Paradoxes if instantaneous signals

[RandallB]

You could ….. Do you disagree with any of the above?

Almost all of it!

The whole point of an "instantaneous signal" is that it is received at the same time it is sent, otherwise it wouldn't be instantaneous. Of course, because of the simultaneity rules, a signal which travels instantaneously in one frame wouldn't travel instantaneously in all frames; in some frames it would seem to travel FTL but forward in time …..

Nowhere does simultaneity allow you to presume to know what reference frame is a good one to use as THE PREFRRED FRAME that would be able to predict where and when a “instant Message Machine” would signal in all locations wrt all frames.

IE. No currently definable frame can claim to know that an "instantaneous signal" would be received at all locations based on that frames version of Cock Synchronization as Absolute – meaning all other frame clocks are out of synch they just appear to be in synch their own view.
You still do not understand simultaneity.

BUT! If an "instantaneous signal" could and was sent to all locations, by recording all arrival times you could figuring out what frame is “absolute” or preferred. Something we cannot do using SR alone.

If there is a preferred frame for instantaneous signalling (i.e. if it is possible to build a device such that signals can be received at the same moment they are sent according to one frame's definition of simultaneity, but it is not possible to build a device such that signals can be received at the same moment they are sent according to any other frame's definition of simultaneity), then that means relativity is incorrect. …..

That logic is so upside down!
A preferred frame does not allow instantaneous signaling.
Instantaneous signaling would only reveal which frame is best to use as “Preferred”.
No one thinks there is or can ever be anything like instantaneous signaling.
But if a preferred frame was established it would in no way make relativity incorrect it could only make relativity more complete by making simultaneity a resolvable paradox and resolving it.

It is not about establishing a classical ether theory – it about understanding the meaning of simultaneity. You and Fred give lip service to “no preferred frame” but claim to order causality based on clock Synchronizations of a randomly selected frame. That is a de facto recognition of a preferred frame and not acceptably within SR Simultaneity.

It’s not like I’m going to agree to disagree on this – you’re just wrong.
But if you cannot figure that out, I’m not going to waste my time arguing with you over it.
I’m done with this thread it long enough as it is.

 

[JesseM]

The whole point of an "instantaneous signal" is that it is received at the same time it is sent, otherwise it wouldn't be instantaneous. Of course, because of the simultaneity rules, a signal which travels instantaneously in one frame wouldn't travel instantaneously in all frames; in some frames it would seem to travel FTL but forward in time …..

Nowhere does simultaneity allow you to presume to know what reference frame is a good one to use as THE PREFRRED FRAME that would be able to predict where and when a “instant Message Machine” would signal in all locations wrt all frames.

What do you mean by "simultaneity" here? Are you:
1) using the word the way it's used in relativity, to refer to the question of how a given frame decides whether events at different locations have the same time-coordinate in that frame (with different frames disagreeing on the question of whether two events are simultaneous, and there being no 'right answer'),

or are you:

2) using the word to refer to some non-relativistic notion of absolute simultaneity, where there is a single "real truth" about whether two events happened at the same time or not?

Your reference to "THE PREFERRED FRAME" would suggest #2, since there is nothing inherent in the notion of a device which communicates instantaneously in one frame that implies that this device has any preferred frame whatsoever. To sharpen this point, please address the following thought-experiment: suppose you come across a pair of alien devices which allow you to type a message at one device and have it appear on the screen of the other device. You run some tests with these devices, and you find the following amazing result: if you move the devices a significant distance apart and then bring them to rest in your frame, and then use clocks synchronized in your rest frame to assign time-coordinates to the event of sending a message from one device and the event of the message being received at the other device, you find the two events have the same time-coordinate in your frame! So, the devices seem to send messages "instantaneously" in your frame when they are at rest in your frame. Now, say you have a friend Alice who is on a ship which is moving at 0.9c in your frame. You put the two devices on a rocket taxi which catches up to her ship, so that she can test the devices when they are at rest in her frame. Now, before actually learning the results of her tests with the devices, would you simply assume that once the devices are at rest on her ship (and therefore moving at 0.9c in your frame), the time-coordinate of her sending a message from one will continue to be identical to the time-coordinate of the other device receiving the message, using the time coordinates of your own (not her) frame? In other words, do you simply assume without testing that these devices are picking out a single "true" definition of simultaneity which matches that of your own frame's coordinates? Or are you willing to consider the possibility that the devices work in a Lorentz-invariant way, so that once they are at rest on her ship, the time-coordinate of a message being sent will be the same as the time-coordinate of it being received in her rest frame, which necessarily means that the time-coordinates will be different in your own frame?

Also, would you agree that in the first case where the time-coordinates of messages being sent and received are always the same in your frame regardless of how the devices are moving, the devices are violating the first postulate of relativity, and picking our a preferred frame? Would you agree that in the second case where the time-coordinates of messages being sent and received are always the same in whatever frame the devices happen to be at rest in, there is nothing about this experiment which necessarily conflicts relativity, and no need for any preferred frame?

Please give specific answers to which options you'd pick so I can better understand how you are interpreting the phrase "instantaneous signals" and why you seem to think this phrase automatically implies a preferred frame.

IE. No currently definable frame can claim to know that an "instantaneous signal" would be received at all locations based on that frames version of Cock Synchronization as Absolute – meaning all other frame clocks are out of synch they just appear to be in synch their own view.
You still do not understand simultaneity.

Since you use the word "Absolute", that seems to mean you are talking about the notion of absolute simultaneity. But do you agree that in the standard theory of SR, there is no such thing as absolute simultaneity, only different (and equally valid) definitions of simultaneity used by different inertial frames?

That logic is so upside down!
A preferred frame does not allow instantaneous signaling.
Instantaneous signaling would only reveal which frame is best to use as “Preferred”.
No one thinks there is or can ever be anything like instantaneous signaling.
But if a preferred frame was established it would in no way make relativity incorrect it could only make relativity more complete by making simultaneity a resolvable paradox and resolving it.

Here you are definitely confused, all physicists agree that the essence of relativity is that there is no preferred frame (that's the meaning of the first postulate, that all laws of physics must work the same way in every frame), if there was that would be a falsification of relativity. I can provide quotes from various professional physicists if you doubt this.

You and Fred give lip service to “no preferred frame” but claim to order causality based on clock Synchronizations of a randomly selected frame.

Huh? The point is that the first postulate says that the laws of physics must work the same way in every frame (including a 'randomly selected one'), if you do an experiment with your devices at rest in one frame and then repeat the experiment with your devices at rest in a different frame, you must get the same result in both cases or you've falsified relativity.

 

[Fredrik]

so that's what this thread is really about. a chance to beat up on aether theory. well count me out.

Huh? Who's talking about the aether? I certainly haven't had a single thought that included that word during my participation in this thread.

It’s not like I’m going to agree to disagree on this – you’re just wrong.
But if you cannot figure that out, I’m not going to waste my time arguing with you over it.
I’m done with this thread it long enough as it is.

Pretty much everything in that post made no sense. If you don't want to argue about it, then don't, but in that case maybe you should be a bit less arrogant.

If a signal is instantaneous, it's detected at the same time as it's emitted. That's what "instantaneous" means. And according to SR, if the emission and detection events are simultaneous in one inertial frame, there's another where they aren't simultaneous, so in that inertial frame, the signal is not instantaneous.

If you claim that an instantaneous signal is such that detection and emission are simultaneous in all frames, then you have denied the existence of inertial frames (with the properties they have in SR). The existence of inertial frames is a property of Minkowski space, so this would mean that you're also denying Minkowski space. And Minkowski space is the mathematical model used in SR, so it would also be a denial of SR. (This is just a fancier way of making the same point as Jesse when he brought up the first postulate).

I don't really know if this is what you're claiming. I couldn't really make sense of what you said, and it appears that Jesse had difficulties with that too.