Warp - any scientific take on it?

[TCO]

So he was wrong. Thanks.

[KrazyHorse]

I didn't read his responses carefully enough to know if he said something mistaken. But he has fundamental understanding of what he speaks.

FTL is a no-no in the simplest understanding of relativity we have.

To break it you need some messed-up stuff.

[TCO]

I could buy that. But he is wrong in the bback in time, no?

[TCO]

besides, what's so bad about info moving FTL. I mean as long as I'm not trying to accelerate something which has mass climbing up an assymptote.

[KrazyHorse]

No, if you are allowed to move one with respect to the other (accelerating in spaceship) then you can end up sending back in time...

this is best layman's explanation of this I could find.

I don't feel like running through 3 sets of lorentz transforms to demonstrate this rigorously right now

http://www.theculture.org/rich/sharpblue/archives/000089.html

[TCO]

Why do you need Lorentz. Say it with rocket ships.

[KrazyHorse]

Basically, the problem is that a purely spacelike transmission in Carol and Dave's frame (Q to R) has a negative time component in Alice and Bob's frame

[TCO]

That's just a frame thing. I want to know how you actually really truly send a message to yourself last week.

[KrazyHorse]

Read link. Experiment goes as follows:

A and B at rest. C and D travelling at same constant v relative to A and B.

D passes A at some time before A sends signal. C passes B at exact moment A sends signal to B. C sees B receive signal, sends signal to D. D receives signal when he passes A, before A even sends signal

WTFFFFF!!!!

[KrazyHorse]

The problem is that even though C passing signal to D looks like a purely spatial transfer to both C and D, to A and B signal goes backward in time...

[TCO]

But wait, you are having the moving guys do stuff. My device just works with the guys stationary. And I'm still not sure how even with the moving guys that it really works. I got you to the part where C sends the signal to D. No, it's not back in time (in terms of when he passed A). He's already passed it.

[KrazyHorse]

Originally posted by TCO
But wait, you are having the moving guys do stuff. My device just works with the guys stationary.

????

So you're tossing relativity out the window?

First principle of (special) relativity: the laws of physics are the same for all observers in all inertial frames. If you can send a signal from one guy to another guy who are both at rest in some frame (A and B) then you can send a signal from one guy to another guy who are both moving with constant velocity wrt that frame (C and D), since they have their own inertial frame in which they are both at rest...

[KrazyHorse]

Originally posted by TCO
But wait, you are having the moving guys do stuff. My device just works with the guys stationary. And I'm still not sure how even with the moving guys that it really works. I got you to the part where C sends the signal to D. No, it's not back in time (in terms of when he passed A). He's already passed it.

No, it isn't. You are ignoring the interrelationship between space and time in SR

Even if C and D have synchronised watches so that they share the exact same time, and only differ in their placement (and are at rest wrt one another, so watches stay synchronised), observers A and B see them as separated both in time and in space

A signal which is simply instantaneous spatial movement when you ask C or D what happened looks like a signal travelling backwards in time to A and B

[KrazyHorse]

Relativity breaks simultaneity. If A and B have set stopwatches so that they perform same action at what they observe to be same time, then C and D will observe them performing that action at different times

[TCO]

Yeah, but there is no way for them to know it happened and to really deliver a message back in time to myself. Kust some messed up doiagrams.