Why haven't aliens visited us?

What is the best way to explore the galaxy?

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Episode Transcript

Speaker 1 (00:08):
Hey, Daniel, I've got a question for you about aliens.
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? Are you
joking or are you being serious? Well? I mean, would
I joke about science? Isn't that what this podcast? Is

(00:28):
you joking about science? Me? Now, I don't think I
joke about science. I think we are a jostle science. Well, um,
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,

(00:51):
or I think I know who an alien is. Um,
I have a lot of confidence in you, but I
think you know, I need to see some evidence on
such a big claim and don't take it personally. You know,
I don't think I 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 I am jorhe I'm the

(01:29):
creator of DHD 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 host of this podcast, Daniel and Jorge Explained
the Universe, a production of I Heart Radio. That's right,

(01:50):
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
asking 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 gonna launch into Doctor SEUs type

(02:12):
of Ryan there, But did Doctor So let's 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
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,

(02:33):
the tentacles you'll meet on aliens who come and visit. Yeah,
we uh 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

(02:54):
this huge universe. It's an amazing question, and it's my
favorite type of question because does 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.
What that means I don't know, but spiritually that's pretty important, right,

(03:18):
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

(03:39):
that universe where we have neighbors, and they're gonna 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.

(04:02):
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

(04:26):
called U or d M, does or sent the text
message at least you know, let's you know what. Maybe
they're using Google Plus and they didn't realize they's been canceled.
That would be a t they were early adopters, but
it worked against them. Maybe Google, maybe people like Google
are the aliens and they tried. That's right, they tried.

(04:48):
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 why do we have to assume it? Well, um,
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 university.

(05:11):
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 Neolograsty 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,

(05:33):
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. Um, that's kind of
the paradox, right, It's like it it seems like we
should assume aliens exists, but why haven't we heard from them?
That's right, That's right. That's that's the other question. I

(05:55):
think the second assumption we should make is that we haven't. Right,
there's a lot of talk their people say they've seen
UFOs and maybe pilots see weird stuff over the ocean.
And there's this ridiculous documentary featuring Bubba Lazar and his
absurd claims about having worked in an alien you know,
technology re re engineering base. But he has absolutely no

(06:18):
evidence to back up any of these claims. That we
could dissect some of those claims, etcetera. But I think
it was in the Joe Rogan podcast to 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,

(06:41):
and are maybe not reliable eye witnesses. Right, Well, I
think this 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. Aren't closely? That's right,

(07:01):
and that's the question we want to answer. Today's 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?
And then you can take your own skepticism if you
like to, to listen to Bob Lazar's claims or the
claims of anybody else who who says they've been abducted
by aliens, has been experimented on by aliens, etcetera. But

(07:25):
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 d predictable
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,

(07:48):
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 if it takes us
years to get even to the neighboring planet. Right, we've
got a rocket ship and wanted to fly to Mars.
That would take years, and so to get to a
nearby star or do you get to you know, several
to explore a space of stars that's a significant fraction

(08:10):
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 entertainedly. You know, everyone has seen the Avengers movies.
They're they're aliens there in Star Wars. In the Avengers

(08:35):
movies that like, some of the aliens look like raccoons,
which is that would be weird? Raccoons are like the
central race of the 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,

(08:56):
we meet aliens, we learned about the physics of the university,
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 they're trash is
something we love? Right? Like they poop out gold bars
or something chocolate. Well, would you eat a chocolate bar

(09:19):
and 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 there
of bacteria. Right, chocolate is fermented. What I think? I
think they ferment that they ferment cocoa beans like they
harvest them and then they lead them on the sun.
They rot a little and then they I could, I could,

(09:42):
I could be saying physically impossible things. Well, um, 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
have cheese and bread and beer. We're definitely building up
my cribial poop all the time, and some of it's delicious. Yeah,

(10:04):
until he's 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 are the aliens? Right, if we
had a sufficient technology, could we explore the galaxy? How

(10:25):
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?
To 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

(10:45):
an unlimited budget and unlimited time. What's the best way
to fait 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, vonouma probes? Where's that? Uh? So it's the

(11:07):
idea by voneuman and by self replicating your robot. So
they sent them out in all directions, and then they
have the blueprint to replicate themselves using raw materials to
find and then send out other probes. So you keep
expanding in the swear you can cover the galaxy probably
and uh the under tousing years or so, and since
we had like two mc swear right, so that would

(11:29):
be the I remember someone told me that would be
the best way to do that through a telescope because
they'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, well,
I need to certainly I'm trying to visit them via

(11:52):
telescope or other means. Well, I mean you need a rocket.
I don't know, jeez, that would take a long time.
I would assume that that would be like years and
years and years. If there's a means of some kind
of fassion that might travel, it would be feasible. Otherwise,

(12:13):
I feel like the it would just be near impossible
to do that within a lifetime. All right, So what
do you think of people's answers? Uh? They all sound
pretty pretty reasonable to me. I mean, somebody said you
could use empty square or two empty square? Was that?
Is that a typo or a smire? Is that a
new theory? No? No, No, that's like you know, maybe

(12:34):
mc squared is not enough. So we've got to upgrade
physics squared. I'm gonna wait for five MC squared to
come out before I get my new physics. Do you
do you have to upgrade? Do you have to? Um?
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

(12:55):
it went is too slow. No, there's some good ideas here.
I mean some people said, like the just use telescopes, right,
why do you have to go to every planet? And
that was really intriguing. Um, And I guess it's true
that if you had really powerful telescopes, if you could
really image things like across the galaxy and the one
way to do it. But you know, you can't see
the other side of the galaxy because the center of

(13:17):
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 gonna be able to
see anything I see. You're I think that the idea is,

(13:39):
why should I go over to my neighbors and shake
their hands to welcome them to the neighborhood when I
could choose spy on them with a telescope? Is kind
of That's right, exactly exactly and uh, 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 in audible moment in the history

(14:01):
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 tell or is there a
cloudy atmosphere or is there blue water under it? You

(14:21):
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, the zillions of stars, this
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,

(14:46):
just to to see other alien filications, but not talk
to them and 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.

(15:06):
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, Let me say what you say? Huh,
that's sixty years gone by, you know. Um, So that
would be crazy. That would be a pretty slow If
you looked in out your window and you saw your

(15:28):
neighbors were having a huge raccoon party, you can go
over and knock on the doorway. No, I would send
him a letter and wait thirty three years, like, hey,
look they have a chocolate fountain at that party, let's
go over there. Um. But I think you know that
with the takeaways 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

(15:52):
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 to 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.

(16:15):
Who we are assuming that nobody has come to visit,
And so then the question is why not? Right, if
the life, 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

(16:37):
and radio for decades and decades, so it's possible, 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,

(17:00):
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 to television
or 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,

(17:23):
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 broadcast that we've been sending out
inadvertently into space, right? Or when can we expect people
to hear our our nineteen fifties television right? That's right, exactly.
And you know some of us have sent messages into

(17:43):
space specifically, right, Like we used the air CBO radio
telescope to send a message back in response to the
wild signal that we got in in seventy seven. That's
very sporadic. Mostly we've just been broadcasting random stuff and
that just sends goes out into into interstellar space. So
if you had a really fine telescope, you might pick
it up, but of course physics limits us. Right those

(18:05):
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 to the Earth. That's a tiny, tiny fraction
of the galaxy, which you remember is a hundred thousand
light years across to our radius of influence right now,

(18:27):
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 a chance to build a ship and come visit us.

(18:48):
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 traveled like half
this beat 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 a hundred
years since we broadcast the first message, then sort of

(19:11):
the outer shell that's fear would actually be like thirty
three light years away, right, people a hundred light years away.
They're just now getting the messages we sent a hundred
years ago, so we could expect to see them in
two are 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

(19:33):
in our direction, been traveling a half the speed of
light 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 gotta 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, ah ha, this is what we

(19:55):
were waiting for. And then they just head out to
do a trash more like this. Think fan, that guy's
super hilarious. Let's go meet him. 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,

(20:16):
that they're interested, etcetera, 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

(20:36):
a few hundred stars within that sphere, right, and we
know that about twenty 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. Again,
precision physics right there. Well, you know, decision six out

(21:01):
of a quarters plus or minus seven ten dollars. Here's
two dollars. That's pretty enough. Did you say it was
gonna cost ten billion oops to cost a hundred billions? 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? You know, can we figure out, you know,

(21:23):
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
expected 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,

(21:45):
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 earthlike planets have life on them? Is it?
Is it one in fifty, is it one in fifty trillion?
Or is it one over infinity right as an only Earth.

(22:08):
And so the fascinating thing about doing these measurements is
that we've learned something. We know it's not 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 earthlike planets have
intelligent technological aliens that are interested in visiting us is

(22:30):
less than one in fifty. Say that again, what's that's
the disc There are fifty planets out there that have
received our messages. Fifty earthlike planets have received our messages
and none of them have come to visit us. So
that means that the rate at which earthlike planets have
technological aliens that are interested in visiting us and willing
to take the trip is less than one in fifty.

(22:51):
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 answers is, you know, less
than one in fifty, and so that starts to answer
the question, right, We know it's not a percent. We
know that not every earthlike planet out there has technological
aliens desperate to visit us. Oh, I see, you're flipping
it around a little bit, right, You're you're using these

(23:11):
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 if every single
earthlike planet out there had trash eating raccoons desperate to

(23:33):
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 earthlike planet is filled with
technologically advanced trash eating raccoons or other animals. Yeah, so
other similar aliens. And you know, there's there's a sequence

(23:55):
of assumptions built into their. Right, they have to be technological,
they have to use radio, they have to be interested, right,
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, No, I see, So
we're ruling out sort of a class of aliens based

(24:15):
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
visitors means that it's less likely that there are aliens
like that exactly every year we don't get visited. If

(24:36):
next year they arrived, then boom, the number goes up.
Every year that we that that our sphere of influence
expands without being contacted, then we know we we have
a better and lower estimate of the rate at which
there are again technological, intelligent aliens interested in willing to

(24:59):
come and visit it. That are answering in 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

(25:20):
just saying, sometimes it happens, you know, it's 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
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.
But what if they don't, you know, like, yeah, they

(25:42):
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 stumble upon us like Columbus stumbled

(26:04):
upon the Native Americans, which is a great scenario for 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. All right, let's get into that,
but first let's take a quick break. All right, we're

(26:36):
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 um water bags that move around and
have podcasts exactly, and there's sort of too compe heating

(27:00):
things going on from the physics point of view. On
one hand, the galaxy is huge. It's a 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

(27:20):
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 to mension
into account to not just how big space is, but
how old it is. Also makes it more what 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

(27:43):
has been around for you know, more than ten billion
years um, 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 a 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

(28:04):
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 O,
C D, how long and you wanted to visit every
single star because you're you're like an intense tourist, how
long would it take? Care that's right, you have the

(28:28):
ultimate bucket lift, and yeah, how long would that take?
And and then I thought, well, let's not visit every
single star. Maybe these folks are out hunting four 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

(28:49):
the Milky Way to visit. That's the fraction we think
have Earth like Oh I see, they would only you
would only pick stars you think might have life on him. Yeah, exactly,
because we're interested 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

(29:09):
you could be totally wide open to lots of different
kinds of life. And I'm a huge fan of that.
I 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 gonna come from earthlike planets. Okay, so how
long would it take us? Yeah, how long would it take? Well, Um,
the average distance between earthlike planets is about ten or

(29:31):
eleven light years, right, the average distance between stars is
about four ish light years, But there are not every
star as an earthlike planet, so it's about ten or
eleven light years between earthlike planets, and so again, assuming
you can travel at half the speed of light, it
takes you know, something like five years to go from
one to the other. Oh, I see, And that's assuming

(29:52):
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 but there are path 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.

(30:13):
And again that's a factor to maybe and we're just
interested in sort of generally getting this answer right. And
so of course you're gonna get ended 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 just in our galaxy, just
for our galaxy. And you know, you might imagine aliens

(30:34):
and 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 worms. That's why I's
focusing on just our galaxies. 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

(30:55):
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

(31:15):
visited a significant fraction in the galaxy, you know, So
it could certainly be what that 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

(31:36):
be that sexy when I'm tread. 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 million ships? What if there are billion aliens out there? Right?
And you can do these calculations for for lots of

(31:58):
different ships. 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,

(32:19):
you know then it tis takes it takes about a
thousand years to explore the whole galaxy, 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
um And so what that tells you is there are
not a billion alien exploring ships. And again, you know,

(32:42):
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 in the government is
covering it up, etcetera, etcetera. But what if they came
while we weren't ready? You know, like what if they
came knocked on the door we weren't ready or maybe
even existing because humans have only been around for like,
you know, a couple of ten tens of thousands of years. Right, Yeah,

(33:03):
that's a great question. That time to mension 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 look back right and say like, okay, well,
you know, I got this one billion of the galaxy
to sort of patrol. I'm gonna come back every thousand

(33:23):
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.
You're saying that maybe they could have come a thousands
or tens of thousands of years ago, but then said,
you know, their trash is not quite ripe yet, Let's

(33:44):
come back when they're totally abusing their environment, throwing out
prime trash. Yeah, exactly, and the time tomension 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 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

(34:05):
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. But 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 will take about
a million years to explore the whole galaxy. And so
then you can wonder, like, well, if aliens came here

(34:26):
a million years ago, would they have stuck around where
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 on that's right, we

(34:48):
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, Right There
could be a million alien ships exploring the galaxy and
they would only get to Earth every million years or so.

(35:10):
And so it certainly could be that there are 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 anies 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

(35:32):
here until they keep going. Yeah, exactly, ruling out aliens
that 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 that helps narrow it down a little bit, Yeah, exactly,
that helps narrow down. It's like exploring the kind of
ways they could see us, and does physics limit us?

(35:54):
And it turns out that you know, physics doesn't really
limit us because while the galaxy is large, there is
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. Well, there is a way you were telling

(36:14):
me that shoots that number up super high and makes
it super likely that we would have been contacted by
aliens um, 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. Okay, so I

(36:41):
think we can sort of rule out that there are
billions of aliens out there that have heard is and
one of visitors or that even are out there exploring
and want to say hi to us. UM. 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

(37:03):
explore the galaxy that we should have seen by Now,
that's right, and the idea is you want a lot
of ships because you 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
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

(37:27):
by von Neumann. So Neuman 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.

(37:48):
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've got a billion rats, right kind of Or like viruses, right,
Like they invade a cell and they use the cell
to replicate exactly just like a virus. So we should

(38:08):
be the virus, rats and viruses. This is not not
favorable not favorable analogies here. Yeah, well, um and that's
the idea. And you know that might seem like, what
is that crazy? It's it's a little crazy, but it's
it's sort of weirdly not that far off technologically. I mean,
we have factories now that are mostly stocked with robots.

(38:31):
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,

(38:54):
and you know, I would estimate where maybe a 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 so you have like a satellite orbiting

(39:17):
every single earth like planet in the entire galaxy within
tens of thousands of years. You can go viral. Yeah,
that's exactly we go viral. So that's fascinating, right. Um,
Now there's another question like, are these crude probes or uncrude?
I don't want to say man, because you know there
are men or women on them. You know, I don't

(39:37):
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. 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,

(39:59):
you can flip it around. You can say, well, shouldn't
aliens have thought of this idea? Um? 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, and so that's kind
of disappointing. If you can have this viral exploration scenario,

(40:23):
then you might have even more than a million probes
out there. You could have billions of probes out there eventually. Yeah,
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, and yet it's not.

(40:45):
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. Uh well,
it seems like a pretty crazy idea, isn't it. Why
would you even do that just just to reach out

(41:06):
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

(41:28):
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

(41:48):
that there are aliens who would have this idea and
the resources and the smarts. Yeah, exactly. The fact that
that we haven't seen them, that it has doesn't seem
to have happened, means that there's nobody else out there
who had this idea and did it right and and
would make themselves known. Maybe maybe they have come to
our solar system, but they just reported back and moved on. Perhaps,

(42:12):
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 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 mind an asteroid and then left. But

(42:34):
you know, if the idea is you could leave a
probe in every solar system sort of sitting there orbiting
earthlike planets, waiting for intelligence to crop up, and so
it should still be here and we certainly would have
found it if there was a probe orbiting the Earth
from that was not terrestrial. Well, that's such an interesting exercise,
you know, to think about how it's possible to get

(42:54):
contacted by aliens and then flip it around and say, well,
if we have, that's the fact that we haven't been
contacted means that we can rule 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 sent probes the physics Earth, that makes me doubt.

(43:17):
That makes me wonder, like 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. So frankly that 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.

(43:39):
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 are

(44:00):
many ways that they could be out there exploring the star,
you know, checking out their bucket list and oh c
d um compulsions to to visit every star. And and
the fact that we haven't um maybe tells you a
little bit about how alone we are in the galaxy exactly.
And so I think buried in the in the physics message,

(44:20):
there is the reason for hope, right, it's possible to
go across the stars and define aliens. And then there's
also a reason for a disappointment. Um, 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 didn't
understand it, or maybe they came here and saw us

(44:42):
and weren't interested. You know. So there are lots of ways.
There are lots of ways this could happen. 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

(45:03):
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 could be wrong by a factor
ten um. But you know, it gives us an idea.
And and that's the kind of thing that I that
I stay up late wondering about. When I'm camping and
I'm looking up in the stars and I'm wondering who
else is out there? Um, and my physics brain gets
engaged and tries to give me a reason for why

(45:25):
they haven't yet contacted us and made themselves know them. Well,
I stay up late wondering how do I stop these
recruits from going through my trash? And and why would you?
Because your trash is their chocolate? All right? Well, Hopefully
that gives you some solids that maybe we are alone
in the universe. But hey, Daniel, at least you still

(45:45):
have physics, that's right, and chocolate and gold pood 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

(46:06):
hear from you. You can find us at Facebook, Twitter,
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email us at Feedback at Daniel and Jorge dot com.
Thanks for listening, and remember that Daniel and Jorge Explain
the Universe is a production of I Heart Radio from
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(46:29):
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