Originally Posted by Anon La Ply
Guys, it's one thing for aliens to be likely to exist due to weight of numbers, another for them to come to Earth. How is an alien going to come here across a hundred thousand light years?
Not only travel time but they have to be alive in our era. It's taken 13.7 billion years for us humans to turn up. Will we still be around in 10,000 years time (which is almost nothing on a universal time scale)? The aliens could miss us by 1 minute or by 5 billion years.
As Hawking suggests, if aliens are advanced enough to reach us, why do they just keep whizzing by (stopping off for the odd probe or two) and going back home? Why not take over the Earth, like any other colonising nation? If they have the technology to reach here, I imagine their weapons would be scary. Our only hope would be if they were wise and peaceful guru-like aliens, in which case we could nab 'em and dissect them ;-)
You raise a good point. It's just about distance, but also about time
. Time is just as vast as distance and is even more of a barrier. It's very possible that sentient life develops only rarely, separated by hundreds of millions of years. Many planets with life could never develop sentient life - the entire drama and beauty of ecosystems, life and natural creation on a planet, and no sentient life there to ever appreciate it for 12 billion years.
My son did a science experiment. If every second was a year, then the Earth is about 150 years old (American Civil War). Dinosaurs died out about two years ago. Homo sapiens evolved a couple of days ago and our oldest cities are about an hour and a half old. And we're about in the middle of the lifespan of our universe, 20 or so billion years. Entire sentient civilizations may have come and gone already, and have yet to come into existence.