Last week, a group of scientists announced that they had identified more than 1,000 new "exo-planets" — planets orbiting stars other than our sun. The discovery of more than 2,000 such planets over the past few years has excited a lot of people who see these planets as harboring intelligent life or a livable environment for earthly humans to colonize after Earth has been depleted.
It appears that solar systems like our own are the norm for all of the billions of stars throughout our Milky Way galaxy and, presumably, among all the trillions of start in other galaxies. With so many planets orbiting so many stars, surely there are thousands, if not millions of exo-planets with life like our own planet's.
That's the thinking behind the Search for Extra-Terrestrial Intelligence (SETI). Both learned scientists and somewhat knowledgeable laymen dream of contacting intelligent beings on other worlds and even visiting and studying those other creatures populating our universe.
This thinking comes with a major "BUT ..." BUT ... any forms of life out there are so far away that we can never expect to visit them and probably can never hold a conversation with them. Our galaxy, the Milky Way, is estimated to be 100,000 to 120,000 light years across. A light year (the distance light travels in one year) is 6 trillion miles. The light we see in the night sky is light that is tens of years, even hundreds of years old. The light we cannot see (because it is too faint) is even older — many thousands of years old.
And that presents a problem for our goal of conversing with extra-terrestrial intelligent beings. Radio waves travel at the speed of light. If we were successful at discovering radio signals from our nearest neighbors outside our solar system, the radio message would be 4 to 10 years old upon arrival on Earth. Our SETI reply would take another 4 to 10 years to reach the other world. If no intelligent life was found around the first dozen (or hundred) closest stars, the search would continue on to worlds that are within dozens or hundreds of light years away and then to those thousands of light years away. Communication would be, at best, an inter-generational effort.
As for direct contact — traveling to distant worlds — just visiting planets within our solar system requires interplanetary travel lasting years. No one knows whether humans can endure such a trip either physically or psychologically. Would you take on a mission to Jupiter's moons, for example, knowing that you (and your family and friends) would have aged 20 years or more on the trip, even if you dodged the solar radiation and small asteroids that could destroy your space ship?
Travel to planets outside our solar system would be totally unfeasible, despite the dreams of "Star Trek" and other science fiction. "Star Trek" imagines vehicles that travel faster than the speed of light. Einstein theorized that nothing can travel faster than light, and no scientist has found a way around Einstein's barrier. Inter-galactic travel cannot be done.
So why are we so intent on finding extra-terrestrial intelligence? We're a curious species and want to know. But any discovery is likely to be a disappointment, perhaps a signal originated from a distant world whose inhabitants have gone extinct or whose world has been swallowed by a dying star.