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Artists pose in a laser projection entitled 'Speed of Light' at the Bargehouse on March 30, 2010 in London, England.
First you get excited. Then you get depressed.
The big news in planet hunting has been the Kepler space mission's discovery of more than 1,000 new planets. These planets were found based on searching only a small portion of the sky. When the scientists extrapolate their findings to the galaxy as whole the estimate the number of planets in our cosmic neighbor hood (i.e. the Milky Way Galaxy) to be over 50 billion. 50,000,000,000 planets! The galaxy is literally teaming with worlds.
It's a stunning, mind-boggling result. The shear number of worlds seems to validate countless science fiction visions of starships darting between planetary systems in a trans-galactic multi-world culture of intrigue and adventure. Or does it? Sadly, if we keep our heads on straight and do not extrapolate to a future scientific miracle it does not. While the planets might be out there our ability to build a star-spanning civilization appears so limited that, perhaps, the idea is all but impossible.
Let me explain.
If I want to travel to Buffalo from my home in Rochester I get in my car and travel at 60 miles an hour and get there in about an hour. Then I turn around and drive back which takes another hour. During my trip I have aged 2 hours. When I get back I find, of course, that everyone else has aged 2 hours. But what if I returned from my trip to find that it was the year 2256 and everyone I had ever known had long since past away? That is pretty much the situation we face when dealing with interstellar travel and it's all due to an effect from Einstein's theory of relativity called time dilation.
Relativity tells us that clocks run at different rates for different "observers" depending on how fast they move relative to each other. Nothing can travel faster than the speed of light (about 1 billion km/h) The closer you get to the speed of the light the more the clocks (and all rhythmic biological process associated with time's passage and aging) will run at different rates. This is the basis of the famous twin paradox where one twin takes a roundtrip space journey at near light speed and returns to find her sister has aged much more than she. There is really no paradox, it's just weird. Here is what the light speed barrier and time dilation means for an interstellar civilization.
There are about 1400 star systems within 50 light years of us. That is certainly a large enough number to imagine a thriving interstellar culture. Let's imagine we wanted to visit one of these stars at say 30 light-years from us. Since the fastest we can travel is the speed of light, from the viewpoint of observers on Earth the round trip will take at least 60 years. That is already so long that it is difficult to see how you could maintain any kind of meaningful contact. But the problem gets worse when you account for the fact that a traveler on starship traveling at 99.9% of the speed of light would complete the roundtrip not in 60 years of their own time but only 2.7 years. They would return after just about 3 years to find themselves completely out of joint with the world they left. Parents would be long dead. Friends and lovers, if they were still alive, would be aged and infirm. The problem gets worse the larger the distances we expect to cover with our imaginary interstellar society. 50 light years is only about 0.1% of the Milky Way galaxy's radius. There is a lot of space out there. Thus those who travel and those who stay behind will be living an entirely different existence.
So unless we discover a Warp Drive, or somehow learn to marshal Wormholes, this is what we will be stuck with. I know its tempting to say "Of course we will figure out new science like the Warp Drive" but it might be more realistic to say these are laws of physics we are given and understand their long term consequences for human evolution.
It is still possible to imagine some kind of interstellar culture emerging within the restrictions of relativity. Perhaps those who travel will form their own emissary culture, stitching the stars together though never living long amongst the planet bound. There have been a few science fiction authors have explored this territory. The point for now however is it will not look anything like Star Trek or Star Wars.
The stars may be our home someday but, in a real sense, we may never be able to live amongst them together.