reply to post by gimme_some_truth
Excuse me for being stubborn, but I would like to explain again what I mean and why Einstein wouldn't be against faster-than-light travel as we
imagine it in the future warp drives, and, therefore, against the FTL-based time machine.
I think it's very important that you and other readers of this thread get a clear picture of this very important aspect of reality because it has
many philosophical implications.
Einstein/relativity says: there is no local
faster than light travel. Locality in physical jargon means objects with which the observer (the
one who tests physical laws) may interact. Indeed, if it were possible, the observer would register absurd values of infinite energy and imaginary
time from this superluminally moving object.
Well, the warp drive designs use a bit of "cheating" here: they try to circumvent locality. And since the normal spacetime in the universe is
"smooth", and all objects can send and receive signals through this smooth medium, there seems to be no place in the universe to "hide" from the
observer. No place, except, maybe, an isolated pocket of spacetime, which is not casually connected to the rest of the universe. Is this kind of
pocket possible? It appears to be, and the first mathematical expression for the geometry of this pocket (also called metric) was found by Miguel
Alcubierre, out of Einstein's equations, and them alone. No 'God playing dice' quantum mechanics ever mentioned.
(side note: Here we see again that the physical laws somehow depend on the observer, and the observer somehow can influence the outcome of physical
experiments. Einstein resented this feature in quantum mechanics, but, it appears, it has returned to his theory with warp metrics.)
Let the reader understand very clearly: due to the causal isolation of this warp pocket, it is no longer a part of our universe, along with objects
contained therein. No interaction with our universe is possible from inside this pocket or vice versa. No paradoxes appear if this pocket is moving
superluminally in our spacetime - it does not have a mass, nor electric charge nor magnetic moment and cannot exert any forces on anything.
A simple analogy is a light spot that you project on a distant wall with your flashlight. If you move your flashlight fast enough, the spot will
appear to move faster than light
in its linear motion along the wall. This doesn't break any laws of physics, since that spot is not a physical
object, it's a geometric area where photons from your flashlight hit the wall. The same way, the warp bubble is not a physical object
physical object by definition must interact with something to be detectable.
And what about the enormous tidal forces on the edges of the bubble. you may ask? They cause real effects on particles in our universe. Yes, but
these are technically not part of the bubble. The outer edges of the bubble are the edges of our universe, beyond them another universe begins which
is inside the bubble. And these outer edges are just defects in our spacetime, same as cosmic strings or event horizons of black holes. They are
permitted to move faster than light because they are not real physical objects, they are just defects in spacetime. They have no mass, no charge, no
magnetic moment, but they can exert forces on other objects which are gravitational forces. This is perfectly legal according to the general
relativity (the g-tensor components cause these forces to appear in the equations). In other words, massless objects (which have no T tensor
components) may move at the speed of light or faster
. Indeed, in case of photons we observe them moving at exactly the speed of light, and only
because they are massless.
Hope this helps, please don't hesitate to ask any questions if something is not clear.
[edit on 12-8-2009 by veles77]