Could we spot an alien nuclear blast?

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Speaker 1: Hey, Daniel, what do you think will happen the day we discover alien life? Oh? I'm imagining like a huge worldwide celebration. Oh yeah, and you think it'll be good news. Yeah, I think we'll learn something very deep and important about the nature of life and the universe and everything. But what if it's not good news? What do you considered darker possibilities about alien life? Like if they're not friendly to humans they show up in space and zappaus, Well, they could be friendly to humans. You know, they might find us delicious. I guess that depends on which kind of humans they find delicious. We probably all taste the same, you know, like chicken. Maybe chickens taste like humans. I'm sure there are people in this world who know the answer to that question. What if we find out about aliens because of some giant space battle they're having with themselves. Oh well, that sounds pretty exciting. In that case, I'd like to reserve a front row seat. Well really, Oh you do that, I'll be running away in the other direction, and I'll be popping the popcorn. Hi, am Orham and cartoonists and the creator of PhD comments. Hi, I'm Daniel I'm a particle physicist and a professor at UC Irvine, and I don't wish any aliens to die, but I do want to see a giant alien space battle. Wait, so how would they have a battle but without any even dying. Isn't just like a virtual battle or they're like plane laser tag? What are you talking about here? I mean it's like a wortal battle. Are they having a wortal battle? Maybe they've evolved to a higher plane of combat exactly. No, it's tension within me. As much as I would like to see alien space battles, I also don't want any aliens out there to die. But you know some of our favorite stories are about alien space battles. Isn't that what Star Wars is all about. Star Wars is about aliens. That's what you told me. It's in another galaxy, far far away, right, they're all aliens. Maybe we're the aliens in the Star Wars universe. Well, we're not capable of putting on giant space battles yet. Also, people don't die in Star Wars. They just come back as ghosts, Jedi ghosts more powerful than you could even imagine, Or do you the Emperor did they just keep bringing you back for all the movies. Don't the Stormtrooper die though, or do they also come back as Jedi ghosts. I guess it's not clear. You know, they get zapped with their little armor and they just fall down. Maybe they're just taking a nap. There you go. I'd like a giant alien space battle where the losers just take a nap. Yeah, I want to see that movie. Star naps were Welcome to our podcast Daniel and Jorge Explain the Universe, a production of iHeartRadio, in which we try to zap your brain with all sorts of incredible information about the universe. We know that everything out there is amazing and mysterious and confusing, but we hope to help you understand what little of it human entity has managed to decode. And we hope that one day aliens come and give us a little bit more information about what's going on out there in the universe, if indeed they do exist. That's right, because it is a pretty incredible universe, and we do battle every day here with the mysteries of it, and we go to war with our ignorance about how it works and what's going on in the universe. We're trying to drop a knowledge bomb on everybody's ignorance. That's right. You can think of us as a laser gun of amazing facts zapping people's brains. There's that warm, fuzzy feeling you get when you understand something about the universe. But there's also lots of things that we still don't understand about the universe, things that give you that gnawing feeling of desperate curiosity, that desire to just know what's going on out there. There's some of the deepest questions in human existence which have answers, which are facts about the universe which maybe one day people will know. How frustrating is it to live in the era of dark to not know the answers to basic questions like are we alone in the universe? Yeah? What bigger question can there be about the existence of humans than the question of whether we are the only living thing or intelligent thing living and existing in this universe? And we wonder about it, we speculate about it, but we have a very very deep lack of information about it. The universe is vast, and from our tiny little rock we have done a pretty good job of exploring a tiny, little corner of it. We have telescopes to tell us about nearby star systems and compeer further and deeper into the universe, but we've only begun recently to identify other planets and other places in the universe where life might spring independently from Earth. Yeah, we know that here in our Solar systems there aren't on at the signs of life, and so we know that if there is alien life out there, it has to be kind of far away. Right, how close is the nearest planet to us light years away? The nearest planet to me is about zero meters away. It's right here under my feet. There are other places in the Solar System people think there might be life, like under the frozen crust of Europa. So there are still exciting places in our backyard. But you're right, other Solar systems are frustratingly far away, several light years. The closest identified exoplanets around Proxima Centauri, which happens to be their closest star, just under four light years away. And what that tells us is that there are planets everywhere in the galaxy and in the universe. We now think that almost every star out there has planets around it, and a huge fraction of them have even earthlike planets, maybe around this size, maybe around this kind of surface temperature, maybe even with liquid water on their surface. And so with so many places that life could be out there in the universe, sometimes we wonder, why haven't we found it already. Yeah, it's a very big question, one that would kind of determine our place in the universe. Because if the answer is that there isn't life out there, that is that humans are pretty special right in the entire universe. Imagine what it'd be like to know that we're the only intelligence species in such a big place. Yeah, it would make you feel special. It'll also make you feel kind of lonely being the only intelligent life in the entire universe. It's kind of a lot of responsibility also, like we're the only ones out there doing anythinking. We're the only ones trying to figure out this huge puzzle about the nature of the universe, trying to crack the cosmic mystery of how all these quantum particles weave themselves together into this experience. I prefer to imagine that there's lots of other civilizations out there, and maybe they've even solved some of these questions and have the answers waiting for us. But we don't know. And we've been looking out in the cosmos and listening for signals from aliens, hoping that they are as excited as we are to meet their neighbors, and sending us messages which we might capture in radio waves or other electromagnetic signals. Of course, so far we've heard nothing conclusive. Wait, so you want aliens to exist just to take some of the pressure off of your job. Is that kind of what you're you're talking about? You know, I'm very strongly believe in funding basic research and expanding science, and that goes beyond the limits of our species. I think science should be funded here on Earth and everywhere in the universe, and I hope that budget aliens out there are, you know, giving a healthy dose of funding to those science aliens out there struggling to understand the nature of the universe, burned by the same curiosity that we have. Or maybe they don't. Maybe they just don't care about the nature of the universe and they're not even doing science. I feel like you're like little kid in class who's looking at his test or her tests and going like, I have no idea what's going on, and you're sort of like looking around to see if anyone else knows the answers. Yes, I definitely want to cheat off of alien physicists. I would love to get like an alien physics textbook and then win like a whole string of Nobel prizes here on Earth just by copying their ideas. Yes, I will completely admit that is my fantasy. Really, So wait, you would get the secrets from the alien I'm just trying to figure this scenario. Let's work through it. You would get the secrets from the aliens, but you wouldn't tell anyone that aliens exist, and you would use that knowledge for your own personal game. That sounds fantastic. Yes, remind me not to tell you any secrets. Then, If you are holding a Nobel prize winning secret, please do share it with me. I would love to hear it. You would be the last person I would share with, obviously. I hope you would share it with all of humanity, Like if somebody gave me secrets from aliens, I would share it with all of humanity absolutely, But the aliens themselves would be the biggest secrets. I just said it's the biggest question in human existence. No, you're right, And of course, if aliens do come or communicate with us, probably physicists wouldn't be at the front of the line of people who get to chat with them, right, probably would send like engineers or doctors, or politicians or linguists or mathematicians or philosophers before the physicists even get their shot. I think I would send the physicists first for sure. Yeah, because you know what, if they're hungry, we got to test the waters here. So you don't want me to learn the secrets from the aliens, but you do want me to be there first. I mean, there's two sides to that coin. Well, I want you to learn the secrets, but I want you to share the secrets verybody. I will share the secrets with you and the Nobel Committee. And if their secret is what their stomachs look like, well, you know you can't share it, but at least we would know. Just like going inside a black hole, you learn some deep secrets about the universe, but only you can know them. But it's interesting you talk about some of the ways that people usually think that we're gonna meet aliens or know about aliens, which is getting signals from them. I mean that's sort of like one way we can learn about them. I guess another way is to go to another planet and see them too, right, Yeah, And this is a really common thing in science. When you have no idea how hard a problem is, you start with the easiest things, like maybe the universe is filled with aliens and they're all sending messages and we just haven't been listening, and as soon as we turn on our electronic ears and use our radio satellites to tune in, maybe we could instantly tap into the galactic internet and hear all those conversations. There's some scenario in which it would have been easy, and as soon as we started listening, we discovered it. So it makes sense to first do the easy thing and see if alien messages our feeling space. Of course, we've been listening and we haven't heard anything, and so people are starting to try to be creative and think about, like, well, what are other ways we could hear from aliens, or what are other ways we could detect their existence? As you say, maybe we could go to those planets and discover them. Right. That's limited, of course, by our ability to travel from star to star. These stars are so far away and the speed of light is such a stubborn limitation. But until we develop a warp drives or practical wormholes, it's not realistic to think that we could explore a significant fraction of the galaxy. Yeah, Like, what would it take, I guess to send a probe to Alpha Centauri? Right, it's four light years away. That's like zillions of miles away. Right now, it seems kind of impossible because I think the furthest we've send a probe right now is just barely outside this Solar system, right, and it took like thirty years, yes, exactly, the most distant object send by humanity. Some of these old Voyager and Pioneer probes are not very far outside the Solar system, so it would take a long time for anything to get anywhere. But you know, if you were thinking about it on long time scales, it's not going to take like millions of years. We're talking like thousands or tens of thousands of years. And if you send a few probes to other planets, and if those probes are very clever, they're like AI driven self replicating probes, so they can land on some distant moon, they can find materials on those moons to make more of themselves, and then they can send those probes out, and those probes make more of themselves, and those make more of themselves. It's not impossible to imagine rapidly exploring the entire galaxy, where by rapid we mean on the time scale of like fifty to one hundred thousand years. So that's a really interesting argument because it suggests that with technology not super far in our future, some other civilization could have explored the whole galaxy with self replicating probes. And then you have to ask, like, well, why haven't we been visited by such a probe yet? Are there no other advanced civilizations out there who have this idea? Yeah, we address this question and this whole scenario in our book. Frequently asked questions about the universe. That was one of the chapters, right like why haven't we seen aliens? And maybe we can do that with these self repulating robots, which would litter the universe in no time exactly. And one basic assumptions a lot of these scenarios make is that aliens want us to find them, or that they are trying to talk to us, or they are curious about the rest of the universe as well, so they're sending messages out or they're sending probes out there explorational the same way that we are. But of course we don't know what alien psychology is like, and what does aliens want, or even what it means to want something as an alien. So these days a lot of people are imagining other ways to detect aliens when they're not trying to be detected. Are there things the aliens can do imprints they leave on the universe that aren't intended for us to discover them, but might allow us to spot them anyway. So today on the program, we'll be asking the question could we detect alien nuclear explosions? I imagine you're saying these are like accidental nuclear explosions or on purpose nuclear explosions, either one, right, we don't discriminate. We just like to know the aliens are there, and whatever they do in their normal civilization extrapolasition, we'd like to see if we could detect it. Maybe they're just doing testing like we're doing, or maybe they have some globe spanning nuclear annihilation. The question is, could we see it right, If aliens are blowing up nuclear bombs, is it possible for us to spot that? Yeah, because as you mentioned, you know, one scenario is that they're sending out signals on purpose, either to talk to us directly or just like that's their TV, maybe their broadcast TV. But I think we talked in an earlier episode about how like for us to detect the signal from an alien, it would have to be like a pretty focus beam, right, like the like the club we're just listening to their TV broadcast is pretty low, that's right. If you're just sending signals in every direction, then you pay a really big price because those signals get weaker with distance, and they get weaker with distance squared. So when signals go twice as far, they're four times as week, When they go ten times as far, they're one hundred times as week. That makes it really really hard to detect non focus signals. And if we wanted to detect signals that we could generate using technology that we have, we would not be able to spot signals of the kinds we can generate using our own technology from planets that are more than like one light year away. If however, they're like beaming us messages, they're shooting laser beams in our direction. Then the math works differently and we could get messages from further away, But then they'd have to know we were here and try to send us messages on purpose, which seems less likely. I think here today we're exploring a different scenario, which is like, what if they're doing something without trying by accident maybe or through some sort of event, and then that's what we see, and that's how we know that there are aliens exactly. And people have been thinking about this and wondering like, well, what's the most visible thing that you can do, not just broadcasting Rick and Morty episodes into the cosmos? All right, Sometimes our civilization does things which generate very bright flashes of radiation, and hey, what's brighter than a nuclear explosion? But what if there's a kid in that alien planet pointing a laser partner directly Ow my eye? Ow alien burnt my eye? Yeah, I know, that's why you should be careful you knock about this guy. So then the scenario here is that somehow this alien civilization out there is exploding nuclear their own nuclear bombs, either by accident, or some testing or something. Maybe they have their own nuclear war, and so the question is like, could we see those nuclear explosions exactly? All right? Well, as usual, we were wondering how many people out there had the interesting curiosity to ask this question about alien life and how we could detect them. So, as usual, Daniel went out there. Did you go to the internet or are you? Are you going on campus? Now these are still Internet based questions. I felt a little bit weird walking around campus asking people about aliens and nuclear bombs. That's never stopped you before. I thought it might get reported to the UCI police. Yeah, you have tenure. They're not gonna fire you. Anyways, usually have to do worst things. So thanks very much to our internet volunteers who responded with enthusiasm to this question. If you would like to play this part in future episodes, please write to me to questions at Daniel and Jorge dot com. We can do it all over email. It's fast, it's easy, it's fun to think about it for a second. Do you think we could detect alien nuclear explosions? Here's what people have to say. Yes, So it depends whether the detonation happened on Earth or a planet from Solar System or somewhere far away. In any of these cases, I think we might be able to detect. Considering that why decaying of the matter and the amount of radiation that is being exposed out of that location on Earth, we might be able to analyze whether it's man made or alien, and if it is happening on some other planet. Considering the amount of information that we have already gained with the telescopes in place, we will be able to do it. That's what I believe. By now, we have satellites now that can detect detonations on Earth. I don't think it would work at interstellar distances, especially considering that there's so many sources of radiation in space, you know, from stars to gamma ray burst everything in between. So no, I don't think we could. Well, I guess so. I guess it would depend on how good the detector was and how far away it was away from you. If there was set off over your head, you might be able to detect it pretty soon. I feel like we probably could detect alien nuclear detonations if there was like enough radiation to reach far enough, But other than that, I don't really think we could all right. Some people said yes, some people said no, some people said maybe yeah. I think they really put their finger on the issue, which is that nobody knows, not even us. It's all about brightness and distance. You know, what's the faintest radiation we could pick up? And how close would these bombs have to be for us to spot them. I feel like you're missing one important factor, which is how big are these bombs? That's a huge unknown. You're right, and we'll get into it in a minute. And the only standard we have is like how big are our bombs? So we can imagine whether we could detect nuclear explosions of the size we could make if aliens also did them. All right, we'll dig into it, but I guess first let's start with the basics, Like Daniel, what happens during a nuclear explosion? Besides the explosion part of it. Yeah, to understand whether we could see a nuclear explosion on another planet, you have to think about what the signals are, like what signals does a nuclear explosion generate? And we had a whole episode about how nuclear bombs work where we went to a lot of detail, but not enough detail for you to build a nuclear bomb. Hopefully but human nuclear weapons at least are either fission weapons or fusion weapons triggered by fission. And remember that the basic processes here fission involved breaking up of a heavy nucleus like plutonium or uranium, which then shoots off a bunch of neutrons and rams into other nuclei, which breaks them apart and sets off a chain reaction where you very rapidly are releasing energy. And the fusion bomb is similar except it uses a fission bomb to compress a bunch of fusion fuel that it fuses, and in both scenarios the key thing is releasing a huge amount of energy very very quickly, but not just energy, right, You're releasing energy but also a lot of radiation. Yeah, maybe step us through like what's actually being released, Like when you fuse things together they click together, to nuclear click together, and then what actually gets released like light or particles or Yeah, so fusion produces high energy photons. It also produces neutrons and electrons and neutrinos. Right, so all these kinds of things are produced and then much just produced, but they're like they're produced, but then they're flying really fast. Yes, they're produced, and they're carrying a lot of energy is what you actually see from the bomb from like a certain distance. Depends on how that energy is absorbed or not absorbed. So, for example, a lot of the energy gets dumped into the matters immediately surrounding the bomb, right, and so it's absorbed very very rapidly by the st around the bomb, which expands that matter and creates a shock wave. I mean like the bomb casing or like whatever, if it's on the ground, that that's what it's going to push out. Yeah, I mean whatever material is around the bomb, like the air or the water or the ground, and you get very different scenarios if you have an in air explosion or underground explosion or just above the water. But the material that surrounds the bomb is inundated with a huge amount of energy, a lot of it from gamma rays, and a lot of that gets rapidly absorbed and that material gets heated up to like tens of millions of degrees and then you get this shockwave. So in the end, on average, and it depends on exactly what you've surrounded the bomb with, about half of the energy of a nuclear bomb go these shockwaves, these expanding waves of matter basically sound waves through matter that carry away a lot of this energy, doesn't It depend on what's around the bomb. Like if you explode it in water, all of it's going to go into the water, But if you put it in air, you know there's maybe a chance for that energy to go out further. Even in air, a lot of that energy is absorbed by the air and you get shock waves. So yes, it definitely does depend on the kind of material surrounded. Like if you blow it up underground, it's absorbed differently than if you blow it up in the air. But you know, since we're just dealing with like approximate numbers here, roughly on average, over all those circumstances, about half of the energy gets dumped into shock waves and then like another forty percent of the energy comes out in what we call thermal radiation, basically photons to which the atmosphere is transparent visible light, infrared light, UV light, things that are not immediately absorbed by the surrounding material which conduct fly out through that material because that material is transparent to this kind of radiation. Why is it transparent. Is it because it just doesn't absorb because of quantum effects, or is it just that it's so like air is so thin that it just doesn't hit enough air molecules. Yeah, air is transparent to visible light, right, we know that because we can see the sun through the air. Why is the air transparent to visible light, You're right, is quantum effects. You have certain gases under certain conditions, and they either like to absorb photons of various frequencies or they don't. These air molecules can't just absorb a photon of an arbitrary frequency. They have to have like a quantum state that their electron can jump up into, or like a new rotation that they can do. So atoms can only absorb certain frequencies of light, and the other frequencies pass right through. So air is mostly transparent to visible light and also infrared light. It's less transparent in the UV, which is one reason why we have like UV space telescopes above the atmosphere. But you know a lot of energy is dumped out and so some of these very high energy UV light does survive passing through the atmosphere. If you're near a nuclear bomb, so you have like fifty percent of it roughly in the shock wave, like another forty percent in thermal radiation these photons that don't get absorbed, and then another ten percent in other particles like neutrons or very high energy photons we call gamma rays or electrons. Is it sort of like lightning and thunder? Like you will see the flash of a nuclear bomb before you actually get hit by the shockwave. Yeah, it's really cool. You actually see two flashes of a nuclear bomb. You see the first flash because the visible light reaches you before the shockwave. But at some point the shock wave passes the fireball because the shockwave is making the material more dense, which acts to obscure the fireball. So the shockwave itself is opaque to the kind of light being generated by the nuclear bomb. So then for a moment you can't see the fireball, but then it dissipates and you can see it again. So it's like you see fireball and then you see the shock wave, and then you see the fireball. So it's sort of like lightning and then thunder and then a second flash of lightning. Whoa, I mean, assuming you survived the first event to get to see the other two. Yeah, So this is a very characteristic signature of nuclear bombs. This double peak of gamma radiation over several milliseconds. Well, it's definitely an event and nuclear explosion. And so the question is if aliens exploded nuclear bombs in their planets, could we see them from here. Let's dig into that question and what we should be looking for if we're looking for those kinds of signals. First, let's take a quick break. All right, we are spending today imagining aliens blowing themselves up. We're not hoping they blow themselves up, but if they do, we hope to see it. We're not hoping they blow themselves up, but if they do, it would be nice. Is that what you say? Is that? What are you saying? I mean, I don't aliens living in obscurity forever, or aliens killing themselves about then we find out about them. I mean, it would also be kind of sad to discover aliens only to discover they had all killed themselves, that they were the last ones. Yeah, that would be that would be pretty tragic. Yeah, that would be a bummer. Well, we've talked about what a nuclear explosion is and what happens to it. So you said about half of the energy is really just pushing the stuff around it so I imagine that won't get very far. Maybe forty percent of it goes into just light, basically invisible light or light you'd be light, And about ten percent of it goes into shooting out basically radiation, right, like charged particles. Yeah, not just charged particles, but neutrons, gamma rays, and also electrons. Well, gamma rays are light, right, Gamma rays are very high energy photons, Yeah, even more high energy than X rays or UV. These are all ionizing radiation. They all have the capacity to knock electrons off of materials. And because they're ionizing and electrons themselves have charge, they can also generate an electro magnetic pulse. This is a common feature a lot of movies nuclear weapons knocking out electronics because of a very high energy pulse of electromagnetic radiation. Oh interesting, it's not just that it's like a giant magnet. It's like it's actually shooting out little magnets. Yeah, exactly. And so all those gamma rays and all those electrons can damage a lot of electronics. So if you have electronics near a nuclear weapons blast, then you will feel it. They could get knocked offline. They don't shoot protons explosions or neutrinos. They do generate a lot of neutrinos. He has absolutely fusion and fission both generate neutrinos, but not so many protons. Mostly neutrons and neutrinos and electrons. What about later rays and sound effects like in Star Wars? They don't go pupupu as far as I've seen. It's not in the literature. But the sounds of thousands of souls being snuffed at the same time, Oh, that's sad. I don't know if they create a great disturbance in the force. We don't have detectors that can measure the force yet, so I'm not sure about that, not yet at least, although I have a good acronym for them. They should be a named Jedi, right, And how does that work? Just the Electron Detection Institute sounds good? Are you setting that up with some funding? Are you going to endow the Jedi Institute? Maybe I have already, I'm just not telling you. No. That's extra frustrating. But you know, there are a lot of scientists here on Earth that are developed very sensitive technology for a studying nuclear weapons, both because we want to understand what happens when they blow up, because we have done tests and we want to understand whether our nuclear weapons are working and are still working and are surviving the test of time as they sit in our stockpiles. But also because we wanted to detect if other countries are blowing up their nuclear bombs. So there's been a lot of investment in detection of nuclear weapons activity, you mean, like here on Earth. Like if you wanted to detect whether a nuclear bomb exploded here on Earth, not in an alien planet, we have techniques here on Earth to do that because I guess if someone explodes a nuther bomb on the other side of the world, in the middle of the ocean, you may not necessarily know what happened, right, And if you're a big country in a cold war or not, you might want to know if your enemies are exploding bombs or testing them, that's right, and you might not want the other country to know that you're doing it. So, like secret testing of nuclear weapons was a big industry and a sort of an arms race of hiding nuclear bomb detonations and nuclear weapons detections. I grew up in Los Almos, which was certainly a nerve center for this kind of stuff. My mom actually worked on a nuclear non proliferation technology when she was at Los Almos, trying to detect if people are blowing up nuclear bombs and all this kind of stuff. So we have a lot of ways to try to figure out if someone has blown up a nuclear bomb here on Earth. Yeah, it sounds like you would want to know. And it's kind of interesting that we test nuclear bombs right Like, first of all, I guess you have to test them right now or the wise do not even know they work. But it's amazing to me that we have tested nuclear bombs here in the US, right in the desert back in the fifties and sixties that there was all they did. Yeah, they have done above ground tests here in the US. You know, Alamagordo was the first site in New Mexico and they tested them on a bunch of islands, which was terrible and like totally obliterated them. And then there was an atmosphereic test ban treaty, so you couldn't test the nuclear weapons in the atmosphere anymore, which is good, and they moved the testing underground. So in the United States, for example, there's the Nevada underground test site where they blow these weapons up underground. But there hasn't been any recent testing. There's a Comprehensive Test Band treaty now and so instead people now do simulations. They try to understand what would happen in the event of a nuclear explosion, or try to model what's happening to the nuclear weapons we have now, are they going to survive? The whole big industry called stockpile stewardship to try to make sure that our nuclear weapons would still work if we fired them. Interesting, So it's a treaty. So like with Russian other countries, we have a handshake agreement that you can't test. Basically, you can't test nuclear weapons anymore. Yeah, there's a Comprehensive Nuclear Test Band Treaty signed in nineteen ninety six. And you know, these treatings are always complicated because some nations don't ratify them. They're signed by presidents and then their local parliaments don't agree to them. But yeah, it's been a long time since there was sort of a public test of a nuclear weapon out in the open, all right. So if someone did test the weapon or use one here on earth, how can we detect them? So we have a few ways to try to spot this. Number one is seismic. If you do test underground, then it's going to shake the earth and the earth will ring like a bell. Shock waves will pass all the way around the Earth, and you can detect them in other places the same way we can put detectors in California that can spot earthquakes in Japan or in other parts of the world. You can detect large seismic events all over the world. Right because I guess the shock waves of these earthquakes or nuclear explosions, they kind of go through the rock of the Earth, right, even though it's like lava and molten it'll still kind of propagate sound waves lava sound waves. Imagine the Earth is just like a ball of metal and you ring it with a hammer, then those sound chock waves are going to bounce all around inside it. And this is actually really cool for studying the interior of the Earth. You ring the earth and how those shockwaves move through the earth tells you about what's inside of it. And like the boundary layers, that's actually given us a lot of clues about what's inside the earth. Is watching the impact of earthquakes sending shockwaves through the earth. It can be hard, however, to tell the difference between an earthquake and a smaller nuclear weapons explosion, and they try to do a lot these days to hide the nuclear weapons explosions by having like dampers materials which will absorb a lot of this energy instead of properly getting it into the earth. And one thing that they've done to try to distinguish between earthquakes and nuclear bombs is to listen to it, to take the data and translate it into an audio file. And it turns out the human brains are pretty good at distinguishing the sound of an earthquake versus the sound of a nuclear bomb going off. Okay, so sound waves through the earth is one way we can detect them here on Earth. What are some of the other ways? Other ways are through the air and through the water. So if you, for example, blowing up underwater, then you create hydroacoustic signals. It's just like shock waves through the earth, but instead now you're make sways through the water, and water is very good at transmitting sound. Right. The speed of sound through water is faster than it is through air, and so sound travels pretty far. All the way across the globe, which is one reason why they think that like whales can talk to each other from different parts of the planet. You know, they think whales in Japan might be able to hear the songs of whales off of Alaska, this kind of stuff. And so in the same way, if you blow up a nuclear bomb anywhere neither its not even just in the water, then the seismic waves will propagate through the ocean. And we have a lot of listening stations underwater to try to listen for all sorts of activity, but including nuclear explosions. Is that allowed? Can you test nuclear weapons in the water? Definitely not allowed, but has been done in the past, right, all right, how else you can also look more directly for the radioactivity, right if you do blow up a nuclear bomb, and there's a lot of radiation emitted and radioactive elements. So one thing we do is we try to sample by airplane. You know, you have airplanes flying all around the world, and they're sampling for unusual radioactive isotopes, some of which are indicative of nuclear explosions. Even if you like test it underground, a little bit of these radioactive isotopes will eventually leak. It's not always easy to tell where the nuclear bomb explosion happened using these techniques, because it depends on how it's carried by the wind and the weather and how recently it happened. But you can sort of tell that one maybe did happen if you pick up a signal of these particular fingerprints of a nuclear bomb through their radioactive isotopes. So that's happening right now. Like there are aeroplanes out there up there basically sweeping the earth like a like a roombay. Exactly. I don't know the details because they're not public because like the US doesn't want Russia, for example, to know exactly how it's monitoring it, because then Russia will know how best to evade it. So it's a whole game of secrecy. But absolutely I'm sure that the Russians and the Americans are both monitoring the atmosphere in high altitude planes to try to detect whether the other side is cheating on the Test band treaty. We're also basically looking for these explosions, right like if you can have satellites maybe with camera strain at the Earth looking waiting for these flashes of light, absolutely, and that's one of the most powerful ways we can see these and one of the ways that might apply to alien detonations, which is just look with satellites, right, we have pictures basically the entire surface of the Earth, and we can look for high energy sources of gamma rays and X rays, which are unusual and you don't expect to produce these things in lots of different ways. And so if you see one of these signals, flashes of gamma rays, especially the double peak signature, then you have a very strong smoking gun signature of a nuclear detonation. But what if you detonated underground, like deep underground would be with the X rays and gamma rays still make it through all those layers of rock. It depends a lot on the shielding, right, and sometimes they try to shield it with heavier metals or they go deep deep underground. X rays can penetrate a lot of material. Rays tend to be more ionizing, so they do end up getting absorbed, but it depends a lot on the depth. All right, Well, that's how you can tell if someone exploded something here on Earth. But what about the question of aliens exploding things in their planets? Could we detect alien explosions or an alien nuclear war. So if aliens have the same kind of technology that we have, meaning they're blowing up bombs similar to the ones we have, then we can look for the same signatures from their planets that we would look for on Earth. Obviously, we can't look for seismic activity or hydroacoustic activity, and we can't sample their atmosphere directly. The best way to do it would be to look for these gamma ray flashes. And of course we already have telescopes that are scanning the sky looking for gamma rays because lots of non alien sources of gamma rays are very interesting to us, and there's even a huge fun physics mystery about gamma ray flashes. These things are called gamma ray bursts that come from all over the sky. We don't really understand them. They last for like sometimes a few seconds, sometimes like thirty seconds. We think they might be due to the collapse of supermassive stars, but they generate very bright flashes of gamma rays that are sort of similar to what you might expect from a nuclear detonation. M I think you're sort of painting the scenario where We're basically looking at the sky right with giant antennas that can detect gamma rays. And if we somehow are pointing to a particular planet or star and we see a big flash or a signal, then that could be the sign that the amiens blew themselves up. It could be the sign. As one of the members of Listener Panel pointed out, it might be hard to distinguish. Right. On one hand, it's cool that supermassive stars collapse and give off gamma ray bursts. On the other hand, it's a bit of a bomber because it makes it harder to distinguish between alien nuclear bomb gamma ray bursts and just natural sources of gamma ray bursts. But I guess if it was a super massive star collapsing, wouldn't we also see other signs that go along with it that wouldn't go along with a nuclear explosion. It could be, And one thing we're doing is to try to study these gamma ray bursts in more detail and see whether they come along with other signs like flashes of neutrinos or other things we can see in the optical To try to figure these things out. We don't always have a lot of warning, right, We don't know when it's going to happen. We just see like, oh wow, that was a big flash of gamma rays from this spot in the sky. You don't always have time to train other telescopes on that spot to get sort of multi channel data, and they do look kind of similar. In fact, when we first discovered gamma ray bursts, scientists thought that what they were seeing were gamma rays from earthbound detonations of nuclear weapons. They thought they had just picked up the Russian explosions because I would explain the signal too, Yeah, because that would have explained the signal. Now, gamma ray bursts come from really really incredibly powerful events. These things release enormous amounts of energy, so we can see gamma ray bursts from all across the universe. We've seen them from really really far away, like millions and millions, almost a billion light years away, because they are so powerful. Some of these things released like ten to the forty four jewels of energy just in the gamma rays, and so they're very bright, very powerful. We can see these things from very very far away. Our nuclear bombs are not nearly as powerful as these other natural sources of gamma rays, so they would be relatively dim in comparison. You mean if there was an alien looking at us for these gamma ray bursts, Yeah, exactly. If aliens were watching our nuclear explosions and they had technology similar to hours, they would not be able to see our explosions from very very far away because our explosions are not that bright compared to gamma ray bursts. Well, sort of depends on how many nukes we detonate at the same time. It does. But if you imagine, like a doomsday scenario, you take all of our nuclear weapons, you set them all off at the same time, you can calculate, like how much energy in gamma ray bursts would be emitted. It's only like ten to the nineteen jewels, Like obviously cataclysmic, terrible scenario, enough energy to devastate civilization on Earth. But compared to gamma ray bursts, which are ten to the forty four jewels, we're talking about ten to the twenty five times less powerful than a gamma ray burst, So they're relatively dim compared to these other astrophysical sources. It's twenty five orders of magnitude weaker, but I guess you're saying, like, if we do see a gamma ray burst and we're not sure if it's an alien or a star collapsing, I mean that would mean that this alien civilization blew up twenty five orders of magnude, many more bombs than we did. We're a bomb that was twenty five orders of magnitude bigger than ours. Yeah, it depends on how far away they are. If they are as far away as some of these really distant gamma ray bursts, then you're right, they would have like much much bigger nuclear arsenals than we have, like ten to twenty five times as powerful, or they had or they exactly exactly kind of tense. But if you're imagining an alien civilization with the power of our nuclear weapons and they had some sort of cataclysmic event where they blew them all up at once, then you can ask how far away would they be for us to detect it. Our gamma ray sensors are pretty sensitive, but remember that things get much dimmer as you get further away, so the sources have to be very bright to be visible. For an alien nuclear war at human levels to look about as bright as a typical gamma ray burst, that we see it could only be around eight to ten astronomical units away because it wouldn't be nearly as bright as its source as gamma ray bursts that are typically much further. So eight to ten AU that's like the distance to Pluto. Beyond that, we might still be able to pick it up, but it would start getting dimmer very fast because remember the next star over is much further away than Pluto. So it's possible to see it in another star system, but not a guarantee, and our abilities fade very quickly as you consider even further star systems. So if like there are aliens in Pluto and they had a nuclear war and they detonated all their nuclear weapons, then we would see it through the gamma ray radiation. But if it happened like and in another source system, it'd be way too dim, or would it, or maybe maybe just need better instruments. I mean, you're not saying it's impossible, or you're saying it's impossible, or that it's really hard. I'm not saying it's impossible. I'm saying it's at the edge of our ability currently, like we can barely pick up super bright, very distant gamma ray bursts, or we could pick up less bright closer gamma ray bursts. Right, there's sort of a line there between distance and brightness. But we could also improve our technology and make our gamma ray detectors more sensitive. Then we could see dimmer things that were further away, including gamma ray bursts or alien technology. Is definitely not impossible. But I think you said that gamma ray are only one of the things that come out of a nuclear explosion. There's also like the actual visible light flash tour, and that's like many times bigger than the gamma ray burst. Do we see a star war happening just on the visible spectrum? We might be able to, but the universe is a little bit less transparent to that kind of light. Gamma rays are awesome because most of the universe is transparent to them, but visible life, for example, is more likely to get blocked by gas or dust or these kinds of things. But it is possible, and we should look for multiple signatures. Right, So we can look at the gamma rays, we can look in the visible light. We certainly should keep an eye on that. There are also other more subtle ways that we might be able to detect nuclear weapons explosions on other planets and to distinguish them from gamma ray bursts. The point you were making earlier about telling the difference between nuclear weapons and gamma rays. All right, let's get into those other ways we could detect an alien nuclear war and whether or not it might ever happen. But first let's take another quick break. All right, So what do you think is the scenaro here where aliens have a nuclear war? Do you think they just disagree about something? Do you think it's inevitable for all civilizations to eventually snuff themselves out? I don't know. I've heard this theory, you know, the great filter that the reason we haven't seen aliens or been visited by their probes is that technological civilizations don't tend to last very long because they tend to destroy themselves through climate change or annihilation or war or whatever. And that's possible, I suppose, but it seems to me like a huge amount of projection. It's imagining that aliens are a lot like humans, and their psychology and their struggles and their sociology is a lot like ours. And that's possible, But it also seems to me to be possible for it to be completely different, for their politics to be totally different, and they never even invent nuclear weapons. So I think it's too big a question without really data to speculate on. Yeah, it's a big unknown, but I think it has maybe kind of the basis and the idea that, you know, anything that evolves evolution works by competition, right, and so basically any intelligent society will most likely it kind of come up like we did, being having this kind of balanced, this idea of competition and killing each other but also being nice to each other. Yeah. We had an astrozoologist on the podcast recently who made that point. He said, predation is inevitable in evolution. You will eventually have one guy that wants to eat the neighboring guy. And that's probably true, but it doesn't mean that it doesn't mean you can't like progress past your evolutionary impulses. Right. Our behavior now is quite different from the behavior in which we evolve, much more complex cooperative society. So I don't know that it's inevitable that you're dominated by that competitive nature, but hey, let's find out hopefully, listen, let's not find out the negative outcome the hard way. So you're saying before that for us to see alien nuclear explosions in other planets, I mean they would have to basically detonate twenty five orders of Maude, many more bombs that all of humanity has for us to even have a chance to see it. Yes, for us to detect these bright flashes, they would have to have a much more substantial arsenal than we have twenty five orders of magnitude more right, like bombs that could destroy you. I don't even know the number for that, but twenty five orders of magnitude many more planets. Yeah, sorry, I don't know if I said twenty five times right, it's ten to the twenty five times, So it's one with a lot of zeros in front of it. Absolutely, But if they do have a canterclismic nuclear war, there will also be other impacts on their planet that we might be able to detect even if we don't spot the gamma ray burst. And these are the kind of things we might be able to spot from planets in other solar systems. And number one on that list is changes in their atmosphere. You mean, like maybe we don't detect the explosion itself, that of the nuclear war. But we can detect their nuclear winter exactly, their nuclear winter. If you do have this kind of event where you blow up a lot of nuclear bombs in your atmosphere, it would really change your atmosphere. Number One, it would very briefly make your atmosphere glow. Right, you're dumping a huge amount of energy into your atmosphere. It would ionize a bunch of the gases from the radiation produced by a lot of the byproducts, and so the atmosphere itself would glow sort of like the Northern lights. Ionized air tends to emit this kind of glow. We've seen it on Earth, we've seen it on Venus, we've seen it on Mars. And so if you have a lot of nuclear bombs, then their atmosphere would have this air glow and we might be able to spot that. Wait wait, wait, we could see their atmosphere glow like how like with telescopes. Yeah, telescopes pointed at these planets might be able to gather some information about the light that's coming directly from the planet. Right, we now have direct imaging of exoplanets. And if you see, for example, a spike in the oxygen line, that increases the oxygen rapidly by a factor of ten than our telescopes could spot that. But wait, if we can see their amosphere glow, surely we would see their explosions themselves, right, Like explosions would be pretty flashy, right, he said, forty percent of a nuclear explosions energy goes into visible light. I mean, if we can see their atmospherre glow, surely we would see their like a big flash before the explosion or during the explosion. The explosion itself might not be bright enough for us to see. It'll also be really short lived. What we're talking about here is seeing a change in the atmosphere chemistry, which we usually detect from how the light from the planet's star passes through its atmosphere or reflex off its atmosphere. So the light we get from these planets is not from any source on the planet itself, but from the star, which is why it's visible at all. The air glow might last longer than the flash, and so it might be easier to spot. But what we're doing is thinking about, like what are the multiple signatures, Because in the end, the story is going to be that you probably can't conclude that you've seen an alien an explosion based on only one of these signatures, because there are other ways to mimic any one of them. So to conclude you've seen alien signatures, what you're going to want is multiple pieces of evidence. I see, like the afterglow will last longer, so there's more likelihood that will see it. But also it's sort of like more of a telltale sign. If planet is glowing more than it should, then you can maybe infer that there was an explosion there exactly, like maybe you see a gamma ray burst and you see a bright flash of light from the visible light emission and you're wondering, like, well, was that some sort of star collapsing or was it an alien nuclear bomb? Then you can look for the air glow. There are other effects in the atmosphere as well, like these blasts tend to produce a lot of nitrogen oxides which react with and deplete ozone, And so if you're watching the atmosphere of this planet, then you're looking in the UV light, you can detect changes in the ozone layer. So a lot of these other signals require you to be looking at one of these planets already in studying its atmosphere and seeing change in its atmosphere, so it increases an ionization of the gases that lead to air glow or decrease in the ozone layer by interaction from some of the byproducts of the blast. Or if you just like see the atmosphere become opaque, Right, you have a bunch of nuclear bombs go off, it's going to throw up a huge amount of either vapor or dust or something to make the atmosphere more opaque, and that could last for years. Right, We're talking about a nuclear winter. And so if you see an atmosphere becomes suddenly more opaque than it was before, that tells you something big happened in that atmosphere, Like if there's more dust in the atmosphere, Although that could also be an asteroid, right, Like if an asteroid hits planet, it would also cause a big flash of light and also a lot put a lot of stuff in the atmosphere, right, Or would it look differently? Is it's not radioactive? Yeah, an asteroid wouldn't look exactly the same as a nuclear bomb because it wouldn't deplete the ozone in the same way. It might not cause the same amount of air glow because it wouldn't have the same sort of radioactive byproducts, but a lot of the signatures would be the same. It would throw up a lot of dust in the atmosphere, probably make the atmosphere opaque for years as well, but you probably wouldn't also get the gamma ray burst. So there's lots of things out there in the universe that could make signatures similar to alien nuclear total annihilation, global thermonuclear war, but not all of them. So if you happen to see like several of these signatures all together from an exoplanet, then you could probably conclude that there were aliens and they had just had a very very bad day. Or maybe they were celebrating something, you know, it's just how they do fireworks in that ailing culture. Maybe they detected us and they were celebrating because they were going to get to eat a good mule latter. Or maybe they try to have some fireworks and they accidentally shot the fireworks right at their nuclear arsenal and set it off. I think I've seen that on TikTok. All right, well, I kind of feel like we have to be looking for these things though, right, like gamma rays, it's not like we have a camera looking out the whole universe looking for gamma ray. Gamma detectors here on Earth are very specific. Likely we have to point them at specific stars and stuff, right, So it seems kind of unlikely that will just happen to catch another civilization having their nuclear war just as we're pointing our telescope at them. I yeah, exactly. I think some people were hoping that this would be a very easy way, a very obvious way to identify alien civilizations. But unfortunately they're not as bright as you might imagine, and the universe is very very large, and there are other ways to create a lot of these signals, and so you have to be very lucky. You'd have to be looking at a planet basically when this happens, and have been looking at it beforehand so you could see the changes. And this is one of the big problems in detecting alien civilizations is just the deep length of time. Right, Maybe alien civilizations have existed and they've all killed each other and those signals came to Earth, but like a few hundred years ago and we missed it, right. Jill Tarter is famous for saying that we've been watching for aliens for a cosmically insignificant amount of time, and adding looking for nuclear explosions is a good way to increase our ability to see them, But it doesn't change this problem that we've only been looking very very briefly, and aliens could have existed and lived for millions of years and died off recently and we still wouldn't have seen it. Yeah, I see what you're saying. You're saying like, maybe these star wars happened a long long time ago and the galaxy far far away. Is that kind of what the conclusion of scientists is, Yes, exactly, that's entirely possible. Which I feel like I've seen that in a movie already. Did somebody have that idea already? Dang it, man, every time I have a good idea, it's still your Nobel Prize again and my ten billion dollars in box office receipts. All right, Well, I think it's still kind of interesting to think about, right, It's still worth thinking about because we do happen to see the city signals, right then we would know a lot about not only the idea that we're out there alone or not, but also like what these other aliens are capable of. Yeah, and these aliens could have court developed technologies that are far beyond what we have and create flashes of light much much brighter than the kinds of things we're imagining, and we should keep our eyes open for that. I think the spirit of this is just to try to be inclusive about the kind of things we're looking for, to increase our chances of seeing anything at all. Yeah, or I think, as we talked about in other episodes, like you might be limited in your imagination, right, Like maybe if you imagine giant space civilizations and have bombs that are twenty five orders of mine need to bigger than our bombs, then we would be able to see that kind of spectacle. Yeah, we talked about the Kardaship scale of civilizations. Some aliens might have tapped into all of the energy output of their sun and built a huge laser capable of vaporizing planets. You know, I think I've seen that in the movie also, but it could be real, and if they shoot that laser in our direction, we might be able to see it. That is exactly the plot of these Star Wars trilogies. They literally suck a son into their gun and then shoot it at other planets. Not something we're recommending, but if it happens, we might be able to see it. Yeah, and you'll be there with your popcorn, gleefully looking at the extinction of thousands or billions of alien lives as they melt my eyeballs. All right, well, we hope they give you something to think about, and maybe think about the trajectory of our own civilization, Like do we want to be known to other alien species by our last moments? Or should we be working harder to work things out between us so that they see us for other reasons. Or maybe we should take all of our nuclear bombs and launch them into space and blow them up out there so aliens know we're here. You mean, like a dinner bell, Like ring a different dinner bell. No, like an invitation to a party, right, a dinner party? Sounds like maybe we should put that up for a vote before we do that. All right, Well, we hope you enjoyed that. Thanks for joining us, See you next time. Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of iHeartRadio. For more podcasts from iHeartRadio, visit the iHeartRadio, app, Apple podcasts, or wherever you listen to your favorite shows.