I’m in the middle of reading Neal Stephenson’s Anathem (which is awesome by the way – please don’t post any spoilers since I’m not done!). Anyway, it inspired me to think a bit about interstellar travel from a realistic point of view. In other words, I decided to try to put some hard numbers to things. Specifically, I wanted to put some relativistic numbers on a trip to the nearest extrasolar planet (which, as of now, happens to orbit Epsilon Eridani and is 10.5 light-years from earth).
So, the first thing I did was to look up about how many “g’s” the human body can take without blacking out. It turns out it can handle about 5. Then I made the assumption that my hypothetical spacecraft would be able to travel at 3/5 the speed of light (I’ll let the engineers figure out how to do that). If our ship accelerates constantly up to that speed, it would take about 42 or 43 days or so which is really pushing it for the humans. So maybe we draw that out a bit more – say we double it.
Next, I drew a spacetime diagram and, in the absence of a good ruler but with an approximate straight-edge, estimated that the ship would arrive (with a lengthier deceleration since the human body has a harder time with that I believe) at its destination in about 18.5 years of earth-time. To the astronauts onboard this would actually be closer to 14.8 years since they spent a great deal of time travelling at relativistic speeds. Let’s assume that, considering the time and effort expended to get them there, they spend a good two years checking the place out before heading home.
All told, that means that they would be gone for a total of 39 years of earth-time which, to them, would be closer to 31.6 years. That’s a long time – but not an entirely unreasonable amount. Consider this: Saint Simeon Stylites sat on a pole for 37 years. Considering we just celebrated the 40th anniversary of the Apollo 11 Moon landing, just think if we had actually sent Neil, Buzz, and Mike – who are all still alive – to Epsilon Eridani instead (with the proper equipment, of course)!
In short, aside from the obvious engineering hurdles, interstellar travel does not seem quite as far fetched when you actually look at the numbers. It’s a long way away from happening – if it ever does – but it seems to me that if the human race put its mind to it (and doesn’t annihilate itself beforehand), this feat could be accomplished (for one particular engineering idea on how to keep the astronauts alive, see Arthur C. Clarke’s Rama series of books).