Question: Why do you believe we’re unlikely to find aliens closer than 1,000 light years away?
Paul Davies: It’s almost impossible to guess the number of communicating civilizations that are out there because as I’ve described the fraction of planets on which life emerges is not known. It could be anything from zero to one and so the uncertainties in that number really mean that it is a fool’s errand trying to estimate the further consequences of there being intelligent life and communicating civilizations, but you can of course go to an optimist and I guess there is no one more optimistic than Frank Drake himself and say, “How many do you think are out there in the galaxy?” And he reckons 10,000. That is his currently best guess what there is. So you can then ask well then how close is the nearest one likely to be to us and it’s going to be a few hundred light years, so let’s take 1,000 light years as the round figure. Now the problem here is that a civilization that is 1,000 light years away doesn’t know we exist. They don’t know that we have radio telescopes here on Earth because they see Earth as it was 1,000 years ago. Nothing can travel faster than light, so however good their instruments they can’t see in affect the future. They can only see Earth as it was 1,000 years ago, so there is no particular reason they should be sending us messages at this time and if you put yourself in the position of a SETI enthusiast on this hypothetical distant planet going to a granting agency and saying, “There is a really interesting planet over there, Earth, that we’ve studied it very carefully and we can see they’ve built huge structures like the pyramids and this great wall in China and we think some millennium soon they may have radio telescopes, could we have some money to start broadcasting?” And I can tell you what the grant agency would say. It would say, “That is a great idea. You come back in a few thousand years when, you know, they are actually on the air and we’ll give you the money to send them some messages.” And that is the situation we’re in, so I think it’s a bit of a fool’s errand to be looking for deliberately beamed messages. We might stumble across a message intended for somebody else or it may be that we see a beacon or something like that. These things are long shots and so my feeling is, well, we should carry on trying because who knows what is out there, but meanwhile we should be finding other ways of looking for ET.
Question: Why would “older, wealthier” alien civilizations be found closer to the center of the galaxy?
Paul Davies: The history of the galaxy is pretty well understood and the stars started forming towards the center first. The age of the galaxy is a little over 13 billion years. Earth is only 4 ½ billion years. The very earliest stars didn’t have the sort of heavier elements like carbon and oxygen and so on that are necessary for life, but after a short period of time these elements were manufactured when the first stars made them and then blew up and spread them around and so in the early days the main action was towards the center of the galaxy where the superstars had exploded, and then right out on the edges of the galaxy there was a paucity of these heavy elements and so every time what has happened is that this Goldilocks zone which could support life has expanded out and we’re some way in the middle suburbs of our Milky Way galaxy. The Goldilocks zone is now moved out to here and but that is because of course we’ve… we’re Earth and the solar system is only about half or a third as old as the galaxy, so if we’re thinking about old civilizations, those that formed a long time ago and there were stars and planets around long before Earth even existed, then these are going to be towards the center of the galaxy. That is the place to look if you think there are ancient civilizations that have made beacons or some other way of attracting our attention.
Recorded April 15, 2010
Interviewed by Austin Allen