Wednesday, December 15, 2004

Fermi’s paradox: Is there anybody out there?

A big place
It would seem logical that we are not the only form of intelligent life in the Universe.

After all, the Universe is a big place. In our galaxy alone there are some estimated 400 billion stars like our own Sun. And there are billions and billions of galaxies. And scientists think that many, perhaps most, stars have planets orbiting them. Which means billions and trillions of planets.

So given the maths, it seems improbable that there could not have been some, in fact, many thousands of planets with conditions suitable for the emergence of life.

Not only that, but there’s also been plenty of time for highly intelligent life to evolve many many times over. Homo sapiens only emerged about 200 thousand years ago, and already we’ve sent men into space. Our galaxy meanwhile, is over 10 billion years old.

So the chances are that there are many intelligent forms of life out there, and that many of them have had an enormous headstart on us.

Fermi’s paradox

But there’s a problem with this. A chap called Enrico Fermi worked out that it wouldn’t take very long (5 to 50 million years, which, relatively speaking, is a piddling amount of time) for a civilisation with modest rocket technology to colonise our entire galaxy. Or at least, to contact every planet in the galaxy.

So the question is: where are they?

That’s Fermi’s paradox: if, as seems mathematically probable, there are many lifeforms out there, why haven’t we observed them?

It’s a bit like the objection to the possibility of time travel. While Einstein and Hawking bend our brains with talk of wormholes and the space-time continuum, a very simple question remains unanswered: “if time travel is possible, then where are all the visitors from the future?”

Possible answers
There have been many attempts to answer Fermi’s paradox. These include:

1) The premises of the paradox are wrong: in fact, the conditions for the emergence of life are extremely rare and unlikely, so the aliens don’t exist
2) The aliens are here but hide themselves from us
3) The aliens were here but we don’t understand their signals or we missed them
4) The universe is so big that we just haven’t come into contact with them yet
5) They do exist but there’s no motivation for contacting us or colonising the galaxy

You can find out more about this on the excellent Wikipedia site.

5 comments:

martpol said...

Very interesting - have never heard of this paradox before. One of the answers to it - the one about the conditions for life being rare - is interesting, but I wonder (with a totally unscientific hat on) whether it's a bit naive. I've often thought that if there is life/intelligence 'out there', why should it even be composed of the same elements as life on this planet, or follow the same rules? Though I'm sure that scientists have somehow provde that all the laws they've come up with are truly universal or something.

Brit said...

Martin -

For the purposes of the paradox, the figures are such that there's more than enough chances for carbon-based life similar to our own to emerge, let alone other possibilities, as you point out.

Whether life in the Universe could conceivably be significantly different to carbon-based life like that on Earth, is something that's being debated by scientists.

Some argue that the Universe is arranged in such a way that evolution is naturally going to favour development in certain directions.

For example, it used to be thought that if you could wind back time and start evolution all over again, you'd end up with flora and fauna that looked utterly unlike that which exists now. That's because evolution's direction is arbitrary, and depends on tiny chance instances (remember that Ray Bradbury short story about the chap who goes back in time, steps on a butterfly and finds that the world changes completely?). So the way life on Earth looks now is only one of an infinite number of wholly different possibilities.

However, biologists have recently begun to modify that view, because of what's called 'convergent evolution'. That's where you get the same thing evolving independently in unrelated species. eg. flying has evolved separately in birds, bats and insects. The light-sensitive eye has evolved independently many times. Others are the use of haemoglobin, sex, carnivorousness, etc.

That doesn't mean that evolution is directed - it's random and purposeless. But it's random within some fairly strong environmental restrictions.

So, applying this logic to the rest of the Universe, many scientists think that if there is life out there, and other planets operate on the same basic material and scientific principles, it might well look pretty similar to life on earth. eg. it will be carbon-based, there'll be things that fly, things that eat other things, things that react to light (have eyes and can see), things that sexually reproduce etc

All speculation mind, but informed speculation.

Evolution is one of my pet subjects, so I'll be putting quite a lot of stuff about it on here in the future.

Shangamuzo said...

The universe is rather large. Even if we could travel near the speed of light, which we can't, it would take a very, very, very long time to cross even one galaxy, never mind passing from one galaxy to another. How do you build a self-sustaining spaceship capable of crossing the universe over a period of hundreds of millions of years ? How could you ensure the necessary life support for the thousands of generations of humans needed ? These are matters which any ambitious life forms from elsewhere in the universe would also have to solve.

Really, I think we are alone. Why do so many people find that thought frightening ?

Best wishes
Shangamuzo

Brit said...

Shangamuzo -

Thanks for your comment.

I don’t think your conclusion that we are probably alone follows from your preamble.

The argument you put forward is like the number (4) in the main post. It would normally be used by someone who believes that there probably is intelligent life out there, and the size of the universe is the reason why we haven’t heard from them, thus resolving the paradox.

Several scientific writers have tried to estimate how long it would take, not just to cross the galaxy, but to colonise it. They reckon somewhere between 5 and 50 million years. Which is a very long time from a human perspective, but vanishingly insignificant from a geological perspective, never mind a galactic one.

As to being frightened, I suppose this depends on which side of the religious/human-centric divide you fall. If you think that the world and the universe were created specifically for humans by God, then you’ll find the prospect of alien life frightening.

If you think the opposite, and that there’s nothing particularly special about humans other than that we happen to be here now, then you might find the idea of being the only intelligent life in such an enormous emptiness a rather disconcerting burden of responsibility.

David said...

"... the Universe is arranged in such a way ..."

Oh, that clever, clever Universe.