September 17, 2020 • 42 mins
Is there dark matter in black holes? Are gravitons and gravitational waves the same thing? Daniel and Jorge answer the most common listener questions!
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Speaker 1 (00:08):
Hey, Daniel, how's our email inbox looking these days? Is happening?
There are so many fun questions, and there's so many
people wondering about the mysteries of the universe. Well, do
you know if any patterns or trends or maybe frequently
asked questions? Oh for sure. Actually most of the questions
we get, our questions we have seen before. Yeah. Really
(00:28):
a lot of people have the same questions. Yeah, just
the same concepts tend to trip up a lot of people.
So if you still don't understand quantum mechanics or relativity,
you're not the only one. No, In fact, you're in
very good company because I'm still confused about it. May
you should submit it as a question to our podcast.
And who's going to answer it? Not me? I am
(01:06):
more handmade cartoonists and the creator of PhD Comics. Hi,
I'm Daniel. I'm a particle physicist and I've never stopped
asking questions about the universe. And welcome to our podcast,
Daniel and Jorge Explain the Universe, a production of I
Heart Radio in which we dive deep into your questions
about the universe and two scientists questions about the universe
into everybody's questions about the universe. How does it work?
(01:29):
What is it made of? Why does it work this
way and not that way? Why don't I have a
taco stand around my corner? Every deep and important question
about the universe handled on one podcast. Have you actually
checked all four corners? I do a scan every day
for taco chucks, and there's still not one on my corner.
You live in southern California and you have trouble finding
(01:49):
a taco truck. You need to get out more man. Yes,
that's definitely my problem. Yeah, we all have questions, and
it seems to be kind of a innate part of
human nature to be cure us about what's going on
around them and how things work. And fortunately the universe
is happy to provide mysteries and strange things for us
to ask questions about. Yeah, we're lucky that the universe
(02:11):
is both amazing, beautiful and mysterious. Yet it also seems
to be discoverable that we have this incredible technique for
divining knowledge from the universe by asking questions and then
answering them in a structured way. So we're fortunate to
be surrounded by amazing but accessible mystery yeah, especially you,
I guess, because you know the universe was simple and
(02:33):
easy to understand, we might be out of a job, Daniel,
that's right, especially if the whole field of physics lasted
like ten minutes of human history. They're like, let's knock
that off before lunch. We we've done it, we've done it.
Fire all the physicists put them to work somewhere else
doing Mataga trunk. You're right, there is a sort of
exquisite balance there. Physics was too easy, it'd be done
(02:54):
too soon. If it was too hard, nobody would give
us any money because we weren't making any progress. So
it's got to be just part of to be worth doing.
And so physicists, as part of their jobs, ask questions
about the universe, and they all have. They have all
kinds of amazing questions about how things work. And the
public also has a lot of questions. And sometimes those
questions are one and the same. That's right, and we
on this podcast do our best to answer those questions,
(03:17):
to dig deep, to explain them to you in a
way that makes sense. But sometimes our explanations inspire more questions.
We'll talk about a topic like black holes and then
we'll get five or ten very similar questions about some
little wrinkle that we didn't cover or something we said
that didn't quite make sense to a few people, and
so we thought it'd be fun to dig into some
of those emails and answer those questions and iron out
(03:38):
those wrinkles. So today on the podcast, we'll be tackling
our most common listener questions. That's right. We have a
series of episodes on this podcast where we talk about
the most unusual and interesting listener questions, the ones that
are sort of tricky and hard and require me to
do a bunch of research. But there's a whole other
(04:00):
category of questions that we want to share with you,
and these are the common questions, the one that a
lot of people are asking. And so today will be
asking most of a lot of the top questions that
we get through email, through Twitter, through Instagram. Daniel, do
you check Instagram? Do you know what Instagram is? Do
we have a TikTok account too? I don't use grams
because you know, I'm an American, and so I use
(04:23):
instat pounds good. That sounds like a bad diet to
go on. I don't recommend it. Actually, that's the name
of my taco truck is instat pounds, so we put
sour cream on everything. Maybe it's good that you don't
have a taco truck. Then maybe that's why I don't
have a talk. Yeah. So we're gonna be asking all
these questions, and they're all great questions, and they have
(04:44):
to do with the dark matter and black holes and
particles and all kinds of things, even philosophical questions and
questions about life and how to get involved in physics.
So we'll dive right in. Our first question comes from
Thomas and he us a question about is there a
dark matter inside of black holes? And what about neutrinos? Now,
(05:05):
because he asking if there's a dark matter inside of
neutrinos or is he asking the neutrinos inside of black hole?
I think he's asking if he can get a side
of neutrinos with his tacos. Everyone has a side of
neutrinos and the tacos, don't they. Yeah. I think that
this question is basically asking, like what kind of stuff
gets sucked into a black hole? Dark matter, which we
know is out there, this invisible kind of matter giving
(05:28):
gravity to the universe, even though we can't see it,
does that also get sucked into black holes? And that's
I think also why he's asking about neutrinos, Like neutrinos
feel hardly anything and have almost no mask, Did they
also get sucked into black holes? So I think that's
the origin of the questions. Are black holes sort of
universal sucker ruppers or do they only eat regular matter
(05:49):
like the kind that we're made out of. Yeah, And
the other angle of this question is, you know, what
are the structures of dark matter? If dark matter is
here in the universe, is it just big fluffy clouds,
or is it making like dark plant? It's dark stars,
dark black holes, and dark podcasts a right, So is
there dark matter inside a black holes? Daniel almost certainly. Yes.
Black holes are basically just very strong sources of gravity,
(06:11):
and they can suck in anything anything that has mass.
It doesn't matter if you are moving very fast or
if you're moving very slow, if you're low mass or
high mass. All forms of energy are trapped by black holes,
even if they have no other kinds of interactions. Right.
That's the thing that makes dark matter unique is that
we think it has no other kinds of interactions that
(06:32):
we're aware of. But you can still get sucked into
a black hole, right, Yeah, I guess the question is
it can only interact with gravity. I think we have
a podcast that covers that what would keep it inside
of the black hole. Couldn't it escape if it wasn't
being crunched down by other stuff. It's not being crunched
down by the other stuff, but it's gravity that's holding
things inside a black hole. Remember, these days, we don't
(06:53):
think about gravity as a force, so you shouldn't think
about it like tugging on this stuff and keeping it
in the black hole. We think of gravity as the
bending of the shape of space. Einstein told us that
this is some crazy relationship where matter bends space and
then space tells matter how to move because of its curvature.
And a black hole is this crazy intense bending of
(07:15):
space such that essentially becomes one directional inside a black hole,
you can only move towards the center. Space is one
directional inside a black hole, sort of the way time
is one directional outside a black hole. Time only moves
forward outside a black hole. Space only moves towards the
center inside a black hole. So it doesn't really matter
what you are if you have any mass or energy.
(07:36):
You are moving towards the center of the black hole
once you fall in, right, But then once it gets
to the center, wouldn't it come out the other end
Once it gets to the center, gravity is going to
keep holding it at the center, right, I mean, unless
there's like a wormhole at the center attached to a
white hole or something crazy. But if you follow general relativity,
and you know, we think general relativity is correct, although
we don't think it works inside a black hole. But
(07:58):
if you're assuming the general relativity inside a black hole,
then once you fall in, you're moving towards a singularity,
even if you're dark matter. Interesting. I guess if that's
the case, then wouldn't we expect most black holes to
be mostly dark matter? Since there's five times more dark
matter in the universe and regular matter. It's a great question.
We don't know what fraction of the stuff inside a
(08:19):
black hole came from dark matter. But remember that dark
matter is much more diffuse, it's much more spread out
through the universe. It doesn't clump as much as normal
matter because it doesn't have those other kinds of interactions
like dark matter. These big swirling clouds of stuff that's
surround our galaxy. But it's harder for dark matter to
make dense structures because to make dense structures you need
(08:40):
other kinds of interactions. You need other kind of interactions
to hold stuff together, like the electromagnetic forces a thing
that's holding you together, not gravity, and you need those
interactions to sort of radiate away energy and fall in.
Like the reason something doesn't just orbit a black hole
forever is that it loses some of its energy and
falls in. To do that, you have to be able
(09:01):
to like radiate off a photon or a z or something,
and dark matter just can't do that. So dark matter
is much more spread out. So we don't think that
dark matter is sort of the primary seed for black holes.
But some of it must have eventually fallen in, but
maybe not as much as you might think, because it's
it's kind of hard for it to fall in. Yeah, precisely.
And if you take, for example, the volume of our
(09:23):
solar system, the volume of our solar system is mostly
filled with normal matter. There's a lot of dark matter
in there, and there's more dark matter in the universe,
but in the vicinity of our Solar system, it's mostly
normal matter. So if our star went black hole, it
would suck in some of the dark matter that's nearby,
But most of the matter in our solar system is
normal matter. And what about neutrinos? Can neutrinos fall into
(09:46):
a black hole? I guess anything. I think what you're
saying is that black hole has been space and time,
so it's more like a space trap rather than just
a gravity trap. Yeah, exactly, it's a space trap. It
space is gravity. Gravity is space, and so you're exactly right,
And anything can fall into a black hole and nothing
can escape. So the answer to your question, can X
fall into a black hole? Is always yes? Or any X?
(10:09):
Can the letter X daniel as a concept of fall
inside of a black hole? Oh? Man, can philosophical ideas
fall into a black hole? Well? There is this crazy
theory that information has mass, and you know that's never
really been proven, but so perhaps, yeah, you come up
with a crazenough idea that your head becomes a black hole,
and you were thinking about the letter X, then yeah,
(10:30):
Well I believe we renamed black holes to space traps.
I feel like that's more accurate and more descriptive. All right,
well we'll start using that on the podcast from now
on and we'll see if it catches on your space trap.
All right, well, I think that answers the questions forms contraras.
Thank you for asking the question. Our next question is
(10:51):
about the universe small topic and whether it's stretching and expanding.
So Steve slopeck as, if the universe is stretching and expanding,
what's it expanding into? Now you said, this is another
common question we get. This is a question we get
like once a week. People are hearing about how the
universe is getting bigger, and they're wondering, like, if the
(11:13):
universe is everything, how can it be getting bigger. Doesn't
that mean it's sitting inside something else that's holding it
that it's now like filling up. I think people are imagining, like,
you know, a blob of molecules inside an empty room
spreading out to sort of fill out all those corners.
I have that question, and it's an amazing question. But
the answer is no, that the universe is not expanding
(11:35):
into anything, because the expansion is not like relative to
some outside external space or metric right, The expansion is intrinsic.
It means that distances between points are getting larger. So
we don't have our space, you know, our three dimensional
space sitting inside some other box. It's just stretching, it's
(11:56):
creating new space between existing points. Well, I feel like
what you're saying is that there's nothing outside of space.
But isn't nothing something? There isn't anything outside of space,
so I avoid saying the word nothing. What do you
mean What makes you uncomfortable about the word nothing? Well,
it depends what you mean by space. I mean the
origin of space was sort of like the backdrop on
(12:17):
which things happen, you know, you like define distances and
you could have empty space and then stuff in it.
Sort of the origin of the concept of space originally.
But now we know that space is not like that.
Space is dynamic. It's flexible. It can shimmer and wiggle
and stretch and grow and bend. Right, But you're tempted
to put it in some now static, larger space. Right,
(12:40):
there's nothing on which this like goo of space actually sits.
But we don't have any evidence that that exists. We
don't know that there's some other external, true deep meta
space in which our space exists. It seems like all
the math is consistent with just our space bending relative
to itself. But I guess the question is if we
(13:01):
can expand I think maybe what trips people up is like,
what are we expanding into? If we're expanding into something,
then you must be able to measure it, And so
wouldn't it be like empty space kind of right that
you can measure. I think the confusion there is expansion, right.
We're not expanding into anything, We're expanding relative to ourselves.
(13:22):
So if you have two points in space and you wait,
you will notice, thanks to dark energy and the expansion
of the universe, that they are getting further and further apart.
So you can that's how you measure it. You don't
step outside of the universe and be like, hey, the
universe is fourteen inches wide and last year was thirteen
Look how much it's grown. You measure the points between
(13:42):
things in space because that's all you can do. You
can't step outside of space. It doesn't even really mean anything.
Maybe the way to think about it is that the
space is not growing. It's almost like it's stayed the
same size, but we're shrinking inside of it. You know. Actually,
Dan Hooper, who we've had on the program, a cosmologist,
likes to make that point that you can't actually tell
the difference between the expansion of space and the shrinking
(14:05):
of stuff that looks exactly the same. There you go.
So maybe that will help people from reading confused, because
you know, sort of just think about it more like
we're the same, space is the same, but we're shrinking.
I mean that invites lots of other questions, like if
I eat so many tacos, how could I possibly be
shrinking because the tacas are shrinking. Yeah, that's a that's
(14:26):
another way to think about it. And you know, remember
that we don't understand why the universe is expanding. It's
not something that we understand and can make sense of.
We don't know why it's happening, why it started happening
five billion years ago, whether it will continue to happen.
All we have are these observations that distances between things
in space are expanding and expanding at an accelerating rate.
(14:47):
So it's something we observe, and you have to just
go back to the root experiment, like what is it
we actually see, rather than you're trying to get tangled
up in the various theories of cosmological constants. It's almost
like the opposite of what happens when you grow up.
Like I feel like when you're a kid, distances seemed huge,
like sitting in the car for an hour, it takes forever.
(15:07):
But when you grow up and you're an adult, distance
this kind of shrink no way, right, like sitting in
an hour for I think that tour doesn't seem long
enough actually, and so it's kind of the opposite of that.
It's almost like relationship that matter has to space is changing.
And that's what this does mean by its expansion of
the universe. You're staying in the universe is just growing
up an eventual it's gonna have a midlife crisis, not
(15:30):
going down. It's pulling Benjamin button. Do you think for
the universe, like now a billion years just like flits
by in a moment, whereas when it was a kid
it took forever. Yeah, kind of in a way, right, yeah, yeah,
maybe that that explains time dilation. Man, Man relativity is
just about getting mature. I'll take the Nobel price right now,
(15:51):
I'll buy you a taco Alright. We have a lot
more of these most common questions that we get through
the inbox, but first let's take a quick break. All right.
(16:14):
I know we're answering our most common questions that we
get through the inbox and through Twitter, and we've answered
questions about black holes and the universe expanding, and we
also have questions about particles, which is kind of your
field of expertise particles and tacos. Don't forget, I'm quite
(16:35):
an expert talca particle, tacas or taco particles. Let's talk
about it. Is that what a takito is? That's right,
that's when your tacos exchanged particles with your friends takings. Well,
that's not that's a no no these days, but that's right.
Stay safe out there people, all right. So our next
question is asking about the charge of particles. For example,
(16:59):
me Brown asked, I was wondering how particles could be
charged and what that even means? Exclamation point question mark.
Oh man, I love this question because I have this
same question and we still don't really know what particle
charge is. It's very confusing. Yeah, I like how she asked,
what does that even mean? It's wonderful because you know,
(17:20):
it's something where that's very familiar. People think about charge
and electric charge and familiar with lightning and whatever. But
down at the particle level, like what does it mean
for a particle to have electric charge? Like is it
carrying something? Is they're charge like stuffed into it somewhere.
Why does some of them have it some of them don't.
It's a great deep question, Yeah, because I guess she's
really wondering, like because it seems arbitrary, like a particle
(17:42):
has charged or it doesn't have charge, or it has
positive charge, or it has a color charge. You know
what determines that and why do they have it? And
the answer is that we don't know, and we have
to just sort of root ourselves and what we have seen.
Remember that all of these ideas about particle physics and
the universe they come out of experiments that we've done,
things we've seen, and that we're trying to describe about
(18:04):
the universe. We don't always understand what's going on, and
we're just sort of trying to build a structure that
let's it all hang together. And for particle charge, the
root thing that we see is that some little bits
of matter, some particles, are affected by electric fields and
magnetic fields. Like you put electrons through an electric field,
they will get accelerated. You put other particles, you know,
(18:26):
particles that don't have electric charge through an electric field,
they don't get accelerated. That's what it means to have
electric charge. That's the root thing. We've seen that some
particles are pulled by electric fields and some particles are not.
That's really what a charge means. So you're saying it's
part of a philosophical answer, like they have charged because
we've seen them. I have charged, or at least Daniel
has seen them. They have charged. Yeah, Well, we see
(18:48):
that some particles are affected by electric fields, and so
we say, all right, let's say that those particles are different,
and we'll create this idea of charge, and we'll use
that as a description to say which particles are affected
by elect fields and which ones are not. And then
we'll look for patterns, and we'll look for trends, and
we'll look for symmetries, and we'll try to understand that
more deeply. But fundamentally, it's just really a label for
(19:11):
the things we've observed. Now, I wonder if what she's
trying to get at is whether charge is a property
of particles or the field that make up the particles,
You know what I mean, Like Is it something that
gets a sign when the particle pops up, or is
it something that's just like a property of the field
that they're part of. Yeah, that's a great question. Mathematically,
(19:33):
we sort of put it in the middle, like we
think of particles, you know, as fields. Mathematically we think
of it's sort of in the middle, like we write
these things into our theories. And we said that the
charge is the thing that connects the field with the particle.
So for example, the photon field only interacts with things
that have electric charge, and so it's really right there
(19:56):
in between is how the two talk to each other.
It's the thing that lets them talk to each other,
the field and the particle. So it's sort of a
property of their interaction. Oh, I see, it's kind of
maybe a property of both, kind of what you're saying, Yeah, exactly.
And you know, we have noticed some amazing interesting things
about charge, like charge is conserved. You know, you can't
(20:18):
create it or destroy it. No matter how many particles
you create or destroy, the total charge is unchanged. And
that tells us that it must be something interesting and
fundamental to the universe, sort of like energy. We think
energy isn't changed in these interactions, and so that tells
us it might be something deep, that it's connected somehow
to something really deep about the universe and particles and fields.
(20:40):
But the truth is we don't exactly know what. Like
it could be a thing itself, you know what I mean,
Like it's like something that's being conserved. So it's kind
of like something that can be quantified in a way.
It can definitely can be quantified, yeah, absolutely, And you know,
there are other kinds of charge also, right, as you
mentioned earlier, Like the strong force has its own equivalent
of charge. We call it color to be confusing and
(21:02):
attempting to be poetic, and it has a lot of
similar properties to electric charge, and that some particles have it,
some particles don't. And there's one for the weak force.
Some particles have it, some particles don't. Whi's one of
the deep mysteries of physics is of why some particles
have some of these charges and don't have other charges.
It's very confusing, and what we're trying to do is
(21:22):
make a unified vision understand how this all shook out
and why it's this way and not the other way.
But the truth is, we just really don't know, it
sounds like it's almost like that the language of the
universe is this charge, you know. Yeah, like some particles
speak like romannitism, so some don't, and that's how they
interact with the fields around them and other particles. Yeah,
but why right, Why do some particles feel this and
(21:43):
others don't? How did that happen? And what does that
even mean? What does that even mean? Question mark? Exclamation point.
That's like the reason I got into physics because I
love asking that question what does that even mean? You know,
we want to gather together these weird experiments we've seen
and get some sort of deep understanding, appeal back a
layer of reality, and reveal the way the universe like
actually works. Man, you guys used exclamation points and question
(22:06):
marks at the same time in your physics papers, only
in the best ones. All right, thanks for that question.
Our next question is another common question that we get,
and this one in particular came from Roger Grenna, and
the question goes, how do particles which I understand, how
zero volume make up matter? So that stuff has volume.
(22:26):
That's a great question. If particles have no volume, how
can we have volume? If the recipe for making of
you is a bunch of particles and that each have
zero volume, then why isn't your volume just the sum
of a bunch of zeros which is zero? Right? Right? Yeah?
Or I guess maybe is my volume kind of an illusion?
Kind of like if if you drill down and there's
no real volume to any of my particles, does that
(22:49):
mean that I am also devoid of volume? I'll avoid
a lot of bad jokes there. But if I eat
a taco, Daniel, how does that effect my volume? Where
does that taco actually go? Well? And there's lots of
ways to attack this problem, and the most philosophicals to ask,
like what do you mean by volume? And we had
(23:11):
a whole podcast episode about like how small are particles?
What do we mean by their size? Etcetera, etcetera. But
that's a whole rabbit hole. Let's put that aside and
say particles are points. Let's assume for now the particles
actually have zero volume. Right, it's a good point. Yeah,
So to try to get to the point here, the
idea is that you can build something with non zero
(23:32):
volume out of particles that have zero volume if you
have a way to space them. There's something keeping them
from overlapping from crunching on top of each other, and
you do, and they have forces. They have electric forces,
for example, And so the reason that, like when you
build a molecule, the atoms don't just lie on top
of each other is that there are electrons circling those
(23:54):
atoms that keep the nuclei apart, and the nuclei are
positively charged and they keep each other apart. So there
are forces there that creates sort of like a spacing,
like a lattice that keeps everything from collapsing into the
tiniest dunk. I guess that, yeah, you're ready. It does
depend on what you mean by volume, because if by
volume mean like when something is there and it's not there,
(24:15):
then particles almost have zero volume. But they're also kind
of infinite volume, right because you can feel a particle
all the way across the galaxy. Technically, yeah, yeah, technically,
And so you could also say that if you're made
of zero volume particles, even if they have spacing between them,
then your real volume is still just the sum of
all those zeros, even though they're distributed into sort of
(24:36):
a cloud. And you guy, it's like, well, where do
you stop if you're made of a bunch of particles
that are spaced apart, where do you stop. Do you
stop at the edge of the most like right most particle,
or where it pushes back, as you were saying, like
where it feels something and and where it pushes back.
Is also not very satisfying because then it depends on
what you're pushing with or against, yeah, or against. If
(24:58):
you push against dark matter, matter will pass right through
you like you're not there. If you push against neutrinos,
it will very lightly touch you. If you push against
you know, a regular object like a stick, then you're
pushing against the electromagnetic forces. So it depends on the
kind of thing you're probing with. So it's not really
very well defined. But if you just say, like, hey,
you can make a cloud out of non zero particles
(25:21):
that keep their spacing because of the forces between them,
then you get a pretty good sense for why you
aren't just a tiny dot. Yeah, I guess maybe, like
if you go by effect and technically we all have
infinite volume, like you know, if someone across the universe
feels me in a way and feels the forces that
like particles exert. But if you talk, if you call volume,
(25:43):
like where are the particles center that make up rhead?
Then because I have more than one, then you can
sort of define a range of space like a volume
of space, and that's maybe that's volume. Yeah, and so
it's a slippery topic volume, you know. Microscopically, it does
really have a great analog to the way we think
about it, like intuitively and macroscopically. And this is something
(26:05):
we struggle with all the time when we take our
common knowledge about how things work mass, volume, velocity, you know, time,
and we try to apply them to the microscopic where
the rules are really just totally different, and sometimes the
very ideas break down and don't really have a great analog.
All right, mind bending question. All right. Our next question
from our most common question pile is a bit of
(26:28):
a career question, and I'm curious that's why you get
this a lot. So the question goes, I've always loved
physics but studied something else. Is it too late for
me to learn physics for real? I'd like to for real.
At the end, we do get this question a lot,
and I think that that's because our podcast has attractive
(26:48):
folks who are really interested in questions of the universe.
And have a passion for understanding these things, but because
of whatever happened to them in life, didn't end up
studying physics. They studied computers or ended up in something
else in their life. And maybe this has reignited their
interest a little bit, and they're wondering, like, is the
door closed? Is there still a path for me to
like go back to school and get a degree in
(27:09):
physics and actually do physics for real? Yeah? And the
answer is no, Right, anyone can study physics even for real. Yeah,
it's never too late, And it depends on your life
and your personal situation, of course, and whether you have
the time available in the financial means to go back
to school. But there are lots of paths back into physics.
(27:30):
And something I think that a lot of people don't
understand is that you don't need like a formal physics
undergraduate degree from a fancy university to get back into physics.
I can tell the story of somebody here in Irvine
who was always interested in physics but ended up in
computers and working in software for fifteen years and then
came to me one day to my office and said, look,
(27:52):
I want to get back into physics. What can I do,
And he just ended up taking a bunch of classes
at u C I not as an enrolled student, just
like taking classes, which you can do at most universities
without getting into it like a degree program. You don't
need to apply to become a freshman. You just take
the classes you need. Then you can apply to graduate
schools and you can say, look, I've done these courses,
(28:13):
I've got reasonable grades in them. And that student, for example,
he's now a grad student at an Ivy League university
in physics. And so it's totally possible. If you have
the interest and you can do it in your spare
time and sort of build up the basic knowledge you need,
then you can jump right back in and the doors
can still be open. Yeah, you can still be like
(28:33):
a physicist at any point in your life. I mean,
people change careers all the time, And I mean I
know this one guy who was an engineer but then
he turned into a cartoonist. It sounds crazy, but you
can change careers. I heard he's now running a taco Chuck.
Isn't that true? Unfortunately it doesn't have a happy ending.
(28:54):
It's actually worse. He's doing a podcast. But the other
side to This is that you don't need to be
an official physicist with a hat p to ask interesting
questions about the universe and to think about it and
even to make progress. You know, there are lots of
people out there who have figured this stuff out on
their own, and physics is not owned by physics professors.
It belongs to everybody. Wondering and curiosity about the universe
(29:16):
belongs to everybody. So even if you aren't in a
situation in your life where you can't go back to
grad school in physics, you can still enjoy wondering about
the universe and learning about physics. Al Right, we have
a couple of more questions here from our most commonly
Asked Questions pile, and we'll get into them. They're about
black holes and gravitational waves. But first let's take another
(29:37):
quick break. All right, Daniel, we are going down our
list of most commonly asked questions to the podcast, and
our next question has to do with black holes. Question
(29:59):
goes do black holes move? And does this moving black
hole leave any trail quote unquote trail a stretched space?
And this is a question from a six year old
in particular. That's right, are you saying that a lot
of six year olds asked this question, or does this
six year old ask one of our most common questions. Yeah,
this six year old put his finger on a question
(30:22):
that we get a lot, which is, you know our
black holes sitting around or are they moving? And did
they leave with some sort of like wake in space
as they move the way like a boat leaves awake
in the lake. But I love that this question came
from a six year old thinking about black hole. So
congrats to is Sean and to his parents for encouraging
(30:42):
wonder and curiosity about the universe. Yes, so I guess
the question is, first of all, can black holes move
or are they so massive and monumental that they're basically
static in space? It's a great question, and we have
to remember, first of all that motion and position is
always relative, right, so there's no like absolute motion. You
can't ask is a black hole moving without saying what
(31:04):
is it moving relative to? The other side of that
is that black holes follow the same rules as everything else,
Stars and planets and galaxies, right, They all can move
through space or relative to each other, just like black holes.
And sometimes you'll see two black holes that are bound
to each other and orbiting each other. So yes, they
definitely can move through space just like everything else. Yeah,
(31:26):
and they can. I mean they basically add like any
other object in space to the things around them, right, Like,
you can have a black hole orbiting our solar system
for example. Yeah, you can't tell the difference gravitationally between
a black hole and another object of the same mass.
If you're at the same distance between those two, you
just can't tell the difference. They have the same gravitational effect.
(31:48):
So yeah, we could orbit a black hole the way
we orbit the Sun. We could have a tiny black
hole as part of our solar system that we wouldn't
even have noticed. In fact, there are those folks that
wonder about Planet nine whether it's a primordial hole that's
somehow stuck out there in the depth of our solar system.
So black holes can move through space, and you know,
there's even the possibility of black hole could move through
(32:09):
space and come disrupt our solar system. We did a
whole podcast episode about that. So yeah, they're not like
nailed in place there. They can move just like everything right. Yeah.
I wonder if what trips people up is that people
often talk about black holes or should I say, space
traps as being kind of these like holes punctured in
spacetime itself, or like these bubbles of space time. And
(32:33):
so maybe it's hard to think about it moving around
because it's I mean, when you punch a hole through
a piece of paper, it doesn't you can't move it.
That's a good point, but remember that's true for everything.
All kinds of matter change the shape of space, they
change the curvature they bend space, and where that is
just depends on your frame of reference, and whether it's
(32:53):
moving depends on whether you're moving. So if you can
move past a black hole, then a black hole can
move past you. There's no like absolute frame in which
these black holes are anchored. All right, Well, I guess
then the answer is yes, they can move. Space traps
can move, And so if you're out there in space,
watch out like you should look both ways before crossing
(33:14):
the Solar System lane. That's right. And the other part
of his question was whether or not they like leave
any trail behind them, and he like wake through space.
And we said earlier that the location of a black
hole and its velocity depends just on its frame of reference,
Like are you moving with respect to it. If so,
then it has velocity. But if a black hole is accelerating,
(33:35):
if it's changing its velocity, then it absolutely will leave
a wake through space the way a boat will when
it moves through a lake, and those weeks are called
gravitational waves. They will make these ripples in space. It's
like the change in velocity of something that is what
generates a gravitational wave. Yeah, exactly, because these frames of
(33:56):
reference are called inertial frames of reference, and you can't
tell the difference mean any of them as long as
they have no relative acceleration. But as soon as something
has an acceleration is changing its velocity, then it leaves
a signal through space. And those signals are these gravitational waves.
And that's what we've detected. In those underground detectors where
they have the long laser beams to measure the stretching
(34:17):
of space itself, they see two black holes, for example,
orbiting each other and leaving all these ripples in space,
which leads us to our next question. Speaking of gravitational waves,
another common question we get is our gravitational waves the
same as a graviton, meaning is a graviton a gravitational
wave or Can a gravitational wave be a graviton or
(34:40):
can just have a wave without a graviton. It's a
great question, and it's very natural because people think about
like electromagnetic waves, you know, they think about light, and
they know that light is made out of photons, these
little quantized units of electromagnetic radiation, and so it's very
natural to think about well, for gravity, if you have
gravitational waves, you know, is at the same thing as
(35:00):
a graviton, this whole particle wave duality. And the answer
is no. And the reason basically is that gravitational waves
are really really big. They're huge effects in gravity, and
gravitons if they exist, we expect them to be really
really really small. So a gravitational wave might be made
out of like zillions and zillions of gravitons the way,
(35:22):
for example, like a beam of light is made out
of lots and lots of photons, So they're not the
same thing. There are different scales and also gravitational waves,
and we know they exist. Gravitons still totally theoretic, right,
we don't know if they're actually real because we don't
know if gravity is quantum, that's right, The only theory
we have of gravity is this classical theory that says
(35:43):
that gravity is smooth and continuous. It's not like chopped
up into little units like everything else is. Like electromagnetic
waves are made out of little units we call photons.
You can't have an arbitrarily small size of them. They
come in discrete bits. And we don't know that about gravity.
We think probably it is because everything else is, but
we don't actually know that. We don't have a theory
(36:03):
for it. So the graviton is the particle you would
invent if you did have a theory of gravity. But
we know the gravitational waves are real. So those things
are out there, we've seen them. We don't know if
they're made out of tiny little gravitons. Right, it's kind
of like a water I guess, you know, like a
a wave in water. That's not the same as a
molecule of water. Yeah, we'd love to discover those water molecules.
(36:26):
We'd love to figure out if gravity is quantum and
if it's made out of gravitons. But we haven't seen
those yet. And it's really hard because even the gravitational
waves are hard to spot because gravity is really, really
weak compared to all the other forces. It's like billions
and trillions times weaker, which means it's very hard to
see it effects. And so to see a graviton would
(36:46):
be to see a even tinier little bit of gravity.
We're just not nearly sensitive enough, all right, So I
guess the answer is a gravitational wave is a gravity nut,
not necessarily graviton. All right. Then I think we have
time for one more of our most commonly asked question pile,
and I'm going to pick this one here, which says,
(37:06):
if he equals mc squared and a photon is massless,
then how does a photon have any energy? How can
a photon have energy if it's massless? Yeah, this is
a great question, and I love that people are doing
this thinking they're like, I have this one idea and
this other idea. Can I bring them together? Does this
make sense? And that's physics, right, that's doing physics. It's
(37:26):
saying I have this rule, where does it apply? Let
me check make sure that it applies everywhere I understand it.
And so it's great. Kudos to everybody who thinks about
this and to ask this question. This one came from
James Chad. And so the answer is that the formula
equals m C squared. It is not false, it's true,
but it's not the most general formula. It's only talking
(37:47):
about the energy that you get from mass. And there
are lots of forms of energy, right, there's energy and
mass is also energy of motion. Right, there's energy of rotation,
the energy of vibration. These are are other forms of energy, right,
But don't they all get lumped at the same energy
at the end, right, Like if I have a slow
moving particle and a fast moving particle, then the fast
(38:10):
moving particle has more energy and can transform into you know,
heavier particles. Yes, that's true. And so the most general
expression for energy is not E equals mc squared. That's
the expression you would use for a particle that's essentially
not moving. There's a more general expression that says E
equals mc squared plus momentum times the speed of light
(38:31):
P time c. So there's another term there. And so
for a photon, mass is zero. It doesn't have any
of this rest mass that the other particles have, but
it does have momentum. Photons are essentially are pure momentum.
There the wiggle of the electromagnetic field. There are pure motion,
there's no mass to them. But wait, it doesn't momentum
(38:52):
imply mass like it. Remember an engineering, when you study momentum,
it's M times V, so mass times velocity. That's the
non relativistic expression for momentum M times v. In relativity
we have a more general expression for momentum, and we
can dive deeper into that rabbit hole. But now you
do not have to have mass to have momentum, and
(39:12):
photons we know have momentum. We talked about for example,
solar sales. Photons themselves from the Sun can push on something.
When they bounce off of it, they transfer their momentum
to the solar sale. So we know physically empirically the
photons definitely do have momentum and they are essentially pure momentum.
And so equals mc squared is the best known formula,
(39:33):
but it's not the most general case, and imparticle physics,
we use equals mc squared plus pc and so for
the photon m equal zero and the energy is just
momentum times the speed of light p time c. So
it does have energy. Photons have energy, it just doesn't
come from it having mass. It just comes from its motion.
That's right. There are other ways to have energy, and
(39:53):
that's what photons do, and they're weird because they have
exactly zero mass. And it's more general. Formula applies to
me in you too, Like my energy is both how
much I wait, but also how much a movie? Yeah, exactly,
you have more energy if you're in motion then when
you're sitting on your couch. Who all right, Well, those
are some of our most common questions, Daniel. What do
(40:16):
you sort of make of all these questions? I make
that we have smart listeners, then that we have people
out there that are intrigued by the way the universe works,
and that this stuff is complicated, and that if you
try to download it into your brain and play around
with it, you'll find little rough edges that you don't
quite understand, or little bits that don't quite click together,
and that that's not unusual, and that there are a
(40:38):
lot of other people out there wondering about those same
tricky bits. So I hope that these answers have helped
a lot of people collect those pieces together, and if not,
feel free to write into us. We would love to
help you resolve little questions you have about your understanding
about the universe. Yeah, and in some cases I feel
like your answer was we don't know, which means that
these are questions that physicists are also asking themselves at
(41:01):
the forefront of science. Yeah. Basically, at the end of
every question, you could add and what does that even mean?
Exclamation point question mark? And we'll add a few more
question marks there at the end. Two. That should be
the alt title for our podcast exclamation point question mark
or maybe our next book, Daniel, what does that even mean?
(41:21):
Exclamation point question mark? To which the answer is the
title of our first book. We have no idea. It's
a recursive book. Really, that's right. Book three. Let's just
go get tacos. Go go back and read our first
book while eating some tacos and increasing your volume. That's
all right. Well, we hope you enjoyed that and maybe
(41:41):
connected a little bit more with people out there, because
we all have a lot of the same questions about
the universe and don't be shy about writing to us,
were engaging with us on Twitter at Daniel and Jorge
or sending us email to questions at Daniel and Jorge
dot com. We love your listener questions and we answer
all of our email. Yeah, and don't be shy but
ask questions and pursuing knowledge and even maybe getting a
(42:03):
physics degree late in life. Thanks for joining us, see
you next time. Thanks for listening, and remember that Daniel
and Jorge explained The Universe is a production of I
Heart Radio. For more podcast from my heart Radio, visit
(42:24):
the I Heart Radio Apple Apple Podcasts, or wherever you
listen to your favorite shows.
Hey, Daniel, how's our email inbox looking these days? Is happening?
There are so many fun questions, and there's so many
people wondering about the mysteries of the universe. Well, do
you know if any patterns or trends or maybe frequently
asked questions? Oh for sure. Actually most of the questions
we get, our questions we have seen before. Yeah. Really
(00:28):
a lot of people have the same questions. Yeah, just
the same concepts tend to trip up a lot of people.
So if you still don't understand quantum mechanics or relativity,
you're not the only one. No, In fact, you're in
very good company because I'm still confused about it. May
you should submit it as a question to our podcast.
And who's going to answer it? Not me? I am
(01:06):
more handmade cartoonists and the creator of PhD Comics. Hi,
I'm Daniel. I'm a particle physicist and I've never stopped
asking questions about the universe. And welcome to our podcast,
Daniel and Jorge Explain the Universe, a production of I
Heart Radio in which we dive deep into your questions
about the universe and two scientists questions about the universe
into everybody's questions about the universe. How does it work?
(01:29):
What is it made of? Why does it work this
way and not that way? Why don't I have a
taco stand around my corner? Every deep and important question
about the universe handled on one podcast. Have you actually
checked all four corners? I do a scan every day
for taco chucks, and there's still not one on my corner.
You live in southern California and you have trouble finding
(01:49):
a taco truck. You need to get out more man. Yes,
that's definitely my problem. Yeah, we all have questions, and
it seems to be kind of a innate part of
human nature to be cure us about what's going on
around them and how things work. And fortunately the universe
is happy to provide mysteries and strange things for us
to ask questions about. Yeah, we're lucky that the universe
(02:11):
is both amazing, beautiful and mysterious. Yet it also seems
to be discoverable that we have this incredible technique for
divining knowledge from the universe by asking questions and then
answering them in a structured way. So we're fortunate to
be surrounded by amazing but accessible mystery yeah, especially you,
I guess, because you know the universe was simple and
(02:33):
easy to understand, we might be out of a job, Daniel,
that's right, especially if the whole field of physics lasted
like ten minutes of human history. They're like, let's knock
that off before lunch. We we've done it, we've done it.
Fire all the physicists put them to work somewhere else
doing Mataga trunk. You're right, there is a sort of
exquisite balance there. Physics was too easy, it'd be done
(02:54):
too soon. If it was too hard, nobody would give
us any money because we weren't making any progress. So
it's got to be just part of to be worth doing.
And so physicists, as part of their jobs, ask questions
about the universe, and they all have. They have all
kinds of amazing questions about how things work. And the
public also has a lot of questions. And sometimes those
questions are one and the same. That's right, and we
on this podcast do our best to answer those questions,
(03:17):
to dig deep, to explain them to you in a
way that makes sense. But sometimes our explanations inspire more questions.
We'll talk about a topic like black holes and then
we'll get five or ten very similar questions about some
little wrinkle that we didn't cover or something we said
that didn't quite make sense to a few people, and
so we thought it'd be fun to dig into some
of those emails and answer those questions and iron out
(03:38):
those wrinkles. So today on the podcast, we'll be tackling
our most common listener questions. That's right. We have a
series of episodes on this podcast where we talk about
the most unusual and interesting listener questions, the ones that
are sort of tricky and hard and require me to
do a bunch of research. But there's a whole other
(04:00):
category of questions that we want to share with you,
and these are the common questions, the one that a
lot of people are asking. And so today will be
asking most of a lot of the top questions that
we get through email, through Twitter, through Instagram. Daniel, do
you check Instagram? Do you know what Instagram is? Do
we have a TikTok account too? I don't use grams
because you know, I'm an American, and so I use
(04:23):
instat pounds good. That sounds like a bad diet to
go on. I don't recommend it. Actually, that's the name
of my taco truck is instat pounds, so we put
sour cream on everything. Maybe it's good that you don't
have a taco truck. Then maybe that's why I don't
have a talk. Yeah. So we're gonna be asking all
these questions, and they're all great questions, and they have
(04:44):
to do with the dark matter and black holes and
particles and all kinds of things, even philosophical questions and
questions about life and how to get involved in physics.
So we'll dive right in. Our first question comes from
Thomas and he us a question about is there a
dark matter inside of black holes? And what about neutrinos? Now,
(05:05):
because he asking if there's a dark matter inside of
neutrinos or is he asking the neutrinos inside of black hole?
I think he's asking if he can get a side
of neutrinos with his tacos. Everyone has a side of
neutrinos and the tacos, don't they. Yeah. I think that
this question is basically asking, like what kind of stuff
gets sucked into a black hole? Dark matter, which we
know is out there, this invisible kind of matter giving
(05:28):
gravity to the universe, even though we can't see it,
does that also get sucked into black holes? And that's
I think also why he's asking about neutrinos, Like neutrinos
feel hardly anything and have almost no mask, Did they
also get sucked into black holes? So I think that's
the origin of the questions. Are black holes sort of
universal sucker ruppers or do they only eat regular matter
(05:49):
like the kind that we're made out of. Yeah, And
the other angle of this question is, you know, what
are the structures of dark matter? If dark matter is
here in the universe, is it just big fluffy clouds,
or is it making like dark plant? It's dark stars,
dark black holes, and dark podcasts a right, So is
there dark matter inside a black holes? Daniel almost certainly. Yes.
Black holes are basically just very strong sources of gravity,
(06:11):
and they can suck in anything anything that has mass.
It doesn't matter if you are moving very fast or
if you're moving very slow, if you're low mass or
high mass. All forms of energy are trapped by black holes,
even if they have no other kinds of interactions. Right.
That's the thing that makes dark matter unique is that
we think it has no other kinds of interactions that
(06:32):
we're aware of. But you can still get sucked into
a black hole, right, Yeah, I guess the question is
it can only interact with gravity. I think we have
a podcast that covers that what would keep it inside
of the black hole. Couldn't it escape if it wasn't
being crunched down by other stuff. It's not being crunched
down by the other stuff, but it's gravity that's holding
things inside a black hole. Remember, these days, we don't
(06:53):
think about gravity as a force, so you shouldn't think
about it like tugging on this stuff and keeping it
in the black hole. We think of gravity as the
bending of the shape of space. Einstein told us that
this is some crazy relationship where matter bends space and
then space tells matter how to move because of its curvature.
And a black hole is this crazy intense bending of
(07:15):
space such that essentially becomes one directional inside a black hole,
you can only move towards the center. Space is one
directional inside a black hole, sort of the way time
is one directional outside a black hole. Time only moves
forward outside a black hole. Space only moves towards the
center inside a black hole. So it doesn't really matter
what you are if you have any mass or energy.
(07:36):
You are moving towards the center of the black hole
once you fall in, right, But then once it gets
to the center, wouldn't it come out the other end
Once it gets to the center, gravity is going to
keep holding it at the center, right, I mean, unless
there's like a wormhole at the center attached to a
white hole or something crazy. But if you follow general relativity,
and you know, we think general relativity is correct, although
we don't think it works inside a black hole. But
(07:58):
if you're assuming the general relativity inside a black hole,
then once you fall in, you're moving towards a singularity,
even if you're dark matter. Interesting. I guess if that's
the case, then wouldn't we expect most black holes to
be mostly dark matter? Since there's five times more dark
matter in the universe and regular matter. It's a great question.
We don't know what fraction of the stuff inside a
(08:19):
black hole came from dark matter. But remember that dark
matter is much more diffuse, it's much more spread out
through the universe. It doesn't clump as much as normal
matter because it doesn't have those other kinds of interactions
like dark matter. These big swirling clouds of stuff that's
surround our galaxy. But it's harder for dark matter to
make dense structures because to make dense structures you need
(08:40):
other kinds of interactions. You need other kind of interactions
to hold stuff together, like the electromagnetic forces a thing
that's holding you together, not gravity, and you need those
interactions to sort of radiate away energy and fall in.
Like the reason something doesn't just orbit a black hole
forever is that it loses some of its energy and
falls in. To do that, you have to be able
(09:01):
to like radiate off a photon or a z or something,
and dark matter just can't do that. So dark matter
is much more spread out. So we don't think that
dark matter is sort of the primary seed for black holes.
But some of it must have eventually fallen in, but
maybe not as much as you might think, because it's
it's kind of hard for it to fall in. Yeah, precisely.
And if you take, for example, the volume of our
(09:23):
solar system, the volume of our solar system is mostly
filled with normal matter. There's a lot of dark matter
in there, and there's more dark matter in the universe,
but in the vicinity of our Solar system, it's mostly
normal matter. So if our star went black hole, it
would suck in some of the dark matter that's nearby,
But most of the matter in our solar system is
normal matter. And what about neutrinos? Can neutrinos fall into
(09:46):
a black hole? I guess anything. I think what you're
saying is that black hole has been space and time,
so it's more like a space trap rather than just
a gravity trap. Yeah, exactly, it's a space trap. It
space is gravity. Gravity is space, and so you're exactly right,
And anything can fall into a black hole and nothing
can escape. So the answer to your question, can X
fall into a black hole? Is always yes? Or any X?
(10:09):
Can the letter X daniel as a concept of fall
inside of a black hole? Oh? Man, can philosophical ideas
fall into a black hole? Well? There is this crazy
theory that information has mass, and you know that's never
really been proven, but so perhaps, yeah, you come up
with a crazenough idea that your head becomes a black hole,
and you were thinking about the letter X, then yeah,
(10:30):
Well I believe we renamed black holes to space traps.
I feel like that's more accurate and more descriptive. All right,
well we'll start using that on the podcast from now
on and we'll see if it catches on your space trap.
All right, well, I think that answers the questions forms contraras.
Thank you for asking the question. Our next question is
(10:51):
about the universe small topic and whether it's stretching and expanding.
So Steve slopeck as, if the universe is stretching and expanding,
what's it expanding into? Now you said, this is another
common question we get. This is a question we get
like once a week. People are hearing about how the
universe is getting bigger, and they're wondering, like, if the
(11:13):
universe is everything, how can it be getting bigger. Doesn't
that mean it's sitting inside something else that's holding it
that it's now like filling up. I think people are imagining, like,
you know, a blob of molecules inside an empty room
spreading out to sort of fill out all those corners.
I have that question, and it's an amazing question. But
the answer is no, that the universe is not expanding
(11:35):
into anything, because the expansion is not like relative to
some outside external space or metric right, The expansion is intrinsic.
It means that distances between points are getting larger. So
we don't have our space, you know, our three dimensional
space sitting inside some other box. It's just stretching, it's
(11:56):
creating new space between existing points. Well, I feel like
what you're saying is that there's nothing outside of space.
But isn't nothing something? There isn't anything outside of space,
so I avoid saying the word nothing. What do you
mean What makes you uncomfortable about the word nothing? Well,
it depends what you mean by space. I mean the
origin of space was sort of like the backdrop on
(12:17):
which things happen, you know, you like define distances and
you could have empty space and then stuff in it.
Sort of the origin of the concept of space originally.
But now we know that space is not like that.
Space is dynamic. It's flexible. It can shimmer and wiggle
and stretch and grow and bend. Right, But you're tempted
to put it in some now static, larger space. Right,
(12:40):
there's nothing on which this like goo of space actually sits.
But we don't have any evidence that that exists. We
don't know that there's some other external, true deep meta
space in which our space exists. It seems like all
the math is consistent with just our space bending relative
to itself. But I guess the question is if we
(13:01):
can expand I think maybe what trips people up is like,
what are we expanding into? If we're expanding into something,
then you must be able to measure it, And so
wouldn't it be like empty space kind of right that
you can measure. I think the confusion there is expansion, right.
We're not expanding into anything, We're expanding relative to ourselves.
(13:22):
So if you have two points in space and you wait,
you will notice, thanks to dark energy and the expansion
of the universe, that they are getting further and further apart.
So you can that's how you measure it. You don't
step outside of the universe and be like, hey, the
universe is fourteen inches wide and last year was thirteen
Look how much it's grown. You measure the points between
(13:42):
things in space because that's all you can do. You
can't step outside of space. It doesn't even really mean anything.
Maybe the way to think about it is that the
space is not growing. It's almost like it's stayed the
same size, but we're shrinking inside of it. You know. Actually,
Dan Hooper, who we've had on the program, a cosmologist,
likes to make that point that you can't actually tell
the difference between the expansion of space and the shrinking
(14:05):
of stuff that looks exactly the same. There you go.
So maybe that will help people from reading confused, because
you know, sort of just think about it more like
we're the same, space is the same, but we're shrinking.
I mean that invites lots of other questions, like if
I eat so many tacos, how could I possibly be
shrinking because the tacas are shrinking. Yeah, that's a that's
(14:26):
another way to think about it. And you know, remember
that we don't understand why the universe is expanding. It's
not something that we understand and can make sense of.
We don't know why it's happening, why it started happening
five billion years ago, whether it will continue to happen.
All we have are these observations that distances between things
in space are expanding and expanding at an accelerating rate.
(14:47):
So it's something we observe, and you have to just
go back to the root experiment, like what is it
we actually see, rather than you're trying to get tangled
up in the various theories of cosmological constants. It's almost
like the opposite of what happens when you grow up.
Like I feel like when you're a kid, distances seemed huge,
like sitting in the car for an hour, it takes forever.
(15:07):
But when you grow up and you're an adult, distance
this kind of shrink no way, right, like sitting in
an hour for I think that tour doesn't seem long
enough actually, and so it's kind of the opposite of that.
It's almost like relationship that matter has to space is changing.
And that's what this does mean by its expansion of
the universe. You're staying in the universe is just growing
up an eventual it's gonna have a midlife crisis, not
(15:30):
going down. It's pulling Benjamin button. Do you think for
the universe, like now a billion years just like flits
by in a moment, whereas when it was a kid
it took forever. Yeah, kind of in a way, right, yeah, yeah,
maybe that that explains time dilation. Man, Man relativity is
just about getting mature. I'll take the Nobel price right now,
(15:51):
I'll buy you a taco Alright. We have a lot
more of these most common questions that we get through
the inbox, but first let's take a quick break. All right.
(16:14):
I know we're answering our most common questions that we
get through the inbox and through Twitter, and we've answered
questions about black holes and the universe expanding, and we
also have questions about particles, which is kind of your
field of expertise particles and tacos. Don't forget, I'm quite
(16:35):
an expert talca particle, tacas or taco particles. Let's talk
about it. Is that what a takito is? That's right,
that's when your tacos exchanged particles with your friends takings. Well,
that's not that's a no no these days, but that's right.
Stay safe out there people, all right. So our next
question is asking about the charge of particles. For example,
(16:59):
me Brown asked, I was wondering how particles could be
charged and what that even means? Exclamation point question mark.
Oh man, I love this question because I have this
same question and we still don't really know what particle
charge is. It's very confusing. Yeah, I like how she asked,
what does that even mean? It's wonderful because you know,
(17:20):
it's something where that's very familiar. People think about charge
and electric charge and familiar with lightning and whatever. But
down at the particle level, like what does it mean
for a particle to have electric charge? Like is it
carrying something? Is they're charge like stuffed into it somewhere.
Why does some of them have it some of them don't.
It's a great deep question, Yeah, because I guess she's
really wondering, like because it seems arbitrary, like a particle
(17:42):
has charged or it doesn't have charge, or it has
positive charge, or it has a color charge. You know
what determines that and why do they have it? And
the answer is that we don't know, and we have
to just sort of root ourselves and what we have seen.
Remember that all of these ideas about particle physics and
the universe they come out of experiments that we've done,
things we've seen, and that we're trying to describe about
(18:04):
the universe. We don't always understand what's going on, and
we're just sort of trying to build a structure that
let's it all hang together. And for particle charge, the
root thing that we see is that some little bits
of matter, some particles, are affected by electric fields and
magnetic fields. Like you put electrons through an electric field,
they will get accelerated. You put other particles, you know,
(18:26):
particles that don't have electric charge through an electric field,
they don't get accelerated. That's what it means to have
electric charge. That's the root thing. We've seen that some
particles are pulled by electric fields and some particles are not.
That's really what a charge means. So you're saying it's
part of a philosophical answer, like they have charged because
we've seen them. I have charged, or at least Daniel
has seen them. They have charged. Yeah, Well, we see
(18:48):
that some particles are affected by electric fields, and so
we say, all right, let's say that those particles are different,
and we'll create this idea of charge, and we'll use
that as a description to say which particles are affected
by elect fields and which ones are not. And then
we'll look for patterns, and we'll look for trends, and
we'll look for symmetries, and we'll try to understand that
more deeply. But fundamentally, it's just really a label for
(19:11):
the things we've observed. Now, I wonder if what she's
trying to get at is whether charge is a property
of particles or the field that make up the particles,
You know what I mean, Like Is it something that
gets a sign when the particle pops up, or is
it something that's just like a property of the field
that they're part of. Yeah, that's a great question. Mathematically,
(19:33):
we sort of put it in the middle, like we
think of particles, you know, as fields. Mathematically we think
of it's sort of in the middle, like we write
these things into our theories. And we said that the
charge is the thing that connects the field with the particle.
So for example, the photon field only interacts with things
that have electric charge, and so it's really right there
(19:56):
in between is how the two talk to each other.
It's the thing that lets them talk to each other,
the field and the particle. So it's sort of a
property of their interaction. Oh, I see, it's kind of
maybe a property of both, kind of what you're saying, Yeah, exactly.
And you know, we have noticed some amazing interesting things
about charge, like charge is conserved. You know, you can't
(20:18):
create it or destroy it. No matter how many particles
you create or destroy, the total charge is unchanged. And
that tells us that it must be something interesting and
fundamental to the universe, sort of like energy. We think
energy isn't changed in these interactions, and so that tells
us it might be something deep, that it's connected somehow
to something really deep about the universe and particles and fields.
(20:40):
But the truth is we don't exactly know what. Like
it could be a thing itself, you know what I mean,
Like it's like something that's being conserved. So it's kind
of like something that can be quantified in a way.
It can definitely can be quantified, yeah, absolutely, And you know,
there are other kinds of charge also, right, as you
mentioned earlier, Like the strong force has its own equivalent
of charge. We call it color to be confusing and
(21:02):
attempting to be poetic, and it has a lot of
similar properties to electric charge, and that some particles have it,
some particles don't. And there's one for the weak force.
Some particles have it, some particles don't. Whi's one of
the deep mysteries of physics is of why some particles
have some of these charges and don't have other charges.
It's very confusing, and what we're trying to do is
(21:22):
make a unified vision understand how this all shook out
and why it's this way and not the other way.
But the truth is, we just really don't know, it
sounds like it's almost like that the language of the
universe is this charge, you know. Yeah, like some particles
speak like romannitism, so some don't, and that's how they
interact with the fields around them and other particles. Yeah,
but why right, Why do some particles feel this and
(21:43):
others don't? How did that happen? And what does that
even mean? What does that even mean? Question mark? Exclamation point.
That's like the reason I got into physics because I
love asking that question what does that even mean? You know,
we want to gather together these weird experiments we've seen
and get some sort of deep understanding, appeal back a
layer of reality, and reveal the way the universe like
actually works. Man, you guys used exclamation points and question
(22:06):
marks at the same time in your physics papers, only
in the best ones. All right, thanks for that question.
Our next question is another common question that we get,
and this one in particular came from Roger Grenna, and
the question goes, how do particles which I understand, how
zero volume make up matter? So that stuff has volume.
(22:26):
That's a great question. If particles have no volume, how
can we have volume? If the recipe for making of
you is a bunch of particles and that each have
zero volume, then why isn't your volume just the sum
of a bunch of zeros which is zero? Right? Right? Yeah?
Or I guess maybe is my volume kind of an illusion?
Kind of like if if you drill down and there's
no real volume to any of my particles, does that
(22:49):
mean that I am also devoid of volume? I'll avoid
a lot of bad jokes there. But if I eat
a taco, Daniel, how does that effect my volume? Where
does that taco actually go? Well? And there's lots of
ways to attack this problem, and the most philosophicals to ask,
like what do you mean by volume? And we had
(23:11):
a whole podcast episode about like how small are particles?
What do we mean by their size? Etcetera, etcetera. But
that's a whole rabbit hole. Let's put that aside and
say particles are points. Let's assume for now the particles
actually have zero volume. Right, it's a good point. Yeah,
So to try to get to the point here, the
idea is that you can build something with non zero
(23:32):
volume out of particles that have zero volume if you
have a way to space them. There's something keeping them
from overlapping from crunching on top of each other, and
you do, and they have forces. They have electric forces,
for example, And so the reason that, like when you
build a molecule, the atoms don't just lie on top
of each other is that there are electrons circling those
(23:54):
atoms that keep the nuclei apart, and the nuclei are
positively charged and they keep each other apart. So there
are forces there that creates sort of like a spacing,
like a lattice that keeps everything from collapsing into the
tiniest dunk. I guess that, yeah, you're ready. It does
depend on what you mean by volume, because if by
volume mean like when something is there and it's not there,
(24:15):
then particles almost have zero volume. But they're also kind
of infinite volume, right because you can feel a particle
all the way across the galaxy. Technically, yeah, yeah, technically,
And so you could also say that if you're made
of zero volume particles, even if they have spacing between them,
then your real volume is still just the sum of
all those zeros, even though they're distributed into sort of
(24:36):
a cloud. And you guy, it's like, well, where do
you stop if you're made of a bunch of particles
that are spaced apart, where do you stop. Do you
stop at the edge of the most like right most particle,
or where it pushes back, as you were saying, like
where it feels something and and where it pushes back.
Is also not very satisfying because then it depends on
what you're pushing with or against, yeah, or against. If
(24:58):
you push against dark matter, matter will pass right through
you like you're not there. If you push against neutrinos,
it will very lightly touch you. If you push against
you know, a regular object like a stick, then you're
pushing against the electromagnetic forces. So it depends on the
kind of thing you're probing with. So it's not really
very well defined. But if you just say, like, hey,
you can make a cloud out of non zero particles
(25:21):
that keep their spacing because of the forces between them,
then you get a pretty good sense for why you
aren't just a tiny dot. Yeah, I guess maybe, like
if you go by effect and technically we all have
infinite volume, like you know, if someone across the universe
feels me in a way and feels the forces that
like particles exert. But if you talk, if you call volume,
(25:43):
like where are the particles center that make up rhead?
Then because I have more than one, then you can
sort of define a range of space like a volume
of space, and that's maybe that's volume. Yeah, and so
it's a slippery topic volume, you know. Microscopically, it does
really have a great analog to the way we think
about it, like intuitively and macroscopically. And this is something
(26:05):
we struggle with all the time when we take our
common knowledge about how things work mass, volume, velocity, you know, time,
and we try to apply them to the microscopic where
the rules are really just totally different, and sometimes the
very ideas break down and don't really have a great analog.
All right, mind bending question. All right. Our next question
from our most common question pile is a bit of
(26:28):
a career question, and I'm curious that's why you get
this a lot. So the question goes, I've always loved
physics but studied something else. Is it too late for
me to learn physics for real? I'd like to for real.
At the end, we do get this question a lot,
and I think that that's because our podcast has attractive
(26:48):
folks who are really interested in questions of the universe.
And have a passion for understanding these things, but because
of whatever happened to them in life, didn't end up
studying physics. They studied computers or ended up in something
else in their life. And maybe this has reignited their
interest a little bit, and they're wondering, like, is the
door closed? Is there still a path for me to
like go back to school and get a degree in
(27:09):
physics and actually do physics for real? Yeah? And the
answer is no, Right, anyone can study physics even for real. Yeah,
it's never too late, And it depends on your life
and your personal situation, of course, and whether you have
the time available in the financial means to go back
to school. But there are lots of paths back into physics.
(27:30):
And something I think that a lot of people don't
understand is that you don't need like a formal physics
undergraduate degree from a fancy university to get back into physics.
I can tell the story of somebody here in Irvine
who was always interested in physics but ended up in
computers and working in software for fifteen years and then
came to me one day to my office and said, look,
(27:52):
I want to get back into physics. What can I do,
And he just ended up taking a bunch of classes
at u C I not as an enrolled student, just
like taking classes, which you can do at most universities
without getting into it like a degree program. You don't
need to apply to become a freshman. You just take
the classes you need. Then you can apply to graduate
schools and you can say, look, I've done these courses,
(28:13):
I've got reasonable grades in them. And that student, for example,
he's now a grad student at an Ivy League university
in physics. And so it's totally possible. If you have
the interest and you can do it in your spare
time and sort of build up the basic knowledge you need,
then you can jump right back in and the doors
can still be open. Yeah, you can still be like
(28:33):
a physicist at any point in your life. I mean,
people change careers all the time, And I mean I
know this one guy who was an engineer but then
he turned into a cartoonist. It sounds crazy, but you
can change careers. I heard he's now running a taco Chuck.
Isn't that true? Unfortunately it doesn't have a happy ending.
(28:54):
It's actually worse. He's doing a podcast. But the other
side to This is that you don't need to be
an official physicist with a hat p to ask interesting
questions about the universe and to think about it and
even to make progress. You know, there are lots of
people out there who have figured this stuff out on
their own, and physics is not owned by physics professors.
It belongs to everybody. Wondering and curiosity about the universe
(29:16):
belongs to everybody. So even if you aren't in a
situation in your life where you can't go back to
grad school in physics, you can still enjoy wondering about
the universe and learning about physics. Al Right, we have
a couple of more questions here from our most commonly
Asked Questions pile, and we'll get into them. They're about
black holes and gravitational waves. But first let's take another
(29:37):
quick break. All right, Daniel, we are going down our
list of most commonly asked questions to the podcast, and
our next question has to do with black holes. Question
(29:59):
goes do black holes move? And does this moving black
hole leave any trail quote unquote trail a stretched space?
And this is a question from a six year old
in particular. That's right, are you saying that a lot
of six year olds asked this question, or does this
six year old ask one of our most common questions. Yeah,
this six year old put his finger on a question
(30:22):
that we get a lot, which is, you know our
black holes sitting around or are they moving? And did
they leave with some sort of like wake in space
as they move the way like a boat leaves awake
in the lake. But I love that this question came
from a six year old thinking about black hole. So
congrats to is Sean and to his parents for encouraging
(30:42):
wonder and curiosity about the universe. Yes, so I guess
the question is, first of all, can black holes move
or are they so massive and monumental that they're basically
static in space? It's a great question, and we have
to remember, first of all that motion and position is
always relative, right, so there's no like absolute motion. You
can't ask is a black hole moving without saying what
(31:04):
is it moving relative to? The other side of that
is that black holes follow the same rules as everything else,
Stars and planets and galaxies, right, They all can move
through space or relative to each other, just like black holes.
And sometimes you'll see two black holes that are bound
to each other and orbiting each other. So yes, they
definitely can move through space just like everything else. Yeah,
(31:26):
and they can. I mean they basically add like any
other object in space to the things around them, right, Like,
you can have a black hole orbiting our solar system
for example. Yeah, you can't tell the difference gravitationally between
a black hole and another object of the same mass.
If you're at the same distance between those two, you
just can't tell the difference. They have the same gravitational effect.
(31:48):
So yeah, we could orbit a black hole the way
we orbit the Sun. We could have a tiny black
hole as part of our solar system that we wouldn't
even have noticed. In fact, there are those folks that
wonder about Planet nine whether it's a primordial hole that's
somehow stuck out there in the depth of our solar system.
So black holes can move through space, and you know,
there's even the possibility of black hole could move through
(32:09):
space and come disrupt our solar system. We did a
whole podcast episode about that. So yeah, they're not like
nailed in place there. They can move just like everything right. Yeah.
I wonder if what trips people up is that people
often talk about black holes or should I say, space
traps as being kind of these like holes punctured in
spacetime itself, or like these bubbles of space time. And
(32:33):
so maybe it's hard to think about it moving around
because it's I mean, when you punch a hole through
a piece of paper, it doesn't you can't move it.
That's a good point, but remember that's true for everything.
All kinds of matter change the shape of space, they
change the curvature they bend space, and where that is
just depends on your frame of reference, and whether it's
(32:53):
moving depends on whether you're moving. So if you can
move past a black hole, then a black hole can
move past you. There's no like absolute frame in which
these black holes are anchored. All right, Well, I guess
then the answer is yes, they can move. Space traps
can move, And so if you're out there in space,
watch out like you should look both ways before crossing
(33:14):
the Solar System lane. That's right. And the other part
of his question was whether or not they like leave
any trail behind them, and he like wake through space.
And we said earlier that the location of a black
hole and its velocity depends just on its frame of reference,
Like are you moving with respect to it. If so,
then it has velocity. But if a black hole is accelerating,
(33:35):
if it's changing its velocity, then it absolutely will leave
a wake through space the way a boat will when
it moves through a lake, and those weeks are called
gravitational waves. They will make these ripples in space. It's
like the change in velocity of something that is what
generates a gravitational wave. Yeah, exactly, because these frames of
(33:56):
reference are called inertial frames of reference, and you can't
tell the difference mean any of them as long as
they have no relative acceleration. But as soon as something
has an acceleration is changing its velocity, then it leaves
a signal through space. And those signals are these gravitational waves.
And that's what we've detected. In those underground detectors where
they have the long laser beams to measure the stretching
(34:17):
of space itself, they see two black holes, for example,
orbiting each other and leaving all these ripples in space,
which leads us to our next question. Speaking of gravitational waves,
another common question we get is our gravitational waves the
same as a graviton, meaning is a graviton a gravitational
wave or Can a gravitational wave be a graviton or
(34:40):
can just have a wave without a graviton. It's a
great question, and it's very natural because people think about
like electromagnetic waves, you know, they think about light, and
they know that light is made out of photons, these
little quantized units of electromagnetic radiation, and so it's very
natural to think about well, for gravity, if you have
gravitational waves, you know, is at the same thing as
(35:00):
a graviton, this whole particle wave duality. And the answer
is no. And the reason basically is that gravitational waves
are really really big. They're huge effects in gravity, and
gravitons if they exist, we expect them to be really
really really small. So a gravitational wave might be made
out of like zillions and zillions of gravitons the way,
(35:22):
for example, like a beam of light is made out
of lots and lots of photons, So they're not the
same thing. There are different scales and also gravitational waves,
and we know they exist. Gravitons still totally theoretic, right,
we don't know if they're actually real because we don't
know if gravity is quantum, that's right, The only theory
we have of gravity is this classical theory that says
(35:43):
that gravity is smooth and continuous. It's not like chopped
up into little units like everything else is. Like electromagnetic
waves are made out of little units we call photons.
You can't have an arbitrarily small size of them. They
come in discrete bits. And we don't know that about gravity.
We think probably it is because everything else is, but
we don't actually know that. We don't have a theory
(36:03):
for it. So the graviton is the particle you would
invent if you did have a theory of gravity. But
we know the gravitational waves are real. So those things
are out there, we've seen them. We don't know if
they're made out of tiny little gravitons. Right, it's kind
of like a water I guess, you know, like a
a wave in water. That's not the same as a
molecule of water. Yeah, we'd love to discover those water molecules.
(36:26):
We'd love to figure out if gravity is quantum and
if it's made out of gravitons. But we haven't seen
those yet. And it's really hard because even the gravitational
waves are hard to spot because gravity is really, really
weak compared to all the other forces. It's like billions
and trillions times weaker, which means it's very hard to
see it effects. And so to see a graviton would
(36:46):
be to see a even tinier little bit of gravity.
We're just not nearly sensitive enough, all right, So I
guess the answer is a gravitational wave is a gravity nut,
not necessarily graviton. All right. Then I think we have
time for one more of our most commonly asked question pile,
and I'm going to pick this one here, which says,
(37:06):
if he equals mc squared and a photon is massless,
then how does a photon have any energy? How can
a photon have energy if it's massless? Yeah, this is
a great question, and I love that people are doing
this thinking they're like, I have this one idea and
this other idea. Can I bring them together? Does this
make sense? And that's physics, right, that's doing physics. It's
(37:26):
saying I have this rule, where does it apply? Let
me check make sure that it applies everywhere I understand it.
And so it's great. Kudos to everybody who thinks about
this and to ask this question. This one came from
James Chad. And so the answer is that the formula
equals m C squared. It is not false, it's true,
but it's not the most general formula. It's only talking
(37:47):
about the energy that you get from mass. And there
are lots of forms of energy, right, there's energy and
mass is also energy of motion. Right, there's energy of rotation,
the energy of vibration. These are are other forms of energy, right,
But don't they all get lumped at the same energy
at the end, right, Like if I have a slow
moving particle and a fast moving particle, then the fast
(38:10):
moving particle has more energy and can transform into you know,
heavier particles. Yes, that's true. And so the most general
expression for energy is not E equals mc squared. That's
the expression you would use for a particle that's essentially
not moving. There's a more general expression that says E
equals mc squared plus momentum times the speed of light
(38:31):
P time c. So there's another term there. And so
for a photon, mass is zero. It doesn't have any
of this rest mass that the other particles have, but
it does have momentum. Photons are essentially are pure momentum.
There the wiggle of the electromagnetic field. There are pure motion,
there's no mass to them. But wait, it doesn't momentum
(38:52):
imply mass like it. Remember an engineering, when you study momentum,
it's M times V, so mass times velocity. That's the
non relativistic expression for momentum M times v. In relativity
we have a more general expression for momentum, and we
can dive deeper into that rabbit hole. But now you
do not have to have mass to have momentum, and
(39:12):
photons we know have momentum. We talked about for example,
solar sales. Photons themselves from the Sun can push on something.
When they bounce off of it, they transfer their momentum
to the solar sale. So we know physically empirically the
photons definitely do have momentum and they are essentially pure momentum.
And so equals mc squared is the best known formula,
(39:33):
but it's not the most general case, and imparticle physics,
we use equals mc squared plus pc and so for
the photon m equal zero and the energy is just
momentum times the speed of light p time c. So
it does have energy. Photons have energy, it just doesn't
come from it having mass. It just comes from its motion.
That's right. There are other ways to have energy, and
(39:53):
that's what photons do, and they're weird because they have
exactly zero mass. And it's more general. Formula applies to
me in you too, Like my energy is both how
much I wait, but also how much a movie? Yeah, exactly,
you have more energy if you're in motion then when
you're sitting on your couch. Who all right, Well, those
are some of our most common questions, Daniel. What do
(40:16):
you sort of make of all these questions? I make
that we have smart listeners, then that we have people
out there that are intrigued by the way the universe works,
and that this stuff is complicated, and that if you
try to download it into your brain and play around
with it, you'll find little rough edges that you don't
quite understand, or little bits that don't quite click together,
and that that's not unusual, and that there are a
(40:38):
lot of other people out there wondering about those same
tricky bits. So I hope that these answers have helped
a lot of people collect those pieces together, and if not,
feel free to write into us. We would love to
help you resolve little questions you have about your understanding
about the universe. Yeah, and in some cases I feel
like your answer was we don't know, which means that
these are questions that physicists are also asking themselves at
(41:01):
the forefront of science. Yeah. Basically, at the end of
every question, you could add and what does that even mean?
Exclamation point question mark? And we'll add a few more
question marks there at the end. Two. That should be
the alt title for our podcast exclamation point question mark
or maybe our next book, Daniel, what does that even mean?
(41:21):
Exclamation point question mark? To which the answer is the
title of our first book. We have no idea. It's
a recursive book. Really, that's right. Book three. Let's just
go get tacos. Go go back and read our first
book while eating some tacos and increasing your volume. That's
all right. Well, we hope you enjoyed that and maybe
(41:41):
connected a little bit more with people out there, because
we all have a lot of the same questions about
the universe and don't be shy about writing to us,
were engaging with us on Twitter at Daniel and Jorge
or sending us email to questions at Daniel and Jorge
dot com. We love your listener questions and we answer
all of our email. Yeah, and don't be shy but
ask questions and pursuing knowledge and even maybe getting a
(42:03):
physics degree late in life. Thanks for joining us, see
you next time. Thanks for listening, and remember that Daniel
and Jorge explained The Universe is a production of I
Heart Radio. For more podcast from my heart Radio, visit
(42:24):
the I Heart Radio Apple Apple Podcasts, or wherever you
listen to your favorite shows.
Hosts And Creators
Daniel Whiteson
Kelly Weinersmith
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