Proof of impossibility of superluminal signals?

[rjbeery]

Within a second according to their watch and the clocks of the place they left behind.

Just because the place they left behind doesn't see them appear 100,000 light years away until 100,000 years later (assuming they had a telescope to see the other side of the galaxy) doest mean they weren't there one second after they jumped into the wormhole.

"Within a second" is still presuming that there is an actual moment 100,000 LY away which represents "instantly", when the reality is this moment changes based on the movement of the observers at each point.

That's the crux of the entire argument! If we had a way to transport "instantly" across the galaxy then I could travel 100,000 LY away and you, waiting for me there and under relative motion, could travel "instantly" back to my departure point before I left.

You are having a problem because you're thinking of time marching forward uniformly across the entire Universe as Newton did.

 

[phyti]

phyti, it's impossible to tell what your point is. I don't even understand what you're talking about. Increasing radar speed? We're talking about special relativity, not fantasy.

Currently, SR deals with events that communicate at light speed c.
If a method of faster than light communication was discovered that propagated in space at c', coordinate measurements would have to be done at c' to maintain compatibility.
Speed c' would assume the role of c as the limiting speed.
Pics 3 & 4 show the ftl signal becoming more horizontal in the B frame as the measurement signals increase to c'.
Using space-time pics shows the backward in time interpretation results from the measurement signal speed not equal to the info/message speed!

 

[Fredrik]

Currently, SR deals with events that communicate at light speed c.
If a method of faster than light communication was discovered that propagated in space at c', coordinate measurements would have to be done at c' to maintain compatibility.
Speed c' would assume the role of c as the limiting speed.

We're talking about the possibility that something that carries information can move faster than the invariant speed. If such a thing moves at c'>c, it wouldn't change the role of c, the only invariant speed in the theory.

 

[stevendaryl]

Currently, SR deals with events that communicate at light speed c.
If a method of faster than light communication was discovered that propagated in space at c', coordinate measurements would have to be done at c' to maintain compatibility.

Look, we've already verified that a clock moving at constant speed $v$ relative to an inertial reference frame experiences time dilation according to

$\dfrac{d\tau}{dt} = \sqrt{1-\frac{v^2}{c^2}}$

If that formula is correct, then it can't also be correct if you substitute $c'$ for $c$.

So no, you can't just replace $c$ by some other speed $c'$. That would be nonsensical.

 

[Mark_Laverty]

@peterdonnis

I just wrote out a nice reply in which I agreed with you and said I think we were saying similar things but you explained it better than me!

E.g. I missed your emphasis on the word 'proof'.

I hit post and it didn't post and I'm struglinng for time to rewrite it (pun not intended!).

You are having a problem because you're thinking of time marching forward uniformly across the entire Universe as Newton did.

OK, this may be the problem, I'll think about this.