It's an old conundrum. Given the high probability of life being out there in an incredibly massive universe, why have we not received any contact?
Explanations range from the unlikely (there are no aliens at all) to the terrifying (gamma-ray bursts that wipe out civilizations are too frequent to allow complex life to develop and make contact with other worlds).
To the even more terrifying (all other civilizations are out there keeping their space mouths shut, knowing that it only takes one species of aliens hell-bent on destruction to wipe out all the others).
Professor Brian Cox has once again weighed in on the problem, known as the Fermi Paradox. In the past, he has speculated that “one solution to the Fermi paradox is that it is not possible to run a world that has the power to destroy itself and that needs global collaborative solutions to prevent that.”
His latest take on the topic is not quite as bleak but nonetheless remains not pretty.
Asked on BBC's Sunday Morning show if there was a chance intelligent lifeforms had found their way to Earth, he replied that "there are two trillion galaxies in the observable universe, I'm sure there are others out there."
However, he suggests that life that makes it to the point of intelligence may be few, and incredibly far between.
"You can make an argument, just from looking at biology and the history of life on Earth, that civilizations might be extremely rare. There could be on average one per galaxy, perhaps just a handful."
"Imagine that this is the only place with collections of atoms that can think and build a civilization."
Though he suggests that intelligent life may be rare, he believes microbial life may be abundant—just as it has been on Earth for billions of years.
“If you forced me to guess, I would say there may be microbes all over the place, that’s why we’re looking for life on Mars, for example, but in terms of intelligence, one thing to think about, the origin of life on Earth, it looks like we have good evidence life was present 3.8 billion years ago and the first civilization to appear on Earth was about now, give or take," he told the program.
“So it took the best part of four billion years to go from the origin of life on Earth to a civilization. That’s a third of the age of the universe, and that is a long time, so that may indicate that microbes may be common, but things like us may be extremely rare.”
If we're one of only a few intelligent species occupying our galaxy, finding others would be an incredibly difficult task, with the vast number of stars to look at, assuming we even lived in the same time frame or have the same requirements for life as other intelligent alien species.
As lonely as that may feel, he believes it could sharpen the minds of political leaders here on Earth.
“I mean, as we began talking, the idea that we might be the only civilization, for thousands or even millions of light-years, I think that science, it’s useful on many levels, but one of the things it’s very useful at is giving us a perspective, which is a wider perspective and actually I don’t think many of us think – many of our political leaders maybe don’t really think in terms of, is it possible that this is the only, let’s say, the only island of meaning in a galaxy of 400 billion Suns. That matters.
“I don’t think that’s some kind of whimsical idea. It might focus the mind.”