Daniel and Jorge Explain the UniverseDaniel answers Listener Questions about the smell of space, the electroweak force and spotting distant aliens.
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Why do we care so much about understanding the universe, about revealing its deep truths? Why aren't we just happy to live in it? I mean, does it change your life to understand the Higgs boson? Does it matter to your day whether there's intelligent life on the other side of the galaxy? Not practically, but it matters. It doesn't matter to build spaceships or death stars, or to become masters of the universe, but it matters to us to know, to understand it's just who we are as human beings. Hi, I'm Daniel I'm a particle physicist, and welcome to the podcast. Daniel and Jorge Explain the Universe, a production of iHeartRadio in which we marinate in our desire to understand everything in the universe. We cast our minds out in the furthest reaches of space and hope to understand what's going on out there. We turn our mental eye down to the very smallest particles in our universe and ask does this make sense to us? Can this possibly make sense to us? Is there a mathematical way that we could understand it? We talk about all of these things on the podcast, and we try to make sure they make sense to you, because we think that everybody deserves to understand the universe. Because we know that everybody wants to understand the universe. It's part of being human to look around you and to try to understand. And I don't know if there's an evolutionary reason to want to understand our universe. Maybe fundamentally deriving the laws of physics helps us plan the hunt for a mammoth or chase down an antelope on the savannah. I'm not sure, but here we are, we are curious creatures and we have this desire inside us to make sure that the world around us makes sense, to sort of pull all of our observations together inside our mind into a mental model that we can manipulate, that we can probe, and that we can use to predict what's going to happen to us in the future and to make plans. But also just to appreciate. There's a lot of talk in science these days about whether science and whether physics should be searching for beauty. And I don't know if we should be searching for it or whether we should prefer it, but we can definitely appreciate it. There's a lot of gorgeous, beautiful results in physics that when we do reveal something new and true about the universe, we are amazed. We stand agg and think, wow, there are some real beauty and elegance to our universe. And so typically on the podcast, it's me and Jorge and we are talking about some difficult to understand things about physics and explaining it to you or he is not here today, so I'm going to take the opportunity to catch up not on the questions that science is asking, but on the questions that listeners are asking. You Specifically, you. That's right. I'm talking about you. You are sitting there, or standing there, or driving around listening to our podcast because you have questions about the universe, and I want to hear those questions. I want to know what is it you'd like explained, and so send us your questions to questions at Danielandjorge dot com. If you're thinking that physicists will never answer my email, you're wrong. I answer all of our emails, and sometimes I put those questions up on the podcast when I think somebody else might want to hear the answer, when I think, ooh, that's a particularly interesting question that I bet a lot of our listeners would like to hear about. So that's what we're going to do today. On today's program, We'll be answering real questions from listeners. And I love answering your questions because they give me a sense for what people are thinking about. What do people know about physics? What makes sense to them? Because I've been doing physics for decades and my brain is fully marinated in physics as a language and as a way of thinking. So it's very helpful to me to hear about the way people ask about it. When they're on the outside. So it's very helpful to me to hear about what your questions are, the way that you think about the universe, and the things that don't make sense to you. And also because while most podcasts are directional, it's just a couple of voices sending information and audio out there into your brain, this podcast is interactive. That's right. We want to hear from you. We want to know what you need to understand. So please don't be shy. Send us your questions to questions at Danielandjorge dot com. And if you don't like writing emails or don't want to interact with us on Twitter at Daniel and Jorge, then hey, just come to my free public office hours. I hang out once a month for an hour on Zoom and answer questions from all comers. It's an opportunity to have a little bit more interactivity. You can ask a question, you can ask a follow up question. I'll make sure you go away with some understanding of the universe. So, without further ado, let's dig into today's awesome pile of listener questions. And thanks again to everybody who writes in, and please don't be shy. So Today's first question is a rather stinky one from Bob Bayer.
Hi, Daniel, this is Bob from Men's Washington. Say. I have always wondered if space might smell like something, or even if it has a smell. I was thinking maybe astronauts reported a smell after returning to the space station when they're inside their decompression chamber and they take off their helmets, or maybe Apollo mission astronauts after walking on the Moon's surface and return back to their landing craft and they take off their helmets inside there might be residual smell from outdoors, and what would that smell like? So anyway, I hope you can shed some light on that question. Thanks a lot.
All Right, that's a super fun question. Thank you so much Bob for sending that in. I'm excited to talk about the smells of space or the stinks of space, But first I want to think for a minute about the motivation for this question. I think it's super fun to look up at the night sky and wonder about it and want to understand it. And what does understanding mean. It means somehow transforming that knowledge into something that makes sense to us, something that relates to our everyday experience, and you know, how do we interact with the world. We taste it, we touch it, we smell it. And so there's a little bit there about like trying to hook in the sky and bring it down to Earth, and wonder like, what would it be like to interact with the sky using our earth based senses. So I totally applaud this idea. I think it's wonderful, and frankly, it follows in the footsteps of geniuses like Isaac Newton. He's the guy who thought, hmm, if I have a theory of gravity that describes how an apple falls from a tree, can I also use it to describe the motion of the stars. It was this idea that you could unify our understanding of what happens here on Earth with what happens out there, the idea that the Earth is not a special place, and the laws of physics that we find should apply equally everywhere. And so flip that around and think, well, if I can smell stuff down here on Earth, could I smell stuff out there in space? And what would it smell like? So super fun, wonderful question. Now, of course, the easy answer is that if you opened your helmet in space, you wouldn't smell anything because your nose would freeze. Right. Space is mostly a vacuum. It's very cold and very low pressure, and so if you exposed yourself to the vacuum of space, then of course you wouldn't smell anything. But that's not the only way to smell space, right, because space is not actually empty. We talk on this podcast a lot about how space is actually filled with stuff. And we're not talking here about like quantum fields and other crazy low energy phenomena. I'm talking about actual particles. There's a whole podcast episode we did about where's the emptiest place in space? And as you leave the Earth, of course, the atmosphere gets thinner and thinner and thinner. And then when you're out there in sort of interplanetary space, it's not like there's nothing there. There are a lot of particles out there, from big rocks which are pretty rare and down to tiny grains of space dust which are frankly everywhere. Space is not really empty at all. Add to that, of course, the solar wind, which is pumping out huge numbers of particles all the time, protons and electrons and other kinds of small particles mostly, but there's a lot of stuff bumping around up there. So it's a really fair question to ask, what would those things smell like if you could somehow use your nose to probe them, Because remember, the human nose is amazing. It's a very sensitive, basically molecular detector. The way your nose works is that you suck in air and it has a bunch of molecules in it, and those molecules hit various sensors. Those sensors are all sort of differently shaped and they can lock into different molecules to detect it. So they can detect lots of different molecules, and it's very related to the sense of taste. You know, the taste buds on your tongue, for example, are apt to two sugar molecules or other kinds of molecules or salt, and you have a handful of different sensors on your tongue that can taste different kinds of molecules, just the same way. Your eyeballs, for example, have different cones and rods inside them, and they use that to build up a picture of what you are seeing. But there again, there's only a few rods and cones. There's only really three different kinds of colors that you can see, and the rest is interpolated by your brain. But when it comes to your nose, it's actually much much more powerful than those other senses. Your nose can sense hundreds of individual different molecules. It can identify them, it can pick them out even if they are very very faint. You ever smell something just a tiny little bit, that's your nose picking out the tiniest little serving of whatever it is that you're smelling. So your nose is actually a pretty good way to explore what's going on out there, and there really is plenty of stuff out there to smell. Space is not just filled with hydrogen gas. There are complex organic molecules out there. We know because when we sample comets or get bits of asteroids or meteors, we see these things. We see the molecular composition, and there's fascinating stuff out there. You know that, Like moons of Jubiter and Saturn have really interesting organic molecules on them. Not signs of life we're talking about here, like molecular precursors of life, like the amino acids you might need to build life and it's very reasonable to expect that those molecules might smell like something. So how would you actually go about smelling it. You can go out there into space and open your helmet and take a deep whiff, right. Well, what you can do is you can collect those molecules and then smell them when you're back in an aerated chamber. And one way this has actually happened is by astronauts going out into space and then coming back inside. Like if you come back into the space station, then your suit and your helmet have collected some of those particles that are out there in space. They've stuck to you, and when you go back inside into the air lock, then the air releases them, and they swirled all around, and some of them go up your nose and you smell them. The most common thing that you're going to be smelling if you do take a whiff of space are these things called aromatic hydrocarbons. These are molecules built out of carbon and hydrogen, which is why they're called hydrocarbon, and they're aromatic, which means you're gonna smell them. And most of these things smell sort of like hot metal or like diesel gas, and some people have described them as like smelling like a barbecue, and that's because those are the processes on Earth that generate similar kinds of molecules. So it's not like somebody out there is having a barbecue in space or run into a diesel engine. But those things on Earth produce similar molecules which end up in your nose on Earth, and you remember them, and so when you smell them out there in space, or when you just come back inside from space, then that's the association you're going to get. But there are lots of different possible smells of things in space. For example, there's a vast dust cloud to the center of our galaxy that's made of a chemical called ethyl formate, and evil formate itself is something you can make here on Earth, and it smells sort of like rum. That's right. It smells like the pirate cloud of the galaxy. And if you separate it, then one part of it esther, among other things, is the chemical responsible for the flavor of raspberries. So yeah, we're talking about vast dust clouds that might smell like raspberry rum. But you know, all the amino acids out there have different smells. I was looking at a chart yesterday, and some of them have different smells. Some of them would smell sour, some of them would smell sweet, some of them would smell like umami. So it really just sort of depends on the particular mixture of stuff that you encounter, sort of like asking what does Earth smell like? Well, it depends that you with the center Manhattan, or the top of a mountain, or in a wheat field in Kansas, right, and places have different stuff floating around, and so lots of different smells. And I think that's the most important answer, is that space does have a smell because it's filled with interesting stuff, and those smells depend on where you are. So I also looked up a bunch of reports from what astronauts have said what do they think it smells like? Because there haven't been a lot of scientific studies because these studies require people. You know, another really fascinating thing about the nose is that it's something that's escaped digitization so far. You know, we've been able to capture visual images and store them digitally and recreate them with a screen. We've been able to capture sounds right and store them digitally as information and recreate them with a speaker. We haven't yet been able to capture digital sense and store that information electronically in a way so that some sort of digital smell speaker would be able to recreate them so you could experience them. That would be pretty awesome or maybe pretty terrible. I'm not sure if you want your like movies and necessarily have smells to it. But one reason that we haven't yet is that the nose is much more complicated than the eye or the tongue in terms of the complexity of sensors that it has, and so the complexity of the information that needs to be stored and then reproduced. So it's particularly difficult anyway. So here are some reports from astronauts. Some report that it smells like burned steak. Astronaut Tom Jones says that a quote carries a distinct odor of ozone, a faint acrid smell, a little like gunpowder, maybe sulfurous. Don Pettitt said it had a quote rather pleasant, sweet metallic sensation. Three times spacewalker Tom Jones says it quote carries a distinct odor of ozone, a faint acrid smell. There was even a time when NASA was considering commissioning a perfume that smelled like space to sort of get folks used to it so they weren't sort of surprised and put off by the smell of space when they came back inside from their spacewalks. But I think they ditch that plan. And there's also another side interesting question, which is what does the space station smell like? Because the space station is sort of like the inside of a tent, right, These folks can't go outside, they're stuck inside. They're living together a lot, and so you might wonder, like, does this smell good inside the space station? So here's one report I found of what mirror smells like. They said, quote, just imagine sweaty feet, stale body odor, and then mix that odor with nail polish remover and gasoline. So that doesn't sound particularly nice. I'd like to go out for a walk into space and smell a raspberry rum if I was stuck inside with all those sweaty feet. All right, So thanks very much Bob for that super fun question. I'd like to dig into some more questions, but first let's take a quick break with big wireless providers. What you see is never what you get Somewhere between the store and your first month's bill. The price you thoughts you we're paying magically skyrockets. With mint Mobile, You'll never have to worry about gotcha's ever again. When Mint Mobile says fifteen dollars a month for a three month plan, they really need it. I've used mint Mobile and the call quality is always so crisp and so clear. I can recommend it to you. So say bye bye to your overpriced wireless plans, jaw dropping monthly bills and unexpected overages. You can use your own phone with any mint Mobile plan and bring your phone number along with your existing contacts. 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Hello, it's my favorite physicist and roboticist turn cartoonist team. This is Larry Garfield's Illinois. We all know there are four fundamental forces in the universe. You've also said many times in previous episodes that you figured out that the weak nuclear force and electromagnetism are really the same thing, or different aspects of the same thing, or linked or something. I don't quite understand. It doesn't that mean there's only three forces? More to the point, how can there be different representations of the same thing. If particles like Neutrino's only interact with the weak force. If the weak force and electromagnetism are really the same thing, how can a particle only interact with one of them? I'm very confused.
All right, super awesome question, Larry, Thanks so much for asking this. This is one of my favorite topics to think about, not just to talk about, and to explain the unification of all the forces, trying to understand whether there are connections and patterns between the forces and whether we can pull them together into some sort of unified concept. And you might wonder like, well, why would we want to do that, why do we think it's even possible. Well, that's basically the goal of physics is to look around us, observe what we see, and try to explain all of it using a small set of ideas. It's not hard to explain the universe if you need a different explanation for every single event. Right If you say, well, that apple falls down because that apple falls down, and this apple falls down because this apple falls down, what you want is a theory of apples that describes how every apple works. So what we've done in physics is collect all the weird effects that we've seen and try to describe them in terms of a set of forces, and then look at those and say, oh, look this is electricity. That's electricity. Let's describe all of it using one theory. Oh this is a magnet. That's a magnet. Let's have a theory of magnetism. And then we slowly pull those things together and look for relationships between the different forces and see are these actually just two sides of the same coin. So what we've accomplished so far is breaking it down to a few fundamental forces. And how many fundamental forces are there depends a little bit on how you count. Some people are taught that there are five fundamental forces, the strong nuclear force that's what holds the nucleus together, gravity, electricity, magnetism, and then the weak nuclear force, the one that's responsible for radioactive decay and all sorts of cool neutrino effects. But about one hundred and fifty years ago, physicists realized that electricity and magnetism are not the same thing, but there are two parts of a larger thing, and that's the essential concept. We're not showing that two things are the same. We're showing that they are two parts of something bigger, a more complete idea that includes both of them, rather than just having a list. Right, we don't want to explain the universe in terms of just like, here's a big list of ideas. We want a single concept that simplifies things, that pulls back a layer of reality and shows us what's going on underneath. So when we unified electricity and magnetism, we didn't say, hey, magnets and lightning are the same thing. We just showed that electricity and magnetism are so tightly connected, that is that moving charges make magnetic field and magnetic fla fields can bend the path of charges. We showed that it makes more sense mathematically and conceptually to think of them as two parts of the same thing. And so that's what's happened in the last fifty years with the weak force. We've been able to integrate the weak force into a theory of electromagnetism. We call this the electroweek theory, which I always thought was weird because we basically just ignore magnetism.
Right.
It's like when a law firm gets a lot of partners, and they start dropping names from the title of the law firm. Nobody was advocating for a magnetism. They should call it the electromagnetic weak force, but instead they just call it electro week. So let's dig in for a moment about what that means. What does it mean to have electroweak force. Well, first, let's remind ourselves what electricity and magnetism and the weak force do. And the question was specifically about why neutrinos only feel the weak force if the weak force is connected to electricity and magnetism. So let's talk about the interactions. What do we actually mean by these forces. We mean that particles can interact. Right, That's what a force is. It's a way for things to push or pull on each other, including particles. So electricity and magnetism, that force is carried out by photons. Every time there's an electromagnetic interaction, some lightning or a magnetic field or anything that's carried by photons. And you can think about this in two different ways. You can think about in terms of the fields they're like electromagnetic fields that fill the universe, or you can think about in terms of particles, little photons passing back and forth. It's really the same thing. You can think also as photons as little ripples in those fields. They're two totally equivalent but different conceptual ways of thinking about it. So what do photons interact with? Well, photons fly around the universe and they can interact with anything that has electric charge. So, for example, electrons interact via photons. When you push two electrons together, they exchange photons, or you can think about their electric fields affecting each other. So photons only interact with things that have electric charge. Right, If you put a neutral particle in an electric field, it just ignores it. It can't tell it's there, it's not affected at all. So what does that mean, right, Why do photons only interact with particles that have electric charge? We don't really know, and you can kind of turn the question around. Electric charge is sort of just like a description of the fact that the particle does interact with an electric field. We don't know what generates it, or where it comes from, or why it's there. It's sort of like a label that says whether or not the particle feels the electric field, whether or not the particle can interact with photons. So The picture we have of electromagnetism is that the photons fly through the universe and they touch stuff that have this special property we call electric charge, either positive or negative. All right, So let's take that sort of framework for understanding and turn it around and look at the weak force. The weak force has different particles it uses to interact, or equivalently, different fields it uses to interact with. These particles are the W and Z bosons. There's three of them. There's the Z boson and two W particles. There's a W plus that has a positive electric charge and a W that has a minus electric charge. So the weak force has these three particles. These particles fly around and they interact with any particle that has the weak version of electric charge. So every particle out there has either a positive, negative, or zero charge that tells you whether a photon interacts with it. There's a version of that electric charge which operates for the weak force, and it works the same way. If a particle has we call it weak hypercharge, that means that it feels the W and Z bosons, it can interact with them. And so now you can think about every particles having two kinds of charges. One that we used to just call charge now we think about as electric charge because it refers to whether it interacts with electromagnetism, and another kind of charge that tells us whether it interacts with the weak So we have electric charge and weak hypercharge, and only particles that have weak hypercharge will interact with the weak force, and every particle that we discovered so far has weak hypercharge. For those of you super into particle physics, you'll know that that's a little bit of a lie because, for example, electrons have a left and a right handed version, and only the left handed version interacts with the weak force. The right handed version doesn't have weak hypercharge. But anyway, everything out there has it, including the Higgs boson. So what does it mean then, to say that electromagnetism and the weak force are linked. Are they the same thing? If they were the same thing, they should do the same thing, and for example, the photon should interact with neutrinos. Right. Well, they are not the same thing. There are two parts of something larger. It's like saying, oh, our heads and tails the same thing. No, they're connected, they're two parts of the same coin. It doesn't mean that they are the same thing, right, But what it means that when you fit them together you get an oddject which makes sense, which sort of reflects a larger concept. And so what we do here is we take these three weak bosons, the two ws and the Z, and the single electromagnetic boson, the photon, and we put them together and we have four bosons. But there's something very cool that happens when you put these four particles together, because they snap together mathematically and they work together. And when you consider them all together instead of individually, you notice something really cool happens, something physical, which is there's a new conserved quantity. You know, for example, how energy is usually conserved, but parts of energy are not always conserved. You can go, for example, from having kinetic energy to potential energy and back. So kinetic energy by itself is not conserved. Potential energy by itself is not conserved. But when you put those together, boom, you get a larger concept energy which is conserved. So when you put these three bosons from the weak force together with this boson from electromagnetism, they operate together to create a new symmetry, a symmetry that protects this property called the weak isospin that we don't have to get into. But that's what tells us that we think they really are related. We think they really are part of something larger. There's a lot of really beautiful mathematics that tells us that these things really do fit together. And you know, these four particles we think have more in common than you might think. Three of them operate for the weak force, one of them operates for electricity magnetism, And while they look different, they do have a lot in common. One way that they look different is that the photon doesn't have any mass, but the w and the z bosons do have a lot of mass. And that's why the weak force is weak. It's weak because those particles are so massive that they don't last very long. The weak force becomes a very weak and very short range force, whereas photons that have no masks can fly all through the universe and last for billions of years before they get to your eyeball or hit another star or whatever. Well, the reason that the wuns and the z bosons have mass and the photons don't is the Higgs field. The Higgs field is an idea that came out of this question. We saw that all these particles had a lot in common. It made perfect sense to fit the photon in with the weak bosons, except for this one puzzle, which is why is the photon have no mass while the other ones do and the Higgs field is the answer to that. It breaks what we call electroweak symmetry, the symmetry that protects weak isospin this way that these four particles fit together. They fit together beautifully and perfectly if all the particles have no mass. But then the Higgs field comes along and it gives mass to three of those particles, which become the weak force, and so the Higgs boson sort of breaks that otherwise beautiful symmetry. So it's awesome and we think it's real because it led us to discover the Higgs boson. It was like a fun, interesting mathematical puzzle that told us something was going on and led us to discover the Higgs boson. So we don't think that the weak force and electricity and magnetism are exactly the same thing. We think they fit together to make a larger hole that sort of makes more conceptual sense and reflects something physical about our universe. That doesn't mean they always have to do the same thing. And so, for example, why don't neutrinos feel the photon. It's because they have no electric charge, and the photon only interacts with things that have electric charge, and so that might seem like a non answer. Like you might also ask why do newtrinos have no electric charge? And that's a great question and not a question we have an answer to. This is the kind of thing that we observe, we discover, we catalog and we wait for the future generations of physicists to understand these patterns. There are lots of obvious, apparent patterns in the sort of periodic table of the fundamental particles, the quarks and the leptons, that are not explained at all, and one of them are these weird charges, you know. Another one is like why do the charges of the proton and the electron exactly balance? The proton gets its electric charges from the quarks that make it up, but we don't have any relationship in the standard model between those charges. They could have any value basically, and yet they magically add up so that the proton and the electron of exactly the opposite charge, not like opposite by one percent or by point one percent exactly opposite. So that seems like a clue. So there are lots of really deep mysteries remaining about why particles have charge, why some don't have charge, why other ones, for example, feel the strong force, and electrons and neutrinos don't feel the strong force. Not something we understand at all, just something we are observing. But we're noticing these patterns, and we're fitting them together into larger ideas that we think reflects sort of deeper understandings of how these forces are connected and might one day lead us on a path to unify even more forces and take steps towards our goal of having the one force that rules them all. All right, super fun question, Thanks very much. I want to answer another question, but first let's take a second break. 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All right, we're back. We've been talking about the smells of space and the nature of fundamental particles, and so now I want to turn our minds again out into the depths of space and answer a super fun question from Masa about aliens.
Hi, Daniel and Jre. This is Masa from Boston. I love your podcast and have listened to every episode so far. I have a question that was inspired by a recent episode about how we can detect exogalactic exoplanets. If there were a solar system identical to ours, where Alpha centaur is four light years away, complete with a copy of our Sun as well as a copy of Earth with over seven billion people and their r F and atmospheric output, would we be able to detect that planet's presence. Would we be able to detect life? Would we be able to detect intelligent life if it had our level of technology, and if not, at the rate at which our detection capabilities presently a fancy Roughly, when might we be able to detect human activity from a range of four light years? Would it be ten years, fifty years? For the sake of this hypothetical exercise, let's assume that whatever alignment necessary to use the various detection methods is in place.
Keep up the good work, guys.
All right, thank you very much Masa for that really fun and detailed question. I'm really looking forward to digging into how we might detect life around our nearest star. So it's a reasonable question because you know, now we are developing this capability to see planets around other stars and to study their atmospheres, and our technology is increasing, so you might ask, you know, is it likely that we could find aliens around nearby stars? And you know, should we be expecting this news any day or equivalently, the fact that we haven't yet announced to discovery of aliens, does that mean that we haven't found them or that we're just not yet capable. So super fun question. Let's break it up into three parts. First, he was just wondering, could we tell if there was a planet around Alpha Centauri. Alpha Centauri is a nearby star system. It's one of the closest ones and in our neighborhood in the Milky Way, there just aren't that many stars. Is on average several light years between stars, which means you want to get from here to there, it's going to take you a long long time. And so that's why I think Masa picks like the nearest solar system one that we might possibly be able to visit or at least talk to or observe aliens. So let's remind ourselves how do we find planets around other stars, because mostly looking at them is impossible. These plants are very close to their stars compared to their distance from Earth, so they're basically right on top of the star, which makes it very hard to distinguish them from their star. You can't see the reflected light from a planet that's so far away and so close to something else really really bright. So we have a few methods of observing planets around other stars. The first one, it's called the wobble method, is just using the gravitational tug of the planet on the star. The planet, of course, is also a big, massive object that has its own gravity, and so it pulls on the star and makes it wobble a little bit, and we can use that to detect the existence of a planet. Another method, which is even more powerful, it's called the transit method. This allows us to find a planet when it passes in front of the star, effectively blocking some of the light from the stars like a many planetary eclipse. Of course, it doesn't completely block the star because the star is much much bigger than the planet, but by the fraction of the stars light that dips, we can tell how big that planet is. So that's pretty awesome because it lets us measure the radius of that planet, and by the orbital period we can tell the mass of the planet. So then we can get a pretty good sense of how big and how large, and therefore how dense that planet is, and therefore what it's made out of. Is it big and fluffy like cotton candy, or does it have the density of Jupiter or like the density of Earth. So we can get a pretty good sense for what's going on with these planets. And these methods work for really distant planets. We have study planets across a big swath of the Milky Way. The Milky Way, remember, is about one hundred thousand light years across, and we've detected planets as far away as about twenty five thousand light years away. That's because some of these methods are pretty insensitive to the distance of the star. If you're looking at the wobble method, for example, we get that information by how the light from the star is shifting as the star is wobbling, and that information doesn't fade as the star gets from or further away, so we can detect planets around stars that are much further away than Alpha Centauri. Typically, though, it's easier to detect really big planets, like Jupiter sized planets, because they're bigger, they block more light, they have more mass, so they tug on their star and they block their star more dramatically. But for a nearby star like Alpha Centauri, it's really no problem. And in fact, there's even a star that's a tiny bit closer. It's called Proxima Centauri, and we have found an earth like planet around Proxima Centauri. It's about the same size of Earth, it's about twenty percent bigger, and it has about the right density to be a rocky planet. So we think that there is an Earth like rocky planet in a habitable zone around a nearby star. So that one we can definitely check off the answer to be yes, we can detect nearby planets in nearby solar systems, So that we have done. The next question is much harder. Could we detect life on that planet? How could we do it? This is really chicky because before you even get started, you have to ask a definitional question. Right, orgeywood hear He would say, a whole. On a second, what do you even mean by life? Do we mean animals, do we mean plants? Do we just mean microbes? Are we open to something which is completely different from life on Earth? And it sort of gets to what question are you asking? What do you want to discover? And for me, I'd like to discover life on other planets just because it gives me a sense that there might be life all over the universe, which tells me there might be intelligent life, There might be an incredible diversity of things to learn from. And so I don't want to discover life as we know it. I don't want to find an alien planet with trees and slugs and all sorts of other familiar things on it, because that would be kind of boring. I want to see other examples of life, things I couldn't have imagined myself. That's the joy of doing science in this universe is being surprised, is finding things you couldn't have imagined that even science fiction writers and considered of those are the best moments in science. Those are also the hardest discoveries to make because you somehow have to be open to them. The only ways we know to look for life are the ways we have thought to look for life, which are limited to the kinds of life we have thought of. So let's focus on that, even though I would prefer to discover something super weird and something super surprising. But could we detect life as we know it? Massa was imagining, you know, a bunch of people around a planet a few light years away? Could we tell they were there? So the only way we can really study distant planets and ask the question about whether there's life on them is looking at their atmosphere. And you might think, hold on a second, we only recently figured out how to detect the existence of those planets. How are we going to possibly sample their atmosphere. We can sample their atmosphere using light from their star. When that planet eclipses the star, the light passes through the atmosphere of the planet before coming to Earth, and we can tell we can tell when the planet starts to eclipse the star. We can try to study just that light that sort of skimmed the surface of the planet, went through that atmosphere and came to us, and that light will be changed by what's in the atmosphere because the atmosphere, based on its chemistry will absorb different things. If there's water in that atmosphere, it will absorb light at the right energy levels for water to absorb it, and then we will notice some frequencies missing in the light that comes from the atmosphere, or if there's methane in the atmosphere, or if this phosphene for example, in that atmosphere, and so we can use that technique to sort of probe the atmosphere of that alien planet. It's not great, it's not super high precision, but we're getting much much better at it, and it's very promising. On the other hand, it's not always conclusive. Right, So we see methane around Mars, does that mean that there's life on Mars. We don't really know. Nobody really believes that there's life on Mars until we see those critters wriggling around. We know that there's methane production on Mars. We even know that it's seasonal. It seems like maybe something is waking up on Mars and farting and during the summer and then in the winter less so. But there are other explanations you could come up with, like geological explanations for a production of methane on Mars, and we recently saw the signal on venus of phosphine production. Phosphena is something people imagine could only be produced by processes we understand to be life. But it's a difficult thing to see and there's a lot of background, and recently those discoveries have been kind of debunked. It looks like the signal isn't really there. That's sort of a data analysis problem, but the takeaway messages it's hard. You might be able to detect specific gases in the atmospheres on planets around other stars, but having like a really smoking gun signal for life just from atmosphere composition, it's pretty difficult. So what we really need is a much clear signal that there's intelligent life. Maso was asking if there are folks on that planet broadcasting the golden age of television, would we be able to see it? And so this again is more like life as we know it, except it's intelligent life as we know it. Questions, you know, could there be intelligent life that's out there that's broadcasting messages that we're missing because we don't know to look for them, or we haven't imagined the format they could exist in. Absolutely, there could be life that exists on very long time scales and their message takes one hundred years even just to listen to, or life that lives on short time scales, or life that's communicating in some medium we haven't even imagined. Maybe they've discovered axions and they are the best way to communicate in the universe, and we don't even know the exist and so we're missing all the information. Think about how many thousands of years humans lived on Earth and didn't understand all the information around us before we even knew neutrinos existed, and the wealth of information they encode about the nature of the universe and what's going on in supernova. So it's certainly very possible that this is a huge amount of information, maybe even about alien life that's just washing over us now because we do not know how to recognize it. But that's again sort of an unprobable question. It's potentially infinite. It's the unknown unknowns, So let's focus on the known knowns. If there was a civilization on this planet around Proxima Centauri, would we be able to pick up their signals? Well, if they're not broadcasting to us, then probably not. The reason is that they are still pretty far away. Remember that signals fade with distance, and not a little bit, they fade with distance squared. If you shine a flashlight, for example, then the photons you're sending out from your flashlights spread out, and as the area that they cover gets bigger and bigger, the density of photons per area falls. And so for example, if you broadcast a signal in every direction, then it gets spread across the inside of a sphere, and as the radius of that sphere grows, the area of that sphere grows with the radius squared. So that's why signals fall by one over the distance square. Same thing for the law of gravity and electromagnetism. It's all very geometrical. But the problem is if you're not beaming us a signal, then your signal has to be really powerful at the source for it to still be detectable by the time it lasts four light years. The reason we can see those stars is because they are incredibly bright. If you were close to Alpha Centauri, of course, it would blind you. The reason that we can see the light from the star is because that sun is so luminous. So a message from a planet around Proxima Centauri would have to be extraordinarily strong. We are not yet capable as a species of generating a signal that strong if it's beamed in all directions. For example, our most powerful radio telescope until recently was Aricibo. Aricibo could detect a message from a similar telescope to Aricibo if it was within one light year, But of course there are no other stars within one light year, and even the closest star is four light years away, so we couldn't detect on the directional messages sent in every direction from a technology similar to ours. They would have to be beaming it to us, which is totally possible. If you knew we were here, you could send a message directly to us from that planet. But they would somehow have to know we were here and then send us a message, and that we could definitely hear. If we detected somehow aliens existing on that planet, we could definitely beam them a message that they would be able to pick up. Now, remember that conversation would last, you know, decades, because it takes five years almost just for our message to arrive. Then they have to argue about how to respond and then send us a reply. So it's like ten years between responses, and you know how we're going to figure out how to even talk to them. It takes ten minutes even just to start a Skype conversation these days, and make sure everybody can hear you. Imagine how many back and forth it takes to establish like the basis for communication and learn each other's languages and understand what a language even is and do they use mathematics? Who would have a lot to learn? And taking ten years between questions and answers, It would take a long time, But I hope that it happens, and I look forward one day listening to that message from Proximo Centauri. All right, so thank you everybody for sending in your questions and for coming along with us on this ride of curiosity and wondering about the universe. I want to make sure your questions are answered. That's right, I'm talking to you specifically. You got a question in there you haven't asked, Please send it to us to questions at Daniel and Jorge dot com. I promise you you'll get an answer. 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. When you pop a piece of cheese into your mouth, you're probably not thinking about the environmental impact. But the people in the dairy industry are. That's why they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. House US dairy tackling greenhouse gases. Many farms use anaerobic digestors to turn the methane from manure into renewable energy that can power farms, towns, and electric cars. Visit you as dairy dot COM's Last Sustainability to learn more.
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