12 January 2009

FTL, Causation, and Travel to Remote Timespace Locales

I've been kicking around a sort of sci-fi idea. Conventional scientific thought has it that travel faster than light (FTL) is inherently impossible because it violates causation. (If you don't know why, you can read about it any number of places). Also because the energy necessary for any mass to travel at the speed of light is infinite, and asymptotically approaches infinity as you get closer and closer to that velocity. Nature abhors infinities, just as it abhors vacuum.

However, since the universe (as opposed to the observable universe) is, while not infinite, very very large, it stands to reason that there are many, many worlds, some perhaps a lot like Earth, all over the place, that are outside the time horizon of our current location in space and time. In other words, they are not and can never be causally connected to anything happening here.

If this isn't clear, think about this. The universe is no more than 13-14 billion years old, but there are regions of space much further than 13 billion light years distant, due to the expansion of space. A star in such regions isn't even theoretically visible from here, and it never will be. In fact, no form of communication whatsoever with such regions, which are by far most of the universe, will ever be possible. Unless...

If space is, as some believe, all twisted and interconnected with trapdoors and wormholes, maybe there are ways to connect more or less instantly, say across some kind of 'gateway', with places (timespace locations) which are vastly far away from here; so vastly that they cannot see us and we cannot see them, effectively, ever, in normal space and time.

Might it be at least conceivable that there could be a permanent or at least stable connection between two locales, vastly separated in normal spacetime but immediately proximate in twisty spacetime, so that you could routinely travel between them with no concern for violating either the energy considerations of FTL travel or the problems of timetravel paradoxes which normally arise when FTL is being considered? Travel of signals between such places in normal spacetime is impossible, so there's no way either could causally effect the other in normal spacetime. So the issue of timetravel paradoxes which would otherwise arise from any travel from one such location to another will never arise.

Anyway, an odd consequence of this is that it might be possible to immediately, or at least relatively quickly, travel to extremely remote locations in the universe, while it remains effectively impossible to travel quickly to even the very nearest stars, or anywhere in our own Galaxy, for example.

UPDATE (Nov. 2011):
Here is a more recent exposition of this same speculation. One problem that came to my attention after this, is created by relativity, whereby simultaneity is effectively nonexistent. The spacetime angle created by even small relative motion between very widely separated points in "normal space" might make synchonous travel through such points of contact effectively impossible even if they did exist. But it remains an intriguing idea, at least to me:

This is my idea, and it's how I think it's just possible that the universe actually is.

Accept, if you will, the following premise (I can explain why this is almost certainly so, if you like, but for now please just take it as a premise):

Faster than light travel by massive particles (and anything made out of them, including us and our spaceships, now and in the future, as well as those of any other creatures and their spaceships, now, and in the past and the future)....is impossible. For reasons of General Relativity, and because FTL is actually the mathematical equivalent of backwards time travel, which creates the possibility of violation of causality. For FTL to be possible, the many-worlds hypothesis of Quantum reality is necessarily true, and branching would have to occur both forwards and backwards; once you travel faster than light, you effectively break the connection with the universe you came from and you can never get back to it, although you could seemingly return to a world that resembled the one you left. Anyway, for purposes of my idea, please assume that this is not the case, that FTL is not now and never will be possible.

Now, accept, if you will, just as a thought experiment, the following:

The universe is so structured that places that are too far apart to be causally connected to each other (because light could never reach from one point to the other in the entire history since the Big Bang; rest assured that most locales in the universe are separated from almost all other locales in the universe in just this way)... nevertheless can be immediately adjacent to each other in the additional dimensions through which the normal space we live in is curved and re-curved. Picture three dimensional space projected like a map onto twisted spaghetti: locations distant along the threads might touch each other from one thread to another, or even one thread to another part of the same thread.

Then accept the following additional thought experiments:

There are points of contact, where it is possible to cross over from one part of space to another. The distance from A to B through this transit contact point is negligible, even though the distance between the same two points in normal space would typically be tens of billions of light years.

Such points of contact are relatively common (say, several, but not a huge number, accessible from any given place), and are possible, albeit technologically difficult, to detect.

Such points of contact are gravitationally associated with largish masses, like stars, but are typically found well outside the main mass of star systems, where planets and such are found, so that travel to them from such planetary systems is feasible, but not trivially easy. This makes them stable over time, and associated for long periods of time with particular stars and their planets.

A technological civilization arising anywhere in the universe could use these points of trans-spatial contact to create a whole network of accessible worlds, which were located some few tens to hundreds of billions of kilometers through normal space and a limited number of "link jumps" through the extra dimensions, without ever traveling faster than light and without violating causality. None of these linked worlds would be even theoretically visible from any of the others, and would be located literally all over the universe in "real space." (Yes, incidentally, the universe really is plenty large enough for this to be actually possible). Thus, a Trans-Galactic "Empire," even while travel to even the nearest stars remains effectively impracticable.

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