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By Visual on 12/4/2006 6:17:08 AM , Rating: 2
One aspect of space travel that i didn't see mentioned in this thread, and quite an interesting one I think, is that relativity effects kick in.

No long travel times are needed...
... well, from a certain point of view, anyway.
That is, from the traveller's point of view, the journey to anywhere could be arbitrarily brief.

Open up and scroll down to the Long Relativistic Journeys section. Make sure you have javascript enabled. Then have fun changing the distances and acceleration. Keep an eye at the "Trip time" field...
Theoretically, even if we use the quite comfortable constant 1 g acceleration we can reach the other side of the galaxy (estimates are from 90000 to 160000 ly) in under 24 years, get to the nearest galaxies (all the ones listed at for example) in under 32 years, etc...
Surprised by the results? We can go virtually anywhere in a lifetime.

On the other hand, even getting to the nearest stars is going to take atleast 3 years at 1 g acceleration. Not exactly a quick journey... so while we might not need colony ships spanning multiple generations, we still would need life-support for atleast a few years, or decades for the faraway places.

Perhaps cryogenic sleep would be the way to go?

Or... you can change the acceleration and see what happens. 10 g cuts the travel time around ten times for the larger distances. 100 g would let us cross the galaxy in 4 months... get it into the thousands, and the calculator starts to overflow and give errors, but it'd make huge journeys look like just days or minutes to the travellers.

Another interesting fact to note here, is that the "Earth time" doesn't get much different wether the acceleration is 1 g or 1000 g. A couple of years difference for crossing the galaxy. So we, with a primitive but comfortable 1 g seedship, can get there around about the same time as our superadvanced alien neighbours travelling at 1000g, if we start at the same time and distance :p

Sure we can't survive a journey at even 10 g. 1 g is the best option we can start with, it will be just like artificial gravity for the ship. I bet we can also manage slightly more than that, for example adapt to 2 g. In cryostasis we might be able to survive an order of magnitude more, but we'd never get much beyond that.

But maybe we'll find a way around this - some technology that would allow us to apply this acceleration uniformly to the whole ship, or atleast uniformly to the whole human body, so it doesn't feel the stress. Remember, you can fall even with 10000000000 g acceleration in a uniform gravity field without feeling a thing, just because it is uniform.

Ok, now a reality call of sorts. That page I showed you, it is just math. It assumes we can keep up a constant acceleration (from the traveller's viewpoint) for half the journey and the same constant deceleration for the other half. But can we? No, definitely not at our technology state, even if we assume we get the antimatter engine itself. As we get closer and closer to the speed of light, collisions with interstallar matter or even the light of the stars infront of us will become a significant problem. Relativistic aberration would mean that the closer we are to c, the bigger part of the universe will appear to be infront of us instead of behind us, so we'd get more light trying to slow us down (on the same principle that light we emit behind us accelerates us). Also light we receive from infront will be increasingly more blueshifted and energetic, increasing its slowdown effect. On the plus side, we can use this as a bonus for the deceleration phase of the journey, but facts are there is no free lunch - we'd have spent much more energy during acceleration.

And things slowing us down might be the least of our problems... rather, i think things might just be destrying us :P I.e. at some point even non-harmful light will appear to us like gamma rays and become deadly. And we won't be hitting just light on our way, but massive matter too - a single hydrogen atom might destroy the whole ship at a velocity high enough.

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