The majority of writers who chose to respond to this essay seem to have misunderstood special relativity and gotten lost in the so-called Twin Paradox without discussing the physiological effects of living in space on the human body.
Now that I mention it, it is rather more fun to discuss relativity than the depressing health problems associated with space travel.
There is no twin paradox; time dilation is real and has been verified in many experiments. (People can’t travel close to the speed of light, but they can measure very small fractions of a second.) Time does pass slower for the twin who ACCELERATED and went on the space voyage. If he travels close enough to the speed of light, almost no time will pass for him. The twin on earth never accelerates, breaking the symmetry that leads to the “paradox.” He can’t claim that the earth moved and the ship stood still, because his frame experienced no acceleration while the space ship did. In other words, when the ship was blasting off, did the people watching on the ground get squished into their lawn chairs by many g’s of acceleration? Of course not, so they can’t claim the earth moved away from and returned to a stationary space ship. Special Relativity doesn’t handle acceleration; it’s just a coordinate transformation between inertial, as in non-accelerated, reference frames. Ask a real physicist how to apply the much more complex General Relativity to this situation.
The short answer, at least according to the the engineer and hard science fiction writer Stephen Baxter, is that radiation, inactivity, confinement, and prolonged weightlessness, are very bad for you. Especially if you plan to return to Earth after your space trip. Bones become weaker, you develop circulatory problems, and you might get irradiated if you’re unlucky. So space travel can age, if not kill, you very quickly if you’re not careful. But does it have to be this way? Without resorting to cheesy, Star Trek wormholes, is there any way to go on a longish interplanetary voyage within our solar system without ruining your health?
To avoid your crew’s wasting away in weightlessness, your spaceship could simulate some gravity by rotating. Imagine living, like ants in a soda can, on the walls of a great cylindrical spaceship that spins about its central axis. Perhaps your ship could be made of a dense material or have a double hull with water in it to screen out radiation. Of course radiation shielding will increase the mass of the ship, requiring more fuel to make the trip. In addition, the ship’s precession due to rotation will have to be taken into account when steering. (Hint: Did you ever play with a gyroscope when you were a kid?) While this ship is heavier and harder to control, these problems are not insurmountable.
I wonder about the psychological impact of even a relatively short voyage to the outer planets on the crew. Decades living and working with a small group of people is going to cause cabin fever from hell. And things are bound to go wrong, resulting in brief periods of panic punctuating long stretches of boredom. That is, assuming the problem is survivable. One could acquire more than a few grey hairs having to cope with occasional life-and-death emergencies with only the help people you are sick to death of seeing. And you can forget about calling Mission Control for help: by the time your radio signal has traversed the lighthours back to earth, the emergency is over and the problem is either solved or you’re all too dead to hear the reply.
Is it possible to avoid the horrible consequences of prolonged life in space by going on a VERY fast trip? If you had limitless energy to propel your ship, couldn’t you minimize your travel time by going very, very close to the speed of light so that time would almost stop for you and any voyage would be nearly instantaneous? Unfortunately, even if you had the ability to travel very close to c, your ship would be Swiss cheese from impacts with interstellar gas and dust; even the space between the stars isn’t that empty when you’re going fast. (Sir Arthur C. Clarke has estimated for his novel “The Songs Of Distant Earth” that even at 20% of c your ship would require a very heavy shield of some dense material out in front of it. His spacemen used ice.)
Could the crew be kept in suspended animation, while intelligent computers handle the day-to-day maintenance of the ship? In fact, unless your mission is colonization-unlikely since no place is remotely habitable in the solar system-why send people at all if thinking machines can carry out exploration and radio back their discoveries? The computers don’t need food or water, get weak from prolonged weightlessness, go nuts, except in the movies, and nobody gets killed if an American engineer thought the blueprints had been labelled in inches. There’s no point in asking about the effect of space travel on aging, because it just does not make much sense to send people into space when a computer can do the job. So much for the romance of exploration….
