Could black holes actually be fuzzballs?

Daniel and Jorge talk about whether the dark massive objects we've observed could be something stringier and stranger than black holes.

 

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Episode Transcript

Speaker 1 (00:08):
Or hey, does your family have any pets these days?
We have a wild rabbit that les to hang out
in our yard. Does that count? Are you it's pet
or is it yours? That's a great question. I'll have
to ask the rabbit. Do you have a dog? Right? Yes,
we have a wonderful little dog named Pepito, an immigrant
from Incinada. Now, is he called Pepita because he's he's

(00:29):
actually peppit or or a seed? He is quite peppy,
but he is not a seed, but he came with
that name, so we don't actually know why he was
called Peppita. But interestingly, he does seem to violate the
laws of physics. Wait, what what do you mean your
dog travels back in time? Is it actually from the teacher? No,
he's amazingly a short haired dog, but seems to shed

(00:51):
enough hair that we find these incredible fur balls around
the house. And that is why we don't have a pet.
Does a dog actually clean up after itself at least? Oh?
Absolutely not. He just seems to turn dog food into fur.
But how does that violate the laws of physics? Because
I swear the fur balls he produced I have more
masks than the food we're feeding them. What Maybe the

(01:12):
dog is from the future. Maybe dogs know more about
physics than we do. That's an extraordinary claim. Daniel, are
you sure about this? Have you actually run the experiments?
If you wait, how much food you've give him versus
you measured the mass these furballs. I'm still waiting to
hear back on my grant proposal from the Daniel Science
Foundation to study your dog. It's very niche organization. Sounds

(01:33):
like you have to work on a no hair theorem
for your dog. Hi am poor handmade cartoonists and the
co author of Frequently Asked Questions about the Universe. Hi.

(01:56):
I'm Daniel. I'm a particle physicist and a professor at
uc or Rhyne, and I'm no longer the hairiest thing
in my family. Oh that's good. Who's the Who's the
next in line for your title? The dog is number one,
and I'm number two, and who's number three? I think
I want to answer that question exactly. Some things are
best left of mystery in this universe. I believe it

(02:18):
that as a mystery in the listeners imagination. Welcome to
our podcast. Daniel and Jorge Explain the Universe, a production
of I Heart Radio, in which we dig into the
hairiest tangly mysteries about the universe. We want to understand
how everything works. We want to pull it apart and
straighten it out for you and for us. We want
to walk you right up to the place where our

(02:39):
brains get twisted into not trying to understand how this
universe works, how we can describe it all using simple
mathematical equations, and how we can talk about it to
each other, to other physicists, and to you and to
your dog. Maybe because it is a pretty incredible universe.
It's a dog gone universe. And we love to answer

(02:59):
questions here on the podcast, all kinds of questions, amazing, incredible,
deep questions about the universe, and also pet questions that
people have about how things work, and sometimes questions about
their pets. I think if you offered my dog like
a scratch on the head or the answer to one
of the deepest questions in the universe, probably go for
the scratch on the head. Maybe a scratch on the
head is the answer to everything, Daniel. Seems like a

(03:21):
pretty simple answer but deep profound at the same time.
We all want a little scratch in our hands maybe
the answer is the sort of scratch on that internal
itch in your mind, the one that makes you curious
about how everything works. Or maybe it's all relative as
Einstein set you know, to dog, Maybe a scratch on
the head is the answer to the universe. Well, we
already know the answer to life, the universe and everything.

(03:42):
That's forty two. We just need to know what the
question was. How many scratches to your dog do you
have to give to for it to be happy? Definitely
more than forty two. I'm on like forty two never
seems to lose interest. Sounds like you have a greedy pet.
Petpito is a wonderful addition to our family. We do
like to answer questions here in the podcast, and we
like to answer questions not just that people have in

(04:03):
mind that are they're curious about it, but also questions
that even physicists are answering at the cutting edge of
our knowledge of the universe. That's right. The goal of
physics is not just to explain why cannonballs fly over
castle walls or why the Earth goes around the Sun,
but to explain everything in the universe. We seek a unified,
holistic description of the entire universe in terms of a

(04:27):
simple equation the basic rules by which the universe runs,
and that means that we have a pretty tall order.
We have to explain everything that's out there. One thing
that breaks the rule means the rule is not the
right rule. So we go out there and look for
the most extreme, the craziest, the bonkers situations where our
understanding of the universe bends and breaks and snaps. That

(04:50):
also gives us an opportunity to be creative and think
about what is out there beyond our understanding. Yeah, because
there are still big questions about the universe, big holes
in our a theory of how everything works. May one
of the biggest holes in our theory and our understanding
of the universe is actually a hole, or at least
we call it a hole. These objects that we call
black holes are an enduring mystery and really capture the

(05:12):
fascination not just of scientists but of the general public
because they are so weird. We've been studying what we
think our black holes for a few decades now, and
yet deep questions remain about what might be inside them
and if they are in fact black holes after all,
you mean, they might not be holes. Maybe they're more
like a ditch, Is that what you're saying, more like

(05:33):
a dog, like something a dog would do in your
yard to bury a bone. Well, they are very frustrating
to study because you cannot see them directly because they
are black, and so proving that something is a black
hole is really quite challenging because you have to develop
theories for how a black hole would look different from
some other idea that also looks black. And you can't,

(05:54):
of course go inside a black hole. So any proof
that a black hole exists has to come from the outside,
which means it has to be a little bit indirect.
That forces us to develop like clever theories for what
might be going on inside and to try to find
hints for how that inside might somehow affect the outside
where we live. You have to say, Daniel, I felt

(06:14):
a little betray when you told me that black holes
might not exist. I feel like we've been talking about
them as if they exist for so long and then
suddenly tell me that it's just kind of a little
bit of a theory right now, we don't actually know
they exist. Yeah, Well, there's always nuance to this understanding, right, Like,
in the end, what do we really know about the
nature of the universe. We have experiments which verify our models,

(06:35):
but there are always questions there. There's always a level
of refinement. There's always more to learn about what's really
going on out there in the universe. And black holes
are very slippery because they are so indirect. Unlike electrons
or other things. You can't observe them directly. You can
only see their influence on the parts of the universe
that are near them. Well, that's a philosophical question. Can

(06:57):
a black hole be slippery? You lose grasp of a
black hole? I guess you studied it with physics. Theoretically
and conceptually, they are very slippery. It's hard to hold
a black hole in your mind. And you know, we
don't even really have a great idea for what a
black hole is, put aside all the crazy alternative ideas.
Even the concept of a black hole is not super

(07:19):
well defined right now in modern physics, because we have
two descriptions of the universe, quantum mechanics and general relativity,
and they disagree about what might be happening at the
heart of a black hole. Yeah, it's hard to hold
a black hole in your mind, and also in your hand.
I hear, that's a bad idea, not recommended. Leave that
black hole at the dollar store. Even if it's just

(07:39):
a dollar, it's not worth it. Can you play catch
with your pet with a black hole? Depends on how
much you like your pet. I guess my pet does
seem like a black hole. He just like inhales. All
of that dog food is incredible, and those head scratches
as well, I'm sure. But it is interesting that black
holes may not be actually black holes. They could be
something else. Physicists think, maybe something fuzzy, because in the

(08:00):
end we are left to infer what might be in
those crazy dark patches of space that we can't see directly.
So theorists have been very creative coming up with all
sorts of alternative suggestions for what might be sitting there
in the blackness to be On the podcast, we'll be
asking the question, what if black holes are actually fuzzballs?

(08:26):
Daniel at these fuzzballs or fun balls? Are they fun fuzzball?
I don't think they would be very fun to fall into,
even if they are actually part of the universe. It's
never fun to fall into a hole, but they are
fun to think about and to imagine, and all the
artists conceptions of fuzzballs I fund on the internet are
pretty fun to look at. I think anything on the

(08:47):
Internet is probably fun to look at. Out to a
point perhaps to be careful about googling fuzzy balls on
the internet, though, or any kind of balls really, or
really anything on the Internet. Be careful of the Internet
in general. You might fall into a black hole looking
up random things. But as usually, we were wondering how
many people out there had considered the question where their

(09:09):
black holes could actually be fuzzballs. I imagine this is
not a question people ask themselves every day. That's the
job of physics, though, right to raise the deep dark
questions about the universe, sorry, the deep dark questions, and
the fuzzy questions as well. Daniel went out there into
the Internet to ask people what is a fuzzball? So
thanks very much everybody who volunteers for these. If you

(09:31):
would like to participate for a future episode so that
other people can hear your ideas about some difficult questions
in physics, please don't be shy. Right to us two
questions at Daniel and Jorge dot com. Here's what people
have to say, possible is a type of baseball that
it's playing the windowsill. And I'm sure I'm right, but

(09:54):
it's not this type of baseball, not you asking me about.
And I'm really curious what would be it? So what
is fusiball? Fussiball? It sounds like something a cat would
choke up. I've heard of the no hair theorem for
black holes, so I'm guessing a fuzzball is the inverse

(10:15):
theorem for white holes. A fuzzball is a little bit
of lint that you pick off your sweater. I don't
know what a fuzzible is, but if I had to
take a guess, I think it's a collection of nucleons um.
I don't know, all right, A lot of people associated
this with pets as well. I didn't give people clues

(10:37):
about black holes. I just wanted to know if they
had heard the idea of a physics fuzzball. Someone thought
it was maybe a type of pitch that you do
in baseball. Isn't they also a drink? Isn't there a
drink called a fuzzball or something? Everything is a drink
these days? Some people they did associated with maybe black holes, right,
They mentioned no hair theorem. Yeah, that's another tortured analogy

(10:59):
in physics whether black holes have hair or not. So
fuzzballs are sort of the other extreme. They're like the
hairiest possibility for a black hole. That doesn't necessarily make
them white holes. Though someone mentioned cats that they like
the balls that cats regurgitate, yet another reason not to
have pets. That's are wonderful additions to the family. Man,
I encourage everybody out there to adopt a dog, or

(11:21):
a cat or a wild rabbit. So this is an
interesting question. Are black holes actually fastballs? I'm curious to
know how this came up, Like who's that in their
couch one day and thought, hey, I wonder if a
black hole could be a fuzzball. Well, there's a big
opportunity there in physics to solve one of the deepest
outstanding questions, which is who describes the universe that we

(11:41):
live in. Is it general relativity that tells us that
space is smooth and continuous and classical, that objects move
in smooth paths through that space, or is it quantum
mechanics that tells us that everything is discreet and that
objects don't have smooth classical paths. They have probabilities to

(12:02):
be here and then probabilities to be there, but they
don't have to go from here to there, and that
space itself might actually be discreete. These two things are
in conflict at the heart of a black hole. The
description of a black hole in general relativity is inconsistent
with our understanding of quantum mechanics. So there's definitely an
opportunity here to be creative. Well, at least the conflict

(12:23):
is inside of what we think might be a black hole.
We don't know exactly. We don't know what's out there
in the universe, but whatever is out there in the
universe has to be following some rules, right. We think
that the universe does follow laws, and that we can
discover those through creativity and experimentation. And so something is
happening out there. And if we could only see what
was going on at the heart of a black hole

(12:45):
or whatever thing is there in those black spots in space,
then we could get a clue as to what rules
it's following. All right, Well, let's dig into it, and
let's start with the basics. I guess for those listeners
that are not so familiar with black holes, Daniel, what
are the basics of black holes, Why are they? Why
do we think we've seen them? So it comes out
of predictions from general relativity. About a hundred years ago,

(13:06):
Einstein developed his theory that gravity is not a force
between two objects with mass like Newton thought, where the
Earth's gravity, for example, pulls on an apple or the
Sun's gravity pulls on the Earth. Instead, Einstein said that
space is bent by the presence of mass. But you
can't see this bending directly, Like you have a chunk
of space in front of you. It would look the

(13:27):
same if it was curved or not curved, until you
try to pass something through it. You shine light beams
through space that's not curved, for example, and they just
go through parallel. You shine light beams through space that
is curved, then they change direction. But because we can't
see that curvature directly, like with our own eyes, then
it looks like there's a force there. It's sort of

(13:47):
like if you were watching a soccer game and you
could only see the ball and not the players, you
would imagine, oh, there's something out there applying a force
to the ball because it's changing direction, right, And the
same way we see things moving paths that don't seem
natural to us. The Earth moves in a path around
the Sun, so we imagine a force of gravity, and
actuality is just space being curved. So Einstein came up

(14:09):
with this description of gravity as bending of space, and
people played with it and thought, well, how much can
space get bent? And it's about a hundred years ago.
People came up with this solution to Einstein's equations that
predicted that if you've got enough mass in one little spot,
it would compactify itself so much that space would curve
infinitely and the things that got really close to it
would be trapped forever. It's kind of natural to think

(14:32):
of gravity as a force, right, I mean, we sort
of looked at electromagnetic forces. We saw magnets, you know,
repel each other. We see that you can push against
your chair and things like that. Those are still forces, right,
and so it was I guess natural to think of
gravity also. And it is natural to think of gravity
also as a force. Yeah, there are definitely forces in
the universe, and we've been able to describe them with theories,

(14:52):
first classical theories like of electromagnetism and now quantum field
theories of electromagnetism. So it's reasonable to say a b
gravity is a force. Einstein's description of gravity is that
it's not a force, is that it's a bending of space.
It's a fictitious force that comes out of our inability
to see that bending, and fictitious forces like this occur,
and lots of other situations. Imagine, for example, you are

(15:15):
on a Merry go Round and you try to throw
a ball to your friend. Well, the ball wouldn't move
in what looks to you like a straight line because
the Merry go Round is spinning, and so you might imagine, oh,
there's some force they're pushing the ball sideways. It's a
fictitious force. It's just because your Merry go Round is spinning.
Is no real force there. And so that's just Einstein's
description of it. And you know, that works really well,

(15:36):
and it predicts lots of things in our universe, and
it's been tested out the wazoo. But fundamentally it is
inconsistent with quantum mechanics. And yet as we look out
into the universe, we do see some evidence for these
black holes being out there. Well, I think that that's
why you brought up general relativity, is because black holes
were originally thought of because of this idea of relativity, right,

(15:57):
I mean, it was initially kind of a theoretical concept.
For about fifty years, it was only theoretical. People were
playing around with this in the math you know, Einstein
came up with this description of the universe, and then
people are explored it mathematically and said, well, what else
can this do? What is this predict about the universe?
And this is a pretty basic process in physics, right.
We come up with a description of what we see,

(16:17):
what we think we understand, and then we tested in
other scenarios. We try to understand its limitations and its strengths.
And so people playing with the mathematics came up with
this prediction of a singularity, although it took them a
long time to even develop the mathematical concept of an
event horizon, that something coming close to this object in
space would be trapped and never be able to escape.

(16:40):
And it was more than fifty years before we saw
sort of any evidence that these things were actually out
there in the universe. But I wonder if someone have
come up with the idea of a black hole without
general relativity, Like can you just imagine something having so
much density and so much maths that the force of
gravity is too much even for light. Yeah, the idea
of an object so massive that it might pull light

(17:01):
to its surface pre dates general relativity. It comes from
like the middle of the seventeen hundreds, where people were
thinking about very massive objects. So even in Newtonian gravity,
people were wondering, like, is it possible to pull on light? Remember,
back then we didn't even know what light was. The
theory of light as electromagnetic radiation didn't come to like
a hundred years after that. So people have been playing

(17:22):
around with these ideas before relativity. Wait what So then
people came up with black holes in the middle of
the seventeen century. Not the name maybe, but you know,
if you imagine a planet so dense that it trapped light,
then that's basically a black hole, isn't it. Yeah. It
was seventy four a guy named John Mitchell was wondering
what happens if you make a star so massive, it's
gravity so strong that essentially it's escape velocity would be

(17:46):
at the speed of light. He was just doing a
mental thought experiment, and he thought, well, any light that
leaves that would not be able to escape, and it
would essentially come back to the star. He called these
things dark stars, not black holes. M interesting. Wow, So
maybe we should just call black holes dark stars, although
dark stars are now used to describe something else that

(18:07):
we talked about on the podcast recently, which is a
different quantum mechanical version of a black hole. So that
name has already been used twice. It's in there like
an International Copyright Office for physics names. If you file
an nobody else can use that name. Shouldn't there be one?
Like why if I come up with a new consept
then I call it a black hole? Can I do that?
You can try. I don't know if anybody is going

(18:27):
to use it. It's sort of the wild wild West
out there. All right. Well that's the basics of black holes,
and so let's get into whether we see black holes
and whether they're even holes at all. They might not
be holes, they might be fuzzy balls. But first let's
take a quick break. Alright, we're talking about pets. I

(18:55):
guess holes and black holes and fuzzballs. Somehow it all
makes sense because pets are fuzzy usually, and black holes
are bad pets. Please don't get a black hole for
your pet. Yeah, it'll eat everything, I mean literally everything
in your house, and then your neighbor's house, and then
your neighbor's neighbor's house, and then your neighbor's neighbor's pets
as well. But yeah, we're talking about whether black holes

(19:16):
are actually hold. Maybe they're not black holes, and they
might be something called a fuzzball. Is that the actual
physics name fuzzball? That is the actual physics name a fuzzball.
And so with the whole judgment until you hear more
about what it is. But I think it's not a
terrible description of this theoretical idea. Well, let's find out.
Now we're talking about the basics of a black hole,
which is like a play sorce. Space is so bent

(19:39):
by the density of matter that an energy that it
sucks up even light. Now, Daniel, we've seen black hole now, right,
a couple of years ago. Now, they've had pictures of
black holes, so we know they exist. There are pictures
on the internet of black holes that look like big,
giant black holes. Yeah, if there are pictures on the Internet,
then it must be true. Right, I've also seen pictures
of Jedi warriors on the internet. Are you saying NASA

(20:01):
put out tissues from images. No, Unfortunately, I'm going to
give you a very legalistic quibble about the definition of
the word seen. Right, So we have an image of
a black hole, but does that mean that we have
seen a black hole? I think if you have an
image of something that you've captured, then yeah, you've technically
seen it. I mean, I suppose if you keep the

(20:21):
lens cap on your camera and you take a picture
and you have a pure black image, have you taken
a picture of the inside of your lens cap or
is it just sort of a non picture? Wait? Wait, wait,
what of the wait what? Yeah? Technically if I take
a picture of your inside of your let's cap, is
that what you're saying? Yeah? I mean the issue here
is that we don't see any photons from a black hole,

(20:43):
or in a black hole, if it exists, wouldn't give
off any light. So the only thing we can do
is look at the impact of the black hole on
nearby space and ask is that consistent with what we
expect from a black hole. That doesn't tell us necessarily
that the black hole is there. The history of the
discovery of black hole in the sort of slowly accumulating
evidence for their existence is all a little bit indirect.

(21:07):
It's all evidence for what black holes do to the
stuff near them. I see you're getting a little technical
here on the definition. But um well, let's maybe step
people through it. How do we know black holes actually
sort of exists because we've seen different kinds of evidence
for them. Right, it dates back to the mid sixties.
The first evidence we had that suggested the black holes

(21:27):
might be real were very bright X ray sources. Now,
remember black holes, they don't emit any light because any
light that hits them gets absorbed, and they don't give
off any light because the event horizon. But they're typically
surrounded by stuff that's very affected by the strong gravity.
So if you have a bunch of gas and dust
that's about to fall into the black hole, and the
intense gravity makes it very very hot, and so it

(21:48):
emits in the X rays. So in the sixties, people
saw these X rays from a spot in the sky
that they didn't see anything else. It's called sidneys X one,
and they didn't really understand it. And then later people
were studying a blue super giant which seemed to have
some heavy object orbiting it that was emitting X rays
but otherwise totally dark. So these are sort of like
the first clues that there was something massive with very

(22:09):
strong gravity that wasn't giving off any light, right, Because
it's weird for something not to emit regular light, but
for it to admit X rays, which is also light,
but it's just light in a different frequency. So it's
weird for something to emit X rays but not regular light. Right. Yes,
stuff in the universe emits light based on its temperature. Right.
As stuff gets hotter, it emits light in higher and

(22:31):
higher frequencies. So the Sun emits in the visible light
because of its temperature, the Earth emits in the infrared
because of its temperature. Very very hot gases out there
in the universe emit X rays because they're very very hot,
And so here we have a very compact source of
X rays, but we don't understand what the object is
because it's not emitting in any other frequencies, right, And
so they thought if it's only emitting super duper high

(22:53):
frequency light, then it must be something extreme, like maybe
a black hole exactly. And that's also similar to the
picture that we've seen of a black hole. What is
that a picture of Well, if you look at it,
it's a ring of glowing gas and at the center
it's black. So the part that you're actually seeing is
the ring of gas around the black hole. It's emitting light,

(23:14):
it's emitting X rays because it's super duper hot. And
that's the picture that we've seen. What are we seeing
from the actual black hole itself? If it's there, What
we're seeing no photons, it's like you're seeing the inside
of your camera lens cap right, Right, Well, let's get
to the picture. But first let's talk about some of
the other ways we've seen black holes, right, because we
know they're they're also from their gravity, right exactly. We

(23:35):
can find places in space where there's very intense gravity
but no obvious source of it, like the center of
the Milky Way. When we look at stars in the
very center of the Milky Way, we see them going
really really fast and then changing direction on these very
tight orbits, as if there was a very heavy object
right there at the center of the Milky Way. And
folks in nearby U. C. L A. Won the Nobel

(23:55):
Prize for this discovery last year. They've been tracking these
stars for like twenty years. Recons directing their orbits, and
the orbits are consistent with some very massive object at
the heart of our galaxy, and yet it admits no
light directly. So that's very suggestive of the existence of
a black hole. Right, We've all the same black holes
sort of through gravitational waves, right, Yeah, any object in

(24:17):
the universe that accelerates is going to give off gravitational waves.
That just means that everything that has mass has a
gravitational field, right it pulls on things or bends space
in a certain way. If that thing now accelerates, then
that gravitational field changes. Just like if you delete an
object from space or add an object to space, you're
changing the gravitational field and that information propagates out through space.

(24:39):
You don't instantly change the gravitational field of the Sun.
If you deleted it, the change in the field would
propagate out through space. So gravitational waves are essentially just
updates to the gravitational field because something has changed. They
have a really big, heavy object and you accelerate it.
For example, if two black holes are orbiting each other
and then they're falling into awards each other and becoming

(25:01):
one single massive black hole, then you will see gravitational
waves from those orbits, and we have seen that, we've
seen a bunch of those things. What is that actually
evidence of its evidence that some very dense, massive objects
were orbiting each other and collapsed into one. Right, So
it seems like maybe, you know, at the beginning of
the last century, we came up with this idea more

(25:21):
officially over a black hole. And over the years we
saw all this evidence that you know, there are really
super duper dance things out there in space that are
not bright, so they're not like stars. They don't seem
to emit regular light, only X ray, which is the
super intense kind of light. And so people thought, hey,
that maybe those those things, those super dense objects are

(25:42):
black holes. But then actually a few years ago they
saw they we got pictures of a black hole. But
now you're telling me that made black holes are not
black holes. Well, all that evidence is a little bit indirect.
It supports the conclusion that there's something small, something dark,
and something heavy, right, but not exactly what it is is.
And for a long time, the only thing in our

(26:02):
sort of category of ideas that could be that small, dark,
and heavy were black holes. So that was evidence that
black holes exist because we see things out there that
are consistent with black holes, and there were no other candidates.
And one thing to keep in mind is sort of
how close to the black hole our observations come. When
you think about like stars orbiting the central black hole

(26:23):
in the Milky Way, they don't ever really get that
close to the black hole. So yeah, it could be
a black hole. It could also just be some really
big dark object not a black hole, because the stars
don't get close enough to distinguish between those scenarios. So
what was exciting about the black hole image is that
now we're looking directly at the gas that's right around
the black hole, it really shows us sort of how

(26:45):
small the black hole or whatever this massive object is
has to be. So again, the black hole image doesn't
tell us definitively that it is a black hole. It
just says, well, whatever it is, it's very very small.
It's smaller than any other picture or any other measure.
It told us it had to be, right, But I
feel like the image, you know, it shows an aero
space out of which no light seems to be escaping, right,

(27:08):
is something small, something dan, something that not even light
can escape isn't that the definition of a black hole.
Wouldn't you just say, look at that giant black dot
and say, hey, that's a black hole because it's a
hole and it's black. Well, we don't see any light
from it, right, but it's not definitive proof that there
is an actual event horizon there. We don't know that
there's an event horizon. Well, we talked on the podcast
once about this other idea of a dark star. Maybe

(27:31):
black holes don't have an event horizon. But the intense
gravity of a collapsing star bends space and so it
like stretches all the light to super long frequencies like
massively red shifts and everything, and slows down time so
that it looks like no light is emitted. But the
light that submitted is just like very low intensity because

(27:52):
time is slowed, and very long wavelength like the wavelength
of the galaxy, which makes it impossible to see. We
couldn't disting whish between those two scenarios. Wait, you're saying
that maybe there's something there that it could be that
we're just seeing a black spot that's not trapping light,
it's just maybe stretching light beyond our sensors. Exactly. We

(28:12):
don't definitively know that it's an event arise, and we
haven't been there to test it, to observe it closely
and directly. We're very very far away from these things,
and all we're seeing is a lack of photons. But
there are other ways to explain a lack of photons, right,
like massive gravitational redshift from an object that doesn't actually
have an event horizon where it's technically possible for it

(28:34):
to mat radiation. We wouldn't notice or be able to
observe that radiation. Right. But isn't it a little suspicious
that you see this ring of light, right, and then
it suddenly stops and you just see a black hole? Right?
Like would something like a star that's collapsing or something
that's just stretching light. Wouldn't that make it more continuous? Right?
Because the whole ring is kind of consistent with this

(28:56):
idea that there's stuff, you know, orbiting around and then
some of it falls in and then it has to disappear. Otherwise,
where is it going? Why isn't it shining light? Even
for a black hole? It's fairly continuous, right, Things get
gradually redder and redder and more and more slow down
before they fall in the event horizon. Even for a
black hole, you never actually see something fall into the
event horizon, unless, of course, there's something else coming behind

(29:18):
it to pull the event horizon over it. So these
scenarios actually look the same, right, having just a very
intense gravitational source to gradually red shift and slow everything
down as it falls in, or there being an actual
event horizon beyond which things can't leave. Those two things
actually do look the same from a distance. But wouldn't
people have seen these maybe in the infrared, Like if

(29:40):
we look out into the center of our galaxy, for example,
with our infrared telescopes, wouldn't then we see a huge
source of infrared light. Yeah, but the infrared radiation would
be crazy long wavelengths. We're talking about like wavelengths the
size of the galaxy, And we do not have sensors
that can pick up infrared radiation at those frequencies, right,
but we don't need We see it sort of ramp
up towards the infrared spectrum. Yeah, but that would look

(30:02):
the same for a black hole, right. A black hole
would also show you more and more infrared as you
get closer and closer to the event horizon because everything
is getting red shifted, so they look the same from
the outside because they have the same gravitational effect on
things outside the event horizon. What are saying, there's no
way to tell between a black hole and a not
black hole. The only way to tell us to go

(30:24):
visit close up, or to maybe sense things in the
long infrared. Maybe if you had the ability to sense
things in the very very far infrared, then something falling
into a non black hole would continue to emit light
that you would very faintly see in the very very
long infrared, whereas things that fall actually past the event
horizon of a black hole would stop emitting. Although you know,

(30:45):
if you just drop a single object into a black hole,
it's going to admit forever because it never actually falls
past the event horizon, right, So it's really quite tricky.
M all right, Well, I think what you're saying is
that there's some doubt about whether even the images that
we have of a black hole or even a black
hole or represent the black hole, because there's a very
technical definition about what counts as a black hole, that

(31:06):
it's not just a big round circle in space. So
if it's not a black hole, what could it be.
So in a previous episode, we did talk about this
idea of a collapsing star slowed down by a gravity
that would look just like a black hole, and that's
a really cool idea. But today we wanted to talk
about a different idea because there are several ideas for
what might be there that looks like a black hole
but actually isn't. The idea here is to sort of

(31:28):
take a neutron star and extended to a super duper
neutron star. A fuzzball is like a very very dense
state of matter where matters condensed even beyond the ability
of a neutron star, but not quite to a black hole. Right,
we talked about neutron stars, which are like the densest
things in the universe, right before you might get to

(31:49):
a black hole. Maybe recap for us what a neutron
star is and how they occur. Yeah, so gravity is
pulling everything together, right, It's gathering gas and dust to
form stars, and the only way to stop gravity is
to push back in some way. Our Sun has massive gravity,
but it doesn't collapse because it's pushing out with its
nuclear fusion. Creating a lot of energy and radiation pushing back.

(32:10):
When that ends, though, when the Sun runs out of
fuel or gets too cool because it's made too many metals,
then it collapses even further. But there are other ways
to resist gravity. You can have, for example, a white
dwarf where matter is compressed really really intensely, but it's
pushing back because the electrons and the atoms don't like
to overlap. That can resist gravity. Or you can compress
it even further so that you squeeze all those electrons

(32:33):
inside the nucleus where they meet up with protons and
convert into neutrons. So now you get a very very
dense object which is essentially just a huge blob of
neutrons all squeezed together. Right, because neutrons are neutral, so
I guess they don't repel each other kind of right,
So they're pretty happy, I guess, to be in that
super duper dense state. Yeah, though they do feel the

(32:54):
strong force and the quarks that are inside the neutrons
push against each other, and so it resists the compress
shouldn due to gravity, and it wants to stay as
a neutron. Though we don't know what's going on at
the very very heart of the neutron stars, where the
pressure and the density against even crazier we talked about
in the podcast, it might form weird states of matter
like cork, gluon plasmas, or nuclear pasta. The point is

(33:16):
that you still have objects, You still have matters, still
resisting the compression of gravity. You probably have those fundamental particles,
the quarks and gluons, swimming around at the heart of
a neutron star. And that we thought was sort of
the last defense of matter against gravity. That if you
made a neutron star heavier more than like maybe two
or three times the mass of our Sun, that it

(33:37):
could no longer resist the compression of gravity and it
would collapse to a black hole. A fuzz ball is saying, wait,
maybe there's one more like interior fortress. Maybe there's one
more way to resist that collapse. Maybe the things that
are inside corks and gluons can do their own thing
and form a new state of matter to resist gravity.
M Right, Well, first of all, I guess, can a

(33:59):
neutron star see what's inside of what we think is
a black hole? Like can a neutron star trap light
or at least slow it down enough that it looks
like a whole. Neutron stars are very dense gravitationally, and
so they definitely have these kinds of effects on light,
but they're not massive enough to create a black spot
in space. We can see neutron stars. We can even

(34:20):
image X rays from hot spots on their surfaces and
see them spinning, So we know the neutron stars are there.
They're hard to spot because they don't go very much
in the visible but we have seen them. We know
that they're there, and that they do not have an
event horizon, not even like a soft event horizon or
like what sort of looks like to the visible eye
like an event horizon. But they're also bending light to right,

(34:41):
and they're also sort of, if not trapping, then slowing
light down enough so that it looks black to us.
They're definitely slowing down time, and they're definitely red shifting
light because of their gravity, but they do not have
an event horizon. We can see emissions directly from neutron
stars absolutely, all right. So then inside of an image
of the black hole, it's definitely not a neutron star.
So you're saying, maybe a neutron star. There's a one

(35:04):
thing it can turn into that would look like a
black hole, but that is not a black hole. Exactly.
As you add more mass to a neutron star, then
the gravity gets stronger and stronger, maybe so strong that
the corks and gluons now crack open. Our experiments can't
see what's inside quarks and gluons. We don't know if
there is anything inside them at all, and if that
is what it is. We have several candidate theories, but

(35:26):
it's all basically just mathematical speculation. We know corks and
gluons are real, we don't know what's inside them. But
if corks and gluons are made out of these things
called strings, out of string theory, that it might be
possible when you make that neutron star more massive than
instead of collapsing all the way to a black hole,
that those strings come out of the corks and gluons

(35:47):
and do their own weird dance to create this bizarre
object called a fuzz ball, which would be capable of
resisting gravitational collapse. M I see. So like if you
take a neutron star add more mass to it, into
the gravity is so great it cracks open the corks
and the strong force that's holding them together and sort
of apart. And once you crack those open, maybe there

(36:09):
are strings that then stay whole. They don't collapse into
a black hole because there might be some string force.
I guess it's keeping them from collapsing into a black hole.
Exactly is there is something inside corks and gluons and
it's held together with some force we don't know yet,
Not the strong force that's the one that holds corks
and gluons together to each other. But whatever is inside

(36:29):
corks and gluons is being held together with some other
force we haven't yet discovered. The string force, not the
strong force, the string force. What's stronger the string force
or the strong force? What stringing here? The string force
or the strong force. It's a mess. Maybe it's the
strange force. Maybe to pick another vowel, you know, the
string force stirm and dring, the strong force, the strong

(36:50):
strong force. There you go, Well, whatever is inside corks
and gluons, if there is something inside there would have
some force and you have to overcome that to crack
it open. And yeah, maybe those would be strings, and
those strings interact in ways that we don't even really
fully understand because string theory math is very very hard
to do, very complicated. But the idea is that if

(37:11):
you squeeze a bunch of these strings close enough together,
then they might tie themselves into these really weird, very
very long strings. Like strings. We think, if they do exist,
that they're super duper small. They're like ten to the
minus thirty five meters wide distance we call the plank length.
But if you take a bunch of strings and you
squeeze them together, we think they might loop up and

(37:32):
form super duper big strings. Like as you squeeze them together,
weirdly they get larger, right, like real string. Well, let's
get into the details here of a string hoole. I
guess you would have to change the name of it, right,
Maybe fause ball is not the right name. Maybe it
should be a string ball. So let's get into the
details of that and whether or not we might ever
be able to detect such a thing in space. But

(37:53):
first let's take another quick break. I feel like you're
stringing me along here, Daniel, to answer the question whether
or not the black hole really exists or is what

(38:14):
we think a black hole? What we think is an
image of a black hole is actually an image of
something else that is technically not a black hole, but
maybe something called a string ball. Well, the Adventures of
It could have called it a string ball, but they
decided to go with a fuzz ball instead, right, even
though string ball would be more accurate, wouldn't it. I
don't know the images I've seen online that describe what

(38:35):
these scientists are thinking about. It looks pretty fuzzy, so
you know, I like buzz ball. Well, I think the
idea is that if you take a neutron star, which
is a super duper heavy object, and then you squeeze
it even more, you break open the neutrons and the corks,
and you spill out all the strings that might be
inside of a cork, and then you make a ball
out of those things before they actually collapse into an

(38:58):
infinite singularity, which is but would be a black hole exactly,
these things would resist collapse because of their stringiness. And also,
really interestingly, strings themselves can't be part of a singularity
because they have an extent, right, they have a minimum size.
Strings are not point objects the way electrons are or
quarks are in our current theory or in any theory

(39:20):
of fundamental particles. Strings themselves have a minimum size there
are quantum object so they can never have infinite density,
which is sort of cool. Even if you had a
single string, right, it's not a singularity. And here you
take a bunch of strings, you put them together into
a string ball or a buzz ball, whatever you want
to call it, and it's actually quite big and quite massive.
So this thing would be like a huge object. But

(39:42):
it's also like made out of this weird fundamentally quantum
thing a string. So you know, the sort of the
way like a Bose Einstein condensate is a macroscopic object
that obeys quantum properties. This thing also would be like
a really big, huge macroscopic object that shows it's stringing nature.
M So it'd be made out of strings. And you

(40:03):
said that the strings would tie themselves together or you know,
sort of become longer strands of strings. Strings when you
combine them, their tension actually decreases, right, So as you
put more strings together, the tension decreases as they get
longer and longer. So are similar to like a guitar string, right,
A guitar string that you shorten has a higher tension

(40:23):
and makes a higher sound, whereas if you let your
guitar string get longer than it makes a deeper sound. Right,
And that's how it works on the fretboard, right, you're
shortening the length of the string, you're increasing the tension,
so you're increasing the frequency. The same thing happens for
these kinds of strings. As you tie a bunch of
them together, they tend to get longer and the tension decreases.
And so if you can squeeze a bunch of strings together,
they can make really big macroscopic objects like a fuzzball,

(40:47):
sort of like a new state of matter. You can
imagine it as all right, So then I guess you
can compact all that mass even more, so you get
even more intense density and even more bending at space.
Would you then be able to trap light? Yeah, fuzzball
has so much gravity in such a tiny spot that
from the outside it looks like a black hole, right,

(41:09):
the same way a dark star does. You don't actually
have to have a singularity in order to bend space
enough to create gravitational redshifting and time dilation to look
like a black hole, or to be indistinguishable with our
technology from a true general relativistic black hole, so it
would have an event horizon. It doesn't have an event horizon, right,

(41:30):
like a black hole, there is no event horizon there.
But it does distort light in the same way a
dark star wood. It makes the frequencies very very long,
very red, and it slows everything down. Wait, why wouldn't
it have an event horizon. Couldn't you imagine putting so
many strengths in one spot that it would create an
event horizon. You could, But this thing resists collapse to
that density because the strings have the sort of like

(41:53):
outward pressure like puff up, providing enough outward pressure to
avoid collapsing to that density. But that's only as ming
SEMs that the force that keeps them together is strong
enough to prevent the event horizon from forming. But couldn't
you also imagine a string ball where the force is
strong enough not to create a singularity, but maybe strong
enough to create an event horizon. In principle, what you're

(42:14):
describing is like a quantum mechanical black hole, where you
have enough mass within like the short styles radius to
create an event horizon. That is technically possible if you
can get some matter to that density This is the
suggestion that strings are preventing the matter from getting to
that density, so there is no event horizon there. You're
right that if in principle, you could squeeze the strings

(42:35):
down even further, you could satisfy that condition and create
a classical black hole. But the calculations here suggest as
strings are puffy enough that they resist compression, so they
don't actually form a black hole. That's what makes this
different from a black hole. There's no event horizon here,
right right, We're not asking the question like how can
you make a black hole without a singularity. We're asking

(42:55):
the question, can you create something that looks like a
black hole that wouldn't turn into a black hole? Exactly?
Is there another step between neutron star and actual density
of objects that create an event horizon? And this suggestion
from string theory is that you can form this new
state of matter called a fuzzball, which is not dense
enough to create an event horizon, but sort of looks
a lot like an event horizon to our technological eyeballs.

(43:17):
Right because before the only step we knew was a
neutron star, and we know that a neutron star wouldn't
look like a black hole. But maybe because we know
enough about the strong force, I guess to make that call.
But maybe there's something that neutron star would collapse to
that wouldn't be a true black hole. Yeah, exactly, you
add mass to a neutron star, maybe there's another step
there before it collapses to the density you need to

(43:38):
create an event horizon. But from a distance, this thing
is so close to an official black hole in terms
of density that it acts almost like one. It's indistinguishable
using our sensors from an actual black hole with the
real event horizon, right, would be more like a black
divid like vivid sort of looks like a hole from
a certain press practice because there is it's trapping some things,

(43:58):
but it's not actually a whole. Yeah, or maybe it's
like an off black hole. Right, it's not black. If
you look at really really carefully with the right instrument,
you might detect some radiation, right, Yeah, But I think
what it would sort of pretty much act like a
black hole, like if you get near it, it would
spaghettify you perhaps, right. Absolutely, gravity from a distance is
the same as from any object of that mass, And

(44:20):
because it is really really dense, you could get close
enough for the tidal forces to be very dramatic. Right,
And it would also form the rings around itself. Right, Yeah,
it would form an acretion disk exactly. Just that. The
difference is that it doesn't create an event horizon exactly.
That's the difference. And it's not just speculation. These guys
have done these calculations in string theory and suggested that
this thing could actually form. That's really as possible for

(44:42):
strings to create this state of matter. It's not just like, hey,
maybe there's some state of matter. It actually does come
from the calculations of how we think strings would behave
if they were real. Right. But strength theories totally made up,
so you know, it's the same thing. And if you
make something up, if you prove something with a made theory,
it's still made up, isn't it. It is still made

(45:02):
up in this case, though it does match everything we
see in the universe. Right. They basically give the same
predictions for the observations as the classical general relativistic black hole.
And it solves the quantum mechanics problem because these things
do not create singularities that violate quantum mechanics. They are
actual quantum mechanical objects. Plus they solve a bunch of
other problems related to black holes, so theoretically they are

(45:24):
very attractive for those reasons. Although you're right, we can't
tell the difference between a black hole and a string
ball or a fuzz ball, and so from that sense,
it is just still made up, right. And also you've
got to ask the question, like what happens if you
do have a string ball and you put more strings
into it? Is it eventually going to collapse into a
black hole? Or are they saying that string balls can
never become black holes? These would never become black holes

(45:46):
because as you add more strings, they get larger and larger,
so they don't get denser. Tension on the strings actually
get smaller as they get larger. So as you add
more and more strings, you just get a bigger string ball.
M hm. So you ever increase the density, that's what
you're saying. Yeah, the density never crosses that threshold. But
if the force relaxes, wouldn't you be able to compress

(46:07):
them more more stuff? You mean, like the force just
took a vacation. It's like, hey, it's Friday, I'm tired
of holding the string ball up yeah, pasically right, Like,
if he's saying that the strings get more relaxed, wouldn't
you be able to slip in more smaller strings in there?
The strings getting more relaxed means length goes up, right,
because the tension and the length are inversely proportional. That's
why these things get bigger and bigger. So maybe in

(46:28):
some versions of string theory these things wouldn't be allowed.
But in the calculations that these folks have done, they
suggested these things would never collapse to have an object
with an event horizon. All right, So then this is
an idea that maybe says that the things that we
think are black holes are actually not black holes. Although
even if these things do exist, would that make black
holes impossible or just not likely? These would make black

(46:52):
holes impossible at least out of matter that is made
of strings. Couldn't I smash two strings together, a bunch
of strings together, so fast and so hard that they
form a real black hole. You know, that's a great
question if temporarily you could overcome this stringy puffinus to
create that density. I don't know the answer to that,
and I don't know if anybody does, Because you know,
these calculations are very very hard to do. String theory

(47:14):
is very complex. These calculations are done in like eleven
or twenty six dimensions because that's the space in which
strings work. And so I don't think anybody knows the
answer what would happen if you collided to string balls?
Let's do it. But I feel like it's convenient that
made up theory is so complex you can actually do
a lot of calculations in it. You know, the people
who do string theories say it's beautiful and it's wonderful.

(47:37):
I've never done any string theory calculations myself, so I
can't attest to that. But it is very complicated, as
only a few people in the world who know how
to do string theory calculations. And also we should say
that they haven't done the full calculation here. They've taken
like a lot of simplifications and they've solved it in
like a few different cases that are related to our universe,
but not exactly our universe. So they sort of suggestive calculations,

(47:59):
not like really conclusive results. Interesting, well, we might need
to change the name of black holes to spring balls
or or fuzzballs, and this is also convenient like this
idea of a fuzz ball or a string ball is
interesting too because you said it solves other inconsistencies about
real black holes. Classical black holes, the ones imagined by

(48:19):
Einstein's theory of relativity, have a lot of problems with
quantum mechanics, but they also have problems with information. You know.
One problem is that things are falling into the black hole,
and a classical black hole just sort of eats them.
But we know that black holes eventually will evaporate. They
admit this faint radiation at their edges called Hawking radiation,
and so they disappear, and so in our universe that

(48:40):
means that the information falls into a black hole and
then is gone. We had a fun episode about the
black hole information paradox, so check that out. But this
is a real problem with the sort of the structure
of classical black holes. What happens to information that falls
inside of them? And so this solves them because there
is no event horizon, and so nothing falls past the
event horizon and disappears. So it sort of solves that

(49:02):
problem by deleting it from the universe. M I see,
if there is no event horizon, then there's no problem
with an event horizon. Basically, stuff that you throw into
the string ball just becomes more strings, and this quantum
information is not lost, is still there on the string ball,
all right, And that would make more sense in the universe,
or it would just be more more easier to study,

(49:24):
that would make more sense. Quantum mechanics says that information
cannot be lost, that everything you do imprints itself on
the future of the universe, and then in principle, you
could reverse engineering to find out exactly what happened in
the past. It's very deep principle in quantum mechanics. And
if that is wrong, then like everything we think we
understood abou quantum mechanics is wrong. So according to our

(49:44):
current theories, information should not be lost in the universe,
and yet classical black holes do seem to delete it.
So this would nicely avert that problem, all right. Well,
it sounds like every time you look at an image
of a black hole, you should, in the back of
your mind think, maybe it's not a black hole, maybe
it's a string ball. And you know, science is a process.
We start out with an idea and we get closer

(50:05):
and closer to the truth. But you always have to
keep in the back of your mind, what do we
actually know? Have we really verified this? Is there a
possibility for it to be something else, something other than
the current theoretical idea, And so it's exciting to hear
people thinking about what else black holes might be that
would still look like the black holes we think we

(50:25):
see out there in the universe. Right. Yeah, it's good
to remember that this idea of a fastball is really
just a theory, right, and in fact based on strength theory,
which is sort of not like a real theory, It's
more like a like a pet theory, right, more like
a pepito theory. I do like to scratch the heads
of string theories whenever I see them, just to give
them some encouragement. That sounds really inappropriate, Daniel, Do you

(50:46):
get consent before he's crashed their heads? They tend to purr.
So what can I say? But yes, string theory is
a speculative theory of what might be happening inside particles,
and it makes this really fun prediction or what happens
if you get like the mass of the sun in
terms of strings and lease them all together. So it's
a really fun prediction that would solve a bunch of
problems and also be kind of awesome to think about. Yeah,

(51:06):
at least in some universe, my not br universe, in
some universe. Alright, Well, we hope you enjoyed that. Thanks
for joining us, see you next time. Thanks for listening,
and remember that Daniel and Jorge explained. The Universe is
a production of I Heart Radio. For more podcast for

(51:29):
my heart Radio, visit the i heart Radio app, Apple Podcasts,
or wherever you listen to your favorite shows.