Having trouble understanding why FTL implies time travel

[Austin0]

The two-way speed of light is isotropic, constant, and frame invariant regardless of your synchronization procedure. The Einstein synchronization procedure just makes the one-way speed match the two-way speed.

It is understood that the speed of light is isotropic,constant and frame invariant regardless of your synch procedure. Otherwise the motion of a frame would be detectable, yes?
The path length of a photon moving from the front of a moving system in the direction to the rear must necessarily be shorter than the path from the rear to the front, agreed??

In a reflected, two-way measurement this is not true. The path length and the measurement is the same in either direction , agreed?

So necessarily half of the two way measurement is not going to be the same as a one way measurement in either direction. Unless the clocks are desynchronized , with the clocks in the rear running ahead of the clocks in the front.
Yes?
If for instance two way measurements were made from the center. This information [dt/2]was then sent at c [radio] to the clocks at the front and rear . It would reach the rear faster and based on the assumption of [ dx/dt=c] the clock would be set ahead. The reverse being true in the other direction ,,,yes?
I was not suggesting that the clocks had to be light synchronized to produce the invariance , I assume that is definitely not the case. I was only pointing out that the light procedure would automatically produce the exact same degree of desynchronization.
As far as I can see this desynchronization is one of the universe's little tricks on us like time dilation and length contraction. A conspiracy to keep us from being able to determine absolute motion. Just kidding.

As far as I can see the mystery of the invariance of light , which certainly twisted my mind when I first encountered it through Micholson-Morley, is only rationally explained and made possible through SR and the conception of clock desynchronization. DO you have any other way to look at it or understand it?

 

[Dale]

It is understood that the speed of light is isotropic,constant and frame invariant regardless of your synch procedure. Otherwise the motion of a frame would be detectable, yes?
The path length of a photon moving from the front of a moving system in the direction to the rear must necessarily be shorter than the path from the rear to the front, agreed??

In a reflected, two-way measurement this is not true. The path length and the measurement is the same in either direction , agreed?

So necessarily half of the two way measurement is not going to be the same as a one way measurement in either direction. Unless the clocks are desynchronized , with the clocks in the rear running ahead of the clocks in the front.
Yes?
If for instance two way measurements were made from the center. This information [dt/2]was then sent at c [radio] to the clocks at the front and rear . It would reach the rear faster and based on the assumption of [ dx/dt=c] the clock would be set ahead. The reverse being true in the other direction ,,,yes?
I was not suggesting that the clocks had to be light synchronized to produce the invariance , I assume that is definitely not the case. I was only pointing out that the light procedure would automatically produce the exact same degree of desynchronization.
As far as I can see this desynchronization is one of the universe's little tricks on us like time dilation and length contraction. A conspiracy to keep us from being able to determine absolute motion. Just kidding.

As far as I can see the mystery of the invariance of light , which certainly twisted my mind when I first encountered it through Micholson-Morley, is only rationally explained and made possible through SR and the conception of clock desynchronization. DO you have any other way to look at it or understand it?

I'm sorry, but it is very difficult for me to understand what you are saying when you deliberately use non-standard terminology. As far as I can tell your "clock desynchronization" is what everyone else calls "the relativity of simultaneity", and your post is just a rough sketch of how to derive the relativity of simultaneity from the two postulates. If so, I agree.

But the point is, how could you use baseballs to synchronize clocks? If Alice is 10 m away from Bob and throws a baseball at Bob when her clock reads t0, what time should Bob set his clock to when he catches it? Because the speed of baseballs is not frame invariant you don't know. Similarly for tachyons.

 

[Austin0]

=DaleSpam;2052727]I'm sorry, but it is very difficult for me to understand what you are saying when you deliberately use non-standard terminology. As far as I can tell your "clock desynchronization" is what everyone else calls "the relativity of simultaneity", and your post is just a rough sketch of how to derive the relativity of simultaneity from the two postulates. If so, I agree.

I think there is a definite difference between the two concepts; Relativity of simultaneity and clock desynchronization.
Relative simultaneity is relevant to observations and the relationship between inertial frames.
Clock desynchronization must be viewed as an intrinsic reality because it occurs with regard to light ,which we consider the only actual constant velocity.
Ie. If you have a frame at some unknown state of motion, you then accelerate the system to a new steady velocity and measure light you get the same measurement. You then accelerate to a new velocity.,,etc etc.
Obviously there is no basis to determine a quantitative velocity for any of these stages but logiclly we can assume that they are all different in relation to light propagating in both directions along the same vector.
So if SR holds and light is constant the only possible explanation that I can see for the invariance of the measurements at these different velocities is that the clocks desynchronize proportionately. If you have a different explantion I would be interested to hear it.

But the point is, how could you use baseballs to synchronize clocks? If Alice is 10 m away from Bob and throws a baseball at Bob when her clock reads t0, what time should Bob set his clock to when he catches it? Because the speed of baseballs is not frame invariant you don't know. Similarly for tachyons

Actually if the 1st P holds you should be able to use any reasonable means to synchronize clocks.
For instance linear accelerators. The degree of desynchronization derived from this method would of necessity perfectly match that of light. If it didnt then physics would not be symetric and also the state of motion would be detectable.This is assuming of course that you have already determined a velocity through normal methods for a particle at a given energy /acceleration in some frame to apply to other frames.
The reason it would agree with light , as far as I can see, is because Newtonian ballistic mechanics, which is based on the complete isotropy of direction [ie. that an equal force is going to produce an equal acceleration of a particle with the motion of a system as counter to that motion] would not hold at relativistic velocities.
Acceleration forward would mean pushing a particle up the Lorentz mass slope with increasing energy demands for further acceleration ,while acceleration counter to the system motion would be down the slope with decreasing mass.
SO a particle moving forward would have a lower relative speed than a particle moving backward if accelerated with equal energy. But of course that is exactly what is required if the clocks in back are running ahead and the ones forward are behind.Just as a photon moving forward must take longer to reach the front which is moving away than to reach the rear..
But this could not hold for FTL because the clocks are not synchronized the necessary amount. So clocks synchronized with tachyons would not and could not agree with clocks synchronized with light or any sub c particle.

 

[Austin0]

Originally Posted by Austin0
Without SR the concept of light being measured at the same speed traveling in the same direction as the inertial frame as it is measured traveling counter to the motion of the frame is a logical impossibility yes? SR provided a rational consistent explanation for how this was possible through the desynchronization of clocks. Correct??

=JesseM;2051784]Yes, although the clocks are only "desynchronized" in the frame where they are moving of course.

You mean they are only perceived to be desynchronized from a frame which is moving wrt them,,,right?
That they are not perceived to be desynched in the frame in which they are at rest.
I agree,,,the desynchronization ,just like motion is undetectable.
But it must still be assumed to be present to explain the invariant measurement of the speed of light. Without reference to any other frame but only in relation to light a single frame at any possible velocity will measure the same speed .
How do you explain this or consider it possible if the clocks are not desynchronized by comparable degrees for each of these different velocities?
Obviously it is not possible to assume any quantitative velocity for a single frame but only the general logical assumption that the velocities must be different wrt the only constant we know , the propagation of light.

Yes, if all frames agreed on what it meant for clocks to be synchronized (i.e. if they all agreed about simultaneity), then it would be impossible for light to have the same speed in both directions in all frames.

I still don't really understand what your original comment "The overall results of the application of the basic assumption to bi-directional assigments and the many questions that arise from those results." Application of what basic assumption? And what does "the basic assumption to bi-directional assignments" mean? I understand that in the context of light you are using "bi-directional" to mean measuring the speed of light in both directions is, but I don't understand what "bi-directional assignments" are. What is being assigned, and what is it being assigned to?

The basic assumption is : The assumption that a velocity of 2c could be assigned on the basis of the rational 1/2 of the dx/dt for c,,, in frame A.
For the purposes of analysis I have taken the liberty of assuming that this should apply in the same way in the opposite direction and since you seem to be applying Newtonian mechanics to a FTL particle this should be valid,,,,,, yes?

5. By the first postulate of SR, if it is possible in one frame to send a tachyon signal in such way that the reception-event happens at an earlier time than the transmission-event in that frame,

5) just said it would be possible to send a different tachyon signal that goes back in time in A's coordinates, it doesn't say that that specific tachyon signal (the one that was sent at (0,0) and received at (20,10) in A) is going back in time in A's coordinates

.


Austin0
The 1st P allows us to track a photon trans-reception happening in another frame , to observe this reception event and have complete agreement between frames. Correct??

I understand what you're saying, but your language is confused here, the events of a photon being sent and received don't happen "in" any particular frame, they're just events, different frames assign them different coordinates. The second postulate (is that what you meant to write?) does say that if one frame finds that dx=dt for two events (in units where c=1, so both events would lie on the worldline of a photon), then another frame will also find that dx'=dt' when it looks at the same events in its own coordinates.

I understand the semantic difference but is it important? Abstraction is a powerful tool but is reducing events to pure numbers necessarily useful?? Wouldnt you agree that for pedagogical purposes, for communication and even for conceptualization it is sometimes better to see things in a more natural context??
In any case it is not the 2nd P I was referring to ,, although it goes without saying both frames will agree on c.
I ws talking about the workings of the system which allows the analysis of phenomena
from the perspective of different frames and have complete agreement, to apply physics and rational assumptions and achieve rational results.

What do you mean by "look over"? If you're talking about a local observation, the reception event wouldn't happen next to x'=6 in B's frame, it'd happen next to x' = 1.666..*(10 - 0.8*10)=3.333... in B's frame (and so naturally it'd also happen at t'=3.333... in B's frame).

OUCH! This time I truly came out with nonsense. I somehow managed to completely forget about time and jumped to the absurd direct gamma (x=10) ==> x'=6,,,, obviously from this beginning everything following is to be disregarded.
The dilemma of my current life is that I am too pressed to carry on this discussion but too involved to put it on hold and stop thinking about it. Sorry.

 

[Austin0]

I'm sorry, but it is very difficult for me to understand what you are saying when you deliberately use non-standard terminology. As far as I can tell your "clock desynchronization" is what everyone else calls "the relativity of simultaneity", and your post is just a rough sketch of how to derive the relativity of simultaneity from the two postulates. If so, I agree.

But the point is, how could you use baseballs to synchronize clocks? If Alice is 10 m away from Bob and throws a baseball at Bob when her clock reads t0, what time should Bob set his clock to when he catches it? Because the speed of baseballs is not frame invariant you don't know. Similarly for tachyons.

Hi Dale If Alice has an ideally consistant fast ball that always travels 60mph in one frame
wouldn't it be expected that whatever relative frame she was placed in, the rulers and clocks within that frame would measure her throws at 60mph?

So if in some frame, a clock was placed 176ft away from another clock and a ball was clocked at t=10 by the frist clock and arrived at the second [unsynched clock] at t=49
it would be calculated that the passage should take 2 seconcds and arrive at clock 2 at t=12 so therefore clock2 was 37 secs fast and being set back that amount should then be in synch with clock 1 and would then measure light or any other phenomena just the same as any of the other clocks in that frame.
Is this not correct??
Of course baseballs would not be frame invariant like light as far as being measured the same from other outside frames but they should be invarient just like the rest of physics within fames of differing velocities. For synchronization purposes this is what's important , right??
As for my terminology; I learned what I know of SR by myself, until I discovered this forum there was never anyone with either the understanding or interest for me to discuss these things with so I am just learning the terminology and forms in common use. I am learning as fast as I can Thanks for your parience

 

[Austin0]

Yes, although the clocks are only "desynchronized" in the frame where they are moving of course.

The paradox of the invariance of light drove me crazy until I knew enough about SR and clock desynchronization to come to a consistant explanation through that clock desynchronization. As I learned this by myself , before I discovered this forum, I assumed that this was the same explanation that everyone else arrived at.
If this is not the case I would very much appreciate knowing what the other explanation might be.
How a system that is accelerated to a different steady velocity can still measure the speed of light at the same value.
Thanks