starlight6x6: I believe in aliens but not like in the conspiracy theorist sense more like in the…

Friday, October 30th, 2015


I believe in aliens but not like in the conspiracy theorist sense more like in the “the notion that in this infinitely-huge universe our planet is the only one with life on it is fucking absurd” sense

Unpopular (oh, so unpopular) opinion below the cut.

I wanted to reply to @of-a-toast-and-tea‘s tags (hope that’s okay):

#i feel like the difference here is#do you believe that it is statistically likely that life exists somewhere else in the universe?#vs#do you think pod people are secretly controlling our government#and dive bombing farmers with their spaceships#which#i mean#i feel like there is a line the size of the grand canyon between the two

The thing I find really interesting about this is how many people – including highly numerate scientists – agree with the “extraterrestrial life is statistically likely” idea. Because I don’t agree with it.

I appreciate the enormity of space, and the magnificent huge-os-i-ty of the number of potentially habitable planets. But I happen to believe, in all seriousness, that “the notion that in this infinitely-huge universe our planet is the only one with life on it” is not fucking absurd. From my sense of the available data, it’s not possible to assert any particular likelihood for or against that idea.

Because we just don’t know. We don’t have a meaningful sample that would allow us to put a value on that number.

To argue that we can put a value on that number, by arguing that the probability is greater than .5 by saying “it is statistically likely that life exists somewhere else in the universe”, is to focus only on the convenient part of the equation, while ignoring the inconvenient part. But math doesn’t work that way.

Here’s the inconvenient part: we don’t know how likely or unlikely it is that given a planet with conditions suitable for life, life will actually emerge there. We have direct evidence that this has happened once (and only once) here on earth. We have no evidence (so far) that it has ever happened any other time, on earth or anywhere else. It could be a commonplace occurrence. It could be a rare occurrence. It could be so extraordinarily rare that it only has ever happened once in the entire history of the universe.

Now, I’ll grant you that that seems, on the face of it, like an absurd thing to say. But that sense of absurdity is not rooted in mathematics. It’s rooted in our everyday experience here on earth, in which life appears to be commonplace, and things that we see happening on occasion, even extraordinarily unlikely things like winning the lottery, are nevertheless likely enough that we do see them happening once in a while, given enough throws of the dice. And so, since the universe is so unimaginably huge, we have an intuitive sense that surely the odds of rolling “life” with that many rolls of the dice must be greater than 50%. Because again, look around us: we rolled it here on earth. Tada! says our intuitive sense.

But in this case our intuitive sense is being an ass.

The universe is under no obligation to have any particular value for the likelihood of life’s emergence. Well, okay, that’s not quite true: It’s obligated to have a number greater than zero, because we’re here to ask the question. But that’s the universe’s only obligation in that regard. Life’s emergence given suitable conditions could be likely. It could be unlikely. It could be unimaginably unlikely, even so unlikely as to make it so our own emergence was the only time it ever happened despite the unimaginably large number of earth-like worlds in the cosmos.

We could totally be living in that universe, the one in which life emerged just once. Just as we could totally be living in a universe in which life emerged more times than that. As long as our sample of life having emerged consists only of the single case required by us being here to ask the question, there is no mathematical reason to argue for one scenario over the other.

I’m not saying NASA should stop making the search for extraterrestrial life a key part of their fundraising appeal. I think it’s a super interesting question, one we can only answer by going out and looking. I just don’t agree that we actually know, at all, how likely it is that the search is ever going to pay off.

As long as we’ve been looking at the heavens, we’ve operated with this assumption that extraterrestrial life is out there. As technology has extended our senses we’ve had to move that imagined life farther away, but we keep imagining it. But that’s because we want it to be true, not because we’ve run the numbers and determined that it is likely that it is.

We (including scientifically minded folks) used to believe we would find life on the Moon. These days we get excited about the possibility of finding it in places like Mars, Titan, or Europa. If the solar system eventually turns up empty we’ll focus our hopes on habitable-zone extrasolar planets. But we’ll continue to imagine it being out there, even as we continue to accumulate negative evidence. It just makes sense to us. It’s what we’re familiar with.

I’m fine if people want to believe there is life beyond earth. I just don’t think they’re using math to decide that, or that they can back up the assertion that it is likely.

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