Aliens may resemble little green men or tentacle monsters in sci-fi films, but the Astronomer Royal claims they may be far less organic.

British astrophysicist and cosmologist, Sir Martin Rees, believes if we manage to detect aliens, it will not be by stumbling across organic life, but from picking up a signal made by machines.

It's likely these machines will have evolved from organic alien beings, and that humans will also make the transition from biological to mechanical in the future.

British astrophysicist and cosmologist, Sir Martin Rees, believes if we manage to detect aliens, it will not be by stumbling across organic life, but from picking up a signal made by machines (illustrated)

Writing for Nautilus, Sir Martin said that while the way we think has led to all culture and science on Earth, it will be a brief precursor to more powerful machine ‘brains’.

He thinks that life away from Earth has probably already gone through this transition from organic to machine.

On a planet orbiting a star far older than the sun, life ‘may have evolved much of the way toward a dominant machine intelligence,’ he writes.

Sir Martin believes it could be one or two more centuries before humans are overtaken by machine intelligence, which will then evolve over billions of years, either with us, or replacing us.

Writing for Nautilus, Sir Martin (pictured) said that while the way we think has led to all culture and science on Earth, it will be a brief precursor to more powerful machine ‘brains’

‘This suggests that if we were to detect ET, it would be far more likely to be inorganic: We would be most unlikely to “catch” alien intelligence in the brief sliver of time when it was still in organic form,’ he writes.

Despite this, the astronomer said Seti searches are worthwhile, because the stakes are so high.

Sir Martin believes it could be one or two more centuries before humans are overtaken by machine intelligence. A 'cyborg' is illustrated

Seti seeks our electromagnetic transmissions thought to be made artificially, but even if it did hit the jackpot and detect a possible message sent by aliens, Sir Martin says it is unlikely we would be able to decode it.

He thinks such a signal would probably be a byproduct or malfunction of a complex machine far beyond our understanding that could trace its lineage back to organic alien beings, which may still exist on a planet, or have died out.

He also points out that even if intelligence is widespread across the cosmos, we may only ever recognise a fraction of it because ‘brains’ may take a form unrecognisable to humans.

For example, instead of being an alien civilisation, ET may be a single integrated intelligence.

He mused that the galaxy may already teem with advanced life and that our descendants could ‘plug in’ to a galactic community.

However, he says there’s a chance Earth’s biosphere may be unique and searches will fail, meaning our planet could be the most important place in the cosmos.

‘We would then be of especially great cosmic significance, for being the transient precursor to the deeper cogitations of another culture - one dominated by machines, extending deep into the future and spreading far beyond Earth.’