This sounds like if you move at vY takes zero time, and finally moving at v>c allows negative distances(!) and X->Y takes negative time (thus travelling in the past).
Oops, something got munched. That should have read:
This sounds like if you move at v<c, distances are positive and moving from X to Y takes a positive time, moving at v=c effectively makes distances moot and X->Y takes zero time, and finally moving at v>c allows negative distances(!) and X->Y takes negative time (thus travelling in the past).
I blame HTML, as always. ^_^
Sorry 'bout that.
Nicolas Briche nbriche@free.fr ============ "If you try to stay sane in life, it'll just drive you crazy. So, you may as well go crazy now and have fun with life." --MegaZone, of Eyrie Productions =========== "Outside! What's it like?" "Well... It's sort of big" --Terry Pratchett
See my other reply [slashdot.org], which is the one that should have been moderated up, not the one you are replying to.
Interesting material; I'm going to have to read it entirely (and find a way to keep the diagrams from displaying over the text... damn.)
But you can't make that assumption; if a ship coming from Earth at high (but still sublight) speed crosses the Centauri system as you break the news, they will get the message although in their frame of reference the event really has not occurred yet.
Hm; that's the part I don't get. Why wouldn't the event have occured yet? Sure, the flash hasn't reached them yet, and that would be the only way for them to know that anything happened. But that doesn't mean anything about the Earth being totalled. Just because they can't yet observe an event, doesn't mean that the event didn't already happen. This sounds like if you move at vY takes zero time, and finally moving at v>c allows negative distances(!) and X->Y takes negative time (thus travelling in the past). This is... weird. (But a somehow interesting concept. Hm. I can use that. ^_^)
Did I miss something in your exemple? Could you describe the chain of events in more details?
About FTL itself, the whole point is making the travel's duration approach zero. An ideal FTL travel would make us go from one side of the universe to the other in no time flat, whatever size the universe is. No time travel involved. You wouldn't be 15+ billions years in the past, or future, or whatever, but exactly at the same time than anyone who didn't travel.
Anyone where? At what speed? In which gravity field?
Sorry. Let's say that:
point X: point of departure, an Earth-like body orbiting a Sol-like star at one end of the universe (well, supposing the universe _has_ an end, of course)
point Y: point of arrival, similar to X, on the other side of the universe.
Guy G decides to travel to Y, say to visit his girlfriend L, using an ideal FTL device ID (ship, stargate...)
t0, X: G enters ID
t0, Y: L is waiting whereever G is supposed to arrive.
t1, X: ID activates, does its stuff.
t2, Y: ID arrives, stuff is done.
t3, Y: G leaves ID, sees L, much happiness ensues (well, I like happy endings. Sue me. ^_^).
In this case, t2-t1 approaches zero.
As for speed, I don't think that a FTL device should be concerned about how fast it goes but how long it can go over c. Depending of the drive it uses, a FTL device may have some problems surviving a shift under the light barrier. If you think speed, you also have to think acceleration and deceleration, and I don't think a FTL can do that around the light barrier.
Since, ideally, the events "departure" and "arrival" are in different places, they cannot be simultaneous in all frames of references; otherwise, you are implicitly supposing the existence of an "absolute" time, shared by everyone at every place in the Universe; this is exactly the hypothesis Relativity drops in favor of lightspeed being constant.
They're not actually simultaneous, or we'd have two travellers while the travel physically occurs. We'd then say goodbye to sanity while we try to determine where general relativity ends and quantum physics begins (that's the best case scenario; we also could end up with an infinity of travellers between the two points, or one traveller the size of the universe -- see the book Spirit of Wonder for that last one). A FTL can't have a delta of zero, for the same reason a STL can't go to c: if it did, it probably would degenerate into energy. It can only hope to approach it.
As for the 'absolute' time, it would be convenient (like in my previous post), but not necessary. t2-t0X can be positive, negative or, by a randomness so random it can't possibly be random, null, t2-t1 will _still_ be positive approaching zero. The only way to notice any difference would be to isolate one's time from the rest of the universe's. If there was a way to do _that_, then there wouldn't be a _point_ to a FTL device. That, and one would effectively leave the space-time continuum, which isn't a smart thing to do unless one know a way to come _back_. This hasn't happened yet (we haven't seen any conqueror-wannabes from the far future/past), or, if it happened, it's obviously not enough of a paradox for the universe to go boom.
That said... I don't really think that the 'absolute time' theory nullifies Relativity... After all, we're still stuck with one time dimension for three physical ones plus the superstrings (also considered physical). Although I never discussed this on the I-net at large, I usually think of time as three-dimensional at the very least (we have to put those parallel universes _somewhere_ after all).
Okay, now to retrieve that FAQ you mentioned for a nice offline reading. Where's a tarball...
Nicolas Briche nbriche@free.fr ============ "If you try to stay sane in life, it'll just drive you crazy. So, you may as well go crazy now and have fun with life." --MegaZone, of Eyrie Productions =========== "Outside! What's it like?" "Well... It's sort of big" --Terry Pratchett
Slashdot Mirror
This sounds like if you move at vY takes zero time, and finally moving at v>c allows negative distances(!) and X->Y takes negative time (thus travelling in the past).
Oops, something got munched. That should have read:
This sounds like if you move at v<c, distances are positive and moving from X to Y takes a positive time, moving at v=c effectively makes distances moot and X->Y takes zero time, and finally moving at v>c allows negative distances(!) and X->Y takes negative time (thus travelling in the past).
I blame HTML, as always. ^_^
Sorry 'bout that.
Nicolas Briche
nbriche@free.fr
============
"If you try to stay sane in life, it'll just drive you crazy. So, you may
as well go crazy now and have fun with life."
--MegaZone, of Eyrie Productions
===========
"Outside! What's it like?"
"Well... It's sort of big"
--Terry Pratchett
See my other reply [slashdot.org], which is the one that should have been moderated up, not the one you are replying to.
Interesting material; I'm going to have to read it entirely (and find a way to keep the diagrams from displaying over the text... damn.)
But you can't make that assumption; if a ship coming from Earth at high (but still sublight) speed crosses the Centauri system as you break the news, they will get the message although in their frame of reference the event really has not occurred yet.
Hm; that's the part I don't get. Why wouldn't the event have occured yet? Sure, the flash hasn't reached them yet, and that would be the only way for them to know that anything happened. But that doesn't mean anything about the Earth being totalled. Just because they can't yet observe an event, doesn't mean that the event didn't already happen. This sounds like if you move at vY takes zero time, and finally moving at v>c allows negative distances(!) and X->Y takes negative time (thus travelling in the past). This is... weird. (But a somehow interesting concept. Hm. I can use that. ^_^)
Did I miss something in your exemple? Could you describe the chain of events in more details?
About FTL itself, the whole point is making the travel's duration approach zero. An ideal FTL travel would make us go from one side of the universe to the other in no time flat, whatever size the universe is. No time travel involved. You wouldn't be 15+ billions years in the past, or future, or whatever, but exactly at the same time than anyone who didn't travel.
Anyone where? At what speed? In which gravity field?
Sorry. Let's say that:
point X: point of departure, an Earth-like body orbiting a Sol-like star at one end of the universe (well, supposing the universe _has_ an end, of course)
point Y: point of arrival, similar to X, on the other side of the universe.
Guy G decides to travel to Y, say to visit his girlfriend L, using an ideal FTL device ID (ship, stargate...)
t0, X: G enters ID
t0, Y: L is waiting whereever G is supposed to arrive.
t1, X: ID activates, does its stuff.
t2, Y: ID arrives, stuff is done.
t3, Y: G leaves ID, sees L, much happiness ensues (well, I like happy endings. Sue me. ^_^).
In this case, t2-t1 approaches zero.
As for speed, I don't think that a FTL device should be concerned about how fast it goes but how long it can go over c. Depending of the drive it uses, a FTL device may have some problems surviving a shift under the light barrier. If you think speed, you also have to think acceleration and deceleration, and I don't think a FTL can do that around the light barrier.
Since, ideally, the events "departure" and "arrival" are in different places, they cannot be simultaneous in all frames of references; otherwise, you are implicitly supposing the existence of an "absolute" time, shared by everyone at every place in the Universe; this is exactly the hypothesis Relativity drops in favor of lightspeed being constant.
They're not actually simultaneous, or we'd have two travellers while the travel physically occurs. We'd then say goodbye to sanity while we try to determine where general relativity ends and quantum physics begins (that's the best case scenario; we also could end up with an infinity of travellers between the two points, or one traveller the size of the universe -- see the book Spirit of Wonder for that last one). A FTL can't have a delta of zero, for the same reason a STL can't go to c: if it did, it probably would degenerate into energy. It can only hope to approach it.
As for the 'absolute' time, it would be convenient (like in my previous post), but not necessary. t2-t0X can be positive, negative or, by a randomness so random it can't possibly be random, null, t2-t1 will _still_ be positive approaching zero. The only way to notice any difference would be to isolate one's time from the rest of the universe's. If there was a way to do _that_, then there wouldn't be a _point_ to a FTL device. That, and one would effectively leave the space-time continuum, which isn't a smart thing to do unless one know a way to come _back_. This hasn't happened yet (we haven't seen any conqueror-wannabes from the far future/past), or, if it happened, it's obviously not enough of a paradox for the universe to go boom.
That said... I don't really think that the 'absolute time' theory nullifies Relativity... After all, we're still stuck with one time dimension for three physical ones plus the superstrings (also considered physical). Although I never discussed this on the I-net at large, I usually think of time as three-dimensional at the very least (we have to put those parallel universes _somewhere_ after all).
Okay, now to retrieve that FAQ you mentioned for a nice offline reading. Where's a tarball...
Nicolas Briche
nbriche@free.fr
============
"If you try to stay sane in life, it'll just drive you crazy. So, you may
as well go crazy now and have fun with life."
--MegaZone, of Eyrie Productions
===========
"Outside! What's it like?"
"Well... It's sort of big"
--Terry Pratchett