Listener Questions about light and black holes

Daniel and Jorge absorb listener questions, reflect on the answers and emit some silly jokes

See omnystudio.com/listener for privacy information.

Episode Transcript

Speaker 1 (00:08):
Hey, Daniel, I have a light question for you. I
hope I am bright enough to answer it. See I
can tell you're taking this a little too lightly. Well,
you know, I'm happy to answer it and try to
lighten your intellectual load. Now I need a pretty awesome
answer here, something totally lit as the kids would say,
all right, what is it? I can illuminate for you?
All right, are you ready? What is a photon? Anyways,

(00:33):
that is not a lighthearted question, but go ahead, light
it up. Unfortunately, I don't have a very enlightening answer
for you. Just light puns. My puns are massless. Ye

(00:58):
Hi am or handmade cartoonists and the creator of PhD comics.
I'm Daniel. I'm a physicist and a professor at u
C Irvine, and now I find myself very light on
the puns. You're a shining example of in academia. No,
I just used up all my light puns, and now
my brain is like a black hole of ideas for
how to make more puns about light. You're dimming on

(01:20):
the punts there. Welcome to our podcast, Daniel and Jorge
Explain the Universe, a production of My Heart Radio in
which we try to shine a bright light on the
deepest mysteries of the universe. We wonder how everything works.
We wonder why it works at all. We wonder why
there is anything, how much of it there is, and
what rules it follows. We are amazed that we can

(01:43):
make sense of any of this incredible, crazy cosmos that
we find ourselves in, but we are appreciative that we can,
and we seek to share that little sliver of understanding
with you. That's right, It is a pretty amazing universe
full of light and shiny things for us to wonder
and ask questions about, like, for example, light or the
opposite of light, like black holes, big stars, giant stars,

(02:06):
small stars, dark matter, all kinds of things for us
to wonder about, because it's not just a universe filled
with stuff. It's a universe filled with stuff that is
sending us messages. We couldn't see stars in other solar
systems if they were not shooting light at us or
sending other kinds of particles. So don't imagine a universe
out there doing its mysterious stuff in the darkness. Instead,

(02:29):
all the crazy dancing that's happening in the physics inside
stars and inside black holes and all over the galaxy
is beaming you answers, beaming you clues at least to
lead you towards answers and understanding of the fundamental physics
that would explain it all. Yeah, the universe is bathing us,
but information about itself and have the laws that it
follows to make everything work, from giant stars and galaxies

(02:52):
to the tiny smallest molecules and particles. Assuming of course,
that the universe does follow laws. He's saying the universe
is some kind of out law, some kind of criminal universe.
Is it gon need to go to university jail. I
don't want to put a black mark on the reputation
of the universe in any sense I think you just did.
I'm just asking questions. You know, I wonder if Daniel

(03:17):
Whiteson broke the law again today. Is that the kind
of question that wouldn't that is harmless? Yeah? Yeah, exactly.
And I'm impressed with how well the universe so far
has been following laws, or put another way, how we've
been able to discover the laws the universe seems to
be following. But you know, there is a deep and
fundamental mystery there which is like, why is the universe

(03:39):
following laws at all, and is it possible to ever
come up with a single law that describes everything in
the universe. That's a little bit of an article of
faith in the whole process of science. Yeah, it's a
big question. Fortunately, the universe, as you said, is bright,
and it is full of things that shine and give
up light, and and that like gets to us, and
we can use that information to figure out if the

(04:02):
universe should be arrested or not. And that raises another
deep question, which is if the universe breaks the law,
who punishes it? Does it go to universe jail? In
what universe is that jail? Obviously there's a multiverse department
of justice. I'm amazed that I've never read that science
fiction novel. I think I think Marvel has it pretty

(04:23):
well covered. But a whole universe in jail, Wow, that's
quite the budget. Now they kill universes, oh man, they
shut them down. The death penalty for a universe. Usually
that gives me the shirts. Yeah, it's pretty pretty. It's
called the time authority. Oh that's right. Yeah, they do
cancel whole branches of the timeline. That's true. Well, let's

(04:44):
hope that never happens to us. We are just here
trying to figure out how the universe works. We're trusting
that it is following some laws and it's not putting
us in existential danger because we would like to understand
how it works. We look at all these photons that
come to our eyeballs and we try to make a
mental picture of how everything works. And sometimes we're confused.
Sometimes we see something we don't quite understand, and that,

(05:06):
of course leads to my favorite part of science, asking questions. Yeah,
and it's not just scientists who ask questions or love
to ask questions or have questions about the universe. It's everybody.
We all, at some point in our lives look up
at this guy and think, where did it all come from?
How does it all work? Why are we here? Who
is it that stole my chocolate? And how can I
put them in universe jail? These are big questions basically

(05:28):
everybody asks in their lifetime, because science is not just
a process that professors can do in their offices or
in their basement labs. It's just part of being human.
It's just like a way to codify and systematize the
natural feelings that we have of curiosity and investigation. It's
something that everybody can do, and it's something that everybody

(05:48):
is always doing as they maneuver in this world. Yeah,
all you have to do is observe the universe, think
about it, and use logic to work things out. That's
that's basically science right now. That's basically science. Also, drink coffee.
Coffee is a big part of it. I think you
don't drink any coffee anymore though, Does that mean that
you don't do any science? Well, I don't get paid

(06:09):
for it. If that's what you means. It's the coffee
drinking that I'm getting paid for over here, that's true.
It's the extra mile. Yeah, when you're ingest chemicals for something,
that means you're a pro. That's what goes to my
time sheets. Nine espressos today. Oh I'm getting over time,
over time, uh yeah, and overclocking your heart as well,

(06:30):
exactly and my brain. But what we love to do
is not just ask questions ourselves and talk about them,
but encourage you to ask questions. We hope that this
podcast tickles that inquisitive part of your brain and makes
you look around at your universe and think, do I
understand how this works? Can I figure this out? And
when you don't, we want you to write to us
with your questions so we can help you understand them.

(06:52):
So today on the podcast, we'll be tackling listener questions
light addition. Now it's just like a low calorie version
of our usual listener question episode. Welcome to Daniel and
Jorge on an intellectual diet. That's right, it's all cottage
cheese and can't to look today, folks, what is it? Aspertame?

(07:15):
We're going to give aspertain answers, the sweetest questions to
the sweetest mysteries in science, but with no calories. It's
gonna feel sweet when you listen to our answers, but
don't worry, you're not going to learn anything that is
promising here. Or maybe we should have very heavy answers
and people should like bench press us, you know, like

(07:36):
really massive, deep answers to the heaviest questions in the universe.
Maybe that should be a different podcast, the heavy edition,
the fitness version. The massive addition. We should be playing
like fitness music in the background, so I've already can
be like doing their crunches as they listen. That might
make it a little hard to talk. Yeah, I would
think of physicists would know that. But we do love

(07:56):
encouraging you to ask questions and to send us your question.
If you have questions about the way the universe works,
or there's something that's always puzzled you, please please please
write to us two questions at Daniel and Jorge dot com.
We answer all our emails. We answer all these questions,
and sometimes we might pick your question to answer here
on the podcast. Yeah, so today we have three awesome

(08:18):
questions and they're all in one way or another about
light kind of right or the lack thereof perhaps, Yeah, exactly, photons,
what they do when they hit stuff, how far they
can travel, and what's going on inside a black hole?
As always, I feel like everything comes back to the
black hole, one of the most massive mysteries in science.
Feel like it's kind of the rug for physicist. When

(08:38):
you hit a question that you don't know the answer to,
you're like, black hole on there. Why didn't I answer
your email? Oh it must have been routed into a
black hole. My apologies. So that works. Yeah, an email
black hole. That's how I would describe my regular imbob
exactly want to exceed a certain number of unread messages,
it just collapses. It creates a distorted and uh in

(09:01):
space and time? Yeah, all right, we'll start here with
our first question, which is about photons and what happens
when they hit stuff? And this question comes from Matthew
Daniel and horror. Hey, what's up? I loved the episode
about photons bumping into each other, but it really got
my brain spinning here, which is not difficult. What happens

(09:25):
to photons when they hit my skin? Are they just
absorbed and turned my skin a beautiful golden brown? What
happens when they hit solar panels? Why do things heat
up when they're hit by photons? What happens when photons
hit the opaque plastic cover on my little camper and

(09:48):
I can see light through it? Do some get through
and some don't? What happens when photons hit a mirror?
What happens when photons hit rock versus water, versus clouds?
I think you get the point. Boy, let's uh, let's
really dig in. It's going to be fotastic. All right, Wow,

(10:12):
I love that question. Yeah, that question or questions that
was like twenty different questions there. It was fotastic do
you think he was eating a bowl of fun as
he was thinking about these things. Hopefully it was diet foe. Yeah.
But uh, well, first of all, we should just say
what's up? Pat you back to you. Let me just
say how much I enjoyed hearing him spin out on

(10:34):
this question, realizing that there are really basic, deep questions
about how photons interact with matter and everything around us.
It is really complicated, So thank you very much for
inviting us to dig into it. Yeah. I think he
seemed to expand in his head as he was asking
the question on the idea that first of all, light
is everywhere. It's bouncing around everything and hitting everything. But

(10:54):
also there's kind of a huge variety of things that
like does. When it does seem to hit things right,
some lines, that goes through things, sometimes it bounces back,
sometimes it gets absorbed, sometimes it heats things up right,
there's kind of a wide range of things that light does. Yes,
light is very amazing and very complicated, and even though
it's everywhere in the world, it does react very differently

(11:15):
to different kinds of stuff. It's a great way to
show off like the fundamental quantum mechanics of our universe.
To understand all these different behaviors when light hits different
kinds of stuff. Yeah, so let's dig in, as Matthew requested,
So Daniel's started with the basics. What is light? What
is this thing we call light? Yeah? So the short
answer is, we really just don't know. Done. If we

(11:36):
don't know what light is and we don't know what
it does when it hits other things. Next question. We
don't know what light is in the sense that we
don't have like a good intuitive analog. I can't say
it's like a beach ball, or it's like a wave
in water. It's not like anything else we know. On
the other hand, we do have a very nice mathematical

(11:57):
description of what light does, so we can predict very
well what happens when light hits metal, or when light
hits plastic, or when light hits water, or when light
hits your skin. We can do all those calculations even
if we don't fundamentally know what light is in the
sense that we can't like translate it into something familiar. Wait,
what do you mean we don't know what it is?
I thought that light was, you know, excitations or wiggles

(12:21):
in the electromagnetic field that propagates across the universe, right,
isn't that the idea that the universe is filled with
quantum fields and the electromagnetic force is one of them,
and the wiggles in it are the photons. Yeah, that's
part of the mathematical description of how light works. We
can model light as a wiggle in the electromagnetic field,

(12:42):
and what happens to light when it hits something can
be predicted by solutions to these wave equations, which we
know mostly how to deal with in lots of circumstances,
like when they hit a barrier, or when they go
from air to water, or when it goes from air
to skin. We know mostly how to solve these problems.
We don't know what light is in the sense that
we don't really understand the fundamental quantum mechanics of it.

(13:04):
Like light is a wave in the sense that it's
fluctuations in this electromagnetic field. On the other hand, it
also acts like a particle because you can't observe all
of these waves directly. What you see are individual packets
of light that like go here or go there. So
there's something fundamentally probabilistic and quantum mechanical about light, and
in that sense, we don't really know like what light is,

(13:25):
that we do have the mathematics to describe it. Well,
you could also say that about everything else in the universe, right,
all the matter particles, all of the force particles, they're
all just quantum mechanical wave packets. Right. Yeah, absolutely, we
don't know, for example, what a particle is. My whole
episode talking about the various philosophical ideas for what it is.
That doesn't stop us from having a theory about it

(13:48):
and having mathematics that describe it, even if we don't
know who the subject of that mathematical story is. Right,
So if you ask me, like what is light? Then
boo boy, that's a whole big philosophical question. If you
ask me, can you predict what happens when light hits
a mirror? Oh? Yeah, that I can certainly do. Well. Fortunately,
this is not a philosophy podcast, so we'll just focus

(14:10):
on the latter part of describing light as as waves
any electromagnetic field. And you're saying that we can with
that description of light, we can tell what happens when
it hits different things. Yeah, that's right. We think about
light is a little packet of energy, a little pulse
in the electromagnetic field propagating through the universe. So you
imagine like light coming out of the star and flying

(14:32):
through space and making it through the atmosphere and hitting
your skin. And his first question was, like, what happens
to that photon? Right? Is it just like absorbed? Right? Well,
hopefully he's wearing sunscreen if he's out there in the sun,
and most of it will get refracted, refracted, reflected. But
maybe just step us through the basics, like what happens

(14:53):
when one of these packets of energy in the electromagnetic
field runs into a matter particle like an electron on
or maybe like an atom, like the atoms and the skin.
What's going on? So if you want to think about
in terms of an individual particle of light, then you
can imagine like the photon flying through space and it
hits the matter. Matter, of course, is made of other
little particles, and so the photon interacts with that matter.

(15:15):
It's not like the photon hits your skin as a
whole big blob. It touches like one particle of your skin.
It would like zero in on a single electron in
an atom on the surface of your skin and interact
with that electron. And one thing that it can do,
for example, is it can be absorbed by that electron.
Electrons can just eat photons, and then that electron now

(15:37):
has the energy of that photon. Yeah, that's pretty well.
Although you said that the photon touches a matter particle
in your skin, but that's not actually true, right, or
at least the idea of things touching each other is
kind of controversial or philosophical. Really, what happens is that
they get close enough to each other where they have
some kind of quantum interaction. Right. Well, the quantum interaction

(15:59):
here is two fields coupling directly, Like you have the
electron field and the photon field, and they overlap in
space and energy passes from one field to another. That's
the fundamental way we describe an interaction is passing of
energy from one field to another. If you're talking about
two matter particles like two electrons, Yeah, they don't actually
touch because they communicate through a photon. Right, So two

(16:21):
electrons don't push against each other directly. They pass photons
back and forth. But a photon interacts directly with an electron.
Its energy flows from the electromagnetic field into the electron field, right,
But I guess I mean like that there's no actual touching.
It's just that the one wiggle gets close enough to
the other wiggle where they somehow, through the magic of
the universe, the energy gets transferred from one field to

(16:42):
the other. I guess that's what touching is, right. So
then now we're in a philosophy podcast again. But that's
an interesting way to think about it, is that it's
it's like energy going from the photon field to the
electron field, right, Like that just magically happens. Is there
there's no conduit, there's no channel for that to happen.
That just automatically happens. These fields are sort of like, uh,

(17:04):
kind of on top of each other in that way. Yeah,
as you said, space is filled with these quantum fields.
Is a bunch of them. Is one for electrons, is
one for quarks, is one for photons, is one for
every kind of particle. A lot of those fields ignore
each other, but some of the fields don't. Some of
the fields do talk to each other. We call that
a coupling, and that coupling is determined by the charges
of the particles. So, for example, the photon field can

(17:27):
pass energy to any field. For a particle that has
an electric charge, that's actually kind of what it means
to have an electric charge. So yeah, the energy can
pass directly from the photon field to the electron field.
Like mathematically, when we describe these fields, we write them
down together in the lagrange and of the standard model,
and we add a term in front of them which
is not zero, which means that energy can pass from

(17:48):
one field to the other. So when the photon flies
out of the sun and hits your skin, that energy
is propagating through the electromagnetic field and now into the
electron field. It's absorbed by the electron. Okay, so that's
one thing that can happen to the photon. It can
get absorbed by the electron, and then after that a
couple of other things can happen. Right. Yeah, it's possible

(18:08):
for that electron to then release that energy like back
into the photon field. Right. That's a two directional interaction.
Electrons can eat photons, They can also create photons. They
can spit photons out. That electron, for example, has a
bunch of energy now, and the universe doesn't like to
have energy density very high in one place. It likes
to relax, likes to roll down to lower potential energy.

(18:30):
So the electron, one thing you can do is jump
back down in energy and give off a photon again.
And that can happen lots of different ways. You can
call that reflection, you can call that fluorescence. But that's
one thing that the bit of matter can do is
they can spit that photon back out into the universe. Yeah.
I guess there's two interesting things about that. One is that,
first of all, the original photon is basically god right,

(18:52):
like when we think of light bouncing off of a
mirror or bouncing off of your skin, like, Actually, what's
happening is that the photon die is right, It disappears
into that electron, and then a neil photon gets split
out by that electron. You know, you keep saying we're
not a philosophy podcast, and then you keep asking philosophy
questions like is the photon killed when it's absorbed? You know,

(19:14):
it's really interesting question, is it the same photon? Well,
that photon didn't exist for a moment. It was absorbed
into the electron. It's quantum information still exists, right, It's
certainly correlated with the original photon, So it's not like
there's no relationship between the new photon and the old photon.
But yeah, you might say it's a new photon, it's
not the same one, I guess. I mean, like in

(19:35):
your views of physicists, is that like an actual sequence
of events, Like the photon got absorbed, the electron realized
it had too much energy, so then it powered down
and spit out a new photon, Like, is there a
certain amount of time that happens in and it was
certain order in which it happens. It's not an instantaneous process, right.

(19:56):
The electron can absorb a photon and can hold onto
it for a little while, and then it can give
it up later with a podcast episode about that process.
It's called fluorescence, and that can be quite delayed, and
there certainly can be a time gap. On the other hand,
sometimes the electron gives it up almost immediately, and it's
more like the photon bounces off of the electron. For example,
in a mirror. What happens is that the photon is

(20:18):
basically just immediately reflected, though it is momentarily held by
the electron. And it's important to consider the other things
that can happen. It's not necessarily the case that the
electron gives up that photon. There are other options. It
can pass that energy to the nucleus of the atom
or into the lattice of the material, basically heating it up.
So there's a few varieties of things that can happen

(20:39):
to the electron after it's absorbed the photon. All right, man,
maybe walk us through a little bit of those options.
So how does it impart energy to the nucleus. So
the electron is interacting with the nucleus in the same
way the electron can interact with the photon, right, it's
bound to the nucleus, and it's also interacting with other
electrons in the material. And so in the same way

(21:01):
that it can like give up a photon, it can
also bump up against other electrons or can push up
against the nucleus. All of these, of course would be
mediated by other virtual photons. But basically, instead of just
giving up that photon back out into space, it can
create a photon which is absorbed by like the next
atom or by another particle, and that particle can have
that energy in terms of like its vibration or its rotation.

(21:24):
There's lots of ways for energy to be stored in matter,
and once the electron has absorbed that photon, it's possible
for that photon to get into like many of these
different kinds of buckets. All right, well, let's get into
some of the examples of what like does as it
hits different materials and whether or not it dies or not.
But first let's take a quick break. All right, we're

(21:56):
answering listener questions today, and our first one was about
light and basically what happens when light hits stuff, and
we talked about how it's actually photons in the electromagnetic
field hitting the particles in the atoms of the things
that you're trying to shed a light on. And one
thing it can do, it can be reflected back, or

(22:16):
it can the electrons can spit out basically an identical
photon back in the same direction or sort of the
same direction that the initial photon came in at. But
you're saying, you could also absorb that photon and you know,
give the atom more energy or the material it hit
more energy. That's kind of what happens when you you're
sitting out in the sun heating up right. Yeah, that

(22:38):
energy comes from the sun via photons and gets absorbed
by your body. When you feel hot, that's because the
atoms in your body are moving faster, they're wiggling or
sliding around faster, and then energy comes from the photon.
So yeah, that photon is now like gone. You know,
maybe every time you sit in the sun you need
to have like ten to the twenty six funerals for
all the photons that you're killing. Yeah, it's pretty sad.

(23:01):
You sound really sad. That's why you should cover yourself
in a liminum foil or mirrors, or just never go
outside your house. That's right. If you want to be
a photo vegan, that's right, you can join the Society
for the Humane Treatment of Photons. But so that's I
guess that's reflection and that's absorption. What about refraction, like
he asked, like, what happens when the light hits like

(23:23):
a semi opaque window like in his camper or you know,
something that's translucent. Maybe what's what's going on there? How
does refraction work? So refraction is complicated. To understand from
this like microphysical picture of a single article, then you
have to back up and really remember that the path
of a photon is determined by the wave equations that

(23:44):
are guiding its motion through the electromagnetic field. Refraction is
very familiar wave phenomena. When a wave hits another kind
of material, part of it reflects, part of it gets transmitted,
and then it gets bent in a slightly different direction.
For example, if you have a straw in new glass
of water, looks like the straw sort of broken in
half because the part of the light that's going through
the water gets bent slightly in a new directions. That's

(24:07):
what we call refraction, and that's tricky to understand for
like the path of an individual photon, but it's very
straightforward from like the mathematics of the wave equation. So
what's going on? Then? Why does lighter any wave change
direction when it changes the medium it's going in. So
when a wave travels through a medium, it's like wiggling
something right, and different kinds of medium wiggle in different ways. So,

(24:31):
for example, if you shout in the air and then
that sound wave hit water, part of it reflects and
part of it goes into the water and changes direction,
But it gets fundamentally transformed when it goes into the water.
Right now, it's wiggling water molecules instead of wiggling air molecules.
In order to balance all the frequencies at the surface
to make the math add up at the surface, so
everything is like making sense and being continuous. Those waves

(24:54):
sort of have to change direction in order to account
for the fact that it's like a new kind of wave.
That's the fundamental physics of like refraction of waves for light.
It's a little bit complicated if you want to think about,
like what happens to one photon when it hits the
surface of the water. How does it know how much
to bend right? And that's determined by the wave equation.
That's why it's fundamentally quantum mechanical. Two photons hitting a

(25:17):
surface might bend in slightly different directions, but a bunch
of photons hitting the surface sort of average out to
give you the answer you would expect from the wave equations.
But I guess what, like, what's happening to the individual photon,
how does it change direction? For example, you can't really
ask the question what happens to an individual photon unless
you're actually observing, unless you're seeing it. You can only

(25:38):
really think about photons as particles when you're observing them.
So you shoot a photon out, it hits the surface
of the water, then you detect it somewhere in the water, right,
and you want to know, like what happened at the
surface of the water. That's like going to the double
slit experiment and asking like which slit did the photon
go through? Really, the photon has many possible paths between

(26:00):
the source of the light and where you're detecting it,
and quantum mechanically speaking, it does all of them together. Right.
There's not a single story for what happened to that
individual photon, right, But I guess it's a little bit
different because to the photon, it didn't change mediums, right,
Like it didn't change how it was. The electromagnetic field
didn't change between outside the water and inside the water. Right.

(26:23):
To a photon is just going through the electromagnetic field.
The difference is that it's suddenly surrounded by a bunch
of water molecules, right, And so are you saying, like
all those water molecules basically act like little double slits. Yeah,
all those water molecules are like little interactions. How do
water molecules change the path of the wave. Well, remember

(26:43):
that the water molecules are charged particles, so they interact
with the photon field. You know. One way to think
about it is that like the photon is getting pulled
on by all those molecules. But you can't really have
like a single picture of the path of an individual
photon and say this one got bent in this particugular way.
There's lots of different possibilities for what might happen to
the photon when it goes through, and one photon will

(27:05):
go in one direction, another in the other direction. If
you average up over many many photons, millions of photons,
then you'll get this sort of average behavior you expect
from a classical wave. But for an individual particle, it's
a little bit random. Because I guess the photon from
its point of view, it's like it's going along. Suddenly
it sees a wall of water molecules, and some of

(27:26):
those molecules bounce it this way or bounce it that
way or right. Is that what you're saying, m Yeah, exactly.
And when you say bounce it you mean reflection. Yeah,
we mean interaction, which of course means like absorption and
re emission, and I guess the angle of that reflection
will change because the water molecules are you know, in
random pocisitions. And so you're saying the aggregate effect is

(27:49):
that it refracts light along a certain angle. M hmm, exactly.
It's the aggregate effect that's controlled by the wave equations.
It's maybe crisp is when you think about like reflection,
what happens when light hits a mirror, for example, Sure,
it gets absorbed by the atoms in the surface of
the mirror, but how do those atoms know what direction
to send the light? Out? Right? Light when it hits

(28:11):
the mirror doesn't just come off at any angle, comes
off at a very precise angle, like it bounces off
right following Snell's law. How do the atoms that absorbed
the photon know in what direction to send it? We
can't really answer that question from the particle point of view,
because you know, they don't really know. But there's a
lot of wave mechanics that are guiding what's happening to
the average photon. Because nobody's actually watching a single particle

(28:34):
absorbed that photon and re emit it. It's just like
an average process for many, many possible paths, and a
lot of those conflict and interfere, giving you overall the
photon being emitted in the right direction that's predicted sort
of by classical optics. Right, doesn't it all have to
do a lot with the crystals, right, and the order

(28:56):
of the things that you're shining a light on. Then
that's when you get something that can mirror, which bounces
things more neatly. Right, Mirrors do bounce things more neatly.
It has mostly to do with the conductivity properties of
the surface. Conductors are things that don't allow electric fields
very deep in them, have a bunch of electrons inside
them which rearrange themselves to like cancel out any electric field.

(29:18):
And so photons when they hit something that's like a mirror,
don't go very deep. They bounced right off the surface,
whereas things that are not mirrors, like your wall, which
is white which reflects a lot of light, doesn't act
like a mirror. Because the photons can get sort of
deeper in and interact with things further inside, and because
different photons will get different distances inside, they come out
a little bit scrambled. So images are, for example, scrambled

(29:41):
by a white wall, whereas they're not scrambled by a mirror,
because the mirror reflects everything basically from the very same depth,
which is right at the surface, right right, Well that's interesting, yeah,
but I mean it also has to do with the
surface sector, right, That's why you can polish things to
make them look shiny. Yeah, exactly, want a very flat surface.
So all the photons are bouncing off at the same instance,
and that's why conductors like silver or steel whatever make

(30:03):
good mirrors. All right, Well, I think that answers Matthew's
question what happens when photons hit stuff? The answer is
they die, Yeah, Daniel, I think that's our basic conclusion today. Yes,
every interaction is an absorption and a re emission, which
means the original photon is gone, baby gone. I mean,

(30:23):
it's we joke about it, but it's kind of true. Right,
like all light interactions reflection when something shining not shining
black white colors, you know, all that is uh in
every interaction. Every time light bounces off with something, it
dies and then it gets resurrected. I prefer to think
of it, it's like having children, because the original photon
is influencing the new photons certainly, man, And now you

(30:46):
get into whether photons are house photons reproduced? Is that
what you're I think that's gets into philosophical biological podcast right.
We only allow certain kinds of baseless philosophy on this show.
That's where we have standards here, only fantastic discussions here. Well,

(31:10):
thank you very much Matthew for that really intriguing question.
All right. Our next question comes from Tim and it
has to do with stars. Hey, Daniel and Core Hey,
I had a question. Is there such a thing as
a star that is so big or so bright that
it would actually affect the daytime nighttime cycles of planets

(31:34):
in a nearby solar system. I'm not talking about like
a binary solar system, talking about a star that is
in a neighboring system. Just listen to your podcasts about
twinkling stars and that made me thinking about it. Thanks
for the answers, because I know you'll have them. Well,
thank you Tim for that question and the faith that

(31:54):
you have that we will have answers. I come in
every time having the same confidence. Did you do well?
We'll definitely have something to say, even if we can't
answer the question definitively that's right, that's right. Anything techniquely
counts as an answer. I learned with my kids. When
questions hit the podcast, they die. That's right, to get absorbed,
and then we burth and back out into your ear.

(32:18):
We admit something. All right. Well, Tim's question is that
is it possible for a light from a different solar
system to affect the feeling of day and night in
a planet in another solar system? Right? That's the basic question. Yeah, Basically,
can stars change the day night pattern? Like? Could stars

(32:39):
be bright enough that they cause shadows? For example, I've
been out at night looking at but the stars and
then checking out behind me to see, like, am I
casting a star shadow? Star shadow? Sounds like a good
gamer tag. But of course, as you look up at
the night sky, those stars are obvious to your eyes,
but they're not bright enough to make the night sky

(33:00):
bright right, to make it feel like it's daytime? Well,
technically they do cast. You do cast a star shadow, right,
or a shadow star right? Like the technically, yeah, you
are blocking light from stars and preventing something behind you
from getting that light. Yeah, And it's fundamentally the same
process as getting a shadow from our sun. It's just
that our sun is closer, right, and so it's brighter,

(33:23):
so you notice it much more because it does dominate
the brightness of our planet. And the thing I love
about Tim's question, he says he's wondering about these two
different categories, our sun and the distant stars, and wondering
if there's something that bridges them. Is it's possible to
have something in between other stars that are close enough
to be sort of like part of our day night cycle.
Really cool way to think about it. I guess maybe

(33:44):
the question is like, how close can two solar systems
get so that one sun actually changes the day night
time feeling of another solar system? Yeah? Maybe Tim's working
on a science fiction novel, and this is an important
part of the plot, Right, isn't everybody working on a
science fic novel? I don't know. I feel like science
fiction gets absorbed by the reader and then not always
re emitted as a new novel. Right. Sometimes science fiction

(34:06):
novels just die. I see, they die in the reader's brain.
Maybe the reader just goes to an excited state of
knowledge and enlightenment. Oh there you go, transforms that energy
into you know, their their own work, their own imagination.
But anyway, here we are not answering Tim's question once again, Yes,

(34:26):
but we are trying to hear and um So, I
guess the question is how far canto solar systems get
before maybe they're not two different solar systems. I wonder
if that's kind of part of the question. Yeah, because
he specifically ruled out like a binary solar system where
you have two stars. It's a really interesting question and
there's a couple of different parameters we can play with here.
One is where you are in the galaxy, which really

(34:48):
determines how far apart stars are, and also how big
the stars are, because there's a huge variation in the
brightness and the size of stars. Right there are big ones,
small ones, and out in our neighborhood of the galaxy,
we're sort of like halfway out from the center of
the galaxy. Things are not very tightly packed. We're sort

(35:09):
of like in the suburbs of the galaxy. Like the
closest star to Earth is about four light years away.
That's really really far away. And remember that the brightness
of a star gets dimmer as you get further away,
and it gets dimmer by that distance squared, So if
you're ten times further away, a star is a hundred
times dimmer. If you're a thousand times further away, then

(35:32):
it's a million times dimmer. So that mathematics really works
against the distant stars. It's why the Sun really dominates
our experience. Yeah, and it's why if we were ten
times closer to the Sun, we would feel it's heat
a million times more, right, we need toast. Yeah, and
in our neighborhood the stars are pretty diffused, but if

(35:53):
you go to the center of the galaxy, things are
much more cozy. Right in the center of the galaxy,
it's not uncommon to have stars that are less than
a light year apart, or even less than a tenth
of a light year apart, And so those stars benefit
from that short distance. They get the same math, but
working in their favor to boost their brightness. You're ten

(36:13):
times closer, now you're a hundred times brighter. To give
you a sense of like what that means, if we
had another star as bright as our sun that was
like half a light year away, we would see it
during the daytime. It would be like bright enough in
our sky to see during the daytime, be about as
bright as venuses, which you can see during the daytime.
So like we would look up into the day sky

(36:35):
and maybe among the clouds you would see a little
pinpoint of light. Yeah, you'd see a pinpoint. It wouldn't
change the day night cycle, right, you could see it
during the day of the way you can see the moon,
but doesn't mean that the night would feel like the day,
but it would be something that's visible. So you could
see another sun that was like point forward light years away,
you know, if it was even closer than it would

(36:56):
be even brighter and in the center of the galaxy.
That does happen stars very close together, But I guess
at what point does it become part of a binary system?
You know, like how close can two stars get without
them basically being the same in affecting each other gravitationally,
so that they become one big solar system. Well, stars
are always going to pull on each other gravitationally, right,

(37:18):
we are getting pulled on by our neighboring stars even
though they are four light years away, and our galaxy
is getting pulled on by the neighboring galaxy even though
it's millions of light years away. So it's just sort
of like a cosmic web of gravitational interactions. And in
the center of the galaxy, these stars are all tugging
on each other, but they're not like in stable orbits
around each other. I think for a binary star system

(37:41):
you want them to be like gravitationally captured by each other.
But it's more like a mosh pit than a bunch
of dancing couples in the center of the galaxy. It's
kind of crazy down there. So I guess if you're
close to the center of the galaxy, uh, there's not
just probably one star that's have a light year a way.
There's a Brazilian stars that are light your way. So
if our solar system was and near the center of

(38:02):
the galaxy, we would look up at the day sky
and it would be filled with pinpoints, right, maybe just
a huge cloud that it would all just kind of
be super bright everywhere. Yeah, exactly. And it wouldn't be
unreasonable that your night sky might have a very very
bright star in it. You might have a neighbor which
is pretty close and just the same way, when you're

(38:23):
trying to sleep, if your neighbor has like floodlights on
in their house, it can go through your windows and
disturb your sleep. Near the center of the galaxy, you
might have a neighboring star that's bright enough to disturb
your night, especially if that neighboring star is not like
the Sun, if it's one of the big monster stars.
Because stars have a huge variation in their brightness. You know,

(38:43):
our sun is britty bright, but there are many more
stars out there that are much much brighter than our sun. Right,
I guess it's all relative, right, Like what what we
consider daytime here might be equivalent to nighttime on a
planet near the center of the galaxy, right, just from
all the life from all the by stars. Yeah, potentially, Yeah,
that's true exactly, And just to give you a sense

(39:04):
of the range, you know, like in our night sky,
there are other stars we can see that are much brighter.
Like Serious is a star in our sky, and it's
twenty five times as bright as the Sun. If you're
at the same distance from Serious as you were from
the Sun, it would be twenty five times as bright.
But that's just like a little step up. There are
other stars, like the biggest stars in our galaxy, one

(39:25):
is called Eta Carina, that are like two million times
as bright as the Sun two million, and so any
star in the neighborhood of Eta Carina is basically going
to be bright all night long. Yeah, And I guess
it also opens the possibility that like that, like maybe
if you're a planet orbiting a dim star, like maybe

(39:46):
like a brown dwarf or something that's just kind of simmering,
they're not really shining as bright as our sun. Then
for you, if you are near the center of the galaxy,
then really your son maybe doesn't even influence the day
a night cycle, right, Like maybe for you in that
Solar system, day and night is when your planet's facing
the center of the galaxy or not facing the center

(40:08):
of the gap, right, Like a day could be like
a whole year. Yeah, and the darkest times could be
when your son who clips is the other bright neighbor,
so you can have like a star star eclipse. Wow. Yeah,
who said science fiction dies? On this podcast, we're not
just absorbing science fiction here. We are emitting it in
real time. We are creating it. You're redirecting it. We

(40:32):
are reflecting these ideas back again. We want to hear
this story. Send us the draft of your novel when
you finished it. Yeah, but make sure we sign an
NDA here. I wouldn't trust us not to copy your ideas. Copy.
We're collaborators, we're co authors, we're here workshopping it live man.
All right, well, thank you Dann for that awesome question. Um,
I guess the answer is yes, there could be stars

(40:54):
so bright that they do affect the night day time cycle.
And in fact, if you're closer far away from the
center of the galaxy, it might make an bigger or
smaller difference. Yeah, the whole definition of day and night
would be really different, and it would lead to really
complicated patterns of life on that planet, which could be
really fun to explore in Tim's future debut science fiction novel,

(41:14):
Tim Jorgan Daniels new debut. Right, yes, of course, in fact,
you did he go first on the author list. I
don't know. We'll take that question off the air. All right,
let's get into our last question here about black holes
that are maybe made out of dark matter. We'll jump
right into that hole, but first let's take another quick break.

(41:50):
All right, we're answering listener questions and also stealing their ideas.
Apparently we're interacting with them, and we're interacted. I see,
that's right. The universe is not a criminal it's just
very interactive. That's right. The podcast host Field is interacting
with the podcast listener Field. Right, there's a couple and

(42:10):
there's a charge there. I can feel it. Yes, I
didn't still any classified documents. I just interacted with them
in my private home. Let's hope we don't get charged officially. Alright.
Our last question here comes from Matteo's and it's about
black holes. Hello, Daniel and Jorge, this is Mats from Poland.
I was wondering about the possibility of having a black
hole made entirely from the dark matter. I understand that

(42:33):
it's unlikely to happen because of the dark matter properties,
but I was wondering how could we detect one if
we can measure the black holes electric charge. Would a
zero charge mean that there is no normal matter inside?
How likely would it be for a black hole to
have zero electric charge? This also has led me to
some more general questions. Is the total electric charge in

(42:53):
the universe equal to zero? How about on galaxy or
planet level? I'm eager to hear your answers to my questions.
Thanks a lot for your great work with the podcast.
All right, thank you Matteos for that great question, and
it came to us free of charge, as all questions do. Now,
this is an interesting question he's asking. First of all, well,
he's asking several questions, but the first one was what

(43:16):
would happen if a black hole was made entirely out
of dark matter? He said, you know, he caveats that
it's unlike, he knows it's unlikely to happen. But what
if you made a black hole with dark matter? Would
it be different? Could? Could you tell the difference between
a regular black hole? Yeah? And even suggests a way
of maybe distinguishing dark matter black holes from a normal

(43:38):
matter black holes, which I thought was pretty clever. He's
thinking like a scientist. He's like, if this were to happen,
if I basically speculate about this, can this help me
write a ground Yeah? And so there's a bunch of
stuff going on here. First is the idea of what's
in a black hole? What can you make a black
hole out of? And you know, we think that black
holes can eat anything. They can eat normal matter, they

(43:59):
can eat dark matter, they can eat other black holes,
they can eat basically anything and grow because the curvature
space is determined not just by mass but by anything
with energy. That's what general relativity tells us. So black
holes can basically eat anything. You can make them out
of normal stuff or dark matter. But we think that
most black holes are probably dominated by normal matter because

(44:21):
it's harder for dark matter to fall into black holes. Mostly,
we think dark matter swirls around in big clouds, doesn't
clump together and fall into black holes as often as
normal matter. Right, because it's harder to make a black
hole out of dark matter, I think Matteo's kind of
acknowledged that they're harder to make and therefore less likely

(44:42):
to happen in the universe. But the basic answer is
that you can make a black hole out of dark matter. Like,
if you can somehow take dark matter squeeze it down
to a small enough radius, it would form a black hole.
In principle, absolutely yes, it would. And the reason that
it's harder to squeeze dark matter down is that we
don't think dark matter feels any other forces other than gravity,

(45:03):
so you can't push on it, for example, to compact.
It doesn't stick to itself, and that means it's hard
for it to give up angular momentum if it's spinning
around a black hole in the accretion disk, for example,
why do things fall into the black hole and not
just spin around them forever. They do that because they
lose angular momentum, They bump into something else in the
acreation disc and then head towards the black hole. Dark matter,

(45:25):
because it doesn't feel those forces we think, just passes
right through itself, doesn't bump into anything, doesn't stick together
into big blobs and fall into the black hole. But
it is possible if you somehow got a bunch of
dark matter together, it would make a black hole. Right,
And like also given enough time, right, Like, if you
have a blob of dark matter out in space, eventually
maybe in trillions of years, and it will all collapse

(45:47):
into a black hole. Right, that's right, Because rotation is acceleration,
which means it's giving off gravitational waves. So even something
that feels nothing else but gravity will eventually lose its
orbit because it's giving off energy out into the universe
and it will fall in. So, yes, eventually dark matter
will fall into a black hole, right, isn't there? I

(46:08):
mean there's a lot of dark matter out there in
the universe, a lot more than regular matter, and the
universe is pretty old, isn't it possible that at this
point some dark matter may have fallen and created a
dark matter black hole. It's almost certainly the case that
every black hole contains some dark matter. While a big
cloud is hard to collapse into a black hole, if
you have an existing black hole and a dark amoutter

(46:29):
of particle just like heads towards it, it's just going
to fall in. There's no like special protection. So every
black hole probably contains some dark matter. He's asking about,
like if it's possible to have a black hole that's
only dark matter, right, So imagine some big blob of
dark matter that's gotten separated from normal matter, which could happen,
right like the Bullet cluster collision stripped dark matter from

(46:50):
the normal matter in those galaxies, and of these big
vast clouds of dark matter basically all by themselves, wait
long enough, and that would collapse into a hole. Right.
He's asking, like, I think you're saying that, you know,
most black holes are like milk chocolate, you know, maybe
dark chocolate. But he's asking, can you have a dark

(47:11):
chocolate bark? Can you have a black hole made entirely
out of dark matter, and the answer is yes, right,
that can happen. The answer is yes, that can happen.
And then we have the question of like, how could
you tell? And now we run up against the problem,
which is that we can't know very much about what's
going on inside the black hole. The no hair theorem
tells us we can know the mass of the black hole,
basically how much stuff is in it. We can know

(47:33):
whether it's spinning, and we can know it's electric charge.
And that's the key that Mattheos is focusing on to
tell us whether or not the black hole is built
from dark matter or normal matter. Because if you take
a black hole and you throw electrons into it, you
can't tell what happens to those electrons once they pass in,
but it does change the overall electric charge of the
black hole, and you can measure that the same way

(47:55):
you can measure a black hole's mass increasing. You can
measure it's charge increasing or decreasing as you add charge
to it, because charge is conserved in our universe. But
how do you measure the charge of a black hole
if no information can come out? You can measure the
charge of a black hole the same way you measure
its mass, right, you measure the field it creates. Black
Holes can make gravitational fields that go past their event horizon,

(48:19):
and in the same way they can make electric fields
that go past their event horizon. You don't need information
to come out of the black hole in order for
that electric field to exist outside the black hole. Now,
I guess the question is that Mattes was thinking about.
It was that, you know, dark matter doesn't feel the
electromagnetic force. That's one of the things we know about it.
That's why it's invisible. You can't see it. So if

(48:41):
you made a black hole out of dark matter, does
that mean that the black hole wouldn't feel the electromagnetic force. Yeah,
that's true. If a black hole is made out of
dark matter, then it has no charge, and then it
wouldn't feel electromagnetism. An electron flew by a dark matter
black hole, it wouldn't feel any force, just the same
way it doesn't feel any force from any other neutral object. Well,

(49:04):
we will feel the force of gravity, it just wouldn't
feel the electromagnetic force. Right, Yes, it wouldn't feel any
electromagnetic force. It would only feel the gravity, just the
same way when it flies by any other neutral object.
It doesn't feel an electromagnetic force from it, only its gravity,
all right, So then I guess Matteos was thinking. If
that's true, then could we tell whether a black hole

(49:24):
is made out of dark matter or not by measuring
its charge? Like, if you see a black hole, you
measure its charge, you see that it's zero charge, or
that electrons are not affected by are not attracted or
repelled by this black hole. Would that be evidence that
this black hole is made out of dark match? Yeah,
And the last wrinkle there is to think about normal
matter black holes. Would they also have zero electric charge,

(49:46):
in which case you couldn't distinguish them from dark matter
black holes, or do they typically have some amount of
residual charge, in which case an exactly zero charge black
hole would be weird and would be a nice signal
of a dark matter black hole. So that's sort of
the last part of the question is how likely is
it for a normal matter black hole to have zero

(50:06):
electric charge? I see, So if a normal black hole
somehow in its formation aid more electrons than to say,
protons or positrons, then it would have an overall negative charge,
or if it ate didn't need enough electrons it would
have a positive charge. You're saying, maybe a zero charge
black hole wouldn't tell us that it's made out of

(50:27):
dark marror because it can also happen normally in a
black hole. It can't also happen normally, and it's a
bit of a probability thing. Black holes are just randomly
eating particles. What's the chances that it's exactly balanced that
it eats exactly as many positive particles as negative particles?
On one hand, is very unlikely to get exactly that balance.
On the other hand, is also the most likely outcome.

(50:50):
In the same way that like, if you flip a
coin a million times, what are the chances you're gonna
get exactly fifty percent heads and exactly fifty tails. Well,
it's unlikely to get exactly that number, it's also the
most likely outcome, right right. And also, I guess it
would be kind of hard to make a pure dark
matter black hole, right, Like, if you have a pure

(51:11):
dark matter black hole and one electron falls into it,
then suddenly it's got a charge. Yes, so that would
make this pretty challenging. But it is really interesting to
think about what is the charge distribution of black holes
out there in the universe. Are they all basically zero
or very close to zero? What is the overall charge
of these things? We have a whole episode planned about
the charge of the entire universe and the galaxy. But briefly,

(51:34):
most of the stuff that's out there is close to
neutral because the electromagnetic force is so strong that anything
that isn't neutralized, the force basically cancels it out. It
will like suck electrons off of something to balance it out.
Mostly like the Sun, for example, actually has a slight
charge because it's solar wind, has electrons and protons, but

(51:56):
it's easier for the electrons to escape the Sun than
protons because they have a lower mass. So the Sun
gives off more electrons and protons, so it has a
very slight positive charge. Interesting, I do agree the Sun
is a very positive influence on my life at least
for sure. I mean, it's not free of charge, but
I do have to wear some blood. So the answer

(52:17):
to this question, it's a really clever way to think
about what might be inside a black hole, but I
think be very challenging to prove that a black hole
is a dark matter, because it's possible to get zero
overall charge even without dark matter. Right. And also, I
guess it maybe points to this idea that black holes
are black holes, right, Like, even if it's dark matter

(52:37):
that falls into it, dark matter eventually just gets transformed
into pure energy. Right, So, like a black hole really
kind of grinds everything up and maybe makes it impossible
to tell if what you put in was dark matter
or not. Yeah, we don't know the quantum states of
the things inside the black hole. It's one of the
deepest questions in modern physics, like what is the form
of matter inside there? We don't know the answer because

(52:59):
we don't have a theory of quantum gravity. We don't
understand how gravity works for individual particles. So once the
dark matter is inside the black hole, it's not really
dark matter anymore. It's something weird and new that we
don't understand. Interesting. All right, Well, thank you mass for
that question. These were all pretty good questions, not really light.

(53:19):
They're pretty heavy and content. Last one is super extra heavy.
So for those of you on an intellectual diet, sorry
for the heavy meal. Hopefully we had expanded your brain
your waistline. But thank you for emitting these questions. These
particles of curiosity that we love to absorb and to
shoot back at you. Yeah, we hope we shed some
light on these topics and then you come back for more.

(53:42):
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 the i heart Radio app, Apple Podcasts,

(54:03):
or wherever you listen to your favorite shows. H