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Brian Cox: The terrifying possibility of the Great Filter — Transcript

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0:00- Enrico Fermi is one of the great physicists,
0:03legendary Italian physicists
0:05who laid many of the foundations
0:07of modern 20th century physics,
0:09so-called Fermi-Dirac statistics and all sorts of things.
0:13If you do a degree in physics, then you will spend
0:15a lot of time revising equations
0:18and theories that Fermi did.
0:19One of the great legends.
0:21The Fermi paradox is probably the thing
0:25he spent least time on actually,
0:27is almost one throwaway remark that he delivered.
0:32And the question is, where are they?
0:36By they, I mean aliens. (pensive music)
0:40- [Announcer] The Great Filter,
0:41Why Civilizations May Not Survive.
0:45- The heart of the Fermi paradox is this.
0:48We know that we live in a big old galaxy,
0:54in a big old universe.
0:56And let's, for the purposes of this discussion,
0:59confine ourselves to the Milky Way galaxy.
1:02The Milky Way galaxy we now know
1:04has something like 400 billion suns.
1:08And we now know that most of those suns
1:11have planetary systems around them,
1:13so trillions of planets.
1:15The galaxy's been around for pretty much
1:17the age of the universe, 10 billion years plus.
1:20And so there's a lot of real estate,
1:22and there's been plenty of time
1:25for civilizations to develop in the galaxy.
1:29The Fermi paradox at its heart
1:32is the statement that, not withstanding the fact
1:37that there have been billions of years
1:40on billions of worlds for civilizations to arise,
1:46we see no evidence of any of them in the galaxy at all.
1:51So the paradox is why it's a paradox.
1:54And I think it's a very good question.
1:57It's an extremely good question,
1:59and there can be many answers.
2:00And the great fun or the great,
2:03I would say, the intellectual value
2:04of the Fermi paradox.
2:06So if we accept that we haven't seen any,
2:08so let's accept that.
2:09Let's accept that, you know, there isn't a UFO
2:12sat in some warehouse in Roswell or something like that.
2:15Let's accept that we haven't seen any.
2:17Let's accept, well, we have to accept the picture
2:20that I've just given you about the Milky Way galaxy
2:22and its age 'cause that's a measurement, so we know that.
2:24The question is then why, how do we resolve
2:28these apparent contradictions and paradoxes?
2:32So one answer to the Fermi paradox,
2:35this is the idea that we don't seem to see anyone,
2:38is that no one ever evolved, right?
2:42So life didn't get complex.
2:44Why might we think that?
2:46Well, what did we need to produce
2:49our civilization on this planet?
2:52Well, on this planet, one thing we needed was time.
2:56We have good evidence that life
2:59was present on this planet 3.8 billion years ago,
3:03perhaps even earlier.
3:04The planet is four and a half billion years old.
3:07So we know, as a matter of fact,
3:10as an observation on this planet,
3:13that life was present 3.8 billion years ago.
3:16But it took 3.8 billion years,
3:19give or take a few tens of thousands of years,
3:23to go from the origin of life to a civilization,
3:25let's say, from cell to civilization, 4 billion years.
3:29That's one third of the age of the universe.
3:32So a possible answer to the Fermi paradox,
3:36the question of why there are no civilizations,
3:39is because the Earth is pretty much unique
3:43in the Milky Way galaxy, in that it was stable enough,
3:48the climate, the conditions on Earth were stable enough
3:51for long enough for life to go from cell to civilization.
3:57If you think about it, that's a big ask.
3:59What I'm saying is on this planet,
4:01an unbroken chain of life existed
4:05for almost 4 billion years,
4:07not withstanding the fact that we live
4:09in a violent universe.
4:10The Sun must have been stable enough for long enough.
4:15We know the output of the Sun has changed
4:17over those billions of years, but it's not changed
4:20so radically that it managed to erase,
4:23destroy life on Earth.
4:25We know that we live in a violent universe.
4:28We know there are supernova explosions all over the place.
4:31It turns out that there have been no stars
4:35massive enough to explode as a supernova
4:39in a way that would damage life on Earth
4:41or erase life on Earth in this vicinity for 4 billion years.
4:46We know that nothing has happened,
4:48like we know that there there've been impacts
4:50on the Earth, right?
4:51We know that the famous impact that wipes out
4:54the large dinosaurs, there's been no impact
4:58big enough to destroy the unbroken chain
5:00or break the unbroken chain of life for 4 billion years.
5:03So maybe, maybe it's the case
5:07that whilst there are billions of planets
5:10which may have liquid water on the surface,
5:13may have oceans that can support life,
5:16it may be that none of those planets in the Milky Way galaxy
5:19have been stable enough for long enough
5:21to produce a civilization.
5:22So that would be a property of the planet itself,
5:26the so-called rare Earth hypothesis.
5:28Actually I should say it's a property of a solar system.
5:31It's not really just a property of the planet,
5:34it's a property of the parent star.
5:36You could ask the question, well, if it was a binary system,
5:39for example, a binary star system,
5:40many stars are binary star systems,
5:43is it possible to have a planet with a stable climate,
5:48stable enough orbit in a binary star system
5:52to support an unbroken chain of life for 4 billion years?
5:55Perhaps not.
5:56When we talk about Earth, I think I would like to talk
6:00about rare solar system,
6:02another possibility with the Fermi paradox
6:05is that it's not a paradox, they are here.
6:07So there are intelligent civilizations out there,
6:10and they are present in the solar system.
6:12It's possible.
6:13Let's think, for example, what such an intelligence
6:16might look like.
6:17Well, who knows?
6:18They could have sent nano machines to our solar system.
6:23There could be probes all over the place
6:25in the solar system, but if they're the size of an iPhone,
6:27then we'd have no way of detecting them.
6:30So it could be the technology
6:33of a sufficiently advanced alien species, a civilization,
6:37is so beyond anything we can comprehend or detect
6:41that we haven't seen it, and we've been fooled into thinking
6:44that there are no advanced civilizations in the galaxy.
6:47And that's certainly entirely possible.
6:52Another possibility, another possible resolution
6:54to the Fermi paradox is just that the galaxy is so big,
6:59the distances between stars are so great
7:03that if you imagine there's another civilization,
7:07even if they had the most powerful radio transmitters
7:11you could imagine, or even if they'd spread out
7:13to neighboring solar systems,
7:15then it may just be that the distances are so great
7:19that the signals are diluted, that we can't detect them
7:22because they're too weak.
7:24Or that it is just very, very, very difficult
7:28in an engineering sense to build interstellar spacecraft.
7:32Now, perhaps you can build a spacecraft
7:33that can hop a few light years away
7:36to the nearby solar system,
7:37four light years, in our case to Alpha Centauri.
7:40But you can't build spacecraft that can traverse a galaxy.
7:45That's a possibility.
7:47One of the arguments against that for me
7:50is the argument, it's called the space travel argument
7:52against the existence of extraterrestrial life.
7:56And it's often framed in terms of self-replicating machines,
7:59so-called Von Neumann machines.
8:01So imagine it's possible for us,
8:04for a civilization, to build a machine,
8:07some kind of AI that's sufficiently smart and capable,
8:12that it can fly to a nearby solar system,
8:15reproduce itself, copy itself, and then send the copy out
8:19to the next solar system and so on.
8:21So you have, if you build a, one, successful replicator,
8:28you have an exponentiation of replicators.
8:32You have one, and then two, and then four,
8:35and then eight and so on, exponential growth.
8:37And you can show that, even given our rocketry technology,
8:42you can cover a galaxy like the Milky Way
8:45in a reasonably short space of time.
8:48By reasonably short, I might even mean
8:51a hundred million years, right?
8:53That's reasonably short on galactic timescales.
8:56But the key point is once a single
8:59successful replicator has been launched,
9:03then it is inevitable that over a few tens
9:07of millions of years, the galaxy will be covered
9:10with replicators, and we don't see any evidence of them.
9:14It's possible that we can infer,
9:17that if we assume that we could detect them,
9:20then the absence of them may allow us to infer
9:24that no civilization has ever got to that point.
9:27And I think that's quite a persuasive argument.
9:30Now, it's possible that there are many civilizations
9:33out there, but the advanced civilizations
9:36choose to remain hidden,
9:38sometimes called the dark forest hypothesis,
9:41the quarantine hypothesis.
9:43We've been asked to make moral judgments
9:45or judgments on how a civilization will behave,
9:50what they will choose to do.
9:51And that's, of course, impossible (chuckles) to judge.
9:54But let's imagine civilizations,
9:57when they get technologically advanced
9:59also get intellectually and morally advanced.
10:02And let's say that they choose, perhaps for good reason,
10:06let's say they choose to remain hidden
10:07because they don't want to draw attention to themselves.
10:10Let's say it's inevitable
10:12that if you think about it carefully
10:15and you think there are other advanced civilizations
10:17out there, then you choose to remain silent.
10:21You hide yourself as best you can.
10:23It's possible that that's the way
10:25that a civilization would think.
10:26Maybe that's a logical thing to do.
10:28I find it difficult to believe,
10:34given human history, that that's the way
10:38that intelligence civilizations behave.
10:40We certainly haven't made any attempt
10:43to remain hidden so far.
10:45We've broadcast radio signals out to the stars,
10:49the Arecibo message, for example, albeit weak ones.
10:52We've launched on our space probes, like Voyager,
10:56maps, pulsar maps in that case,
10:59which shows the location of our solar system
11:02should any other civilization find it.
11:04So at least at the moment, we haven't come to the view,
11:08which may be a wise view, but we haven't got there
11:11that we should remain silent.
11:12Quite the opposite, we've tried (chuckles)
11:15at every opportunity to broadcast our existence.
11:19Maybe that's 'cause Carl Sagan argued, I think,
11:23that a sufficiently advanced civilization,
11:26a civilization that can build interstellar spacecraft
11:29and communicates across interstellar distances,
11:32perhaps is wise enough to have overcome
11:36those primitive instincts, the instinct to cause trouble,
11:40to fight wars, to colonize,
11:43to walk over other civilizations.
11:45Perhaps it's inevitable that with technological advance
11:48ultimately comes wisdom, but it's hypothesis.
11:51Maybe it is.
11:52Maybe it's just anybody sufficiently clever
11:55to build an interstellar spaceship
11:57will be also sufficiently clever to hide it
11:59and not draw attention to themselves.
12:02Maybe it's a moral, maybe it's like "Star Trek."
12:04Maybe it's the Prime Directive.
12:05Maybe it's morally certain
12:08that if you're sufficiently advanced,
12:10you decide to take the position
12:13that you will never introduce yourself
12:15or interfere with another civilization.
12:17Maybe that becomes a kind of law of nature
12:20for sufficiently intelligent beings.
12:22Maybe that's conceivable as well.
12:24Another explanation for the Fermi paradox
12:26might be that civilizations live and die.
12:29They rise and then they fall.
12:32And because of the sheer timescales involved
12:36and the sheer size of the galaxy,
12:39no two civilizations ever overlap.
12:42I once had the great pleasure of meeting Frank Drake,
12:46the Drake equation legend, in his house.
12:50And he also grows orchids.
12:52And I arrived at his house just coincidentally
12:55on the day that this rare orchid flowers,
12:58and it flowers for I think one or two days.
13:01And then goes away again for the year.
13:03And then flowers again the next year for one or two days.
13:07And he used it as an analogy.
13:08He said, "Well, maybe civilizations are like that."
13:10So maybe civilizations are like rare orchids.
13:13And so they flower and die and flower and die.
13:15And just because of the sheer timescales involved,
13:18none of them ever overlap.
13:19And so there could be the wreckage,
13:22the ashes, the fossils of civilizations out there.
13:25But of course, we'd have no way of knowing
13:29until we explore the galaxy
13:31and maybe find the ruins of these other civilizations.
13:34Who knows?
13:35I mean, it's quite plausible if you think about it.
13:37Are we gonna exist in 10,000 years time?
13:40It's, to a large extent, in our hands.
13:43Maybe we're (chuckles) sufficiently stupid
13:46that we won't exist beyond the next century.
13:49There's an idea in this field.
13:52I'm trying to explain the Fermi paradox
13:53called the Great Filter.
13:55Now, the Great Filter can lie in our future or our past.
14:00So let's think about what it would mean for a Great Filter
14:02to lie in our future.
14:04That would mean that civilizations
14:07do arise in the Milky Way galaxy
14:10and get to somewhere like the position that we are at now.
14:15So they develop rocketry, they develop nuclear power,
14:19nuclear weapons, for example, they industrialize.
14:22But then there's a filter in the future
14:25that stops them becoming true space-fairing civilizations.
14:29So stops them becoming multi-planetary species
14:32and stops them ultimately traveling between solar systems
14:36to begin to colonize a galaxy.
14:39So why might that be?
14:40Why might there be a filter
14:43waiting for us in our not-too-distant future
14:47that's gonna stop us going onto Mars
14:49and stop us escaping our solar system?
14:51What might stop us from becoming an interplanetary species
14:55and ultimately traveling out beyond our solar system?
14:58I don't think it's technology, as far as I can see,
15:01I don't see anything in the laws of nature in principle
15:05that would stop us from becoming an interstellar species.
15:10Might be 1,000 years in the future,
15:1210,000 years in the future,
15:14might be 100,000 years in the future.
15:16Even that, right, 100,000 years,
15:19it's a blink of an eye in the lifetime of the universe,
15:22in the lifetime of a galaxy.
15:24So I don't see any reason in principle
15:26why we couldn't become an interplanetary,
15:29interstellar species
15:31other than potentially our own stupidity.
15:34And I think that probably, it could be one of the reasons
15:38why we don't see any other civilizations around.
15:42It could be that our knowledge,
15:45our scientific prowess exceeds our wisdom,
15:50exceeds our political skill.
15:53It could be that once a civilization develops
15:56the means to destroy itself in the form,
15:59for example, of nuclear weapons or biological weapons
16:03or maybe some kind of a lack of control of AI, who knows?
16:09It may be that once a civilization acquires
16:12that technical know-how, then it goes ahead
16:16and destroys itself essentially inexorably
16:19because it's just too difficult politically
16:22to run a civilization that has the power to destroy itself.
16:26If you look back through our recent history,
16:27there've been several occasions that we know about,
16:31that I know about and you know about,
16:33where we came very close to destroying ourselves,
16:35or at least setting us back to the Stone Age, basically.
16:38The Cuban Missile Crisis, well-documented events
16:42in the 1980s, for example, where there could
16:45have been nuclear launches and weren't,
16:46and I'm sure there are many others that we don't know about.
16:49There's the challenge of climate change.
16:51We're completely incapable of coming together at the moment
16:57as a global civilization to address that challenge.
17:00That could set our civilization back.
17:02Biological weapons, the threat of AI,
17:06we seem to be completely incapable
17:08of regulating those threats.
17:10So it might just be almost a law of nature.
17:12Things like us, (chuckles) things that can build
17:16an industrial civilization are just inherently too stupid
17:21to get out there to the stars.
17:22And I wouldn't put that past us.
17:24My favorite's the other one.
17:25So I'll do the other Great Filter.
17:28If I was to guess, and this is a guess, right?
17:30If I was to guess why we see no evidence
17:34of other civilizations out there,
17:36the so-called Great Silence is what astronomers call it,
17:40is because there aren't any, and there never have beat any.
17:43That's my guess.
17:44The reason I guess that, and I emphasize it's a guess,
17:48is biology.
17:49So if you look at the history of life on Earth,
17:51then we see that life began 3.8 billion years ago,
17:55let's say.
17:56But then we see for the best part of 3 billion years
18:00on this planet that there's nothing more complex
18:02than a single cell, 3 billion years.
18:05It's suddenly in the last billion years or so,
18:07perhaps a little bit less, that multicellular life
18:11has existed on this planet.
18:12And there could be good biological reasons for that.
18:15One that springs to mind is the evolution
18:18of what's called the eukaryotic cell,
18:20which is the cell with the cell nucleus
18:22and all little organelles and chloroplasts in plants
18:25and all those things which form
18:26all multicellular living things on the planet.
18:29Those cells, which seem to be prerequisite
18:33for complex multicellular life,
18:35evolved once on this planet as far as we can tell.
18:40It's pretty widely accepted.
18:42It's called the Fateful Encounter hypothesis.
18:44And so it seems that there is a very unusual
18:46evolutionary event at some point, maybe a billion,
18:51a billion and a half, even 2 billion years ago,
18:53that laid the foundations for us.
18:56If that's typical, if it typically is the case
19:00that it takes 4 billion years from cell to civilization,
19:04then I think there may be very few planets
19:06in a typical galaxy which are stable enough
19:09for long enough for that process to proceed.
19:13And we could be, for all we know, on the fortunate end
19:16(chuckles) of evolutionary timescales, we don't know.
19:20Let's imagine that actually we were on the lucky side
19:23and really on a typical planet, if there is such a thing,
19:27then it takes three or four times as long.
19:30That would exceed the current age of the universe.
19:33My guess is that whilst I think there might be microbes
19:36all over the place, I wouldn't be surprised,
19:39I'd be delighted, but I wouldn't be surprised
19:41if we found evidence of microbes on Mars,
19:44Europa, Enceladus,
19:47even in the subsurface oceans of places
19:50potentially even as far out as Pluto, right?
19:53Subsurface lakes, if they exist,
19:56liquid water below the surface, who knows?
19:58I wouldn't be surprised if we find microbes
19:59all over the place.
20:00But a galaxy full of complex living things,
20:04other planets with not only complex life, but sentient life,
20:08things as smart as us, things smart enough to build rockets
20:12that head out to the stars,
20:14my guess is that a typical galaxy may have less than,
20:20on average, less than one civilization per galaxy,
20:24let's put it that way.
20:25But actually, just to say it is a very famous book
20:27as strongly recommend, Barrow and Tipler
20:29called "The Anthropic Cosmological Principle."
20:30It's a great book, one of the books I grew up with.
20:33And in that book, Barrow and Tipler say that in their view,
20:38there might be one civilization in the observable universe,
20:43(chuckles) which should be us, right?
20:46So who knows whether we should go that far,
20:49but I think civilizations are very rare.
20:51And I think it's the biology.
20:53So I'm guessing, I'm giving you a guess,
20:55I'm saying that in my opinion,
20:57I think there's one civilization in the Milky Way galaxy,
21:01and there only has ever been one,
21:03and there might only ever be one.
21:04And that's us, which by the way means
21:07that we have a tremendous responsibility
21:08not to mess this up, because as I said to the,
21:11I was asked to give a video introduction
21:13to the climate summit, the COP26 climate summit
21:16in Glasgow recently.
21:17"Give the world leaders one minute," they said.
21:19"You've got a video, say something to them."
21:22And I said, "I think, let's assume that we're
21:24the only civilization currently in the Milky Way galaxy,
21:27perhaps the only civilization there will ever be.
21:30That means the Earth is the only island of meaning
21:32in a sea of 400 billion suns.
21:35And so if we destroy this,
21:36we might destroy meaning in a galaxy forever.
21:39Discuss."
21:40So that's my guess.
21:43However, that's a hypothesis.
21:46I will be delighted if it turns out that's not true.
21:50And that's not just because it removes
21:52some responsibility from me and you and everybody else.
21:56To preserve intelligence in a galaxy of 400 billion suns,
22:00the weight of responsibility is heavy.
22:03But also every scientist should be delighted
22:08if they are shown to be wrong.
22:10Because the moment you are shown to be wrong,
22:12it means you've learn something.
22:14And that's the way that knowledge progresses.
22:16So nobody should be worried about making a guess,
22:19advancing a hypothesis, an educated guess,
22:23or even an uneducated guess.
22:24Don't worry about doing that
22:26as long as the moment it turns out you're wrong,
22:30and me being wrong, by the way,
22:31would constitute a flying saucer landing
22:34and some aliens coming out like ET and saying hello.
22:37So that would be brilliant.
22:38But it would be doubly brilliant because it would turn out
22:42that I'd learned something about the universe,
22:44which is that complex civilizations are not as rare
22:46as I think they are, or civilizations aren't the rare.
22:49So that would be a good thing. So there's a lesson.
22:51(pensive music)
22:52- [Announcer] Wanna support the channel?
22:53Join the Big Think members community

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