Star Travel is an immensely fascinating topic to me and I have spent decades marveling about its possibilities, opportunities, effects and of course its viabilities. I have read dozens of books about star travel, mostly science fiction novels, but also some scientific books that seriously analyze star travel and what it might entail.
First I need to define what I mean by star travel. It’s not flying, of course, and it’s not space travel as we know it today. Besides the few Apollo moon missions between 1969 and 1974, space travel for humanity has been nothing but low earth orbit jumps. We haven’t really left the gravitational well of our planet. We are now contemplating interplanetary trips, like missions to Mars. Those are still decades away from reality given today’s technology and budgetary environment. Part of missions to Mars is a return to Luna first.
Star travel means leaving the solar system and traveling to another star. The closest stars to Earth are Alpha Centauri and Proxima Centauri, both about four light-years away. If we could travel at the speed of light, it would take four years to get to Alpha Centauri, and that is ignoring the time it would take to accelerate to that speed (zero to sixty in four seconds…) and then decelerating on the other end. Then it would take another four years to come back, again ignoring acceleration and deceleration. So the round-trip would take eight years, in our grossly oversimplified calculation.
Of course, we do not have the capability to travel anywhere near the speed of light. But it’s fascinating to speculate what a world with star travel would be like. The only viable and economic reason to have starships at all would be trade.
Let’s assume in some distant future there are about 30 planets inhabited by humans in our galactic neighborhood inside a sphere of a radius of 50 light years around Earth. With the immense costs and energy requirements of a starship, humanity could perhaps afford to build and maintain 100 of those ships at any given time. As a result, 100 ships would be busy traveling between planets that are five to 50 light years apart. If you lived on one of those planets, a starship would arrive at best once every few decades, in some cases much longer, like once every century. You could live an entire lifetime and never experience a visit of a starship. Such a visit could also not be scheduled, since radio waves travel not much faster than the ships themselves. At best, an announcement of an arrival would arrive shortly before the ship itself.
Obviously, a starship visit on any planet would be a major event. Work would be suspended. Celebrations would take place. Holidays would be created. People would trade goods and exchange information. The starfarers would go on the talk show circuit and share news from other planets.
Now we get to the complicated part. Einstein discovered that as an object approaches the speed of light, its mass approaches infinity and time elapsed approaches zero. In the simplest form this means that for the travelers on a starship, time slows down drastically the faster they travel.
Let’s say you are 40 years old on Earth and your son is 20. Your son decided to take a job on a starship leaving for a planet 20 light years away. He will spend a year at the destination, and then come back. Again ignoring acceleration and deceleration, the trip of your son would take 20 years outbound, one year on site visiting, and 20 years inbound, for a total of 41 years. You would be 81 years old when your son came home from this one trip.
However, from your son’s perspective, the time spent is entirely different. His trip out, from his time-dilated point of view, would take perhaps a month subjective time on the ship, while the 20 years run by in the outside world. Then the year at the destination would also take a year. Then the return trip would take another month. When your son arrived home he would be about one year and two months older, or about 21 years old. You’d be 81.
It gets worse. If he didn’t come right back, and visited four or five other planets in a big round-trip, he might be en route for 200 years. When he came home, you would be long dead and gone and eight or ten more generations would have lived and died. If he left in the year 2012, he’d come back in the year 2200 or so, and he would still be in his twenties. It would be like leaving in the times of Thomas Jefferson’s presidency and coming back to George W. Bush.
Starfarers would never be able to enter into relationships with anyone not traveling with them on their own ships. They could not come home to their families or lovers, since they’d always be long gone. Even a relationship of two starfarers on two different ships could never work. The ships would not travel the exact same distances, so one or the other of the two would age faster and fall behind the other. That would be if the two different ships would ever be at the same place at the same time again, a highly unlikely scenario by itself. So if a starfarer ever parts with a lover, it’s parting forever. Their destinies can never line up again.
Traveling amongst the stars may never be possible for humans or aliens. We may be forever locked in our small worlds, trapped not by bars or prisons, but by immense distances that are insurmountable with lifetimes measured in decades. Even entire civilizations may be rising and falling throughout our galaxy and universe, like fireflies, sparkling for a few hundred or even thousand years, the equivalent of a few eye blinks on the cosmic timescale, before winking out, never to even know about each other’s presence.
Yet, if there were a starship, and if they were hiring, I’d be on in a heartbeat.