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It's free and available to everyone online. Check them out at Give Weblog. Welcome to, rationally speaking, the podcast, where we explore the borderlands between reason and nonsense.

I'm your host, Julia Gillard, and I'm here with today's guest, Stephen Webb. Stephen, as a physicist, he's at the University of Portsmouth and he's the author of several books on cosmology, science fiction and other topics, including Where Is Everybody, 75 Solutions to the Fermi Paradox and the Problem of Extra Extraterrestrial Life. That's what we're going to talk about today. Stephen, welcome to rationally speaking.

Hi, Julian. Thank you for inviting me.

So I just want to say, one of the many things that I really appreciated about your book is the structure of laying out a taxonomy of different approaches or solutions, or I just wish that more books out there presented taxonomy is I just find it incredibly instructive to have, you know, this juxtaposition of different ways that people have thought about a problem and and even even sort of the basic structure of that list. The basic categories that you've grouped those solutions into was super helpful in organizing my thinking.

So I want to get too ahead of myself and talking about those categories. But I just wanted to to put a plug in there for the idea of taxonomy books. It's pretty great. Well, thank you very much.

And a tip for authors. It's a good way of writing. You can focus on one solution on one topic. Forget it for a while. Go and do something else. Yeah, I can imagine.

So to begin at the beginning, could you tell our listeners the basics of what is the Fermi paradox and maybe tell the story of how it arose or how it was first proposed?

OK, well, back in 1950, Enrico Fermi, who was one of the great physicists of the last century, he was based at Los Alamos during the summer of 1950. And there was a cultural, sociological thing happening. You might know more than I do.

There's a spate of UFO sightings in America and it was in all of the newspapers, lots of discussion going on. And family in Los Alamos lunch was discussing these UFO sightings and he asked out of the blue, where is everybody? So it's a it's a question rather than a paradox. But there are there are paradoxical elements to the question. And we know pretty much, I think, what Fermoy, what his thought processes were in asking that question because he was a wizard at mental calculation.

This was before everyone had calculators on their smartphones. He could come up with order of magnitude answers to questions in his head. And pretty much what he'll have done is come up with a form of the Drake equation, which I'm sure your listeners will have heard of. To paraphrase it, we know there are a trillion planets in the galaxy, maybe more. Actually, Fermi wouldn't have known that. But we do now and we want to know how many civilizations, advanced technological civilizations on those planets.

So you run that trillion planets through a series of barriers, if you like. So habitability is the first barrier. What fraction of those planets in that Goldilocks zone where water flows is a liquid? If a planet is too close to a star, it's going to fry. If it's too far away from the star, it's going to freeze. So what's that fraction of habitable planets?

Abiogenesis is the next barrier, what fraction of those habitable planets does life start from non-life? Right. And once you have life, what fraction of those planets go on to develop a technological civilization? Incidentally, not all planets with life presumably would go on to have a technological civilization, we have alien intelligences here on Earth so elephants can collaborate with other elephants to solve problems. Octopuses, octopi, they can recognize individual humans and act differently, ravens and parrots that these aquatic creatures, but they're not going to build a technological civilization.

And finally, what fraction of those civilizations actually wants or choose to communicate when we need them to disturb the universe in some way that we can then detect? Right.

So you run, you make estimates and your guess is as good as mine, as good as Fermi's. But he'd have done it in his head. And typically when I run this by physical scientists, they come up with a number in the thousands. Frank Drake himself came up with 10000. Some people go even more so possibly 10000, maybe more civilizations out there in the galaxy. The paradoxical element comes up when you realize that the universe is thirteen point eight billion years old and some of those civilizations could have come into being billions of years ago.

And if they follow the technological path that we seem to be on and Fermi himself would have experienced, you know, he was born into a world that didn't have airplanes. We were literally a terrestrial species. Before he died, he saw humankind just reach space. So if a technological civilization lasts just for a few thousand years, maybe a bit longer, just think of what abilities they would have. They could build self replicating probes to visit every planetary system in the galaxy, or they could build Dyson spheres to collect all that free sunlight, or they could build antimatter rockets or hyper relativistic craft or whatever, something that we would see.

Or maybe they'd just shout out to the universe. Here we are. But nothing, you see nothing, and that's the paradoxical element we expect to see them and firmly, I think himself would have expected to see life, but so far we don't.

Where is everybody?

And could you I imagine for many listeners that the point that their mind is going to is, you know, well, maybe it's just not feasible to traverse the immense distances in space, even if you have a spacefaring technology. And so we shouldn't be surprised that even if aliens exist and our space faring, we shouldn't be surprised that we haven't seen them because space is just so vast. Could you talk a little about that? That's a possibility, although Stuart Armstrong and Andy Samberg recently came up with a proposal for how with.

Technology that is based on known physics, I'm not talking wormholes or what drives anything, anything like that. Nothing magical. Even with that sort of technology that is imaginable, this sort of technology we might be able to achieve in a few hundred years time.

They came up with a scheme whereby a civilization could send out tiny, tiny probes, self replicating probes, acting, if you like, is some sort of virus to colonize not just our galaxy, but potentially millions of galaxies in the neighborhood. So the family paradox isn't just why aren't they here? They being intelligences from our galaxy, intelligences actually from from other galaxies, it's not any more difficult under their skin. It just takes a lot longer. Now, you might say, OK, that's pie in the sky.

Science fiction stuff. Space is a pharmacist. The never going to be able to travel or traverse that distance. Fair enough. But it doesn't address this question. Why don't we hear from them? Why don't we see signs of their what would science look like potentially?

It depends.

I think we have to adopt a stable Darwinian viewpoint. After Olaf Stapledon, he was a philosopher and a science fiction author. And I think we just have to try and take the constraints of our imagination and just think what might be possible for an extremely advanced civilisation to do. So possibly build Dyson spheres. To. Capture all of the sunlight around a star that would leave a signal in terms of infrared radiation that we could pick up, but if they wanted to deliberately draw attention to themselves, they could, for instance, alter the stellar spectrum of their star.

They could dump material into the star with that would create stellar lines, spectral lines that we would clearly understand were not natural, or they could put swarms of particles up there to make a star flash on and off, or that the holy grail of Setit, if you like, is to look at from a deliberately broadcast signal. They could send the signal via radio by laser. Towards us, Paul. Towards the galaxy in general, so there's all sorts of things you can imagine, imagine them doing.

We haven't yet seen any of that. The question is in my mind, is that silence telling us anything yet? I think many of my colleagues would simply say we have to listen a bit longer. We have to listen a bit smarter. There's a huge phase space that we haven't yet investigated and it's a matter of time.

But when you say phase space, what do you mean in the sense that we need to scan a variety of wavelengths? We need to ensure that our telescope is pointing in the right direction. It's got to be pointing in the right direction at the right time. Are we looking for narrow, narrow band or broadband signals and so on? There's lots and lots of different possibilities that make this much, much more difficult than looking for a needle in a haystack.

But we are throwing a lot more resource at the the problem than we were back in 1961 when Frank Drake first started looking for the communications. So I guess it's a balance.

Do you think that. If we wait a little bit longer, if we throw more computational resources at this, if we throw more observational resources, this will eventually find something. What do you think that the silence is is already telling us something? Have we gotten any evidence in the last, say, 50 years that, you know, obviously nothing is conclusive, but has any evidence pointed towards or away from any of the potential solutions to the Fermi paradox?

For me, problem, I should really call it the Fermi problem, that's more accurate than paradox. Yeah, I think family problems are a better way of stating it since he just asked the question. Well, it's interesting that back when Fermi asked that question, he wouldn't have known for certain whether other stars have planets. Yeah, and that was a feasible answer to the question. Back in the last century, certainly the early part of the last century, some astronomers believed that planets came into being through the close collision of two stars.

If that were the case, then planetary systems would be rare and that would be a solution to the problem. Of course, we now know that stars come with planets. There are a trillion or more planets in the galaxy. And I think we're almost taking it for granted nowadays that astronomers can find exoplanets at the rate of, I don't know, one a month or whatever. But it's an incredible. Technological advance to be able to do that, and certainly when I was a student studying astronomy, it was deemed back then unlikely that we'd have the sort of technology that we have now to find exoplanets almost on demand.

So this, though, again, harks back to this paradoxical element. Our technology is increasingly, increasingly impressive. Last year, the discovery of. Multi messenger astronomy, we can discover colliding neutron stars through their gravitational wave. It's an incredible technological advance so we can study now astronomical events not just throughout the electromagnetic spectrum, but with gravitational waves to these are fantastic developments in technology. If you can imagine an alien civilization following the same technological. Path of progress, what might they be able to do in a thousand years, in 10000 years, if they survive presumably very, very impressive things.

So where are they? I think, yeah, our experience, if we attribute it to them. Does. Really? Add to that that paradoxical element. So I alluded at the when I was just introducing the book that you break down the 75 solutions into roughly three kinds of solution, there's well, actually aliens have already been here or that, you know, there are signs we just haven't detected them. That's number one. Number two is we shouldn't expect that aliens, if they do exist, would would have made it to our corner of the of the galaxy.

And then number three is there aren't aliens. We're essentially alone. Could you and feel free to correct my summary of either any of those three categories if you want, but could you maybe, maybe, maybe pick like one or two of your favorite solutions in each category just to give us a sense of the range?

Well, in terms of then being here, it's an immediate answer to the problem, isn't it? And it's probably the most popular solution.

If you were going to go out and ask a hundred people not expert on experts yet to see people in the street, they'd tell you that while they're here and the evidence is UFOs, science isn't the democratic process. So I don't think we should put too much store by that. I've seen a UFO, but it's much more likely that my brain was misinterpreting the data that my eyes were feeding it. It was technically a UFO.

It was an unidentified flying object, not necessarily a spacecraft.

I think that's the problem, isn't it, that people identify them?

Right. UFOs very quickly become Ivo's.

Exactly.

But they're still interesting twists actually on this idea that they're here, for example, directed panspermia.

It's this idea that Earth was deliberately seeded by life, so meaning that humans are we actually.

Are aliens in a sense that life came to? Earth, quite deliberately, earth itself was seeded deliberately and, you know, lesser scientists than Francis Crick came up with this sort of idea. Panspermia is an old idea that life somehow floats from star to star or planet to planet goes back a long way. But Crick came up with this idea of directed panspermia. So some other intelligence deliberately seeds a planet.

I think Star Trek have used that idea or the zoo hypothesis, this idea, which a surprising number of of my colleagues don't dismiss it as being that.

But we're in a zoo yet that we're deliberately being sheltered, if you like, from the notion that there are lots and lots of many more advanced civilizations out there. I find that myself not convincing, but some people do adhere to it. Yeah, there's an interesting you mentioned alien life on Earth.

There's another possibility that there really is.

Alien life here on Earth in the sense that we don't know how life got started here on Earth, and that's one of the reasons for directed panspermia as an idea, it sort of pushes back the the problem of the origin of life. Right. That if life really were easy to come into being from non-life, it's possible that it started several times here on Earth. It might then have, you know, a different genetic code or it might use right handed amino acids or something might be different from the life that we know it.

I think it's interesting that it's possible that alien life, alien life that came into being here on Earth at the same time as the life we know could potentially still be around. And it would be great to look for that sort of sign.

Wouldn't it be kind of coincidental if if there if life on Earth had originated from the stars and also independently on Earth, like, are we sort of violating Occam's razor by positing both of those things?

Well, now, this would be a separate thing. So forgetting panspermia, the notion that maybe life just came into being multiple times here on Earth. So it came into being once we know, because it gave rise eventually to us. But all life on Earth, for instance, uses left handed amino acids, has a certain genetic code. And so it's possible if life really is easy to come into being from non-life, that some different version of life came into being back when Earth was really young, just as a natural process.

Right. And I think it would be really interesting to try and find that sort of shadow biosphere, it's called, because that would prove or if we could find life on Enceladus or Mars or wherever life that came into being independently of the life that gave rise to us, then I think we'd know that life is easy to start and the barriers that there might be towards creating a technological civilisation. The barrier isn't abiogenesis because if it's right hand it multiple times, it's going to happen everywhere.

It would be an incredible coincidence if it was hard to create and happen multiple times in our own solar system. Yeah, yeah. Right.

And so we know the barrier can to be the number of of potentially habitable planets because we've already estimated that and we know that it can be. Well, sorry. In the scenario you've outlined, it couldn't be abiogenesis. So it would have to be the difficulty of developing intelligence like human level intelligence or the difficulty of making it to spacefaring capability as a civilisation. Or it would have to be, I guess, well, or the solution would have to do something to do with, you know, the will to travel or the type of travel or signal sent out or something like that.

Exactly.

I think it pushes the barrier to a different spot. Of course, at present, we don't know whether abiogenesis is difficult or not. I think that's why it's such an important job for scientists to go and look for other examples of life. And, you know, we need to explore Mars and solidness. Perhaps those are the moons where more water might exist. We really need to try and find out whether life. Has come into being independently of life here on Earth, because if it has, then I think that vastly raises the odds that the universe is teeming with life.

And then, as you say, why then don't we see intelligent, intelligent life? Then the question is, perhaps that barrier is the rise of intelligence or. Quite chillingly, maybe the barrier lies ahead of us, right, which would right, it would foretell a much higher risk of doom in our own path if if if our solution to the problem is that civilizations that are intelligent enough to potentially develop spacefaring technology end up destroying themselves before getting to that point.

That would be the one.

Yeah, right. So can we to jump ahead a bit to the third category, which is we are, you know, essentially alone in the universe. Can we talk about how to estimate how to even begin to start trying to estimate the how hard it is or how rare we should think it would be for intelligent life to develop conditional on life? I mean, in a sense, we just don't know, do we?

And that's one of the reasons why I tried to add so many qualifiers to my estimate begin to start trying to maybe someday estimate. Yes.

The. To my mind, when we look at intelligence, I mentioned earlier that there are a number of intelligent species I would classify them as intelligent species on this planet will know about dolphins, but birds, certain types of birds, a really very clever. The brain is small, but the computational capacity within them is really quite impressive.

Or cephalopods, right?

Octopi are pretty amazing, absolutely amazing creatures and a very different sort of intelligence as well and very different to to humans. And the last common ancestor that we shared with these creatures goes way back. So. They presumably are perceiving and understanding the world in very different ways, but they are not going to go.

On to create a star fairing civilizations, why should they? I mean, evolution doesn't have that as an end goal. They quite happily doing the stuff that cephalopods or birds do. It's just what they do.

That's that's correct, of course. But still, doesn't it seem like human level intelligence probably isn't mind bogglingly rare if we got several sort of partway successes just on Earth, like, wouldn't it be a weird, weird world in which it was pretty easy to, you know, pretty easy in the sense that evolution did it multiple times on Earth to create, you know, partway to human level intelligence. But there was only one actual human level intelligence in the whole universe.

Well, I'm not arguing necessarily that the barrier is there, but if you look at Earth, I mean, of the 50 billion species or however many there have been, there's only one species that is remotely capable of delivering a star faring civilization. And that would be us.

And I think that's because we have a very, very specific set of attributes that happen to enable us to do this. But evolution didn't have that as an end goal. You know, we're not at the top of some sort of evolutionary tree. It just happens to be our set of characteristics that enable us to be able to do that. So I can quite see a solution to the Fermi paradox being not necessarily one. Large barrier, but a succession of smaller barriers and you don't need many of them just relatively difficult to overcome quite well, if you start, say, with habitability, general habitability of the planet, then you need a planet to be stable, climate stable over a period of billions of years.

Then you need a planet where abiogenesis takes place. Then you need a planet where complex multicellular life forms come into being. Then you need a planet where that complex multicellular life form develops intelligence. That intelligence has to be of a social nature. We're looking for social creatures with the ability to communicate via a complex grammar because reaching the stars is not going to be the pursuit of an individual right. They need to these creatures, these social creatures with a complex form of language they need to develop.

An advanced technology, they need to develop mathematics and science to understand the universe, and they need to persist for a certain length of time. There are plenty of external threats. Gamma ray burst is a supernova. An asteroid strikes plenty of internal threats that they have to overcome. So that's a barriers. If there's a one in 1000 chance at each of those eight barriers, that immediately knocks the chances down to be effectively zero of their being.

Yeah, it's interesting. One of the things I was going to bring up is you several times in the book you make reference to this principle. I don't know if you gave it a name, but I've been thinking of it as the nonexclusive principle or problem, which is that many solutions that seem to the problem, the Fermi problem that seem plausible, like, for example, you know, well, maybe alien civilizations decide that it's not safe to try to contact other civilizations.

And so that's why we don't see any signs of them. The problem with a lot of solutions like that is, as you point out, there would have to apply to basically all the alien civilizations, that it would have to be true that all the alien civilizations would think that way, because even if a few of them didn't, then, you know, we would see signs of alien life. So they're kind of they're very brittle solutions. But it sounds like you're saying now that if we allow for multiple small solutions to the problem, then the brittleness kind of goes away.

Is that right?

I think so. I have a problem with people who generalize that they are quite happy to suggest that there are 10000 advanced civilizations out there. But the reason that they don't appear, for instance, is that they're all following the prime directive. Star Trek prime directive. Right. Right. And I find that sort of cultural homogeneity that's assumed across 10000 very, very different, presumably different life forms. I find that implausible and as you say, brittle, a brittle solution.

But personally, I find it plausible that a series of small barriers, if you like, or perhaps one large barrier may be abiogenesis is a barrier. We don't know how life got going either. One very large barrier early on or multiple smaller barriers, I think has the capacity to address the Fermi problem. But we don't know. I think that's why it's absolutely vital that we search you know, we need to look for other forms of life within the solar system.

We don't spend nearly enough money on the search for extraterrestrial intelligence. And I don't think we're as creative as we could be in looking for signs of what might be very, very strange civilizations out there. So although I don't think there are civilizations to be found, I really do think that's your that's your preferred solution.

Is it Category three?

It's not my preferred solution, as I preferred epistemically.

Not necessarily emotionally.

I'd very much like to to live in one of these interesting Star Wars Star Trek galaxies. But the silence of the universe tells me, I think, that we're that we're alone. But I do think it's such an important question in science now. It addresses it asks us about our place in the universe. We can't let it go without significant, I think, amount of resource being thrown at this problem. There was one other solution that I wanted to see if you've encountered it's pretty recent, so it wouldn't have made it into your book, but it's a paper by Andrew Sanberg, Toby Audin, Eric Drechsler, and it's called Dissolving the Fermi Paradox.

And what they say is, look, the way people have approached the family paradox in the past is they've plugged in plausible values into the Drake equation for, you know, a number of habitable planets and probability of life per planet, et cetera. And then they've multiply those together. But that's not actually what you should be doing. You should not be multiplying point estimates together. You should be essentially multiplying distributions. So you should have some probability distribution over the number of habitable planet and some probability distribution over, you know, how hard it is for life to develop, etc.

. And when you multiply distributions together, you actually get a much more probability weight on on sort of the low end of the spectrum. In addition to the high end of the spectrum, it just means more uncertainty distributed across the board. So, you know, it's much more plausible that you could end up with only, you know, Earth being the only intelligent, containing the only intelligent civilization because you've just spread out more uncertainty than you would have had with point estimates.

And I think the thing they you know, they unclear what the distribution should be, but they just, you know, take some example point estimates from different people who have estimated these the values of the Drake equation. And they do a lot of normal sampling, but they end up with something like an eight percent chance, given the point estimates people have made for the values in the Drake equation, an eight percent chance that Earth is the only intelligent civilization.

How do you feel about that solution?

Yes, it came out, unfortunately, after the book was published. I find it really quite an elegant approach, and I think you've summed it up perfectly. They that they take their distributions from the estimates that appear in the literature as the proxy. But yeah, exactly. If you do that, I think the conclusion of the paper is that you shouldn't be surprised if we live in a universe that is empty. It's certainly given the uncertainties in these estimates, it's not surprising if we find ourselves in that situation.

But that's again, not to say that we are alone, right.

It's just that right to be less less surprising. Yes. It's just not a surprising result necessarily. Yeah.

It's just so interesting that we can take the estimates that people have already made that caused them to find find it surprising if we lived in an uninhabited universe or if we were the only intelligent civilization. You take those exact estimates and then create distributions instead of letting people just use their point estimates and get a very different result. That's yeah, I guess that that's why I agree with elegant an elegant solution.

Yes, it's a nice paper and I'd recommend anyone to read it. It's interesting as well that if you talk to biologists about this problem, they're much less likely, in my experience, to be of the opinion that there must be hundreds, thousands, tens of thousands of intelligent civilizations out there. Then physicists, physicists tend to be, I think, much more of the opinion that we've got this big numbers, ten to the twelve planets out there. And they tend, I think, to make this point estimate.

They do what Fermi did and they come up with a large number. And it's it's an interesting, perhaps scientific, cultural.

What's your diagnosis of the that the divide? I think we physicists were just arrogant. We know epic arrogance, I mean, I'm not disputing that, but but arrogance in the sense that you think like how is it arrogant to think that life that abiogenesis would be easy?

Well, I think there are elements that a biologist would think of as contingence, whereas a physicist might well take a much more deterministic view. I'm generalizing and. Well, I ask you to. So don't bother.

But but in my experience, those two populations tend to look at it in a slightly different way. So biology biologists would look at just the unlikeliness of. Our sort of intelligence perhaps appearing this is a physicist who might well look, it's perhaps implicitly in the thinking being that intelligence is a goal towards which evolution is heading.

I don't think it is interesting. Well, I want to let you go, Steven, but before I do, I want to invite you to nominate the rationally speaking pick of this episode. And I I'd like it to be some things, some book or blog or article that you don't agree with, or at least you definitely don't fully agree with, but that you think is nevertheless well reasoned or, you know, compelling enough that it deserves attention. What would your pick be?

It's it's a ball. It's not a book that I disagree with, but it's a book that takes perhaps a different approach to what I've been explaining here. It's called The Cosmic Zoo Complex Life on Many Worlds. It was published in, I think, December 2017. So it's quite recent. It's by Dick Schulz on the couch. And Dick takes this approach that once life starts and we don't know how, that almost inevitably it's going to explore various pathways that lead to a complex biosphere, that sort of biosphere that we experience here on planet Earth.

So we would take the view that many of the steps that I might argue are perhaps unlikely are actually likely. And it's well-written. It's beautifully argued and well recommended. Excellent. Well, we'll link to the cosmic zoo along with where is everybody and your website, where people can check out several of your other books as well. And Steven, it's been a pleasure having you on the show. Thanks so much for joining us.

I really enjoyed it. Thank you, Julia. This concludes another episode of Rationally Speaking. Join us next time for more explorations on the borderlands between reason and nonsense.