The known universe contains more than one trillion billion stars and up to 40 billion planets – so it’s a fair bet one of these is home to intelligent lifeforms.
But despite the high likelihood of aliens existing somewhere way out in deep space, humanity has been unable to find them.
The search for extraterrestrial intelligence (SETI) is one of the most glamorous areas of astronomy even though it’s so far failed to answer the biggest question in the cosmos: are we alone?
To help solve this dilemma, stargazers are now searching for traces of alien technology in an emerging, yet controversial, area of research called artefact SETI.
Supporters of the drive to find extraterrestrial artefacts (objects made by aliens) are already peering deep into space in a bid to discover cities, satellite networks or gigantic ‘megastructures’.
Some even think our own solar system could contain probes sent by an advanced civilisation, wreckage from old spaceships or even evidence of ancient settlements on planets like Mars or Venus.
Yet other experts slammed this headline-grabbing, easily sensationalised discipline as ‘entertainment science’ and questioned whether there’s any point looking for such tiny needles in the mega-haystack of our breathtakingly gigantic universe.
Professor Avi Loeb, chair of Harvard University Astronomy Department, is among the world’s most respected astrophysicists. He stunned the scientific community last year by refusing to rule out the possibility that a strange cigar-shaped object which sped through our solar system may have been alien in origin.
Astronomers named the space rock ‘Oumuamua – Hawaiian for ‘scout’ – and said it was an interstellar visitor which formed in another star system before travelling here through the void of deep space.
Loeb did not simply dismiss the idea that it was built by an extraterrestrial civilisation and suggested it could have been a ‘lightsail’ craft, calling on his fellow scientists to keep an open mind about its origins.
We spoke to Professor Loeb to ask what sort of alien technology astronomers are searching for right now.
‘Examples include artificial light, industrial pollution or reflection of starlight from photovoltaic cells [solar panels] on the surfaces of planets around other stars, mega-structures or fleets of satellites,’ he told Metro.
‘Space archaeology with our best telescopes might reveal technological equipment floating in space, similar to the two Voyager probes that we launched and are now leaving the Solar System.
‘But we should keep in mind that the travel time is very long between stars; it would take the Voyagers about a hundred thousand years to reach the nearest stars to the Sun.
‘The equipment could, therefore, be defunct if it belongs to a civilization that died by now.’
He said the artefacts we’re most likely to find include the ‘defunct debris of highly sophisticated technologies’, which could be the wreckage of alien spaceships.
‘Perhaps our best way to put our hands on them is to find objects that collide with the Earth and survive as meteorites,’ Professor Loeb added.
Is the truth out there?
When astronomers peer out into deep space in search of alien technology, they are often looking for big objects such as a Dyson Sphere – a theoretical, Death Star-style space station built around a star to harvest its energy.
A civilisation capable of building a Dyson Sphere would have to be highly advanced because it would take decades or even centuries to build such a structure.
Jason T. Wright, associate professor of astronomy and astrophysics at Penn State University, became world famous after speculating that the mysterious behaviour of a distant sun called Tabby’s Star was caused by a ‘megastructure’ moving in front of it – although this hypothesis was later dismissed.
He told us that artefact SETI suffers from a poor public perception driven by fake or overegged news stories which have ‘tarnished this idea to the point where most scientists won’t touch it and many tabloids can’t resist sensationalizing it’.
‘The idea that we should look scientifically for evidence of alien technology in the solar system goes back to Ronald Bracewell in 1960, although of course people have speculated about Martians and such for centuries,’ he said.
‘Just 100 years ago it was totally reasonable for scientists to discuss the possibility of technological life on Mars. In the 1960s the Mariner probes showed that the Martian surface has no obvious signs of large technology, and so people assumed it (and the rest of the Solar System) must not have any sort of technology on it at all.
‘But no one has put scientific numbers to that assumption. How much of the Solar System have we checked?’
As well as distant megastructures, clues about alien life could be lurking right under our noses on the surface of nearby planets.
‘Sure we can rule out the existence of big cities on nearby planets, but what about smaller things?’ Wright asked.
‘How long would something last on the surface before we would not recognize it as technological? I hope these questions will finally be addressed scientifically soon.’
The search for bigger structures out in space requires a different strategy.
‘Finding artefacts outside the solar system is a whole different matter,’ Wright continued.
‘In that case we would not be looking at images of things, but perhaps for the heat it gives off, or its shadow as it passes in front of a star.
‘Those sorts of artefacts would have to be tremendously huge—bigger than Earth—for us to notice them.’
We asked what sort of chance we’d have of contacting aliens if we really did spot one of their megastructures.
‘Pretty low,’ he replied.
‘Space is large, so if we find something around a star 1,000 light years away, our radio waves haven’t even gotten to them yet.
‘Even if we do ever set up communication, it will be thousands of years between messages, so contact will be pretty limited and slow.’
However, Wright does believe that if we do find signs of an alien civilisation, then it’s probably still alive.
‘On a cosmic timescale, things don’t tend to last very long after their creators or maintainers go away,’ he added.
So what about the possibility of finding alien probes near to Earth?
‘There’s no reason to think that such probes couldn’t be constructed, but you would have to build an enormous number of them for us to notice one flying through the solar system,’ Wright replied.
‘There are hundreds of billions of stars in the galaxy, and if there are artefacts moving among those stars they will spend most of their time in deep space where no one would ever notice them.
‘For one to just happen to be passing through the Solar system around now there would have to be thousands of trillions of trillions of them throughout the Galaxy.
‘But sure, it’s possible to build that many machines, if they are what are called von Neumann machines.
‘Johnny von Neumann was a scientist who discussed the implications of building a machine that could build a copy of itself.
‘If you built one of those in space on an asteroid, the idea goes, it could build a copy of itself, then those copies would build copies. Eventually, they’d run out of asteroid and so have to be able to hop over to the next one.
‘Eventually, they’d run out of asteroids altogether and have to move on somewhere else.
‘If they could go between stars, then at each star they could turn all of the asteroids into more copies. With a scheme like that, you could eventually have enough that they would be everywhere.’
The Great Silence
Despite our best efforts, humanity has so far failed to discover even the most basic form of alien life.
Dr Paul Davies, a professor at Arizona State University, is author of The Eerie Silence: Searching for Ourselves in the Universe.
His book grapples with the Fermi Paradox, an argument which discusses the contradiction between the high likelihood that aliens live somewhere in the universe with humanity’s inability to find them, which is often called ‘The Great Silence’.
He has previously called for a search of the moon to look for traces of aliens as well as discussing the possible existence of a ‘shadow biosphere’ on Earth populated by undiscovered creatures which behave very different to all other known forms of life on our planet.
‘There is a scaling law: we could spot small things nearby and large things far away,’ he said.
‘I am a fan of searching nearby because we are doing that anyway for other reasons.
‘Some years ago I wrote a paper with a student on searching for alien artefacts on the moon. If there was alien technology in the solar system, this is a good place to look because the lunar surface is relatively stable.
‘The idea I really like is ‘genomic SETI’. We search right here on Earth for artefacts in the genomes of terrestrial organisms. This might be as simple as a message uploaded into the DNA sequence of a microbe (human scientists now do this all the time), or in the existence of a ‘shadow biosphere’ implanted here, say, 100 million years ago. For the concept of the shadow biosphere, see attached.
However, there is a risk that we might not even recognise alien life or technology if we encountered it.
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‘As Arthur C. Clarke famously remarked, sufficiently advanced technology would be indistinguishable from magic,’ Davies said.
‘More problematic is the fact traditional SETI looks for messages. A maximally compressed data transmission is indistinguishable from random, so we would not recognize it as a message unless we had the key.’
We also asked him about a theory which suggests that a species will never evolve to become because it ends up destroying itself before it’s capable of setting sail to the stars.
‘I think once a civilization squeezes through a ‘risk bottleneck’, then astroengineering is entirely feasible,’ he said.
‘I do feel, however, that very advanced technologies will be post-biological (AIs, if you like).’
However, the astrophysicist did not seem particularly optimistic about humanity’s chances of actually finding alien artefacts – and questioned the point of the discipline dedicated to looking
‘I should say that SETI and SETA are extremely speculative enterprises that used to be dismissed as nonsense when I was a student,’ he added.
‘Today they seem to be taken more seriously, for reasons that elude me, because they are still extraordinary long-shots.
‘We have no evidence whatever of any life beyond Earth, let alone intelligent life, so almost everything written on the subject is based on philosophical arguments, speculation and extrapolation of human society. However, it is undoubtedly great fun and very popular with the public. Also, it doesn’t cost much, so I am strongly in favour of doing it.
‘As to whether the wider scientific community takes it seriously, I can’t say.’
The Future Of Everything
This piece is part of Metro.co.uk’s series The Future Of Everything.
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