Warp - any scientific take on it?

[TCO]

Originally posted by KrazyHorse


No. No, no, no. No.

You have separated time and space. They are not separate. When C sees B get the message, he is at time t = 1 minute. BUT HE OBSERVES A SEND THE MESSAGE AFTER HE OBSERVES B RECEIVE IT. And not just because of lightspeed delay.

Well duh. A hundred years later. Same with B. He gets the radio message 100 years after the IM arrives. Still not understanding how any of that makes A get messages before he sent them.

[TCO]

Originally posted by KrazyHorse
I think so, yes.

Cool.

[KrazyHorse]

Originally posted by TCO


Well duh. A hundred years later. Same with B. He gets the radio message 100 years after the IM arrives. Still not understanding how any of that makes A get messages before he sent them.

What didn't you understand about this:

And not just because of lightspeed delay.

?

[TCO]

B and C's clocks are synchronised at the same point in space, and A and B's clocks are synchronised everywhere, BUT A's CLOCK IS NOT SYNCHRONISED WITH C. If you ask A and B what time it is at B, they will agree. So will C. But if you ask what time it is at A, A and B will agree, but C will DISAGREE.

I need this explained in baby steps. What's important about the clocks?

[TCO]

Originally posted by KrazyHorse


What didn't you understand about this:

And not just because of lightspeed delay.

?

I got that part, but couldn't resist. Anyhow. Don't understand what you mean otherwise.

[KrazyHorse]

If C traces back the message from A and figures out how long ago, in his reference frame, A sent it, it looks to him like A sent it AFTER B

[TCO]

Originally posted by KrazyHorse
If C traces back the message from A and figures out how long ago, in his reference frame, A sent it, it looks to him like A sent it AFTER B

That's still not sending a message to yourself. And did you include my minute pause in there.

And I still don't see how it works. I'm all either IMing or waiting a minute. How is that going to make the message come in sooner that went around the block, than the one on it's first leg?

[KrazyHorse]

Originally posted by TCO


I got that part, but couldn't resist. Anyhow. Don't understand what you mean otherwise.

Basically, through a combination of length contraction and time dilation, C gets the message, plots back how long ago, in his reference frame, A sent it, and arrives at an answer. THAT ANSWER IS NOT GOING TO BE AT THE SAME TIME AS HE SAW B SEND HIS OWN MESSAGE.

When we use the term "observe" it implies an intelligent observer who understands the lightspeed delay. If I "observe" something that happened at coordinates (t,x,y,z) then I might get the message some time later, by light or by tin can telephone or whatever. I apply what I know about travel times of these things and get the coordinates for the event.

Even once I do this, the answers different people get are going to be different. This is not because the observers are stupid; it's because there is no consistent way to define coordinates so that everybody arrives at the same answer. Whether or not I think two things happen at the same time or not depends on my frame of reference

[KrazyHorse]

Originally posted by TCO


That's still not sending a message to yourself. And did you include my minute pause in there.

And I still don't see how it works. I'm all either IMing or waiting a minute. How is that going to make the message come in sooner that went around the block, than the one on it's first leg?

I'm not talking about that any more. I've gone simpler. I'm trying to explain to you this basic concept.

A and B agree about what time it is everywhere. If you ask them what time it is on Earth, or Mars, or in Andromeda they agree with each other.

A, B and C agree about what time it is at B, at the moment that C passes B. But even at the moment C passes B, C disagrees with A and B about what time it is at A.

In the FTL radio case, A and B think that B receives the signal at time 0 (or 1 minute, if you prefer). C agrees with them. A and B also agree that A sent the signal at time 0. C doesn't agree with them!!!!. If C waits for the light from A sending signal to get to him, then traces back how long ago it must have been sent (plotting intercept between light and A) he gets an answer which occurs AFTER B received the signal

[TCO]

Wait, but that is a bit of a rowback from saying one can send messages to oneself in the past. Now, you are saying that looking at the messages and doing some math one, thinks that the timing is messed up (relying on assumptions of light speed).

But this is almost a teleology, since we already assumed that in the first place.

In any case, I want to know how one actually gets a message to go to one's own past, using the IMer.h

[KrazyHorse]

Originally posted by TCO
Wait, but that is a bit of a rowback from saying one can send messages to oneself in the past. Now, you are saying that looking at the messages and doing some math one, thinks that the timing is messed up (relying on assumptions of light speed).

But this is almost a teleology, since we already assumed that in the first place.

In any case, I want to know how one actually gets a message to go to one's own past, using the IMer.h

It is not a rowback. You can still do what I said. I was trying to demonstrate to you what was happening with a simpler example.

Given simple SR, FTL travel is impossible without also allowing time machines.

Period. Point, set, match. Classic demonstration. In any good relativity textbook.

[TCO]

But you have failed to make me understand it.

[KrazyHorse]

That's because you refuse to start from the beginning.

Learn about the Lorentz transforms and what they mean.

[self biased]

question: gravity warps space making it "bigger" for lack of a better term. if it existed, would 'anti-gravity' warp space in the opposite way?

i have only a fast and loose grasp of GR, and a more fleeting grasp of SR mostly due to laziness.

[Kuciwalker]

Originally posted by KrazyHorse
By the way, this is standard material for any class teaching special relativity to undergrad physics students.

It's standard even for advanced HS physics classes