I could imagine and put them in a room. Next I find they all tick proportionally to each other in all experiments I could do if they're not accelerating relative to each other (the higher frequency clocks ticking faster allowing for a more accurate measurement). You know how I would define time? I would define it by the ticks of my clocks. Even in an absolute rest frame time is still measured by the ticking of clocks.... I don't know how you're defining time. Sure, I got it in LET that there's a frame where the ticks are locally the fastest. OK. So?

They do not both remain valid - all SR models have either been shown not to function in a viable manner, or in the case of the static block model have been shown to lack real causation because no effects have can have been caused by their apparent causes.

I know others would disagree. I know you don't like SR got it.

Quote
Yes, one (or at least one convention) is most definitely right and all others are probably wrong.

That claim is not compatible with SR where there is asserted to be no absolute frame. If it was accepted by the SR camp, we wouldn't be arguing about anything.

That's why you don't understand what a convention is. SR uses a convention to arbitrarily set ε =1/2 locally for all reference frames. This is ONE convention and SR sets ε by this one convention (we must believe in a truly 4D spacetime to do this). LET also sets ε by one convention but we must arbitrarily set the absolute rest frame (or absolute foliation in a general LET to do this).

It's only in the static block that you have the illusion of it working because nothing is moving at all

OK. So it works for the static block......... You're dragging this into a pro LET / pro SR debate again.

Which is no different from saying that you're selecting a frame of reference and then using the assumption that light moves relative to it at c as a basis for measuring the speed of light as c.

But you don't understand what a convention is.

[guest4091]

Bored chemist;
I originally thought you understood spacetime drawings. If you don't, study this one, and the short math example.
It shows that regardless of setup, you will only measure light speed as c.
If you assume a rest frame for yourself, you accept the equality of out and back transit times.
https://app.box.com/s/z84l6wbpm4b291ve47i911ijnear6uqj

[Bored chemist]

  regardless of setup, you will only measure light speed as c.

If every possible experiment I could do to measure my mass  indicated that it's about 70 Kg, would it be reasonable to conclude that my mass is about 70 Kg?

What's the difference between saying " no matter what the setup, you will always measure the speed of light as  C"
and
" The speed of light is C"
?

[David Cooper]

The time a clock measures is due to its internal ticking. ... They measure the local time (proper time).

None of which negates the fact that they fail to record all the time that's passing for them if they're moving (and if they're in a gravitational field) and that the times they record are therefore out by an error.

The same thought experiment you have above must also work if most of the stuff in the universe was moving relative to the absolute rest frame while the twin was not. In this case everything in the universe except the twin would be younger but the twin would still be fried because f' would still be the same.

The moving twin may well be stationary on one leg of the tirp, but will then be moving at much higher speed on the other leg of the trip and will always end up "younger" than the stay-at-home twin, but the events involving encounters with gamma rays have continued at a high rate which do not speak of a slowing of time for the moving twin at all. Another experiment could put one twin near to a black hole and send the same radiation through them from a distant source - again the "younger" one can be more damaged at the end of the process, and indeed, the more extreme the reduction in growth ageing, the more extreme the overall damage will be.

Except if you were to go to bed and I would freeze you solid or even significantly lower you body temperature that would be very noticeable to everyone. If you were on a spacecraft and it accelerated slowly while you slept you would be able to act normally when you woke up.

Different methods of slowing functionality have different side-effects, and some have none, but the key point is that time is not being slowed. Cycles are being slowed. Functionality is being slowed. To say that time is slowed is taking a step into the irrational.

Even in an absolute rest frame time is still measured by the ticking of clocks.... I don't know how you're defining time.

No - that's a bad definition. Time should never be defined by cycle counters when the cycle length can lengthen without time running slow.

They do not both remain valid - all SR models have either been shown not to function in a viable manner, or in the case of the static block model have been shown to lack real causation because no effects have can have been caused by their apparent causes.

I know others would disagree. I know you don't like SR got it.

Liking or disliking things doesn't come into it. It's about what is possible within the bounds of reason, and those people who think they have an SR model that works viably are badly mistaken. No SR model functions rationally - the one that comes closest to appearing to function properly (without adding features not specified [or banned] in the model description) can only account for imaginary physics in a static block where there is never any movement or change at all, and that means the model in completely incapable of accounting for causality as it gives it no room whatsoever to operate - no effects in this model can be caused by their apparent causes. Those who believe the static block model is sufficient are fantasists.

That's why you don't understand what a convention is. SR uses a convention to arbitrarily set ε =1/2 locally for all reference frames. This is ONE convention and SR sets ε by this one convention (we must believe in a truly 4D spacetime to do this). LET also sets ε by one convention but we must arbitrarily set the absolute rest frame (or absolute foliation in a general LET to do this).

I see, so you don't call it selecting a frame of reference in the 4D models even though it's still selecting a frame of reference.

It's only in the static block that you have the illusion of it working because nothing is moving at all

OK. So it works for the static block......... You're dragging this into a pro LET / pro SR debate again.

No, it doesn't work for the static block - it merely gives the illusion of working. It's a broken model that has no way of generating the block without switching to different laws of physics.

But you don't understand what a convention is.

A convention can be many things, but in this case it clearly means selecting a frame of reference.

One important point to look at though is what happens to the speed of light in those 4D models where movement is possible and causality can be real. In all of these models light shrinks every single path it takes to zero length and it therefore has no speed at all. In one of the 4D models where "time" never runs slow for any clocks, that means that light travels the whole way from the start of the universe (timewise) to the end in an instant, failing along the way to interact with any of the objects it's supposed to encounter because they aren't there yet as it takes them longer to reach the same Spacetime loactions (longer under a Newtonian time which must be brought into the model to make it possible for clocks never to run slow relative to each other). In the other 4D models, light covers all its zero-length paths in >0 lengths of Newtonian time (which again isn't part of SR but has to be brought in to make the models function viably). The amount of time (of the Newtonian variety) that it takes to cover any given path will vary though depending on the frame of reference chosen to govern the running of the model. The SR models have all been shown to be incapable of generating a real universe without bringing in Newtonian time and a frame of reference to coordinate the unfolding of events, and it's high time people pushing SR's dogma woke up to the fact that their models are broken and dysfunctional. What they do though is point at different incompatible broken models to account for different aspects of the universe while they make out that they have a single viable model. They are experts in self delusion. The only viable models are radical departures from SR.

[guest4091]

" The speed of light is C"
?

I'm agreeing with you, and on the basis of a degree of synchronization that presents no significant difference. We can't use the ideal conditions, we don't have ideal clocks. I'm also discouraging anyone with a complex or simple setup thinking they can somehow circumvent the light postulate.

[Bored chemist]

I'm quite happy to accept that I'm wrong, but nobody seems to have come up with a viable reason yet.
OK from the PoV of a passing astronaut, I get the wrong answer- but his view of everything would be different.
Certainly, the expression here for the error in timekeeping
https://en.wikipedia.org/wiki/Time_dilation#Simple_inference_of_velocity_time_dilation

 tends to zero  for slow transport of the clock.
So  I should be able to have two clocks, separated in space, but still essentially synchronised.
I can record when a flash of light reaches them.
And if one is "near" and the other "far" from the flash I can establish a time difference, and a distance difference.

[David Cooper]

Certainly, the expression here for the error in timekeeping
https://en.wikipedia.org/wiki/Time_dilation#Simple_inference_of_velocity_time_dilation

 tends to zero  for slow transport of the clock.

It only tends to zero for one frame of reference. For all other frames, it tends to a different value, but we're talking about a hidden error, so you can't detect whether it applies to your frame or not. If you happen to be stationary and move your clock into position very slowly, your clocks will remain almost exactly in sync, but if you happen to be moving at very high speed instead, the further you move the clock, the further out of sync the two clocks will become (and you won't notice because they'll always look in sync to you as you move along with them, which means you'll always think the error tends to zero for you even when it doesn't in the underlying reality). The result will be that you record the speed of light from one clock to the other as c no matter how long it really takes the light to make that trip.

[dutch]

I'm quite happy to accept that I'm wrong, but nobody seems to have come up with a viable reason yet.
OK from the PoV of a passing astronaut, I get the wrong answer- but his view of everything would be different.
Certainly, the expression here for the error in timekeeping
https://en.wikipedia.org/wiki/Time_dilation#Simple_inference_of_velocity_time_dilation

tends to zero  for slow transport of the clock.
So  I should be able to have two clocks, separated in space, but still essentially synchronised.
I can record when a flash of light reaches them.
And if one is "near" and the other "far" from the flash I can establish a time difference, and a distance difference.

Say you've got 100 red and green apples and only a blind man can count all of them. The blind man confirms there's 100 apples. You also know at least one apple is red and at least one apple is green.

The equation:   R + G  =  100     R and G are integers > 0

You could set R = 1/2 G  and use this convention for all apple counts. You could even claim this is your "point of view." If the blind man counts 500 apples you could proclaim 250 of them are red and 250 are green.

Because we can't get any more information than the total count and the fact that we know at least one apples is red or green we would never be wrong to our knowledge to use the convention R = 1/2 G. However,  R = 4 G is also valid as is any R = α G for all α where both R and G form integers > 0.

In this case of R = 4 G and R + G = 100, G = 20 and R = 80.

We can confirm the two-way speed of light and get everyone to agree on it (barring GR curvature). There's math that allows the one-way speed of light to take on any value from 1/2 to ∞ relative to a reference frame. We have nothing absolute to set our clocks to that we can find. We can select ANY valid value for c- and c+.

The valid values relative to our reference frame are:

c± = 1/(1 ± κ)      where κ any value 0 to 1

Attributing ε =1/2 to "our point of view" of our own reference frame is a CONVENTION. A standardized agreed upon way to apply ε (that goes beyond choosing a reference frame). LET agrees to apply a different ε to each reference frame absolutely as shown in the Lorentz Transformation (forming an absolute rest frame where ε =1/2 only in one frame; with LET there's an infinite number of different possible conventions) and SR/GR agrees to locally apply ε =1/2 to all reference frames (seemingly requiring a 4D block universe to work). Within a convention you can measure the one-way speed of light exactly (for LET you need to know the absolute rest frame) but this convention may or may not be correct. The value for the one-way speed depends on convention.

The one-way speed of light is simply impossible to measure without applying an arbitrary convention by any known means.

[Bored chemist]

If I ever get caught breaking the speed limit I'm going to get you guys as my defence.
"But m'lord, from my point of view, the car was stationary; the police helicopter caught up with me so, from his point of view I was actually going backwards and so it's only from the unique perspective of the arresting officer that I was actually doing more than 70 MPH".

"Yes- but his is the viewpoint that counts"

Any two items in relative motion are moving- or not- depending on your point of view.
So, almost nothing has a well defined speed - it's always a matter of viewpoint.
For light it's different- everyone measures the speed as C.

Now there's this strange world where I say that I can measure the speed of light as it makes a one-way trip. And I explain how.
And I get the answer C
And you tell me it's wrong, because someone else- who is moving- would disagree.
Well, how is that different from, for example the points of view of the police and me, giving rise to different views on the speed of my car?

Of course it's an arbitrary point of view.
All measurements of speed are based on an arbitrary point of view.

So, as you say:
The one-way speed of light everything: whether it's light, or the number nine bus is simply impossible to measure without applying an arbitrary convention by any known means.

[dutch]

"Yes- but his is the viewpoint that counts"

Any two items in relative motion are moving- or not- depending on your point of view.
So, almost nothing has a well defined speed - it's always a matter of viewpoint.
For light it's different- everyone measures the speed as C.

If I define the "velocity" v of an object with mass as a certain f'/f (= t'/t = (E'/h)/(E/h)) it is symmetrically defined between any two reference frames. It's an observable between reference frames. We can use a radar gun to define the speed of another object as v via f'/f and that other object will also report the same exact  v because the Doppler Shift is symmetric. It doesn't matter what reference frame or convention you choose you'd expect the same f'/f. If the cop has a 500 MHz light source and it shifts to 499.9 MHz then the same thing would happen to your light source. When you collide with the cop both will agree on how severe the impact was.

Light does not Doppler Shift itself but rather there is a Doppler Shift from source to receiver. The source and receiver are objects with some mass m. This Doppler Shift is symmetric (Doppler shift is independent of which one's the source) REGARDLESS of convention or reference frame choice.

Again...

Like I've shown a dozen times on this thread:

t'/t = f'/f = (1 - v/c) / γ = γ / (1 + v/c) =  (1 - a/c)  / (1 + b/c)  γb/γa  where  v = (a + b) / (1 + a b /c²)

The absolute round trip speed of light c is VERY well defined for everyone. The velocity v between two objects when defined by a certain f'/f = (E'/ h)/(E/ h) is also well defined and symmetric by anyone's viewpoint.

An absolute speed of an object isn't defined without convention and neither is the one-way speed of light. You can use the very observable Doppler Shifts to define a very non-arbitrary v between any two objects.

If you Doppler Shift from point X to Z through Y via the below    (let   X to Y =a   and Y to Z = b)

f (1 - a/c) / γa * (1 - b/c) / γb

The above is exactly the same as

f (1 - v/c) / γv = f (1 - a/c) / γa * (1 - b/c) / γb

Solve for v

v = (a + b) / (1 + a b /c²)  =  Relativistic Velocity Addition Formula

This v is defined not by how long it takes to get from point A when the clock starts to point B when the other clock stops but rather by the shift in frequency, observable shift in t', and therefore the shift in energy.

We cannot pin down the absolute start time nor the absolute end time for ANY spatially separated clocks at all. We can only choose one via convention but we can pin down the shift in frequency and shift in energy.

"But m'lord, from my point of view, the car was stationary; the police helicopter caught up with me so, from his point of view I was actually going backwards and so it's only from the unique perspective of the arresting officer that I was actually doing more than 70 MPH".

Everyone can agree on the shift in frequency between the ground and the car. Defined this way we have a definite v. We can't say in an absolute sense when the car started its journey or ended it (or if there is or isn't an absolute time). A traditional view of velocity where we don't choose a convention needs to know these values. However, we can define f'/f, t'/t, and E'/E.

The light may have frequency ratio f'/f in one direction but it may take 1 million years to make a certain journey (from another perspective we could choose or a hidden absolute rest frame). In the other direction it may also have frequency f'/f but it takes only an instant to make the journey. Defining v with f'/f is really measuring a two-way speed. The v we measure is also a very real two-way speed. I never claimed the constant c wasn't exactly defined nor did I ever say a "v" couldn't be exactly defined. However, both are only defined without choice of convention two-way.

Trying to measure frequency shift (f'/f -1), energy shift (E'/E -1), momentum shift (k'/k -1), observable time shift (t'/t-1) is EXACT. Trying to pin down what "now" is for two spatially separated clocks is only done via convention. Without knowing what now is in two different locations (and we can't; Relativity is a local theory) we have NO idea what a one-way speed is in the classical sense. Many have stated "now" is a meaningless concept in the physics we can run experiments on unless you're discussing a "now" at a single event.

Define v as:

      v = c (1 - (f’/f)²) / (1 + (f’/f)²)               frequency
or   v = c (1 - (E’/E)²) / (1 + (E’/E)²)         energy
or   v = c (1 - (t'/t)²) / (1 + (t’/t)²)               time
or   v = c (1 - (κ’/κ)²) / (1 + (κ’/κ)²)            wavenumber
or   v = c (1 - (x’/x)²) / (1 + (x’/x)²)            distance
or   v = c (1 - (ρ’/ρ)²) / (1 + (ρ’/ρ)²)           momentum

All the above three are defined with "two-way" measurements.

[dutch]

More of the math:

c± = c / (1 ± κ)   for  κ = 0 to 1

 t = ½ ( x/c- + x/c+) = x/c  →   two-way speed of c

Define v+ as:

      v+ = c/(1 + κ)  (1 - (f’/f)²) / (1 + (f’/f)²)               frequency
or   v+ = c/(1 + κ)  (1 - (E’/E)²) / (1 + (E’/E)²)         energy
or   v+ = c/(1 + κ)  (1 - (t'/t)²) / (1 + (t’/t)²)               time
or   v+ = c/(1 + κ)  (1 - (κ’/κ)²) / (1 + (κ’/κ)²)            wavenumber (non-angular wavenumber k = 1/λ)
or   v+ = c/(1 + κ)  (1 - (x’/x)²) / (1 + (x’/x)²)            distance
or   v+ = c/(1 + κ)  (1 - (ρ’/ρ)²) / (1 + (ρ’/ρ)²)           momentum

Define v- as:

      v- = c/(1 - κ)  (1 - (f’/f)²) / (1 + (f’/f)²)               frequency
or   v- = c/(1 - κ)  (1 - (E’/E)²) / (1 + (E’/E)²)         energy
or   v- = c/(1 - κ)  (1 - (t'/t)²) / (1 + (t’/t)²)               time
or   v- = c/(1 - κ)  (1 - (κ’/κ)²) / (1 + (κ’/κ)²)            wavenumber (non-angular wavenumber k = 1/λ)
or   v- = c/(1 - κ)  (1 - (x’/x)²) / (1 + (x’/x)²)            distance
or   v- = c/(1 - κ)  (1 - (ρ’/ρ)²) / (1 + (ρ’/ρ)²)           momentum

For example:

f'/f = (1-0.99)/(1-0.99^2)^0.5   = .070888

v = (1 - (f’/f)²) / (1 + (f’/f)²)  = .99

Let κ = .6

(1 - (f’/f)²) / (1 + (f’/f)²) /(1+0.6) = .61875 = v+

(1 - (f’/f)²) / (1 + (f’/f)²) /(1-0.6)  = 2.475 = v-

t (two-way trip)= 1/2 * ( x/v+ + x/v-)  =  1/2 * ( x/.61875 + x/2.475) = 1.010101 x

velocity = distance/time = x/t

1/1.010101 = v = .99

The v is the well-defined round trip average speed by ANYONE'S perspective (assuming a relatively flat region of spacetime). We can assume ε = 1/2 where κ =0 if we wish to simplify the math. This is just a convention, nevertheless the value v as a two-way average is very real for all perspectives.

There is a whole lot of symmetry going on here. HOWEVER, nothing tells us the one-way speed. We only assume it.

[Bored chemist]

On a related note, all the arguments put forward for my measurement of the one way tipped of light seem independent of the fact that it was light.
So,
How do I determine the one way speed of  Usain Bolt?
I look forward to being told this is impossible.