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Alex Filippenko

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2020-11-08

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2020-11-08

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1. “There was one event, Toba, I think it was 70 plus thousand years ago that caused a gigantic decrease in temperatures on Earth because 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 supervolcanoes, one of which, by the way, exists under Yellowstone, you know, in the central US. I mean, it's not just one or two states. 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.”

   2020-11-08 · Lex Fridman Podcast · #137 – Alex Filippenko: Supernovae, Dark Energy, Aliens & the Expanding Universe · IDENTIFIED FROM THE TRANSCRIPT · source

2. “I don't know whether it's more because, as I said, I actually think human induced threats or things that occur naturally on Earth, either a natural pandemic or perhaps a bioengineering type pandemic, or, you know, something like a supervolcano, right?”

   2020-11-08 · Lex Fridman Podcast · #137 – Alex Filippenko: Supernovae, Dark Energy, Aliens & the Expanding Universe · IDENTIFIED FROM THE TRANSCRIPT · source

3. “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, astronomers, I like to say support your local astronomer. They may help someday 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 absorb before they hit and do something about.”

   2020-11-08 · Lex Fridman Podcast · #137 – Alex Filippenko: Supernovae, Dark Energy, Aliens & the Expanding Universe · IDENTIFIED FROM THE TRANSCRIPT · source

4. “Astronomers are monitoring the Sun twenty four seven with various satellites, and we can tell when there's a flare or a coronal mass ejection. And we can tell that in a day or two, a giant bundle of 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 expensive and hard to replace and hard to transport and all that kind of stuff. If we can warn the power companies and they can shut down the grid before the big”

   2020-11-08 · Lex Fridman Podcast · #137 – Alex Filippenko: Supernovae, Dark Energy, Aliens & the Expanding Universe · IDENTIFIED FROM THE TRANSCRIPT · source

5. “Only one of the mass extinctions was caused by a star blowing up, in particular a special kind called a gamma ray burst. And I think it's the Ordovician Solarian Silurian, Ordovician Sullurian 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. Those kinds of existential threats are reasonably rare. The greater danger, I think, is civilization changing events where it's a much smaller asteroid, which those are harder to detect, or a giant solar flare that shorts out the grid in all of North America, let's say. Now, you know.”

   2020-11-08 · Lex Fridman Podcast · #137 – Alex Filippenko: Supernovae, Dark Energy, Aliens & the Expanding Universe · IDENTIFIED FROM THE TRANSCRIPT · source

6. “So that might be more like a billion or two billion years before one of those hits us. So maybe we have to worry about the sun getting brighter on that time scale. 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, Estimates are that.”

   2020-11-08 · Lex Fridman Podcast · #137 – Alex Filippenko: Supernovae, Dark Energy, Aliens & the Expanding Universe · IDENTIFIED FROM THE TRANSCRIPT · source

7. “system. 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 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 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. Unfortunately, those With comets that come in without any warning, hardly. And so”

   2020-11-08 · Lex Fridman Podcast · #137 – Alex Filippenko: Supernovae, Dark Energy, Aliens & the Expanding Universe · IDENTIFIED FROM THE TRANSCRIPT · source

8. “You know, that might cause just so much panic that I'm how would you do with New York City or Los Angeles or something like that, right?”

   2020-11-08 · Lex Fridman Podcast · #137 – Alex Filippenko: Supernovae, Dark Energy, Aliens & the Expanding Universe · IDENTIFIED FROM THE TRANSCRIPT · source

9. “The name of the game would be to try to predict where it would hit. If it's in a heavily populated region Try Try to start an orderly evacuation, perhaps”

   2020-11-08 · Lex Fridman Podcast · #137 – Alex Filippenko: Supernovae, Dark Energy, Aliens & the Expanding Universe · IDENTIFIED FROM THE TRANSCRIPT · source

10. “You have to deflect at 90 degrees or more, right? 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...”

    2020-11-08 · Lex Fridman Podcast · #137 – Alex Filippenko: Supernovae, Dark Energy, Aliens & the Expanding Universe · IDENTIFIED FROM THE TRANSCRIPT · source

11. “Yeah. 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 early action are key. Because when it's far away, you only have to deflect it by a tiny little angle. And then by the time it reaches us, the perpendicular motion is big enough to miss Earth. All you need is one radius or one diameter of the Earth, right? 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 that time. So it doesn't take much. But you can imagine if a thing is about to hit you.”

    2020-11-08 · Lex Fridman Podcast · #137 – Alex Filippenko: Supernovae, Dark Energy, Aliens & the Expanding Universe · IDENTIFIED FROM THE TRANSCRIPT · source

12. “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, but you thought it was going to 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.”

    2020-11-08 · Lex Fridman Podcast · #137 – Alex Filippenko: Supernovae, Dark Energy, Aliens & the Expanding Universe · IDENTIFIED FROM THE TRANSCRIPT · source

13. “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 gases when the ices sublimate, that outgassing.”

    2020-11-08 · Lex Fridman Podcast · #137 – Alex Filippenko: Supernovae, Dark Energy, Aliens & the Expanding Universe · IDENTIFIED FROM THE TRANSCRIPT · source

14. “A deep freeze, Sergeant. Oh, the deep freeze is sort of out beyond Neptune. There's this thing called the Kuiper belt, 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 even bigger area called the scattered disk, 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, O R T after 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 come in with little warning. You know, by the time...”

    2020-11-08 · Lex Fridman Podcast · #137 – Alex Filippenko: Supernovae, Dark Energy, Aliens & the Expanding Universe · IDENTIFIED FROM THE TRANSCRIPT · source

15. “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. 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 year.”

    2020-11-08 · Lex Fridman Podcast · #137 – Alex Filippenko: Supernovae, Dark Energy, Aliens & the Expanding Universe · IDENTIFIED FROM THE TRANSCRIPT · source

16. “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? In our own solar system, the sun burning out is not the immediate existential threat. That'll happen in about 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 they're compensatory atmospheric changes, the oceans will evaporate away. 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 within one or two billion years, probably the oceans will evaporate away.”

    2020-11-08 · Lex Fridman Podcast · #137 – Alex Filippenko: Supernovae, Dark Energy, Aliens & the Expanding Universe · IDENTIFIED FROM THE TRANSCRIPT · source

17. “And intelligent. I don't know. Yeah. So, no way will we as humans reach the heat death of the universe. I mean, it's conceivable that machines, which I think will be our evolutionary descendants, might reach that, although even they.”

    2020-11-08 · Lex Fridman Podcast · #137 – Alex Filippenko: Supernovae, Dark Energy, Aliens & the Expanding Universe · IDENTIFIED FROM THE TRANSCRIPT · source

18. “Sure. Astronomy Newton's great work, right? The Principia, it was based in part on Galileo's observations of balls rolling down inclined planes, supposedly falling off the leaning tower of Pisa, but that's probably apocryphal In any case, the Inquisition actually did, or the Roman Catholic Church did history a favor, not that I'm condoning them, but they placed Galileo under house arrest. And that gave Galileo time 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 had he not been under house arrest. And so Newton, of course, very much used Galileo's observations.”

    2020-11-08 · Lex Fridman Podcast · #137 – Alex Filippenko: Supernovae, Dark Energy, Aliens & the Expanding Universe · IDENTIFIED FROM THE TRANSCRIPT · source

19. “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 its crescent, so it should appear smaller, and indeed it did. So that was the nail in the coffin in a sense. And then Galileo's other great observation was that Jupiter has moons going around it, the four Galilean satellites. 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. And, you know, things would move with it. 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 big breakthrough as well. But it wasn't as definitive, in my opinion, as the phases of Venus.”

    2020-11-08 · Lex Fridman Podcast · #137 – Alex Filippenko: Supernovae, Dark Energy, Aliens & the Expanding Universe · IDENTIFIED FROM THE TRANSCRIPT · source

20. “Tuco Braz data. And so that's, again, a great example of science and observations and experiments working together with hypotheses. And 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 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 gibbus to full to waning, gibbus, 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.”

    2020-11-08 · Lex Fridman Podcast · #137 – Alex Filippenko: Supernovae, Dark Energy, Aliens & the Expanding Universe · IDENTIFIED FROM THE TRANSCRIPT · source

21. “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 he needed to Cobra's really great data to show that distinction was that 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 Copernicus' view. And Kepler needed the better data.”

    2020-11-08 · Lex Fridman Podcast · #137 – Alex Filippenko: Supernovae, Dark Energy, Aliens & the Expanding Universe · IDENTIFIED FROM THE TRANSCRIPT · source

22. “Right, this is why I'm saying that as an objective scientist, one needs to have an open mind to crazy sounding new ideas. 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.”

    2020-11-08 · Lex Fridman Podcast · #137 – Alex Filippenko: Supernovae, Dark Energy, Aliens & the Expanding Universe · IDENTIFIED FROM THE TRANSCRIPT · source

23. “He knew from other studies that 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, 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.”

    2020-11-08 · Lex Fridman Podcast · #137 – Alex Filippenko: Supernovae, Dark Energy, Aliens & the Expanding Universe · IDENTIFIED FROM THE TRANSCRIPT · source

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

    2020-11-08 · Lex Fridman Podcast · #137 – Alex Filippenko: Supernovae, Dark Energy, Aliens & the Expanding Universe · IDENTIFIED FROM THE TRANSCRIPT · source

25. “So it could have worked arbitrarily well, but other data show that, in fact, Earth is going around the Sun. So our 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's a possibility as well. And as a scientist, I have to be open to that possibility as an open-minded scientist.”

    2020-11-08 · Lex Fridman Podcast · #137 – Alex Filippenko: Supernovae, Dark Energy, Aliens & the Expanding Universe · IDENTIFIED FROM THE TRANSCRIPT · source

26. “And 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, so-called retrograde motion. And it was a brilliant mathematical scheme. In fact, he could have added epicycles on top of epicycles and reproduced the observed positions of planets to arbitrary accuracy. And this is really the beginning of what we now call Fourier analysis, right? Yeah, any periodic function can be represented by a sum of sines and cosines of different periods, amplitudes, and phases.”

    2020-11-08 · Lex Fridman Podcast · #137 – Alex Filippenko: Supernovae, Dark Energy, Aliens & the Expanding Universe · IDENTIFIED FROM THE TRANSCRIPT · source

27. “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. So Ptolemy had a geocentric and Aristotelian view of the world. Everything goes around Earth. But in order to explain the backward motion of planets among the stars 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.”

    2020-11-08 · Lex Fridman Podcast · #137 – Alex Filippenko: Supernovae, Dark Energy, Aliens & the Expanding Universe · IDENTIFIED FROM THE TRANSCRIPT · source

28. “Universes are pulling outward on us. That's not a favored explanation right now. 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 perhaps, I guess it's conceivable that, and sometimes I wake up in the middle of the night screaming that...”

    2020-11-08 · Lex Fridman Podcast · #137 – Alex Filippenko: Supernovae, Dark Energy, Aliens & the Expanding Universe · IDENTIFIED FROM THE TRANSCRIPT · source

29. “With names and stuff like that. 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 madman type idea anymore. It's, you know, real card carrying physicists are seriously considering this possibility of a multiverse. And some types of multiverses could have a bunch of bubbles on the outside, which gravitationally act outward on our bubble because gravity or gravitons, the quantum particle that is thought to carry gravity is thought to traverse the bulk, the space between these different little bubble membranes and stuff. And so it's conceivable that these other”

    2020-11-08 · Lex Fridman Podcast · #137 – Alex Filippenko: Supernovae, Dark Energy, Aliens & the Expanding Universe · IDENTIFIED FROM THE TRANSCRIPT · source

30. “I'm very much a person who believes that there's always a cause, you know, there are no miracles of a supernatural nature. So, I mean, there are two broad categories either, it's the vacuum zero point energy, or it's some sort of a new energy field that pervades the universe. The latter could change with time. The former, the vacuum energy, cannot. If it turns out that it's one of these new fields, and there are many, many possibilities, they go by the name of 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. 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.”

    2020-11-08 · Lex Fridman Podcast · #137 – Alex Filippenko: Supernovae, Dark Energy, Aliens & the Expanding Universe · IDENTIFIED FROM THE TRANSCRIPT · source

31. “to a deceleration which then dominated the universe for about nine billion years, and now this small amount of dark energy started causing an acceleration about 5 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 anytime soon.”

    2020-11-08 · Lex Fridman Podcast · #137 – Alex Filippenko: Supernovae, Dark Energy, Aliens & the Expanding Universe · IDENTIFIED FROM THE TRANSCRIPT · source

32. “the vacuum, and so then it could be some sort of a field, some sort of a new energy, a little bit 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 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.”

    2020-11-08 · Lex Fridman Podcast · #137 – Alex Filippenko: Supernovae, Dark Energy, Aliens & the Expanding Universe · IDENTIFIED FROM THE TRANSCRIPT · source

33. “Well, not really, but we're getting progressively better observational constraints. So 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. 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 8, 9, 10, 12 decimal places, what if in the 13th one, the measurements significantly differ from the prediction, then the dark energy isn't this vacuum state, ground state energy of the...”

    2020-11-08 · Lex Fridman Podcast · #137 – Alex Filippenko: Supernovae, Dark Energy, Aliens & the Expanding Universe · IDENTIFIED FROM THE TRANSCRIPT · source

34. “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 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.”

    2020-11-08 · Lex Fridman Podcast · #137 – Alex Filippenko: Supernovae, Dark Energy, Aliens & the Expanding Universe · IDENTIFIED FROM THE TRANSCRIPT · source

35. “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.”

    2020-11-08 · Lex Fridman Podcast · #137 – Alex Filippenko: Supernovae, Dark Energy, Aliens & the Expanding Universe · IDENTIFIED FROM THE TRANSCRIPT · source