October 23, 2018 • 24 mins
What is a black hole, and what would it be like to fall into one?
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Speaker 1 (00:04):
Sometimes science comes up with the worst name for things
they discover. I know, like killer whales, which aren't killer
and are not actually whales, they're actually dolphins. Excellent point.
But I was actually thinking about black holes. Okay, that's
one of my favorite space names. What's round with black holes?
It's an awesome name. But black holes aren't totally black
(00:26):
and they're not actually holes. Their dolphins, all right? Who
runs the science pr department here? I think it's run
by a bunch of dolphins, a bunch of killer dolphins.
So long and thanks for all the fish. We're heading
to the black hole. Hi. I'm Jorge and I'm Daniel,
(00:56):
and this is Daniel and Jorge. It's explain the Universe today.
We're going to ask the question what is inside a
black hole? Maybe the deepest, darkest mystery in the universe.
But first, as usual, we went around and asked people
on the street what do they know about black holes
(01:17):
and what's hiding inside them. Here's what they had to say.
A bunch of destroy destroyed matter and energy. I don't
know exactly what's inside, but like it like captures light,
and it has a gravity so like strong that like
after a certain point you can't escape it Isn't it
(01:37):
like a vacuum? The anti universe, I don't know. Holy moly,
I love some of those answers the anti universe. It
seems like most people kind of had had had a
good idea of what a black hole was, right, Like
a lot of people knew it was like a dance mass, right, Yeah,
it's like a gravitational trap things can't escape from. People
seem to have the basics out there, right that they're ends,
(02:00):
they're dark, and things can't escape from them. Right, But
nobody named knew what's inside of one. That's right. Nobody
could tell us what was inside a black hole. Apparently
just walking around in the street isn't the best way
to get a solid scientific answer. But anyway, it's a
black hole. So I guess you know, before we talked
about what's inside a black hole, we should still recap
what is a black hole? Yeah? What is a black hole?
(02:21):
Black Holes are sort of fascinating ideas because for a
long time people thought black holes were just sort of
like a mathematical curiosity, like the kind of thing that
you see in an equation. Then if you believe that
equation describes reality, then it suggests black holes might exist.
But it's the kind of thing that makes you wonder,
is this really true or it's just so sort of
like a weird feature of the equation, something people are
(02:43):
not going to actually discover. What do you mean, like
this is the origin of the idea of black holes,
Like it was actually a theory first wasn't observed or
anything exactly. The idea of black holes came from general relativity,
and it wasn't observed for decades later. In fact, Albert
Einstein thought black holes would never or be seen. He
thought they didn't really exist, even though his theory predicted them.
What did the theory predict. Einstein's basic idea is that
(03:07):
gravity is not a force like other forces things that
pull and push on each other, like electromagnetism and the
weak force. He thought gravity instead was just a bending
of space time that his idea was any mass which
is sort of bend space. So imagine like a rubber
sheet spaces that rubber sheet, you put something big and
heavy on it, it bends things down. Now, if you
(03:29):
want to marble, you roll marble across that sheet instead
of just going flat across the sheet. If it encounters
someplace where the sheet is bent, it's going to change
its path. So the marble thinks it's going straight. But actually,
like the rubber it's it's on is curved. That's right.
It's that the most direct path is now curved with
respect to your previous path. And that's a tricky concept
(03:50):
for people to understand that. It's the bending of space,
and it's the sort of intrinsic bending. It changes the
natural straight lines. Um. But I love how you say
the marble thinks it's going straight, Like you have this
tendency to anthromorphize everything, like we were talking about that
last time. In this case, like the marble has an
opinion like, hey man, I'm going straight. I don't care
(04:10):
what space says. Cartoon is I imagine that you look
at the world and see little cartoon thought bubbles on everything.
That's my world. So we were talking about very heavy objects.
So the idea is very heavy masses bend space. Right,
the bend space so that when you move through space,
you end up moving through a curved path. Right, and
(04:32):
Einstein and some then some later folks realized that there
are some solutions to the general relativity equations where space
has bent so much that you can imagine it's like
a bottomless hole in that rubber sheet, so the things
can never escape them. And Einstein and these other folks
they discover these features the equations, but they were like,
(04:52):
is this real? You know? And this goes to the
heart of some of the stuff I love, like the
connection between physics and math, right, we like we use
math as a language of physics to describe the universe,
and sometimes the math takes this in directions where we're like, no,
that doesn't really work here. The math is not physical, right, Well,
like throw away mathematical ideas that we say are not
physical because they don't describe what actually happens. Sometimes the
(05:16):
math describes something which we think is unphysical it turns
out to be real and that's that's what happened here,
which is pretty cool. Well. Um, so the math predicted
that if you you might have a situation where we
have so much mass in such a small space that
will distort space so much that it will sort of
create almost like a hole in space. Yeah, like a
bottomless hole in this rubber sheet, so that even light
(05:39):
which travels you know, the fastest thing in the universe. Um,
can't escape because the all the straight line paths are closed. Now. Wow,
So like you're so dabbed down into the whole of
the barberschee, you'd have to be pointing up basically to
get out. There's no path out. Yeah, exactly. Um, you
know those big funnels they have in lots of science museums.
You can put a penny in and it rolls around.
(06:01):
It goes faster and faster and faster than it drops
down to the hole. You can think of it sort
of like that, but imagine that when you're down in
the hole, right, there's no way for the penny to
roll up and out of that hole. Right, Okay, So
so that so it started off as a mathematical weird case,
right for Einstein, and he was a smart guy, but
he didn't think that that could actually exist in real life. Yeah,
(06:22):
he thought it wouldn't actually happen because he thought that
everything spins and because things spin, it it's harder for
them to collapse. Right. You can think of most of
the stuff in the universe as sort of a battle
between gravity and some sort of pressure keeping it from collapsing.
Like gravity wants to suck stuff together, rightsh them together. Yeah,
(06:44):
it's weak, but you give it enough time, it's going
to pull things together and make them tighter and denser
and denser. So you might ask, well, why isn't everything
in the universe a black hole? Like it's fourteen billion
years in the gravity has had a lot of time.
You know, why is the Sun not a black hole?
Or why is the Earth not a black cool? Because
gravity has compressed them. Um. And the answer in many
cases is that they're spinning, and the spinning provides a
(07:07):
sort of a rotational pressure. Think about what happens when
you're standing on a merry go round, right, Um, somebody
spins it, you can get thrown off the merry go round.
And so that's sort of rotational pressure that keeps you
from getting sucked in. And our galaxy and the Sun
and the Earth, all these things are spinning, and it
does make it harder to become a black hole. And
so Einstein thought that there's no way you could ever
(07:29):
see this because things were spinning, and that we wouldn't
ever actually see a black hole would be impossible for
them to create. He thought gravity could never actually crunch
anything down that's small, because at that size things would
sort of spin outwards more than gravity could crunch them in.
But then he was proven wrong, Like, we actually saw
black holes. That's right, and I want to talk a
(07:51):
little bit more about that, but first a quick break. Yeah, so, um,
we should talk about how you can see a black hole. Right.
I imagine you see like a little black dot or
(08:12):
a black circle in the sky or something. So a
black hole is so heavy that light can't escape it,
and that means that it doesn't reflect any light. Right,
you shot a flashlight on it, no light comes back. Right,
you shot a spotlight on it, shot a laser on it,
shown anything on it, No light comes back. Even if
there has the sun next to it, who won't bounce off.
That's right. No light reflects, and it also doesn't admit
(08:35):
any light. Now, there's a tiny asterisk we should talk
about later, which is called hawking radiation. Turns out, black
holes do give off a little bit of energy, but
you can't really see it. So from the point of
view was seeing a black hole, it's basically invisible. It's
just like a black circle, right, So how could you
possibly see that a black hole is there? Well, you know,
I watched the movie Interstellar, which I know could be
(08:57):
a whole topic of conversation, but that your research for
the podcast. That and I read the Wikipedia page for
the black Hole movie, which is a classic seventies movie.
Did you ever watch the movie? Yes? It did. In fact,
I saw that movie a few weeks ago with my kids.
No way, really. I think it was supposed to be
like a response to Star Wars or something, um and
it's much weirder than Star Wars. According to Wikipedia, it's
(09:22):
like the first Disney movie ever to get a PG rating.
My kids were like, why did you show us this movie?
Was this supposed to be good? Or is this educational?
But this that movie was a huge part of my childhood,
you know. It was like made a huge impression on me.
You saw the black Hole movie as a kid? Yeah,
you didn't see this again? You might have been the
only one. I don't think it was very It was
(09:44):
huge in Panama. What are you talking about? Huge in Panama?
I rest my kids. Yeah, let's hope this podcast is
huge in Panama. Let's hope we we achieved that level
my fellow Panamanians. I hope they're listening. So how could
you actually see a black hole? Let's shift out of
the fictional world and back into the what we imagined
to be the real world. How could you see a
(10:04):
black hole? Well, it's biggest to funding feature is it's gravity,
and so it has very powerful gravity, and you can
see the effect of gravity on nearby stuff. So, for example,
one of the biggest black holes that's near us is
at the very center of the Milky Way. There's an
enormous black hole there. It's huge. It's called super massive
and um that's the category of black hole. And we
(10:26):
can see that it's there because we see stars orbiting it.
So we see the path of stars that are going
around the black hole, so we can tell these stars
are orbiting something, but we see nothing there. So you
can do the calculations. You can say, oh, all these
stars orbits are consistent with something really heavy here. Like
imagine you were looking at the Solar System and you
(10:48):
couldn't see the Sun. You could guess that there was
something really massive there because see, look all these planets
they are going around and they're all consistent with orbiting
one thing that's really heavy, and you can even calculate
its mass from the orbits and all that stuff. You
could deduce that the Sun was here without actually seeing it.
That would be a pretty silly way to see the sun.
But you could definitely tell. And we can use that
(11:08):
same approach, and we have to see the huge black
hole in the center of the Milky Way for example.
I see. Maybe that's the problem is that the closest
black holes to us is at the center of the
Milky Way galaxy. Now that's the closest, really big one.
It's like twenty seven thousand light years. I think that's
pretty far away. There are closer black holes to us
than the one at the center of the Milky Way,
(11:28):
but they're not as large, I see. But there's a
theory about what they sort of look like, which is
like a black ball, right, yeah, and there's other stuff
near the black hole, right Like say, for example, you
have a black hole and it's near a star. What's
it gonna do. It's gonna shred the star. It's gonna
suck all the stuff out of the star into the
black hole. And you can see that also before stuff
(11:50):
falls into the black hole, you can see it like
on the way you know. Um, So for example, imagine
there's like a you know, a hole in the sidewalk
and everybody's falling into it. If you notice that trail
of people walking along the sidewalk and then nothing on
the other side, Oh my gosh. Exactly. So there's lots
of black holes where you can see the stuff falling
(12:11):
into it because it and sometimes it's like orbit once
or twice before it falls in. This this thing called
the accretion disk, which is like the stuff orbiting the
black hole before it comes in. And so a lot
of times you can see that around the black hole. Um,
it's sort of like a warning, like, you know, abandoned,
hope all you who fly near here because you are
entering the black hole. But that also brings up another
(12:33):
really interesting point, which is like a black hole is
not a hole. You know, it's a clever name and
it sounds awesome, and it's connects to this sort of
geometric idea of like having a hole in the bottom
of the rubber sheet. But I think most people think
of a black hole is like a hole in space,
like something you could fall into, right, But as you
said earlier, a black hole is something that's really dense,
(12:55):
it's really heavy, it's really thick. You can't fall into it.
It's more like a black Man as sort of like
a black rock. You know, it's like saying, can you
fall into the earth? Right, Like, you can't fall into
the earth, you fall onto the earth. Right. Well, you're
sort of assuming you know what's inside a black hole? Right? Well,
we know it's really dance, right, we know there's a
lot of stuff in there. But in terms of like space,
(13:16):
like space is so distorted. It's sort of like a hole,
isn't it. It's like the rubber sheet analogy. It is
sort of a like a three D hole. It's like
it's through a hole in three D space. Right, it's
a gravitational well that you can't climb out of. But
that doesn't mean that it's like empty inside. You can
like once you go in, you can like dance all
around is playing the room. Let's think about that this
(13:38):
sort of where is the edge of the black hole?
And a lot of people think of the edge of
the black hole as something we call the event horizon. Okay,
what's the event horizon? Besides being a bad science fiction
movie with Sam Neil, the Event Horizon is another movie.
I see you're not up on your bad sighest fiction cinema.
Did this? Did this? Only come out in Panama. No,
(13:58):
this was a real movie. It had like fishburn I
think Sam Neil. It was like a big deal. But anyway, so,
what is the event horizon of a black hole? Yeah,
so that's the point after which you can't escape, right,
if you are closer to the center of the black
hole than the than this threashold you can't escape. Outside
of that, there's still a possibility. Inside there are no paths.
(14:21):
It's like, you could escape if you could move faster
than light. But even if you were like moving at
the speed of light, you could not escape. But be
careful because people like to say, oh, maybe if you
went faster than the speed of light, blah blah blah.
But going faster than the speed of light, that's a
whole other podcast we should do. Right, it's impossible, And
so saying something like going fast in the speed of
light is like saying like, well, then if you had magic,
(14:43):
then sure all the rules would be off. So like
an interstellar when they shared the black hole, is this
black sphere, that's the event horizon, right, that's like the
edge of that sphere black circle is the event horizon
because anything inside would just look black. So Is this
a PHY six podcast asked or a film podcast? Film
six podcast? No? But I mean, I guess you know what.
(15:07):
The reason I bring it up is that, you know,
I think a lot of people have heard of the
event of horizon, right, and the conceptually what it is
you can't escape after that, but like a representation of
a black hole, that that circle is kind of the
event horizon, right, Yeah, you're exactly right. And so you
would see like the accretion disk around the black hole,
the stuff that's about to fall in, like what's on
deck to get sucked up by the black hole. But
(15:29):
you're right, the black hole itself would be black, and
that's the event horizon. You're seeing the edge because you
can't see anything in it, nothing can escape it, and
so it's surrounded by matter which you can normally see.
But the actual black hole itself is the edge of
the event horizon, and that's what that's what makes the
questions how interesting. Because you can't see in there, people
wonder what's in there? Right. Einstein's original idea was that
(15:51):
there was something called a singularity that's a point of
essentially infinite density at the very center of it. Right,
that's right, Yeah, an infinite least small space, right, super
super dense. As soon as you cross some threshold of
mass density, then you've created this hole in the bottom
of the rubber sheet, a gravitational well that nothing can escape.
(16:12):
But it's not necessary that the whole event horizon is
filled in with mass. I think this is the point
you were trying to make earlier. There's got to be
a dense core in there somehow, but it creates a
gravitational well that's larger than that core um. And so
this is the original idea in stands. Original idea was
that there's this singularity, this really really dense point. Okay,
so maybe a black hole is like some kind of
(16:34):
point surrounded by who knows, but it sort of goes
out to the sphere of blackness. That's going to be
the name of our band, right, Sphere of Blackness or
my next Panamanian bad sci fi movie. I think that's
a la. There's so many concepts tied together into a
(16:55):
black holes. But I think people still wonder what's inside
a black hole because we're pretty sure that this idea
of a singularity can't be right, pretty sure that there
aren't singularities inside black So not even our theory about
what's inside is right, yeah, And you know, Einstein's theory
is wonderful and it's beautiful, and it's predicted lots of
(17:15):
stuff which seemed weird but actually happens, like gravitational waves. Right.
Einstein predicted gravitational waves, these ripples in space time when
massive objects slam into each other or spin around each
other a hundred years before we saw them, right or
hurt them as yeah, yeah, decades and decades, I don't
remember the exact date, but a long time before we
(17:36):
saw them. And the problem with Einstein's theory is that
it doesn't include any quantum mechanics. And that's because we
figured out quantum mechanics sort of at the same time
or in the decades after general relativity. And something really
important about quantum mechanics is that it doesn't allow things
to be located in infinitely small spaces. There's a basic
fuzziness to the universe and you just can't violate that.
(17:58):
So having a singular already like a point of matter
in its zero volume is you know, it would blow
a quantum mechanics mind, right, but it's it's I guess
technically quantum mechanics is about momentum, right, Momentum has a
minimum size. Right, Well, it is about momentum, but it's
about actually most measurable things like time, energy, space, and momentum.
(18:21):
All these things come in finite grains like little quantum,
a little basic units that you can't get smaller than.
But even if, what if, like it's infinite mass, like
a black hole, or like infinite density. Yeah, well, the
quantum mechanics tells us that doesn't exist. You know that
there's a there's a finite width to everything, and so
you can't have infinitely small objects um. Quantum mechanics says,
(18:45):
it just can't happen. But something is happening in there, right,
there's something going on inside a black hole, and whatever
it is, it's intense enough and dense enough to create
a black hole. You don't need infinitely small points to
create a black hole. You just need a density above
a certain thresh hold. Genel relativity tells us it's an
infinite singularity, but coonum mechanics says it can't be infinite. Right. Yeah,
(19:06):
there's this idea that I thought was really cool that
anything can become a black hole. Like if you squeeze
it enough, it becomes a black hole. Right, Like if
somebody squeezed me and my mass into a small enough volume,
I would just like become a black hole, right. Yeah,
it's a great idea, And I'm not sure like technically
anything can become a black hole because you need to
(19:28):
have a certain amount of mass per volume. But I
guess in principle, if you compress something down far enough
and it had some mass, then it would be dense
enough to become a black hole. And black holes don't
have to be huge. Black holes can also be tiny.
For example, we're trying to create black holes at the
large age on collider and those would be black holes
like the size of protons. That is a great thought
(19:49):
that I don't think a lot of people know is
that black holes can be different sizes. Yeah. Absolutely, you
can have a tiny one, or a huge one or
an super massive gigantic one. That's right. And basically the
only thing you can know about a black hole from
the outside is um it's mass, which means its size,
and it's rotation, so it's whether it's spinning or not.
(20:09):
And so that's why we desperately want to know what's
inside a black hole beyond our just our curiosity. Like
anytime there's something in the universe you can't it's something
in your house, for example, that you aren't allowed to
look inside. Like if I said or I never look
inside this box, you'd be definitely curious to see inside it. Right,
So you're saying it's like the universe has has created
a box and it it refuses to tell us what's inside.
(20:32):
That's right, Well, this is a perfect point to take
a break. If you could see inside it, um, you
would learn something really deep about the way gravity works
(20:52):
and quantum mechanics and how they're connected. It's like, you know,
ten Nobel prizes worth of stuff hiding inside a black hole,
maybe even an actual Nobel prize. So that's the answer
to the question what's inside a black hole? Is uh,
fame and fortune, a trip to Stockholm. So what would
happen if you try to get near a black hole? Well,
(21:14):
this is something you have to understand, which is something
called a tidal force and um best way to understand
it maybe is to think about what happens when things
get near the sun for example. So one of my
favorite examples came in when this comet came into our
solar system and approach really close to the Sun. It's
called comet Shoemaker Levy. That is that the one that
(21:36):
almost missed Jupiter, That's the one that slammed right into Yeah. Yeah,
it was pretty awesome to watch cosmic collisions. Um, but
before it got there, it got torn apart by tidal forces.
Oh shredded. Yeah, I got shredded. And um, say you're
near a black hole, or you're near the Sun or something,
(21:56):
then your head and your feet are not the same
distance from the Sun. And because gravity depends on the distance,
so like your head will be pulled in with greater
force than your feet. If your head or closer than
your feet, then yeah, there'll be a stronger force on
your head than there is on your feet, right and
effectively that means it's tearing you apart. But the difference
would have to be greater than the forces holding me together. Exactly.
(22:19):
Like right now you are sitting on the earth, and
there is a greater force on the on your feet
then there's on your head. So whatever part of your
body is on the floor right now is feeling a
stronger gravitational force than whatever part is elevated, right, Because
it's further from the center of the Earth, gravity falls
like one of the distance squared. So that's that's a
pretty big factor. But the difference is not enough to
(22:39):
overcome the forces that are holding me together. That's right,
you're saying near a black hole, those differences are so
huge he would actually shred your part. Yeah, exactly, like
that comment that came into the Solar System got shredded
by Jupiter and by the Sun. If you got too
close to a black hole, you would get torn apart
before you got anywhere near it. So it's in my
view it's impossible to get very close to a black
(23:00):
hole unless you're incredibly strong, like you need to build
an object with really really tight bonds. Right. The things
that are holding me together are the electromagnetic bonds between
the atoms in my body, and gravity is constantly tugging
on those if I'm near the Earth or near the Sun,
tugging on those. But you know, not so hard and
and where we've evolved to be strong enough to to
(23:20):
not be shredded by the Earth, but not it's strong
enough to be to not be shredded by a black hole. Right,
So basically we may never be able to like go
to a black hole and see what's inside, right, it's
hard to imagine and and I hate to say never.
I disamber because it prescribes future generations intelligence and there's
probably some genius out there was a clever idea for
how to do it. It's not theoretically impossible to be
(23:41):
near a black hole. It's just practically very difficult, which
makes it, you know, a pretty tough engineering problem. So
we know black holes are out there, we know they're mysterious,
we know they contain some deep, dark secret. We don't
think they contain the anti universe. I don't believe they
contain worm whole. I don't know, you know, they don't
(24:02):
believe they contain worms or anything else weird. But I
would love to get to know what's inside a black hole.
I don't know about visiting one, or seeing one, or
getting too close to one and getting shredded, and desperately
want to know what's inside a black hole. Maybe side
will find my marbles lost for sure. All right, thanks
everyone for listening to Daniel and Jorge explain the universe.
(24:24):
Thanks for listening. Do you have a question you wish
we would cover send it to us. We'd love to
hear from you. You can find us on Facebook, Twitter,
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us to feedback at Daniel and Jorge dot com
Sometimes science comes up with the worst name for things
they discover. I know, like killer whales, which aren't killer
and are not actually whales, they're actually dolphins. Excellent point.
But I was actually thinking about black holes. Okay, that's
one of my favorite space names. What's round with black holes?
It's an awesome name. But black holes aren't totally black
(00:26):
and they're not actually holes. Their dolphins, all right? Who
runs the science pr department here? I think it's run
by a bunch of dolphins, a bunch of killer dolphins.
So long and thanks for all the fish. We're heading
to the black hole. Hi. I'm Jorge and I'm Daniel,
(00:56):
and this is Daniel and Jorge. It's explain the Universe today.
We're going to ask the question what is inside a
black hole? Maybe the deepest, darkest mystery in the universe.
But first, as usual, we went around and asked people
on the street what do they know about black holes
(01:17):
and what's hiding inside them. Here's what they had to say.
A bunch of destroy destroyed matter and energy. I don't
know exactly what's inside, but like it like captures light,
and it has a gravity so like strong that like
after a certain point you can't escape it Isn't it
(01:37):
like a vacuum? The anti universe, I don't know. Holy moly,
I love some of those answers the anti universe. It
seems like most people kind of had had had a
good idea of what a black hole was, right, Like
a lot of people knew it was like a dance mass, right, Yeah,
it's like a gravitational trap things can't escape from. People
seem to have the basics out there, right that they're ends,
(02:00):
they're dark, and things can't escape from them. Right, But
nobody named knew what's inside of one. That's right. Nobody
could tell us what was inside a black hole. Apparently
just walking around in the street isn't the best way
to get a solid scientific answer. But anyway, it's a
black hole. So I guess you know, before we talked
about what's inside a black hole, we should still recap
what is a black hole? Yeah? What is a black hole?
(02:21):
Black Holes are sort of fascinating ideas because for a
long time people thought black holes were just sort of
like a mathematical curiosity, like the kind of thing that
you see in an equation. Then if you believe that
equation describes reality, then it suggests black holes might exist.
But it's the kind of thing that makes you wonder,
is this really true or it's just so sort of
like a weird feature of the equation, something people are
(02:43):
not going to actually discover. What do you mean, like
this is the origin of the idea of black holes,
Like it was actually a theory first wasn't observed or
anything exactly. The idea of black holes came from general relativity,
and it wasn't observed for decades later. In fact, Albert
Einstein thought black holes would never or be seen. He
thought they didn't really exist, even though his theory predicted them.
What did the theory predict. Einstein's basic idea is that
(03:07):
gravity is not a force like other forces things that
pull and push on each other, like electromagnetism and the
weak force. He thought gravity instead was just a bending
of space time that his idea was any mass which
is sort of bend space. So imagine like a rubber
sheet spaces that rubber sheet, you put something big and
heavy on it, it bends things down. Now, if you
(03:29):
want to marble, you roll marble across that sheet instead
of just going flat across the sheet. If it encounters
someplace where the sheet is bent, it's going to change
its path. So the marble thinks it's going straight. But actually,
like the rubber it's it's on is curved. That's right.
It's that the most direct path is now curved with
respect to your previous path. And that's a tricky concept
(03:50):
for people to understand that. It's the bending of space,
and it's the sort of intrinsic bending. It changes the
natural straight lines. Um. But I love how you say
the marble thinks it's going straight, Like you have this
tendency to anthromorphize everything, like we were talking about that
last time. In this case, like the marble has an
opinion like, hey man, I'm going straight. I don't care
(04:10):
what space says. Cartoon is I imagine that you look
at the world and see little cartoon thought bubbles on everything.
That's my world. So we were talking about very heavy objects.
So the idea is very heavy masses bend space. Right,
the bend space so that when you move through space,
you end up moving through a curved path. Right, and
(04:32):
Einstein and some then some later folks realized that there
are some solutions to the general relativity equations where space
has bent so much that you can imagine it's like
a bottomless hole in that rubber sheet, so the things
can never escape them. And Einstein and these other folks
they discover these features the equations, but they were like,
(04:52):
is this real? You know? And this goes to the
heart of some of the stuff I love, like the
connection between physics and math, right, we like we use
math as a language of physics to describe the universe,
and sometimes the math takes this in directions where we're like, no,
that doesn't really work here. The math is not physical, right, Well,
like throw away mathematical ideas that we say are not
physical because they don't describe what actually happens. Sometimes the
(05:16):
math describes something which we think is unphysical it turns
out to be real and that's that's what happened here,
which is pretty cool. Well. Um, so the math predicted
that if you you might have a situation where we
have so much mass in such a small space that
will distort space so much that it will sort of
create almost like a hole in space. Yeah, like a
bottomless hole in this rubber sheet, so that even light
(05:39):
which travels you know, the fastest thing in the universe. Um,
can't escape because the all the straight line paths are closed. Now. Wow,
So like you're so dabbed down into the whole of
the barberschee, you'd have to be pointing up basically to
get out. There's no path out. Yeah, exactly. Um, you
know those big funnels they have in lots of science museums.
You can put a penny in and it rolls around.
(06:01):
It goes faster and faster and faster than it drops
down to the hole. You can think of it sort
of like that, but imagine that when you're down in
the hole, right, there's no way for the penny to
roll up and out of that hole. Right, Okay, So
so that so it started off as a mathematical weird case,
right for Einstein, and he was a smart guy, but
he didn't think that that could actually exist in real life. Yeah,
(06:22):
he thought it wouldn't actually happen because he thought that
everything spins and because things spin, it it's harder for
them to collapse. Right. You can think of most of
the stuff in the universe as sort of a battle
between gravity and some sort of pressure keeping it from collapsing.
Like gravity wants to suck stuff together, rightsh them together. Yeah,
(06:44):
it's weak, but you give it enough time, it's going
to pull things together and make them tighter and denser
and denser. So you might ask, well, why isn't everything
in the universe a black hole? Like it's fourteen billion
years in the gravity has had a lot of time.
You know, why is the Sun not a black hole?
Or why is the Earth not a black cool? Because
gravity has compressed them. Um. And the answer in many
cases is that they're spinning, and the spinning provides a
(07:07):
sort of a rotational pressure. Think about what happens when
you're standing on a merry go round, right, Um, somebody
spins it, you can get thrown off the merry go round.
And so that's sort of rotational pressure that keeps you
from getting sucked in. And our galaxy and the Sun
and the Earth, all these things are spinning, and it
does make it harder to become a black hole. And
so Einstein thought that there's no way you could ever
(07:29):
see this because things were spinning, and that we wouldn't
ever actually see a black hole would be impossible for
them to create. He thought gravity could never actually crunch
anything down that's small, because at that size things would
sort of spin outwards more than gravity could crunch them in.
But then he was proven wrong, Like, we actually saw
black holes. That's right, and I want to talk a
(07:51):
little bit more about that, but first a quick break. Yeah, so, um,
we should talk about how you can see a black hole. Right.
I imagine you see like a little black dot or
(08:12):
a black circle in the sky or something. So a
black hole is so heavy that light can't escape it,
and that means that it doesn't reflect any light. Right,
you shot a flashlight on it, no light comes back. Right,
you shot a spotlight on it, shot a laser on it,
shown anything on it, No light comes back. Even if
there has the sun next to it, who won't bounce off.
That's right. No light reflects, and it also doesn't admit
(08:35):
any light. Now, there's a tiny asterisk we should talk
about later, which is called hawking radiation. Turns out, black
holes do give off a little bit of energy, but
you can't really see it. So from the point of
view was seeing a black hole, it's basically invisible. It's
just like a black circle, right, So how could you
possibly see that a black hole is there? Well, you know,
I watched the movie Interstellar, which I know could be
(08:57):
a whole topic of conversation, but that your research for
the podcast. That and I read the Wikipedia page for
the black Hole movie, which is a classic seventies movie.
Did you ever watch the movie? Yes? It did. In fact,
I saw that movie a few weeks ago with my kids.
No way, really. I think it was supposed to be
like a response to Star Wars or something, um and
it's much weirder than Star Wars. According to Wikipedia, it's
(09:22):
like the first Disney movie ever to get a PG rating.
My kids were like, why did you show us this movie?
Was this supposed to be good? Or is this educational?
But this that movie was a huge part of my childhood,
you know. It was like made a huge impression on me.
You saw the black Hole movie as a kid? Yeah,
you didn't see this again? You might have been the
only one. I don't think it was very It was
(09:44):
huge in Panama. What are you talking about? Huge in Panama?
I rest my kids. Yeah, let's hope this podcast is
huge in Panama. Let's hope we we achieved that level
my fellow Panamanians. I hope they're listening. So how could
you actually see a black hole? Let's shift out of
the fictional world and back into the what we imagined
to be the real world. How could you see a
(10:04):
black hole? Well, it's biggest to funding feature is it's gravity,
and so it has very powerful gravity, and you can
see the effect of gravity on nearby stuff. So, for example,
one of the biggest black holes that's near us is
at the very center of the Milky Way. There's an
enormous black hole there. It's huge. It's called super massive
and um that's the category of black hole. And we
(10:26):
can see that it's there because we see stars orbiting it.
So we see the path of stars that are going
around the black hole, so we can tell these stars
are orbiting something, but we see nothing there. So you
can do the calculations. You can say, oh, all these
stars orbits are consistent with something really heavy here. Like
imagine you were looking at the Solar System and you
(10:48):
couldn't see the Sun. You could guess that there was
something really massive there because see, look all these planets
they are going around and they're all consistent with orbiting
one thing that's really heavy, and you can even calculate
its mass from the orbits and all that stuff. You
could deduce that the Sun was here without actually seeing it.
That would be a pretty silly way to see the sun.
But you could definitely tell. And we can use that
(11:08):
same approach, and we have to see the huge black
hole in the center of the Milky Way for example.
I see. Maybe that's the problem is that the closest
black holes to us is at the center of the
Milky Way galaxy. Now that's the closest, really big one.
It's like twenty seven thousand light years. I think that's
pretty far away. There are closer black holes to us
than the one at the center of the Milky Way,
(11:28):
but they're not as large, I see. But there's a
theory about what they sort of look like, which is
like a black ball, right, yeah, and there's other stuff
near the black hole, right Like say, for example, you
have a black hole and it's near a star. What's
it gonna do. It's gonna shred the star. It's gonna
suck all the stuff out of the star into the
black hole. And you can see that also before stuff
(11:50):
falls into the black hole, you can see it like
on the way you know. Um, So for example, imagine
there's like a you know, a hole in the sidewalk
and everybody's falling into it. If you notice that trail
of people walking along the sidewalk and then nothing on
the other side, Oh my gosh. Exactly. So there's lots
of black holes where you can see the stuff falling
(12:11):
into it because it and sometimes it's like orbit once
or twice before it falls in. This this thing called
the accretion disk, which is like the stuff orbiting the
black hole before it comes in. And so a lot
of times you can see that around the black hole. Um,
it's sort of like a warning, like, you know, abandoned,
hope all you who fly near here because you are
entering the black hole. But that also brings up another
(12:33):
really interesting point, which is like a black hole is
not a hole. You know, it's a clever name and
it sounds awesome, and it's connects to this sort of
geometric idea of like having a hole in the bottom
of the rubber sheet. But I think most people think
of a black hole is like a hole in space,
like something you could fall into, right, But as you
said earlier, a black hole is something that's really dense,
(12:55):
it's really heavy, it's really thick. You can't fall into it.
It's more like a black Man as sort of like
a black rock. You know, it's like saying, can you
fall into the earth? Right, Like, you can't fall into
the earth, you fall onto the earth. Right. Well, you're
sort of assuming you know what's inside a black hole? Right? Well,
we know it's really dance, right, we know there's a
lot of stuff in there. But in terms of like space,
(13:16):
like space is so distorted. It's sort of like a hole,
isn't it. It's like the rubber sheet analogy. It is
sort of a like a three D hole. It's like
it's through a hole in three D space. Right, it's
a gravitational well that you can't climb out of. But
that doesn't mean that it's like empty inside. You can
like once you go in, you can like dance all
around is playing the room. Let's think about that this
(13:38):
sort of where is the edge of the black hole?
And a lot of people think of the edge of
the black hole as something we call the event horizon. Okay,
what's the event horizon? Besides being a bad science fiction
movie with Sam Neil, the Event Horizon is another movie.
I see you're not up on your bad sighest fiction cinema.
Did this? Did this? Only come out in Panama. No,
(13:58):
this was a real movie. It had like fishburn I
think Sam Neil. It was like a big deal. But anyway, so,
what is the event horizon of a black hole? Yeah,
so that's the point after which you can't escape, right,
if you are closer to the center of the black
hole than the than this threashold you can't escape. Outside
of that, there's still a possibility. Inside there are no paths.
(14:21):
It's like, you could escape if you could move faster
than light. But even if you were like moving at
the speed of light, you could not escape. But be
careful because people like to say, oh, maybe if you
went faster than the speed of light, blah blah blah.
But going faster than the speed of light, that's a
whole other podcast we should do. Right, it's impossible, And
so saying something like going fast in the speed of
light is like saying like, well, then if you had magic,
(14:43):
then sure all the rules would be off. So like
an interstellar when they shared the black hole, is this
black sphere, that's the event horizon, right, that's like the
edge of that sphere black circle is the event horizon
because anything inside would just look black. So Is this
a PHY six podcast asked or a film podcast? Film
six podcast? No? But I mean, I guess you know what.
(15:07):
The reason I bring it up is that, you know,
I think a lot of people have heard of the
event of horizon, right, and the conceptually what it is
you can't escape after that, but like a representation of
a black hole, that that circle is kind of the
event horizon, right, Yeah, you're exactly right. And so you
would see like the accretion disk around the black hole,
the stuff that's about to fall in, like what's on
deck to get sucked up by the black hole. But
(15:29):
you're right, the black hole itself would be black, and
that's the event horizon. You're seeing the edge because you
can't see anything in it, nothing can escape it, and
so it's surrounded by matter which you can normally see.
But the actual black hole itself is the edge of
the event horizon, and that's what that's what makes the
questions how interesting. Because you can't see in there, people
wonder what's in there? Right. Einstein's original idea was that
(15:51):
there was something called a singularity that's a point of
essentially infinite density at the very center of it. Right,
that's right, Yeah, an infinite least small space, right, super
super dense. As soon as you cross some threshold of
mass density, then you've created this hole in the bottom
of the rubber sheet, a gravitational well that nothing can escape.
(16:12):
But it's not necessary that the whole event horizon is
filled in with mass. I think this is the point
you were trying to make earlier. There's got to be
a dense core in there somehow, but it creates a
gravitational well that's larger than that core um. And so
this is the original idea in stands. Original idea was
that there's this singularity, this really really dense point. Okay,
so maybe a black hole is like some kind of
(16:34):
point surrounded by who knows, but it sort of goes
out to the sphere of blackness. That's going to be
the name of our band, right, Sphere of Blackness or
my next Panamanian bad sci fi movie. I think that's
a la. There's so many concepts tied together into a
(16:55):
black holes. But I think people still wonder what's inside
a black hole because we're pretty sure that this idea
of a singularity can't be right, pretty sure that there
aren't singularities inside black So not even our theory about
what's inside is right, yeah, And you know, Einstein's theory
is wonderful and it's beautiful, and it's predicted lots of
(17:15):
stuff which seemed weird but actually happens, like gravitational waves. Right.
Einstein predicted gravitational waves, these ripples in space time when
massive objects slam into each other or spin around each
other a hundred years before we saw them, right or
hurt them as yeah, yeah, decades and decades, I don't
remember the exact date, but a long time before we
(17:36):
saw them. And the problem with Einstein's theory is that
it doesn't include any quantum mechanics. And that's because we
figured out quantum mechanics sort of at the same time
or in the decades after general relativity. And something really
important about quantum mechanics is that it doesn't allow things
to be located in infinitely small spaces. There's a basic
fuzziness to the universe and you just can't violate that.
(17:58):
So having a singular already like a point of matter
in its zero volume is you know, it would blow
a quantum mechanics mind, right, but it's it's I guess
technically quantum mechanics is about momentum, right, Momentum has a
minimum size. Right, Well, it is about momentum, but it's
about actually most measurable things like time, energy, space, and momentum.
(18:21):
All these things come in finite grains like little quantum,
a little basic units that you can't get smaller than.
But even if, what if, like it's infinite mass, like
a black hole, or like infinite density. Yeah, well, the
quantum mechanics tells us that doesn't exist. You know that
there's a there's a finite width to everything, and so
you can't have infinitely small objects um. Quantum mechanics says,
(18:45):
it just can't happen. But something is happening in there, right,
there's something going on inside a black hole, and whatever
it is, it's intense enough and dense enough to create
a black hole. You don't need infinitely small points to
create a black hole. You just need a density above
a certain thresh hold. Genel relativity tells us it's an
infinite singularity, but coonum mechanics says it can't be infinite. Right. Yeah,
(19:06):
there's this idea that I thought was really cool that
anything can become a black hole. Like if you squeeze
it enough, it becomes a black hole. Right, Like if
somebody squeezed me and my mass into a small enough volume,
I would just like become a black hole, right. Yeah,
it's a great idea, And I'm not sure like technically
anything can become a black hole because you need to
(19:28):
have a certain amount of mass per volume. But I
guess in principle, if you compress something down far enough
and it had some mass, then it would be dense
enough to become a black hole. And black holes don't
have to be huge. Black holes can also be tiny.
For example, we're trying to create black holes at the
large age on collider and those would be black holes
like the size of protons. That is a great thought
(19:49):
that I don't think a lot of people know is
that black holes can be different sizes. Yeah. Absolutely, you
can have a tiny one, or a huge one or
an super massive gigantic one. That's right. And basically the
only thing you can know about a black hole from
the outside is um it's mass, which means its size,
and it's rotation, so it's whether it's spinning or not.
(20:09):
And so that's why we desperately want to know what's
inside a black hole beyond our just our curiosity. Like
anytime there's something in the universe you can't it's something
in your house, for example, that you aren't allowed to
look inside. Like if I said or I never look
inside this box, you'd be definitely curious to see inside it. Right,
So you're saying it's like the universe has has created
a box and it it refuses to tell us what's inside.
(20:32):
That's right, Well, this is a perfect point to take
a break. If you could see inside it, um, you
would learn something really deep about the way gravity works
(20:52):
and quantum mechanics and how they're connected. It's like, you know,
ten Nobel prizes worth of stuff hiding inside a black hole,
maybe even an actual Nobel prize. So that's the answer
to the question what's inside a black hole? Is uh,
fame and fortune, a trip to Stockholm. So what would
happen if you try to get near a black hole? Well,
(21:14):
this is something you have to understand, which is something
called a tidal force and um best way to understand
it maybe is to think about what happens when things
get near the sun for example. So one of my
favorite examples came in when this comet came into our
solar system and approach really close to the Sun. It's
called comet Shoemaker Levy. That is that the one that
(21:36):
almost missed Jupiter, That's the one that slammed right into Yeah. Yeah,
it was pretty awesome to watch cosmic collisions. Um, but
before it got there, it got torn apart by tidal forces.
Oh shredded. Yeah, I got shredded. And um, say you're
near a black hole, or you're near the Sun or something,
(21:56):
then your head and your feet are not the same
distance from the Sun. And because gravity depends on the distance,
so like your head will be pulled in with greater
force than your feet. If your head or closer than
your feet, then yeah, there'll be a stronger force on
your head than there is on your feet, right and
effectively that means it's tearing you apart. But the difference
would have to be greater than the forces holding me together. Exactly.
(22:19):
Like right now you are sitting on the earth, and
there is a greater force on the on your feet
then there's on your head. So whatever part of your
body is on the floor right now is feeling a
stronger gravitational force than whatever part is elevated, right, Because
it's further from the center of the Earth, gravity falls
like one of the distance squared. So that's that's a
pretty big factor. But the difference is not enough to
(22:39):
overcome the forces that are holding me together. That's right,
you're saying near a black hole, those differences are so
huge he would actually shred your part. Yeah, exactly, like
that comment that came into the Solar System got shredded
by Jupiter and by the Sun. If you got too
close to a black hole, you would get torn apart
before you got anywhere near it. So it's in my
view it's impossible to get very close to a black
(23:00):
hole unless you're incredibly strong, like you need to build
an object with really really tight bonds. Right. The things
that are holding me together are the electromagnetic bonds between
the atoms in my body, and gravity is constantly tugging
on those if I'm near the Earth or near the Sun,
tugging on those. But you know, not so hard and
and where we've evolved to be strong enough to to
(23:20):
not be shredded by the Earth, but not it's strong
enough to be to not be shredded by a black hole. Right,
So basically we may never be able to like go
to a black hole and see what's inside, right, it's
hard to imagine and and I hate to say never.
I disamber because it prescribes future generations intelligence and there's
probably some genius out there was a clever idea for
how to do it. It's not theoretically impossible to be
(23:41):
near a black hole. It's just practically very difficult, which
makes it, you know, a pretty tough engineering problem. So
we know black holes are out there, we know they're mysterious,
we know they contain some deep, dark secret. We don't
think they contain the anti universe. I don't believe they
contain worm whole. I don't know, you know, they don't
(24:02):
believe they contain worms or anything else weird. But I
would love to get to know what's inside a black hole.
I don't know about visiting one, or seeing one, or
getting too close to one and getting shredded, and desperately
want to know what's inside a black hole. Maybe side
will find my marbles lost for sure. All right, thanks
everyone for listening to Daniel and Jorge explain the universe.
(24:24):
Thanks for listening. Do you have a question you wish
we would cover send it to us. We'd love to
hear from you. You can find us on Facebook, Twitter,
and Instagram at Daniel and Jorge One Word, or email
us to feedback at Daniel and Jorge dot com
Hosts And Creators
Daniel Whiteson
Kelly Weinersmith
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