20 light years is still 20,000 years of traveling in space even after taking into account that technology and speed will improve over time by about 90%-100%.
Who and what government would go on a suicidal safari to another planet which "MIGHT" support life which will take trillions and trillions of dollars, and 20,000 years to reach? First it may not be possible to have children in space even with artificial gravity. Second, the radiation would kill the child before he can even speak his first word.
Even if through a magical genie we solved these problems and avoided cancer... Would you feel comfortable living on a space ship for the rest of your life? Bringing children into this world knowing they'll never have a normal life like back on earth. Sacrificing not only your life but the lives of thousands of your 1,000+ generation grandchildren so you can go explore a planet that you think "might" have life.
Just remember that "normal life like back on earth" sucks balls for most of the people on earth. If there was a ship on the pad, there would be a line around the block that made "American Idol" auditions look like a small, intimate gathering.
Assuming we end-up with reasonably efficient fusion power and an even mildly space based economy we are eventually going to start mining the ort cloud. Which set's up a natural path to vary slowly expand into the stars.
Basically, if it's profitable you get exponential growth till it's not and even slow exponential growth ends up with ridiculous growth numbers fairly quickly on a geological timescale let alone a galactic one.
Who and what government would go on a suicidal safari to another planet which "MIGHT" support life which will take trillions and trillions of dollars, and 20,000 years to reach? First it may not be possible to have children in space even with artificial gravity. Second, the radiation would kill the child before he can even speak his first word.
Even if through a magical genie we solved these problems and avoided cancer... Would you feel comfortable living on a space ship for the rest of your life? Bringing children into this world knowing they'll never have a normal life like back on earth. Sacrificing not only your life but the lives of thousands of your 1,000+ generation grandchildren so you can go explore a planet that you think "might" have life.