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Episode Transcript
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Speaker 1 (00:08):
When you look up at the majesty of the night sky,
when you marvel at the intricate beauty of our microscopic,
quantum world, sometimes you just can't help but wonder where
does it all come from? Why does our universe exist
at all? Who or what is responsible for all of
this crazy, beautiful, bonkers universe. That's the biggest hope and
(00:32):
the biggest challenge for physics, not the small question of
why are we here, but the much bigger, deeper question
of why is there here at all? I Daniel, I'm
(01:00):
a particle physicist, and welcome to the podcast Daniel and
Jorge Explain the Universe, a production of I Heart Radio.
On this podcast, we talk about everything in the universe,
the stuff that's really big and vast and hard to understand,
and the stuff that's super small and tiny and mind boggling,
lee weird. We talk about all of it, and we
(01:22):
explain it to you in a way that we hope
actually makes sense and leaves you with the feeling that
you have grappled with a small piece of the world,
and one that you could import part of the universe
into your brain and you can make a little model
inside your head of what's going on out there in
the universe, and that it can work. It can help
(01:42):
you understand how the universe works, think about what it's doing,
and make predictions about what it might mean. The goal
of this podcast is not just for you to hear
a bunch of fancy science sounding words and come away
feeling like you were in the presence of science, but
to invite you to include you in the process of science,
because science is a human endeavor, is by the people
(02:05):
of the people, and for the people, and you are
the people. You're the people we are doing science for.
It's not just for a bunch of folks in white
lab coats and crazy hair. Is for everybody, because humanity
wonders about the universe, and humanity deserves answers about the universe.
And that's why humanity has decided to spend a non
trivial amount of money paying for science. And that's why
(02:28):
I think it's important that US scientists come back and
talk to people and explain to them what we have learned,
what it means, and connect back with that inherent curiosity that,
in the end, is what's responsible for driving this entire wonderful, crazy,
frustrating exhilarating project of unraveling the mysteries of the universe. Normally,
(02:51):
I'm joined by my co host, Orge, him a cartoonist
and roboticist, and we joke about bananas as he asks
me crazy questions. But he's not availed well today, so
I am taking the opportunity to catch up on questions
from you instead. That's right. Our loyal listeners often send
us questions things that they think about, that they are
(03:11):
wondering about. They have imported a little bit of the
universe into their minds and one piece of it doesn't
quite make sense. And so I encourage everybody out there
who has a question about the universe, something they are
wondering about, something they would like to hear understood, to
write to us. Send us your questions either on Twitter
at Daniel and Jorge or via email two questions at
(03:34):
Daniel and Jorge dot com. We right back to everybody.
We answer every email. You will get your question answered.
And sometimes the questions are interesting enough or fun enough
that I want to answer them here on the podcast
because I think other people might want to hear the
answers to these questions. I think that probably a lot
of people are wondering about those partaicular questions, and so
(03:57):
on today's episode will be answering listener questions. I love
all of our episodes, from the science fiction universe to
the extreme universe to the everyday physics, but maybe closest
to my heart are these questions that come from you,
from the listeners who are wondering about the world. Because,
(04:20):
as I said earlier, questions really are at the heart
of science. Science doesn't move forward without people, individual folks
asking questions about the universe and wanting to know the answer.
Think about that graduate student or that physicist or that
biologist out there devoting her life to answering one particular
question about the way microbes work, or about the way
(04:43):
rings form about a planet. It's because that person has
a deep curiosity about that one question and needs to
know the answer. So that's one of the joys of life,
is figuring out who you are and what you want
out of it, and what questions you want answered about
the universe. So please don't hesitate. Send me your questions.
I'd love to encourage them and to help give you
(05:04):
a few answers. And particularly I'd like to encourage our
listeners from Africa and from South America. We get questions
from all over the world, but I was looking at
the demographics recently and realizing that there's a group of
people out there who have been a little more silent
than the other folks. So if you're a listener in
Africa or in South America, please take my special encouragement
(05:26):
to write to us with your questions. We want to
hear from you and we want to help you understand
the universe. All right, so let's get to the first
listener question. This one comes to us from a very
young listener him names Megan. I'm nine years old. I
heard my damma the show, and I want to ask
you a couple of questions. So number one, how long
(05:48):
does it take to get to a black hole? At
number two, why are the stars round? Thank you for
answering my question by well, thank you Megan for sharing
your questions. I think she overheard her dad trying to
answer questions for future topics. So thanks very much Megan's
dad for letting Megan send in her questions and for
(06:10):
encouraging science and curiosity in the next generation. So Megan
asked us two questions. First, how long does it take
to get to a black hole and why our stars around. Well,
my first thought is like, why does Megan want to
go visit a black hole? And is that a good idea?
I mean, I certainly want to go visit a black hole.
(06:30):
I want to go see what's inside them and maybe
learn something deep about the nature of the universe and
help unravel the secrets of quantum gravity. But you know,
I'm not nine years old, and so I think it's
up to Megan's dad to decide whether or not he
should lend Megan the keys to the spaceship for this
particular field trip. So how long does it take to
get to a black hole? Say you wanted to get
(06:52):
into a spaceship and go to visit one. Well, you know,
there are two kinds of black holes out there in
the universe that we've discovered. There are the one at
the centers of galaxies, super massive black holes with masses
like millions of times the mass of our sun. Those
are spectacular and very interesting, but also really far away
and hugely dangerous because they are the centers of galaxies
(07:16):
where the radiation is intense and the X rays just
from the black holes. Creation disc itself would be really intense,
and then just the center of the galaxy is a
pretty crazy spot. So there is another kind of black
hole which I think would be much more reasonable to visit.
And these are stellar black holes, the ones that result
from a star aging and no longer having fusion pressure
(07:39):
to push back against gravity, trying to squeeze it down,
and eventually just giving up the ghost and becoming a
black hole. And so the one that's nearest to us
is actually only about eleven hundred and twenty light years
from the Sun. It's called q V telescopy if you
want to put that into your space navigation system. And
you might ask, how long does it take to get
(08:02):
to something that's eleven hundred light years away? Well, you know,
if you traveled at the speed of light, of course,
it would take eleven hundred years, which seems like a
really long time, and it is. But there's a bit
of a relativistic wrinkle we'll dig into there in a minute.
But we, of course can't travel at the speed of
light unless you develop some technology to like scan your
(08:22):
body and convert it into photons and beam yourself somewhere else.
But then you need some technology on the other side
to receive those photons and reconstruct your body. So a
more realistic way to go and visit a black hole
is to build a spaceship that's actually capable of such flight. Now,
there are two main limits to doing such a thing.
One is acceleration. To get up to that speed, you
(08:43):
have to speed up, and the human body has some
pretty tough limits on how fast we can accelerate. If
you try to accelerate more than five or ten GeSe,
your insides will get liquefied, and so for comfortable travel
over long periods, you really don't want acceleration much more
than one G. So let's do the calculation. Say you
had a spaceship that could accelerate at one G, you
(09:04):
would actually get up to pretty close to the speed
of light within just a couple of years, though most
of the trip would be spent pretty close to the
speed of light. So if you have to travel one thousand,
one hundred and twenty light years, it would only take
you one thousand, one hundred and twenty two years. Now,
the other problem with this scenario, of course, is the fuel.
(09:25):
To accelerate, you need fuel, and fuel makes your ship heavier,
which means you need more fuel to accelerate it. So
you have this rocket equation problem sometimes known as the
toothpick problem, because accelerating something even as small as a
toothpick up to very high velocities would require an enormous
quantity of fuel. And so, for example, if Megan's ship
(09:47):
was ten tons, which is really pretty small for a spaceship,
it would require something like thirteen million tons of fuel
for this kind of trip, and so basically the ship
would be all fuel, and most of that fuel is
there to help push the rest of the fuel. So
this is why we talk about things like black hole
power drives and other kinds of things. Of course, it
(10:08):
would be kind of silly to have a black hole
power drive to go visit a black hole. If you
have a black holed power drive, that means either you
can capture or make your own black holes anyway. But
the relativistic wrinkle is actually quite interesting because while from
Earth's point of view, it takes one thousand, one hundred
and twenty two years before you reach that black hole.
So that's like Megan's dad's clock. If he had a
(10:30):
telescope and he was keeping an eye on Megan during
her trip, he would see her clock running very slowly,
according to him, very very slowly, so that by the
time she reaches the black hole, she would only have
experienced thirteen points seven years, So she would only be
twenty two years old by the time she reached the
black hole. Now, of course, for everybody back on Earth,
(10:52):
more than a thousand years would have passed. And if
she actually wants to turn around and come back to Earth,
that's a whole other relativistic ring goal. When she turns around,
special relativity gets really complicated because that's another kind of acceleration,
and that gets us into the twin paradox, which we
can talk about another time on the podcast. So, Megan,
the answer is, it would take you more than a
(11:12):
thousand years to reach a black hole, but from your
point of view, it would only feel like about fourteen years.
So factor that into your decision about whether or not
to build your spaceship and go business black hole. But
if you go and you do discover secrets of the
universe and quantum gravity, please send me an email now.
Megan's second question was why are things around? Like why
(11:34):
are the stars round? Which is related to another really
interesting question, you know, like why our planets around. Why
is most of the stuff in the universe round? And
the answer is gravity. A little bit counterintuitive, but gravity,
even though it's the weakest force we know about, is
the dominant force when it comes to the structure of
(11:54):
astronomical stuff. The shape of the Earth, the shape of
the Sun, all this kind of stuff is round because
of gravity. And you can think about it pretty simply.
Gravity pull stuff down, right, So if you have the
Earth with anything sticking up on it, eventually that's going
to get knocked down, maybe wind or water, or even
if you don't have any atmosphere or water on the surface,
(12:15):
any kind of process eventually is going to settle into
a lower energy state. And for gravity, the simplest configuration,
the lowest energy state is a sphere. So anything that's
big enough to have its own gravity is eventually going
to be round. That's why small things are not necessarily round,
like asteroids and meteors are sometimes weird shaped because they
(12:36):
don't have the gravity to pull themselves together into a
round object. Whereas things as big as the Earth or
even the Moon, or definitely the Sun, gravity does its
thing and pulls anything that sticks out a little bit
down until eventually you get a sphere. But of course
not everything out there in the sky is a sphere, right,
I mean, our Solar System is not a sphere. It's
(12:57):
like a flat disc, and our galaxy is on a sphere.
It's also a flat disc. So why is it that
those things are not round? And that's because they have
something which can actually overcome gravity, and that's spin, that's rotation.
The Solar System is spinning. The Earth is spinning around
the Sun. That's why it doesn't fall in due to
(13:18):
the Sun's gravity, because it has enough velocity to stay
in orbit. And the same thing with the Sun. The
Sun is spinning around the center of the galaxy, which
is why the Sun and all the other stars don't
just fall into the black hole at the center of
the galaxy. And that's why black holes have an accretion
disk around them, because that rotation keeps stuff from falling in.
(13:41):
So you have a couple of forces here at play.
Mostly you have gravity dominating for things like the size
of the Moon and up to the Sun. But then
if things are spinning fast enough, they will turn into
a disk. Like if you took the Earth and you
spun it faster, it would turn into a disk. In fact,
the Earth itself is not exactly sound because it's spinning.
(14:02):
The distance from the surface to the center of the
Earth is actually greater at the equator because the Earth
is spinning, and if you spun the Earth even faster,
it would eventually turn into a pancake. And the same
with the Sun. So everything out there is balancing a
bunch of different forces. Mostly you don't see the effect
of electromagnetism or the weak nuclear force, or even the
(14:23):
strong force on the shapes of astronomical objects because they're
mostly balanced out. The Earth doesn't have an overall positive charge.
The Sun doesn't have an overall negative charge. If it did,
that force would be so strong, it's so much more
powerful than gravity that you would get these streams of
basically currents until things did get balanced out. But gravity
(14:43):
can't get balanced out. There is no opposite charge to gravity.
There's no negative mass that can create anti gravity to
balance out gravity. Gravity is always there, it always has
to be contended with, has to wait until everything else
gets sorted out and neutralized for it basically gets to
take the field and dominate. But eventually gravity takes over,
(15:04):
and that's why gravity is the dominant force for the universe,
and that's why the Sun and the Earth are around.
All right, Megan, thanks very much for those wonderful questions.
I want to get to some more or lessen our questions,
but first let's take a quick break. Hello, we are
(15:30):
back and this is Daniel and I'm answering questions from
listeners who want to understand the nature of the universe. So,
without further ado, here's our next question. Hello Daniel, So
what happened wondering for some time about anti matter stars?
We know matter is everywhere in the universe, and antimatter
(15:52):
just doesn't exist in quantities that are big enough for
anything like this. But if there was an ant I'm
at their star, or if there is, say one in
the whole universe, how could we tell it's an antime
matter star? How would it be different? It would shine
like a normal star or with it? Thank you? All right,
(16:15):
super fun question. I love this kind of question, like
how do we know what we know? Is it possible
for this weird, crazy scenario I've thought of in my
mind to be our reality? And that's a very important
kind of thought process, and that's basically what physicists are doing.
We're always wondering, all right, here's what we know. What
is that consistent with? Is there a way I could
(16:37):
imagine the universe to be different and still look the
same way. Are we being fooled by our preconceptions? So
it's this kind of creative, out of the box thinking
that's really vital in science. So let's dig into it first.
Let's just remind ourselves, like, what is anti matter? What
do we know about it? The existence of anti particles
is one of the most incredible and beautiful symmetries for me.
(17:00):
In the universe. Every particle that we know of, every fermion,
electrons and corks and neutrinos, and all of these particles
have a partner particle. There's like this symmetry where you
reflect all these particles and boom, they all have an
exact opposite. So the electron, for example, has the positron,
which is a positively charged version of the electron, and
(17:22):
the muan, which is naturally negatively charged, also has a
positively charged version. Each of the corks, like the upcork
and the down core, have an anti up and an
anti down. This is stuff that you hear about in
science fiction, but it's actually real. It's out there in
the universe. It's a kind of thing that can exist.
And when we do particle physics, we're often exploring two
(17:45):
different questions. One is can this stuff exists? Like what's
out there theoretically on Nature's menu, which if you made
the right conditions, could exist in the universe. And then like,
is there any of it? How do you actually make it?
And we created which is a totally separate question. But
antimatter is something that's in the universe, and frankly, we
(18:06):
don't know why. Why does every particle have this mirror
version of itself? Why does that exist? It tells us
something deep about the nature of the universe that every
particle seems to come in pairs. Maybe it means that
we shouldn't even think about the particles as in pairs.
Maybe the fundamental object is the pair, not the particle, right,
(18:27):
because if everything comes as part of a unit, then
maybe that unit is the thing that's part of the universe.
This is kind of the deep fundamental theoretical questions. You
could have been a lot of time smoking banana appeals
and thinking about and we do a lot of experiments
to try to understand antimatter. We make it at certain
but we can't make a whole lot. You have to
smash protons and do a big block of matter, and
(18:49):
some little bits of antimatter come out sometimes and we
can collect it and do experiments about it. And one
really interesting question we have about antimatter is is it
actually an exact copy? Is it really the same thing
as matter, but with the charges reversed, our anti electrons
really just the exact opposite of electron. And one way
(19:10):
to think about that, and this is I think the
direction of this question about antimatter stars is does antimatter
behave the same way as matters? Like can you make
big complicated things out of antimatter the same way you
can out of matter? And we've done these kinds of
experiments so far. We've made things like anti hydrogen, which
is an anti proton with an anti electron in orbit
(19:32):
around it, and we've studied and we've asked like, well,
does it look like hydrogen? Does it radiate energy the
same way? Does it follow the same physical laws? And
so far the experiment suggests that it does. We've never
detected any difference between the way antimatter works and the
way that matter works, So it seems like a perfect symmetry.
And yet there's a big mystery there because we know
(19:55):
it can't be a perfect symmetry. How do we know that, Well,
the universe is most be made of matter, right, I'm
made of matter, You're made of matter. The Sun is
made out of matter, The Solar System is made out
of matter. If matter and antimatter are basically symmetric, and
the universe treats them exactly the same way, why is
there more matter than there is antimatter? This is one
(20:18):
of the deepest questions in physics. We just don't know
the answer. You know, we imagine that when the universe
began that things were symmetric, because it's hard to imagine
anything else. If you imagine the universe started out with
more matter than antimatter, you're just sort of like presupposing
the answer to the question and introducing a new question.
If the answer to the question why does the universe
(20:40):
have more matter than antimatter is just well it started
that way, then you can just ask why did it
start that way? So it's more interesting to start from
the assumption that the universe began with equal amounts of
matter and antimatter. But now we don't have as much matter.
So what happened to it? Well, we know what happens
when matter and antimatter meet each other. They annihilate. What
(21:01):
does that mean? And from a particle physics point of view,
it's not magic. It just means that, like when an
electron meets a positron, they can turn into a photon.
They turn their matter into energy. Right, this is E
equals mc squared. Matter is really just a form of energy,
and so you can turn that matter into energy and
they can annihilate into a photon, or they can annihilate
(21:23):
into a z boson. Quarks can meet anti quarks and
turn into photons. They can also turn into gluons. So
all these kinds of matter can annihilate and turn into energy,
which can then do whatever energy wants to do. So,
if there was an equal amount of matter and antimatter
in the early universe, you would expect it would eventually
meet and annihilate itself, and we would have a universe
(21:45):
just filled with photons and gluons and z bosons and
stuff like that. But we don't. We still have matter
left over, and so people wonder, like, is there some
process in the universe which preferentially turns antimatter into matter,
so that we ended up with a little bit more matter,
and then the rest of an annihilated and we had
some leftover, which is just matter, which is what we are,
(22:08):
which is what created the entire universe that we are
living in. So that's the idea, but we've never explained that.
We don't have an understanding of how that happens. There
are a few processes and particle physics we found which
seemed to prefer creating matter to antimatter, and these things
are like CP violating processes and be in k masons.
And you can listen to our podcast episode about CP
(22:30):
violation if you want to hear more about that. But
these are not big enough to explain the asymmetry. The
account for a tiny fraction of the asymmetry. You need
a much more dramatic way to turn antimatter into matter
to explain the universe that we see. So we don't
understand it. And this suggests to us that there is
some asymmetry between matter and antimatter. There really is some
(22:52):
reason why the universe prefers matter to antimatter, and we
want to know what that is, right, We want to
know why, because that seems like a d truth about
the universe. But then there's another possibility, the other possibilities.
Hold on a second, and this is the question that
was asked ret least, how do we know there isn't
more antimatter out there? Are we just assuming that all
the stars out there are made of matter? What if
(23:14):
they were made out of antimatter? Right? The question is
wonderful because you're exactly right, and antimatter star would look
a lot like a matter of star. If antimatter can
do things like make anti hydrogen, then why can't anti
hydrogen anti fuse into anti helium. If it did, it
would produce photons just like the matter version of that process.
(23:37):
So mostly you're right that antimatter stars would look like
normal stars. And so when you're looking out in the sky,
it is possible that some of those stars might be
anti matter stars. But it's not exactly the same because
stars don't just produce photons. Obviously, they produce lots and
lots of photons. As you're out there sunning your face
(23:58):
on a nice winter morning, it doesn't really matter if
those photons came from a star or an antimatter star.
Because the photon is a boson, it doesn't have an
antimatter version of itself, and so it could come from
an antimatter star. But stars make other things too. You're
familiar with the solar wind, for example, the solar wind
is a stream of particles that come out of the
(24:20):
Sun when fusion happens. In the crazy chaos of a star,
you don't just make light. You make neutrinos, you make electrons,
you spew off protons, And so that solar wind can
tell us something about what kind of star it is,
because an antimatter star would make anti solar wind, right,
it would preferentially produce anti protons and positrons and anti
(24:44):
neutrinos and all sorts of other crazy stuff. All right,
but these stars are still really far away, right, how
would we know if those stars were making this antimatter
solar wind. Well, inside our solar system, we're pretty sure
everything's made of matter, right, don't think that one of
the planets is made out of antimatter. And then we
have two ways of figuring out whether other stars might
(25:06):
be made out of antimatter. One is just to look
at cosmic rays. Cosmic rays, some of them come from
the Sun, but a big proportion of them don't come
from the Sun. They come from the other stars in
our galaxy. And so this like galaxy solar wind, is
an accumulation of all the solar wind from other stars,
and that contains a lot of particles, and some of
(25:28):
them are antiparticles. Right, There are positrons and there are
anti protons in that wind. Cosmic rays sometimes are antiparticles,
but we don't think that comes from anti stars. We
have an explanation for how you can make antiparticles like
pretty simply photons sometimes split into positrons and electrons, and
so we have an idea and we can explain even
(25:50):
how to make anti protons in solar wind. So basically
the cosmic rays that we see here on Earth or
in our telescopes up in space are to totally consistent
with the stars in our galaxy being made out of
matter and not antimatter. If there was antimatter, then we
would see heavier stuff. We would see like anti iron
(26:11):
or anti uranium or anti oxygen stuff like that. We
see heavy versions of those elements in cosmic rays. It's
a tricky topic. We don't have precise measurements, but we
don't see any anti heavy elements in cosmic rays, so
we don't think that there are anti stars sort of
in our galaxy. Now cast your mind a little further, right,
(26:32):
How do we know that Andromeda, for example, isn't made
entirely out of anti stars? Are we measuring the solar
wind from that galaxy? That's a lot harder to do, though.
We do get particles from Andromeda, of course, but more generally,
we have another technique for figuring out if there are
like big antimatter patches to the rest of the universe,
(26:52):
and that's by thinking about where the matter and antimatter
patches might cross. Like if our galaxy was made of
matter and Andromeda was made of antimatter, then the antimatter
particles from Andromeda would be hitting the matter particles from
our galaxy somewhere in between. And what would happen while
they would annihilate and you would see this like surface
(27:13):
of that was creating photons and other kinds of particles
at a particular energy, because you'd expect, for example, when
an electron annihilates with a positron, it turns into a
photon that mostly has the energy of twice the mass
of the electron. So there's this characteristic flash of light
that happens when antimatter and matter annihilate, and we can
(27:35):
look to see sort of at the boundary between our
two galaxies if that's being created and we don't see it.
And this is a very powerful way to look deep
into the universe and see, like, are there surfaces, there
are their boundaries between matter and antimatter regions of the universe,
And so we haven't explored the entire universe this way.
We've looked out past our galaxy cluster in between other
(27:58):
galaxy clusters, and we've ever seen any evidence of like
massive annihilation of matter and antimatter into photons, which is
what you would expect to see again at one of
these sort of like boundaries between a matter region and
an antimatter region of the galaxy. So we haven't ever
detected that. Now, that doesn't mean we can rule it
out entirely in the entire universe, right there could be
(28:20):
a portion of the universe that's so distant that we
just can't probe it yet with these methods. Absolutely, we've
looked sort of like the ten megapars x scale. We
know that our large neighborhood doesn't have any significant antimatter
in it, that doesn't mean that there isn't antimatter in
the rest of the universe. So yes, absolutely, there could
be an antimatter galaxy out there somewhere super far away
(28:43):
and we just haven't seen it yet, or evidence of
its cosmic rays annihilating with a cosmic rays from a
matter galaxy. It's certainly possible, and that would be sort
of a beautiful explanation to this mystery of antimatter. If
it turns out that the universe actually is symmetric to
matter an antimatter, If there are matter patches of the
universe and anti matter patches of the universe, and that
(29:05):
they're in balance somehow, then of course you have to
wonder like, well, why did this become a matter patch
and why did that become an antimatter patch. But you
can imagine such things being answered by quantum mechanical randomness
and the formation of structure and all sorts of fun
stuff like that. But to meanwhile, we're digging into the
question of whether there are larger asymmetries between matter and antimatter. If,
(29:26):
as we suspect, the universe is mostly matter, then we're
trying to understand what that means, because we think that
that's going to tell us something about like why there
is matter at all, why we're not just living in
a universe filled with photons. So if it's true that
the universe is mostly matter, then we should be grateful
that there's an asymmetry, because that is in fact why
(29:47):
we are here. Alright, wonderful question. Thanks very much for
sending that in. I want to answer one more question,
but first let's take another break. Okay, we're back and
(30:08):
we're talking about the nature of the universe, symmetries and
black holes, and now we have a fun question from listeners.
That's maybe one of the deepest questions in physics and philosophy. Hi,
Daniel and Jorge. I know this often gets slumped into
the realm of philosophy, but is there a physics explanation
of why there is anything rather than nothing in the universe?
(30:31):
Why does any of this exist? What may have triggered
any of the matter, energy and forces we observe? Thanks
James Chronister, Thank you James for not being afraid to
ask the biggest and deepest questions and the questions that
overlap with philosophy. I don't think that's a negative thing
to be lumped in with philosophy. I think it's wonderful.
(30:51):
I think it means our questions are relevant. You know,
philosophy tells us what our questions mean and why they're interesting,
and why we want an answer to them and how
to think about them. And so I think that all
of the deepest questions in physics have philosophical implications. That's
why they're exciting. You know, if you knew exactly how
the universe was created, for example, from a physics point
(31:13):
of view, that would definitely have philosophical implications. So I
think the most fun questions in physics are the ones
that also get philosophers excited. And you're right, there's been
a lot of philosophical discussion back to the ancient Greeks
about why is there something rather than nothing? And it's
a really fun question to think about. And first I
think you should think about, like, what do we mean
(31:35):
by nothing? What is the opposite idea that we're considering.
On one hand, we have the universe and us and
there's definitely something here. What is the alternative that we're
wondering about. What is the thing that we're trying to
rule out? What is the nature of nothing? You know?
And let's knock down first some very simple ideas about
(31:55):
what nothing might be from a physics point of view.
It's not just like not having this stuff, not having
these stars and these galaxies and these particles, right, It's
something deeper. It's something about the possibility of things being
in the universe, about the nature of existence itself. It's
a pretty weird thing to consider, you know, a universe
with nothing or not a universe. You couldn't ever like
(32:18):
do an experiment to prove that nothing exists, because of
course your experiment is a thing, and so we can't
really prove it. And so that's why this is a
fun sort of philosophical question. But what I still think
that we can make progress on if we think about
what physics has told us about the nature of the
universe and the nature of nothing. By nothing, do we mean,
(32:39):
for example, just space, but with no matter in it,
like delete the stars, delete the galaxies, delete the planets,
delete all the stuff that's out there in the universe.
Is that what we would consider to be nothing. Well,
I think it's an interesting question, like why doesn't that
universe exist rather than ours? But I think the question
goes deeper, right because I think and that's question, you
(33:01):
will still ask, well, why is there space? Why is
there a universe for things to be in? Even if
there don't happen to be anything's in it right now,
that universe still has the possibility of things. And more specifically,
we know that physics tells us that even space is
not really empty a bowl. There's no such thing really
as empty space. If you somehow remove all the matter
(33:24):
in space and make as good a vacuum as you can,
then there's still a thing there, and that's space because
space has inside of it quantum fields, and those quantum
fields we know, are always buzzing with energy. Despite your
best effort to reduce the energy of that space, quantum
fields can't go down to zero energy. It's a fundamental
(33:47):
property of quantum fields that their lowest state is not
add zero energy. And in our universe at least there's
one field, the Higgs Boson field, which is totally rife
with energy. It's stuck. It's at this weird a minimum
that has a lot of energy in it, and so
there's a lot of energy and even what we think
about as empty space. And some people who think about
(34:08):
the nature of the universe and why is there something
rather than nothing take this as the answer. They say, well,
there has to be something because space is filled with
quantum fields, and those fields have energy and so boom,
therefore there has to be something. I don't really find
that answer to be satisfactory, because it really just suggests
another question, which is, you know, well, why do those
quantum fields even exist? And I like the way that
(34:31):
a philosopher David Albert put about it. He says, quote,
the fact that some arrangements of fields happen to correspond
to the existence of particles and some don't is not
a whit more mysterious than the fact that some of
the possible arrangements of my fingers happen to correspond to
the existence of a fist and some don't. Really, he's
saying that it's not really that interesting to think about
(34:51):
why are the fields sometimes making a planet and why
are the fields sometimes making empty space? The question really
is why are the fields right? Why do we have
fields at all? Why do we have space even that
has the possibility for fields. And this is the deep
question I think that physics should answer, and this is
sort of where physics is. We know that space is
(35:13):
out there, We know that every bit of space is
filled with quantum fields, and those quantum fields have energy.
And so from that starting point we can ask the question,
what does physics have to say about the nature of
nothing and why there is anything? Because remember, the goal
of physics is to try to grapple with the universe
to make sense of it. And I think an important
(35:35):
part of making sense of the universe is just understanding
why it exists. You know, we want to understand that
if the universe exists, it should be because it has
to exist or because it cannot not exist. The nature
of physics is to get the simplest possible explanation for
the universe as we see it. You know, we use
(35:55):
Acam's razor and we remove anything from our explanation that's
not necessary. We want to boil it down to the smallest,
simplest description. That doesn't mean we want to boil it
down to nothing, right, That's why I think about the
question in this way, is the simplest thing something or
is the simplest thing nothing. It might be that nothing
is sort of incoherent. You know, what do we even
(36:17):
mean by nothing? So from that point of view, if
we understood the simplest, deepest nature of the universe, we
might be able to point to it and say, oh, look,
this is the simplest possible thing. It's even simpler than nothing.
So that might be why the universe sort of has
to exist. So we're jumping ahead of us a little
bit and digging into the implications of the answer. But first,
(36:40):
let's talk a little bit more about what quantum physics
and general relativity tell us about the nature of space
and what that says about why it exists. So, of
course we have two different voices in this story. We
have the voice of quantum mechanics and the voice of
general relativity, which tell us two very different stories about
the nature of space and give us two very different
(37:02):
answers about why the universe should or shouldn't exist. So
let's start with quantum mechanics. Quantum mechanics treats space and
time very very differently. Quantum mechanics says space is the
place where quantum fields are. Every point in space is
just a place where quantum field has a value over here,
the electron field has one value. Over there, the electron
(37:23):
field has another value. That's all a quantum field is.
It's just a point in space with a value in it.
Sometimes that values a vector, Sometimes it's a number, sometimes
it's more complicated. Whatever, it's just a point in space.
But time is separate. Time is how those fields evolved.
And the most famous equation in quantum mechanics the Shortinger equation.
That's what that equation is about. It tells you if
(37:45):
you have a quantum wave function or graduate that to
a quantum field. It tells you how that changes with time.
And the most important thing about the Shorteninger equation is
that it says that quantum information is never lost. Like
a quantum wave function, changes as time goes on. Maybe
a photon spreads out, or maybe interact with the wall
or something happens, but the information is not lost. According
(38:08):
to quantum mechanics and the shorting Your equation, everything about
the past is encoded in the present. This means that
you can reconstruct what happened in the past just by
looking at the information about the arrangement of quantum particles
now and the really fascinating thing about this is that
it says that this works backwards and forwards. Right. The
shorting your equation can tell you how your wave functions
(38:31):
will change as the future goes on. It won't tell
you what the actual outcomes of experiments are, right. That
depends on this whole measurement problem that we're not going
to dig into today. But it tells you how the
probabilities evolved and how they have evolved in the past.
What that means is that quantum mechanics says the universe
should basically be eternal because quantum information can't be destroyed,
(38:53):
which means if it exists now, it always has to
exist and it can't have not existed in the past.
So from the wanting to you quantum mechanics, the universe
has to have always existed. There can't be a point
in the time line of the universe where it doesn't
exist if it does exist today. So it sort of
requires this like consistency as a function of time. Now,
(39:15):
the mystery is that general relativity tells us a different story. Right.
General relativity tells us that space and time are very
very closely connected. It prefers a tightly bundled space and
time where the two react together to the presence, for example,
of mass in the universe and general relativity is what
helps us understand the fact that the universe is expanding.
(39:37):
It's not just that we have a universe, and not
just like why is there something? Why is there every
year more of that something than there was before? Right,
the universe is expanding, it's growing, and when we think
about the nature of that space, right, it tells us
that space can be created. What's happening now between us
and other galaxies is the stretching of space, the creation
(40:00):
of new space. That means that space isn't eternal. It's
being made right now by some process that we do
not understand, and that tells us a different story about
the nature of space, this basic fundamental thing that we're
struggling to understand why it has to exist. Maybe it
doesn't have to exist because there's some process that can
(40:20):
make it, which means maybe the opposite is true as well.
And in fact, because we don't understand the mechanism of
this creation of space, is suggests that the mechanism might
be reversible. And there's still this possibility that dark energy
will stop and it will halt the accelerating expansion of
the universe and turn things around and bring it all
(40:40):
back and crunch it back together to make a new singularity,
the time symmetric version of the Big Bang right pulled
together down to a big crunch. And this would involve
not just the compactification of space, but the destruction of space,
the shrinking of distances between things, exactly the same way
that dark energy right now is expanding the distances between
(41:04):
things by creating new space. This would involve the compactification.
This would involve the destruction of space, the shrinking of
distances between things, not just moving things through space, but
actually destroying the space between them. That's pretty hard to
think about, but it gives you a clue about like
what's fundamental to the universe. Now. The problem is, we
(41:26):
don't really believe that either these theories are correct. We
look at general relativity and we look at the history
of the universe, and we say, it doesn't really make
sense for the universe to always have existed. The quantum
mechanical view that the universe can't have had a beginning
because the information in the wave function of the unverse
can't be destroyed doesn't seem quite right. It doesn't job
(41:47):
with our observation that the universe does seem to have
had a beginning, it seems to only have been fourteen
billion years old. On the other hand, if we retreat
to the corner of general relativity, we say some problems
with this theory also. First of all, it ignores the
obvious quantum mechanical nature of our universe. All of our
particle physics experiments and investigations in the last hundred of
(42:09):
years have revealed that the fabric of reality is quantum mechanical,
and general relativity ignores that. But more importantly, when we
look back at the very beginning of the universe and
try to understand, like, well, if the universe is being created,
what is the beginning of that process, general relativity leaves
us with a question mark. That singularity, the moment of
(42:29):
infinite density that begins our universe in the general relativistic story,
doesn't make any sense. Infinite curvature and infinite density is
not something we think is physically true. We don't think
it's a historical, actual accounting of events. It's a failure
of general relativities. When the theory breaks down and can
no longer give us a sensible answer. So what does
(42:51):
physics tell us about why there is something rather than nothing?
It tells us that we have a lot of work
to do before we understand what is the thing that
we are trying to explain. If we want to understand
why there is something rather than nothing, we need physics
to lead us closer to understanding what that thing is.
(43:11):
Because when we know what that thing is, that we
can ask interesting and fascinating questions about why it should
exist and what it would be like for it to
not exist. But we don't even know the fundamental nature
of the universe. We need that unification of quantum mechanics
and general relativity into some theory of quantum gravity so
that we can look at it. We can say, okay,
(43:31):
the basic element of the universe is a string. For example,
why do strings have to exist? Would it be simpler
to not have them? There are some people who think
really interesting and fascinating thoughts sort of about that future
without actually knowing what that future is. For example, one
of my favorite books is Our Mathematical Reality by Max
tad Mark, and he makes a fascinating argument which I
(43:53):
don't actually believe but I think it's super fun. He
says essentially that because our universe can be this scribed mathematically,
therefore it is a mathematical construct, and that's why it exists.
In his mind, you have to imagine, like every set
of mathematical laws that do hold together and make a
consistent universe, that universe exists because the mathematics works. I'm
(44:18):
not sure I can take that last step that every
mathematical self consistent universe that you can write down on
paper actually does exist out there. It seems like you
would have more really really simple universes than like vastly
complex universes like ours. And then you also have to imagine,
like what is the mathematical substrate on which all of
these like meta universes are running on. But it's a
(44:40):
really fun question, so I hope that answers your question.
Physics basically doesn't yet know what the thing is in something,
so we can't really answer the question why is there
something rather than nothing? Thank you everybody who sent in
all your super fun questions. Keep thinking deeply about the
nature of the universe and how quant particles work, and
(45:00):
please keep sending us your questions. They are the light
of our day. We will answer all of your emails,
trust me, or interact with us on Twitter if that's
what you prefer. So please keep thinking deeply about the
universe and keep asking questions. Tune in next time. Thanks
(45:23):
for listening, and remember that Daniel and Jorge explained The
Universe is a production of I Heart Radio. Or more
podcast from my heart Radio, visit the I heart Radio app,
Apple Podcasts, or wherever you listen to your favorite shows.
Ye
When you look up at the majesty of the night sky,
when you marvel at the intricate beauty of our microscopic,
quantum world, sometimes you just can't help but wonder where
does it all come from? Why does our universe exist
at all? Who or what is responsible for all of
this crazy, beautiful, bonkers universe. That's the biggest hope and
(00:32):
the biggest challenge for physics, not the small question of
why are we here, but the much bigger, deeper question
of why is there here at all? I Daniel, I'm
(01:00):
a particle physicist, and welcome to the podcast Daniel and
Jorge Explain the Universe, a production of I Heart Radio.
On this podcast, we talk about everything in the universe,
the stuff that's really big and vast and hard to understand,
and the stuff that's super small and tiny and mind boggling,
lee weird. We talk about all of it, and we
(01:22):
explain it to you in a way that we hope
actually makes sense and leaves you with the feeling that
you have grappled with a small piece of the world,
and one that you could import part of the universe
into your brain and you can make a little model
inside your head of what's going on out there in
the universe, and that it can work. It can help
(01:42):
you understand how the universe works, think about what it's doing,
and make predictions about what it might mean. The goal
of this podcast is not just for you to hear
a bunch of fancy science sounding words and come away
feeling like you were in the presence of science, but
to invite you to include you in the process of science,
because science is a human endeavor, is by the people
(02:05):
of the people, and for the people, and you are
the people. You're the people we are doing science for.
It's not just for a bunch of folks in white
lab coats and crazy hair. Is for everybody, because humanity
wonders about the universe, and humanity deserves answers about the universe.
And that's why humanity has decided to spend a non
trivial amount of money paying for science. And that's why
(02:28):
I think it's important that US scientists come back and
talk to people and explain to them what we have learned,
what it means, and connect back with that inherent curiosity that,
in the end, is what's responsible for driving this entire wonderful, crazy,
frustrating exhilarating project of unraveling the mysteries of the universe. Normally,
(02:51):
I'm joined by my co host, Orge, him a cartoonist
and roboticist, and we joke about bananas as he asks
me crazy questions. But he's not availed well today, so
I am taking the opportunity to catch up on questions
from you instead. That's right. Our loyal listeners often send
us questions things that they think about, that they are
(03:11):
wondering about. They have imported a little bit of the
universe into their minds and one piece of it doesn't
quite make sense. And so I encourage everybody out there
who has a question about the universe, something they are
wondering about, something they would like to hear understood, to
write to us. Send us your questions either on Twitter
at Daniel and Jorge or via email two questions at
(03:34):
Daniel and Jorge dot com. We right back to everybody.
We answer every email. You will get your question answered.
And sometimes the questions are interesting enough or fun enough
that I want to answer them here on the podcast
because I think other people might want to hear the
answers to these questions. I think that probably a lot
of people are wondering about those partaicular questions, and so
(03:57):
on today's episode will be answering listener questions. I love
all of our episodes, from the science fiction universe to
the extreme universe to the everyday physics, but maybe closest
to my heart are these questions that come from you,
from the listeners who are wondering about the world. Because,
(04:20):
as I said earlier, questions really are at the heart
of science. Science doesn't move forward without people, individual folks
asking questions about the universe and wanting to know the answer.
Think about that graduate student or that physicist or that
biologist out there devoting her life to answering one particular
question about the way microbes work, or about the way
(04:43):
rings form about a planet. It's because that person has
a deep curiosity about that one question and needs to
know the answer. So that's one of the joys of life,
is figuring out who you are and what you want
out of it, and what questions you want answered about
the universe. So please don't hesitate. Send me your questions.
I'd love to encourage them and to help give you
(05:04):
a few answers. And particularly I'd like to encourage our
listeners from Africa and from South America. We get questions
from all over the world, but I was looking at
the demographics recently and realizing that there's a group of
people out there who have been a little more silent
than the other folks. So if you're a listener in
Africa or in South America, please take my special encouragement
(05:26):
to write to us with your questions. We want to
hear from you and we want to help you understand
the universe. All right, so let's get to the first
listener question. This one comes to us from a very
young listener him names Megan. I'm nine years old. I
heard my damma the show, and I want to ask
you a couple of questions. So number one, how long
(05:48):
does it take to get to a black hole? At
number two, why are the stars round? Thank you for
answering my question by well, thank you Megan for sharing
your questions. I think she overheard her dad trying to
answer questions for future topics. So thanks very much Megan's
dad for letting Megan send in her questions and for
(06:10):
encouraging science and curiosity in the next generation. So Megan
asked us two questions. First, how long does it take
to get to a black hole and why our stars around. Well,
my first thought is like, why does Megan want to
go visit a black hole? And is that a good idea?
I mean, I certainly want to go visit a black hole.
(06:30):
I want to go see what's inside them and maybe
learn something deep about the nature of the universe and
help unravel the secrets of quantum gravity. But you know,
I'm not nine years old, and so I think it's
up to Megan's dad to decide whether or not he
should lend Megan the keys to the spaceship for this
particular field trip. So how long does it take to
get to a black hole? Say you wanted to get
(06:52):
into a spaceship and go to visit one. Well, you know,
there are two kinds of black holes out there in
the universe that we've discovered. There are the one at
the centers of galaxies, super massive black holes with masses
like millions of times the mass of our sun. Those
are spectacular and very interesting, but also really far away
and hugely dangerous because they are the centers of galaxies
(07:16):
where the radiation is intense and the X rays just
from the black holes. Creation disc itself would be really intense,
and then just the center of the galaxy is a
pretty crazy spot. So there is another kind of black
hole which I think would be much more reasonable to visit.
And these are stellar black holes, the ones that result
from a star aging and no longer having fusion pressure
(07:39):
to push back against gravity, trying to squeeze it down,
and eventually just giving up the ghost and becoming a
black hole. And so the one that's nearest to us
is actually only about eleven hundred and twenty light years
from the Sun. It's called q V telescopy if you
want to put that into your space navigation system. And
you might ask, how long does it take to get
(08:02):
to something that's eleven hundred light years away? Well, you know,
if you traveled at the speed of light, of course,
it would take eleven hundred years, which seems like a
really long time, and it is. But there's a bit
of a relativistic wrinkle we'll dig into there in a minute.
But we, of course can't travel at the speed of
light unless you develop some technology to like scan your
(08:22):
body and convert it into photons and beam yourself somewhere else.
But then you need some technology on the other side
to receive those photons and reconstruct your body. So a
more realistic way to go and visit a black hole
is to build a spaceship that's actually capable of such flight. Now,
there are two main limits to doing such a thing.
One is acceleration. To get up to that speed, you
(08:43):
have to speed up, and the human body has some
pretty tough limits on how fast we can accelerate. If
you try to accelerate more than five or ten GeSe,
your insides will get liquefied, and so for comfortable travel
over long periods, you really don't want acceleration much more
than one G. So let's do the calculation. Say you
had a spaceship that could accelerate at one G, you
(09:04):
would actually get up to pretty close to the speed
of light within just a couple of years, though most
of the trip would be spent pretty close to the
speed of light. So if you have to travel one thousand,
one hundred and twenty light years, it would only take
you one thousand, one hundred and twenty two years. Now,
the other problem with this scenario, of course, is the fuel.
(09:25):
To accelerate, you need fuel, and fuel makes your ship heavier,
which means you need more fuel to accelerate it. So
you have this rocket equation problem sometimes known as the
toothpick problem, because accelerating something even as small as a
toothpick up to very high velocities would require an enormous
quantity of fuel. And so, for example, if Megan's ship
(09:47):
was ten tons, which is really pretty small for a spaceship,
it would require something like thirteen million tons of fuel
for this kind of trip, and so basically the ship
would be all fuel, and most of that fuel is
there to help push the rest of the fuel. So
this is why we talk about things like black hole
power drives and other kinds of things. Of course, it
(10:08):
would be kind of silly to have a black hole
power drive to go visit a black hole. If you
have a black holed power drive, that means either you
can capture or make your own black holes anyway. But
the relativistic wrinkle is actually quite interesting because while from
Earth's point of view, it takes one thousand, one hundred
and twenty two years before you reach that black hole.
So that's like Megan's dad's clock. If he had a
(10:30):
telescope and he was keeping an eye on Megan during
her trip, he would see her clock running very slowly,
according to him, very very slowly, so that by the
time she reaches the black hole, she would only have
experienced thirteen points seven years, So she would only be
twenty two years old by the time she reached the
black hole. Now, of course, for everybody back on Earth,
(10:52):
more than a thousand years would have passed. And if
she actually wants to turn around and come back to Earth,
that's a whole other relativistic ring goal. When she turns around,
special relativity gets really complicated because that's another kind of acceleration,
and that gets us into the twin paradox, which we
can talk about another time on the podcast. So, Megan,
the answer is, it would take you more than a
(11:12):
thousand years to reach a black hole, but from your
point of view, it would only feel like about fourteen years.
So factor that into your decision about whether or not
to build your spaceship and go business black hole. But
if you go and you do discover secrets of the
universe and quantum gravity, please send me an email now.
Megan's second question was why are things around? Like why
(11:34):
are the stars round? Which is related to another really
interesting question, you know, like why our planets around. Why
is most of the stuff in the universe round? And
the answer is gravity. A little bit counterintuitive, but gravity,
even though it's the weakest force we know about, is
the dominant force when it comes to the structure of
(11:54):
astronomical stuff. The shape of the Earth, the shape of
the Sun, all this kind of stuff is round because
of gravity. And you can think about it pretty simply.
Gravity pull stuff down, right, So if you have the
Earth with anything sticking up on it, eventually that's going
to get knocked down, maybe wind or water, or even
if you don't have any atmosphere or water on the surface,
(12:15):
any kind of process eventually is going to settle into
a lower energy state. And for gravity, the simplest configuration,
the lowest energy state is a sphere. So anything that's
big enough to have its own gravity is eventually going
to be round. That's why small things are not necessarily round,
like asteroids and meteors are sometimes weird shaped because they
(12:36):
don't have the gravity to pull themselves together into a
round object. Whereas things as big as the Earth or
even the Moon, or definitely the Sun, gravity does its
thing and pulls anything that sticks out a little bit
down until eventually you get a sphere. But of course
not everything out there in the sky is a sphere, right,
I mean, our Solar System is not a sphere. It's
(12:57):
like a flat disc, and our galaxy is on a sphere.
It's also a flat disc. So why is it that
those things are not round? And that's because they have
something which can actually overcome gravity, and that's spin, that's rotation.
The Solar System is spinning. The Earth is spinning around
the Sun. That's why it doesn't fall in due to
(13:18):
the Sun's gravity, because it has enough velocity to stay
in orbit. And the same thing with the Sun. The
Sun is spinning around the center of the galaxy, which
is why the Sun and all the other stars don't
just fall into the black hole at the center of
the galaxy. And that's why black holes have an accretion
disk around them, because that rotation keeps stuff from falling in.
(13:41):
So you have a couple of forces here at play.
Mostly you have gravity dominating for things like the size
of the Moon and up to the Sun. But then
if things are spinning fast enough, they will turn into
a disk. Like if you took the Earth and you
spun it faster, it would turn into a disk. In fact,
the Earth itself is not exactly sound because it's spinning.
(14:02):
The distance from the surface to the center of the
Earth is actually greater at the equator because the Earth
is spinning, and if you spun the Earth even faster,
it would eventually turn into a pancake. And the same
with the Sun. So everything out there is balancing a
bunch of different forces. Mostly you don't see the effect
of electromagnetism or the weak nuclear force, or even the
(14:23):
strong force on the shapes of astronomical objects because they're
mostly balanced out. The Earth doesn't have an overall positive charge.
The Sun doesn't have an overall negative charge. If it did,
that force would be so strong, it's so much more
powerful than gravity that you would get these streams of
basically currents until things did get balanced out. But gravity
(14:43):
can't get balanced out. There is no opposite charge to gravity.
There's no negative mass that can create anti gravity to
balance out gravity. Gravity is always there, it always has
to be contended with, has to wait until everything else
gets sorted out and neutralized for it basically gets to
take the field and dominate. But eventually gravity takes over,
(15:04):
and that's why gravity is the dominant force for the universe,
and that's why the Sun and the Earth are around.
All right, Megan, thanks very much for those wonderful questions.
I want to get to some more or lessen our questions,
but first let's take a quick break. Hello, we are
(15:30):
back and this is Daniel and I'm answering questions from
listeners who want to understand the nature of the universe. So,
without further ado, here's our next question. Hello Daniel, So
what happened wondering for some time about anti matter stars?
We know matter is everywhere in the universe, and antimatter
(15:52):
just doesn't exist in quantities that are big enough for
anything like this. But if there was an ant I'm
at their star, or if there is, say one in
the whole universe, how could we tell it's an antime
matter star? How would it be different? It would shine
like a normal star or with it? Thank you? All right,
(16:15):
super fun question. I love this kind of question, like
how do we know what we know? Is it possible
for this weird, crazy scenario I've thought of in my
mind to be our reality? And that's a very important
kind of thought process, and that's basically what physicists are doing.
We're always wondering, all right, here's what we know. What
is that consistent with? Is there a way I could
(16:37):
imagine the universe to be different and still look the
same way. Are we being fooled by our preconceptions? So
it's this kind of creative, out of the box thinking
that's really vital in science. So let's dig into it first.
Let's just remind ourselves, like, what is anti matter? What
do we know about it? The existence of anti particles
is one of the most incredible and beautiful symmetries for me.
(17:00):
In the universe. Every particle that we know of, every fermion,
electrons and corks and neutrinos, and all of these particles
have a partner particle. There's like this symmetry where you
reflect all these particles and boom, they all have an
exact opposite. So the electron, for example, has the positron,
which is a positively charged version of the electron, and
(17:22):
the muan, which is naturally negatively charged, also has a
positively charged version. Each of the corks, like the upcork
and the down core, have an anti up and an
anti down. This is stuff that you hear about in
science fiction, but it's actually real. It's out there in
the universe. It's a kind of thing that can exist.
And when we do particle physics, we're often exploring two
(17:45):
different questions. One is can this stuff exists? Like what's
out there theoretically on Nature's menu, which if you made
the right conditions, could exist in the universe. And then like,
is there any of it? How do you actually make it?
And we created which is a totally separate question. But
antimatter is something that's in the universe, and frankly, we
(18:06):
don't know why. Why does every particle have this mirror
version of itself? Why does that exist? It tells us
something deep about the nature of the universe that every
particle seems to come in pairs. Maybe it means that
we shouldn't even think about the particles as in pairs.
Maybe the fundamental object is the pair, not the particle, right,
(18:27):
because if everything comes as part of a unit, then
maybe that unit is the thing that's part of the universe.
This is kind of the deep fundamental theoretical questions. You
could have been a lot of time smoking banana appeals
and thinking about and we do a lot of experiments
to try to understand antimatter. We make it at certain
but we can't make a whole lot. You have to
smash protons and do a big block of matter, and
(18:49):
some little bits of antimatter come out sometimes and we
can collect it and do experiments about it. And one
really interesting question we have about antimatter is is it
actually an exact copy? Is it really the same thing
as matter, but with the charges reversed, our anti electrons
really just the exact opposite of electron. And one way
(19:10):
to think about that, and this is I think the
direction of this question about antimatter stars is does antimatter
behave the same way as matters? Like can you make
big complicated things out of antimatter the same way you
can out of matter? And we've done these kinds of
experiments so far. We've made things like anti hydrogen, which
is an anti proton with an anti electron in orbit
(19:32):
around it, and we've studied and we've asked like, well,
does it look like hydrogen? Does it radiate energy the
same way? Does it follow the same physical laws? And
so far the experiment suggests that it does. We've never
detected any difference between the way antimatter works and the
way that matter works, So it seems like a perfect symmetry.
And yet there's a big mystery there because we know
(19:55):
it can't be a perfect symmetry. How do we know that, Well,
the universe is most be made of matter, right, I'm
made of matter, You're made of matter. The Sun is
made out of matter, The Solar System is made out
of matter. If matter and antimatter are basically symmetric, and
the universe treats them exactly the same way, why is
there more matter than there is antimatter? This is one
(20:18):
of the deepest questions in physics. We just don't know
the answer. You know, we imagine that when the universe
began that things were symmetric, because it's hard to imagine
anything else. If you imagine the universe started out with
more matter than antimatter, you're just sort of like presupposing
the answer to the question and introducing a new question.
If the answer to the question why does the universe
(20:40):
have more matter than antimatter is just well it started
that way, then you can just ask why did it
start that way? So it's more interesting to start from
the assumption that the universe began with equal amounts of
matter and antimatter. But now we don't have as much matter.
So what happened to it? Well, we know what happens
when matter and antimatter meet each other. They annihilate. What
(21:01):
does that mean? And from a particle physics point of view,
it's not magic. It just means that, like when an
electron meets a positron, they can turn into a photon.
They turn their matter into energy. Right, this is E
equals mc squared. Matter is really just a form of energy,
and so you can turn that matter into energy and
they can annihilate into a photon, or they can annihilate
(21:23):
into a z boson. Quarks can meet anti quarks and
turn into photons. They can also turn into gluons. So
all these kinds of matter can annihilate and turn into energy,
which can then do whatever energy wants to do. So,
if there was an equal amount of matter and antimatter
in the early universe, you would expect it would eventually
meet and annihilate itself, and we would have a universe
(21:45):
just filled with photons and gluons and z bosons and
stuff like that. But we don't. We still have matter
left over, and so people wonder, like, is there some
process in the universe which preferentially turns antimatter into matter,
so that we ended up with a little bit more matter,
and then the rest of an annihilated and we had
some leftover, which is just matter, which is what we are,
(22:08):
which is what created the entire universe that we are
living in. So that's the idea, but we've never explained that.
We don't have an understanding of how that happens. There
are a few processes and particle physics we found which
seemed to prefer creating matter to antimatter, and these things
are like CP violating processes and be in k masons.
And you can listen to our podcast episode about CP
(22:30):
violation if you want to hear more about that. But
these are not big enough to explain the asymmetry. The
account for a tiny fraction of the asymmetry. You need
a much more dramatic way to turn antimatter into matter
to explain the universe that we see. So we don't
understand it. And this suggests to us that there is
some asymmetry between matter and antimatter. There really is some
(22:52):
reason why the universe prefers matter to antimatter, and we
want to know what that is, right, We want to
know why, because that seems like a d truth about
the universe. But then there's another possibility, the other possibilities.
Hold on a second, and this is the question that
was asked ret least, how do we know there isn't
more antimatter out there? Are we just assuming that all
the stars out there are made of matter? What if
(23:14):
they were made out of antimatter? Right? The question is
wonderful because you're exactly right, and antimatter star would look
a lot like a matter of star. If antimatter can
do things like make anti hydrogen, then why can't anti
hydrogen anti fuse into anti helium. If it did, it
would produce photons just like the matter version of that process.
(23:37):
So mostly you're right that antimatter stars would look like
normal stars. And so when you're looking out in the sky,
it is possible that some of those stars might be
anti matter stars. But it's not exactly the same because
stars don't just produce photons. Obviously, they produce lots and
lots of photons. As you're out there sunning your face
(23:58):
on a nice winter morning, it doesn't really matter if
those photons came from a star or an antimatter star.
Because the photon is a boson, it doesn't have an
antimatter version of itself, and so it could come from
an antimatter star. But stars make other things too. You're
familiar with the solar wind, for example, the solar wind
is a stream of particles that come out of the
(24:20):
Sun when fusion happens. In the crazy chaos of a star,
you don't just make light. You make neutrinos, you make electrons,
you spew off protons, And so that solar wind can
tell us something about what kind of star it is,
because an antimatter star would make anti solar wind, right,
it would preferentially produce anti protons and positrons and anti
(24:44):
neutrinos and all sorts of other crazy stuff. All right,
but these stars are still really far away, right, how
would we know if those stars were making this antimatter
solar wind. Well, inside our solar system, we're pretty sure
everything's made of matter, right, don't think that one of
the planets is made out of antimatter. And then we
have two ways of figuring out whether other stars might
(25:06):
be made out of antimatter. One is just to look
at cosmic rays. Cosmic rays, some of them come from
the Sun, but a big proportion of them don't come
from the Sun. They come from the other stars in
our galaxy. And so this like galaxy solar wind, is
an accumulation of all the solar wind from other stars,
and that contains a lot of particles, and some of
(25:28):
them are antiparticles. Right, There are positrons and there are
anti protons in that wind. Cosmic rays sometimes are antiparticles,
but we don't think that comes from anti stars. We
have an explanation for how you can make antiparticles like
pretty simply photons sometimes split into positrons and electrons, and
so we have an idea and we can explain even
(25:50):
how to make anti protons in solar wind. So basically
the cosmic rays that we see here on Earth or
in our telescopes up in space are to totally consistent
with the stars in our galaxy being made out of
matter and not antimatter. If there was antimatter, then we
would see heavier stuff. We would see like anti iron
(26:11):
or anti uranium or anti oxygen stuff like that. We
see heavy versions of those elements in cosmic rays. It's
a tricky topic. We don't have precise measurements, but we
don't see any anti heavy elements in cosmic rays, so
we don't think that there are anti stars sort of
in our galaxy. Now cast your mind a little further, right,
(26:32):
How do we know that Andromeda, for example, isn't made
entirely out of anti stars? Are we measuring the solar
wind from that galaxy? That's a lot harder to do, though.
We do get particles from Andromeda, of course, but more generally,
we have another technique for figuring out if there are
like big antimatter patches to the rest of the universe,
(26:52):
and that's by thinking about where the matter and antimatter
patches might cross. Like if our galaxy was made of
matter and Andromeda was made of antimatter, then the antimatter
particles from Andromeda would be hitting the matter particles from
our galaxy somewhere in between. And what would happen while
they would annihilate and you would see this like surface
(27:13):
of that was creating photons and other kinds of particles
at a particular energy, because you'd expect, for example, when
an electron annihilates with a positron, it turns into a
photon that mostly has the energy of twice the mass
of the electron. So there's this characteristic flash of light
that happens when antimatter and matter annihilate, and we can
(27:35):
look to see sort of at the boundary between our
two galaxies if that's being created and we don't see it.
And this is a very powerful way to look deep
into the universe and see, like, are there surfaces, there
are their boundaries between matter and antimatter regions of the universe,
And so we haven't explored the entire universe this way.
We've looked out past our galaxy cluster in between other
(27:58):
galaxy clusters, and we've ever seen any evidence of like
massive annihilation of matter and antimatter into photons, which is
what you would expect to see again at one of
these sort of like boundaries between a matter region and
an antimatter region of the galaxy. So we haven't ever
detected that. Now, that doesn't mean we can rule it
out entirely in the entire universe, right there could be
(28:20):
a portion of the universe that's so distant that we
just can't probe it yet with these methods. Absolutely, we've
looked sort of like the ten megapars x scale. We
know that our large neighborhood doesn't have any significant antimatter
in it, that doesn't mean that there isn't antimatter in
the rest of the universe. So yes, absolutely, there could
be an antimatter galaxy out there somewhere super far away
(28:43):
and we just haven't seen it yet, or evidence of
its cosmic rays annihilating with a cosmic rays from a
matter galaxy. It's certainly possible, and that would be sort
of a beautiful explanation to this mystery of antimatter. If
it turns out that the universe actually is symmetric to
matter an antimatter, If there are matter patches of the
universe and anti matter patches of the universe, and that
(29:05):
they're in balance somehow, then of course you have to
wonder like, well, why did this become a matter patch
and why did that become an antimatter patch. But you
can imagine such things being answered by quantum mechanical randomness
and the formation of structure and all sorts of fun
stuff like that. But to meanwhile, we're digging into the
question of whether there are larger asymmetries between matter and antimatter. If,
(29:26):
as we suspect, the universe is mostly matter, then we're
trying to understand what that means, because we think that
that's going to tell us something about like why there
is matter at all, why we're not just living in
a universe filled with photons. So if it's true that
the universe is mostly matter, then we should be grateful
that there's an asymmetry, because that is in fact why
(29:47):
we are here. Alright, wonderful question. Thanks very much for
sending that in. I want to answer one more question,
but first let's take another break. Okay, we're back and
(30:08):
we're talking about the nature of the universe, symmetries and
black holes, and now we have a fun question from listeners.
That's maybe one of the deepest questions in physics and philosophy. Hi,
Daniel and Jorge. I know this often gets slumped into
the realm of philosophy, but is there a physics explanation
of why there is anything rather than nothing in the universe?
(30:31):
Why does any of this exist? What may have triggered
any of the matter, energy and forces we observe? Thanks
James Chronister, Thank you James for not being afraid to
ask the biggest and deepest questions and the questions that
overlap with philosophy. I don't think that's a negative thing
to be lumped in with philosophy. I think it's wonderful.
(30:51):
I think it means our questions are relevant. You know,
philosophy tells us what our questions mean and why they're interesting,
and why we want an answer to them and how
to think about them. And so I think that all
of the deepest questions in physics have philosophical implications. That's
why they're exciting. You know, if you knew exactly how
the universe was created, for example, from a physics point
(31:13):
of view, that would definitely have philosophical implications. So I
think the most fun questions in physics are the ones
that also get philosophers excited. And you're right, there's been
a lot of philosophical discussion back to the ancient Greeks
about why is there something rather than nothing? And it's
a really fun question to think about. And first I
think you should think about, like, what do we mean
(31:35):
by nothing? What is the opposite idea that we're considering.
On one hand, we have the universe and us and
there's definitely something here. What is the alternative that we're
wondering about. What is the thing that we're trying to
rule out? What is the nature of nothing? You know?
And let's knock down first some very simple ideas about
(31:55):
what nothing might be from a physics point of view.
It's not just like not having this stuff, not having
these stars and these galaxies and these particles, right, It's
something deeper. It's something about the possibility of things being
in the universe, about the nature of existence itself. It's
a pretty weird thing to consider, you know, a universe
with nothing or not a universe. You couldn't ever like
(32:18):
do an experiment to prove that nothing exists, because of
course your experiment is a thing, and so we can't
really prove it. And so that's why this is a
fun sort of philosophical question. But what I still think
that we can make progress on if we think about
what physics has told us about the nature of the
universe and the nature of nothing. By nothing, do we mean,
(32:39):
for example, just space, but with no matter in it,
like delete the stars, delete the galaxies, delete the planets,
delete all the stuff that's out there in the universe.
Is that what we would consider to be nothing. Well,
I think it's an interesting question, like why doesn't that
universe exist rather than ours? But I think the question
goes deeper, right because I think and that's question, you
(33:01):
will still ask, well, why is there space? Why is
there a universe for things to be in? Even if
there don't happen to be anything's in it right now,
that universe still has the possibility of things. And more specifically,
we know that physics tells us that even space is
not really empty a bowl. There's no such thing really
as empty space. If you somehow remove all the matter
(33:24):
in space and make as good a vacuum as you can,
then there's still a thing there, and that's space because
space has inside of it quantum fields, and those quantum
fields we know, are always buzzing with energy. Despite your
best effort to reduce the energy of that space, quantum
fields can't go down to zero energy. It's a fundamental
(33:47):
property of quantum fields that their lowest state is not
add zero energy. And in our universe at least there's
one field, the Higgs Boson field, which is totally rife
with energy. It's stuck. It's at this weird a minimum
that has a lot of energy in it, and so
there's a lot of energy and even what we think
about as empty space. And some people who think about
(34:08):
the nature of the universe and why is there something
rather than nothing take this as the answer. They say, well,
there has to be something because space is filled with
quantum fields, and those fields have energy and so boom,
therefore there has to be something. I don't really find
that answer to be satisfactory, because it really just suggests
another question, which is, you know, well, why do those
quantum fields even exist? And I like the way that
(34:31):
a philosopher David Albert put about it. He says, quote,
the fact that some arrangements of fields happen to correspond
to the existence of particles and some don't is not
a whit more mysterious than the fact that some of
the possible arrangements of my fingers happen to correspond to
the existence of a fist and some don't. Really, he's
saying that it's not really that interesting to think about
(34:51):
why are the fields sometimes making a planet and why
are the fields sometimes making empty space? The question really
is why are the fields right? Why do we have
fields at all? Why do we have space even that
has the possibility for fields. And this is the deep
question I think that physics should answer, and this is
sort of where physics is. We know that space is
(35:13):
out there, We know that every bit of space is
filled with quantum fields, and those quantum fields have energy.
And so from that starting point we can ask the question,
what does physics have to say about the nature of
nothing and why there is anything? Because remember, the goal
of physics is to try to grapple with the universe
to make sense of it. And I think an important
(35:35):
part of making sense of the universe is just understanding
why it exists. You know, we want to understand that
if the universe exists, it should be because it has
to exist or because it cannot not exist. The nature
of physics is to get the simplest possible explanation for
the universe as we see it. You know, we use
(35:55):
Acam's razor and we remove anything from our explanation that's
not necessary. We want to boil it down to the smallest,
simplest description. That doesn't mean we want to boil it
down to nothing, right, That's why I think about the
question in this way, is the simplest thing something or
is the simplest thing nothing. It might be that nothing
is sort of incoherent. You know, what do we even
(36:17):
mean by nothing? So from that point of view, if
we understood the simplest, deepest nature of the universe, we
might be able to point to it and say, oh, look,
this is the simplest possible thing. It's even simpler than nothing.
So that might be why the universe sort of has
to exist. So we're jumping ahead of us a little
bit and digging into the implications of the answer. But first,
(36:40):
let's talk a little bit more about what quantum physics
and general relativity tell us about the nature of space
and what that says about why it exists. So, of
course we have two different voices in this story. We
have the voice of quantum mechanics and the voice of
general relativity, which tell us two very different stories about
the nature of space and give us two very different
(37:02):
answers about why the universe should or shouldn't exist. So
let's start with quantum mechanics. Quantum mechanics treats space and
time very very differently. Quantum mechanics says space is the
place where quantum fields are. Every point in space is
just a place where quantum field has a value over here,
the electron field has one value. Over there, the electron
(37:23):
field has another value. That's all a quantum field is.
It's just a point in space with a value in it.
Sometimes that values a vector, Sometimes it's a number, sometimes
it's more complicated. Whatever, it's just a point in space.
But time is separate. Time is how those fields evolved.
And the most famous equation in quantum mechanics the Shortinger equation.
That's what that equation is about. It tells you if
(37:45):
you have a quantum wave function or graduate that to
a quantum field. It tells you how that changes with time.
And the most important thing about the Shorteninger equation is
that it says that quantum information is never lost. Like
a quantum wave function, changes as time goes on. Maybe
a photon spreads out, or maybe interact with the wall
or something happens, but the information is not lost. According
(38:08):
to quantum mechanics and the shorting Your equation, everything about
the past is encoded in the present. This means that
you can reconstruct what happened in the past just by
looking at the information about the arrangement of quantum particles
now and the really fascinating thing about this is that
it says that this works backwards and forwards. Right. The
shorting your equation can tell you how your wave functions
(38:31):
will change as the future goes on. It won't tell
you what the actual outcomes of experiments are, right. That
depends on this whole measurement problem that we're not going
to dig into today. But it tells you how the
probabilities evolved and how they have evolved in the past.
What that means is that quantum mechanics says the universe
should basically be eternal because quantum information can't be destroyed,
(38:53):
which means if it exists now, it always has to
exist and it can't have not existed in the past.
So from the wanting to you quantum mechanics, the universe
has to have always existed. There can't be a point
in the time line of the universe where it doesn't
exist if it does exist today. So it sort of
requires this like consistency as a function of time. Now,
(39:15):
the mystery is that general relativity tells us a different story. Right.
General relativity tells us that space and time are very
very closely connected. It prefers a tightly bundled space and
time where the two react together to the presence, for example,
of mass in the universe and general relativity is what
helps us understand the fact that the universe is expanding.
(39:37):
It's not just that we have a universe, and not
just like why is there something? Why is there every
year more of that something than there was before? Right,
the universe is expanding, it's growing, and when we think
about the nature of that space, right, it tells us
that space can be created. What's happening now between us
and other galaxies is the stretching of space, the creation
(40:00):
of new space. That means that space isn't eternal. It's
being made right now by some process that we do
not understand, and that tells us a different story about
the nature of space, this basic fundamental thing that we're
struggling to understand why it has to exist. Maybe it
doesn't have to exist because there's some process that can
(40:20):
make it, which means maybe the opposite is true as well.
And in fact, because we don't understand the mechanism of
this creation of space, is suggests that the mechanism might
be reversible. And there's still this possibility that dark energy
will stop and it will halt the accelerating expansion of
the universe and turn things around and bring it all
(40:40):
back and crunch it back together to make a new singularity,
the time symmetric version of the Big Bang right pulled
together down to a big crunch. And this would involve
not just the compactification of space, but the destruction of space,
the shrinking of distances between things, exactly the same way
that dark energy right now is expanding the distances between
(41:04):
things by creating new space. This would involve the compactification.
This would involve the destruction of space, the shrinking of
distances between things, not just moving things through space, but
actually destroying the space between them. That's pretty hard to
think about, but it gives you a clue about like
what's fundamental to the universe. Now. The problem is, we
(41:26):
don't really believe that either these theories are correct. We
look at general relativity and we look at the history
of the universe, and we say, it doesn't really make
sense for the universe to always have existed. The quantum
mechanical view that the universe can't have had a beginning
because the information in the wave function of the unverse
can't be destroyed doesn't seem quite right. It doesn't job
(41:47):
with our observation that the universe does seem to have
had a beginning, it seems to only have been fourteen
billion years old. On the other hand, if we retreat
to the corner of general relativity, we say some problems
with this theory also. First of all, it ignores the
obvious quantum mechanical nature of our universe. All of our
particle physics experiments and investigations in the last hundred of
(42:09):
years have revealed that the fabric of reality is quantum mechanical,
and general relativity ignores that. But more importantly, when we
look back at the very beginning of the universe and
try to understand, like, well, if the universe is being created,
what is the beginning of that process, general relativity leaves
us with a question mark. That singularity, the moment of
(42:29):
infinite density that begins our universe in the general relativistic story,
doesn't make any sense. Infinite curvature and infinite density is
not something we think is physically true. We don't think
it's a historical, actual accounting of events. It's a failure
of general relativities. When the theory breaks down and can
no longer give us a sensible answer. So what does
(42:51):
physics tell us about why there is something rather than nothing?
It tells us that we have a lot of work
to do before we understand what is the thing that
we are trying to explain. If we want to understand
why there is something rather than nothing, we need physics
to lead us closer to understanding what that thing is.
(43:11):
Because when we know what that thing is, that we
can ask interesting and fascinating questions about why it should
exist and what it would be like for it to
not exist. But we don't even know the fundamental nature
of the universe. We need that unification of quantum mechanics
and general relativity into some theory of quantum gravity so
that we can look at it. We can say, okay,
(43:31):
the basic element of the universe is a string. For example,
why do strings have to exist? Would it be simpler
to not have them? There are some people who think
really interesting and fascinating thoughts sort of about that future
without actually knowing what that future is. For example, one
of my favorite books is Our Mathematical Reality by Max
tad Mark, and he makes a fascinating argument which I
(43:53):
don't actually believe but I think it's super fun. He
says essentially that because our universe can be this scribed mathematically,
therefore it is a mathematical construct, and that's why it exists.
In his mind, you have to imagine, like every set
of mathematical laws that do hold together and make a
consistent universe, that universe exists because the mathematics works. I'm
(44:18):
not sure I can take that last step that every
mathematical self consistent universe that you can write down on
paper actually does exist out there. It seems like you
would have more really really simple universes than like vastly
complex universes like ours. And then you also have to imagine,
like what is the mathematical substrate on which all of
these like meta universes are running on. But it's a
(44:40):
really fun question, so I hope that answers your question.
Physics basically doesn't yet know what the thing is in something,
so we can't really answer the question why is there
something rather than nothing? Thank you everybody who sent in
all your super fun questions. Keep thinking deeply about the
nature of the universe and how quant particles work, and
(45:00):
please keep sending us your questions. They are the light
of our day. We will answer all of your emails,
trust me, or interact with us on Twitter if that's
what you prefer. So please keep thinking deeply about the
universe and keep asking questions. Tune in next time. Thanks
(45:23):
for listening, and remember that Daniel and Jorge explained The
Universe is a production of I Heart Radio. Or more
podcast from my heart Radio, visit the I heart Radio app,
Apple Podcasts, or wherever you listen to your favorite shows.
Ye
Hosts And Creators
Daniel Whiteson
Kelly Weinersmith
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