For centuries, great thinkers have pondered why, given the hundreds of billions of planets in the galaxy, we have seen no compelling signs of intelligent life beyond Earth.
Now, scientists are mulling an intriguing possibility: if aliens exist, their technology may be only marginally better than ours. And having explored their cosmic neighbourhood for a while, they simply got bored and stopped bothering, making it difficult to detect them.
The scenario, described in a new paper, embraces the principle of “radical mundanity”, which shuns the notion of extraterrestrials zipping around the universe after harnessing physics beyond our comprehension. Instead, it proposes a Milky Way that is home to a modest number of civilisations with technology not wildly more impressive than our own.
“The idea is that they’re more advanced, but not much more advanced. It’s like having an iPhone 42 rather than an iPhone 17,” said Dr Robin Corbet, a senior research scientist at the University of Maryland, Baltimore County, who is based at Nasa’s Goddard Space Flight Center. “This feels more possible, more natural, because it’s not proposing anything very extreme.”
Corbet came up with the hypothesis after considering researchers’ explanations for the “great silence” or Fermi paradox, the discrepancy between the lack of compelling evidence for alien civilisations and the likelihood of their existence in a vast and aged universe. Most theories struck Corbet as exotic. Perhaps extraterrestrials were too advanced to be detected? Perhaps Earth was a cosmic zoo that aliens had agreed to leave alone? Perhaps Earth was the sole home for life in the galaxy?
The search for extraterrestrial intelligence (Seti) has focused on detecting “technosignatures”. Advanced civilisations could advertise their existence by building powerful laser beacons that can be spotted from other planets. They may reveal themselves by sending robotic probes across the galaxy, or building enormous structures in space to harness the energy of their star. They could even visit other planets or scatter artefacts through the galaxy. All could make them visible.
But the radical mundanity principle says not. It explains the great silence by proposing that extraterrestrial civilisations hit a technology plateau not far above our own capability. “They don’t have faster-than-light, they don’t have machines based on dark energy or dark matter, or black holes. They’re not harnessing new laws of physics,” Corbet said.
If that were the case, alien civilisations would struggle to run powerful laser beacons for millions of years. They would not zip between planets. And after exploring the galaxy with robotic probes, they may get bored with the information sent back and give up on space exploration.
The science fiction author Arthur C Clarke is purported to have said: “Two possibilities exist: either we are alone in the universe or we are not. Both are equally terrifying.” Corbet, whose paper has yet to be peer reviewed, suspects the truth may lie somewhere in between “in a rather more mundane, and so less terrifying universe”. Contact, he adds, “could leave us somewhat disappointed”.
Prof Michael Garrett, the director of the Jodrell Bank Centre for Astrophysics, enjoyed the “fresh perspective” but voiced reservations. “It projects a very human-like apathy on to the rest of the cosmos. I find it hard to believe that all intelligent life would be so uniformly dull,” he said. Any technological plateau could be far above our level, he added.
In a paper to be published in the journal Acta Astronautica, Garrett favours another theory. “I lean towards a more adventurous explanation of the Fermi paradox: that other, post-biological civilisations advance so rapidly that they slip beyond our capacity to perceive them,” he said. “I hope I’m right, but I could very well be wrong. Nature always has some kind of surprise for us around the corner.”
Prof Michael Bohlander, an expert on SETI policy and the law at the University of Durham, said evidence may already have reached us in the form of unexplained aerial phenomena, or UAPs. “If only a small percentage of those objects were found not to be man-made – and the capabilities displayed by them in numerous sightings at the very least suggest a state of advance far beyond current publicly known human technology – then the question posed by Fermi, ‘Where is everyone?’, could be answered empirically,” he said.
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