Can you undress a black hole?

Daniel and Jorge talk about whether it's possible to observe a "naked singularity"

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Episode Transcript

Speaker 1 (00:08):
Hey, Jorgey, do you ever feel guilty when we send
a probe to go poking around another planet? Guilty? What
do you mean guilty? I think we're just being curious, right,
I don't know. It's a bit presumptuous and forward, you know,
like what if I sent a drone into your house
to take pictures and samples? I see you mean, like
for me, we're disregarding the planets privacy. Yeah, like maybe

(00:28):
we should give them some morning so at least they
can get dressed before we show up with our cameras,
or maybe undressed, you know, maybe that's what they prefer.
That makes me wonder what an embarrassed alien looks like anyway,
and what account is not safe for work? I am

(00:57):
R Handy cartoonists and the creator of pH D com Hi.
I'm Daniel. I'm a particle physicist and I always get
dressed for work. Oh nice, that's a good disclaimer to
make in public. Even these days when everything is remote,
you still got to put your pants on when you
get started on your day, you know what I mean?
Known as the naked physicists, I definitely do not want
to be known for that. Absolutely not naked and Curious

(01:20):
could be the name of the reality show Daniel Naked Curiosity.
There you go, but welcome to our podcast. Daniel and
Jorge explain the Universe Wearing Clothes, a production of I
Heart Radio, in which we try to strip the mystery
for everything in the universe. We try to find everything
that makes you curious and peel back the layers, undressing

(01:42):
the confusion and addressing your questions and trying to make
sure that everything in the universe makes sense to you
and give you the bare facts about the cosmos and
everything in it, all the amazing things and all of
the mysterious things, and also the things that we don't
know if they exist. That's right, because we have two
ways to get surprised in our universe. One is to

(02:04):
go out there and see weird stuff that just doesn't
make any sense to us until we can wrap our
minds around it. And the other is to think of
weird stuff, what if this kind of thing exists? What
if that kind of thing exists? Is this even possible?
And then to go out and look for it. Yeah,
because a lot of times it seems like the math
tells us what can exist, and oftentimes we actually go

(02:26):
out there and find it. That's right. There's lots of
times when we make a mathematical theory that describes something
we see in the universe, and then we explore the
corners of it. We say, well, if these rules are real,
what else do they predict? What else should we be
looking for? And you know, some people think that the
universe is mathematical, that these rules are the ones that
control the universe, and so if they have a wrinkle

(02:48):
in them that predicts something weird, that might actually be real.
So if you are not into math, we have news
for you. You might be in math. As you might
be math, math might be you. Yeah. And and I
think a big example of that idea of thinking of
something first and then discovering is black holes. Right. Black

(03:08):
holes were first theorized by Einstein, and then people wondered
about it for a long time, and then we started
finding evidence for them, and then we actually just recently
took a picture of a black hole. Yeah, And more
than just wondered about them, people disregarded them for a
long time. People figured like, well, that can't be real.
That's evidence that there's something wrong with our theory. For
our theory predicts something as absurd and as crazy as

(03:31):
a black hole has got to be something wrong with it,
But then of course they found it, and so the
theory is not wrong, and that teaches you to follow
the math. And this happens all the time, even in
quantum mechanics, where we say, look, quantum mechanics predicts this
totally absurd thing that could never really be real, and
then you go out and you do the experiment and boom,
it actually israel and the universe is as weird and

(03:53):
as mathematical as we thought. Does that mean humans are
not as weird as we should be? Do you think,
like maybe we just to think weirder. Yeah, I think
that's definitely true. I think of all the various layers
of reality, the one we live in is the least weird.
I mean, we live in this sort of large stuff
that's not quantum mechanical and the slow stuff that's not relativistic,

(04:14):
and so our corner of the universe is sort of
very unweird, and if we were much much smaller or
much much faster than physics would be much much weirder.
Maybe that's just a perspective kind of thing, though, right, Maybe,
like if we were smaller or bigger. We might think
that's normal and our size is weird. Yeah, that's a
difficult mental inversion, but you're right, it might be weird

(04:36):
to think, Oh, my gosh, velocities add linearly in objects
have like smooth trajectories. How bizarre is that? It's hard
to put yourself in that frame of mind because this
is the only one we've ever had. But that's exactly
the point that physics tries to take us out of
our familiar frame of mind and make us realize that
the way we see the universe is limited, and the

(04:57):
way the universe really is could be vastly to friends,
And that's why we do these sort of mental and
physical explorations. And black holes are weird, right, They are
one of the weirdest things in the universe, and they
are definitely very weird. They are little pockets of mystery,
and one of the weirdest things about them is that
we cannot see what's in them. We can't go inside

(05:17):
a black hole or look inside a black hole, or
get any information from what's going on inside the black
hole to learn about these crazy corners of the universe. Yeah,
because what's weird about them is what's inside the actual
black hole? Right? What they call the singularity? That's right.
General relativity at least predicts a singularity inside the black hole,
although many other theories of physics, likede quantum mechanics objects

(05:39):
to the existence of a singularity, and various mathematicians suggest
the singularities are impossible in a physical universe. So then
the question is what is inside the black hole? Yeah,
there's a question of whether singularities can even exist, and
unfortunately we can't see the ones inside of a black hole.
So the question then is is it possible to see
a singularity outside of a black hole or a singularity

(06:03):
that's not a black hole? Yeah? Is it possible to
uncloak the singularity, to strip away the event horizon so
that as an observer you could directly see with your
own eyes this bizarre thing, this singularity of space. Such
a really fun, fascinating question. So to be on the podcast,
we'll be asking the question what is a naked singularity

(06:31):
and why doesn't it have any singular clothes? Even just
one pair of pants? Right, if it's a singularity, should
have one of everything, supposed to physicist who were three
pants or four hats? At a time. That's right, And
I love this name naked singularity. I mean, of course
there's the slight blush factor, but also it invokes this

(06:51):
sense that we could like really peel back the layers
of the universe and see the truth, the bare naked
truth of what's going on with space time. I guess
the question is, we don't even know if a singularity
is possible in our universe. I mean, it's theorized inside
of a black hole, but you can't see inside of
the black hole. Yeah, that's right, And so this is
an experimental question and a theoretical question. It's an experimental

(07:14):
question like could we see a singularity, what would it
look like? Can we find one? If they do exist?
And a theoretical question like what would it mean if
they can exist? What would it actually be like? And
then we'll get into this. But like, people don't even
agree about what a singularity is, that there's no singular
answer or a definition. There's a duopoly of singularities. Man. Well,

(07:35):
as usually, we were wondering how many people had heard
these two words together, naked and singularity at the same time,
And so, as usual, Daniel went out there into the
internet to ask people if they knew what a naked
singularity was. So thank you to everybody who have volunteered
to answer questions without any preparation. And if you would
like to similarly give answers to tough physics questions without

(07:58):
using any reference materials, please write to us two questions
at Daniel and Jorge dot com. So think about it
for a second. If someone as you on the street
or on the internet what a naked singularity is, what
would you answer. Here's what people had to say. I
have never heard of naked singularity, but I definitely know
what naked means, and I think I know what you

(08:20):
mean by singularity, so I would imagine it has something
to do with the very earliest of universe stripped of
all forces. Singularity basically means when all the matter condenses
down to one blob. For example, like all the gravitational
force starts to attract all the matter and it just
condenses down to one small blob, and that's you know

(08:45):
how people say our universe is gonna end naked singularity? Um,
I think might be when this blob doesn't feel any force,
any other force from outside the singularity, so it might
be naked to everything else in the universe. I'm not sure. Well,
singularity is an intense amount of matter and energy in

(09:07):
one point in space, so a naked singularity would be
similarity that we could see like a center of a
black hole if you if you took if you could
just see into the center. I think it's something linked
to a black hole. I think a naked singularity is
something like a black hole without a short shirt radios,

(09:29):
so a lot of mass on one point and it
would not be heavy enough to keep light to itself.
But I'm not sure if people agree upon if this
can exist. Maybe this is a black hole without an
event horizon, or maybe there's a start collapsing directly into
a black hole without the supernova. Maybe there's something with
other singularities, like technological singularity. All right, a lot of

(09:54):
people linked it to black holes, which is what we
were just talking about. And a lot of people had
heard the to words separately, not together, naked and singularity,
but maybe they had not heard of them together naked singularity. Yeah,
but I think the name of this thing goes a
long way to explaining it, as you can tell by
people's answers that pretty quickly put together the idea that

(10:14):
maybe a naked singularity is one that you could actually see,
the one that isn't dressed by a black hole. All right,
we'll step us through this, Daniel, First of all, what
is a singularity? Because I think I know what naked means,
and if you don't, I'm not going to be the
one explaining it to you. I've known since I was born.
I think, what's the definition of a singularity? And is

(10:35):
there a singular definition of it? Yeah? So this is
a fun question because you can have an idea about
something before you have like a really precise, theoretical, crisp
definition of what it is. And that's sort of the
case here with singularity. That's sort of like the vague
idea of a singularity, and then there's people trying to
actually work out, well, what do we really mean, like
mathematically when we talk about a singularity, And unfortunately there's

(10:58):
not a whole lot of Chris definitions. It's sort of
like two general ideas about what we mean about a
singularity when we talk about in the theory, like in math.
In the math and also in philosophy. Remember that almost
every field of science in the end was born out
of philosophy people thinking about tough questions and try to
figure out, like how do we make progress on questions

(11:18):
of like what is the universe? And eventually things get
crisp enough and formed well enough and mathematical enough that
like scientists can take over and actually make progress. So
some of these things still are on the boundary between
physics and philosophy because they're sort of like bubbling emerging questions.
And that's the situation here with this question about what
is a singularity? Yeah, so what are these two different

(11:42):
ideas about what it is? You said, there's two, yeah,
And so the first one is probably the one that
comes to mind, and most people think about a singularity,
and that's where the space sort of breaks down, where
something in space becomes unphysical, it becomes like infinite, something
that you figure like can't actually really happen. You know.
For example, a black hole, we imagine might have a

(12:02):
point at the center of it with an enormous amount
of mass in a physical dot in a point with
no volume, and that would be infinite density, and the
curvature of space there is described by general relativity, would
be infinite. And so we talk about that as a
singularity because general relativity breaks down there where the curvature
of space becomes infinite. Yeah. I think it's sort of

(12:25):
related to infinity, right, because infinity is pretty much kind
of the only thing that can break down math, right,
Like we don't really understand it, or it's sort of
like not defined in math, right. Yeah. In some cases though,
it depends on the application, Like and sometimes when physics
gives you an infinity, you say, well, that's wrong, that's nonsense,
that can't happen. Although other times in physics you can

(12:47):
have infinities, like the universe might be infinite in extent,
it might go on forever in every direction, and that
doesn't violate any principle of physics. It would mean the
universe has an infinite amount of energy in it, right,
Or the universe could have existed for an infinite amount
of time or could exist for an infinite amount of
times into the future. So sometimes infinity is allowed in physics,

(13:10):
not a big deal. Other times it doesn't work, and
it just depends on the theory. And in the case
of a black hole. The reason that we don't like
the infinity is that we describe what happens to space
and things moving through space based on how space is curved,
like how much is space bent by the presence of mass?
And you know, for example that like space around the

(13:31):
Sun is curved a little bit, which makes it natural
for an object like the Earth to move in a
circle around the Sun instead of what we would see
as a straight line. So you can make predictions about
what happens to something that moves through curved space. But
you can't do that if the curvature is infinite, Like
the equations just don't work. They give you nonsense answers.
And so the theory general relativity breaks down when the

(13:53):
curvature becomes infinite. So we call that a singularity of
space time. Right, it seems like it it comes to
singularity when something gets infinite in like a very short
amount of space or a short amount of time. Maybe
could that be sort of the one way to define
it or to understand it. Yeah, And it really can
be almost anything that can become infinite. You know, for example,

(14:13):
you can have an electron. Electron is a point particle
and it has a charge to it, and you can ask,
for example, what is the electric field around an electron? Well,
it depends on the distance you are from the electron.
But if the electron is a point particle, then you
can get as close as you want to it right
that distance can basically go to zero, which means that

(14:34):
the electric field or the force from the particle becomes infinite.
And so you can find these singularities not just in
sort of crazy exotic situations like the center of a
black hole, but also in fairly simple, straightforward situations like
an electron with all electrons are singularity. Is that what
you're saying, or mathematically, that's what the math would tell you.

(14:56):
So real electrons are not singularities, and that's because the
simple mathematical description just gave you isn't the right one.
What really happens when you get close to an electron
is that it creates lots of other particles around its photons,
which turned into quantum fluctuating positron electron pairs. We talked
about this on another episode. Is called renormalization, where you
redefine what it means to be the particle, and the

(15:16):
particle becomes not just a point but a bunch of
quantum mechanicals froth slashing around that point, and that becomes
our definition of the particle, which in effect limits how
close you can get to it. So quantum mechanics sort
of covers up the singularity there prevents a singularity from happening.
But in classical electromagnetism, if you just really did have
an electron with a point particle, that would be a singularity.

(15:40):
And so that's an example of how we don't think
that singularity actually happens in the universe because electrons are
not infinitely powerful points of charge. Okay, so that's one
definition of a singularity. It's like when something goes infinite
in a small amount of space or a short amount
of time. So what's the other definition of a singularity. Well,
there's this definition in philosophy of a singularity in space,

(16:01):
which is a path that is not extendable. Like you
can imagine moving through the universe and you can just
keep going right in the path you're on, can just
keep going, Well, what if you came to a spot
where your path just couldn't go anymore? And this, for example,
is what happens to a photon that falls into the
singularity inside a black hole or right doesn't go anywhere anymore.

(16:21):
It's not some other part of space. It goes to.
So it's like another way to look at a singularity.
It's like a weird deformation and sort of the arrangement
of space itself. I mean like a like a stub
in space, kind of like an abrupt end to space.
That's also called a singularity. Yeah, an abrupt end to space.
It's sort of like imagining that space has a boundary,

(16:42):
but instead of that boundary being like on the edge
of the universe, like we're all in some huge universe
that has you know, a crust to it, this is
like a boundary that's in a point, like a weird
spot in the universe, where like there's a point of
space there that's just not there, so you can't like
go there. It's a really weird idea. It's sort of
hard to get your mind around, but it's in some

(17:02):
ways equivalent to the other way of looking at a singularity.
You mean like it could exist in space, like a
stub inside of space. Yeah, it could exist in space
and like like a belly button or so many jokes
to make their absolutely, yeah, it could be just like
a weird feature of space where a particle that passes

(17:22):
into it doesn't emerge and that's another way to think
of a singularity. Right, just like belly bus, you know,
link goes in. When does it ever come out? Nobody knows.
Eventually it makes a black hole unless you're an audy
I guess. All right, well, now that's a good definition
of singularity. Now let's get into what a naked singularity
is and whether or not they're real. But first let's

(17:45):
take a quick break. All right, we're talking about naked singularities, Daniel,
and this is a safer work, right, we can talk
about naked singularities. Nobody's gonna get into trouble. That's right.

(18:06):
I had the singularity sign a waiver also, so we're
allowed to use the description of it as naked without
paying it any royalty. It's comfortable with itself, the singularity.
It's not self conscious singularity, alright. So singularity is either
like a stubb in space, like a belly button in space,
or just anything that kind of goes infinite in a

(18:27):
short amount of space or time. That's a singularity. So
then what is the naked singularity? Like something that is
like that, but it's not close, like it's not covered. Yeah, exactly,
it's just that simple. The idea is what a weird
thing to have in space? What is this bizarre thing
at the center of a black hole? What actually happens there?

(18:49):
And it's frustrating because black holes are always cloaked, right,
you can't see what's inside a black hole? Is there
singularity in there? Is there not? Is there something else
we're going on? We want to know? It? Frustrated and
have this weirdest part of space be hidden from us
by the event horizon. So then the question is it
possible to have a singularity that's naked, that's revealed to us,

(19:10):
a singularity that you could see from the outside, you
know that you could visit and investigate and then report
back to other people and maybe get some answers about
the nature of the universe and what it can and
can't do. Right, Well, the problem with the black hole
singularity is that it bends space and time, and so
it traps light, so we can't and everything else, and

(19:31):
so therefore we can see it or get any information
out of it. Right, Yeah, that's exactly right. The thing
that creates the singularity is an extraordinary density of mass,
and that mass also creates curvature of space around it,
which creates an event horizon, right, it means that there's
some point after which space has bent so much that

(19:51):
every direction forward, every path forward, eventually leads to the
center of the black hole. And you know, remember, the
event horizon itself is not like a physical objects. It's
just like a surface in space where once you pass it,
there's just no way to ever avoid hitting the singularity.
But it does mean that nothing that passes it can
emit light out of it, which means we can get

(20:12):
no information about what's going on beyond the event horizon.
That's what's so frustrating, because of course all love to
study the singularity, to see it, to row it, to
shoot particles at it, to hit it with a tennis
racket or whatever, but as long as it's behind an
event horizon, we can't do that, right, And so a
naked singularity then would be a singularity, but one that
you can actually like walk up to and get right

(20:34):
up next to it and look at it through a
magnifying glass and coke at it. Right, Yeah, exactly, that's
the idea. So if you have a picture in your
mind of sort of like the rubber sheet of space
where space gets bent by heavy mass, and the curvature
grows very very rapidly as you get close to the
black hole and then sort of goes to infinity at
the center of the black hole. Then image you should

(20:54):
have in your mind for naked singularity is more like
just a pin prick, like a point, like space is
mostly flat around the singularity, and then there's just this
point where the curvature goes to infinity very very quickly, right,
like a belly button, Just like a belly button. They
should have called this a belly button of the universe. Yeah,
bellybutton singularity. And in fact it works on multiple levels

(21:14):
because the same way that a belly button tells you
about like the origin of a person, it teaches you
but like their origin story and how they were created
through the placenta. Then a belly button singularity of the
universe can tell you something about the origin of the
universe because it teaches you about space, time and maybe
even helps you understand the Big Bang. Right, And so
I think belly button really is a great name for it.
I think now you just tress it too far there.

(21:37):
That was a little too much. But anyways, it is
sort of like something in space. So I guess the
question is, can you have a singularity without a black hole?
Or maybe you can have other kinds of singularities that
you could see, Yeah, exactly, And so that's the idea,
and people are embarked on this sort of like theoretical exploration.
They're like, can I make one in theory? Can I

(21:58):
satisfy Einstein's equations of the universe and have a naked singularity?
So it's like a way to explore the universe without
ever leaving your living room, just like can I arrange
this in reality? And you know, that's how black holes
were discovered, basically, as people trying to figure out, like, well,
we have these equations for how space and time bend
in response to mass, would they allow the creation of

(22:21):
this weird object. Let's see if the math says yes.
And the math said yes, And so that's where we
are with naked singularities, this sort of like exploring how
you might be able to make one, to figure out
is possible, is it allowed? What would it mean if
it is allowed, what would it mean if it isn't allowed?
All that sort of stuff, And so there's various ways
people have thought of theoretically to try to manufacture a

(22:41):
naked singularity in the equation right, Well, is it even
possible to have like basically a black hole without the
black hole? Can you have a singularity in space time
just like a black hole, but not have the black
you know, trap around it? Is that possible? The short
answer is, we don't know. Some people think it's impossible,
absolutely impossible. Some people think it might still be possible.

(23:03):
And there's lots of areas of investigation and sort of
a few paths people are going down and exploring the
idea of a naked singularity, and one is to create
a singularity using a black hole and then try to
remove the event horizon. What do you mean, how can
you remove the event horizon? Yeah, it's people actually writing
about this all the time. They ask like, could you

(23:23):
destroy a black hole? And we usually we say no,
but we actually had a whole episode about how to
destroy a black hole. And there is one possible way
you could strip away the event horizon, and that's if
you make the black hole spin really really fast. Because
remember that black holes are not just heavy objects that
curve space. The way that space gets curved is actually

(23:44):
quite complicated and depends not just on like how much
mass is there, but on its arrangement, and also on
how fast it's spinning, because angular momentum contains energy, and
space bends not just in response to mass, but also
in response to energy. And there's one class of black holes.
They're called curb black holes k E r R. And

(24:05):
these black holes are spinning. Now, if you take that
black hole and you convert a lot of its energy
into spin, you like, drop something into it which has
a lot of angle momentum but not a lot of mass,
and you can bring the angular momentum up past a
certain level, then the equations predict that the event horizon
will shrink until eventually it hits the singularity and reveals

(24:27):
the singularity. Wait, what too? More energy makes the black
hole smaller? Isn't that weird? Doesn't usually more mass and
energy make the black hole bigger? Yeah? Exactly? How to
spinning it more? Make it small? What you need to
do is somehow get it to convert its existing mass
into spin. So it's not just about adding another object

(24:48):
which is going to add overall mass. You need to
somehow get it to convert its energy into spin. Because
the location of this event horizon depends on the spin
and on the mass, so you have to somehow do something,
and nobody knows how to do this, which is like
totally speculating. Somehow get this black hole to turn its
mass into spin. And if you do that, they think

(25:09):
the singularity will remain at the center, but the event
horizon will essentially shrink because you're reducing the effective mass
by just turning it into England momentum. Oh wow, but
you would have to convert all of its mass into spin,
right or just or some of it, just some of it.
You need to cross some threshold. But if you read
the papers about how to do this, they say, like, physically,
we don't think bus is possible. So it's sort of like, well,

(25:31):
the equations predict that if you violated this basic principle
then the event horizon would disappear. That doesn't mean it's possible.
It's just sort of like there's a region of theoretical
space there where maybe if you could fix one problem,
you might be able to get into this interesting region
where the event horizon becomes part of the singularity. Can
you maybe make a black hole and make it mostly

(25:52):
out of spin, you know, like if you take a
whole bunch of I don't know, fidget spinners and frisbees
and tops, you know, and threw them out, spun them,
throw them all together to make a black hole. Would
that make a naked singularity that would still have more
mass than angular momentum, and so it would be a
spinning black hole and it would have a ring singularity
at the heart of it, but it would still have
an event horizon. So you need to somehow get a

(26:15):
black hole that has like more angular momentum than mass itself,
which is pretty hard to arrange and maybe impossible. All right,
So that's one possibility, doesn't seem very likely. What are
other ways we could maybe make a naked singularity. Another
way to maybe make a naked singularity is to find
a white hole. We talked about this also once on

(26:36):
the podcast. A white hole might be like the opposite
of a black hole. A black hole is a region
in space where if something falls in, it can't ever leave,
and a white hole is a region of space where
things can only leave right they can't enter. And so
a white hole in general relativity is sort of like
the time reversal of a black hole. Like take a

(26:58):
black hole as a star collapses and forms an event
horizon and things get sucked into it. A white hole
is like something that goes the opposite direction, like spews
stuff out and then eventually boom, A star appears. Interesting.
Now does it have a an event horizon like a
black hole or is there such a thing as that

(27:19):
the opposite of a event horizon. So it wouldn't have
an event horizon. It would just be like a point
in space where stuff is coming out of right, Like
things are just flying out of this white hole the
way like things fall into a black hole, things come
out of a white hole. And we sometimes think of
a white holes like the other end of a wormhole.
You have a black hole connected through space somehow be

(27:41):
a wormhole to a white hole and things that fall
into the black hole and come out of the white hole.
And so the white hole would be like a naked singularity,
be at this weird point in space where you know,
some of these metrics of spacetime become infinite, but not
surrounded by an event horizon. I mean you can see it.
Stuff is coming out of it at you. It's emitting light,
or old socks or typewriters or whatever is coming out

(28:02):
of this white hole. You can see those things, and
so you can observe it. And so in that sense,
it's a naked singularity because it's a singularity and it's
something you can actually look at. Right, it would just
look like a really bright pinpoint, right, like a star,
but really really small. Yeah, And it might look like
a bright pinpoint if it happens to be emitting gamma
radiation or whatever, but it might also just look dark

(28:23):
at some points if it's not giving off anything. You
can't predict what a white hole is going to give
out because it depends on what's inside the black hole
it's linked to, and that's not something we can know. Okay,
so that could also be a naked singularity. Are there
any other possibilities can you have? I don't know, like
an infinite charge somehow accumulated, or something else that doesn't

(28:46):
bend spacetime. Well, really, the only kinds of singularities we
can consider our gravitational ones, because everything else, like charge
and particles, these are governed by quantum theory, and quantum
theory prevents these kind of singularities by having uncertainty and
by having fluctuations from random particles. The reason for example,
an electron doesn't actually have negative infinite charge is because

(29:06):
it creates this swarm of particles that surrounds it. And
so quantum mechanics doesn't really allow for singularities in the
same way. So they all have to be sort of
gravitational or like geometric. Singularities of space time have to
be about like the shape and structure of the universe.
And so, for example, the Big Bang was a singularity, right,
that's a timelike singularity. It is one that existed and

(29:28):
no longer exists at the moment in time when the
universe had essentially infinite density, and that was definitely naked
because if you were around at the Big Bang you
could have seen it. Yeah, I suppose. I don't know
what it's like to observe if you're inside and infinite
singularity of infinite density. I don't even know what that
really means. It's like staring at your own belly Patty.

(29:50):
It's like being inside an infinite belly button. And remember
that general relativity doesn't tell us what happens during a singularity.
General relativity tells us that, you know, space get denser
and denser and denser, or a curvature gets infinite, but
it breaks down at that point. You can't calculate with
general relativity and say, what would happen if I did this,
or if I had an eight ball flying through space

(30:11):
and it hit a singularity, what would happen? It just
cannot predict those things because general relativity breaks down when
the curvature becomes infinite. So we need some new theory,
something else to describe what would actually happen to physics
of what would happen in a singularity. Alright, let's talk
about whether or not naked singularities are real and if
we could see one, what would they even look like?

(30:33):
But first let's take another quick break. All right, we're
talking about naked singularities being free, being visible, but also

(30:55):
being almost infinite at the same time, and it sounds
like there are a couple of possibilities. White holes or
super spinning black holes are two possibilities. Daniel, you said
there's another kind that could be out there, like a
boundary point in space. Yeah. These are just points where
a path of a particle ends. And this one, to
me is like the most fun because I feel like

(31:16):
we're sort of trapped in space like we're in this universe,
we're in space. We're trying to understand what are the
rules of this universe, but we're stuck sort of inside it,
and it's hard to get your mind around the universe
when you're looking at it from the inside. People are
always asking us, like what is space expanding into or
with outside of space? Because I think they're trying to
grapple with the notion of the whole universe and its rules,

(31:38):
and they want to do it by looking at it
from the outside. And so if you can find like
the edges of the universe, that gives you some sort
of sense for like you know what the rules are,
what the boundary conditions are. And so this this idea
of a singularity is this like point in space. It's
like a point that's an edge right where a particle
flies in and just doesn't ever go anywhere else. It

(31:59):
doesn't leave not there anymore. It's just there is no
more space. So to me, this is one of the
most fun ideas because it's hardest to think about, but
also if you could actually see it, you'd be like, whoa,
what is this? There's like a wrinkle in space is
like a literal belly button in space? What is going on? Yeah,
it'd be like a prinkle, like a pinch in space. Yeah, exactly,
like a pinch in space. I would love to see

(32:20):
a pinch. But would it become a black hole though,
like when things get trapped inside of it? Well, it
depends on what made it right, Like, first of all,
there's nothing inside it. If we're talking about a boundary
point in space, the inside of the singularity is not
part of the universe, Like the particle just doesn't exist anymore,
Like it's gone from our universe, like it's gone. The
path just ends, right, Like you can think about particles

(32:41):
as having worldlines, like they move through space and time.
The singularity is a point where, like a worldline ends,
it doesn't exist anymore. It's not like in there and
you can't see it. It's just not anywhere anymore. Like,
so what would happen to the particle? It would bounce back,
like it would have to back out, or would it
really disappear from our universe? It would disappear or from
the universe. That's what it means for your world line

(33:02):
to end. In that second definition of a singularity as
a non extendable path, that's what a singularity is, a
point where a particle, if it hits it just doesn't
continue anymore in existing, which is really weird and hard
to think about. What happens to its energy? It just
it's energy disappears from the universe exactly. We talked about
in another episode recently about how general relativity doesn't require

(33:24):
that energy is conserved. It literally is like falling into
a hole. Yeah, but the question is can that thing
actually exist? And this is the kind of thing people
are trying to figure out, like our naked singularity is
real in the sense experimentally, like do they actually exist
out there in reality? Could we see them and study
them the way we can black holes? Or do they
even exist theoretically? Like can you construct the equation in

(33:47):
a way that predicts that they do exist? Whether or
not they actually do in reality is one question. Whether
we can make equations self consistent that describe them mathematically
is a second question, Right, Well, it seemed to work
for black hole holes, like general relativity predicted black holes
and they're sort of consistent and we've seen them, so
doesn't that answer the question? Doesn't that mean yes, that

(34:09):
we can't theoretically make these, except that we know that
general relatively breaks down at the singularity, so we don't
actually know if this is singularity there. Like we know
the black holes are real, yes, but you don't have
to have a singularity inside a black hole to have
a black hole, right, We don't know if there's actually
a singularity in there or not, or something else weird
is going on. We don't have a theory that describes

(34:30):
correctly what happens at the center of a black hole.
So another theory, some quantum gravity theory like glue quantum
gravity might give us a different description of some very
dense mass that's bending space in a weird way that's
not a singularity. So we know that the Big Bang happened,
but we don't really understand what it was. And in
the same way, we know that black holes exist, but

(34:51):
we don't know what's inside them. So we don't actually
have hard proof that there are those gravitational singularities inside
a black hole, or we also and that proof that
they don't exist, right, because that's right. It could be
that quantum physics is wrong in general relativity does maybe
work at the center of a black hole. Well, it
could be that there's some kind of singularity at the
center of a black hole. But we know that general

(35:12):
relativity as it stands can't describe them. You know, it
just basically gives up. It fails there. And that's why
they're so fascinating because we'd love to see general relativity
fail because how it failed, what actually happens there could
give us a clue about how to fix it. That's
why seeing a naked singularity would be so much fun,
because it would be clues to like ten Nobel Prizes

(35:33):
in an afternoon in a singular place, like an infinite
concentration of Nobel prices. Yeah, and one of the ways
that people explore this theoretically is they say, well, here's
a universe. Can I figure out how to make that universe? So,
for example, we just talked about having a hole in space,
a place where paths end, and general relativity tells us
that any configuration to space that smooth can exist, though

(35:56):
it's sometimes tricky to figure out, like how do you
arrange the mass to get that bending of space? And
so what people are doing now is trying to figure out,
like wealthy ioretically, can I construct a universe in which
I have a naked singularity. And they're doing all sorts
of complex simulations, and they figured out ways to make
singularities happen in simulated universes, but not simulated universes like ours.

(36:17):
Simulated universes with like five dimensions instead of three dimensions,
or different dimensions that like roll up and bend Weirdly,
nobody succeeded in making a theoretical naked singularity in a
universe that looks like ours. I see, you need more dimensions,
You need like some extra juice, Yeah, exactly, because the
rules are different in other dimensions. Right, if you have

(36:38):
five dimensional space or nineteen dimensional space, and the way
space bends and twists and wiggles is totally different than
an our universe. And this has led people to wonder, like,
if it's so hard to make a naked singularity, maybe
they're just impossible. And so there was this idea in
nineteen sixty nine by Roger Penrose. Recently when the Nobel
Prize for thinking deeply about singularities and black holes. It's

(37:00):
called the cosmic censorship conjecture, and it's the idea that
the universe will always hide a singularity, so no naked
singularities can exist because the universe will always find a
way to block you from seeing. There's a certain prudishness
to the universe, and that's because you know, anything that
is singular would distort spacetime so much that you could

(37:22):
never see it. Is that kind of the idea. There
isn't really a firm idea. It's just like this idea
makes people uncomfortable, so maybe there's something in the universe
preventing it from happening. And it's very similar to the
idea people had about black holes. Like when people heard
about black holes originally they're like, that seems bonkers. I'm
sure that that situation will never arise, or something about
the universe will prevent it from happening, just the way

(37:44):
that like, electrons are not singularities because quantum physics prevents
it from happening. There's something inherent. It's not like an accident,
and it's not like a conspiracy. There's just something about
an electron and quantum physics that prevents that from happening.
So the ideas maybe there's something going on, but it's
really just a conjecture. It's not like there's a good reason.
It's just like, boy, I kind of hope the universe

(38:05):
prevents this from happening. That was penn Rose's original idea.
Oh I see, it's like he didn't want there to
be singularity. Yeah, you felt uncomfortable. He's like, this doesn't
seem right, and so there must be some reason why
they don't exist. And it sparked a lively debate in
the field. Since then, other giants of black Hole thought,

(38:26):
Stephen Hawking and Kip Thorne and John Preskill were having
like a debate about whether naked singularities could exist, and
they decided to make a bet. And so Hawking bet
Preskill and Thorn that naked singularities are impossible. But then
how would you settle the bet? You would have to
see one or not see one, which is you know
that could never happen. Yeah. Well, actually I think they

(38:48):
were even just wondering, like, theoretically, could you find a
solution to the Einstein equations? Could you describe a universe
theoretically that had a naked singularity in it and didn't
break any other rules? And a few years later some
guy in Vancouver came up with like one very specific,
crazy universe in which you could get a naked singularity,
and so Hawking was forced to concede the bet because

(39:10):
of this very specific exception that everybody agreed you could
never have in reality, and so he lost the bet.
But then they reformulated the bet, you know, removing this loophole. Oh,
I see, so you could have a singularity, just maybe
not in our universe. Yeah, exactly in our universe. It's
maybe impossible. To help, it's maybe impossible. But you know,
there's two ways to explore the universe. One is like

(39:31):
have an idea theoretically proved that it's possible theoretically, and
then go and look for it to see if your
idea is correct. And the other is to actually just
go out and look for the stuff. Like if we
saw a naked singularity, that would sort of settle a
question of whether they're possible theoretically, and then the theorists
would have some work to do to figure out how
to describe it and what does it mean. And so
maybe the more interesting thing is, like, let's just go

(39:53):
look for one. What would it look like? Right? Yeah,
I guess that's the last question I have here is,
you know, what would a naked s gularity look like?
Would it look naked. Would it look shiny, you know,
would it look like a black hole? Would it would
it just you know, look like a weird pension space.
What should we be looking for? Yeah, well, people don't
really have a clear idea. There's lots of different ideas

(40:14):
about what a naked singularity would look like, because there
are different ideas for what a naked singularity would be.
For some people, it would look like nothing. It would
just look like a little hole in space, and the
only way to see it would be like to observe
particles disappearing as they pass into it, as for sort
of the boundary condition, and that'd be pretty tough. It
would be infinitely small too, write like, you know, it

(40:35):
would be maybe hard to see an electron like fly
right into it. Yeah, exactly, So that's pretty tough to
ever spot. Then there's the other kind of singularity, you know,
that one that's like maybe a white hole where things
can come out of it. These could produce massive amounts
of radiation. As you said earlier, a white hole could
be very very bright. They could be glowing. And some

(40:56):
people think that this could be the actual explanation for
some weird stuff we see in our universe. We see
things like gamma ray bursts and fast radio bursts, sources
of really intense radiation that currently do not have any
explanation in known astrophysics, and so it's always very tempting
to say, ah ha, here's this new weird thing I'm
thinking about. Maybe it explains this old weird thing we've

(41:18):
been seeing. So, you know, it's not a great argument,
but the idea is that a naked singularity might be
like a very very bright point, you might explain some
of the mysterious sources of energy, right that we see
in the universe. Yeah, exactly. You know, if we did
see one, to be an opportunity to study something new,
something we haven't ever seen before, something that follows the
rules of the universe, but maybe different rules than we're

(41:40):
familiar with, or follows them in a new way that
we weren't aware it was possible, And that's a great
opportunity to figure out, like, what are the underlying rules?
How does this universe actually work? Yeah, it'd be great
to see one because it would tell us a lot
about general relativity and quantum physics and help us kind
of figure out what's going on with the tool yeah,
And just like the belly button tells you about where

(42:02):
you came from, it could tell us about the origins
of the Big Bang. You know, one of the most
famous singularities in history, of course, is the Big Bang.
We think that the universe probably had this moment of
infinite density, but it's not something that we understand even theoretically,
like we can't calculate what caused it or calculate what
happens during the singularity. So being able to see one

(42:22):
and study it would really give us a handle on that,
and it might also really help us think about future singularities.
Future singularities might exist like the Big Crunch, you know,
we could be heading for a new singular right yeah,
but not for a while though, right not until after
this podcast drops at the very least, so I have
time to clean my belly button. Yes, you definitely do.
The idea there is that the universe could slow down

(42:44):
its acceleration and turn around and collapse back into a
tiny point. So there might be a new singularity in
our future. And you know, there are other kinds of singularities,
you know, Singularities are cases where things go infinite. So
another potential future for the universe is something we all
the big Rip, where the acceleration of the universe doesn't
slow down, but it continues and accelerates and eventually goes

(43:06):
to infinity, and that would also be a singularity. Be
the other kind of singularity with the universe is torn
apart at infinite sping, and then the whole universe would
be a singularity. And then the whole universe would be
a singularity, just like if we had a big crunch,
you would have the whole universe as a singularity. That
would be infinite density. The big Rip would be a
singularity of infinitely accelerating expansion. Man. That would be like

(43:29):
the universe ripping out its clothes and saying I have
my naked singularity exactly, And neither is one that we
want to experience. But maybe to get a better handle
on what that would be like and when it might happen,
it would be great to spot the naked singularity floating
out there in space so we could study it and
get a handle on how this universe works. All right, well,
we should all keep an eye out for naked singularity.

(43:52):
Let us know if you see a belly button floating
in space, shiny one you know, stay away from the
dark ones. All right, Well that was pretty you staying.
I feel like I learned a lot about nakedness and
singular poison space. Yeah, alright, So maybe the next time
you look out into space, think about what could be
out there hiding, what could maybe be right in front
of you. There could be singularities and singular things and

(44:17):
events in space right in front of our noses. Thanks
for joining us, see you next time. Thanks for listening,
and remember that Daniel and Jorge explained. The Universe is
a production at I Heart Radio. For more podcast from

(44:37):
my Heart Radio, visit the I Heart Radio Apple Apple Podcasts,
or wherever you listen to your favorite shows.