Recent content by frakie

Maybe I've found my mistake: I've wrote that M' has moved and it isn't the mid-point anymore thence the simultaneity definition isn't applicable anymore to it. This is untrue, in fact the definition says that the observer must be in the mid-point when the events happen but it doesn't tell he...

Einstein in his "Relativity: The Special and General Theory" ch.VIII explains that simultaneity between events placed in two predetermined places A and B can be asserted if an observer in the mid-point M sees the light coming from the two events places in the same time. In ch.VII he says that...

This image explains what relativity of simultaneity is. And since "simultaneous" means "happening at exactly the same time" it is clear and obvious to me that the consequence is what i wrote in my previous comment.

If that clock belongs to my frame,then how is it supposed to be synchronized with my clock and be brought next to the supernova? I think that travel would break the synchronization. Nevertheless you're right,I need to check some better sources. Have you got any suggestion?

According to special relativity an observer must say two events A and B are simultaneous when he receives - instantly - the two informations "A is happening" and "B is happening". Those informations travel at c speed. So if i receive a supernova light right now i have to tell that the event...

I see your point and I also see there are many contradictions in your example: the very first contradiction is the use of relativistic simultaneity concept; this concept lies on an axiom which states that every event spreads through the spacetime at velocity c. This is in contradiction with our...

Yes you're right, I was wrong because I thought in gamma = 1 / root(1-(v/c)^2) v was the FTL velocity.

I've found a some better explanation, here, but I think that it turns out that what he call "trick" is just an error: Lorentz Transformation can't be applied since the FTL speed is NOT a relative velocity, and this means that the Lorentz transformation gamma can't be calculated that way.

Hi 'body, ok, this is a well known issue, but i still can't find a valid explanation of why FTL implies time travel. I've read lot of explanations, and each one ends up with a nonsense telling something like "if you drive a FTL car when you'll arrive you'll see yourself opening the car door...