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We have long assumed that extraterrestrials would be similar to us, but there is every reason to believe that they represent a form of unfathomable artificial intelligence

It took more than four billion years for intelligent life to evolve naturally on Earth through the process of natural selection, but our planet has billions of years of life ahead. During this time, intelligence could evolve in entirely new directions.

COMMENTARY AND ANALYSIS Lord Martin Rees is the Royal Astronomer of the United Kingdom and works at the University of Cambridge. His latest books, co-authored with Donald Goldsmith, include "If We Are to Survive" and "The End of Astronauts."

We, as human beings, may be approaching the end of Darwinian evolution – we no longer need to become the most adapted for survival. However, the technological evolution of artificial intelligence is just beginning. It may take another century or two before inorganic intelligence catches up to or surpasses humans. If this happens, our species would only represent a brief interlude in Earth's history before machines take over.

This raises a profound question about the broader cosmos: are extraterrestrials more likely to be made of flesh and blood like us, or something more artificial? And if they were more machine-like, what would they be like, and how could we detect them?

Not Like Us

Many assume that humans represent the pinnacle of intelligence, but it's possible that our species is just a stage on the way to more artificial intelligence. This could explain why space seems so empty of life like ours. If the inevitable transition in the universe is toward inorganic intelligence, our telescopes are unlikely to capture human intelligence during the brief period when it existed in this form. Instead, it's more likely that extraterrestrials would be distant electronic descendants of long-extinct organic beings.

The prospect of inorganic extraterrestrial intelligence opens up some remarkable possibilities. If such beings existed out there, they would likely operate and think very differently from us. They might not want to be detected. Indeed, their intentions could be impossible to fathom. To quote Charles Darwin, "A dog might as well speculate on the mind of Newton." However, we can make some conjectures.

Firstly, inorganic intelligence may find little use for planets or atmospheres in which they originated. Interstellar travel – or even intergalactic travel – may hold no terror for entities that are effectively immortal.

Indeed, they may prefer to dwell in the vacuum of space because that's where they can most readily create vast, gossamer-thin structures. If you want to build a vast, intricate, spiderweb-like structure for energy harvesting, for instance, space is easier than a planetary surface.

If they had silicon-based brains, they might realize that the energy required to process 'bits' is less at lower temperatures. Thus, they may expend less energy in colder regions far from planetary systems. They might even prefer to go dormant for billions of years, waiting until the cosmic microwave background radiation – the remnants of the Big Bang – cools even further as the universe continues to expand.

In summary, the future of intelligent life in the cosmos could be profoundly different from our own. It's a future where machines, rather than organisms, may be the dominant form of intelligence.