Atomica
Space and infinityUnsolved

The Fermi paradox

The galaxy is old and huge. So where is everybody?

Enrico Fermi at lunch in Los Alamos, 1950

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The story

Lunch in the desert

In the summer of 1950, at a laboratory in the New Mexico desert, a group of physicists were eating lunch and joking about a newspaper cartoon blaming aliens for missing rubbish bins. Suddenly the great Italian physicist Enrico Fermi looked up and asked, "But where is everybody?"

Everyone knew what he meant. Our galaxy has hundreds of billions of stars, many older than the Sun. Many of them have planets. Even if only a tiny fraction produced a civilisation that could travel between stars, it would have had millions of years' head start on us.

And travelling across the galaxy, even slowly, takes only a few million years at most, a blink compared with the galaxy's age of about 13 billion years. So by now, one of them should have spread everywhere. There should be signals, probes, visitors.

Instead, as far as we can tell, there is silence.

The puzzle

The numbers suggest the galaxy should be full of civilisations, but we see no sign of any.

See it for yourself

First civilisationSo where is everybody?Enrico Fermi, 1950Simulated time: 0 million years
Time to cross the galaxy10 million yearsAge of the galaxyabout 13,000 million yearsIt could be crossedabout 1,300 timesStars reached0%

What's really going on

Scientists have suggested many answers. Perhaps life is far rarer than we think, because the steps from chemistry to cells to intelligence are each very unlikely. Perhaps civilisations tend to destroy themselves, or never leave home. Perhaps they exist but are too far away, too quiet, or use signals we don't recognise. Perhaps we haven't searched for long enough: serious radio searches began only in 1960.

In 1961 Frank Drake wrote an equation that multiplies all these unknowns together. The trouble is that almost every term is a guess, so the answer could be millions of civilisations or just one: us.

Unsolved. This is one of the biggest open questions in science. Telescopes such as the James Webb are now studying the atmospheres of planets round other stars for signs of life.

Think about it

If you were an alien looking at Earth, what signs of our civilisation could you detect from 100 light-years away?

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