Alex Filippenko: Supernovae, Dark Energy, Aliens & the Expanding Universe | Lex Fridman Podcast #137

Lex Fridman 0:00 The following is a conversation with Alex Filippenko, an astrophysicist and professor of astronomy from Berkeley. He was a member of both the Supernova Cosmology Project and the High-Z Supernova Search Team, which used observations of the extragalactic supernova to discover that the universe is accelerating, and that this implies the existence of dark energy. This discovery resulted in a 2011 Nobel Prize for Physics. Outside of his groundbreaking research, he's a great science communicator and is one of the most widely admired educators in the world. I really enjoyed this conversation and I'm sure Alex will be back again in the future. Quick mention of each sponsor, followed by some thoughts related to the episode. Neuro, the maker of functional sugar-free gum and mints that I use to give my brain a quick caffeine boost. BetterHelp, an online therapy with a licensed professional. MasterClass, online courses that I enjoy from some of the most amazing humans in history. And Cash App, the app I use to send money to friends. Please check out these sponsors in the description to get a discount and to support this podcast. As a side note, let me say that as we talk about in this conversation the objects that populate the universe are both awe-inspiring and terrifying in their capacity to create and to destroy us. Solar flares and asteroids lurking in the darkness of space threaten our humble fragile existence here on Earth. In the chaos, tension, conflict, and social division of 2020, it's easy to forget just how lucky we humans are to be here. And with a bit of hard work, maybe one day we'll venture out towards the stars. If you enjoy this thing, subscribe on YouTube, review it with five stars on Apple Podcast, follow on Spotify, support on Patreon, or connect with me on Twitter @lexfridman. And now, here's my conversation with Alex Filippenko.

Lex Fridman 2:08 Let's start by talking about the biggest possible thing, the universe.

Alex Filippenko 2:12 Sure.

Lex Fridman 2:12 Will the universe expand forever or collapse on itself?

Alex Filippenko 2:16 Well, you know, that's a great question. That's one of the big questions of cosmology. And of course, we have evidence that the matter density is sufficiently low that the universe will expand forever. But not only that, there's this weird repulsive effect, we call it dark energy for want of a better term, and it appears to be accelerating the expansion of the universe. So if that continues, the universe will expand forever, but it need not necessarily continue. It could reverse sign in which case the universe could, in principle, collapse at some point in the far, far future.

Lex Fridman 2:53 So, like, in terms of ad- investment advice, if you were to give me, and then to bet all my money on one or the other, w- where does your intuition currently lie?

Alex Filippenko 3:01 Well, right now I would say that it would expand forever, because I think that the dark energy is likely to be just quantum fluctuations of the vacuum. The vacuum zero energy state is not a state of zero energy, that is, the ground state is a, a state of some elevated energy which has a repulsive effect to it. And that will never go away because it's not something that changes with time. So if the universe is accelerating now, it will forever continue to do so.

Lex Fridman 3:31 And yet,

Lex Fridman 3:32 I mean, you so effortlessly mentioned dark energy. Do we have any understanding of, of what the heck that thing is?

Alex Filippenko 3:39 Well, not really, but we're getting progressively better observational constraints. So, you know, different theories of what it might be predict different sorts of behavior for the evolution of the universe. And we've been measuring the evolution of the universe now, and the data appear to agree with the predictions of a constant density vacuum energy, a zero point energy. But one can't prove that that's what it is because one would have to show that the numbers, that the measured numbers agree with the predictions to an arbitrary number of decimal places. And of course even if you've got eight, nine, 10, 12 decimal places, what if in the 13th one the measurements significantly differ-

Lex Fridman 4:25 Mm-hmm.

Alex Filippenko 4:25 ... from the prediction? Then the dark energy isn't this vacuum state, uh, ground state energy of the, of the vacuum, and so then it could be some sort of a, a field, some sort of a new energy, a little bit like, like light, like electromagnetism but very different from light, that fills space. And that type of energy could in principle change in the distant future. It could become gravitationally attractive for all we know. There is a historical precedent to that, and that is that the inflation with which the universe began when the universe was just a tiny blink of an, of an eye old, a trillionth of a trillionth of a trillionth of a second, you know, the universe went whoosh, it exponentially expanded. That dark energy-like substance, we call it the inflaton, that which inflated the universe, later decayed into more or less normal gravitationally attractive matter. So the exponential early expansion of the universe did transition to a deceleration which then dominated the universe for about nine billion years, and now this small amount of dark energy-

Lex Fridman 5:39 (laughs) .

Alex Filippenko 5:39 ... started causing an acceleration about five billion years ago. And whether that will continue or not is something that we'd like to answer, but I don't know that we will any time soon.

Lex Fridman 5:50 So there could be this interesting field that we don't yet understand that's morphing over time, that's changing the way the universe is- is expanding. I mean...It, it's funny that you were thinking through this rigorously like an experimentalist. (laughs)

Alex Filippenko 6:06 Yeah.

Lex Fridman 6:06 But the, w- what about like the fundamental physics of dark energy? Is there any understanding of, uh, what the heck it is? Or is it, or is this the kind of, uh, the god of the gaps or the field of the gaps, uh, so like-

Alex Filippenko 6:23 (laughs)

Lex Fridman 6:23 ... it, there must be something there because of what we're observing?

Alex Filippenko 6:26 I, I'm very much a person who believes that there's always a cause, you know? There-

Lex Fridman 6:31 Right.

Alex Filippenko 6:31 ... there are no, um, miracles, uh, of a supernatural nature, okay?

Lex Fridman 6:37 Yeah.

Alex Filippenko 6:38 Uh, so, I mean, there are two broad categories. Either it's the vacuum zero point energy or it's some sort of a, a new energy field that pervades the universe. The latter could change with time. The former, the vacuum energy, cannot.

Lex Fridman 6:55 Right.

Alex Filippenko 6:55 So if it turns out that it's one of these new fields, and there are many, many possibilities, they go by the name of, you know, quintessence and things like that, but there are many categories of those sorts of fields. We try with data to rule them out by comparing the actual measurements with the predictions.

Lex Fridman 7:16 Okay.

Alex Filippenko 7:16 And some have been ruled out, but many, many others remain to be tested and the data just have to become a lot better before we can rule out most of them and become reasonably convinced that this is a vacuum energy.

Lex Fridman 7:31 So there is hypotheses for different fields, like-

Alex Filippenko 7:34 Oh, yeah.

Lex Fridman 7:34 ... with names and stuff like that?

Alex Filippenko 7:35 Yeah, yeah. You know, generically quintessence like the Aristotelian fifth essence, but there are many, many versions of quintessence. There's K-essence. There's even ideas that, you know, this isn't something from within, this dark energy, but rather there are a bunch of, say, bubble universes surrounding our universe and this whole idea of the multiverse is not some crazy Mad Men-type idea anymore. It's, you know, real card-carrying physicists are seriously considering this possibility of a multiverse.

Lex Fridman 8:05 Yeah.

Alex Filippenko 8:06 And some types of multiverses could have, you know, a bunch of bubbles on the outside which gravitationally act outward on our bubble because gravity or gravitons, the, the quantum particle that is thought to carry gravity is, is thought to traverse the bulk, the space between these different little bubble membranes and stuff. And so it's conceivable that these other universes are pulling outward on us. That's not a favored explanation right now, but, but really nothing has been ruled out. No class of models has been ruled out completely. Certain examples within classes of models have been ruled out, but in general, I think we still have really a lot to learn about what's causing this observed acceleration of the expansion of the universe, be it dark energy or some forces from the outside or, or perhaps, you know, I guess it's conceivable that... And sometimes I wake up in the middle of the night screaming-

Lex Fridman 9:07 (laughs) Yeah.

Alex Filippenko 9:09 ... that dark energy, that which causes the acceleration, and dark matter, that which causes galaxies and clusters of galaxies to be bound gravitationally even though there's not enough visible matter to do so, maybe these are our 20th and 21st century Ptolemaic epicycles.

Lex Fridman 9:28 Mm-hmm.

Alex Filippenko 9:28 So Ptolemy had a geocentric, an Aristotelian view of the world, everything goes around Earth, but in order to explain the backward motion of planets among the stars-

Lex Fridman 9:39 Mm-hmm.

Alex Filippenko 9:40 ... that happens every year or two, or sometimes several times a year for Mercury and Venus, you needed the planets to go around in little circles called epicycles which themselves then went around Earth.

Lex Fridman 9:51 Yes.

Alex Filippenko 9:52 And in this, in this part of the epicycle where the planet is going in the direction opposite to the direction of the overall epicycle, it can appear in projection to be going backward among the stars.

Lex Fridman 10:05 Yeah.

Alex Filippenko 10:05 So-called retrograde motion. And it was a brilliant mathematical scheme. In fact, he could've added epicycles on top of epicycles and reproduced the observed positions of planets to arbitrary accuracy.

Lex Fridman 10:19 Yeah.

Alex Filippenko 10:19 And this is really the beginning of what we now call Fourier analysis, right?

Lex Fridman 10:24 Yeah.

Alex Filippenko 10:24 Any periodic function can be represented by a sum of sines and cosines-

Lex Fridman 10:29 (laughs)

Alex Filippenko 10:30 ... of different periods, amplitudes, and phases.

Lex Fridman 10:33 Yeah.

Alex Filippenko 10:33 So it could've worked arbitrarily well, but other data, you know, show that in fact Earth is going around the sun.

Lex Fridman 10:41 Yeah.

Alex Filippenko 10:41 Um, so are dark energy and dark matter just these Band-Aids that we now have to try to explain the data but they're just completely wrong? That, that's a possibility as well. And as a scientist I have to be open to that possibility, as an open-minded scientist.

Lex Fridman 10:59 How do

Lex Fridman 11:00 you, how do you put yourself in the mindset of somebody that, or a majority of the scientific community or majority of people believe that the Earth, everything rotates around Earth, how do you put yourself in that mindset and then take a leap to, uh, propose a model that the sun is in fact at the center of the s- the, the solar system?

Alex Filippenko 11:26 Sure, I mean, so that puts us back in the shoes of Copernicus, right?

Lex Fridman 11:29 Right.

Alex Filippenko 11:30 500 years ago where he had this philosophical preference for the sun being the dominant body in what we now call the solar system. The observational evidence in terms of the measured positions of planets was not better explained by the heliocentric sun-centered system. It's just that, you know, Copernicus saw that the sun is the source of all our light and heat.

Lex Fridman 11:58 Oh, wow, interesting. So it's-

Alex Filippenko 11:59 And he, and he had, you know, he knew from other studies that it's, it's far away, so the fact that it appears as big as the moon means it's actually way, way bigger, because even at that time it was known that the sun is much farther away than the moon.So, um, you know, he just felt, wow, it's big, it's bright. What if it's the central thing? But the observed positions of planets at the time, in the early to mid-16th century, under the heliocentric system was not a better match, at least not a significantly better match than Ptolemy's system, which was quite accurate and lasted 1,500 years.

Lex Fridman 12:37 Yeah.

Alex Filippenko 12:37 Yeah.

Lex Fridman 12:39 That's so fascinating to think that the philosophical predispositions that you bring to the table are essen- so, like, you have to have a young person come along that has a weird infatuation with the sun.

Alex Filippenko 12:51 Yeah. (laughs)

Lex Fridman 12:51 (laughs) That, that almost philosophically is... Like, however their upbringing is, they're more ready for whatever the more, the simpler answer is.

Alex Filippenko 13:02 Right.

Lex Fridman 13:03 Oh, that's, um, that's kind of sad. It's, uh, sad from an individual descendant of ape perspective-

Alex Filippenko 13:10 Yeah.

Lex Fridman 13:11 ... because then that means, like me, like you as a scientist, you're stuck with whatever the heck philosophies you brought to the table, and you might be almost completely unable to, to think outside this particular box you've built.

Alex Filippenko 13:25 Right. This is why I'm saying that, you know, as an objective scientist, one needs to have an open mind to crazy-sounding new ideas.

Lex Fridman 13:34 Sounding, yeah.

Alex Filippenko 13:34 And, you know, even Copernicus was very much a man of his time and dedicated his work to the Pope. He still used circular orbits. The sun was a little bit off-center, it turns out-

Lex Fridman 13:45 Mm-hmm.

Alex Filippenko 13:46 ... and a slightly off-center circle looks like a slightly eccentric elliptical orbit. So then when Kepler, in fact, showed that the orbits are actually, in general, ellipses, not circles, the reason that, you know, he needed Tycho Brahe's really great data to show that distinction was that a, a slightly off-center circle is not much different from a slightly eccentric ellipse. And so there wasn't much difference between Kepler's view and, uh, Copernicus's view, and, and Kepler needed the better data-

Lex Fridman 14:22 Mm-hmm.

Alex Filippenko 14:22 Uh, Tycho's, Tycho Brahe's data. And so that's, again, a, a great example of, of, of science and obser- observations and experiments working together with hypotheses, and they, they kind of bounce off each other, they play off of each other, and you continually need more observations. And it wasn't until Galileo's work, uh, around 1610 that actual evidence for the heliocentric hypothesis emerged. It came in the form of Venus, the planet Venus going through all of the possible phases, from new to crescent to quarter to gibbous to full to waning gibbous, third quarter, waning crescent, and then new again. It turns out in the Ptolemaic system, with Venus between Earth and the sun, but always roughly in the direction of the sun, you could only get the new and crescent phases of Venus. But the observations showed a full set of phases, and moreover, when Venus was gibbous or full, that meant it was on the far side of the sun. That meant it was farther from Earth than when it's crescent, so it should appear smaller, and indeed it did. So that was a, that was, you know, the nail in the coffin, in a sense. And then, you know, Galileo's other great observation was that Jupiter has moons going around it, the four Galilean satellites-

Lex Fridman 15:44 Mm-hmm.

Alex Filippenko 15:44 ... and even though Jupiter moves through space, so too do the moons go with it. So first of all, Earth is not the only thing that has other things going around it. And secondly, Earth could be moving, as Jupiter does-

Lex Fridman 15:58 Mm-hmm.

Alex Filippenko 15:58 ... and, you know, things would move wi- with it. We, we wouldn't fly off the surface, and our moon wouldn't be left behind, and all this kind of stuff. So that was a, a big breakthrough as well, but it wasn't as definitive, in my opinion, as the phases of Venus.

Lex Fridman 16:13 Perhaps I'm revealing my ignorance, but I didn't realize how much data they were working with.

Alex Filippenko 16:18 Yeah.

Lex Fridman 16:18 So there's, uh... So it wasn't Einstein or Freud thinking in theories. It was a lot of data, and you're playing with it and seeing how to make sense of it. So isn't, it, it isn't just coming up with completely abstract thought experiments.

Alex Filippenko 16:36 Yeah.

Lex Fridman 16:36 It's looking at the data, the astronomy-

Alex Filippenko 16:38 Sure, I mean, look at Newton's great work, right? The Principia. It was based in part on Galileo's observations of balls rolling down inclined planes, supposedly fall- falling off the Leaning Tower of Pisa, but that's-

Lex Fridman 16:51 Okay.

Alex Filippenko 16:51 ... probably apocryphal.

Lex Fridman 16:52 Yeah.

Alex Filippenko 16:53 In any case, you know, um, the, the, the Inquisition actually did, or the Roman Catholic Church, uh, did, did history a favor, not that I'm condoning them-

Lex Fridman 17:03 (laughs)

Alex Filippenko 17:03 ... but they placed Galileo under house arrest-

Lex Fridman 17:06 Yeah.

Alex Filippenko 17:06 ... and that gave Galileo time-

Lex Fridman 17:09 (laughs)

Alex Filippenko 17:09 ... to publish, to assemble and publish the results of his experiments that he had done decades earlier. It's not clear he would have had time to do that, you know, had he not been under, uh-

Lex Fridman 17:20 (laughs)

Alex Filippenko 17:20 ... house arrest. And so Newton, of course, very much used Galileo's observations.

Lex Fridman 17:27 Let me ask, uh, the old Russian overly philosophical question about death. (laughs)

Alex Filippenko 17:34 Yeah.

Lex Fridman 17:34 So we're talking about the expanding universe.

Alex Filippenko 17:36 Sure.

Lex Fridman 17:37 Uh, how do you think human civilization will come to an end if we avoid the, uh, the near-term issues we're having? Uh, will it be our sun burning out? Will it be comets?

Alex Filippenko 17:48 Oh, okay.

Lex Fridman 17:49 Will it be, uh, what is it?

Alex Filippenko 17:51 Yeah.

Lex Fridman 17:52 Or wh- do you think we, we have a shot at reaching the, the heat death of the universe?

Alex Filippenko 17:58 Yeah. So we're-

Lex Fridman 17:59 (laughs)

Alex Filippenko 18:00 ... we're gonna leave out the anthropogenic, uh-

Lex Fridman 18:04 Nuclear war.

Alex Filippenko 18:04 ... causes of our potential destruction-

Lex Fridman 18:07 Yes.

Alex Filippenko 18:07 ... which I actually think are greater than the celestial, uh-... causes. So, um-

Lex Fridman 18:15 So if we get lucky.

Alex Filippenko 18:16 Yeah, if we get lucky.

Lex Fridman 18:16 And, and intelligent. I don't know.

Alex Filippenko 18:18 Yeah, yeah. So no way will we, as humans, reach the heat death of the universe. I mean, it's conceivable that, uh, machines, which I think will be our evolutionary descendants, might reach that. Although even they will have less and less energy with which to work as time progresses, because eventually even the lowest mass stars burn out, although it takes them trillions of years to do so. Um, so the point is, is that certainly on earth, uh, there are other celestial threats, existential threats, comets, exploding stars, the sun burning out. So we will definitely need to move away from our solar system to other solar systems. And then, you know, the question is, can they keep on propagating to other planetary systems sufficiently long? Um, in our own solar system, the sun burning out is, is not the, the immediate existential threat, um, that'll happen in about, you know, five billion years when it becomes a red giant. Although I should hasten to add that within the next one or two billion years, the sun will have brightened enough that unless there are compensatory atmospheric changes, the oceans will, will evaporate away, you know, and, and you need much less carbon dioxide for the temperatures to be maintained roughly at their present temperature. And plants wouldn't like that very much. So you can't lower the carbon dioxide content too much. So, so within one or two billion years, probably the oceans will evaporate away.

Lex Fridman 19:55 Yeah.

Alex Filippenko 19:56 But on a sooner time scale than that, I would say an asteroid collision leading to a potential mass extinction, or at least an extinction of complex beings such as ourselves that require quite special conditions unlike cockroaches and amoebas, you know, to survive. Um, you know, one of these civilization changing asteroids is only one kilometer or so in diameter and bigger and a true mass extinction event is 10 kilometers or larger. Now, it's true that we can find and track the orbits of asteroids that might be headed toward Earth, and if we find them 50 or 100 years before they impact us, then clever applied physicists and engineers can figure out ways to deflect them. But at some point, you know, some comet will come in from the deep freeze of the solar system, and there we have very little warning, months to a, to a year.

Lex Fridman 20:52 What's a deep freeze? Sorry to interrupt.

Alex Filippenko 20:54 Oh, the deep freeze is sort of out beyond Neptune. There's this thing called the Kuiper belt.

Lex Fridman 20:58 Mm-hmm.

Alex Filippenko 20:59 And it consists of a bunch of, you know, dirty ice balls or icy dirt balls. It's the source of the comets that occasionally come close to the sun. And then there's a even bigger, uh, area called the scattered disc, which is sort of a big donut surrounding the solar system way out there from which other comets come. And then there's the Oort cloud, W, double O-R-T, after, uh, Jan Oort, a Dutch astrophysicist, and it's the better part of a light year away from the sun. So a good fraction of the distance to the nearest star, but that's like a trillion or 10 trillion comet-like objects that occasionally get disturbed by a passing star or whatever. And most of them go flying out of the solar system, but some go toward the sun and they, they come in with little warning, you know, by the time we can see them, they're only a year or two away from us. And moreover, not only is it hard to determine their trajectories sufficiently accurately to know whether they'll hit a tiny thing like earth, but outgassing from the comet of, um, gases, you know, when the ices sublimate-

Lex Fridman 22:08 Mm-hmm.

Alex Filippenko 22:08 ... that outgassing can change the trajectory just because of conservation of momentum, right? It's the rocket effect. Gases go out in one direction, the object moves in the other direction. And so since we can't predict how much outgassing there will be and in exactly what direction, because these things are tumbling and rotating and stuff, it's hard to predict the trajectory with sufficient accuracy to know that it will hit. And you certainly don't want to deflect a comet that would have missed-

Lex Fridman 22:38 (laughs)

Alex Filippenko 22:38 ... but you thought it was gonna hit and end up having it hit. That would be like the ultimate Charlie Brown, you know, goat instead of trying to be the hero, right? He ended up being the goat. (laughs)

Lex Fridman 22:49 What would you,

Lex Fridman 22:50 um, what would you do if it, it seemed like in a matter of months that there is some nonzero probability, maybe a high probability that there would be a collision? So r- from a scientific perspective, from an engineering perspective, I imagine you would actually be in the room of people deciding what to do. What, uh-

Alex Filippenko 23:11 Yeah.

Lex Fridman 23:11 ... philosophically too.

Alex Filippenko 23:12 It's a tough one, right? Because if you only have a few months, that's not much time in which to deflect it. Early detection and, and, um, early action are key 'cause when it's far away, you only have to deflect it by a tiny little angle-

Lex Fridman 23:29 Yeah.

Alex Filippenko 23:30 ... and then by the time it reaches us, the perpendicular motion is big enough to, you know, to, to miss Earth. All you need is one radius or, or one diameter of the earth, right? Um, that actually means that all you would need to do is slow it down so it arrives four minutes later or speed it up so it arrives four minutes earlier and earth will have moved through one radius in, in that time. So it doesn't take much, but you can imagine if a thing is about to hit you-

Lex Fridman 24:00 Mm-hmm.

Alex Filippenko 24:00 ... you, you have to deflect it 90 degrees-

Lex Fridman 24:02 Yep.

Alex Filippenko 24:02 ... or more, right?

Lex Fridman 24:03 Mm-hmm.

Alex Filippenko 24:03 You know, and you don't have much time to do so, and you have to slow it down or speed it up a lot if that's what you're trying to do to it. And so decades is sufficient time, but months is not sufficient time. So at that point, I would think the, the name of the game would be to try to predict where it would hit...And if it's in a heavily populated region, (sighs) try to, try to start an orderly evacuation perhaps.

Lex Fridman 24:33 (laughs)

Alex Filippenko 24:33 But you know, that might cause just so much panic that I'm...

Lex Fridman 24:36 Yeah. (laughs)

Alex Filippenko 24:36 How would you do with New York City or Los Angeles, or something like that, right?

Lex Fridman 24:41 I, I might have, I might have a different opinion a year ago. I'm um, a bit, uh, disheartened by... You know, in the movies the, um, there's always extreme competence from the government. (laughs)

Alex Filippenko 24:54 Competence, yeah.

Lex Fridman 24:55 Competence, yeah.

Alex Filippenko 24:56 Right, but we expect extreme incompetence, uh, if anything, right?

Lex Fridman 24:59 Yes, no. So I'm quite, uh, disappointed. But sort of from a medical perspective I think you're saying there, and a scientific one, it's almost better to get better and better maybe telescopes and data collection to be able to predict the movement of these things, or like come up with totally new technologies. Like you can imagine actually sending out, like probes out there to be able to sort of almost have little finger sensors throughout our solar system-

Alex Filippenko 25:28 Yeah.

Lex Fridman 25:28 ... to be able to detect stuff.

Alex Filippenko 25:29 Well, that's right. Yeah, monitoring the asteroid belt is very important. And 99% of the so-called near earth objects ultimately come from the asteroid belt, and so there we can track the trajectories. And even if there's, you know, a close encounter between two asteroids which deflects one of them toward Earth, it's unlikely to be on a collision course with Earth in the immediate future. It's more like, you know, tens of years. So that gives us time. But we would need to improve our ability to detect the objects that come in from a great distance, and fortunately those are, are much rarer. The, the comets come in, you know, 1% of the collisions perhaps are with comets that come in without any warning hardly.

Lex Fridman 26:13 Mm-hmm.

Alex Filippenko 26:14 And so, so that might be more like, you know, a billion or two billion years before one of those hits us,

Alex Filippenko 26:22 um, so maybe we have to worry about the sun getting brighter on that timescale.

Lex Fridman 26:28 (laughs)

Alex Filippenko 26:28 I mean, there's the possibility that a star will explode near us in the next couple of billion years, but over the course of the history of life on Earth, the estimates are that maybe only one of the mass extinctions, you know, was caused by a star blowing up, in particular a special kind called a gamma ray burst, and the, I think it's the Ordovician-Sularian, uh, Silurian, Ordovician-Silurian extinction 420 or so, 440 million years ago that is speculated to have come from one of these particular types of exploding stars called gamma ray bursts. But even there the evidence is circumstantial. So those kinds of existential threats are, are reasonably rare. The greater danger I think is civilization-changing events, where it's a much smaller asteroid, uh, which those are hard to, harder to detect. Or, or a giant solar flare that shorts out the grid in all of North America, let's say. Now, you know, astronomers are monitoring the sun 24/7 with various satellites, and we can tell when there's a, a flare or a coronal mass ejection, and we can tell that in a day or two a giant bundle of el- energetic particles will arrive and twang the magnetic field of Earth and send all kinds of currents through long-distance power lines, and that's what shorts out the transformers, and transformers are, you know, expensive and, and hard to replace and hard to transport, and all that kind of stuff. So if we can warn the power companies and they can shut down the grid before the big-

Lex Fridman 28:18 Mm-hmm.

Alex Filippenko 28:18 ... bundle of particle hits, then we will have mitigated much of this. Now for a big enough bundle of particles you can get short circuits even over small distance scales, so not everything will be saved, but at least the whole grid might not go out. So again, you know, astronomers, I like to say, support your local astronomer-

Lex Fridman 28:38 (laughs)

Alex Filippenko 28:38 ... they may help some day save humanity by telling the power companies to shut down the grid, finding the asteroid 50 or 100 years before it hits, then having clever physicists and engineers deflect it. So many of these cosmic threats, cosmic existential threats, we can actually predict and do something about, or observe before they hit and do something about. So, you know...

Lex Fridman 29:06 It's, it's, uh, terrifying to think-

Alex Filippenko 29:07 (laughs)

Lex Fridman 29:08 ... that people would listen to this conversation. It's like when you listen to Bill Gates talk about pandemics in his TED Talk a few years ago-

Alex Filippenko 29:15 Yeah.

Lex Fridman 29:15 ... and realizing we should have supported our local astronomer more. (laughs)

Alex Filippenko 29:20 Well, I don't know whether it's more, because as I said, I actually think, uh, human-induced threats or things that occur naturally on Earth, either a natural pandemic or perhaps, you know, a bioengineering-type pandemic-

Lex Fridman 29:32 Mm-hmm.

Alex Filippenko 29:32 ... or, you know, something like a super volcano, right?

Lex Fridman 29:34 Yeah.

Alex Filippenko 29:35 Um, there was one event, Toba I think it was, 70-plus thousand years ago, that, that caused a, a gigantic decrease in temperatures on Earth because it sends up, it sent up so much soot that it blocked the sun, right? It's the nuclear winter type disaster scenario that some people, including Carl Sagan, talked about decades ago. But we can see in the history of volcanic eruptions, even more recently in the 19th century, Tambora and other ones, you look at the record and you see rather large dips in temperature associated with massive volcanic eruptions. Well, these super volcanoes, one of which, by the way, exists under Yellowstone, you know, in the central US. I mean, it's not just, it's not just one or two states, it's a, it's a gigantic region.... and there's controversy as to whether it's likely to blow anytime in the next 100,000 years or so. But that would be perhaps not a mass extinction, 'cause you really need to, or, or perhaps not a complete existential threat because you have to get rid of sort of the very last humans for that. But, but at least getting rid of, um, you know, killing off so many humans, truly billions and billions of humans. The one, there, there have been ones tens of thousands of years ago, including this one, um, Toba, I think it's called, where it's estimated that the human population was down to 10,000 or 5,000 individuals, something like that, right? If you have a 15-degree drop in temperature over quite a short time, it's not clear that even with today's advanced technology, we would be able to adequately respond, at least for the vast majority of people. Maybe some would be in these underground caves where you'd keep the president and a bunch of other important people, you know, but the, the typical person is not gonna be protec- protected-

Lex Fridman 31:27 Could be-

Alex Filippenko 31:27 ... when, when all of agriculture is, is cut off, right? And when-

Lex Fridman 31:32 It could be hundreds of millions or billions of people-

Alex Filippenko 31:34 Yeah.

Lex Fridman 31:35 ... starving to death.

Alex Filippenko 31:36 Exactly. That's right. They don't all die immediately, but they use up their supplies, uh, or again, this electrical grid.

Lex Fridman 31:44 First off, toilet paper.

Alex Filippenko 31:45 (laughs) There you go.

Lex Fridman 31:46 (laughs)

Alex Filippenko 31:46 Stash that toilet paper, you know.

Lex Fridman 31:48 (laughs)

Alex Filippenko 31:48 Um, or the electrical grid. I mean, imagine North America without power for a year, right? I mean, we've become so dependent. We're no longer the cave people.

Lex Fridman 31:58 Yeah.

Alex Filippenko 31:58 They, they would do just fine, right?

Lex Fridman 32:00 Yeah.

Alex Filippenko 32:00 What do they care about the electrical grid, right? What do they care about agriculture? They're hunters and gatherers. But we now have become so used to our way of life that the only real survivors would be those rugged individualists who live somewhere out in the forest or in a cave somewhere-

Lex Fridman 32:17 Yeah.

Alex Filippenko 32:17 ... completely independent of anyone else.

Lex Fridman 32:20 Yeah. I've, I've recently, I recommend it, it's totally new to me, this kind of survivalist, uh, folks, but there's a, a few sho- there's a lot of shows of those, but I saw-

Alex Filippenko 32:29 Yeah. (laughs)

Lex Fridman 32:29 ... one on Netflix, and I started watching them, and there's a l- they make a lot of sense. They, they reveal to you how dependent we are on all aspects of this beautiful systems we human have built.

Alex Filippenko 32:44 Right.

Lex Fridman 32:44 And how fragile they are.

Alex Filippenko 32:46 Incredibly fragile.

Lex Fridman 32:48 And-

Alex Filippenko 32:48 Yeah.

Lex Fridman 32:49 ... this, (laughs) this whole conversation is making me realize how lucky we are.

Alex Filippenko 32:53 Oh, we're, we're incredibly lucky, but we've set ourselves up to be very, very fragile, and we are intrinsically complex biological creatures that except for the fact that we have brains and minds with which we can, you know, try to prevent some of these things or respond to them, we, as a living organism, require quite a narrow set of conditions in order to survive. You know, we're not cockroaches. We're not gonna survive a nuclear war.

Alex Filippenko 33:22 (laughs)

Lex Fridman 33:23 So we're kind of... There's this beautiful dance between, um... We've been talking about astronomy, that astronomy, the stars, like, inspires everybody, and at the same time, there's this pragmatic aspect that we're talking about. And so I see space exploration as the same kind of way. That it's, uh, reaching out to other planets, reaching out to the stars is th- this really beautiful idea. But if you listen to somebody like, uh, Elon Musk, he talks about space exploration as very pragmatic. Like we have to, uh-

Alex Filippenko 33:57 Mm-hmm.

Lex Fridman 33:57 ... if we, we have to be... (laughs) He has this ridiculous way of sounding like an engineer about it, which is like, it's obvious we need to become a multi-planetary species if we were to survive long term. So maybe both philosophically, in terms of beauty, and in terms of practical, what's your thoughts on, um, space exploration, on the challenges of it, on how much we should be investing in it, and on a personal level, like how excited you are by the possibility of going to Mars, colonizing Mars, and maybe going outside the solar system?

Alex Filippenko 34:34 Yeah. You know, great question. Uh, there's a lot to unpack there, of course.

Lex Fridman 34:39 (laughs) Sorry. Sorry. (laughs)

Alex Filippenko 34:40 You know, humans are by their very nature explorers, pioneers. They want to go out, climb the next mountain, see what's behind it, um, explore the ocean depths, explore space. This is our destiny to go out there, and, and of course, from a pragmatic perspective, yes, we need to, um, plant our seeds elsewhere really, because things could go wrong here on Earth. Now some people say that's, that's an excuse to not take care of our planet, that, well, we say we're elsewhere and so we don't have to take good care of our planet. No, you know, we should take the best possible care of our planet. We should be cognizant of the potential impact of what we're doing. Nevertheless, it's prudent to have us be elsewhere as well. So in that regard, I actually agree with Elon. Uh, it'd be good to be on Mars. That would be yet another place for us to, from which to, you know, explore further.

Lex Fridman 35:36 Would that be a good-

Alex Filippenko 35:37 Explore further.

Lex Fridman 35:38 Would that be a good next step, would you say?

Alex Filippenko 35:39 Well, that's the good, it's a good next step. I have t- I happe- I happen to disagree with him as to how quickly it will happen.

Lex Fridman 35:45 (laughs)

Alex Filippenko 35:45 Right? I mean, I think he's very optimistic. Now, you need visionary people like Elon-

Lex Fridman 35:50 Yeah.

Alex Filippenko 35:50 ... to, to get people going and to inspire them. I mean, look at the success he's had with multiple companies. Uh, so maybe he gives this very optimistic timeline in order to be inspirational to those who are, who are going out there. And certainly his success with, you know, the rocket that is reusable 'cause it landed upright and all that. I mean, you know, what, uh, that- that's a game changer.

Lex Fridman 36:12 Mm-hmm.

Alex Filippenko 36:12 Sort of like every time you flew from San Francisco to Los Angeles, you discard the airplane, right?

Lex Fridman 36:17 Yeah.

Alex Filippenko 36:18 I mean, tha- that's crazy.

Lex Fridman 36:19 Yeah.

Alex Filippenko 36:19 Right? So that's a game changer. But nevertheless, the timescale over which he thinks that there could be a, a real thriving colony on Mars, I think is far too optimistic.

Lex Fridman 36:30 What's the biggest challenges to you-... one, one is just getting rockets- w- not rockets, but people out there, and two is the colonization.

Alex Filippenko 36:39 Yeah.

Lex Fridman 36:39 Like, wha- do you have thoughts about this, um-

Alex Filippenko 36:42 Well-

Lex Fridman 36:42 ... challenges of this kind of prospect?

Alex Filippenko 36:44 Yeah, I haven't thought about it in, in great detail, uh, other than recognizing that Mars is a harsh environment.

Lex Fridman 36:51 Yeah.

Alex Filippenko 36:51 You don't have much of an atmosphere there. You've got less than a percent of Earth's atmosphere. Um, so you'd, you'd need to build some sort of a dome right away, right? And, and that, that would take time. You need to melt the water that's in the permafrost or have canals dug from which you transport it from the, from the polar ice caps.

Lex Fridman 37:11 You know, I-

Alex Filippenko 37:12 You know? (laughs)

Lex Fridman 37:12 ... I was reading re- recently in terms of, like, what's the most efficient source of nutrition for humans that were to live on Mars, and, uh, people should look into this, but it turns out to be insects.

Alex Filippenko 37:23 Insects?

Lex Fridman 37:24 Yeah. (laughs)

Alex Filippenko 37:25 Yeah.

Lex Fridman 37:25 So you want-

Alex Filippenko 37:25 Yeah.

Lex Fridman 37:26 ... you want to build giant colonies of insects-

Alex Filippenko 37:28 Right.

Lex Fridman 37:28 ... and just be eating them.

Alex Filippenko 37:29 Yeah, insects have a lot of protein, right? So-

Lex Fridman 37:30 Yeah, a lot of protein, and they're easy-

Alex Filippenko 37:32 ... you know.

Lex Fridman 37:32 ... to, uh, gr- like, you can think of them a- as farming.

Alex Filippenko 37:36 Right.

Lex Fridman 37:36 (laughs) So-

Alex Filippenko 37:37 But it's not going to be easy- as easy as growing a whole plot of potatoes like in the movie The Martian, you know, or something, right?

Lex Fridman 37:44 Yeah.

Alex Filippenko 37:44 It's not going to be that easy.

Lex Fridman 37:45 (laughs)

Alex Filippenko 37:45 But, you know, so there's, there's this thin atmosphere. It's got the wrong composition. It's mostly carbon dioxide. Um, there are these violent dust storms. The temperatures are generally cold. You know, you'd need to do a lot of things. You'd need to terraform it, basically, in order to make it nicely livable without some dome surrounding you, and if you, and if you insist on a dome, well, that's not going to house that many people, right? You know? So-

Lex Fridman 38:12 Well, so let's look,

Lex Fridman 38:13 let's look briefly then, you know, we're looking for a new apartment to move into.

Alex Filippenko 38:18 Right.

Lex Fridman 38:18 So let's look outside the solar system. Do you think... You've, you've spoken about exoplanets as well.

Alex Filippenko 38:24 Yeah.

Lex Fridman 38:24 Uh, do, do you think there's, um, possible homes out there for us, uh, outside of our solar system?

Alex Filippenko 38:31 There are lots and lots of homes, possible homes. I mean, there, there's a planetary system around nearly every star you see in the sky, and one in five of those is thought to have a roughly Earth-like planet. You know?

Lex Fridman 38:45 And that's a relatively new-

Alex Filippenko 38:47 Yeah, it's a new discovery.

Lex Fridman 38:48 ... that's exciting.

Alex Filippenko 38:48 I mean, the, the Kepler satellite, which was flying around, uh, above Earth's atmosphere, was able to monitor the brightness of stars with exquisite detail, and they could detect planets crossing the line of sight between us and the star, thereby dimming its light for a short time, ever so slightly.

Lex Fridman 39:07 Yeah.

Alex Filippenko 39:08 And it's, it's amazing. So there are now thousands and thousands of these exoplanet candidates of which something like 90% are probably genuine exoplanets. And you have to remember that only about 1% of stars have their planetary system oriented edge-on to your line of sight-

Lex Fridman 39:26 Mm-hmm.

Alex Filippenko 39:27 ... which is what you need for this transit method to work, right? Some arbitrary angle won't work, and certainly perpendicular, uh, to your line of sight, that is, in the plane of the sky won't work because the, the, the planet is orbiting the star and never crossing your line of sight. So the fact that, um, you know, they found planets orbiting about 1% of the stars that they looked at in this field of 150-plus thousand stars, they found planets around 1%. You then multiply by the inverse of 1%, which is, you know, right? 1% is about how man- what the fraction of the, of the stars that have their planetary system oriented the right way, and that already, back of the envelope calculation, tells you that, uh, of order, 50 to 100% of all stars have planets, okay?

Lex Fridman 40:18 Mm-hmm.

Alex Filippenko 40:18 And then they've been finding these Earth-like planets, et cetera, et cetera. So there are many potential homes. The problem is getting there, okay?

Lex Fridman 40:26 Yeah.

Alex Filippenko 40:26 So then a, a typical bright star, Sirius, uh, the brightest star in the sky, maybe not a typical bright star-

Lex Fridman 40:33 (laughs)

Alex Filippenko 40:33 ... but it's 8.7 light years away, okay? So, uh, that's, that means the light took 8.7 years to reach us. We're seeing it as it was about nine years ago.

Lex Fridman 40:46 Yeah.

Alex Filippenko 40:46 Okay? So then, you know, you ask, how long would a rocket take to get there at Earth's escape speed, which is 11 kilometers per second, okay? And it turns out it's about a quarter of a million years, okay?

Lex Fridman 41:01 (laughs)

Alex Filippenko 41:01 Now, that's 10,000 generations, okay? Let's say-

Lex Fridman 41:04 Yeah.

Alex Filippenko 41:04 ... a generation of humans is 25 years, right?

Lex Fridman 41:06 Yeah.

Alex Filippenko 41:07 So you'd need this colony of people that is able to sustain itself, all their food, all their waste disposal, all their water-

Lex Fridman 41:16 Yeah.

Alex Filippenko 41:16 ... all their recycling of everything, for 10,000 generations. They have to commit themselves to living on this vehicle-

Lex Fridman 41:25 Mm-hmm.

Alex Filippenko 41:25 ... right? I just don't see it happening. What I see potentially happening, if we avoid self-destruction, intentional or unintentional, here on Earth, is that machines will do it, robots that can essentially hibernate. They don't need to do much of anything for a long, long time as they're traveling, and moreover, if some energetic charged particle, some cosmic ray hits the circuitry, it fixes itself, right? Machines can do this. Uh, I mean, it, it's a form of artificial intelligence. You just tell the thing, "Fix yourself," basically-

Lex Fridman 42:00 Yeah.

Alex Filippenko 42:00 ... and then when you land on the pr- on the planet, start producing copies of yourself, initially from materials that were perhaps sent or you just have a bunch of copies there, uh, and then they set up, you know, factories with which to do this. I mean, this is very, very futuristic, but it's much more feasible, I think, than sending flesh and blood-

Lex Fridman 42:21 Yeah.

Alex Filippenko 42:22 ... over interstellar distances, a quarter of a million years to even the nearest stars. You're subject to all kinds of charged particles and radiation. You have to, you know, shield yourself really well. That's, by the way, one of the problems of going to Mars, is that it's not a three-day journey like going to the moon. You're out there for the better part of a year or two-

Lex Fridman 42:43 Mm-hmm.

Alex Filippenko 42:43 ... and you're exposed to lots of radiation.... you know?

Lex Fridman 42:47 Yeah.

Alex Filippenko 42:47 Which typically doesn't do well with living tissue, right? (laughs) Or if living tissue doesn't do well with the radiation, okay?

Lex Fridman 42:54 And then-

Alex Filippenko 42:54 So-

Lex Fridman 42:54 ... the hope is that the robots, the AI systems, might be able to care the, carry the, the fire of consciousness, whatever makes us humans-

Alex Filippenko 43:07 Yeah.

Lex Fridman 43:07 ... like a little drop of whatever makes us humans so special, not to be too poetic about it, but-

Alex Filippenko 43:12 No, but I, I like being poetic about it because it's a, it's an amazing question, you know. Is there something beyond just the bits, the ones and zeros, to us? You know, it's an interesting question. Um, I like to think that there, there isn't anything, and that how beautiful it is that our thoughts, our emotions, our feelings, our compassion all come from these ones and zeros, right? That, to me, actually is a, a beautiful thought. And the idea that machines, silicon-based life, effectively, could be our natural evolutionary descendants, not from a DNA perspective, but they are our creations and they then carry on.

Lex Fridman 43:51 Yeah.

Alex Filippenko 43:51 That, to me, is a, a beautiful thought in some ways, but others find it to be a horrific thought, right?

Lex Fridman 43:56 So that's exciting to you. I, it is exciting to me as well.

Alex Filippenko 43:59 Yeah. Mm-hmm.

Lex Fridman 44:00 Because, uh, to me, from a, purely an engineering perspective, it's, I believe it's impossible to create... Like, whatever systems we create that take over the world, it's impossible for me to imagine that those systems will not carry some aspect of what makes humans beautiful.

Alex Filippenko 44:19 Yeah.

Lex Fridman 44:19 So, like, the, a lot of people have these kind of paperclip ideas that w- we'll bring, we'll build machines that are cold inside or philosophers call them zombies.

Alex Filippenko 44:29 Mm-hmm.

Lex Fridman 44:29 You know, they're, they're... that naturally the systems that will out-compete us on this Earth will be cold and non-, non-conscious, not capable of, uh, all the human emotions and empathy and compassion and love and hate, every... the, the, the beautiful, uh, mix of, uh, what makes us human.

Alex Filippenko 44:52 Yeah.

Lex Fridman 44:53 But, to me, intelligence requires all of that. So in order to out-compete humans, you better be good at the full picture.

Alex Filippenko 45:02 Right, so artificial general intelligence, in my view, encompasses a lot of these attributes-

Lex Fridman 45:08 Yeah.

Alex Filippenko 45:08 ... that you just talked about.

Lex Fridman 45:09 Yeah. I tend to believe-

Alex Filippenko 45:10 Like curiosity-

Lex Fridman 45:11 Yeah.

Alex Filippenko 45:11 ... inquisitiveness, you know, right?

Lex Fridman 45:13 It might look very different than us humans.

Alex Filippenko 45:15 Well, right.

Lex Fridman 45:15 But it will have some of the magic, I think.

Alex Filippenko 45:17 But it'll, but it'll also be much more able to survive the onslaught of existential threats that-

Lex Fridman 45:24 Yeah.

Alex Filippenko 45:24 ... either we bring upon ourselves or don't anticipate here on Earth, or that occasionally come from beyond, and there's nothing much we can do about a supernova explosion that just suddenly, you know, goes off

Alex Filippenko 45:35 and... And, and really if we want to move to other planets outside our solar system, I think realistically that's a much better option than thinking that humans will actually make these gigantic journeys. And, you know, then I do this calculation for my class, you know, Einstein's special theory of relativity says that you can do it in a short amount of time in your own frame of reference if you go close to the speed of light. But then you bring in E equals MC squared, and you figure out how much energy it takes to get you accelerated to close enough to the speed of light to make the time scales short in your own frame of reference, and the amount of energy is just unfathomable, right?

Lex Fridman 46:17 Mm-hmm.

Alex Filippenko 46:17 We can do it at the Large Hadron Collider with, with protons, you know, we can accelerate them to 99.9999% of the speed of light, but that's just a proton. We're gazillions of protons, okay?

Lex Fridman 46:29 Mm-hmm.

Alex Filippenko 46:29 And that doesn't even count the rocket that would carry us, the payload, and you would need to either store the fuel in the rocket, which then requires even more mass for the rocket, or collect fuel along the way, which, you know, is difficult and... So getting close to the speed of light I think is not an option either, other than for a little tiny thing like, you know, Yuri Milner and others are thinking about this, this Starshot project where they'll send a little tiny camera to Alpha Centauri, 4.2 light years away.

Lex Fridman 47:00 Yeah.

Alex Filippenko 47:01 They'll zip past it, take a picture of the exoplanets that we know-

Lex Fridman 47:04 Yeah.

Alex Filippenko 47:04 ... orbit that three or more star system and, uh-

Lex Fridman 47:08 Say hello real quick.

Alex Filippenko 47:09 ... say hello real quickly and then-

Lex Fridman 47:10 (laughs)

Alex Filippenko 47:10 ... send the images back to us, okay?

Lex Fridman 47:12 Yeah.

Alex Filippenko 47:12 So that, that's a tiny little thing, right? Maybe you can accelerate that to, they're hoping 20% of the speed of light, with a whole bunch of high-powered lasers aimed at it. It's not clear that other countries will (laughs) allow us to do that, by the way.

Lex Fridman 47:25 Yeah.

Alex Filippenko 47:25 But that's a very forward-looking thought. I mean, I very much support the idea, but there's a big difference between sending a little tiny camera and sending a payload of people with equipment that could then mine the, um, the, the resources on the exoplanet that they reach and, and then go forth

Alex Filippenko 47:45 and multiply, right?

Lex Fridman 47:46 Well, let's, let's talk about the big galactic things and how we might be able to leverage them to travel fast. I know this is a little bit science fiction, but y- you know, um, ideas of wormholes and-

Alex Filippenko 48:00 Yeah.

Lex Fridman 48:01 ... ideas at the edge of black holes that reveal to us that this fabric of spacetime is, uh, could be messed with-

Alex Filippenko 48:11 Yeah.

Lex Fridman 48:12 ... perhaps. Is that at all a, an interesting thing for you? Uh, I mean, in, in y- in looking out at the universe and studying it as you have, is that also a possible, like, a dream for you that we might be able to find clues how we can actually use it to improve-

Alex Filippenko 48:30 Yeah.

Lex Fridman 48:30 ... our transportation?

Alex Filippenko 48:31 It's an interesting thought. I'm certainly excited by the potential physics that suggest this kind of faster-than-light travel effectively or, you know-

Lex Fridman 48:42 Yeah.

Alex Filippenko 48:42 ... cutting the distance to make it very, very short through a wormhole or something like that.

Lex Fridman 48:47 ... possible, no?

Alex Filippenko 48:48 Well, you know, call me not very imaginative.

Lex Fridman 48:51 (laughs)

Alex Filippenko 48:51 But based on today's knowledge of physics, which I realize, you know, people have gone down that rabbit hole and-

Lex Fridman 48:57 Yeah.

Alex Filippenko 48:57 ... you know, a century ago, Lord Kelvin, one of the greatest physicists of all time, said that all of fundamental physics is done.

Lex Fridman 49:04 Yep.

Alex Filippenko 49:04 The rest is just engineering. And guess what? Then came special relativity, quantum physics, general relativity. How wrong he was.

Lex Fridman 49:12 Yeah.

Alex Filippenko 49:12 So let me not be another Lor- Lord Kelvin.

Lex Fridman 49:14 (laughs)

Alex Filippenko 49:15 On the other hand, I think we k- know a lot more now about what we know and what we don't know and what the physical limitations are. And to me, most of these schemes, uh, if not all of them, seem, uh, very far-fetched if not impossible. So travel through wormholes, for example, uh, you know, it appears that for a non-rotating black hole, that's just a, a complete no-go because the, the singularity is a point-like singularity and you have to reach it to traverse the wormhole and you get squished by the singularity, okay? Now for a rotating black hole, it turns out there is a way to pass through the event horizon, the boundary of the black hole, and avoid the singularity and go out the other side, or even traverse the, the donut hole-like singularity. In the case of a rotating black hole, it's a ring singularity. So there's actually two theoretical ways you could get through a rotating black hole or a charged black hole, not that we expect charged black holes to exist in nature, because they would quickly bring in the opposite charge so as to neutralize themselves. But rotating black holes, definitely a reality. We, we now have good evidence for them. Do they have traversable wormholes? Probably not, because it's still the case that when you go in, you go in with so much energy that it, it, it either squeezes the wormhole shut or you encounter a whole bunch of incoming and outgoing energy that vaporizes you. It's called the mass inflation instability, and it just sort of vaporizes you. Nevertheless, you know, you could imagine while you're in some vapor form, but if you make it through, maybe you could, you know, reform or something (laughs) .

Lex Fridman 50:58 Yeah, so it's still information.

Alex Filippenko 50:59 Yeah, it's still information. It's scrambled information, but there's a way maybe-

Lex Fridman 51:02 (laughs)

Alex Filippenko 51:02 ... of bringing it back, right?

Lex Fridman 51:03 Yeah.

Alex Filippenko 51:04 But then the thing that really bothers me is that as soon as you have this possibility of traversal of a wormhole, you have to come to grips with a fundamental problem, and that is that you could come back to your universe at a time prior to your leaving, and you could essentially prevent your grandparents from ever meeting. This is called the grandfather paradox, right? And if they never met, and if your parents were never born, and if you were never born, how would you have made the journey to prevent the history from allowing you to exist, right? It's, it's a, it's a causal, it's a violation of causality, of cause and effect. Now, physicists such as myself take causality violation very, very seriously.

Lex Fridman 51:53 (laughs)

Alex Filippenko 51:54 We've never seen it.

Lex Fridman 51:55 You took a stand. (laughs)

Alex Filippenko 51:56 Yeah, I mean, you know, I mean, it's one of these, right, Back to the Future type movies, right? And you have to-

Lex Fridman 52:02 Yeah, it's not just philosophy. Yeah.

Alex Filippenko 52:02 ... work things out in such a way that you don't mess things up, right? Some people say that, well, you come back to the universe, but you come back in such a way that you cannot affect your journey. Um, but then, I mean, that, that seems kind of, uh, contrived to me. Or some say that you end up in a different universe, and this also goes into the, the many different types of the multiverse hypothesis and the many worlds interpretation and all that. But again, then it's not the universe from which you left, right? And you don't come back to the universe from which you left, and so you're not really going back in time to the same universe, and you're not even going forward in time necessarily then to the same universe, right? You're ending up in some other universe. So, so you've, you've, what have you achieved, right? You've-

Lex Fridman 52:53 (laughs) You've traveled, but you didn't-

Alex Filippenko 52:54 You've traveled.

Lex Fridman 52:55 (laughs) You, uh, you ended up in a-

Alex Filippenko 52:57 Yeah.

Lex Fridman 52:57 ... different place than you started, uh, in-

Alex Filippenko 52:59 Well-

Lex Fridman 52:59 ... more ways then one, which is-

Alex Filippenko 53:00 Yeah, and then, then there's this idea, um, the Alcubierre drive, where you warp space time in front of you-

Lex Fridman 53:07 Yeah.

Alex Filippenko 53:08 ... so as to greatly reduce the distance, and you can expand the space time behind you.

Lex Fridman 53:12 Yeah.

Alex Filippenko 53:12 So you're sort of riding a wave through space time. But the problem I see with that, beyond the practical difficulties-

Lex Fridman 53:19 (laughs)

Alex Filippenko 53:19 ... and the energy requirements and-

Lex Fridman 53:20 Yeah.

Alex Filippenko 53:20 ... by the way, how do you get out of this bubble through which you're, you know, w- riding this wave of space time and-

Lex Fridman 53:26 Yeah, how do you get out?

Alex Filippenko 53:26 ... Miguel Alcubierre acknowledged all these things. He said this is purely theoretical, fanciful, and all that. But a fundamental problem I see is that you'd have to get to those places in front of you so as to change the shape of space time so as to make the journey quickly, but-

Lex Fridman 53:44 Mm-hmm.

Alex Filippenko 53:44 ... but to get there, you, you got there in the normal way at a speed considerably less than that of light, so in a sense, you, you haven't saved any time, right? You might as well have just taken that journey and gotten to where you were going.

Lex Fridman 53:59 Yeah, there's a-

Alex Filippenko 53:59 Right? You, what have you done? You-

Lex Fridman 54:01 We-

Alex Filippenko 54:01 It's not like you snap your fingers and say, "Okay, let that space there be compressed, and then I'll make it over to Alpha Centauri in the next month." Y- you can't snap your fingers and do that.

Lex Fridman 54:12 Yeah, uh, and, but yeah. And we're sort of assuming that we can fix all the biological stuff that requires for humans to persist, uh, uh, persist through that whole process, because ultimately, it might boil down to just extending the life of the, of the human in some form, whether it's through the robot or the digital form or if there's a, or actually just figuring out genetically how to live forever, because-

Alex Filippenko 54:34 That's right.

Lex Fridman 54:35 ... that, that journey that you mentioned, the long journey, might be different if somehow our, our understanding of genetics, of our understanding of our own biology-

Alex Filippenko 54:44 Yeah.

Lex Fridman 54:44 ... all that kind of stuff would, uh, that's another trajectory that possibly we-

Alex Filippenko 54:47 Well, right, if, if you could put us into some sort of suspended animation, you know-

Lex Fridman 54:51 Yeah.

Alex Filippenko 54:51 ... hibernation or something and greatly increase the lifetime, and so these 10,000 generations I talked about, what do they care? It's just-

Lex Fridman 54:58 Yeah.

Alex Filippenko 54:58 ... one generation-

Lex Fridman 54:59 Yeah.

Alex Filippenko 54:59 ... and they're asleep, okay? They're-

Lex Fridman 55:01 Just need a long nap.

Alex Filippenko 55:02 So then you can do it...... it's still not easy, right? (laughs) Because you've got some-

Lex Fridman 55:06 Yeah.

Alex Filippenko 55:06 ... big old huge colony, and that just through E equals mc squared, right? That's a lot of mass. That's a lot of stuff to, um, to accelerate. The Newtonian kinetic energy is gigantic, right? So you're still not home free, but at least you're not trying to do it in a short amount of clock time-

Lex Fridman 55:25 Mm-hmm.

Alex Filippenko 55:25 ... right? Which, if you look at E equals mc squared, requires truly unfathomable a- amounts of energy because the energy is sort of, it's- it's your rest mass, m naught c squared, divided by the square root of one minus v squared over c squared.

Lex Fridman 55:41 Mm-hmm.

Alex Filippenko 55:42 And if your listeners want to just sort of stick into their pocket calculator, as v over c approaches one, (laughs) that one over the square root of one o- minus v squared over c squared approaches infinity.

Lex Fridman 55:53 Mm-hmm.

Alex Filippenko 55:54 So if you wanted to do it in zero time, you'd need an infinite amount of energy. That's basically why you can't reach, let alone exceed, the speed of light for a particle moving through a pre-existing space. It's that it takes an infinite amount of energy to do so.

Lex Fridman 56:11 So that's talking about us going somewhere. What about... One of the things that inspires a lot of folks, including myself, is the possibility that there's other... That this- this conversation is happening (laughs) on another planet in different forms with, uh, intelligent life forms. (sighs) Well, first we could start, as a cosmologist, what's your intuition about whether there is or isn't intelligent life out there? O- outside of our own.

Alex Filippenko 56:45 Yeah. I would say I'm one of the pessimists in that I- I don't necessarily think that we're the only ones in the observable universe, which goes out, you know, roughly 14 billion years in light travel time, and more like, you know, 46 billion years when you take into account the expansion of space. So the diameter of our observable universe is something like, you know, 90, 92 billion light years. That encompasses, you know, 100 billion to a trillion galaxies with, um, you know, 100 billion stars each. So now you're talking about something like 10 to the 22nd, 10 to the 23rd power stars-

Lex Fridman 57:22 Yeah.

Alex Filippenko 57:22 ... and roughly an equal number of, uh, Earth-like planets and so on. Um, so there- there- there may well be, uh, other intelligent life, but if-

Lex Fridman 57:32 But your- your sense is our galaxy's not teeming with life.

Alex Filippenko 57:35 Yeah, our galaxy, our Milky Way galaxy with several hundred billion stars and- and potentially habitable planets is not teeming with intelligent life. I-

Lex Fridman 57:44 Intelligent.

Alex Filippenko 57:44 Yeah, I wouldn't... Well, I'll get to the primitive life, the bacteria, in a moment, but, um, you know, we- we may well be the only ones in our Milky Way galaxy, at most a handful, I'd say, but I'd probably side with the school of thought that suggests we're the only ones in our own galaxy, just because I don't see human intelligence as being a- a natural evolutionary path for life.

Lex Fridman 58:13 I see.

Alex Filippenko 58:13 Um, I mean, there's a- there's a number of arguments. First of all, there's been more than 10 billion species of life on Earth-

Lex Fridman 58:19 Mm-hmm.

Alex Filippenko 58:19 ... in its history.

Lex Fridman 58:21 Yes.

Alex Filippenko 58:21 Uh, nothing has approached our level of intelligence and mechanical ability and curiosity. You know, whales and dolphins appear to be reasonably intelligent, but there's no evidence that they can think abstract thoughts, that they're curious about the world. They certainly can't build machines with which to study the world. Um, so that's one argument. Secondly, we came about as early hominids only four or five million years ago, and as homo- homo sapiens only about a quarter of a million years ago. So for the vast majority of the history of life on Earth, an intelligent alien zipping by Earth would have said there's nothing particularly intelligent or mechanically able on Earth, okay?

Lex Fridman 59:03 Yeah. Yeah.

Alex Filippenko 59:03 Thirdly, it's not clear that our intelligence is a long-term evolutionary advantage. Now, it's clear that in the last 100 years, 200 years, we've improved the lives of millions, hundreds of millions of people, but at the risk of pot- per- potentially destroying ourselves, either intentionally or unintentionally, or through neglect, as we discussed before.

Lex Fridman 59:26 That's a really interesting point, which is, it's possible that there... A huge amount of intelligent civilizations have been born, even through our galaxy-

Alex Filippenko 59:36 Right.

Lex Fridman 59:36 ... but they live very briefly and they die.

Alex Filippenko 59:38 They're flashbulbs in the night.

Lex Fridman 59:39 They're fly- flight. (laughs)

Alex Filippenko 59:42 That brings me to the fourth-

Lex Fridman 59:43 Flashbulbs in the night.

Alex Filippenko 59:44 ... the fourth issue-

Lex Fridman 59:45 Yeah.

Alex Filippenko 59:45 ... and that is

Alex Filippenko 59:46 the- you know, the Fermi paradox.

Lex Fridman 59:47 Yeah.

Alex Filippenko 59:47 If they're common, where the hell are they? (laughs) You know?

Lex Fridman 59:51 (laughs) Yeah.

Alex Filippenko 59:52 Notwithstanding the various UFO reports in Roswell-

Lex Fridman 59:55 Yeah.

Alex Filippenko 59:55 ... and all that, they just don't meet the bar. They don't clear the bar of scientific- scientific evidence, in my opinion, okay?

Lex Fridman 1:00:02 Yeah.

Alex Filippenko 1:00:02 So, you know, there's- there's no clear evidence that they've ever visited us on Earth here. So a- and, you know, SETI has been now, the Search for Extraterrestrial Intelligence has been scanning the skies. And true, we've only looked a couple of hundred light years out, and that's a tiny fraction of the whole galaxy, a tiny fraction of these 100 billion plus stars. Nevertheless, you know, if- if- if the- if the galaxy were teeming with life, especially intelligent life, you'd expect some of it to have been far more advanced than ours, okay? There's no special, nothing special about when the Industrial Revolution started on Earth, right? The chemical evolution of our galaxy was such that billions of years ago, nuclear processing in stars had built up clouds of gas after their explosion that were rich enough in heavy elements to have formed Earth-like planets, even billions of years ago. So there could be civilizations that are billions of years ahead of ours, and if you look at the exponential growth of technology, uh, among homo sapiens in the last couple of hundred years and you just project that forward, I mean, there's no telling what they could have achieved even in 1,000 or 10,000 years, let alone a million or 10 million or a billion years.And if they reach this capability of interstellar travel and colonization, then you can show that within 10 million years, or certainly 100 million years, you can populate the whole galaxy.

Lex Fridman 1:01:27 Mm.

Alex Filippenko 1:01:27 All right? And they, you know, so then you don't have to have tried to detect them beyond 100 or 1,000 light years. They would already be here.

Lex Fridman 1:01:35 Do you think, as a thought experiment, do you think it, it's possible that they are already here, but we humans are so human-centric that we're just not, like our conception of what intelligent life looks like-

Alex Filippenko 1:01:49 Yeah.

Lex Fridman 1:01:50 ... is, is, um, we don't want to acknowledge it. Like, what, what if trees-

Alex Filippenko 1:01:55 Right.

Lex Fridman 1:01:56 (laughs)

Alex Filippenko 1:01:56 Right, right. Yeah.

Lex Fridman 1:01:57 Like, but, like, okay, I guess the, in the form of a question, do you think we'll actually detect intelligent life, if it came to visit us?

Alex Filippenko 1:02:04 Yeah, I mean, it's like, you know, you, you're an ant crawling around on a sidewalk somewhere-

Lex Fridman 1:02:08 Right. (laughs)

Alex Filippenko 1:02:08 ... and do, do you notice the humans wandering around?

Lex Fridman 1:02:10 Exactly.

Alex Filippenko 1:02:10 And, and the Empire State Building and, you know, rocket ships-

Lex Fridman 1:02:13 Yeah.

Alex Filippenko 1:02:13 ... flying to the moon and all that kind of stuff, right. It, it's conceivable that, um, we haven't detected it and that we're so primitive compared to them that we're-

Lex Fridman 1:02:22 Yeah.

Alex Filippenko 1:02:22 ... just not able to do so.

Lex Fridman 1:02:23 Like if you look at dark energy, maybe-

Alex Filippenko 1:02:25 Yeah, maybe.

Lex Fridman 1:02:25 ... we, we call it as a field.

Alex Filippenko 1:02:27 It's just that my own feeling is that in science now, through observations and experiments, we've measured so many things and basically we understand a lot of stuff, okay? You know-

Lex Fridman 1:02:40 Fabric of reality. Yeah.

Alex Filippenko 1:02:41 Yeah, the fabric of reality we understand quite well. And there are a few little things like dark matter and dark energy that may be some sign of some superintelligence, but I doubt it, okay?

Lex Fridman 1:02:50 Yeah.

Alex Filippenko 1:02:50 You know, why would some superintelligence be holding clusters of galaxies together? Why would they be responsible for accelerating the expansion of the universe? So the point is, is that through science and applied science and engineering, we understand so much now that I'm not saying we know everything, but, but we know a hell of a lot, okay?

Lex Fridman 1:03:10 Yeah.

Alex Filippenko 1:03:10 And so there's th- it's not like there are lots of mysteries flying around there that are completely outside our level of, um, of, of exploration or understanding.

Lex Fridman 1:03:24 Yeah, from a-

Alex Filippenko 1:03:24 You know?

Lex Fridman 1:03:24 ... from a-

Alex Filippenko 1:03:26 It's-

Lex Fridman 1:03:26 I would say from, from, uh, the mystery perspective, it seems like the mystery of our own, like, cognition and consciousness is much grander than, like the degrees of freedom of possible explanations for what the heck is going on is much greater there than in the, in the physics-

Alex Filippenko 1:03:43 Exactly.

Lex Fridman 1:03:43 ... of the observable-

Alex Filippenko 1:03:44 How the brain works.

Lex Fridman 1:03:45 Yeah.

Alex Filippenko 1:03:45 How did life arise?

Lex Fridman 1:03:48 Yeah.

Alex Filippenko 1:03:48 Yeah.

Lex Fridman 1:03:48 That's-

Alex Filippenko 1:03:49 Big, big questions.

Lex Fridman 1:03:50 Yeah.

Alex Filippenko 1:03:50 But they, to me, don't indicate, uh, the existence of, uh, of, of, of an alien or something. I mean, unless we are the aliens. You know, we, we could have been contamination from some rocket ship that, that hit here a long, long time ago, and all evidence of it has been destroyed. But again, that alien would have started out somewhere. They're not, they're not here watching us right now, right?

Lex Fridman 1:04:14 Yeah.

Alex Filippenko 1:04:14 They're not among us. And so though there are expla- potential explanations for the Fermi paradox, and one of them that I kind of like is that the truly intelligent creatures are those that decided not to colonize the whole galaxy because they'd quickly run out of room there-

Lex Fridman 1:04:32 Yeah.

Alex Filippenko 1:04:32 ... because it's exponential, right? You send a probe to a planet, it makes two copies, they go out, they make two copies each, and it's an exponential, right? They, they quickly colonize the whole galaxy. But then the distance to the next galaxy, the next big one like Andromeda, that's two and a half million light years.

Lex Fridman 1:04:49 Yeah.

Alex Filippenko 1:04:49 That's a much grander scale now, right? And so it, it also could be that the reason they survived this long is that they got over this tendency that may well exist among sufficiently intelligent creatures, this tendency for aggression and self-destruction, right? If they bypassed that, and that may be one of the great filters, if there are more than one-

Lex Fridman 1:05:13 Mm-hmm.

Alex Filippenko 1:05:14 ... right, then they may not be a type of creature that feels the need to go and say, "Ooh, there's a nice looking planet, um, and there's a bunch of, you know, ants on it, let's go squish 'em and colonize it." No, it could even be the kind of Star Trek-like prime directive where-

Lex Fridman 1:05:32 Mm-hmm.

Alex Filippenko 1:05:32 ... you go and explore worlds but you don't interfere in any way, right?

Lex Fridman 1:05:37 And, and also-

Alex Filippenko 1:05:38 (laughs)

Lex Fridman 1:05:39 ... we call it exploration, is beautiful and everything, but th- there is underlying this desire to explore is a desire to conquer.

Alex Filippenko 1:05:48 Yeah. It's-

Lex Fridman 1:05:48 I me- I mean, if we're just being really honest about-

Alex Filippenko 1:05:50 Right now for us it is, right?

Lex Fridman 1:05:52 And, and you're saying it's possible to separate, but I would venture to say that you wouldn't... (sighs) That those are coupled. So I could, I could imagine a civilization that lives on for billions of years, that just stays on its, like figures out the minimal effort way of just-

Alex Filippenko 1:06:11 Yeah.

Lex Fridman 1:06:11 ... peacefully existing. It's like a monastery.

Alex Filippenko 1:06:13 Yeah, and it limits itself.

Lex Fridman 1:06:15 Okay. Yeah, it limits itself.

Alex Filippenko 1:06:16 You know, it's, it's planted its seeds in a number of places, so it's not vulnerable to a single point failure, right?

Lex Fridman 1:06:23 Yeah.

Alex Filippenko 1:06:23 Supernova going off near one of these stars or something, or an asteroid su- or a comet coming in from the Oort cloud equivalent of that planetary system and without warning, you know, thrashing them to bits. So they've got their seeds in a bunch of places, but they chose not to colonite, colonize the galaxy and they also choose not to interfere with this incredibly prevelent, primitive organism, homo sapiens, right?

Lex Fridman 1:06:50 (laughs)

Alex Filippenko 1:06:50 Um-

Lex Fridman 1:06:51 Or, or they, uh, this is like a, they enjoy, this is like a TV show for them. (laughs)

Alex Filippenko 1:06:58 Yeah, it could be like a TV show, right?

Lex Fridman 1:07:00 It's like a real- (laughs) So they-

Alex Filippenko 1:07:00 You know.

Lex Fridman 1:07:00 ... just tuned in.

Alex Filippenko 1:07:01 Right.

Lex Fridman 1:07:02 This, to, to this show.

Alex Filippenko 1:07:02 So those are possible explanations, yet I, I think that to me the most likely explanation for the Fermi paradox is that they really are very, very rare. And you know Carl Sagan estimated 100,000 of them.... if there's that many, some of them would have been way ahead of us and, and I think we would have seen them by now. If there were a handful, maybe they're there. But at that point, you're right on this dividing line between being a pessimist and an optimist.

Lex Fridman 1:07:29 (laughs) Yeah.

Alex Filippenko 1:07:30 And, and what are the odds for that, right?

Lex Fridman 1:07:31 (laughs)

Alex Filippenko 1:07:32 If you look at all the things that had to go right for us.

Lex Fridman 1:07:35 Yeah.

Alex Filippenko 1:07:35 And th- then, you know, getting back to something you said earlier, let's discuss, you know, primitive life.

Lex Fridman 1:07:40 Yeah.

Alex Filippenko 1:07:41 That could be the thing that's difficult to achieve, just getting the random molecules together to a point where they start self-replicating and evolving and becoming better and all that. That, that's an inordinately difficult thing, I think, though I'm not, you know, some molecular or cell biologist. But just it's, it's, it's the usual argument, you know, you're wandering around in the Sahara Desert and you stumble across a watch. Is your, is your initial response, "Oh, you know, a bunch of sand grains just came together randomly and formed this watch"? No, you, you think that something formed it or it came from some simpler structure that then became, you know, more complex, all right? It didn't just, uh, form. Well, even the simplest life is, is a very, very complex structure. Even the, even the simplest prokaryotic cells, not to mention eukaryotic cells, although that transition may have been the so-called great filter as well. Maybe the cells without a nucleus are relatively easy to form, and then the big next step is where you have a nucleus which then provides a lot of energy, which allows the cell to become much, much more complex and so on. Interestingly, going from eukaryotic cells, single cells, to multicellular organisms does not appear to be, at least on Earth, one of these great filters because there's evidence that it happened dozens of times-

Lex Fridman 1:09:07 Right.

Alex Filippenko 1:09:07 ... independently on Earth.

Lex Fridman 1:09:08 Right.

Alex Filippenko 1:09:09 So by, by a really great filter, something that happens very, very rarely, I mean that we had to get through, um, an obstacle that is just incredibly rare

Alex Filippenko 1:09:24 to get through.

Lex Fridman 1:09:25 And one of the really exciting scientific things is that that particular point, uh, is something that we might be able to discover even in our lifetimes that find life elsewhere, like Europa or-

Alex Filippenko 1:09:38 Yeah.

Lex Fridman 1:09:38 ... be able to dis-

Alex Filippenko 1:09:39 But see, that would be bad news, right?

Lex Fridman 1:09:41 (laughs) What?

Alex Filippenko 1:09:42 Because if we find lots of pretty advanced life-

Lex Fridman 1:09:46 Yeah.

Alex Filippenko 1:09:46 ... that would suggest... Uh, a- and, and especially if we found some, you know, defunct, you know, fossilized civilization or something-

Lex Fridman 1:09:53 Yeah. (laughs)

Alex Filippenko 1:09:53 ... somewhere else, that would be-

Lex Fridman 1:09:54 Oh, bacteria, you mean, over like-

Alex Filippenko 1:09:56 What's that?

Lex Fridman 1:09:57 ... uh, defunct civilization of, like, prim- primitive life form.

Alex Filippenko 1:09:59 Oh, oh, oh, no. Yeah, I'm sorry. I switched gears there. If we, if we found some intelligent or rather, you know-

Lex Fridman 1:10:03 Yeah.

Alex Filippenko 1:10:03 ... even, even trilobites, right, and stuff, you know-

Lex Fridman 1:10:05 Yeah.

Alex Filippenko 1:10:05 ... elsewhere, that would be bad news for us because that would mean that the great filter is ahead of us, y- you know, right?

Lex Fridman 1:10:11 Oh, interesting, yeah.

Alex Filippenko 1:10:11 Because it would mean that lots of, lots of things-

Lex Fridman 1:10:15 (laughs)

Alex Filippenko 1:10:15 ... have gotten roughly to our level.

Lex Fridman 1:10:17 Yeah.

Alex Filippenko 1:10:17 But, but given the Fermi paradox-

Lex Fridman 1:10:20 Yeah.

Alex Filippenko 1:10:20 ... if you accept that the Fermi paradox means that there's no one else out there, you don't necessarily have to accept that, but if you accept that it means that no one else is out there, and yet there are lots of things we found that are at or roughly at our level-

Lex Fridman 1:10:34 Mm-hmm.

Alex Filippenko 1:10:34 ... that means that the great filter is ahead of us and that bodes poorly for our long term future. You know, but-

Lex Fridman 1:10:41 Yeah, it's funny you said, uh, you started by saying you're a little bit on the pessimistic side. But it's funny because we're doing this kind of dance between pessimism and optimism because I'm not sure if us being alone in the observable universe as intelligent beings is pessimistic. It's-

Alex Filippenko 1:11:00 Well, it's good news in a sense for us because it means-

Lex Fridman 1:11:03 We're special? (laughs)

Alex Filippenko 1:11:04 ... that we made it through.

Lex Fridman 1:11:06 Oh, right.

Alex Filippenko 1:11:06 See?

Lex Fridman 1:11:07 Right.

Alex Filippenko 1:11:07 If we're the only ones and there are such great filters, maybe more than one, formation of life might be one of them, formation of eukaryotic, that is with a nucleus, cells be an- another, development of human-like intelligence might be another, right? There might be several such filters and we were the lucky ones. And you know, then people say, "Well, then that means you're, you're putting yourself into a special perspective and every time we've done that we've been wrong." And yeah, yeah, I know all those arguments, but it still could be the case that there's one of us, at least per galaxy or per 10 or 100 or 1,000 galaxies and we're sitting here having this conversation because we exist, and so there's a, there's an observational selection effect-

Lex Fridman 1:11:51 Yeah.

Alex Filippenko 1:11:51 ... there, right? Just because we're special doesn't mean that we shouldn't have these conversations about whether or not we're special, right? (laughs)

Lex Fridman 1:12:00 Yeah, so that's, that's exciting.

Alex Filippenko 1:12:01 So-

Lex Fridman 1:12:02 That's optimistic. (laughs)

Alex Filippenko 1:12:03 ... yeah. So that's the, that's the optimistic part, that-

Lex Fridman 1:12:05 Yeah.

Alex Filippenko 1:12:06 ... if we don't find other intelligent life there, it might mean that we're the ones that made it. Uh...

Lex Fridman 1:12:13 And, and in general outside the great filter and so on, you know, it's not obvious that, uh, the, the Stephen Hawking thing which is, it's not obvious that life out there is, is gonna be kind to us (laughs) as humans.

Alex Filippenko 1:12:26 Oh, yeah, uh, so you know, I knew Hawking and I greatly respect his, his scientific work, and in particular, uh, the early work on the unification of general theory of relativity and quantum physics, the two great pillars of modern physics, you know, Hawking radiation and all that. Fantastic work. You know, i- if he were alive he should have been a recipient of this year's Physics Nobel Prize, which was for the discovery of black holes and also, uh, by Roger Penrose for the theoretical work showing that given a, a star that's massive enough you, you basically can't avoid having a, a black hole. Anyway, Hawking, fantastic. I, I tip my hat to him. May he rest in peace. But-

Lex Fridman 1:13:05 That would've been a heck of a Nobel Prize-

Alex Filippenko 1:13:07 Oh, it would've, yeah.

Lex Fridman 1:13:07 ... black, black holes.

Alex Filippenko 1:13:08 Yeah, yeah, yeah. It would've been but-

Lex Fridman 1:13:09 Heck of a good group.

Alex Filippenko 1:13:10 But, but, but going back to what he said that we shouldn't be, um, broadcasting our presence to others, there I actually disagree with him respectfully because-... first of all, we've been unintentionally broadcasting our presence for 100 years, since the development of radio and TV, okay?

Lex Fridman 1:13:27 Yeah.

Alex Filippenko 1:13:27 Um, secondly, any alien that has the capability of coming here and squashing us, uh, either already knows about us and, you know, doesn't care 'cause we're just like little ants, and when there are ants in your kitchen, you tend to squash them, but if there are ants on the sidewalk and you're walking by, do you feel some great conviction that you have to squash any of them? No, you, you generally don't, right? We're irrelevant to them. All they need to do is keep an eye on us-

Lex Fridman 1:13:55 Yeah.

Alex Filippenko 1:13:55 ... to see whether we're approaching the kind of technological capability and know about them and have intentions of attacking them, and then they can squash us, right? Um...

Lex Fridman 1:14:08 (laughs)

Alex Filippenko 1:14:08 They, you know, they, they could have done it long ago.

Lex Fridman 1:14:11 Yeah.

Alex Filippenko 1:14:11 They'll, they'll do it if they want to. Whether we advertise our presence or not, is, is irrelevant. So, I really think that that's not a huge existential

Alex Filippenko 1:14:20 threat.

Lex Fridman 1:14:21 So, this is a good place to bring up a difficult topic. You mentioned, uh, they're, they might, they would be paying attention to us to see if we come up with any crazy technology. There's folks who have, uh, reported UFO sightings. There's actually, I've recently found out there's, uh, websites that track this, the da- the data of these reportings, and there's millions of them, as in the past, uh, several decades. So, seven decades and so on that they've been recorded. And the ufologist community, as, uh, they refer to themselves, you know, one of the ideas that I find compelling from an alien perspective, that they kind of started showing up ever since we figured out how to build nuclear weapons.

Alex Filippenko 1:15:12 Mm-hmm. (laughs)

Lex Fridman 1:15:13 That we sh- (laughs)

Alex Filippenko 1:15:14 What a coincidence. (laughs) Yeah.

Lex Fridman 1:15:16 Yeah. (laughs) Uh, so I mean, you know, if I was an alien, I would just start showing up then as well, just to, to-

Alex Filippenko 1:15:21 Well, why not just observe us from afar?

Lex Fridman 1:15:23 No, no, I know, right.

Alex Filippenko 1:15:24 Yeah.

Lex Fridman 1:15:24 I would figure out-

Alex Filippenko 1:15:25 Mm-hmm.

Lex Fridman 1:15:25 But tha- that's why I'm always, uh, keeping a distance and staying blurry.

Alex Filippenko 1:15:29 Right.

Lex Fridman 1:15:30 But...

Alex Filippenko 1:15:31 (laughs)

Lex Fridman 1:15:31 (laughs) But-

Alex Filippenko 1:15:32 Very pixelated.

Lex Fridman 1:15:33 (laughs) Very pixelated. You know, the, there is a, something in the human condition that, uh, cognition that wants to see, wants to believe beautiful things. And, uh, some are terrifying, some are exciting. Uh, ghosts, Bigfoot is a big fascination for folks.

Alex Filippenko 1:15:50 Yeah.

Lex Fridman 1:15:51 And, uh, UFO sightings I think falls into that. There's people that look at lights in the night sky and, I mean, there's, it's kind of a downer to think in a skeptical sense, to think that w- that's just the light.

Alex Filippenko 1:16:07 Yeah.

Lex Fridman 1:16:08 You want to feel like there's something magical there.

Alex Filippenko 1:16:10 Sure.

Lex Fridman 1:16:11 Uh, I mean, I felt that first when my dad, my dad's a physicist. When he first told me about ball lightning-

Alex Filippenko 1:16:18 Yeah.

Lex Fridman 1:16:18 ... when I was like a little kid.

Alex Filippenko 1:16:19 Very weird.

Lex Fridman 1:16:20 Very (laughs) like-

Alex Filippenko 1:16:20 Yeah.

Lex Fridman 1:16:21 Weird physical phenomena.

Alex Filippenko 1:16:22 Yeah.

Lex Fridman 1:16:23 And he said his intuition was, uh, d- d- tellin' me this as a little kid, uh, like I really liked math. His intuition was, "Whoever figures out ball lightning will get a Nobel Prize."

Alex Filippenko 1:16:34 Mm-hmm.

Lex Fridman 1:16:35 Like he, he... I think that was a side comment he gave me. And I, I decided there when I was like five years old or whatever that-

Alex Filippenko 1:16:41 Yeah.

Lex Fridman 1:16:41 ... I'm gonna win a Nobel Prize for figuring out ball lightning.

Alex Filippenko 1:16:44 (laughs) Figuring out ball lightning.

Lex Fridman 1:16:44 That was like one of the first sort of sparks of the scientific mindset. Those mysteries, they capture your imagination.

Alex Filippenko 1:16:51 Yeah.

Lex Fridman 1:16:51 I, I think when I speak to people that report UFOs, that's, that fire, that's what I see.

Alex Filippenko 1:16:57 Sure.

Lex Fridman 1:16:57 That excitement.

Alex Filippenko 1:16:58 Yeah, I understand that. Mm-hmm.

Lex Fridman 1:17:00 But what, what do we do with that? Because there's hundreds of thousands, if not millions.

Alex Filippenko 1:17:06 Mm-hmm.

Lex Fridman 1:17:06 And in the scientific community, you're like the perfect person. You have-

Alex Filippenko 1:17:09 (laughs)

Lex Fridman 1:17:09 ... you have an awesome Einstein, uh, t- shirt. I mean, what, what do we do with those reports? It's, uh, most of the scientific community kind of rolls their eyes and dismisses it.

Alex Filippenko 1:17:21 Yeah.

Lex Fridman 1:17:21 Is it, is it possible that w- a tiny percent of those folks saw something that's worth deeply investigating?

Alex Filippenko 1:17:30 Sure, we should investigate it. It's just one of these things where, you know, they've not brought us a hunk of kryptonite or something like that, right? They haven't brought us actual, tangible physical evidence with which experiments can be done in laboratories.

Lex Fridman 1:17:45 Right.

Alex Filippenko 1:17:46 Uh, it's, it's anecdotal evidence. The photographs are, um, in some cases, in most cases I would say, quite am-ambiguous.

Lex Fridman 1:17:54 I don't know what to think about... So, David Fravor is the first person. He's a Navy pilot commander.

Alex Filippenko 1:17:59 Yeah.

Lex Fridman 1:18:00 And there's a bunch of them, but he's sort of one of the most legit pilots and people-

Alex Filippenko 1:18:06 Yeah.

Lex Fridman 1:18:06 ... I've ever met.

Alex Filippenko 1:18:08 Right.

Lex Fridman 1:18:08 The fact that he saw something weird-

Alex Filippenko 1:18:11 Yeah.

Lex Fridman 1:18:11 ... he doesn't know what the heck it is-

Alex Filippenko 1:18:13 Yeah.

Lex Fridman 1:18:13 ... but he saw something weird. I mean, I don't know what to do with that. And one, on the psy- psychological side... So I'm pretty confident he saw what he says he saw-

Alex Filippenko 1:18:23 Mm-hmm.

Lex Fridman 1:18:24 ... which he's not pro- he's saying-

Alex Filippenko 1:18:25 Mm-hmm.

Lex Fridman 1:18:25 It's something weird.

Alex Filippenko 1:18:27 Right.

Lex Fridman 1:18:28 Th- one of the interesting psychological things that worries me is that everybody in the Navy, everybody in the US government, everybody in the scientific community just kind of like, uh, pretended that nothing happened.

Alex Filippenko 1:18:44 Mm-hmm.

Lex Fridman 1:18:45 That kind of instinct, that's what makes me believe if aliens show up-

Alex Filippenko 1:18:49 Mm-hmm.

Lex Fridman 1:18:49 ... we would all like just ignore th- their presence.

Alex Filippenko 1:18:53 Mm-hmm.

Lex Fridman 1:18:53 Th- that's what bothered me, that you don't, you don't investigate it more carefully and use this opportunity to inspire the world.

Alex Filippenko 1:19:02 Mm-hmm.

Lex Fridman 1:19:02 Like, so in terms of kryptonite, I think the conspiracy theory folks say that whenever there is some good hard evidence-

Alex Filippenko 1:19:13 Mm-hmm.

Lex Fridman 1:19:13 ... that scientists would be excited about-

Alex Filippenko 1:19:15 Mm-hmm.

Lex Fridman 1:19:15 ... the U- uh, there's this kind of conspiracy that I don't like 'cause it's ultimately negative-

Alex Filippenko 1:19:20 Mm-hmm.

Lex Fridman 1:19:20 ... that the US government will somehow hide-

Alex Filippenko 1:19:22 Mm-hmm.

Lex Fridman 1:19:22 ... the good evidence-

Alex Filippenko 1:19:23 Yeah.

Lex Fridman 1:19:24 ... uh, to, uh, to protect it. Of course, there's some legitimacy to it 'cause you want to protect military, uh, secrets, all that kind of stuff, but-... the-

Alex Filippenko 1:19:34 Yeah.

Lex Fridman 1:19:35 ... like, I-I don't know, I don't know what to do with this beautiful mess, because, um, I thi- think millions of people are inspired by UFOs.

Alex Filippenko 1:19:43 Right.

Lex Fridman 1:19:44 And it feels like an opportunity to inspire people about science.

Alex Filippenko 1:19:47 Yeah. So, I would say, you know, a- as Carl Sagan used to say, "Extraordinary claims require extraordinary-"

Lex Fridman 1:19:53 Yeah.

Alex Filippenko 1:19:53 "... evidence." Right? I've quoted him a number of times. Uh, we would, we would welcome such evidence. Uh, on the other hand, you know, a lot of the things that are seen or perhaps even hidden from us, you could imagine, for military purposes, surveillance purposes, the US government doesn't want us to know, or-

Lex Fridman 1:20:16 Yeah.

Alex Filippenko 1:20:16 ... maybe some of these pilots saw Soviet or Israeli or whatever, uh, satellites, right? A lot of the, or some of the crashes that have occurred were later found to be, you know, weather balloons or whatever. You know, the, when there are more conventional explanations-

Lex Fridman 1:20:33 Yeah.

Alex Filippenko 1:20:34 ... science tends to stay away from the, um, from the sensational ones, right? And so, it may be that someone else's calling in life is to investigate these phenomena.

Lex Fridman 1:20:48 Yeah.

Alex Filippenko 1:20:48 And I welcome that, as a scientist.

Lex Fridman 1:20:51 Yeah.

Alex Filippenko 1:20:51 I, I don't categorically actually deny the possibility that ships of some sort could have visited us, because as I said earlier, at slow speeds, there's no problem in reaching other stars. In fact, our Voyager and Pioneer spacecraft, in a few million years, are gonna be in the vicinity of different stars. We can even calculate which ones they're gonna be in the vicinity of, right?

Lex Fridman 1:21:14 Mm-hmm.

Alex Filippenko 1:21:14 Uh, so there's nothing that breaks any laws of physics, if you do it slowly. But that's different, you know, just having Voyager or Pioneer fly by some star, that's different from having active aliens altering the trajectory of their vehicle, in real time, spying on us-

Lex Fridman 1:21:31 Yeah.

Alex Filippenko 1:21:31 ... and then either zipping back to their home planet or sending signals that tell them about us, because they are likely many years, many lightyears away.

Lex Fridman 1:21:43 Yeah.

Alex Filippenko 1:21:43 And they're not gonna have broken that barrier as well, okay? Right? So, so I- I just, you know ... Go ahead, study them. Great. I, you know, for some young kid who wants to do it, it might be their calling, and that's how they might find meaning in their lives is to be the scientist who really explores these things. I chose not to, because at a very young age, I found the evidence, to the degree that I investigated it, to be really quite unconvincing, and I had other things that I wanted to do. But I don't categorically deny the possibility, and I think it should be investigated.

Lex Fridman 1:22:24 Yeah. I mean, this is, uh, this is one of those phenomena that, um, 99.9% of people are almost definitely, there's conventional explanations, and then there's, like, mysterious things that probably have explanations that are a little bit more complicated.

Alex Filippenko 1:22:42 Yeah.

Lex Fridman 1:22:42 It's ... But there's not enough to work with. I tend to believe that if aliens showed up, there would be plenty of evidence, uh, for scientists (laughs) to study.

Alex Filippenko 1:22:53 Yeah.

Lex Fridman 1:22:53 That, like, a- and the, uh, exactly, uh, as you said, a Voyager type of spacecraft, I could see sort of, um, some kind of, kind of a dumb thing, almost like a sensor to, like, probing, like statistically speaking.

Alex Filippenko 1:23:09 Mm-hmm. Just flying by.

Lex Fridman 1:23:09 Flying by, maybe lands, maybe there's some kind of robot type of thingies that just, like, move around and so on.

Alex Filippenko 1:23:15 Yeah.

Lex Fridman 1:23:15 Like, in ways that we don't understand. But, but I feel like ... Well, I feel like there would be plenty of hard, hard-to-dismiss evidence. And I also, especially this year, believe that the US government is not sufficiently competent-

Alex Filippenko 1:23:34 (laughs)

Lex Fridman 1:23:35 ... given the huge amount of evidence that would be revealed from this kind of thing, to conceal all of it.

Alex Filippenko 1:23:41 Right.

Lex Fridman 1:23:41 Uh, at least in modern times. You can say maybe decades ago-

Alex Filippenko 1:23:44 Yeah.

Lex Fridman 1:23:44 ... but in modern times. But, you know, I, uh, the, the people I speak to, and the reason I bring it up, is because so many people write to me they're inspired by it.

Alex Filippenko 1:23:53 By the way, I wanted to comment on something you s- said earlier. Um, yeah, I had said that I'm sort of an, a pessimist, in that I think there are very few other intelligent, mechanically able creatures out there, but then I said, yes, in a sense, I'm an optimist-

Lex Fridman 1:24:09 Yes.

Alex Filippenko 1:24:09 ... as you pointed out, because it means that we made it through-

Lex Fridman 1:24:11 Yeah.

Alex Filippenko 1:24:12 ... the great filter, right. I- I meant originally that I'm a pessimist, in that I'm pessimistic about the possibility that there are many, many of us out there.

Lex Fridman 1:24:21 You know, mathematically speaking-

Alex Filippenko 1:24:23 Yeah.

Lex Fridman 1:24:23 ... in the Drake equation. (laughs)

Alex Filippenko 1:24:24 E- exactly. Right, right. But, but it may mean a good thing-

Lex Fridman 1:24:27 Yeah. (laughs) Yeah.

Alex Filippenko 1:24:27 ... for our ultimate survival, right?

Lex Fridman 1:24:29 Yeah.

Alex Filippenko 1:24:29 So, I'm glad you caught me on that. Yeah.

Lex Fridman 1:24:30 Yeah. I- I definitely agree with you. It, I-

Alex Filippenko 1:24:32 Yeah.

Lex Fridman 1:24:32 ... it is ultimately an optimistic statement.

Alex Filippenko 1:24:33 Yeah. But anyway, I think, you know, UFO, uh, research is, is interesting. And I guess one of the reasons I've not been terribly convinced is that I think there are some scientists who are investigating this, and they've not found any clear evidence. Now, I must admit, I have not looked through the literature to convince myself that there are many scientists doing systematic studies of these various reports, so I can't say for sure that there's a critical mass of them.

Lex Fridman 1:25:01 Well, the one-

Alex Filippenko 1:25:02 But it's just that you, you never get these reports from hardcore scientists. That's the other thing. And astronomers, you know, what do we do? We spend our time studying the heavens, and you'd think we'd be the ones that are most likely, aside from pilots perhaps, at seeing weird things in the sky, and we just never do, of the unexplained UFO type nature.

Lex Fridman 1:25:22 Yeah. I definitely, I, I try to keep an open mind, but for people who listen, um, it's actually really difficult for a scientist. Like, I get probably ... Like, this year, I've probably gotten over-... probably, maybe, maybe over a thousand emails on, in, on the topic of AGI.

Alex Filippenko 1:25:41 Mm-hmm.

Lex Fridman 1:25:42 It's very difficult to, uh... Uh, you know, people write to me. It's like, "How can you ignore this in the AGI side, like this model? This is obviously the model that's going to achieve general intelligence. How can you ignore it? I'm giving you the answer. Here's my document." And they're always-

Alex Filippenko 1:25:57 Mm-hmm.

Lex Fridman 1:25:57 ... just these large, uh, write-ups. The problem is it's very difficult to wheel- weed through a bunch of BS.

Alex Filippenko 1:26:07 Right.

Lex Fridman 1:26:07 It's, it's very possible that you ha- actually saw the UFO, but you have to acknowledge that you n- By UFO, I mean an extrase- terrestrial life.

Alex Filippenko 1:26:17 Right.

Lex Fridman 1:26:17 You have to acknowledge the hundreds of thousands of people who are a little bit, if not a lot, full of BS.

Alex Filippenko 1:26:26 Right.

Lex Fridman 1:26:26 And from a scientist perspective, it just... It's really hard work. And it's, um... When there's amazing stuff out there, it's like, "Why investigate-"

Alex Filippenko 1:26:35 Yeah, yeah.

Lex Fridman 1:26:35 "... Bigfoot when evolution, in-"

Alex Filippenko 1:26:38 Yeah.

Lex Fridman 1:26:38 "... all of its richness, is beautiful?"