Correct phrasing / use of vocabulary for SR

[harrylin]

Or you can simply pair each frame dependent statement with a frame:

"Simultaneous events in A are non-simultaneous in B". [..] The problem is that a frame dependent quantity without a frame is meaningless.

That is also better (no self contradiction), but could be misinterpreted as magic (parallel universes). My preferred way of phrasing:

"Simultaneous events according to A are non-simultaneous according to B".

As so often, more precise statements are increasingly longer than shorthand statements.

 

[Dale]

That is also better (no self contradiction), but could be misinterpreted as magic (parallel universes). My preferred way of phrasing:

"Simultaneous events according to A are non-simultaneous according to B".

Yes, "according to" is good. I also use "with respect to".

As so often, more precise statements are increasingly longer than shorthand statements.

Agreed. I think that it is OK to use the shorthand when the more precise statement is clear from context, but as soon as any confusion arises switch immediately to the longer.

 

[ghwellsjr]

Or you can simply pair each frame dependent statement with a frame:

"Simultaneous events in A are non-simultaneous in B".

The problem isn't with the word "are" and it isn't fixed with the word "appears". The problem is that a frame dependent quantity without a frame is meaningless.

Yes, "according to" is good. I also use "with respect to".

Agreed. I think that it is OK to use the shorthand when the more precise statement is clear from context, but as soon as any confusion arises switch immediately to the longer.

Is it an OK shorthand when A and B are non-inertial observers and the word "frame" is never used?

 

[phyti]

That is also better (no self contradiction), but could be misinterpreted as magic (parallel universes). My preferred way of phrasing:

"Simultaneous events according to A are non-simultaneous according to B".

As so often, more precise statements are increasingly longer than shorthand statements.

How about:
Simultaneous in A can be non-simultaneous in B only if the events are not coincident in space.

 

[harrylin]

How about:
Simultaneous in A can be non-simultaneous in B only if the events are not coincident in space.

"is in A" remains ambiguous jargon that can easily be misunderstood, for example as implying (and I cite from the OP!) that "both observers ARE in different 3D worlds", as if they live in a different reality.

 

[Dale]

Is it an OK shorthand when A and B are non-inertial observers and the word "frame" is never used?

No (IMO). I was thinking of A and B being frames (not observers) defined previously. It is OK if A and B are well-defined non-inertial frames.

 

[harrylin]

Why use 'appearent' or 'appears' if one normally does not say that an immobile clock 'appears' to run normal or is apparent running normal? Do you say that an immobile train has an apparent length of 100 m long? So why doing it for the moving clock or trains?

I had missed this one. Einstein avoided "is" at some points where according to you it should have been "is", and in fact there is one instance in another paper where I also prefer "is". I can see two reasons for choosing a less absolute word: either when one isn't sure that "is" is correct, or when one thinks that "is" can be misunderstood.
I could say for example that an immobile train may appear 99 m long in a "moving" reference system if it appears 100 m long in a "stationary" system - "appears" merely stresses the free choice of perspective and there is no reason to prioritize one frame over the other.

 

[ghwellsjr]

No (IMO). I was thinking of A and B being frames (not observers) defined previously. It is OK if A and B are well-defined non-inertial frames.

Then would you have any problem with the first linked post of this thread? (I don't. I'm referring to PeterDonis's post, not Vandam's response.)

https://www.physicsforums.com/showpost.php?p=4041285&postcount=10

 

[Austin0]

Then would you have any problem with the first linked post of this thread? (I don't. I'm referring to PeterDonis's post, not Vandam's response.)

https://www.physicsforums.com/showpost.php?p=4041285&postcount=10

PeterDonis's usage certainly seems appropriate in meaning. But the word sense feels contrived and somehow misleading. How about internal simultaneity??
As far as being non-inertial frames: as such they were completely undefined in the sense DaleSpam is referring to if I am reading him correctly. The exercise is effectively two inertial frames with the "instantaneous" acceleration phases out of the picture. Not suggesting that considering them explicitly would add anything to the demonstration ;-)

 

[phyti]

No (IMO). I was thinking of A and B being frames (not observers) defined previously. It is OK if A and B are well-defined non-inertial frames.

Why can't A & B be observers?
Example: an a-naut with a clock and a laser, floating ouside his ship (away from Earth if necessary), making measurements.
There is no reason there has to be additional objects. The 'frame' has to be a common reference point for a set of measurements. In the final analysis, whether you use devices substituting for the observer, the measurements only have meaning to the observer.