Daniel and Kelly’s Extraordinary Universe - Why haven't aliens visited us?

Episode Date: July 23, 2019

What is the best way to explore the galaxy? Learn more about your ad-choices at https://www.iheartpodcastnetwork.comSee omnystudio.com/listener for privacy information.

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Hey, Daniel, I've got a question for you about aliens. Oh, did you meet some aliens? Can you introduce me? love to meet some aliens. Well, that's my question. Would you believe me if I just told you that I think there are aliens here on Earth? Well, are you joking or are you being serious? Well, I mean, would I joke about science? Isn't that what this podcast is? You joking about science? Me? No, I don't think I joke about science. I think we, uh, jostle science. Well, um, I think on a question of that magnitude of that, you know, historical importance, I'd

need to see some evidence. Really? You wouldn't trust me if I said, hey, I met an alien or I think I know who an alien is. I have a lot of confidence in you, but I think, you know, I'd need to see some evidence on such a big claim. And don't take it personally. You know, I don't think I'd believe Stephen Hawking or Neil deGrasse Tyson or, you know, anybody on a question of such magnitude. Actually, those are the guys that I think are aliens. Okay, now you have me convinced. Hi, I'm Jorge. I'm the creator of PhD comics and a cartoonist. Hi, I'm Daniel. I'm a particle physicist and probably not an alien. Probably. Keep that in mind.

Who can really say for sure? And together with the co-authors of the book, We Have No Idea, a guide to the Unknown Universe, and the co-host of this podcast, Daniel and Jorge, Explain the Universe, a production of IHeart Radio. That's right, the podcast in which we take you on a journey here and there and everywhere to wonder, where is their life? Who's thinking about the universe? Are we the only ones casting our minds out into the vast reaches of empty space, wondering who else is out there? Are we alone, or is there somebody else out there thinking about the universe? I thought you were going to launch into Dr. Sue's type of rhyme there,

Did Dr. Seuss write a book about aliens? Maybe he was the alien. Maybe that's why his books are so good. No, this is the podcast in which we tackle big questions with a Dr. Seuss sort of mindset, explaining things in simple words. That's right. All the places you'll go. All the places will take you.

Oh, the tentacles you'll meet on aliens who come and visit. Yeah, we kind of, this podcast is a lot about our place in the universe, you know, right? And a big question is, are we alone? Are we the only ones thinking and having existential crises and having podcasts in this huge universe? It's an amazing question. And it's my favorite type of question because no matter what the answer is, it's mind-blowing. Right? Like either we're totally alone in the universe, trillions and trillions of stars and planets.

And we're the only thinking technological creatures. That's incredible. that means, I don't know, but spiritually, that's pretty important, right? Or we're not. And there are thinking aliens out there. Life began on other planets. Intelligence is possible in other areas. Like, that's incredible and what we could learn from those folks.

So either answer is incredible. And one day, I hope humanity will know the answer. They will know whether we live in this universe, where we're all alone, or in that universe, where we have neighbors. And they're going to look back and wonder like, wow, What was it like to live before we knew the answer to this really basic question? Yeah, they might wonder, how could you not know, or how could you not expect there to be other sentient life out there? Yeah, it's incredible. And so, but here we are, living in the dark ages of human knowledge, right, not knowing whether we are alone, and, of course, wondering.

And so that's the kind of question that we wanted to ponder today. Are we alone in the universe? Yeah. Could there be somebody else out there? What does physics say about whether or not aliens could have come to visit? So today on the podcast, we'll be tackling the question. Why haven't aliens visited us or, you know, at least called us, or DM does, or sent a text message at least, you know, stuff.

You know what? Maybe they're using Google Plus and they didn't realize it's been canceled. That would be a tragedy. They were early adopters, but it worked against them. Maybe Google, maybe the people like Google are the aliens. And they tried. That's right. They tried.

That's right. And let's set some assumptions, right? Because you could talk about this question from lots of different angles. But I think we should make two assumptions. One, let's assume that there are aliens out there, right? I mean. Why do we have to assume it? Well, I don't know.

Maybe I just prefer it, you know? It's hard for me to imagine that we live in the universe where we are the smartest things in the universe. You know, that's just difficult to accept. Well, I think this is the core of the paradox, you know, the question. You know, because, you know, we hear a lot from scientists and, you know, science people like Neil deGrasic Tyson and Stephen Hawking perhaps that, you know, the universe is so big and there's so many stars and so many galaxies out there that there must be life out there.

But I think, you know, probably the everyday person listening to this might be thinking, but, you know, why haven't we heard from them, you know, any kind of radio signal or probe or a visit or a postcard, something. That's kind of the paradox, right? It seems like we should assume aliens exist, but why haven't we heard from them? That's right. That's right.

That's the other question. I think the second assumption we should make is that we haven't, right? There's a lot of talk. There are people who say they've seen UFOs and Navy pilots see weird stuff over the ocean, and there's this ridiculous documentary featuring Bob Lazar and his absurd claims

about having worked in an alien, you know, technology, re-engineering base, but he has absolutely no evidence to back up any of these claims. We could dissect some of those claims, et cetera. But I think... Yeah, and it was in the Joe Rogan podcast, too, right? Yeah, exactly. Netflix paid money for it. Joe Rogan had this guy on.

But the guy has absolutely no evidence to back up any of his claim. So I think you can just put him in the same category as lots of other folks that have seen something weird, something they don't understand. and are maybe not reliable eyewitnesses. Right. Well, I think this is kind of the question is, should you just believe someone who says they saw aliens? Does physics say it's impossible and therefore you should pay no attention to them?

Or does physics say that it might be possible, in which case you maybe should think about it or look into it more closely? That's right. And that's the question we want to answer today is, is there a physics reason to say aliens could not have come visit, right? Does physics say it's possible for aliens to have found? us, or does physics say it's impossible? Right.

And then you can take your own skepticism, if you like, to listen to Bob Lazar's claims or the claims of anybody else who says they've been abducted by aliens, been experimented on by aliens, et cetera. Right. But today we're going to focus on that question. Right. Could aliens have contacted us? Right.

Because it could be that it's impossible for aliens to have visited us or contact us, right? I mean, the universe is so vast and unpredictable that we, you know, it could. be impossible for there to be other life out there and it could be impossible for them to ever reaches or get to us, right? That's right. And you're just thinking about it momentarily, like, you know that space is vast. You know that space is mostly empty. You know, it takes us years to get even to the neighboring planet, right? If we got a rocket ship and wanted a flight of Mars, that would take years. And so to get to a nearby star or to get to, you know, several, to explore a space of stars, that's a significant fraction of the galaxy. How long would that take? Is that possible?

Is the galaxy just too big to explore? That's the kind of question we want to dig into today. Right. So this is a question probably a lot of people maybe think about, at least in the back of their minds or entertained at least. You know, everyone has seen the Avengers movies. There are aliens there in Star Wars. In the Avengers movies, though, like some of the aliens look like raccoons. That would be weird. Maybe raccoons are in like the central race of the universe, the mold. Wait, wait, hold on.

Are you saying we have been visited by aliens and they are eating our garbage? Maybe it's a delicacy for them. It's like a tourism. That would be a win-win, right? We meet aliens. We learn about the physics of the universe and we find somebody to finally accept our recycling. Perfect. We just have to put up with their pooping in your yard or something.

And what if their trash is something we love, right? Like they poop out gold bars or something. Oh, chocolate. Well, would you eat a chocolate bar than an alien pooped out already? Well, you sort of do, right? I mean, chocolate cocoa beans are fermented, right? So you're sort of eating kind of the poop there of bacteria, right? Chocolate is fermented?

What? I think they ferment, don't they ferment cocoa beans? Like they harvest them and then they lay them on some. and they rot a little, and then they, I could, I could, I could be saying physically impossible things. Well, I don't know about whether cocoa is fermented, but you're right, we do consume a lot of products that are fermented, which is basically the byproduct of microbial metabolism. So we had cheese and bread and beer. We're definitely gobbling up microbial poop all the time.

And some of it's delicious. Yeah, and so we've totally not derailed this conversation. But back to aliens, back to aliens, exactly. And so I was wondering, what do people think about the possibility? Like, you know, not just aliens, but like, could we explore the galaxy? Say we are the aliens, right? If we had sufficient technology, could we explore the galaxy? How would people do it?

So I walked around campus at UC Irvine and I asked people that question. Not do you think aliens have visited us, but what do you think is the best way to explore the whole galaxy? So think about it for a second. If you were in charge of NASA and or humanity, how would you direct people to explore the universe? That's right. You have an unlimited budget, an unlimited time. What's the best way to visit every solar system and figure out if there are aliens there to find the raccoon home planet? That's right. If you had an unlimited amount of raccoon gold poop, what would you do? Here's what people had to say. Von Neumann probes.

What is that? So it's the idea by Von Neumann, by self-replicating a robot. So you send them out in all directions, and then they have the blueprint to replicate themselves using raw materials they find and then send out other probes. So you keep expanding the sphere. So you can cover the galaxy probably in a few hundred thousand years or so. And since we have like two MCs where, right? So that would be the, I remember someone told me that would be the best way to do that. through a telescope because it'll probably be impossible, right?

Since it's just so far away, I don't know how physically we would be able to do that. So just by viewing it through satellites or trying to get a really big telescope pretty much. Cool. Well, I mean, you could certainly try to visit them via telescopes or other means. Well, I mean, you need a rocket. I don't know. Geez, that would take a long time. I would assume that that would be like years and years.

years and years from now. Pack a lot of snacks, right? Yeah. If there's a means of some kind of faster than light travel, it would be feasible. Otherwise, I feel like it would just be near impossible to do that within a lifetime. All right. So what did you think of people's answers? They all sound pretty reasonable to me.

I mean, somebody said you could use MC squared or two MC squared. Is that a typo or a small error? Is that a new theory? No, no. No, that's like, you know, maybe MC squared is not enough, so we've got to upgrade to the new theory of physics, which is 2.0 MC squared. I'm going to wait for 5 MC squared to come out before I get my new physics. Do you have to upgrade? Do you get new icons on your phone and everything? Yeah, exactly. Every time a new theory of physics comes out, I have to get a new physics phone. It's because otherwise it runs too slow. No, there are some good ideas here. I mean, some people said, like, let's just use telescopes, right? Why? Do you have to go to everything? replanting. And that was really intriguing. And I guess it's true that if you had a really

powerful telescopes, if you could really image things like across the galaxy, that'd be one way to do it. But you know, you can't see the other side of the galaxy because the center of the galaxy is in the way, right? You can see the nearby stars. You can see the rest of the arm that we're on in the Milky Way. You can see the next arm over. But the center of the galaxy is blocking us from the other side, right? It's like we're on one side of Manhattan and you want to look to see a little town on the other side of Manhattan. You're just not going to be able to see anything. Oh, I see.

I think the idea is, why should I go over to my neighbors and shake their hands to welcome them to the neighborhood when I could just spy on them with a telescope? It's kind of the idea. That's right. Exactly. Exactly. And it's true that we're developing more and more impressive telescopes, and we will soon be able to image planets around other stars,

which will be an incredible moment in the history of exploration. I mean, we can see black holes, right? And we have seen planets around other stars, right? Like little blips. Right. We've detected their presence because of their gravitational effects and because they dim the light. But imaging those planets directly,

like seeing the photons that come from those planets so we can like tell, is it a cloudy atmosphere or is there a blue water under it? You know, that kind of stuff. We're not quite there yet, though that's going to come soon. But even still, even if you had incredible telescopes, there's a limit because you just can't see the rest of the galaxy from here

because the center of the galaxy is such a crazy blob. There's a black hole there. There's zillions of stars. There's gas and dust. So if you really wanted to be thorough, telescopes are not going to get you all the way around the galaxy. Well, also, would it be satisfying, you know, just to see other alien civilizations but not talk to them

or exchange information with them? Would that be satisfying? Not for me. I mean, if we used our telescopes and found an exoplanet that was fairly nearby, you know, tens of light years or something, and we saw aliens there. Oh, my gosh, we'd have to send something. We'd have to send a delegation because otherwise the conversation would take forever. I mean, say it's 20 light years away, right?

Then every step of the conversation is 40 years, right? They say, huh? And we say, what? And we say, huh? And that's 60 years gone by, you know? Right. So that would be crazy. That would be pretty slow.

If you looked out your window and you saw your neighbors were having a huge raccoon party, You didn't go over and knock on the door, wouldn't you? No, I would send them a letter and wait 33 years. Like, hey, look, they have a chalked fountain at that party. Let's go on over there. But I think, you know, the takeaway is that there are a lot of ways that we could explore the galaxy out there, right? We could be seeing things out there or sending signals or sending probes or getting on ships and taking off and sending humans out there. And so if you flip it around, the question is kind of like,

Have other aliens done that or why haven't they done that? Yeah, exactly. Why haven't they done that? Because, again, we're assuming we have not been visited by secretive aliens that have taken over the government and are infiltrating the highest levels of power. We're assuming that nobody has come to visit. And so then the question is why not, right? If the galaxy is teeming with life, why have we not been visited or contacted?

So I thought that the first question might be like, well, you know, why would they come here? You know, so what if they know that we're here? What if they hear one of our messages? Because, you know, we've been broadcasting television and radio for decades and decades. So it's possible that even without intentionally trying to contact aliens, that we've made our presence known. It's kind of like, why would they even come to Earth at all? Out of all the billions of planets, why would they come to ours besides the excellent trash that we have? really five-star trash here i'm sure in the michelin guide to the galaxy

earth ranks very high in the quality of our garbage but yeah exactly and so i thought well there is one way we've made ourselves known and that's through these messages television and radio broadcasts oh i think so i thought well let's do a little calculation like is there time for those messages to have gone out into the galaxy been received by aliens and have them have a chance to come back and visit it. Like, should we have expected to be visited because of the radio and TV broadcast that we've been sending out inadvertently into space? Right. Or when can we expect people to hear our 1950s television, right? That's right. Exactly. And, you know, some of us have sent messages into space specifically, right? Like, we use the Erocebo radio telescope to send a message back in response to the wow signal that we got in 77. That's very sporadic. Mostly, we've just been broadcasting random.

stuff and that just sends goes out into interstellar space so if you had a really fine telescope you might pick it up but of course physics limits us right those messages have not penetrated the whole galaxy we've only been broadcasting for you know maybe a hundred years and so you imagine a sphere that's just a hundred light years around centered at the earth that's a tiny tiny fraction of the galaxy which you remember is a hundred thousand light years across to our A radius of influence right now is pretty small. Like the idea that an alien heard us and then came to visit us and we haven't noticed, it seems unlikely because nobody could have heard our message yet so far.

Well, that was the question I had is how many, how many planets are there out there that could have heard our message and had a chance to build a ship and come visit us? So I did a little bit of calculation and I said, well, what if, you know, how fast could they get here? Let's not assume that they have faster than light travel, right? Let's use physics. So assume that they travel at like half the speed of light, which seems pretty reasonable. Which is pretty fast. That's still pretty fast, right?

Yeah, that's pretty zippy. So then if we have 100 years since we broadcast the first message, then sort of the outer shell of that sphere would actually be like 33 light years away, right? People 100 light years away, they're just now getting the messages we sent 100 years ago, so we could expect to see them in 200 years. But the ones 33 light years away, they got the message 66 years ago. So in principle, they could have gotten on a ship immediately, pointed it in our direction, been traveling at half the speed of light for 66 years, and arrived today.

Right. Meaning like they were ready to go. They had the car warmed up in the garage. Spaceship warmed up. They're like, oh, we got a signal. Let's go. That's right. Maybe they have like a trash crisis on their planet.

They're like, we desperately need more trash. And then, you know, they hear our message and they're like, aha, this is what we were waiting for. And then they just head out to do a trash run. They're like, this big Van Dykeyes, super hilarious. Let's go meet him. Yeah, exactly. And so that's sort of the sphere of possibility. Anybody within 33 light years could have heard our messages and had time, you know, given some assumptions that they have the technology, that they're interested, et cetera, to come and visit us.

So then... That seems kind of small, 33 light years. seem kind of small. I mean, compared to the galaxy. So then I thought, well, how many, how many planets are there out there? And so I actually looked up how many stars there are within a certain number of light years. And I did a calculation. And what did you find? It turns out that there's a few hundred stars within that sphere, right? And we know that about 20% of stars have an Earth-like planet. Now, that depends exactly on the kind of star, but let's be generous. So ballparking it, you know, and this is what we do in physics. We're just like

try to get the answer to within the factor of five or ten. That's precision physics right there. Well, you know, eventually you need precision physics. You're made out of quarks. Plus or minus seven? Oh, did you say, oh, you $10? Here's $2. That's pretty close, right?

Close enough. Did you say it was going to cost $10 billion? Oops, it cost $100 billion. Sorry. No. In physics, we do this a lot. We say, well, we don't know. This is a really hard problem.

We don't know the answer precisely. Can we get a rough estimate of it? Can we figure out, you know, to within a factor of two or five-ish, roughly what the answer is. Back of the envelope. And back of the envelope, exactly. And so, approximately 50 is the answer. We expect it to be about 50 Earth-like planets in that sphere where our messages have had time to arrive, and there's been time for them to turn around and come visit us.

Interesting. 50 seems that it's a reasonable number, isn't it? Like, if you had 50 Earths, you know, surely some of them might have people on. on them and listening that's exactly the question we don't know we don't know what fraction of earth like planets have life on them is it 100 percent is it 1 in 50 is it 1 in 50 trillion or is it one over infinity right as in only earth and so the fascinating thing about doing these measurements is that we've learned something we know it's not 100 percent right because there are 50 planets out there that have received our messages and had time to come and they haven't so that means

that the rate at which Earth-like planets have intelligent technological aliens that are interested in visiting us is less than one in 50. Say that again. What's a statistic? There are 50 planets out there

that have received our messages. 50 Earth-like planets have received our messages, and none of them have come to visit us. So that means that the rate at which Earth-like planets have technological aliens that are interested in visiting us and willing to take the trip is less than 1 in 50. That's assuming that someone would get the signal, jump on a rocket ship, and come over.

Yeah, exactly. Right. So with all those assumptions, the answer is less than 1 in 50. So that starts to answer the question, right? We know it's not 100%. We know that not every Earth-like planet out there has technological aliens desperate to visit us. Oh, I see. You're flipping it around a little bit, right?

You're using these back-of-the-envelope calculations to say, you know, if we are going to get visited by aliens, that means that they jumped on a ship when they heard us came to look for us. And so if we haven't already, that means that probably none of these 50 planets have such a civilization. Exactly. If every single Earth-like planet out there

had trash-eating raccoons desperate to visit us, then they would have come because there's been time for them to do it. So because we haven't been visited, therefore not every Earth-like planet is filled with technologically advanced trash-eating raccoons. Or other, you know,

animals that black yeah so other similar aliens and you know there's a sequence of assumptions built into there

right they have to be technological they have to use radio they have to be interested right

oh I see they have to be willing all these things but we have learned something right we have learned something about

what aliens are not out there right oh I see so we're ruling out sort of a class of aliens based on

what hasn't happened yet that's right that's right exactly okay And every year that number gets smaller, right? Because every year our radioways go out further.

And every year that means there are, every year that we don't have aliens visit us means that it's less likely that there are aliens like that. Exactly. Every year we don't get visited. If next year they arrive, then boom, the number goes up. Two and a hundred. Every year that our sphere of influence expands

without being contacted, then we know. we have a better and lower estimate of the rate at which there are, again, technological, intelligent aliens interested and willing to come and visit us. That are answering our call. And any of those assumptions, right, it could be that all those planets have aliens, but they're not intelligent, but they're not technological. Or they're intelligent and technological, but they're snobs,

and they're just not interested in coming to visit us, right? Right. Or sometimes, you know, people have like 47,000 emails in their inbox, and they just can't. Wait, are we talking about aliens now? we're talking about you. I'm just saying sometimes it happens, you know? It's a totally human thing, too. Well, what I like is that you're already empathizing with the aliens.

You know, you're reaching out, you're saying, I get you. I understand. I have a full inbox, too. That's right. That's right. Anyway, so that's the sort of scenario if they hear our messages. Oh, I see. But what if they don't, you know, like, they doesn't have to be that they hear our messages.

It could be that they're like Star Trek. They're just out there exploring, you know, they don't have to necessarily. necessarily know we're here to stumble across us. All right, let's get into another type of alien, which might find us just randomly, right? That's what you're saying. They're just out and about and they find us. So what's the likelihood that they'll stumble upon us, like Columbus stumbled upon the Native Americans? Which is a great scenario for us, by the way.

Yeah, well, for lots of reasons, because how well that went for the Native Americans. But also, if they arrive and they happen to look just like us, then that would be quite interesting. Yeah. All right, let's get into that. But first, let's take a quick break. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage,

kids gripping their new Christmas toys. Then, at 6.33 p.m., everything changed. There's been a bombing at the T.W. the UA terminal. Apparently, the explosion actually impelled metal glass. The injured were being loaded into ambulances, just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, and it was here to stay. Terrorism.

Law and order, criminal justice system is back. In season two, we're turning our focus to a threat that hides in plain sight. That's harder to predict and even hard. harder to stop. Listen to the new season of Law and Order Criminal Justice System on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota, it's back to school week on the OK Storytime podcast, so we'll find out soon.

This person writes, my boyfriend has been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now, he's insisting we get to know each other, but I just want her gone. Now, hold up. Isn't that against school policy? That sounds totally inappropriate. Well, according to this person, this is her boyfriend's former professor, and they're the same age. And it's even more likely that they're cheating.

He insists there's nothing between them. I mean, do you believe him? Well, he's certainly trying to get this person to believe him because he now wants them both to meet. So, do we find out if this person's boyfriend really cheated with his professor or not? To hear the explosive finale, listen to the OK. Storytime podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. Hola, it's Honey German, and my podcast, Grasas Come Again, is back. This season, we're going even deeper into the world of music and entertainment,

with raw and honest conversations with some of your favorite Latin artists and celebrities. You didn't have to audition? No, I didn't audition. I haven't audition in, like, over 25 years. Oh, wow. That's a real G-talk right there. Oh, yeah. We've got some of the biggest actors, musicians, content creators, and culture shifters,

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and all the issues affecting our Latin community. You feel like you get a little whitewash because you have to do the code switching? I won't say whitewash because at the end of the day, you know what I mean? Yeah. But the whole. pretending and, you know, it takes a toll on you. Listen to the new season of Grasasas Come Again as part of My Cultura Podcast Network

on the IHartRadio app, Apple Podcasts, or wherever you get your podcast. All right, we're talking about aliens and how likely they are to have visited us. So now we're exploring this scenario of what are the chances that aliens have could have or could stumble upon us, meaning they're out and about exploring the galaxy and they're like, oh, hey, here's a planet with some cute little water bags that move around and have podcasts.

Exactly. And there's sort of two competing things going on from the physics point of view. On one hand, the galaxy is huge. It's 100,000 light years across. It has billions and billions of stars. So it seems sort of unimaginable to be able to explore,

to check every solar system, right? On the other hand, the galaxy is very old. So even though the speed of light limits how fast you can zoom between stars, there's a lot of time. You know, our galaxy is almost as old as the universe. Right. So you're saying that we should take the time dimension into account too, not just how big space is, but how old it is also makes it more? You're saying it makes it more likely that we'll get visited? Yeah, exactly, because there's been a lot of time.

So the galaxy has been around for, you know, more than 10 billion years, though our planets only existed for, you know, four and a half billion. But even just take a few billion years, like that's a lot of time to explore the galaxy. The galaxy is 100,000 light years across, but it's been around for billions of years. So even though you have the speed of light, it's not actually that impossible to explore the entire galaxy. So I thought, well, what if you have an alien ship and you wanted to do that? And you wanted to go from star to star and explore every single, solar system in the galaxy, how long would that take?

How long would it take for you to check off all the boxes? Like if you're an alien and you have OCD, how long and you wanted to visit every single star because you're like an intense tourist? How long would it take you? That's right. You have the ultimate bucket lift. A bucket of stars.

So I thought, well, yeah, how long would that take? And then I thought, well, let's not visit every single star. Maybe these folks are out hunting for aliens. So let's have them only visit stars. that have Earth-like planets. So that cuts it down by a factor of five. So now you have 50 billion stars in the Milky Way to visit. That's the fraction we think have Earth-like planets.

Oh, I see. You would only pick stars you think might have life on them. Yeah, exactly. Because we're interested in being contacted by aliens that we can talk to and learn physics from and, you know, share the experience of being alive in this universe. And so you could be totally wide open to lots of different kinds of life, and I'm a huge fan of that,

imagining life in the core of stars, whatever. But, you know, life that we can talk to and interact with and have a chance to be technologically similar to, probably going to come from Earth-like planets. Okay, so how long would it take us? Yeah, how long would it take? Well, the average distance

between Earth-like planets is about 10 or 11 light years. The average distance between stars is about four-ish light years. But not every star has an Earth-like planet, so it's about 10 or 11 light years between Earth-like planets. And so again, assuming you can travel at half the speed of light,

it takes something like 20, 25 years to go from one to the other. Oh, I see. And that's assuming that you sort of search efficiently, right? Like you have a pretty good path to get them all. Yeah, exactly. You start from one center and you sort of spiral outwards. And, you know, there's some additional geometrical complications there because, but there are paths to explore the galaxy where you don't have to do a lot of backtracking.

And even if you do, that's not a huge factor. You know, and again, that's a factor of two, maybe. And we're just interested in sort of generally getting this answer right. And so, of course, you're going to end up with a big number, right? You've got 50 billion solar systems with Earth-like planets. Each one takes 20 years to visit. And so, you know, you're talking trillions of years. Right.

Just in our galaxy. Just for our galaxy. And, you know, you might imagine aliens and other galaxies, but the distance between galaxies is ginormous compared to the size of the galaxy. galaxy, and so that's basically totally impractical without wormhole. So that's why I was focusing on just our galaxy. So a single ship would take, you know, order trillions of years to explore the galaxy. Assuming, you meaning like if you're in Captain Picard on the Starship Enterprise and you wanted

to explore every possible planet that might have life on this galaxy, it would take you trillions of years. Yeah, exactly. It would take you much longer than the age of the galaxy. So even if you started when the galaxy was born, you were like the first intelligent race in the galaxy and you started exploring in 10 billion years, you wouldn't have visited a significant fraction of the galaxy.

So it could certainly be, what that means is it could be that there is an alien Picard out there, studiously visiting every solar system in the galaxy. Well, Patrick Stewart is an alien also, but let's not get into that. He also seems to be about a trillion years old. But he looks great. I want to be that sexy when I'm a job.

Yeah, totally. But, you know, so that means there could be an alien ship out there exploring the galaxy, and it's reasonable that it hasn't visited the Earth yet. All right, that's interesting. But then you can start to play the numbers game. You can say, well, what if there are a thousand ships? What if there are a million ships? What if there are billion aliens out there, right?

Oh, I see. And you can do these calculations for lots of different ships. Oh, I see. Not that an alien would make a billion ships, but let's say that each of the billions of alien races out there made one ship to explore, surely one of them would have hit us by now, or found this. Yeah, exactly. So if there, I did the numbers. And if you have a billion exploring alien ships, you know, then it just takes, it takes about a thousand years to explore the whole galaxy.

Wow. Right. Yeah, because, you know, that's lots of ships. And so what does that tell you? Well, we've been around for a thousand years. If aliens had come and made themselves known in the last thousand years, we would certainly be aware of that. And so would that tells you is there are not a billion alien exploring ships. And again, you know, these are aliens that are interested in visiting us and would make themselves known when they arrived. Right. Put aside the question of how they visited and the government is covering it up, et cetera, et cetera. But what if they came while we weren't ready, you know, like what if they came, knocked in the door, we weren't ready or maybe even existent because humans have only been around for like, you know, a couple of tens of

thousands of years, right? Yeah, that's a great question. The time dimension is a great one. But here's the thing is that a billion ships can explore the galaxy every thousand years. And so if you're out there looking for aliens, you might like check on a planet and loop back, right? And say like, okay, well, you know, I got this one billionth of the galaxy to sort of patrol. I'm going to come back every thousand years and say, you know, are there aliens yet? I mean, are there, is there intelligence yet? And so every thousand years, a billion ships can visit every planet in the galaxy. Interesting. So you're saying that maybe they could have come. a thousand or tens of thousands of years ago but then said oh you know their trash is not quite

ripe yet let's come back exactly when they're totally abusing their environment and throwing out prime trash yeah exactly and the time to mention has a lot of complications you know did they come when we couldn't recognize them are they about to come this sort of stuff but a billion ships would have come you know every thousand years or so and then you can crank the numbers down and say okay well there's definitely not a billion ships because then we'd be visiting visited every thousand years and we certainly would have noticed that, you know, but if there were a million ships, what if there were a million ships exploring the galaxy? And so I have the numbers here that would take, you know, about a million years. So a million ships would take about a million

years to explore the whole galaxy. And so then you can wonder like, well, if aliens came here a million years ago, would they have stuck around? Would they have like left us a note saying, hey, when you get it together and figure out technology, here's how to contact us. us or here's what to do or something. Or maybe they just figure, oh, we'll come back into another million and see what's going on. Or maybe they did stick around and they are us. That's right. We are the aliens.

And so this gets harder, but you can also do the same trick where you invert it. You can say, well, look, I'm pretty sure there are not a billion alien ships exploring the galaxy, right? We can't really say there aren't a million, though. There could be a million alien ships exploring the galaxy, and they would only get to Earth every million years or so. And so it certainly could be that there are a million aliens out there exploring the galaxy, looking for us, but they came by a million years ago and we weren't ready. Right. And again, you're assuming that you're ruling out a class of aliens that would be interested in us or making themselves known, right? Like what if they're just looking for, you know, raccoon gold poop and they don't see it here? keep going. Yeah, exactly. Ruling out aliens that don't make themselves known or stay hidden

or just come by and steal the, you know, heavy metals they're particularly interested in and move on. Okay. All right. So then that helps narrow it down a little bit. Yeah, exactly. It helps narrow it down. It's like exploring the kind of ways they could see us and does physics limit us? And it turns out that, you know, physics doesn't really limit us because while the galaxy is large, there's been a lot of time to do this exploration. So if you have enough ships, you certainly can visit every solar system in the galaxy and not a significant fraction of the age of the galaxy, which is billions of years. Yeah. Well, there is a way you were telling me that it shoots that number up super high

and makes it super likely that we would have been contacted by aliens, which is a pretty interesting idea. And then we can get into, have they been here at all? But first, let's take another quick break. December 29th, 1975, LaGuardia Airport. The holiday rush, parents hauling luggage, kids gripping their new Christmas toys. Then, at 6.33 p.m., everything changed. There's been a bombing at the TWA terminal. Apparently, the explosion actually impelled metal, glass.

The injured were being loaded into Enjured. Ambulance is just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged, and it was here to stay. Terrorism. Law and Order Criminal Justice System is back. In Season 2, we're turning our focus to a threat that hides in plain sight. That's harder to predict and even harder to stop. Listen to the new season of Law and Order Criminal Justice System on the IHeart Radio app, Apple Podcasts, or wherever.

you get your podcasts. My boyfriend's professor is way too friendly, and now I'm seriously suspicious. Oh, wait a minute, Sam. Maybe her boyfriend's just looking for extra credit. Well, Dakota, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend has been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now, he's insisting we get to know each other, but I just want her gone.

Now, hold up. Isn't that against school policy? That sounds totally inappropriate. Well, according to this person, this is her boyfriend's former professor and they're the same age. And it's even more likely that they're cheating. He insists there's nothing between them. I mean, do you believe him? Well, he's certainly trying to get this person to believe him because he now wants them both to meet.

So, do we find out if this person's boyfriend really cheated with his professor or not? To hear the explosive finale, listen to the OK Storytime podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcast. Hola, it's Honey German, and my podcast, Grasasas Come Again, is back. This season we're going even deeper into the world of music and entertainment with raw and honest conversations with some of your favorite Latin artists and celebrities. You didn't have to audition? No, I didn't audition. I haven't audition in like over 25 years.

Oh, wow. That's a real G-talk right there. Oh, yeah. We've got some of the biggest actors, musicians, content creators, and culture shifters sharing their real stories of failure and success. You were destined to be a start. We talk all about. what's viral and trending with a little bit of chisement, a lot of laughs, and those amazing

vivras you've come to expect. And of course, we'll explore deeper topics dealing with identity, struggles, and all the issues affecting our Latin community. You feel like you get a little whitewash because you have to do the code switching? I won't say whitewash because at the end the day, you know, I'm me. But the whole pretending and code, you know, it takes a toll on you. Listen to the new season of Grasasas Come Again as part of my culture podcast network on the IHart Radio app, Apple Podcasts, or wherever you get your podcast. Okay, so I think we can sort of rule out that there are billions of aliens out there that have heard us and want to visit us or that even are out there exploring and want to say hi to us. Just from the fact that we haven't been contacted by them sort of rules out that there are a whole lot of them out there ready to do that.

You were saying there's another way that we could explore or they could explore the galaxy that we should have seen by now. That's right. And the idea is you want a lot of ships because there are a lot of stars. And it's sort of awkward to build all those ships like here on Earth. Say we wanted to do this exploration. We want to take this task on. Building a billion ships from Earth sounds kind of hard. Build them one at a time.

So there's a famous idea by Van Neumann. So Neumann probes. And he said, well, what if we build a few ships and those ships build more ships? So essentially, you send out a ship which then finds a planet, uses the raw materials on that planet to assemble a ship-building factory, right? So now one ship builds a factory that makes more ships, right? It's sort of the way like rats fill up a city. You don't have one mama rat have a billion babies, right?

She has 10 babies, and those 10 babies have 10 babies, and those 10 babies have 10 babies and pretty soon you got a billion rats. Right. Or like viruses, right? Like they invade a cell and they use the cell to replicate. Exactly.

Just like a virus. So we should be the virus. Yeah, rats and viruses. This is not favorable. Not favorable analogies here. Yeah. Well, and that's the idea. And that might seem like,

what? Is that crazy? It's a little crazy, but it's sort of weirdly not that far off technologically. I mean, we have factories now that are mostly stocked with robots. Robots can build cars. So can robots build themselves?

I don't think that's too far off. The tricky thing is, you know, landing on a planet, finding those resources, mining them. But you don't even need to land on planets like asteroids we know are filled with valuable materials, iron and all sorts of heavy metals that you might need to build these things. So imagine that we can do that. And, you know, I would estimate we're maybe 100, 2.2. 100 years away from being able to do that, you launch just one of those things, it launches five more, they launch five more. Very quickly, you get up to millions and millions of ships exploring the galaxy. Right.

You do the calculation, it doesn't take very long to explore the entire galaxy. So you have like a satellite orbiting every single Earth-like planet in the entire galaxy within tens of thousands of years. Wow. You can go viral. Yeah, that's exactly. We go viral. So that's fascinating, right? Now, there's another question, like, are these crude probes or uncrued? I don't want to say manned because, you know, there'd be men or women on them. You know, I don't know that we want to send people on these things and then have those people have kids and then put those babies on the ships to explore.

On a mission to just make more ships and more people. Yeah, exactly. I don't know that we want people to go viral. So imagine we're just sending probes, right? Then those probes could send a message back to Earth if they do find something. But again, you can flip it around. You can say, well, shouldn't aliens have thought of this idea? Aliens, you know, if we're pretty close technologically to being able to do this,

aliens probably would be also, given the billions of years that the galaxy has been around. Right. And yet, no self-replicating probes have landed on Earth. Oh. And so that's kind of disappointing. If you can have this viral exploration scenario, then you might have even more than a million probes out there. you could have billions of probes out there eventually. Yeah, absolutely.

Eventually a number of years. It grows pretty quickly. Yeah, you can go from millions to billions pretty quickly. And so you'd expect somebody else to have had this idea. And frankly, for the galaxy to be filled with these things. Right. And yet it's not. And yet it's not.

Which means what? We can put a pretty hard limit. That means like there are no alien species in our galaxy that have had this idea and done it. Not even one. They would take only one to fill the galaxy and completely explore it. Wow. Well, it seems like a pretty crazy idea, isn't it? Why would you even do that?

Just to reach out out there into the universe, I guess. Yeah, because we want to know, right? Like, I want to know if any Earth-like planet in the galaxy has life. So, I mean, if we have the technology to do this, oh, my God, I would send that probe out tomorrow. Absolutely. Interesting. I mean, wouldn't you? Yeah.

Well, it would cost a lot of money, wouldn't it? The R&D would cost a lot to figure out how to get a ship to build a copy of itself, to build a shipmaking factory. But once you send it out, then it doesn't use any more resources, right? It builds more of itself based on what it finds out there. It's like viral marketing, right? It's pretty cheap to launch and pretty effective. Right, right.

But you're saying the fact that we haven't seen these sort of rules out that there are aliens who would have this idea and the resources and the smarts. Yeah, exactly. The fact that we haven't seen them, that it doesn't seem to have happened, means that there's nobody else out there who had this idea and did it, right? And would make themselves known. Maybe they have come to our solar system, but they just report it back and moved on. Perhaps.

But, you know, if they came to our solar system before they moved on, they would need to build more ships, right? And so they'd have to, like, build a ship-making factory somewhere. And if they landed on Earth and mined the Earth, and mine the Earth to make a shipmaking factory. I think we would see signs of that. I mean, it could be there out somewhere in the asteroid belt, and they mined an asteroid and then left.

But, you know, if the idea is you could leave a probe in every solar system, sort of sitting there orbiting Earth-like planets waiting for intelligence to crop up. And so it should still be here. And we certainly would have found that if there was a probe orbiting the Earth from that was not terrestrial. Oh, well, that's such an interesting exercise, you know, to think about how it's possible to get contacted by aliens and then flip it around and say,

well, the fact that we haven't been contacted means that we can rule out these possibilities. Yeah, and frankly, that's the thing that dampens my enthusiasm the most. Like, I'm a big believer that there could be aliens out there that are technological and worth talking to. But the fact that none of them have had this idea and sent probes that visits to Earth,

that makes me doubt. That makes me wonder, like, hmm, maybe we are alone in the galaxy. because surely somebody else would have had this idea. It's not such a brilliant idea that only humans would have come up with it. So frankly, that bums me out a little bit. You're saying you believe physics more than you believe Joe Rogan.

I believe the physics more than I believe Bob Lazard, that's for sure. All right. Well, I think that's sort of the conclusion we set out to explore is that basically you're saying physics says that it is not impossible for us to get contacted by other. intelligent species right you're saying that that's right it's totally possible and there are many ways that they could do it and there are many ways they could have heard us and come visitors or there are many ways that they could be out there exploring the star you know checking off

their bucket list and OCD compulsions to visit every star and and the fact that we haven't maybe tells you a little bit about how alone we are in the galaxy exactly and so i think Buried in the physics message, there is the reason for hope, right? It's possible to go across the stars and to find aliens. And then there's also a reason for a disappointment. Physics isn't the reason why we haven't been contacted. And so you have to think about other reasons why maybe the aliens are just so alien. They heard our message but didn't understand it.

Or maybe they came here and saw us and weren't interested, you know. So there are lots of ways. There are lots of ways this could happen, right? Blame your breath. Don't blame physics. That's right. It's probably your fault. It's not physics.

It is you. That's right. That's right. But this is a really fun kind of calculation. Think about what's possible to do back of the envelope calculations. None of the calculations we did here today are precise. They're all approximate. They can be wrong by a factor of 10.

But, you know, it gives us an idea. And that's the kind of thing that I stay up late wondering about. When I'm camping and I'm looking up in the stars and I'm wondering. and I'm wondering who else is out there. And my physics brain gets engaged and tries to give me a reason for why they haven't yet contacted us and made themselves known.

Well, I say, I blame, wondering, how do I stop these raccoons from going through my trash? And why would you? Because your trash is their chocolate. All right. Well, hopefully that gives you some solace that maybe we are alone in the universe, but hey, Daniel, at least you still have physics.

That's right. And chocolate. And gold poop. Possibly. All right. Thanks for tuning in, everyone. See you next time. If you still have a question after listening to all these explanations,

please drop us a line. We'd love to hear from you. You can find us at Facebook, Twitter, and Instagram at Daniel and Jorge. That's one word. Or email us at Feedback at Danielandhorpe.com. 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. Parents hauling luggage, kids gripping their new Christmas toys. Then everything changed. There's been a bombing at the TWA terminal.

Just a chaotic, chaotic scene. In its wake, a new kind of enemy emerged. Terrorism. Listen to the new season of Law and Order Criminal Justice System on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. My boyfriend's professor is way too friendly. and now I'm seriously suspicious. Wait a minute, Sam.

Maybe her boyfriend's just looking for extra credit. Well, Dakota, luckily, it's back to school week on the OK Storytime podcast, so we'll find out soon. This person writes, my boyfriend's been hanging out with his young professor a lot. He doesn't think it's a problem, but I don't trust her. Now he's insisting we get to know each other, but I just want her gone. Hold up. Isn't that against school policy?

That seems inappropriate. Maybe find out how it ends by listening to the OK Storytime podcast on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts. I'm Dr. Scott Barry Kaufman, host of the Psychology Podcast. Here's a clip from an upcoming conversation about how to be a better you. When you think about emotion regulation, you're not going to choose an adaptive strategy which is more effortful to use unless you think there's a good outcome. Avoidance is easier.

Ignoring is easier. Denials easier. Complex problem solving. Takes effort. Listen to the psychology podcast on the IHeartRadM. video app, Apple Podcasts, or wherever you get your podcasts. This is an IHeart podcast.