Extraterrestrial Civilizations - Isaac Asimov [120]
Some scientists suspect that this interference by interstellar matter will itself be sufficient to keep space vessels from ever reaching speeds of over 1/10 that of light—and at that speed the time- dilatation effect is very minor.
Even if all difficulties are overcome, there remains another problem that lies at the very core of relativity. The slowed time sense affects only the astronauts, not the people back on the home planet.
Making use of 1-g acceleration and deceleration, and time dilatation, to the full, a trip to the star Deneb and back will take astronauts 20 years (even allowing one year in the Deneb system for exploratory purposes). When they return, however, they will find that 200 years have passed on Earth. The longer they travel at this acceleration, the more closely they will creep up to the speed-of-light limit and the more slowly time will pass for them. Thus, the discrepancy between ship-time-passage and Earth-time-passage rapidly increases with distance. A round trip to the other end of the Galaxy will seem to take 50 years to the astronauts, but they will find that some 400,000 years will have passed on Earth. (This would be true to an even greater extreme in the case of the photonic drive.)
One has the feeling that this alone would suffice to make it certain that there would be no great popular demand among the people on Earth (or on any home planet) for investing in stellar exploration by time dilatation. It is difficult enough to get people to deprive themselves of anything now for the sake of having something desirable or even essential come about in 30 years. To invest an enormous effort in something that will return centuries later or hundreds of thousands of years later would not seem to be something we would count on people doing.
Considering, then, the difficulties in energy requirements, in radiation danger, and in time differential, our conservative standards would make it seem that time dilatation is not a practical means, either physically or psychologically, for reaching the stars.
COASTING
Since all methods for traveling near the speed of light or actually beyond it seem to be impractical, we must see what can be done at low speeds.
The advantage there, of course, is that the energy requirements are not exorbitant, nor is the environment of interstellar space then dangerous. The disadvantage rests in the time such a voyage would take.
Suppose a ship were to be accelerated to a speed of 3,000 kilometers (1,860 miles) per second. This would be very fast by ordinary standards since at that speed a ship could travel from the Earth to the Moon in 2 minutes. Still, it is only 1/100 the speed of light, so that the time-dilatation effect is negligible, and it would take nearly 900 years for the round trip to Alpha Centauri, the nearest star.
Are there any conditions under which a 900-year trip could be endurable?
Suppose the astronauts are immortal. We might decide that in that case, coasting there and back (with comparatively small intervals of acceleration and deceleration) for 900 years would represent a trivial fraction of an endlessly protracted life and would offer no problem.
However, even if the astronauts are immortal, we presume they would have to eat, drink, breathe, and eliminate wastes. That means there would have to be a complex life-support system that would work without fail for nearly 1,000 years. We might imagine it being done, but surely it would be expensive.
Then, too, the astronauts would have to have something to occupy their minds. Comparatively close quarters with no chance for a change in company for nearly 1,000 years could be very difficult to tolerate. It might not be too cynical to suppose that murder and suicide would empty the ship long before the trip is over, for it is much easier to imagine a victory over death than a victory over boredom.
And, of course, we have no real reason to think—at