Repositioning clocks: continuing from the switch paradox

[JesseM]

No, you are not since your experiment depends directly on $$dt'=0$$.

I don't know what you mean by "depends directly on". The result of the theoretical calculation is dt'=0, but I start with the measured values of dx=10 and dt=8. Similarly you start with the measured values of dx=L and dt=0, and the result of your theoretical calculation is dt'=gamma*v*L/c^2. What possible difference can you point to that allows you to say your experiment is a "realization" of dt'=gamma*v*L/c^2 but mine is not a "realization" of dt'=0? In both cases we measure a dx and dt, then calculate a dt' theoretically using the equation dt' = gamma*(dt - v*dx/c^2).

 

[starthaus]

I don't know what you mean by "depends directly on".

It means that, according to your own description, you need to observe both clocks simultaneously in frame F'.

 

[JesseM]

It means that, according to your own description, you need to observe both clocks simultaneously in frame F'.

No, I already explained that this was only if you wanted to measure dt' using rulers and clocks at rest in frame F'. But your definition of what it means to "realize" dt'=gamma*v*L/c^2 does not require us to measure dt', it allows us to just calculate it theoretically from a dx and dt that we have measured in F. So you can stop linking back to that post of mine, it isn't relevant to the question of why you think it's possible to "realize" dt'=gamma*v*L/c^2 but not to "realize" dt'=0. If you allow a theoretical determination of dt' from measured dx and dt to count as a "realization" in the first case, why don't you allow it in the second case? Appears to be an irrational double-standard on your part.

 

[starthaus]

No, I already explained that this was only if you wanted to measure dt' using rulers and clocks at rest in frame F'. But your definition of what it means to "realize" dt'=gamma*v*L/c^2 does not require us to measure dt', it allows us to just calculate it theoretically from a dx and dt that we have measured in F. So you can stop linking back to that post of mine, it isn't relevant to the question of why you think it's possible to "realize" dt'=gamma*v*L/c^2 but not to "realize" dt'=0. If you allow a theoretical determination of dt' from measured dx and dt to count as a "realization" in the first case, why don't you allow it in the second case?

Because your experiment relies on simultaneous observation of the two clocks in frame F'. Mine doesn't.

Appears to be an irrational double-standard on your part.

There is no point in starting to sling ad-homs, let's keep the discussion civil.

 

[JesseM]

Because your experiment relies on simultaneous observation of the two clocks in frame F'.

No it doesn't. In both of the experiments I mentioned in post #65, I measured two events in frame F, getting dx and dt for these events in F, then I did a purely theoretical calculation to get dt' in F' (I have already stated this several times, are you reading my posts carefully?) That's exactly what you did too, so I don't see why your experiment is a "realization" of dt'=gamma*v*L/c^2 but mine is not a "realization" of dt'=0.

There is no point in starting to sling ad-homs, let's keep the discussion civil.

My point is that there's no rational argument for treating your type of experiment as a "realization" of dt'=gamma*v*L/c^2 but not treating mine as a "realization" of dt'=0.

 

[starthaus]

No it doesn't. In both of the experiments I mentioned in post #65, I measured two events in frame F, getting dx and dt for these events in F,

How do you do these "measurements"? You are located in frame F', in motion (at very high speed) wrt F.

 

[JesseM]

How do you do these "measurements"? You are located in frame F', in motion (at very high speed) wrt F.

OK, I see we were originally using F' to be the observer's frame, but in more recent posts I got mixed up and started using F as the observer's frame, sorry about the confusion. But is that the definition you have been assuming in all your posts? For example, in post #62 you said:

You are using $$dt'=0$$ which , according to your own admission is impossible to implement practically.
I am using $$dt=0$$ which is very easy to implement (and is implemented in prcatice).

Were you really saying here that it's impossible to "implement" a measurement of two events in our own primed frame such that we find dt'=0 for these events? If we synchronize two clocks at rest in our primed frame using the Einstein synchronization convention, then if we consider an event that was measured to happen next to the left clock when it read T'=5 and another event which was measured to happen next to the right clock when it read T'=5, doesn't this qualify as a measurement of dt'=0 for these two events?

If you got the notation confused too, can you clarify what you meant in this comment from post #60?

All you need to know is that they had been accelerated slowly enough such that they did not get out of synch. For that extent, the clocks may be totally enclosed in arocket, unobservable, you will still be able to determine their desynchroonization in frame F' based only on two things : proper length L and coordinate speed v.

Is F' still supposed to be the observer's frame? And were the clocks accelerated from an initial state of rest in F'? If so, then if they were both accelerated at the same rate, wouldn't they just remain synchronized in F'? Or were you assuming in this comment that F was the observer's frame and F' was the rest frame of the rocket?

 

[starthaus]

OK, I see we were originally using F' to be the observer's frame, but in more recent posts I got mixed up and started using F as the observer's frame, sorry about the confusion. But is that the definition you have been assuming in all your posts?

Yes, all along.

 

[JesseM]

Yes, all along.

OK, so can you answer my requests for clarification about your earlier posts #60 and #62? Specifically these:

If we synchronize two clocks at rest in our primed frame using the Einstein synchronization convention, then if we consider an event that was measured to happen next to the left clock when it read T'=5 and another event which was measured to happen next to the right clock when it read T'=5, doesn't this qualify as a measurement of dt'=0 for these two events?

were the clocks accelerated from an initial state of rest in F'? If so, then if they were both accelerated at the same rate, wouldn't they just remain synchronized in F'?

 

[starthaus]

OK, so can you answer my requests for clarification about your earlier posts #60 and #62? Specifically these:

The clocks are synchronized in the unprimed frame (the rocket frame), F. You (the observer) are located in the primed frame F'. (see above).

There is some work I have to do and I've been spending too much time on this website, so, with apologies, I will not be answering any more questions for another 12-18 hours. Sorry for the inconvenience but I will answer once I catch up with the work I have to do.

 

[JesseM]

The clocks are synchronized in the unprimed frame (the rocket frame), F. You (the observer) are located in the primed frame F'. (see above)

OK, I guess that's an answer to the question in the second quote, about your rocket example. But the question in the first quote wasn't asking about your rocket example at all, I was just asking why you don't think my example involving only clocks at rest in F' (and no rocket) would qualify as a "realization" of dt'=0. Again:

If we synchronize two clocks at rest in our primed frame using the Einstein synchronization convention, then if we consider an event that was measured to happen next to the left clock when it read T'=5 and another event which was measured to happen next to the right clock when it read T'=5, doesn't this qualify as a measurement of dt'=0 for these two events?

Maybe when you say it's impossible to "realize" dt'=0, you're just talking about determining that two events on the worldlines of clocks at rest in F have a dt'=0, not saying that it's impossible to determine dt'=0 for an arbitrary pair of events (like the events on the worldlines of clocks at rest in F' above)?