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

1. 0:00 – 2:08

   Introduction

   1. LFLex Fridman0:00

      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.

2. 2:08 – 3:32

   Universe expansion

   1. LFLex Fridman2:08

      Let's start by talking about the biggest possible thing, the universe.

   2. AFAlex Filippenko2:12

      Sure.

   3. LFLex Fridman2:12

      Will the universe expand forever or collapse on itself?

   4. AFAlex Filippenko2:16

      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.

   5. LFLex Fridman2:53

      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?

   6. AFAlex Filippenko3:01

      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.

   7. LFLex Fridman3:31

      And yet,

3. 3:32 – 11:00

   Dark energy

   1. LFLex Fridman3:32

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

   2. AFAlex Filippenko3:39

      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-

   3. LFLex Fridman4:25

      Mm-hmm.

   4. AFAlex Filippenko4:25

      ... 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-

   5. LFLex Fridman5:39

      (laughs) .

   6. AFAlex Filippenko5:39

      ... 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.

   7. LFLex Fridman5:50

      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)

   8. AFAlex Filippenko6:06

      Yeah.

   9. LFLex Fridman6:06

      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-

   10. AFAlex Filippenko6:23

       (laughs)

   11. LFLex Fridman6:23

       ... it, there must be something there because of what we're observing?

   12. AFAlex Filippenko6:26

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

   13. LFLex Fridman6:31

       Right.

   14. AFAlex Filippenko6:31

       ... there are no, um, miracles, uh, of a supernatural nature, okay?

   15. LFLex Fridman6:37

       Yeah.

   16. AFAlex Filippenko6:38

       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.

   17. LFLex Fridman6:55

       Right.

   18. AFAlex Filippenko6:55

       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.

   19. LFLex Fridman7:16

       Okay.

   20. AFAlex Filippenko7:16

       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.

   21. LFLex Fridman7:31

       So there is hypotheses for different fields, like-

   22. AFAlex Filippenko7:34

       Oh, yeah.

   23. LFLex Fridman7:34

       ... with names and stuff like that?

   24. AFAlex Filippenko7:35

       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.

   25. LFLex Fridman8:05

       Yeah.

   26. AFAlex Filippenko8:06

       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-

   27. LFLex Fridman9:07

       (laughs) Yeah.

   28. AFAlex Filippenko9:09

       ... 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.

   29. LFLex Fridman9:28

       Mm-hmm.

   30. AFAlex Filippenko9:28

       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-
4. 11:00 – 22:50

   Scientific revolutions

   1. LFLex Fridman11:00

      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?

   2. AFAlex Filippenko11:26

      Sure, I mean, so that puts us back in the shoes of Copernicus, right?

   3. LFLex Fridman11:29

      Right.

   4. AFAlex Filippenko11:30

      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.

   5. LFLex Fridman11:58

      Oh, wow, interesting. So it's-

   6. AFAlex Filippenko11:59

      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.

   7. LFLex Fridman12:37

      Yeah.

   8. AFAlex Filippenko12:37

      Yeah.

   9. LFLex Fridman12:39

      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.

   10. AFAlex Filippenko12:51

       Yeah. (laughs)

   11. LFLex Fridman12:51

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

   12. AFAlex Filippenko13:02

       Right.

   13. LFLex Fridman13:03

       Oh, that's, um, that's kind of sad. It's, uh, sad from an individual descendant of ape perspective-

   14. AFAlex Filippenko13:10

       Yeah.

   15. LFLex Fridman13:11

       ... 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.

   16. AFAlex Filippenko13:25

       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.

   17. LFLex Fridman13:34

       Sounding, yeah.

   18. AFAlex Filippenko13:34

       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-

   19. LFLex Fridman13:45

       Mm-hmm.

   20. AFAlex Filippenko13:46

       ... 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-

   21. LFLex Fridman14:22

       Mm-hmm.

   22. AFAlex Filippenko14:22

       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-

   23. LFLex Fridman15:44

       Mm-hmm.

   24. AFAlex Filippenko15:44

       ... 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-

   25. LFLex Fridman15:58

       Mm-hmm.

   26. AFAlex Filippenko15:58

       ... 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.

   27. LFLex Fridman16:13

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

   28. AFAlex Filippenko16:18

       Yeah.

   29. LFLex Fridman16:18

       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.

   30. AFAlex Filippenko16:36

       Yeah.
5. 22:50 – 26:22

   Asteroid hitting Earth

   1. LFLex Fridman22:50

      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-

   2. AFAlex Filippenko23:11

      Yeah.

   3. LFLex Fridman23:11

      ... philosophically too.

   4. AFAlex Filippenko23:12

      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-

   5. LFLex Fridman23:29

      Yeah.

   6. AFAlex Filippenko23:30

      ... 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-

   7. LFLex Fridman24:00

      Mm-hmm.

   8. AFAlex Filippenko24:00

      ... you, you have to deflect it 90 degrees-

   9. LFLex Fridman24:02

      Yep.

   10. AFAlex Filippenko24:02

       ... or more, right?

   11. LFLex Fridman24:03

       Mm-hmm.

   12. AFAlex Filippenko24:03

       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.

   13. LFLex Fridman24:33

       (laughs)

   14. AFAlex Filippenko24:33

       But you know, that might cause just so much panic that I'm...

   15. LFLex Fridman24:36

       Yeah. (laughs)

   16. AFAlex Filippenko24:36

       How would you do with New York City or Los Angeles, or something like that, right?

   17. LFLex Fridman24:41

       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)

   18. AFAlex Filippenko24:54

       Competence, yeah.

   19. LFLex Fridman24:55

       Competence, yeah.

   20. AFAlex Filippenko24:56

       Right, but we expect extreme incompetence, uh, if anything, right?

   21. LFLex Fridman24:59

       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-

   22. AFAlex Filippenko25:28

       Yeah.

   23. LFLex Fridman25:28

       ... to be able to detect stuff.

   24. AFAlex Filippenko25:29

       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.

   25. LFLex Fridman26:13

       Mm-hmm.

   26. AFAlex Filippenko26:14

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

6. 26:22 – 33:22

   Giant solar flares and the power grid

   1. AFAlex Filippenko26:22

      um, so maybe we have to worry about the sun getting brighter on that timescale.

   2. LFLex Fridman26:28

      (laughs)

   3. AFAlex Filippenko26:28

      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-

   4. LFLex Fridman28:18

      Mm-hmm.

   5. AFAlex Filippenko28:18

      ... 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-

   6. LFLex Fridman28:38

      (laughs)

   7. AFAlex Filippenko28:38

      ... 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...

   8. LFLex Fridman29:06

      It's, it's, uh, terrifying to think-

   9. AFAlex Filippenko29:07

      (laughs)

   10. LFLex Fridman29:08

       ... 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-

   11. AFAlex Filippenko29:15

       Yeah.

   12. LFLex Fridman29:15

       ... and realizing we should have supported our local astronomer more. (laughs)

   13. AFAlex Filippenko29:20

       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-

   14. LFLex Fridman29:32

       Mm-hmm.

   15. AFAlex Filippenko29:32

       ... or, you know, something like a super volcano, right?

   16. LFLex Fridman29:34

       Yeah.

   17. AFAlex Filippenko29:35

       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-

   18. LFLex Fridman31:27

       Could be-

   19. AFAlex Filippenko31:27

       ... when, when all of agriculture is, is cut off, right? And when-

   20. LFLex Fridman31:32

       It could be hundreds of millions or billions of people-

   21. AFAlex Filippenko31:34

       Yeah.

   22. LFLex Fridman31:35

       ... starving to death.

   23. AFAlex Filippenko31:36

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

   24. LFLex Fridman31:44

       First off, toilet paper.

   25. AFAlex Filippenko31:45

       (laughs) There you go.

   26. LFLex Fridman31:46

       (laughs)

   27. AFAlex Filippenko31:46

       Stash that toilet paper, you know.

   28. LFLex Fridman31:48

       (laughs)

   29. AFAlex Filippenko31:48

       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.

   30. LFLex Fridman31:58

       Yeah.
7. 33:22 – 38:13

   Elon Musk and space exploration

   1. AFAlex Filippenko33:22

      (laughs)

   2. LFLex Fridman33:23

      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-

   3. AFAlex Filippenko33:57

      Mm-hmm.

   4. LFLex Fridman33:57

      ... 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?

   5. AFAlex Filippenko34:34

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

   6. LFLex Fridman34:39

      (laughs) Sorry. Sorry. (laughs)

   7. AFAlex Filippenko34:40

      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.

   8. LFLex Fridman35:36

      Would that be a good-

   9. AFAlex Filippenko35:37

      Explore further.

   10. LFLex Fridman35:38

       Would that be a good next step, would you say?

   11. AFAlex Filippenko35:39

       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.

   12. LFLex Fridman35:45

       (laughs)

   13. AFAlex Filippenko35:45

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

   14. LFLex Fridman35:50

       Yeah.

   15. AFAlex Filippenko35:50

       ... 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.

   16. LFLex Fridman36:12

       Mm-hmm.

   17. AFAlex Filippenko36:12

       Sort of like every time you flew from San Francisco to Los Angeles, you discard the airplane, right?

   18. LFLex Fridman36:17

       Yeah.

   19. AFAlex Filippenko36:18

       I mean, tha- that's crazy.

   20. LFLex Fridman36:19

       Yeah.

   21. AFAlex Filippenko36:19

       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.

   22. LFLex Fridman36:30

       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.

   23. AFAlex Filippenko36:39

       Yeah.

   24. LFLex Fridman36:39

       Like, wha- do you have thoughts about this, um-

   25. AFAlex Filippenko36:42

       Well-

   26. LFLex Fridman36:42

       ... challenges of this kind of prospect?

   27. AFAlex Filippenko36:44

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

   28. LFLex Fridman36:51

       Yeah.

   29. AFAlex Filippenko36:51

       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.

   30. LFLex Fridman37:11

       You know, I-
8. 38:13 – 45:35

   Exoplanets

   1. LFLex Fridman38:13

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

   2. AFAlex Filippenko38:18

      Right.

   3. LFLex Fridman38:18

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

   4. AFAlex Filippenko38:24

      Yeah.

   5. LFLex Fridman38:24

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

   6. AFAlex Filippenko38:31

      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?

   7. LFLex Fridman38:45

      And that's a relatively new-

   8. AFAlex Filippenko38:47

      Yeah, it's a new discovery.

   9. LFLex Fridman38:48

      ... that's exciting.

   10. AFAlex Filippenko38:48

       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.

   11. LFLex Fridman39:07

       Yeah.

   12. AFAlex Filippenko39:08

       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-

   13. LFLex Fridman39:26

       Mm-hmm.

   14. AFAlex Filippenko39:27

       ... 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?

   15. LFLex Fridman40:18

       Mm-hmm.

   16. AFAlex Filippenko40:18

       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?

   17. LFLex Fridman40:26

       Yeah.

   18. AFAlex Filippenko40:26

       So then a, a typical bright star, Sirius, uh, the brightest star in the sky, maybe not a typical bright star-

   19. LFLex Fridman40:33

       (laughs)

   20. AFAlex Filippenko40:33

       ... 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.

   21. LFLex Fridman40:46

       Yeah.

   22. AFAlex Filippenko40:46

       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?

   23. LFLex Fridman41:01

       (laughs)

   24. AFAlex Filippenko41:01

       Now, that's 10,000 generations, okay? Let's say-

   25. LFLex Fridman41:04

       Yeah.

   26. AFAlex Filippenko41:04

       ... a generation of humans is 25 years, right?

   27. LFLex Fridman41:06

       Yeah.

   28. AFAlex Filippenko41:07

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

   29. LFLex Fridman41:16

       Yeah.

   30. AFAlex Filippenko41:16

       ... all their recycling of everything, for 10,000 generations. They have to commit themselves to living on this vehicle-
9. 45:35 – 47:45

   Traveling close to the speed of light

   1. AFAlex Filippenko45:35

      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?

   2. LFLex Fridman46:17

      Mm-hmm.

   3. AFAlex Filippenko46:17

      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?

   4. LFLex Fridman46:29

      Mm-hmm.

   5. AFAlex Filippenko46:29

      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.

   6. LFLex Fridman47:00

      Yeah.

   7. AFAlex Filippenko47:01

      They'll zip past it, take a picture of the exoplanets that we know-

   8. LFLex Fridman47:04

      Yeah.

   9. AFAlex Filippenko47:04

      ... orbit that three or more star system and, uh-

   10. LFLex Fridman47:08

       Say hello real quick.

   11. AFAlex Filippenko47:09

       ... say hello real quickly and then-

   12. LFLex Fridman47:10

       (laughs)

   13. AFAlex Filippenko47:10

       ... send the images back to us, okay?

   14. LFLex Fridman47:12

       Yeah.

   15. AFAlex Filippenko47:12

       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.

   16. LFLex Fridman47:25

       Yeah.

   17. AFAlex Filippenko47:25

       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

10. 47:45 – 56:11

    Traveling faster than the speed of light

    1. AFAlex Filippenko47:45

       and multiply, right?

    2. LFLex Fridman47:46

       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-

    3. AFAlex Filippenko48:00

       Yeah.

    4. LFLex Fridman48:01

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

    5. AFAlex Filippenko48:11

       Yeah.

    6. LFLex Fridman48:12

       ... 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-

    7. AFAlex Filippenko48:30

       Yeah.

    8. LFLex Fridman48:30

       ... our transportation?

    9. AFAlex Filippenko48:31

       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-

    10. LFLex Fridman48:42

        Yeah.

    11. AFAlex Filippenko48:42

        ... cutting the distance to make it very, very short through a wormhole or something like that.

    12. LFLex Fridman48:47

        ... possible, no?

    13. AFAlex Filippenko48:48

        Well, you know, call me not very imaginative.

    14. LFLex Fridman48:51

        (laughs)

    15. AFAlex Filippenko48:51

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

    16. LFLex Fridman48:57

        Yeah.

    17. AFAlex Filippenko48:57

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

    18. LFLex Fridman49:04

        Yep.

    19. AFAlex Filippenko49:04

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

    20. LFLex Fridman49:12

        Yeah.

    21. AFAlex Filippenko49:12

        So let me not be another Lor- Lord Kelvin.

    22. LFLex Fridman49:14

        (laughs)

    23. AFAlex Filippenko49:15

        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) .

    24. LFLex Fridman50:58

        Yeah, so it's still information.

    25. AFAlex Filippenko50:59

        Yeah, it's still information. It's scrambled information, but there's a way maybe-

    26. LFLex Fridman51:02

        (laughs)

    27. AFAlex Filippenko51:02

        ... of bringing it back, right?

    28. LFLex Fridman51:03

        Yeah.

    29. AFAlex Filippenko51:04

        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.

    30. LFLex Fridman51:53

        (laughs)
11. 56:11 – 59:46

    Intelligent life in the universe

    1. AFAlex Filippenko56:11

    2. LFLex Fridman56:11

       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.

    3. AFAlex Filippenko56:45

       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-

    4. LFLex Fridman57:22

       Yeah.

    5. AFAlex Filippenko57:22

       ... 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-

    6. LFLex Fridman57:32

       But your- your sense is our galaxy's not teeming with life.

    7. AFAlex Filippenko57:35

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

    8. LFLex Fridman57:44

       Intelligent.

    9. AFAlex Filippenko57:44

       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.

    10. LFLex Fridman58:13

        I see.

    11. AFAlex Filippenko58:13

        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-

    12. LFLex Fridman58:19

        Mm-hmm.

    13. AFAlex Filippenko58:19

        ... in its history.

    14. LFLex Fridman58:21

        Yes.

    15. AFAlex Filippenko58:21

        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?

    16. LFLex Fridman59:03

        Yeah. Yeah.

    17. AFAlex Filippenko59:03

        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.

    18. LFLex Fridman59:26

        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-

    19. AFAlex Filippenko59:36

        Right.

    20. LFLex Fridman59:36

        ... but they live very briefly and they die.

    21. AFAlex Filippenko59:38

        They're flashbulbs in the night.

    22. LFLex Fridman59:39

        They're fly- flight. (laughs)

    23. AFAlex Filippenko59:42

        That brings me to the fourth-

    24. LFLex Fridman59:43

        Flashbulbs in the night.

    25. AFAlex Filippenko59:44

        ... the fourth issue-

    26. LFLex Fridman59:45

        Yeah.

    27. AFAlex Filippenko59:45

        ... and that is

12. 59:46 – 1:09:24

    Fermi Paradox

    1. AFAlex Filippenko59:46

       the- you know, the Fermi paradox.

    2. LFLex Fridman59:47

       Yeah.

    3. AFAlex Filippenko59:47

       If they're common, where the hell are they? (laughs) You know?

    4. LFLex Fridman59:51

       (laughs) Yeah.

    5. AFAlex Filippenko59:52

       Notwithstanding the various UFO reports in Roswell-

    6. LFLex Fridman59:55

       Yeah.

    7. AFAlex Filippenko59:55

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

    8. LFLex Fridman1:00:02

       Yeah.

    9. AFAlex Filippenko1:00:02

       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.

    10. LFLex Fridman1:01:27

        Mm.

    11. AFAlex Filippenko1:01:27

        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.

    12. LFLex Fridman1:01:35

        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-

    13. AFAlex Filippenko1:01:49

        Yeah.

    14. LFLex Fridman1:01:50

        ... is, is, um, we don't want to acknowledge it. Like, what, what if trees-

    15. AFAlex Filippenko1:01:55

        Right.

    16. LFLex Fridman1:01:56

        (laughs)

    17. AFAlex Filippenko1:01:56

        Right, right. Yeah.

    18. LFLex Fridman1:01:57

        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?

    19. AFAlex Filippenko1:02:04

        Yeah, I mean, it's like, you know, you, you're an ant crawling around on a sidewalk somewhere-

    20. LFLex Fridman1:02:08

        Right. (laughs)

    21. AFAlex Filippenko1:02:08

        ... and do, do you notice the humans wandering around?

    22. LFLex Fridman1:02:10

        Exactly.

    23. AFAlex Filippenko1:02:10

        And, and the Empire State Building and, you know, rocket ships-

    24. LFLex Fridman1:02:13

        Yeah.

    25. AFAlex Filippenko1:02:13

        ... 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-

    26. LFLex Fridman1:02:22

        Yeah.

    27. AFAlex Filippenko1:02:22

        ... just not able to do so.

    28. LFLex Fridman1:02:23

        Like if you look at dark energy, maybe-

    29. AFAlex Filippenko1:02:25

        Yeah, maybe.

    30. LFLex Fridman1:02:25

        ... we, we call it as a field.
13. 1:09:24 – 1:14:20

    Finding alien life would be bad news

    1. AFAlex Filippenko1:09:24

       to get through.

    2. LFLex Fridman1:09:25

       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-

    3. AFAlex Filippenko1:09:38

       Yeah.

    4. LFLex Fridman1:09:38

       ... be able to dis-

    5. AFAlex Filippenko1:09:39

       But see, that would be bad news, right?

    6. LFLex Fridman1:09:41

       (laughs) What?

    7. AFAlex Filippenko1:09:42

       Because if we find lots of pretty advanced life-

    8. LFLex Fridman1:09:46

       Yeah.

    9. AFAlex Filippenko1:09:46

       ... that would suggest... Uh, a- and, and especially if we found some, you know, defunct, you know, fossilized civilization or something-

    10. LFLex Fridman1:09:53

        Yeah. (laughs)

    11. AFAlex Filippenko1:09:53

        ... somewhere else, that would be-

    12. LFLex Fridman1:09:54

        Oh, bacteria, you mean, over like-

    13. AFAlex Filippenko1:09:56

        What's that?

    14. LFLex Fridman1:09:57

        ... uh, defunct civilization of, like, prim- primitive life form.

    15. AFAlex Filippenko1:09:59

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

    16. LFLex Fridman1:10:03

        Yeah.

    17. AFAlex Filippenko1:10:03

        ... even, even trilobites, right, and stuff, you know-

    18. LFLex Fridman1:10:05

        Yeah.

    19. AFAlex Filippenko1:10:05

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

    20. LFLex Fridman1:10:11

        Oh, interesting, yeah.

    21. AFAlex Filippenko1:10:11

        Because it would mean that lots of, lots of things-

    22. LFLex Fridman1:10:15

        (laughs)

    23. AFAlex Filippenko1:10:15

        ... have gotten roughly to our level.

    24. LFLex Fridman1:10:17

        Yeah.

    25. AFAlex Filippenko1:10:17

        But, but given the Fermi paradox-

    26. LFLex Fridman1:10:20

        Yeah.

    27. AFAlex Filippenko1:10:20

        ... 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-

    28. LFLex Fridman1:10:34

        Mm-hmm.

    29. AFAlex Filippenko1:10:34

        ... that means that the great filter is ahead of us and that bodes poorly for our long term future. You know, but-

    30. LFLex Fridman1:10:41

        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-
14. 1:14:20 – 1:27:30

    UFO sightings

    1. AFAlex Filippenko1:14:20

       threat.

    2. LFLex Fridman1:14:21

       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.

    3. AFAlex Filippenko1:15:12

       Mm-hmm. (laughs)

    4. LFLex Fridman1:15:13

       That we sh- (laughs)

    5. AFAlex Filippenko1:15:14

       What a coincidence. (laughs) Yeah.

    6. LFLex Fridman1:15:16

       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-

    7. AFAlex Filippenko1:15:21

       Well, why not just observe us from afar?

    8. LFLex Fridman1:15:23

       No, no, I know, right.

    9. AFAlex Filippenko1:15:24

       Yeah.

    10. LFLex Fridman1:15:24

        I would figure out-

    11. AFAlex Filippenko1:15:25

        Mm-hmm.

    12. LFLex Fridman1:15:25

        But tha- that's why I'm always, uh, keeping a distance and staying blurry.

    13. AFAlex Filippenko1:15:29

        Right.

    14. LFLex Fridman1:15:30

        But...

    15. AFAlex Filippenko1:15:31

        (laughs)

    16. LFLex Fridman1:15:31

        (laughs) But-

    17. AFAlex Filippenko1:15:32

        Very pixelated.

    18. LFLex Fridman1:15:33

        (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.

    19. AFAlex Filippenko1:15:50

        Yeah.

    20. LFLex Fridman1:15:51

        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.

    21. AFAlex Filippenko1:16:07

        Yeah.

    22. LFLex Fridman1:16:08

        You want to feel like there's something magical there.

    23. AFAlex Filippenko1:16:10

        Sure.

    24. LFLex Fridman1:16:11

        Uh, I mean, I felt that first when my dad, my dad's a physicist. When he first told me about ball lightning-

    25. AFAlex Filippenko1:16:18

        Yeah.

    26. LFLex Fridman1:16:18

        ... when I was like a little kid.

    27. AFAlex Filippenko1:16:19

        Very weird.

    28. LFLex Fridman1:16:20

        Very (laughs) like-

    29. AFAlex Filippenko1:16:20

        Yeah.

    30. LFLex Fridman1:16:21

        Weird physical phenomena.

Episode duration: 2:35:47