What will alien life forms look like? What will their planets be like? Such questions have intrigued creators of TV shows, films and video games. They also fascinate Scottish scientist Fergus Simpson, who holds a PhD in astronomy from the University of Cambridge and has recently been conducting further research at the University of Barcelona’s Institute of Cosmos Sciences. In 2015, Dr Simpson published an article in a reputable scientific journal that caused quite a stir. In it he used statistics to speculate on the probable appearance of intelligent alien life and that of the planets they may live on. We caught up with Dr Simpson in London. We began by asking him about this study and the calculations behind it.
Fergus Simpson (mild Scottish accent): The scientific article focused more on the size of the planets that they’ll be living on, but one particular conclusion was that most intelligent alien species, if they exist – we usually think of them in Star Trek as being maybe humanoid in nature – if they exist, then we should expect them to be physically larger than us. It’s really founded on statistics rather than astronomy. You might think that you can learn nothing about alien life because there are so many uncertainties, but there’s actually some statistics you can apply. So, for example, I’ve never met you before but I could assume that you’re more likely to have a common blood type than a rare blood type, and that you’re more likely to have been born in a country with more people than a country with fewer people; it’s less likely that you were born in Andorra than in China, for example.
A SPECIAL PLANET
Dr Simpson then applies these earthly calculations to planetary effects:
Fergus Simpson: It’s simply a question of crunching the numbers, I suppose, in that there are more individuals in the highly populated worlds, there was no chance that you were born on Mars because there are no people there. So if there was a small colony on the moon there’s very little chance that you’d be living there. And, it’s that tendency to belong to the larger group that presents a bias in what we see, and there are all sorts of examples of these kinds of selection effects that crop up. I was actually not the first person to point out that we’re more likely to be part of a larger civilisation in terms of population, I just took it one step further in saying that a number of things are linked to the civilisation size, such as the size of the planet and the size of the body as well, because larger species tend to have lower population densities: there are far fewer elephants on Earth than ants, for example. The indication is that most planets with intelligent life are actually smaller than the Earth or at least have less land covering their surfaces that you can live on – so, we’re quite a special planet. And, in terms of the species, again, if we expect our population to be large, based on statistics, then that suggests that other alien species are... have lower populations, and they will be physically larger as a result.
POLAR BEARS
So how large are these intelligent life forms likely to be?
Fergus Simpson: If you want to get quantitative it’s a little bit more tricky because you then have to ask how much of a range of body sizes do you expect there to be amongst these kinds of species so, you know, you can reach towards science fiction and get some motivation there or you can look at the species on Earth and get an idea of how much body sizes vary in size. If you can imagine that all intelligent species were the same size then our answer would be very simple, we would expect them to be not significantly larger than ourselves. That seems extraordinarily unrealistic so if you pop in a more realistic spread of body size values, you get an answer of approximately 300 kilograms as being a typical alien species, which would be the mass of a polar bear.
ALIENS ARE FROM VENUS
Since his paper was published, new evidence has come to light yet, Dr Simpson argues, it supports rather than refutes his theory:
Fergus Simpson: There was one interesting piece of evidence that came up shortly afterwards, they noted that something strange happens to planets that are a little bit larger than the Earth and they seem to be less dense than we expected, so for a while I was a little unsure why alien species would not inhabit planets larger than the Earth. But it seems they [the larger planets] have some unusual properties – maybe they hold on to gas atmosphere better than we expected – so it suggests that the Earth may be one of the largest planets you could actually live on, that kind of backs up the statistical calculation.
As the gravity on larger planets makes life improbable, we may speculate that alien beings living on smaller planets than Earth would be larger in size than humans.
Fergus Simpson: If you imagine that most species live on smaller planets, I mean – not as small as Mars, that’s extremely small, that’s about ten times smaller than the Earth – but something in between – more like Venus – then the gravity is a little bit weaker and that actually allows you to have larger body masses and support larger body masses because your legs and limbs are under less stress when you move around, so that gives further reason to believe that they, indeed, could be very much larger than ourselves.
TEAM PLAYERS
Dr Simpson focuses his study on ‘intelligent alien life’, but what is “intelligent life”?
Fergus Simpson: I suppose you have to start to ask things about what... the meaning of consciousness and so on. But the key point from the point of view of the calculation is that someone you would consider on an equal intellectual level, so that you’d consider yourself to be a part of this larger group. So for example you would consider yourself to be an ordinary human, and so if other species of similar mental capacity existed elsewhere then we could consider ourselves one of that larger group. But it’s very difficult, especially at this stage when we don’t really know much about other species, whether dolphins would count, for example.
KEEP LOOKING
And how likely are we to find such extra-terrestrial life?
Fergus Simpson: That’s a really tough question and the answer is that we just have to look because we’re very... it’s very hard to estimate the probability of success, but I will say this: there’s two very different approaches: you can either look for the unintelligent alien life, like microbes that simply will affect, perhaps, the atmosphere of the planet that they are on, and so they’ll be much more abundant in the universe, but they are harder to find in the sense that you need … they need to be on a planet that is close enough for you to study in detail and look at their atmosphere. Now the other more exciting approach is to look for these intellectual life forms, and they’re probably more rare, but on the plus side there is the opportunity that we could detect them from very much further away because they could be sending artificial signals as we are, such as radio waves. And you could potentially detect them from much greater distances than these microbes. So it may well balance out, that the chances of finding alien microbes isn’t actually that much greater than your chances of finding extra-terrestrial intelligence.
DO YOUR SUMS
Finally we asked Dr Simpson how reliable statistics are:
Fergus Simpson: The answer is they’re very good if done carefully! But they’re often abused and misinterpreted so that’s why they have a generally very poor reputation at times, but it’s important to emphasise that every scientific result in history has relied heavily on statistics: the discovery of the Higgs boson was purely statistical and, for example, it was 99.999% sure but still you can’t reach that 100% point, just by the nature of science. So it’s very important that we do our statistics correctly and carefully.