Stephen Hawking isn’t afraid to say what he thinks! In articles in the Times and Daily Mail, he suggests that intelligent life beyond the Earth is practically a formality. Not only that, but they’re probably not the best company. They are most likely to roam the Galaxy in massive spaceships, travelling from planet to planet, consuming resources (cf Independence Day). Is he right?
Stephen has taken the correct logical steps in coming to his conclusion. He starts by estimating the total number of planets in the Universe. Our Galaxy has a hundred billion stars; there are hundreds of billions of galaxies; even if each star only has one planet (which we know is almost certainly an under-estimate, from our understanding of planets), then there are ten billion trillion planets out there. The chances of only the Earth hosting life is incredibly small! This is hardly an iron-clad proof of their existence, but it makes a strong argument.
It only takes a little extension of this chain of thought to presume that some planets have intelligent life. If we are the only intelligent life in the Universe, then we violate a long-held scientific principle, known as the Copernican Principle. When Copernicus unseated us from the centre of the Universe by proposing the Earth went around the Sun, we began to realise that we were probably nothing special – in fact, scientists now begin by assuming that we are not unique in any way. That would all go down the pan if we discovered we were alone. Again, hardly foolproof (the Principle now exists more for spiritual than scientific reasons), but convincing in its own way.
Then Hawking really pushes the envelope. If we’re not unique, then most civilisations will have similar features to ours. They may even have the same political systems as we do – possibly even the same economic systems. They may be as driven by currency and resources as we are. If they are unable to regulate their consumption of resources, then their home planet will be drained. If survival is possible, they will probably have to move on – hence the spaceships, and the nomadic existence Hawking postulates. He makes these assumptions based on our history (especially Western civilisation’s embarrassing track record with conquest and exploration). That doesn’t mean they aren’t very big assumptions, based again on our Copernican Principle which can be violated.
If Hawking is right, then SETI really should stop, and we should be fortifying ourselves against invasion. This article by Dan Drezner puts an interesting spin on the security implications, again based on our own geopolitical machinations.
To be honest, I’m not really sure if this is what Stephen actually believes, or if he’s playing advocate here. That’s not particularly important, because the argument remains valid regardless. There’s not enough evidence to prove/disprove it yet, and it’s a genuine concern (after all, can’t you see human beings doing something similar in our future? You don’t need to see Avatar to understand the concept).
I’ve explained Hawking’s argument here – if you’re listening to Radio 5 Live (in the UK) today at 1.30 pm, then you’ll (hopefully, TBC) get the chance to hear what I think there.
Update: I was on Radio 5 Live at 12.20pm today (26/04/10) with Marek Kukula of Greenwich Observatory. Unfortunately iPlayer can’t put up audio of it for rights restrictions – hope you managed to listen in!