Daniel and Jorge Explain the UniverseWhat is the best way to explore the galaxy?
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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? I'd 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?
You're joking or you're 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'd joke about science. I think we are a jostle science.
Well, I think 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 Old Grass 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 am Jarge. 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 we're the co authors of the book We Have No Idea, A Guide to the Unknown Universe. And the co hosts of this podcast, Daniel and Jorge Explain the Universe, a production of iHeartRadio.
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 re 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 Doctor Seuss type of rhyme there, But.
Did doctor Sewis write a book about aliens?
Maybe he was the alien?
Maybe that's why his books are so good. Now, this is the podcast in which we tackle big questions with a Doctor SEUs 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 is 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. What 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 wonder 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 d md US or send a text message at least you know.
You know what. Maybe they're using Google Plus and they didn't realize they's been canceled. That would be a trick.
They were early adopters, but it worked against them. Maybe Google, maybe people at 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, wait, 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 the grascitizing 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's like it it seems like we should assume aliens exist, but why haven't we heard from them?
That's right, That's right. That's 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 that people say they see UFOs and maybe pilots see weird stuff over the ocean. And there's this ridiculous documentary featuring Bubblazar and his absurd claims about having worked in an alien technology or re engineering base. But he has absolutely no evidence to back up any of these claims. So we could dissect some of those claims, et cetera.
But I think, yeah, 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 claims. 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. 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 bab Blazar's claims or the claims of anybody else who who says they've been abducted by aliens, have been experimented on by aliens, etcetera. But today we're going to focus on that question, 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 reach us 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, even it takes us years to get even to the neighboring planet.
Right.
If we've gotten a rocket ship and want to fly to Mars, that we 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 and star wars.
In the Avengers movies. Though, like some of the aliens look like raccoons, which is that would be weird?
Hey, raccoons are like the central race of the universe.
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 learned 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 chocolate? Well, would you eat a chocolate bar an alien pooped out?
Or well you sort of do, right, I mean chocolate cocoa beans are are fermented, right, so you're sort of eating a kind of the poop.
They're a bacteria, right, chocolate is fermented.
What I think I think they ferment that they ferment cocoa beans, like they harvest them and then they lay them on the sun, they rot a little and then they I could, I could, I could be saying physically possible 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 you have 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, 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're the aliens, right, if we had sufficient technology, could we explore the galaxy? How would people do it? So I walked around campus that you see 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 fit 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, where is that? So it's the.
Idea by Vonoyman. By self replicating your robots, so they you send them out in all directions, and then they have the blueprint to replicate themselves using ro Matiro still find and then send out other probes. So you keep expanding the square so you can cover the galaxy probably in a two hundred thousand years or so.
And since we have like two mc square, so that would be the I remember someone told me this 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 meaned to certainly trying to visit them via telescope or other means. Well, I mean you need to rocket.
I don't know, geez, that would take a long time.
I would assume that would be like years and years and years.
Pack a lot of snacks.
Yeah, if there's a means of some kind of faster than light travel, it would be feasible. Otherwise, I feel like the it would just be near impossible to do that and.
Within a lifetime.
All right, So what do you think of people's answers?
They alsound pretty pretty reasonable to me. I mean, somebody said you could use EMC squared or too mc squared. Was that a is it a typo or a smaller or is it a new theory?
No?
No, No, that's like, you know, maybe mc square is not enough, so we've got to upgrade to the new theory of physics, which is mc squared. I'm going to wait for five mc square to come out before I get my new physics.
Do you have to upgrade? Do you have to get you 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 every planet? And that was really intriguing, And I guess it's true that if you had really powerful telescopes you could really image things like across the galaxy. I'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.
I see, You're I think that 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 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.
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 tell is it a cloudy atmosphere or is there blue water under it? You know, that kind of stuff where we're not quite there yet though, 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 as 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 year or something, and we saw aliens there, Oh my gosh, you'd have to send something. We'd have to send a delegation because otherwise the conversation would take forever. I mean, say it's twenty light years away, right, then every step of the conversation is forty years. Right. They say huh, and we say what we say, huh, that's sixty years gone by, you know, right, So that'd be crazy.
That would be a pretty slow.
If you looked in out your window and you saw your neighbors were having a huge raccoon party, you can go over the knock on the door.
Not I would send them a letter and wait thirty three years.
Like, hey, look they have a chocolate fountain at that party. Let's go. We're there.
But I think, you know, with 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 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. Who are 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 the 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 through television and radio broadcasts. 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, Like should we have expected to be visited because of the radio and TV broadcasts that we've been sending out inadvertently into space? Right?
Or when can we expect people to hear our nineteen fifties television right?
That's right exactly. And you know some of us have sent messages into space specifically, right, Like we use the Arecibo radio telescope to send a message back in response to the Wow signal that we got in seventy seven. That's very sporadic. Mostly we've just been broadcasting random stuff and that just 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 a you know, maybe one hundred years. And so you imagine a sphere that's just one hundred light years around centered at the Earth. That's a tiny, tiny fraction of the galaxy, which you remember is one hundred thousand light years across.
So 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 who there's 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 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 that's pretty zippy. So then if we have one hundred years since we broadcast the first message, then sort of the outer shell that spear would actually be like thirty three light years away, right, people one hundred light years away they're just now getting the messages we sent one hundred years ago, so we could expect to see them in two hundred years. But the ones thirty three light years away they got the message sixty six 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 life for sixty six 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 to sink, 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 muther.
They're like, this stick Van Dyke guy is super hilarious. Go meet them.
Yeah, exactly, And so that's sort of the sphere of possibility. Anybody within thirty three 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. Thirty three light years.
It does seem kind of small, I mean compared to the galaxy. But 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 it 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 twenty percent of stars have an earth like planet. Now that depends exactly on the kind of star, but let's be generous, so ballparking, you know, And this is what we do in physics. We're just like trying to get the answer to within the factor of five to ten.
That's all part of precision physics right there. Well, you know, precision physics. You're made out of a quartz us our minos rights.
Oh did you say, oh you ten dollars, here's two dollars. That's conclus Did you say it was going to cost ten billion oops? To cost one hundred 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 our rough estimate of it? You know, can we figure out, you know, to within a factor of two or five ish roughly with the back of the envelope and back of the envelope exactly, and so approximately fifty is the answer. We expect there to be about fifty 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, fifty seems that it's a reasonable number, isn't it like if you had fifty Earths, you know, surely some of them might have people 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 one hundred percent, is it one in fifty is it one in fifty 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 one hundred percent right, because there are fifty 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 fifty.
Say that again, what's statistic.
There are fifty planets out there that have received our messages. Fifty 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 one in fifty.
That's assuming that someone would get to signal, jump on a rocket ship and come over.
Yeah, exactly right. So with all those assumptions, the answers is, you know, less than one in fifty. So that starts to answer the question, right, we know it's not one hundred percent. 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 and came to look for us. And so if we haven't already, that means that probably none of these fifty 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.
Animals.
But yeah, or other similar aliens. And you know, there's a sequence of assumptions built into their right. They have to be technological, they have to use radio, they have to be interested, 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, right, that's right exactly, Okay.
And every year that number gets smaller, right, because every year our radio ways go out further, and every year that means there are every year that we don't have aliens visitors, 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 one hundred. Every year that we that 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 in willing to come and visit it.
Are answering any.
Of those assumptions, right? It could be that all those planets have aliens, but they're not intelligent, or they're 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 forty seven thousand 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 pull inbox too, That's.
Right, that's right anyway. So that's the sort of scenario if they hear our messages, I see, But what if they don't, you know, like, yeah, 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 know we're here to stumble across us.
All right, let's get into another type of alien, which might find is just randomly right, that's what you're saying. They're just out out and about and they find it. So what are the likely what's the likelihood that they'll well stumble upon us like Columbus stumbled upon the Native Americans, which is a great give us.
Yeah, well for lots of reasons because of 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.
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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 this sort of two competing things going on from the physics point of view. On one hand, the galaxy is huge. It's one hundred thousand light years across. It has billions and billions of stars, so it seems sort of unimaginable to be able to explore it, 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 we were saying, it makes it more likely that we'll get visited.
Yeah, exactly, because there's been a lot of time. So the galaxy's been around for more than ten 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 one hundred thousand 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 and you wanted to visit every single star because you're like an intense tourist, how long would.
It take here. That's right, you have the ultimate bucket lift and a bucket of star. 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 fifty billion stars in the Milky Way to visit. That's the fraction we think have Earth like that us.
Oh, I see, they would only 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. I'm imagining like 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 ten or eleven light years. The average distance between stars is about four ish light years, but there are not every star has an earth like planet, so it's about ten or eleven light years between earth like planets. And so again, assuming you can travel at half the speed of light, it takes you know, something like twenty twenty five 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 get end up with a big number.
Right.
You've got fifty billion solar systems with Earth like planets. Each one takes twenty years to visit, and so you know, you're talking trillions.
Of years right just in our galaxy.
Our galaxy, and you know, you might imagine aliens in other galaxies, but the distance between galaxies is ginormous compared to the size of the galaxy, and so that's you know, 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 ten billion years, you wouldn't have visited a significant infraction in the galaxy, you know. So it could certainly be what 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 isn't 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 child. But you know, so that means there could be an alien ship out there exploring the galaxy, and it's reasonable that hasn't visited the Earth yet. All right, that's interesting. But then you can start to play the numbers game. You could say, well, what if there are a thousand ships, what if there are a million ships? What if there are a billion aliens out there? Right? Oh, and you can do these calculations for 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 us.
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 one thousand years to explore the whole galaxy. Wow, right, yeah, because you know there'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 what 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 arrive. 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 existing 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 that time to mention 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.
So you're saying, maybe they could have come a thousands or tens of thousands of years ago, but then said, oh, you know, their trash is not quite ripe yet, let's come back when they're totally abusing their environment exactly, 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 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, or here's what to do or something. Or maybe they just figure, oh, we'll come back in another million and see what's going on.
Or maybe they did stick around and they.
Are us, we are the aliens. And so this gets harder. But you can also do the same trick whill 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, Right, 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 we weren't ready, right.
And again, you're assuming that you're ruling out a class of eightens 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 until they 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 that helps narrow it down a little bit.
Yeah, exactly, that 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 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 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.
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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. But you're 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 wanted 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 Numann. 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 ten babies, and those ten babies have ten babies, and those ten babies have ten 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 you know 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 where maybe one hundred two hundred 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. 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, you can go viral. Yeah, that's exactly if we go viral. So that's fascinating. Right now, there's another question like, are these crude probes or uncrude? 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.
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, and yet no self replicating probes have landed on Earth. Oh and so that's kind of disappointed.
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, in eventually a number of years. It grows pretty quickly. Yeah, you can go from millions to billions pretty quickly. And so you would expect somebody else to have 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. It 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 pro about tomorrow.
Absolutely interesting, wouldn't you. Yeah, Well, it would cost a lot of money, wouldn't it.
The R and D would cost a lot, you know, to figure out how to get a ship, to build a copy of itself, to build a ship making 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. So, 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 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 reported 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 to like build a ship making factory somewhere. And if they landed on Earth and mind the Earth to make a ship making factory, I think we would see signs of that. Or I mean it could be there out somewhere in the asteroid belt and they like mine 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, if we have 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 sent have had this idea and send probes to visits to Earth. That makes me doubt, That makes me wonder, like, hmmm, maybe we are alone in the galaxy, because surely somebody else would have had this idea. That's not such a brilliant idea that only humans would have come up with it, right, So, frankly that 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 Lazar, 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 it's totally possible, and there are many ways that they could do it, and there are many ways it 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 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, But 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 ten. 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 one 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 up play, wondering how do I stop these recruits from going through my trash?
And why would you? Because your trash is their chocolate?
All right? Well, hopefully that gives you some solas 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.
Before 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 Daniel Andhorge dot com. Thanks for listening, and remember that Daniel and Jorge to 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. How is 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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