FYI.

This story is over 5 years old.

Tech

Science Says Aliens Should Exist (But Also, Probably Not)

It is. Some astronomers say there could be tens of thousands of planets with life on them that we'll have the capability of detecting soon. Or now. Some say there's probably just a few. Not many are saying that there's probably none, at least not...

Some astronomers say there could be tens of thousands of planets with life on them that we’ll have the capability of detecting soon. Or now. Some say there’s probably just a few. Not many are saying that there’s probably none, at least not very loudly. Well, a new paper from David Spiegel at Princeton University and Edwin Turner at the University of Tokyo, argues that the likelihood of ETs being out there is crappy enough to make you feel lonely again.

Advertisement

Again? Why, yes, lonely like the days before the famous Drake equation came about. This equation, derived by alien-hunter pioneer Frank Drake, estimates the number of detectable extraterrestrial civilizations in the Milky Way. Conceptually, it’s pretty simple: take all the stars, take the number that have planets, take the number of planets within habitable areas, the number of planets of those that should have formed life, and then the number of those that should have survived to be intelligent like us.

You might notice that a few of those things in the equation are things we don’t actually know and, so far, can’t know. Instead, we use conjecture. And in the world of alien-hunting, those "should"s seem to be okay.

But Spiegel and Turner think we should be more rigorous, and their new paper examines the probability of finding ETs in Bayesian terms.

Bayesian probability is very basically no-bullshit probability. It is “most often used to judge the relative validity of hypotheses in the face of noisy, sparse, or uncertain data, or to adjust the parameters of a specific model,” explains UC Berkley’s Bruno A. Olshausen.

A thing Spiegel and Turner look at is what it means that life on Earth emerged very quickly in the planet’s life. Some astronomers have tended to think that this means that life is very likely to emerge on habitable planets. That’s the only way life could have evolved as far as it has. If life emerged later, we wouldn’t be here to talk about this.

Advertisement

So it changes the probabilities, from considering that life is x likely to arise on on a planet, to it is x likely that life arose very early on a planet. Which is much, much smaller. Arbitrarily small, according to the paper’s authors.

But, before you get all depressed, consider that the root of what they’re saying is less that we should stop looking: on the contrary, we need to know more. Life emerging on Earth is the only evidence we have for life and that’s not enough to say that life is very likely in the Milky Way. If we found life on Mars, or discovered that life emerged more than once on Earth, then we’re in a different, possibly much more crowded ballpark.

We had to find ourselves on a planet that has life on it, but we did not have to find ourselves (i ) in a galaxy that has life on a planet besides Earth nor (ii ) on a planet on which life arose multiple, independent times. Learning that either (i ) or (ii ) describes our world would constitute data that are not subject to the selection eff ect described above. In short, if we should find evidence of life that arose wholly independently of us { either via astronomical searches that reveal life on another planet or via geological and biological studies that fi nd evidence of life on Earth with a di erent origin from us, we would have considerably stronger grounds to conclude that life is probably common in our galaxy.
s
Keep in mind, also, the Fermi paradox. Simply, the universe is big enough and old enough such that advanced extraterrestrial civilizations ought to exist. But we haven’t seen any evidence of them. It’s an apparent contradiction and one that suggests that either the likelihood of life forming is very small, or that advanced civilizations are incapable of existing for very long. They self-destruct. Like us?

Connections:

Image:

Maarten van Maanen