If you have got your astronomical education from watching science fiction movies, you probably think that travel between stars is a pretty fast experience. You just jump into your interstellar spaceship like Han Solo's Millennium Falcon, turn on the warp drive, and whoosh, you jump through hyperspace arriving at a distant planet. Even more recent movies (like the movie Interstellar) depict the same type of rapid interstellar travel.
But this is fiction, not science fact. There is no known evidence for anything like hyperspace that can be used to enable rapid interstellar travel. Nor is there solid evidence that you can instantaneously transport anything by using a space warp. Scientists have not been able to transport even a grain of sand from one place to another using a space warp.
It seems, regrettably, that interstellar travel will be a very slow affair. According to Einstein's special theory of relativity, the speed of light is the fastest speed that can ever be reached. If you could somehow build a spaceship capable of traveling at the speed of light, it would take you about five years to get to the nearest star. But there are engineering reasons for thinking that a spaceship will never be able to accelerate to more than a small fraction of the speed of light. This means that it would take many years to get from one star to another.
I wonder: what if Hollywood were to make a realistic movie about interstellar travel – a movie that was as realistic as possible about the difficulties of interstellar travel, and also the low chance of finding life in some particular target of an interstellar mission? Let's imagine what such a movie might be like.
You might think that such a movie might involve a plot in which the starship crew was put into suspended animation, so that astronauts slept through the interstellar voyage of many years. But that wouldn't be particularly realistic, since the prospects of people being put into artificial hibernation for many years are pretty dim.
One realistic plot for an interstellar voyage would involve astronauts who left Earth on an interstellar voyage while they were young men in their twenties. By the time the starship got to the distant star, the astronauts would be so old that they would not have energy to do much exploring. That might work as a comedy.
Another realistic possibility would be to depict a multi-generation starship. This is the most plausible scenario for interstellar travel. The ship would be large enough for someone to live his entire life on the ship. The original astronauts would have children while the ship was traveling between the stars. By the time the ship finally arrived, the starship would be manned not by the original astronauts, but by the children of such astronauts – or perhaps the grandchildren or the great-grandchildren of the original astronauts.
Clearly this movie would need an ensemble cast, and it would need to be one of those movies that spans many years. But what would happen when the spaceship reached the distant planet revolving around another star? Would the astronauts find a lush world teeming with life?
The current thought exercise is to imagine a movie about interstellar travel that is as “realistic as possible.” It seems that such a movie should therefore not find the astronauts discovering life on the distant planet the ship finally reached. The origin of life on our planet still seems like quite the little miracle. We have no idea of how self-replicating molecules could have formed from mere chemicals billions of years ago. We have no idea of how the genetic code that life depends on could have arisen through mere chance. The genetic code is what programmers call a lookup table, and we have no known cases of any lookup tables in nature that ever arose through chance processes.
It seems, therefore, that if we are making our interstellar travel movie as realistic as possible, our astronauts should arrive at the planet revolving around a distant star, and find nothing but a dead rock planet. This might make a nice tragic ending, but it wouldn't have the dramatic oomph that makes a good tragic ending. Perhaps our astronauts could perish on the lifeless planet in a kind of “die in the desolate wilderness” ending resembling the ending of the opera Manon Lescaut.
A more hopeful ending might involve terraforming, an engineering effort to make a rocky, lifeless planet more like Earth. The astronauts on the starship could launch an engineering effort to bring earthly life to the lifeless planet. They might have to stay on their multi-generation starship for many years, orbiting the planet, while lifeforms slowly spread around the planet. Finally landing craft from the starship could land on a planet that had grassy fields. This event might occur hundreds of years after the multi-generation starship had arrived in orbit around the distant planet.
So the movie might depict a scenario like this:
Generation 1: Leaves Earth in the multi-generation starship, and dies aboard the starship.
Generations 2, 3, 4, and 5: Lives their entire lives in interstellar space, never seeing a planet.
Generation 6: Lives to see the starship orbit the lifeless planet revolving around another star.
Generations 6, 7, and 8: Lives aboard the starship, in orbit around the planet, waiting for the terraforming process to finish.
Generation 9: Finally gets to land on the planet, which by now has life and grassy fields.
Although highly realistic, such a movie would probably make much less money than absurdly unrealistic sci-fi epics in which traveling to another star is as easy as riding from one subway stop to another.