We Might Be Alone in the Universe

[doubtingthomas]

However, we caution that our analysis purely concerns the Earth, treating abiogenesis as a stochastic process against a backdrop of events and conditions which might be plausibly unique to Earth.

He is using Earth as a model to calculate the odds of intelligent life in the galaxy.

Have a nice day, expert.

[doubtingthomas]

Let’s say that a civilization in our galaxy was advanced and expansionist. What would we see as evidence from where we are if 5,000 years ago, their colonization made them go from from being 3,532,256,385,215,695 km away from us to 3,531,256,385,102,952 km away?

Probably not much, why would a civilization begin 5,000 years ago? Isn't the galaxy like 10 billion years old?

[Doctor Steuss]

Let’s say that a civilization in our galaxy was advanced and expansionist. What would we see as evidence from where we are if 5,000 years ago, their colonization made them go from from being 3,532,256,385,215,695 km away from us to 3,531,256,385,102,952 km away?

Probably not much, why would a civilization begin to expand 5,000 years ago? Isn't the galaxy like 10 billion years old?

Why wouldn't it?

Why would a civilization begin to expand 10,000 years from now? Why would an intelligent civilization colonize in the first place? Why would intelligent life take a technological path similar to our own? Why would intelligent life care about making technological advances? Why would intelligent life look to the cosmos at all?

Everything is predicated on our own hubris, and assuming that our very narrow understanding and view of life and intelligence is the default. There might be a transcendent species of palladium-based tardigrades out there that metabolize x-rays, and can't survive a gravitation force above 1.2N/kg., stuck in a perpetual existential state of ennui, using telepathic hyphae to enjoy the tale of a hermit who lived at Bootes void for a summer.

Because we're a bunch of idiots destroying our own planet, with a penchant for colonization and exploitation, and a drive for technological advancement, doesn't mean that any other potential intelligent life must similarly be driven by the same primate-evolved brains. It doesn't even mean that it's the likely outcome of intelligence. It's just the way it went with the only example we have.

[Res Ipsa]

So, I finally tracked down the Sean Carroll quote. It is a six-year old tweet in response to something stupid that Elon Musk tweeted. https://Twitter.com/seanmcarroll/status ... sdxmy3jPuQ

But, I think I forgot the basic statics I learned long ago, at least for a moment. Here's the tweet: "Not really. Life could just be rare. Probability of life starting could be 10^-100 per planet. We just don’t know." I found this estimate of planets in the observable universe: 10^25 that orbit stars, plus another 10^26--10^30 planets that don't orbit stars. Just looking at the orders of magnitude, I concluded that Carroll was saying that life might be virtually impossible. But I didn't do the necessary math. I think I remember the math, the large numbers throw me. If we assume that the presence of life on each planet is independent (I know, I know) I think the math looks something like: 1-((1-10^-100) * 10^25) (i.e., you have to multiply the odds that there is no life on a single planet times the number of planets and subtract that total from 1).

But even if I have the formula correct, I don't have the first idea how to do the math that gets me from the stated odds of life starting per planet to the odd that life started on any planet in the observable universe. Any hints?

[Doctor CamNC4Me]

I'll find it and give you a timestamp later.

Did you ever find that timestamp, DT?

- Doc

[Physics Guy]

(1+a)^N = sum over n, from 0 to N, of a^n N!/(n!(N-n)!), where n! = n(n-1)(n-2) … (3)(2)(1), the factorial. So for instance 3! =6.

In this case a = - 10^(-100) and N=10^25. Each successive term in the sum brings another factor of something that is never bigger than N, but also gets another factor of a. So as n goes up, the successive terms in this case just become tinier and tinier by a factor like 10^(-75). We can stop at n =1 and make a negligible error.

So (1-10^(-100))^25 = 1 - 10^(-75) + …, where … is no bigger than 10^(-150). So this estimate for the total probability of intelligent life, somewhere on any of the 10^25 planets, is 10^(-75)—essentially zero.

In this case the exact math is not significantly different from the naïve estimate of just multiplying the chance per planet times the number of planets. That estimate works well whenever the chance is much smaller than 1/ the number of chances, as in Carroll’s hypothetical case.

[Physics Guy]

I've heard a few things by Sean Carroll that I thought were right and insightful, so for me he has a good track record. A statement that intelligent life must either be common or entirely absent just sounds like nonsense, however. If Carroll really said something to that effect, I'm betting it was tongue in cheek, or maybe an ironic excuse for arbitrarily picking an opinion on an issue with inadequate evidence.

Looking for intelligent life in the rest of the universe is really on the fringe of science. We just don't know enough to say anything useful about it. It's fascinating to look as hard as we can, and to speculate about why we haven't met anyone else out there yet. It's not a field that I find worthwhile to follow closely, however. It's mostly just noise. Sometime in a slow news cycle, some researcher finds a way to square it with their scientific conscience to say something to a journalist that will sound to the public like more than it really is. Or they make a podcast or something, and wow, We might be alone! or We might not be alone! It's not as hard as it probably should be to get publicity while seeming to stay scientifically honest, because you can announce your most provocative points in plain speech while couching your careful caveats in technical terms, like an Islamist leader saying different things in English and Arabic. The lay public will only hear the clickbait soundbites, while your colleagues won't even notice that your caveats are concealed.

The Fermi paradox was raised by Enrico Fermi in 1950, and the idea had probably been kicking around a while then. If the future is something like Star Trek, then why haven't we already been visited by some alien Star Fleet? All the Fermi paradox really rules out, though, is something like Star Trek, with interstellar civilisations contacting new planetary civilisations each week, all of whom consist of humans in funny clothes speaking English. It's the optimistic extrapolation into the future of the coolest new technology of the 1960s, while unimaginatively assuming that everything else will stay just as it was, forever. We can't imagine what we can't imagine, though.

Maybe there will never be any Star Trek, because we are already close to the ultimate ceiling of technology. Maybe wormholes and warp drives will be forever impossible, and the energetic demands of relativistic travel, or even of interstellar communication, will always be too exorbitant for any species to attempt, and so we and every other intelligent species will always just be stuck in our original solar systems, peering out at stars that will never really be any more accessible than they were in our Stone Age.

Or maybe technologies that we cannot now imagine will come online in just a few centuries, making everything we now think is cool obsolete. Maybe broadband intergalactic communication is easy, once you rig up the right moon-sized quantum-shmantum transceiver, and the universe is a lively online community of bazillions in which nobody ever bothers to leave their own basements, let alone visit other worlds physically. That's the optimistic extrapolation into the future of the coolest new technology of the 2020's, while unimaginatively assuming that everything else will stay just as it was, forever.

Maybe, maybe, or maybe. We don't have any idea, and the only really silly idea is kidding ourselves that we know more than we do. So I don't try to keep up with this stuff. If anything really big happens, it'll be on the news, and I'll be able to tell then if it isn't just another doublespeak bit of clickbait.

[Res Ipsa]

(1+a)^N = sum over n, from 0 to N, of a^n N!/(n!(N-n)!), where n! = n(n-1)(n-2) … (3)(2)(1), the factorial. So for instance 3! =6.

In this case a = - 10^(-100) and N=10^25. Each successive term in the sum brings another factor of something that is never bigger than N, but also gets another factor of a. So as n goes up, the successive terms in this case just become tinier and tinier by a factor like 10^(-75). We can stop at n =1 and make a negligible error.

So (1-10^(-100))^25 = 1 - 10^(-75) + …, where … is no bigger than 10^(-150). So this estimate for the total probability of intelligent life, somewhere on any of the 10^25 planets, is 10^(-75)—essentially zero.

In this case the exact math is not significantly different from the naïve estimate of just multiplying the chance per planet times the number of planets. That estimate works well whenever the chance is much smaller than 1/ the number of chances, as in Carroll’s hypothetical case.

Thank you very much, both for the actual calculation and the rule of thumb.

[malkie]

...
All the Fermi paradox really rules out, though, is something like Star Trek, with interstellar civilisations contacting new planetary civilisations each week, all of whom consist of humans in funny clothes speaking English. It's the optimistic extrapolation into the future of the coolest new technology of the 1960s, while unimaginatively assuming that everything else will stay just as it was, forever. We can't imagine what we can't imagine, though.
...

PG, you forgot the god-like entities that appeared every few weeks, and the almost omnipresent beautiful and seductive women.

Your clear bias in this respect casts some doubt on what ever else you have to say

Anyway, what else would they speak? We know that the god of this universe has a particular liking for KJV English, so presumably any advanced civilization will have at least a decent grasp of the language. Either that, or google translate is still around well into the future.

[Doctor CamNC4Me]

(1+a)^N = sum over n, from 0 to N, of a^n N!/(n!(N-n)!), where n! = n(n-1)(n-2) … (3)(2)(1), the factorial. So for instance 3! =6.

In this case a = - 10^(-100) and N=10^25. Each successive term in the sum brings another factor of something that is never bigger than N, but also gets another factor of a. So as n goes up, the successive terms in this case just become tinier and tinier by a factor like 10^(-75). We can stop at n =1 and make a negligible error.

So (1-10^(-100))^25 = 1 - 10^(-75) + …, where … is no bigger than 10^(-150). So this estimate for the total probability of intelligent life, somewhere on any of the 10^25 planets, is 10^(-75)—essentially zero.

In this case the exact math is not significantly different from the naïve estimate of just multiplying the chance per planet times the number of planets. That estimate works well whenever the chance is much smaller than 1/ the number of chances, as in Carroll’s hypothetical case.

Is there a way to explain the numbers above in a way that a dummy like me could get it? Like, an analogy or fictional narrative that could walk a midwit like me through the math? Like, say, I’m Joe Rogan and I just smoked a phat blunt and my third eye is open, and you’re on the podcast speaking to me while millions of brosefs are listening intently.

- Doc