Here on Earth, you know a country has been conquered when loads of tanks, attacks helicopters and burly great soldiers roll into town.
But aliens could ‘invade’ our solar system using tiny ‘micro-robots’ which astronomers would probably fail to spot unless they knew exactly what to look for.
A new study has revealed that it’s entirely possible an extraterrestrial civilisation has unleashed a massive squadron of microscopic probes which have spread out across the galaxy undetected.
Zaza Osmanov of the Free University of Tbilisi in Georgia has written a paper which discusses ‘extraterrestrial micro replicators’ called Von-Neumann probes that are capable of reproducing themselves.
Currently, the search for alien intelligence is focused on discovering huge ‘megastructures’ such as Dyson Spheres – hypothetical giant power stations built around stars to harvest their energy.
Osmanov suggested that advanced civilisations might actually build tiny machines to explore the galaxy and calculated how they would spread through a cloud of interstellar gas – the name for great billows of gas which exist between star systems.
‘The total number of probes might increase extremely rapidly ”invading” the whole region of an interstellar cloud,’ he wrote.
When we think of aliens invading a star system, it’s often assumed they would land on a planet and begin munching up its resources while enslaving or slaughtering its unfortunate inhabitants.
This approach might actually be counterproductive because it requires more energy and effort than unleashing swarms of robots.
‘Extraterrestrials would prefer to use micro-robots than large-scale macro probe,’ Osmanov continued.
‘Still there is a possibility to make the process of reproduction efficient but for that, the probes need to land on rocky planets.
‘This compared to the continuous process of replication of microdevices in interstellar clouds seems to be less efficient because landing on a planet and fleeing from it require special manoeuvring.’
Thankfully, if a horde of robots colonised a cloud in the Milky Way we would probably notice them.
Osmanov said ‘detection is quite realistic’ because the machines’ luminosity ‘might reach enormous values’, meaning they would give off enough light to be visible.
He wrote: ‘If one detects a strange object with extremely high values of luminosity increment, that might be a good sign to place the object in the list of extraterrestrial Von-Neumann probe candidates.’
The apparent contradiction between the likelihood of aliens existing in our gigantic universe and our inability to find them is called the Fermi Paradox.
This could be solved if we assume extraterrestrial technology is too small for us to spot using our current telescopes.
However, it’s perfectly possible that we are the only intelligent living creatures in the whole of space.
This week, a top British scientist has claimed that humanity could be alone in a vast universe that’s totally devoid of alien life.
Nick Longrich, a senior lecturer in palaeontology and evolutionary biology at the University of Bath, has said that the evolution of intelligent life on Earth (which means us, in case you’re wondering) is so spectacularly unlikely it may have happened just once.
In an article for The Conversation, he wrote: ‘Are we alone in the universe? It comes down to whether intelligence is a probable outcome of natural selection, or an improbable fluke.
[By definition, probable events occur frequently, improbable events occur rarely – or once. Our evolutionary history shows that many key adaptations – not just intelligence, but complex animals, complex cells, photosynthesis, and life itself – were unique, one-off events, and therefore highly improbable.
‘Our evolution may have been like winning the lottery … only far less likely.
‘The universe is astonishingly vast. The Milky Way has more than 100 billion stars, and there are over a trillion galaxies in the visible universe, the tiny fraction of the universe we can see. Even if habitable worlds are rare, their sheer number – there are as many planets as stars, maybe more – suggests lots of life is out there.
‘So where is everyone? This is the Fermi paradox. The universe is large, and old, with time and room for intelligence to evolve, but there’s no evidence of it.’
‘Could intelligence simply be unlikely to evolve? Unfortunately, we can’t study extraterrestrial life to answer this question. But we can study some 4.5 billion years of Earth’s history, looking at where evolution repeats itself, or doesn’t.’
To illustrate just how lucky our species has been to have evolved to our current state of intelligence, he sketched a vivid picture of evolution which shows how many lucky breaks life was given here on Earth.
He added: ‘Humans couldn’t evolve until fish evolved bones that let them crawl onto land. Bones couldn’t evolve until complex animals appeared. Complex animals needed complex cells, and complex cells needed oxygen, made by photosynthesis. None of this happens without the evolution of life, a singular event among singular events.
‘All organisms come from a single ancestor; as far as we can tell, life only happened once.
‘Curiously, all this takes a surprisingly long time. Photosynthesis evolved 1.5 billion years after the Earth’s formation, complex cells after 2.7 billion years, complex animals after 4 billion years, and human intelligence 4.5 billion years after the Earth formed. That these innovations are so useful but took so long to evolve implies that they’re exceedingly improbable.
‘These one-off innovations, critical flukes, may create a chain of evolutionary bottlenecks or filters. If so, our evolution wasn’t like winning the lottery. It was like winning the lottery again, and again, and again. On other worlds, these critical adaptations might have evolved too late for intelligence to emerge before their suns went nova, or not at all.
‘Imagine that intelligence depends on a chain of seven unlikely innovations – the origin of life, photosynthesis, complex cells, sex, complex animals, skeletons and intelligence itself – each with a 10% chance of evolving. The odds of evolving intelligence become one in 10 million.
‘But complex adaptations might be even less likely. Photosynthesis required a series of adaptations in proteins, pigments and membranes. Eumetazoan animals required multiple anatomical innovations (nerves, muscles, mouths and so on). So maybe each of these seven key innovations evolve just 1% of the time. If so, intelligence will evolve on just 1 in 100 trillion habitable worlds. If habitable worlds are rare, then we might be the only intelligent life in the galaxy, or even the visible universe.
‘And yet, we’re here. That must count for something, right? If evolution gets lucky one in 100 trillion times, what are the odds we happen to be on a planet where it happened? Actually, the odds of being on that improbable world are 100%, because we couldn’t have this conversation on a world where photosynthesis, complex cells, or animals didn’t evolve. That’s the anthropic principle: Earth’s history must have allowed intelligent life to evolve, or we wouldn’t be here to ponder it.
‘Intelligence seems to depend on a chain of improbable events. But given the vast number of planets, then like an infinite number of monkeys pounding on an infinite number of typewriters to write Hamlet, it’s bound to evolve somewhere. The improbable result was us.’