Daniel answers Listener Questions about the smell of space, the electroweak force and spotting distant aliens.

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Episode Transcript

Speaker 1 (00:08):
Why do we care so much about understanding the universe,
about revealing its deep truths? Why aren't we just happy
to live in it? I mean, does it change your
life to understand the Higgs Boson? Does it matter to
your day whether there's intelligent life on the other side
of the galaxy? Not practically, but it matters. It doesn't

(00:32):
matter to build spaceships or death stars, or to become
masters of the universe, but it matters to us to
know to understand it's just who we are as human beings.

(00:59):
I'm Daniel, I'm a particle physicist, and welcome to the
podcast Daniel and Jorge Explain the Universe, a production of
I Heart Radio in which we marinate in our desire
to understand everything in the universe. We cast our minds
out in the furthest reaches of space and hope to
understand what's going on out there. We turn our mental

(01:21):
eye down to the very smallest particles in our universe
and ask does this make sense to us? Can this
possibly make sense to us? Is there a mathematical way
that we could understand it? We talked about all of
these things on the podcast, and we try to make
sure they make sense to you, because we think that
everybody deserves to understand the universe. Because we know that

(01:43):
everybody wants to understand the universe. It's part of being
human to look around you and to try to understand.
And I don't know if there's an evolutionary reason to
want to understand our universe. May be fundamentally deriving the
laws of physics helps us plan the hunt for a
mammoth or chase down an antelope on the savannah. I'm
not sure, but here we are. We are curious creatures

(02:06):
and we have this desire inside us to make sure
that the world around us makes sense, to sort of
pull all of our observations together inside our mind into
a mental model that we can manipulate, that we can
probe and then we can use to predict what's going
to happen to us in the future and to make plans.
But also just to appreciate. There's a lot of talking

(02:27):
science these days about whether science and weather physics should
be searching for beauty. And I don't know if we
should be searching for it or whether we should prefer it,
but we can definitely appreciate it. There's a lot of
gorgeous beautiful results in physics that when we do reveal
something new and true about the universe, we are amazed.
We stand a gog and think, wow, there is some

(02:49):
real beauty and elegance to our universe. And so typically
on the podcast it's me and Jorge and we are
talking about some difficult to understand thing about physics and
explaining it to you or hey is not here today,
So I'm going to take the opportunity to catch up
not on the questions that science is asking, but on
the questions that listeners are asking you, specifically you. That's right,

(03:10):
I'm talking about you. You are sitting there or standing
there or driving around listening to our podcast because you
have questions about the universe, and I want to hear
those questions. I want to know what is it you'd
like explained, and so send us your questions to questions
at Daniel and Jorge dot com. If you're thinking that
physicists will never answer my email, you're wrong. I answer

(03:32):
all of our emails, and sometimes I put those questions
up on the podcast when I think somebody else might
want to hear the answer. When I think, oh, that's
a particularly interesting question that I bet a lot of
our listeners would like to hear about. So that's what
we're gonna do today. On today's program will be answering

(03:54):
real questions from listeners. And I love answering your questions
because they give me a sense for what people are
thinking about. What do people know about physics, what makes
sense to them? Because I've been doing physics for decades
and my brain is fully marinated in physics is a
language and is a way of thinking, So it's very
helpful to me to hear about the way people ask
about it when they're on the outside. So it's very

(04:16):
helpful to me to hear about what your questions are,
the way that you think about the universe and the
things that don't make sense to you. And also, because
while most podcasts are one directional is just a couple
of voices sending information and audio out there into your brain,
this podcast is interactive. That's right. We want to hear
from you. We want to know what you need to understand,

(04:39):
so please don't be shy. Send us your questions to
questions at Daniel and Jorge dot com. And if you
don't like writing emails or don't want to interact with
us on Twitter at Daniel and Jorge. Then hey, just
come to my free public office hours. I hang out
once a month for an hour on Zoom and answer
questions from all all commerce. It's an opportunity to have

(05:01):
a little bit more interactivity. You can ask a question,
you can ask a follow up question. I'll make sure
you go away with some understanding of the universe. So,
without further ado, let's dig into today's awesome pile of
listener questions. And thanks again to everybody who writes in,
and please don't be shy. So today's first question is
a rather stinky one from Bob Buyer. All right, Daniel,

(05:25):
this is Bob from Edmonds, Washington. Uh. Say, I have
always wondered, um if space might smell like something, or
even if it has a smell. I was thinking maybe
astronauts reported a smell after returning to the space station
when they're inside their decompression chamber and they take off

(05:47):
their helmets, or maybe Apollo mission astronauts after walking on
the Moon surface and returned back to their landing craft
and they take off their helmets inside there my be
residual smell from outdoors, and what would that smell like?
So anyway, I hope you can shed some light on

(06:09):
that question. Thanks a lot. All right, that's a super
fun question. Thank you so much Bob for sending that in.
I'm excited to talk about the smells of space or
the stinks of space, But first I want to think
for a minute about the motivation for this question. I
think it's super fun to look up at the night
sky and wonder about it and want to understand it.

(06:29):
And what does understanding mean. It means somehow transforming that
knowledge into something that makes sense to us, something that
relates to our everyday experience. And you know, how do
we interact with the world. We taste it, we touch it,
we smell it, and so there's a little bit there
about like trying to hook in the sky and bring

(06:49):
it down to Earth and wonder like what would it
be like to interact with the sky using our earth
based senses. So I totally applaud this idea. I think
it's wonderful, and frankly, it follows in the footsteps of
geniuses like Isaac Newton. He's the guy who thought, if
I have a theory of gravity that describes how an
apple falls from a tree, can I also use it

(07:10):
to describe the motion of the stars. There was this
idea that you could unify our understanding of what happens
here on Earth with what happens out there, the idea
that the Earth is not a special place, and the
laws of physics that we find should apply equally everywhere.
And so flip that around and think, well, if I
can smell stuff down here on Earth, could I smell
stuff out there in space? And what would it smell like?

(07:33):
So super fun, wonderful question. Now, of course, the easy
answer is that if you opened your helmet in space,
you wouldn't smell anything, because you're a news would freeze. Right.
Space is mostly a vacuum. It's very cold and very
low pressure, and so if you exposed yourself to the
vacuum of space, then of course you wouldn't smell anything.

(07:55):
But that's not the only way to smell space, right,
because space is not actually empty. We talked on this
podcast a lot about how space is actually filled with stuff.
And we're not talking here about like quantum fields and
other crazy low energy phenomena. I'm talking about actual particles.
There's a whole podcast episode we did about where is
the Emptiest Place? In space, and as you leave the Earth,

(08:18):
of course, the atmosphere gets thinner and thinner and thinner.
And then when you're out there in sort of interplanetary space,
it's not like there's nothing there. There are a lot
of particles out there, from big rocks which are pretty
rare and down to tiny grains of space dust which
are frankly everywhere. Space is not really empty at all.

(08:39):
Add to that, of course the solar wind, which is
pumping out huge numbers of particles all the time, protons
and electrons and other kinds of small particles mostly, But
there's a lot of stuff bumping around up there. So
it's a really fair question to ask, what would those
things smell like if you could somehow use your nose
to probe them, Because remember, the human nose is amazing.

(09:02):
It's a very sensitive, basically molecular detector. The way your
nose works is that you suck in air and has
a bunch of molecules in it, and those molecules hit
various sensors. These sensors are all sort of differently shaped
and they can lock into different molecules to detect it,
so they can detect lots of different molecules, and it's
very related to this sense of taste. You know, the

(09:24):
taste buds on your tongue, for example, are receptive to
sugar molecules or other kinds of molecules or salt, and
you have a handful of different sensors on your tongue
that can taste different kinds of molecules just the same way.
Your eyeballs, for example, have different cones and rods inside them,
and they use that to build up a picture of
what you're seeing. But there again, there's only a few

(09:45):
rods and cones. There's only really three different kinds of
colors that you can see, and the rest is interpretated
by your brain. But when it comes to your nose,
it's actually much much more powerful than those other senses.
Your nose can sense hundreds of individual different molecules. You
can identify them, It can pick them out even if

(10:06):
they're very, very faint. You ever smell something just a
tiny little bit that your nose picking out the tiniest
little serving of whatever it is that you're smelling. So
your nose is actually a pretty good way to explore
what's going on out there, and there really is plenty
of stuff out there to smell. Space is not just

(10:26):
filled with hydrogen gas. There are complex organic molecules out there.
We know because when we sample comments or get bits
of asteroids or meteors, we see these things. We see
the molecular composition, and there's fascinating stuff out there. You
know that, Like moons of Jupiter and Saturn have really
interesting organic molecules on them. Not signs of life we're

(10:48):
talking about here, like molecular precursors of life, like the
amino acids you might need to build life. And it's
very reasonable to expect that those molecules might smell like something.
So how would you actually go about smelling it. You
can't go out there into space and open your helmet
and take a deep whiff, right, Well, what you can

(11:08):
do is you can collect those molecules and then smell
them when you're back in an aerrated chamber. And one
way this has actually happened is by astronauts going out
into space and then coming back inside. Like if you
come back into the space station, then your suit and
your helmet have collected some of those particles that are
out there in space. They've stuck to you, and when

(11:29):
you go back inside into the airlock. Then the air
releases them and they swirled all around, and some of
them go up your nose and just smell them. The
most common thing that you're gonna be smelling if you
do take a whiff of space are these things called
aromatic hydrocarbons. These are molecules built out of carbon and hydrogen,
which is why they're called hydrocarbon, and they're aromatic, which

(11:51):
means you're gonna smell them. And most of these things
smells sort of like hot metal or like diesel gas,
or and some people have described them as like smell
thing like a barbecue, and that's because those are the
processes on Earth that generates similar kinds of molecules. So
it's not like somebody out there is have a barbecue
in space or or running a diesel engine. But those

(12:12):
things on Earth produce similar molecules which end up in
your nose on Earth, and you remember them, and so
when you smell them out there in space, or when
you just come back inside from space, then that's the
association you're going to get. But there are lots of
different possible smells of things in space. For example, there's
a vast dust cloud to the center of our galaxy

(12:34):
that's made of a chemical called ethyl formate, and evil
formate itself is something you can make here on Earth,
and it smells sort of like rum. That's right. It
smells like the pirate cloud of the galaxy. And if
you separated, then one part of it esther, among other things,
is the chemical responsible for the flavor of raspberries. So yeah,

(12:54):
we're talking about vast dust clouds that might smell like
raspberry rum. But you know, all the amino acids out
there have different smells. I was looking at a chart
yesterday and some of them have different smells. Some of
them would smell sour, some of them would smell sweet,
some of them would smell like, oh mommy. So it
really just sort of depends on the particular mixture of

(13:16):
stuff that you encounter, sort of like asking what does
Earth smell like? Well, it depends are you at the
center Manhattan or the top of a mountain or in
a wheat field in Kansas, Right, Different places have different
stuff floating around, and so lots of different smells. And
I think that's the most important answer is that space
does have a smell because it's filled with interesting stuff.

(13:37):
And those smells depend on where you are. So I
also looked up a bunch of reports from what astronauts
have said, what do they think it's smells like, because
there haven't been a lot of scientific studies because these
studies require people. You know, another really fascinating thing about
the nose is that it's something that's escaped digitization so far.
You know, we've been able to capture visual images and

(14:00):
store them digitally and recreate them with a screen. We've
been able to capture sounds right and store them digitally
as information and recreate them with a speaker. We haven't
yet been able to capture digital sense and store that
information electronically in a way so that some sort of
digital smell speaker would be able to recreate them so
you could experience them. That would be pretty awesome or

(14:23):
maybe pretty terrible. I'm not sure if you want your
like movie to necessarily have smells, do it. But one
reason that we haven't yet is that the nose is
much more complicated than the eye or the tongue in
terms of the complexity of sensors that it has, and
so the complexity of the information that needs to be
stored and then reproduced, so it's particularly difficult anyway. So

(14:45):
here are some reports from astronauts. Some report that it
smells like burned steak. Astronaut Tom Jones says that a
quote carries a distinct odor of ozone, a faint, accurate smell,
a little like gunpower, maybe sulfurous. Don Pettit said it
had a quote rather pleasant, sweet metallic sensation. Three times

(15:08):
Spacewalker Tom Jones says it quote carries a distinct odor
of ozone, a faint, acrid smell. There was even a
time when NASA was considering commissioning a perfume that smelled
like space to sort of get folks used to it
so they weren't sort of surprised and put off balance
by the smell of space when they came back inside

(15:30):
from their spacewalks. But I think they ditched that plan.
And there's also another side interesting question, which is what
does the space station smell like? Because the space station
is sort of like the inside of a tent, right,
These folks can't go outside. They're stuck inside there, living
together a lot, and so you might wonder, like, does
this smell good inside the space station? So here's one

(15:50):
report I found of what mirror smells like. They said, quote,
just imagine sweaty feet, stale body odor, and then mix
that odor with nail polish remover and gasoline. So that
doesn't sound particularly nice. I'd like to go after a
walk into space and smell the raspberry rum if I
was stuck inside with all those sweaty feet. All right,
so thanks very much Bob for that super fun question.

(16:13):
I'd like to dig into some more questions, but first
let's take a quick break. All right, we are back
and we were talking about the smells of space, but

(16:34):
now we're gonna turn our minds inwards and ask questions
about the tiniest little particles and how they work. So
here's a super fun question from Larry. Hello, it's my
favorite physicist and roboticist term cartoonist team. This is Larry
Garfield's Illinois We all, though there are four fundamental forces
in the universe, you've also said many times in previous

(16:55):
episodes that you've figured out that the week nuclear force
and electromagnetism are really the same thing, or different aspects
of the same thing, or linked or something. I don't
quite understand. It. Doesn't that mean there's only three forces.
More to the point, how can there be different representations
of the same thing if particles like neutrinos only interact
with the weak force. If the weak force and electromagnetism

(17:18):
are really the same thing, how can a particle only
interact with one of them? I'm very confused. All right,
super awesome, Western Larry, Thanks so much for asking this.
This is one of my favorite topics to think about,
not just to talk about and to explain the unification
of all the forces, trying to understand whether there are
connections and patterns between the forces and whether we can

(17:39):
pull them together into some sort of unified concept. And
you might wonder like, well, why would we want to
do that, Why do we think it's even possible. Well,
that's basically the goal of physics is to look around us,
observe what we see, and try to explain all of
it using a small set of ideas. It's not hard
to explain the universe if you need a different explanation

(18:01):
for every single event. Right If you say, well, that
apple falls down because that apple falls down, and this
apple falls down because this apple falls down, which you
want is a theory of apples that describes how every
apple works. So what we've done in physics is collect
all the weird effects that we've seen and try to
describe them in terms of a set of forces, and
then look at those and say, oh, look this is electricity.

(18:22):
That's electricity. Let's describe all of it using one theory.
Oh this is a magnet. That's a magnet. Let's have
a theory of magnetism. And then we slowly pull those
things together and look for relationships between the different forces
and see are these actually just two sides of the
same coin. So what we've accomplished so far is breaking
it down to a few fundamental forces. And how many

(18:45):
fundamental forces are there depends a little bit on how
you count. Some people are taught that there are five
fundamental forces. The strong nuclear force that's what holds the
nucleus together, gravity, electricity, magnetism, and then the weak nuclear force,
the one that's responsible for radioactive to k and all
sorts of cool neutrino effects. But about a hundred and

(19:07):
fifty years ago, physicists realized that electricity and magnetism are
not the same thing, but there are two parts of
a larger thing, and that's the essential concept. We're not
showing that two things are the same. We're showing that
there are two parts of something bigger, a more complete
idea that includes both of them, rather than just having

(19:28):
a list. Right, we don't want to explain the universe
in terms of just like, here's a big list of ideas.
We want a single concept that simplifies things, that pulls
back a layer of reality and shows us what's going
on underneath. So when we unified electricity and magnetism, we
didn't say, hey, magnets and lightning are the same thing.

(19:48):
We just showed that electricity and magnetism are so tightly connected.
That is that moving charges make magnetic field, and magnetic
fields can bend the path of charges. We showed that
it makes worse since mathematically and conceptually to think of
them as two parts of the same thing. And so
that's what's happened in the last fifty years with the

(20:08):
weak force. We've been able to integrate the weak force
into a theory of electromagnetism. We call this the electroweak theory,
which I always thought was weird because we basically just
ignore magnetism. Right. It's like when a law firm gets
a lot of partners, and they start dropping names from
the title of the law firm. Nobody was advocating for magnetism.

(20:29):
They should call it the electromagnetic weak force, but instead
they just call it electroweak. So let's dig in for
a moment about what that means. What does it mean
to have electroweak force. Well, first, let's remind ourselves what
electricity and magnetism and the weak force do. And the
question was specifically about why neutrinos only feel the weak
force if the weak force is connected to electricity and magnetism.

(20:53):
So let's talk about the interactions. What do we actually
mean by these forces. We mean that particles can interact, Right,
That's what a force is. It's a way for things
to push or pull on each other, including particles. So
electricity and magnetism that forces carried out by photons. Every
time there's an electromagnetic interaction, some lightning or magnetic field

(21:14):
or anything that's carried by photons. And you can think
about this in two different ways. You can think about
in terms of the fields they're like electromagnetic fields that
fill the universe, or you can think about in terms
of particles, little photons passing back and forth. It's really
the same thing. You can think alsose photons is little
ripples in those fields. They're two totally equivalent but different

(21:35):
conceptual ways of thinking about it. So what do photons
interact with? Well, photons fly around the universe and they
can interact with anything that has electric charge. So, for example,
electrons interact via photons. When you push two electrons together,
they exchange photons, or you can think about their electric
fields affecting each other. So photons only interact with things

(21:59):
that have electric charge. Right, If you put a neutral
particle in an electric field, it just ignores that. It
can't tell it's there, it's not affected at all. So
what does that mean, right, Why do photons only interact
with particles that have electric charge? We don't really know,
and you can kind of turn the question around. Electric
charge is sort of just like a description of the

(22:21):
fact that the particle does interact with an electric field.
We don't know what generates it, or where it comes from,
or why it's there. It's sort of like a label
that says whether or not the particle feels the electric field,
whether or not the particle can interact with photons. So
the picture we have of electromagnetism is that the photons
fly through the universe and they touch stuff that have

(22:43):
this special property we call electric charge either positive or negative.
All right, So let's take that sort of framework for
understanding and turn it around and look at the weak force.
The weak force has different particles it uses to interact
or equivalently, different fields and uses to interact with. These
particles are the W and Z boson. There's three of them.
There's Z boson and to W particles. There's a W

(23:05):
plus that has a positive electric charge and a W
minus that has a minus electric charge. So the weak
force has these three particles. These particles fly around and
they interact with any particle that has the weak version
of electric charge. So every particle out there has either
a positive, negative, or zero charge that tells you whether
a photon interacts with it. There's a version of that

(23:28):
electric charge which operates for the weak force, and it
works the same way. If a particle has we call
it weak hypercharge, that means that it feels the W
and Z boson so it can interact with them. And
so now you can think about every particle is having
two kinds of charges. One that we used to just
call charge. Now we think about as electric charge because

(23:48):
it refers to whether it interacts with electromagnetism, and another
kind of charge that tells us whether it interacts with
the weak force. So we have electric charge and weak hypercharge,
and only particles that have weak hypercharge will interact with
the weak force, and every particle that we discovered so
far has weak hypercharge. For those of you super into

(24:10):
particle physics, you know that that's a little bit of
a lie, because for example, electrons have a left and
a right handed version, and only the left handed version
interacts with the weak force. The right handed version doesn't
have weak hypercharge. But anyway, everything out there has it,
including the Higgs boson. So what does it mean then,
to say that electromagnetism and the weak force are linked?

(24:31):
Are there the same thing? If they were the same thing,
they should do the same thing, and for example, the
photon should interact with neutrinos. Right, Well, they are not
the same thing. There are two parts of something larger.
It's like saying, oh, our heads and tails the same thing. No,
they're connected. There are two parts of the same coin.
It doesn't mean that they are the same thing, right,

(24:53):
But what it means that when you fit them together
you get an object which makes sense, which sort of
reflects a larger concept. And so what we do here
is we take these three week bosons, the two ws
and the Z and the single electromagnetic boson, the photon,
and we put them together and we have four bosons.
But there's something very cool that happens when you put

(25:14):
these four particles together, because they snap together mathematically and
they work together. And when you consider them all together
instead of individually, you notice something really cool happens, something physical,
which is there's a new conserved quantity. You know, for example,
how energy is usually conserved, but parts of energy are
not always conserved. You can go, for example, from having

(25:36):
kinetic energy to potential energy and back. So kinetic energy
by itself is not conserved. Potential energy by itself is
not conserved. But when you put those together, boom, you
get a larger concept energy which is conserved. So when
you put these three bosons from the weak force to
gather with this boson from electromagnetism, they operate together to

(25:57):
create a new symmetry, as symmetry that protects this property
called weak isospin that we don't have to get into.
But that's what tells us that we think they really
are related. We think they really are part of something larger.
There's a lot of really beautiful mathematics that tells us
that these things really do fit together. And you know,
these four particles we think have more in common than

(26:20):
you might think. Three of them operate for the weak force,
one of them operates for electricity magnetism, And while they
look different, they do have a lot in common. One
way that they look different is that the photon doesn't
have any mass, but the W and the z bosons
do have a lot of mass. And that's why the
weak force is weak. It's weak because those particles are

(26:40):
so massive that they don't last very long. The weak
force becomes a very weak and very short range force,
whereas photons that have no mask can fly all through
the universe and last for billions of years before they
get to your eyeball or hit another star or whatever. Well,
the reason that the W and the Z bosons half
mass and the photons don't is the higg field. The

(27:01):
Higgs field is an idea that came out of this question.
We saw that all these particles had a lot in common.
It made perfect sense to fit the photon in with
the weak bosons, except for this one puzzle, which is
why is the photon have no mass while the other
ones do and the Higgs field is the answer to that.
It breaks what we call electro weak symmetry, the symmetry

(27:24):
that protects weak isospin this way that these four particles
fit together. They fit together beautifully and perfectly if all
the particles have no mass. But then the Higgs field
comes along and it gives mass to three of those particles,
which become the weak force, and so the Higgs boson
sort of breaks that otherwise beautiful symmetry. So it's awesome,

(27:44):
and we think it's real because it led us to
discover the Higgs boson. It's like a fun, interesting mathematical
puzzle that told us something was going on and led
us to discover the Higgs boson. So we don't think
that the weak force and electricity and magnetism are exactly
the same thing. That we think they fit together to
make a larger hole. That sort of makes more conceptual

(28:06):
sense and reflects something physical about our universe. That doesn't
mean they always have to do the same thing. And so,
for example, why don't neutrinos feel the photon. It's because
they have no electric charge, and the photon only interacts
with things that have electric charge, and so that might
seem like a non answer, Like you might also ask
why do neutrinos have no electric charge? And that's a

(28:28):
great question and not a question we have an answer to.
This is the kind of thing that we observe, we discover,
we catalog and we wait for the future generations of
physicists to understand these patterns. There are lots of obvious,
apparent patterns in the sort of periodic table of the
fundamental particles, the quirks and the leptons, that are not

(28:48):
explained at all, and one of them are these weird charges,
you know. Another one is like why do the charges
of the proton and the electron exactly balance? The proton
gets it's electric charges from the corks that make it up,
but we don't have any relationship in the standard model
between those charges. They could have any value basically, and

(29:08):
yet they magically add up to the proton and the
electronic exactly the opposite charge, not like opposite by one
percent or by point one percent exactly opposite. So that
seems like a clue. So there are lots of really
deep mysteries remaining about why particles have charged, why some
don't have charge, why other ones, for example, feel the
strong force, and electrons and neutrinos don't feel a strong force.

(29:32):
Not something we understand at all, just something we are observing.
But we're noticing these patterns, and we're fitting them together
into larger ideas that we think reflects sort of deeper
understandings of how these forces are connected and might one
day lead us on a path to unify even more
forces and take steps towards our goal of having the
one force that rules them all. All right, super fun question,

(29:55):
Thanks very much. I want to answer another question, but
first let's take a second break. All right, we're back.
We've been talking about the smells of space and the

(30:16):
nature of fundamental particles, and so now I want to
turn our minds again out into the depth of space
and answer a super fun question from Matha about aliens. Hi, Daniel,
and Hore. This is Massa from Boston. I love your
podcasts and have listened to every episode so far. I
have a question that was inspired by a recent episode
about how we can detect exo galactic exo planets. If

(30:39):
there were a solar system identical to ours, where Alpha
Centauri is four light years away, complete with a copy
of our Sun as well as a copy of Earth
with over seven billion people, and there are f and
atmospheric output, would we be able to detect that planet's presence.
Would we be able to detect life? Would we be
able to detect intelligent life if it had to our

(31:00):
level of technology, and if not, at the rate of
which our detection and capabilities presently advantacy roughly one, might
we be able to detect human activity from a range
of four light years? Would it be ten years, fifty years?
For the sake of this hypothetical exercise, let's assume that
whatever alignment necessary to use the various detection methods is
in place. Keep up the good work, guys. All right,

(31:22):
thank you very much Maza for that really fun and
detailed question. I'm really looking forward of digging into how
we might detect life around our nearest star. Though. It's
a reasonable question, because you know now we are developing
this capability to see planets around other stars and to
study their atmospheres. And our technology is increasing, and so
you might ask, you know, is it likely that we

(31:45):
could find aliens around nearby stars? And you know, should
we be expecting this news any day? Or equivalently, the
fact that we haven't yet announced to discovery of aliens,
does that mean that we haven't found them or that
we're just not yet capable. So super fun question. Let's
break it up into three parts. First, he was just wondering,
could we tell if there was a planet around Alpha Centauri.

(32:08):
Alpha Centauri is a nearby star system. It's one of
the closest ones in our neighborhood in the Milky Way.
There just aren't that many stars. Is on average several
light years between stars, which means you want to get
from here to there, it's going to take you a
long long time. And so that's why I think massa
pick like the nearest solar system, one that we might

(32:28):
possibly be able to visit or at least talk to
or observe aliens. So let's remind ourselves how do we
find planets around other stars? Because mostly looking at them
is impossible. These planets are very close to their stars
compared to their distance from Earth, so basically right on
top of the star, which makes it very hard to

(32:50):
distinguish them from their star. You can't seem the reflected
light from a planet that's so far away and so
close to something else really really bright. So we have
a few methods of observing planets around other stars. The
first one is called the wobble method, is just using
the gravitational tug of the planet on the star. The planet,
of course, is also a big massive object. It has

(33:12):
its own gravity, and so it pulls on the star
and makes it wobble a little bit, and we can
use that to detect the existence of a planet. Another method,
which is even more powerful. It's called the transit method.
This allows us to find a planet when it passes
in front of the star, effectively blocking some of the
life from the starts like a many planetary eclipse. Of course,

(33:34):
it doesn't completely block the star because the star is
much much bigger than the planet, but by the fraction
of the star's light that dips, we can tell how
big that planet is. So that's pretty awesome because it
lets us measure the radius of that planet, and by
the orbital period we can tell the mass of the planet,
so then we can get a pretty good sense of

(33:56):
how big and how large, and therefore how dense that
and it is, and therefore what it's made out of.
Is it big and fluffy like cotton candy or does
it have the density of Jubiter or like the density
of Earth. So we can get a pretty good sense
for what's going on with these planets, and these methods
work for really distant planets. We have studied planets across

(34:16):
a big swath the Milky Way. The Milky Way remembers
about a hundred thousand light years across, and we've detected
planets as far away as about twenty five thousand light
years away. That's because some of these methods are pretty
insensitive to the distance of the star. If you're looking
at the wobble method, for example, we get that information
by how the light from the star is shifting as

(34:38):
the star is wobbling, and that information doesn't fade as
the star gets further and further away, so we can
detect planets around stars that are much further away than
Alpha Centauri. Typically, though, it's easier to detect really big
planets like Jupiter size planets, because they're bigger, they block
more light, and they have more mass, they tug on
their star and they block their star more dramatically. But

(35:00):
for a nearby star like Alpha Centauri, it's really no problem.
And in fact, there's even a star that's a tiny
bit closer. It's called Proxima Centauri, and we have found
an earth like planet around Proxima Centauri. It's about the
same size of Earth's about bigger, and it has about
the right density to be a rocky planet. So we

(35:20):
think that there is an Earth like rocky planet in
ahabitable zone around a nearby star. So that one we
can definitely check off the answer to be yes, we
can detect nearby planets in nearby solar systems, So that
we have done. The next question is much harder. Could
we detect life on that planet? How could we do it?

(35:42):
This is really chicky because before you even get started
you have to ask a definitional question. Right if Jorgey
would hear, he would say, hold on a second, what
do you even mean by life? Do we mean animals,
do we mean plants? Do we just mean microbes? Are
we open to something which is completely different from life
on Earth? And it sort of gets to what question

(36:02):
are you asking? What do you want to discover, And
for me, I'd like to discover life on other planets
just because it gives me a sense that there might
be life all over the universe, which tells me there
might be intelligent life, there might be an incredible diversity
of things to learn from. And so I don't want
to discover life as we know it. I don't want
to find an alien planet with trees and slugs and

(36:23):
all sorts of other familiar things on it, because that
would be kind of boring. I want to see other
examples of life, things I couldn't have imagined myself. That's
the joy of doing science in this universe is being surprised,
is finding things you couldn't have imagined that even science
fiction writers hadn't considered. Those are the best moments in science.

(36:45):
Those are also the hardest discoveries to make, because you
somehow have to be open to them. The only ways
we know to look for life are the ways we
have thought to look for life, which are limited to
the kinds of life we have thought of. So let's
focus on that. Even though I prefer to discover something
super weird and something super surprising, But could we detect
life as we know a massa was imagining, You know,

(37:08):
a bunch of people around a planet a few light
years away, could we tell they were there? So, the
only way we can really study distant planets and ask
the question about whether there's life on them is looking
at their atmosphere. And you might think a whole lot
of second, we only recently figured out how to detect
the existence of those planets. How are we going to
possibly sample their atmosphere. We can sample their atmosphere using

(37:30):
light from their star when that planet eclipses the star.
The light passes through the atmosphere of the planet before
coming to Earth, and we can tell We can tell
when the planet starts to eclipse the star, and we
can try to study just that light that sort of
skimmed the surface of the planet went through that atmosphere
and came to us. And that light will be changed

(37:51):
by what's in the atmosphere because the atmosphere, based on
its chemistry, will absorb different things. If there's water in
that atmosphere, it will absorb light at the right energy
levels for water to absorb it, and then we will
notice some frequencies missing in the light that comes from
the atmosphere. Or if there's methane in the atmosphere, or
if there's phosphing, for example, in that atmosphere, and so

(38:14):
we can use that technique to sort of probe the
atmosphere of that alien planet. It's not great, it's not
super high precision, but we're getting much much better at it,
and it's very promising. On the other hand, it's not
always conclusive. Right, So we see methane around Mars, does
that mean that there's life on Mars. We don't really know.
Nobody really believes that there's life on Mars until we

(38:36):
see those criters wriggling around. We know that there's methane
production on Mars. We even know that it's seasonal. It
seems like maybe something is waking up on Mars and
farting and during the summer and then in the winter
less cell. But there are other explanations you could come
up with, like geological explanations for the production of methane
on Mars. And we recently saw the signal on Venus

(38:58):
of phosphing production. Phosphing is something people imagine could only
be produced by processes we understand to be life, but
it's a difficult thing to see in there's a lot
of background, and recently those discoveries have been kind of debunked.
It looks like the signal isn't really there. That sort
of a data analysis problem, but the takeaway messages it's hard.

(39:19):
You might be able to detect specific gases in the
atmospheres on planets around other stars, but having like a
really smoking guns signal for life just from atmosphere composition
is pretty difficult. So what we really need is a
much clear signal that there's intelligent life. Massa is asking
if there are folks on that planet broadcasting the golden

(39:40):
age of television, would we be able to see it?
And so this again is more like life as we
know it, except it's intelligent life as we know it. Questions,
you know, could there be intelligent life that's out there
that's broadcasting messages that we are missing because we don't
know to look for them, or we haven't imagined the
format it could exist in. Absolutely, there could be life

(40:02):
that exists on very long time scales and their message
takes a hundred years even just to listen to, or
life that lives on short time skills, or life that's
communicating in some medium we haven't even imagined maybe they've
discovered axions and they are the best way to communicate
in the universe, and we don't even know the exist
and so we're missing all the information. Think about how

(40:23):
many thousands of years humans lived on Earth and didn't
understand all the information around us before we even knew
new trinos existed, and the wealth of information they encode
about the nature of the universe and what's going on
in supernova So it's certainly very possible that there's a
huge amount of information, maybe even about alien life that's
just washing over us now because we do not know

(40:45):
how to recognize it. But that's again, that's sort of
an unprobable question. It's potentially infinite. It's the unknown unknowns.
So let's focus on the known knowns. If there was
a civilization on this planet around Proxima Centauri, would we
be able to pick up their signals. Well, if they're
not broadcasting to us, then probably not. The reason is

(41:06):
that they are still pretty far away. Remember that signals
fade with distance and not a little bit. They fade
with distance squared. If you shine a flashlight, for example,
then the photons you're sending out from your flashlights spread out,
and as the area that they cover gets bigger and bigger,
the density of photons per area falls. And so, for example,

(41:27):
if you broadcast a signal in every direction, then it
gets spread across the inside of a sphere, and as
the radius of that sphere grows, the area of that
sphere grows with the radius squared. So that's why signals
fall by one over the distance squared. The same thing
for the law of gravity and electromagnetism. It's all very geometrical.
But the problem is if you're not beaming us a signal,

(41:50):
then your signal has to be really powerful at the
source for it to still be detectable by the time
it lasts four light years. The reason we can see
those stars is because they are incredibly bright. If you
were close to the Centauri, of course, it would blind you.
The reason that we can see the light from the
star is because that sun is so luminous. So a

(42:11):
message from a planet around Proximus Centauri would have to
be extraordinarily strong. We are not yet capable as the
species of generating a signal that strong if it's beamed
in all directions. For example, our most powerful radio telescope
until recently was Arecibo. Aricibo could detect a message from

(42:32):
a similar telescope to Aricibo if it was within one
light year, but of course there are no other stars
within one light year, and even the closest star is
four light years away, so we couldn't detect omnidirectional messages
sent in every direction from a technology similar to ours.
They would have to be beaming it to us, which
is totally possible. If you knew we were here, you

(42:54):
could send a message directly to us from that planet,
But they would somehow have to know we were here
and then send us a message, and that we could
definitely hear. If we detected somehow aliens existing on that planet,
we could definitely beam them a message that they would
be able to pick up. Now, remember that conversation would last,
you know, decades, because it takes five years almost just

(43:16):
for our message to arrive. Then they have to argue
about how to respond and then send us a reply,
so it's like ten years between responses, and you know
how we're going to figure out how to even talk
to them. It takes ten minutes even just to start
a Skype conversation these days, and make sure everybody can
hear you. Imagine how many back and force it takes
to establish like the basis for communication and learn each

(43:38):
other's languages and understand what a language even is and
do they use mathematics, and like, we would have a
lot to learn and taking ten years between questions and answers.
It would take a long time, but I hope that
it happens, and I look forward to one day listening
to that message from Proximus Centauri. Alright, so thank you
everybody for sending in your questions and for coming along
with us on this ride and curiosity and wondering about

(44:01):
the universe. I want to make sure your questions are answered.
That's right, I'm talking to you specifically. You've got a
question in there you haven't asked. Please send it to
us to questions at Daniel and Jorge dot com. I
promise you you'll get an answer. Thanks for listening, and

(44:24):
remember that Daniel and Jorge explained. The Universe is a
production of I Heart Radio or more podcast from my
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