Is the Universe a hologram?

Could the 3D entire Universe be a projection from a 2D surface somewhere?

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Episode Transcript

Speaker 1 (00:08):
Hey, Daniel, how many dimensions do you have? More than
i'd like these days? Too many late night snacks from
the fourth dimension? Yeah, or from the fridge dimension. Actually, yeah,
that's like its own mini universe of deliciousness where I'm
both the master and the slave. But aside from how
many cookies are involved, how do you know you're a

(00:31):
three dimensional being? I mean, I don't know. The world
seems to be three dimensions. Yeah, but so does the
stuff on my TV. But that's just like how your
brain perceives it, all right. Well, then, if I'm just
like in a two dimensional matrix, does that mean I
can eat as many snacks as I want? Uh? Well,
technically as if you're in a to the world, you
can eat all the two these snacks you want and

(00:52):
gain zero weight. I'll be right back. Hi. I'm Organ.
I'm a cartoonist and the creator of PhD comics. Hi,

(01:13):
I'm Daniel. I'm a particle of physicist and a professor
at you see Irvine, and I enjoy any dimension snack really,
even a one dimensional snack. I guess spaghetti is a
one dimensional snack technically, especially the spaghettini or the angel hair. Yeah, exactly.
I don't discriminate. I'm not a dimensionist. I see all
dimensions as equal. So welcome for a podcast Daniel and

(01:34):
Jorge Explain the Universe, a production of My Heart Radio
in which we take a part the universe into its
various dimensions, the ones that are understood and the ones
that remain puzzling. We take your mind on the journey
into all of those dimensions, trying to understand what we
do know about the universe and what we don't. We
range from the smallest of questions about the smallest of

(01:55):
things and their color and shape and whether they spin,
all the way out to the biggest and deepest and
broadest of questions about the nature of the human context
in this crazy and beautiful cosmos. Because it is a
pretty wild universe, and we like to take you on
the up and the down, on the front and the back,
and the left and the right, and the and the
good and the bad jokes as well. That's right. There's

(02:17):
a lot to explore in the universe, is what I'm saying.
We spend the entire dimension of humor, all the way
from puns to dad jokes. Is there anything else? Aren't
this in the same access or the same you know. Point,
is there such a thing as a non silly death.
My teenagers say that any joke I make is a
dad joke. Oh, I see, you have no death, according
to them. That's right, it's all one dimension. There's so humor,

(02:40):
seems we one dimensional two because you're pretty funny, Daniel.
For a physicist, I guess that's a two dimensional compliment
right there. Projected onto the surface of physicists, you'll look
pretty funny. But yeah, we like to explore all the
big questions about the universe, what's real and possibly what's
not real in this universe because this universe seems to
have a lot of super crisis in store for us.

(03:01):
That's right, We as an intelligent species have been digging
into the question of the nature of reality, What is
actually out there and is it different from what we perceive.
We would like to know something true, something universal about
the universe, not just what humans think it might be,
but something we could like compare notes with aliens about right,

(03:22):
But what if the aliens are since they're in the
same universe, what if they're just as fooled as we
are by this crazy kind of tricks. Their universe we
live in. I believe in the wisdom of the crowd.
You know, if you average over infinite intelligent races, somebody
out there has kind of figured out what the universe
is actually like. I don't like the idea that we've
all been fooled in just the same way. And you

(03:44):
know that from the Internet. I guess it's a good
test bed for that idea. Yeah. Absolutely, On the Internet
you can find every possible opinion with evidence, without evidence,
it doesn't really matter. You can find all the dimensions there,
you certainly can. But our goal on this podcast and
as a species is to unravel the fundamental nature of
the universe, to see it for what it is, and

(04:05):
to ask the most basic questions about what it's like
and its structure and its shape. Yeah, and sometimes these
questions sort of make you uncomfortable, maybe Daniel as a physicist,
because you know, we're sort of questioning how real is
real or how real are the things that physicists think
are real. That doesn't make me uncomfortable. That makes me excited.

(04:26):
When we are on the verge of like revealing that
the universe is totally different from the way that we
thought it was. That we're all just you know, projections
on the wall of Plato's cave. That's exciting because it
means we're gonna learn something. We're going to emerge from
like some shroud of ignorance and actually understand something deep
and true about the universe, even if it up ends
everything we thought we knew and changes the entire context

(04:48):
of our existence. That's sort of the goal of physics.
Maybe I'm just projecting here, Daniel. It makes me a
little bit uncomfortable to think that everything I know is
to be real is not actually real. Well, I'm pretty
sure that's true. Well, they were gonna be asking a
one one sort of version of this question, is the
universe real? And it has to do with sort of
like the dimensionality of the universe and how many dimensions

(05:10):
it actually has, and is it different than the number
of dimensions we feel and see and touch and can
feel ourselves in. That's right, And we're gonna use the
word dimension here, and we don't mean, you know, like
the alternate dimension where everything is made out of marshmallows,
or where aliens escape to as sort of a parallel universe.
You see that a lot in science fiction. What we
mean by dimension here really is the mathematical description of it,

(05:33):
meaning just like a direction of possible motion. And I've
always found it fascinating that our universe has three dimensions
or seems to have three dimensions, because you've got to
wonder like why three three is such a weird number. Yeah,
So to be on the program, we'll be asking the
question is the universe a hologram? Now? Daniel? Are you

(05:59):
sure we can't just talk about the marshmallow dimension where
all all the gatings are. That sounds like a pretty
good podcast topic. Are the aliens made of marshmallows in
that dimension or that Do they just eat marshmallows? I
don't know. You tell me you're the one projecting this
image into my brain. Maybe they go hunting for marshmallows.
So the question is is the universe a hologram? Now?
This is a pretty interesting question. Are you saying, like

(06:20):
the whole universe where we live in is a hologram?
Like an illusion? Kind of? Yeah, that's sort of the
idea that maybe the universe doesn't actually have three dimensions.
Maybe it's actually just the projection in our minds or
in our experience of what's actually a two dimensional universe.
That's sort of like feels like three dimensions that we

(06:42):
can experience as if it was three dimensions, sort of
like a hologram. Although you know, it makes the universe
sound like a cheap trick and like one of those
baseball cards or those little tinfoil things you put on
dollar bills. Yeah, like by yourself universe sounds like a bargain.
But I love these kinds of questions because they go

(07:02):
to the very core of the nature of reality. You know,
if we are wrong about the number of dimensions of space,
what else are we wrong about? Maybe everything? And that
might make some people uncomfortable, but it makes me excited
because it means that there might be crazy, mind blowing
revelations about the very nature of reality around the corner. Yeah,

(07:23):
so this is a pretty tricky question. Is the universe
a hologram? And so, as usual, we were curious how
many people out there had thought about this question or
have an opinion on this question. So Daniel went out
there into the Internet to ask people is our universe
a hologram? So thank you people of the Internet for participating.
And if you are a person of the Internet and
you'd like to volunteer to answer random questions. Please, It's

(07:46):
very easy and fun and just takes a few minutes.
Right to us two questions at Daniel and Jorge dot com.
I think about it for a second. Do you think
the universe you live in is nothing but an illusion?
A hologram? Here's what people had to say. Sure, doesn't
seem like it a holograph, as I understand it is

(08:07):
just a trick of light. I don't know what hollow means.
I am part of the universe and I feel like
I have substance, And even if that's just a trick
of my brain and I am just an image, how
can a light based image create self awareness? So I'm

(08:28):
guessing no, it could be somebody else's dream. Um, yeah,
I think no. No, I don't know why. It sounds
like somebody gave up and said, well, it's a holograph, man,
and that's it. It's a holograph. But well, even if
it's a holograph, who made it? Why? And who's paying

(08:52):
for it? I'm not paying for that. I would say no,
because a holograph is a three D display of light.
So photos which are massless and as far as I
can see, stuff around me and reused myself. We have
mess so I find it very hard to imagine that

(09:13):
the universe is a holograph. Of course, of course the
universe is a holograph. No, I'm not sure if the
universe is a holograph or not. I have heard some
theory that maybe the universe is it's a two dimensional
image projected onto three dimensional space or something like that.

(09:34):
I have heard this theory, but it's been a long
time and I don't quite remember how it goes. Well. Technically,
a holograph, I think, is a written something that someone
has written in the earned hands. Or maybe the uniograph
universe is a holograph if you call God the writer
of the manuscript. I'm not sure there. Maybe from our

(09:55):
perspective on Earth, the universe actually is a holograph, for example,
with bends and refracts and reflects like in many different
directions depending on where you are in it a thort
of the holographic principle. I can't remember exactly what that is,
but I think it might be related to the modest

(10:17):
sin A conjecture, which is that we'll assuming the universe
is a d is in other words, that has negative curvature.
Then everything in the universe, all the information that is
important in the universe, can be represented on the surface

(10:40):
of a boundary surrounding the entire universe. All Right, some
pretty confident answers here. Some people were like, of course.
Some people were like, no, I don't think so. I
think what people said. It sounds very technical, Yeah, exactly.
And I also like the ones that focus on the
definition of a holograph M or a holograph or those

(11:02):
two things different a holograph and a hologram. Yeah, Confusingly,
the two things have almost nothing in common. Like, hologram
is what we're talking about. It's a trick of light
that it gives the impression of a three D volume
from a two D surface. You know, this is the
kind of thing you'll see on a baseball card or
on a dollar bill, etcetera. A holograph is actually just

(11:24):
like an essay written by one person in their own
handwriting what I know. And then holography is the study
of holograms, not the study of holographs. And the holographic
principle that we're gonna be talking about today, that the
universe might be a hologram is not the hologramic principle.

(11:44):
It's the holographic principle. Oh man. That's before we even
get to English units, right, because then you have to
talk about the holo pounds and the hollow ounces, and
then eventually you have to talk about the hollow deck,
which you know, and then we get into real nurse
territory exactly. This entire podcast has been nothing but an
exercise of the holo deck. None of this has been real.

(12:04):
Your whole life, we're all just you know, aiyes, in
your little cosplay here, Daniel. No, I thought I was
in your holo deck experience. I thought you were the
real I thought I thought you were what were both eyes?
Somebody over here better be real otherwise this whole thing
is a bad joke. It's holograms all the way down.
That's the real hologramic principle. So yeah, it seems to

(12:26):
have a lot of definitions, and so I guess let's
get down the business and let's lay it down for people, like,
what is the one that we're talking about today? We're
talking about holograms, right, and I guess what does that mean?
That's right, we're talking about holograms, which is part of
this idea of a holographic principle that the universe might
be a hologram. And so again what we mean by

(12:47):
a hologram is the projection of two dimensional surface into
a three dimensional space. And that sounds fancy and mathematical,
but really what we mean is something that looks like
it has volume, like it's three dimensions x, y and z,
but really there's only enough information for X and y
that you can take all the information and volume and
somehow encoded on a flat surface. And you might be

(13:10):
familiar with. One of these things. Is something you can
look at like a sheet of paper. As you change
your angle, the image changes, just as if you were
looking at something that had three dimensions. So we think
it has three dimensions, but really it's we're just looking
at a two D surface, which means that all of
that sort of three D information is sort of encoded

(13:31):
or or you know, written down in that too D
piece of paper somehow exactly, because a three D object,
when you look at it, you only ever see a
two D slice, right, you see one side of it,
or you see another side of it, or you see
another side of it. So a three D object has
all of those two D slices somehow encoded into it, right,
And so a hologram is a two D surface with

(13:52):
all that three D information encoded into it somehow, so
that when you look at it from different angles, you
see the right to D slice. So you're rain is like, oh,
that's a three D object, just sort of like in
Star Wars when Princess Leiah is projected out of R
two D two, right, it's not just she's on a screen.
It looks like she's there. And they have these all

(14:12):
over Star Wars all the time, so they're like confusingly
low tech, right, they're always like weird and flickery. Anyway,
Princess Leiah says, you know, help me, Obi one, you're
my only hope, And that's a hologram because it looks
like she's sort of taking up physical volume rather than
just printed onto a screen, right, and right now you're
my only hope, Daniel, because I'm a little bit confused
here because it gets tricky, right, because you're talking about

(14:36):
Princess Leab and so she's been projected into that three
D world, but we're looking at it on a flat
screen and then we're looking at it through two eyeballs,
which also kind of take two D pictures. So are
we talking about the sort of illusion of death or
are we talking about things having actual depth encoded in
a two D service. We're talking about having enough information

(14:58):
to describe of volume, but encoded on a two D surface.
So hologram is when you can describe something using only
two dimensions, but it has enough information to describe the
full three D volume. And that's not always possible, right,
It's not always possible to describe a three D object
in terms of a two D surface. It depends on

(15:19):
what you can do with that two D surface, Like
how do we make holograms? How do you have those
like baseball cards where it looks like the players moving
as you turn it. And they do that by adding
information to the two D surface, Like they have these
little ridges on the surface, so that when you look
at the image, you're seeing like a different part of
those ridges, and they have like different images on different

(15:41):
parts of those ridges. So they've done something to encode
add information to the two D surface so that you
have the whole three D thing actually printed down there
on two D. Right, Because they sort of like fool
your eyeballs into thinking it's three D, right, Like they
give one image to one eyeball and they give another
image to the other eyeball, and somehow you think it's

(16:02):
three D. But really it's all on a two D surface,
except that on that surface they sort of cleverly print
thing so that it somehow delivers different information to each eye. Yeah,
and different information to each eye gives you the illusion
of depth. But also I think it's crucial that as
your head turns in relation to the two D surface,
you see a very different image. Like if you just

(16:23):
have a picture printed on a flat piece of paper,
then as your head turns, you're seeing the same picture.
You're seeing it from a different angle, but you're seeing
the same actual information in a hologram. As your head
turns and you're looking at the two D surface from
a different angle, you're actually getting a different image. The
image you're seeing is changing, and just the same way

(16:44):
it would if it were a three D object and
you could like look behind it or look over its
shoulder or something, and you're revealing more information. That's the
experience that makes your mind think it's a three D object. Now,
how did those work really quickly? Do they do they
encode like the image from every possible angle or is
there something more to like? You know how they use
lasers and stuff like and special materials to sort of

(17:06):
encode that three D information. There's a lot of different
ways to do it. None of them are perfect. We
can't do a complete, perfect hologram yet in our universe.
You know, like those baseball cards, they have a little
bit of an angle there. It's obviously not a three
D object. That's done by having these little ridges so
that when you look at it from a different angle,
you actually see a different image, sort of like those

(17:27):
billboards that change as you drive by them, because there's
actually like a bunch of different pictures printed at different angles.
And the more clever ones and more impressive ones use
interference tricks. They send multiple beams of light from every
point on the surface, and then where you are you
get a different kind of interference from those different beams,
and that's what creates the sort of illusion of three D.

(17:48):
The dependence on your angle comes from the interference effects.
All right, pretty cool, And then I guess the question is,
how could our universe be a hologram? Are you saying
that we're like maybe printed on its surface, is somewhere
with the ridges or do you think maybe we're you know,
what we think is the our three D universe is
actually printed on a surface somewhere, or maybe there are
everything one surface. Is that what you're saying? Yeah, that's

(18:11):
the idea that maybe our universe can be described the
three dimensions of our universe of space and time and
gravity can be described by information you could put onto
a two D surface. And so then that begs the question, like, well,
if our universe feels like it's three D but it's
equivalent to a two D universe, what's the real universe?

(18:33):
Is the real universe two dimensions with some weird extra
bits encoded onto that two dimensions? Or is it actually
three dimensions? You know which one is like physically fundamentally
the true universe and which one is like mathematical equivalence. Well,
I guess the question here would be we're actually like
a three D universe printed on a two D surface.

(18:54):
Then like, who which which of the dimensions is fake?
Do you know what I mean? Like, is up and
down phase? Then somehow it's encoded in the left and right,
front and back? Or how would that even like how worthy,
What do you do with the extra dimension or what
is Yeah, that's a great question. Well, you know, out
in the depths of space, of course, every direction is
the same. You could just pick a direction and it's

(19:16):
just as good as any other direction. So it's not
like up and down or left or right or back
and forth really have any meaning in terms of the universe.
So on that two D surface, it's not like two
of our space dimensions exist and the other one is
just deleted. It's some other kind of space. So like
take our three dimensions X, Y, and Z. They map

(19:37):
two two weird dimensions on that surface, called them I
don't know A and B, but they're not like physical
space dimensions the way we think about them. And then
there's something else going on on that surface that lets
you like encode Z, that lets you take that third
dimension and make sure that that information is not lost.
But I guess if that information is there, wouldn't it

(19:58):
basically be and other dimension or are you saying that
it's somehow encoded through some trick by the first two dimensions. No,
it's basically there, and so the information is fundamentally equivalent,
but it's like a different sort of structure, Like we're
talking about mapping our universe, which has three dimensions and
gravity and all this kind of stuff into like an
abstract space something which is like where we talk about

(20:21):
quantum field theory on that space and we talk about
the relationships between points on that two dimensional surface, and
so that has effectively three dimensions because it's two dimensions
plus some other weird piece of information in the quantum field.
There really are two different sort of visions of the universe.
One is you have three dimensional space and gravity and

(20:44):
everything moves along, and the other is that you have
a two dimensional space. But then on that space is
this quantum field which is capable of encoding a third dimension.
All right, sounds a bit technical, so let's dig into
the details of that. But first let's take a quick break.

(21:11):
All Right, we're wondering if the universe is all it
seems to be, or whether it's kind of inflated in
a way, whether it's it's fooling us into thinking there
it has three dimensions, but really you're saying it could
have two dimensions plus like a little pocket the value
or field that tells you that gives you that third
extra feeling of a third dimension. Yeah, and you know,
all of this goes into trying to understand what is

(21:34):
the nature of space itself, Like what is this thing
we call space? And I think that's really interesting and
like historically to think about how the ancient thinkers thought
about space, you know, Newton and Descartes and those folks
just thought about spaces like the backdrop of the universe.
It was absolute, it was fundamental. Obviously you have to
have space, and everywhere in the universe has to have space.

(21:55):
And more recently we've learned this space does weird things.
It bends and wiggles, it's shakes that expands, it does
all these crazy things. And now we're not even sure
what space is. We talked about it on a podcast
episode recently, whether it's possible to even have parts of
the universe that don't have space in them, you know,
a universe without space. So part of this just goes

(22:15):
to like trying to understand what is the nature of
this space, what are the rules of it? Is it
really three dimensions where all those three dimensions are equivalent?
Where is it actually two dimensions with one extra tricky
dimension that's making us feel like it's three dimensions, and
that's why these are I think are deep and important questions.
It's like, maybe we think we're in you know, X,
y and Z space, you know, front, back, top, down, left, right,

(22:38):
but really we're actually in like A B space, and
each point in A B space has a little special
C value that maybe somehow those three things combine give
us the feeling of X, Y and Z, but really
it's just A and B with a little extra cy. Yeah,
and that all motion, all actual physical motion, only occurs
along that surface, right, that A and B value. All right,

(23:00):
So um, let's get into why we would think that.
It sounds like a pretty crazy idea. I mean, if
I think about it, I'm pretty certain we are in
three D space. You know, I can move up and down,
left and right, front and back, and I can things
when I touched them, they feel like there's three dimensional
Why would we think it's not. For a long time,
we did think it was three D space, and that
felt pretty settled. Though. There are ideas about how the

(23:22):
universe might have more dimensions, you know, eleven or twenty six,
But this particular idea that the universe might be two
D instead of having more dimensions came from the craziest
thing in the universe, and so of course it came
from studying black holes. And you know how on the
Extreme Universe series, I'm what were saying, like, we look
at the extremes of the universe because it shows us

(23:42):
what's possible. It breaks the rules, it stretches them. That's
exactly what happened here. People were looking at black holes
and trying to understand, like what is on the inside
of a black hole? What's it like in there? And
some people have this crazy idea maybe it's not like anything.
Maybe there is no inside black hole. Maybe all there
is to the black hole is the event horizon. Maybe

(24:04):
black holes are actually just two dimensions. Yeah, we've had
episodes about what happens when you go inside of a
black hole and what they are, and I think it
is that like when something sort of goes towards a
black hole, because of the way it bends space and time,
it never actually goes in right, like it basically stops
at the surface forever. In a way, it depends on

(24:26):
who you ask, which is the tricky bit. So if
you are watching something fall into a black hole, then
as it gets closer and closer to the black hole,
space is curved more and more, and then there's more
and more gravitational time dilation, which is an effect where
time slows down where space is curved, and so the
closer you get to the black hole, the more time

(24:47):
slows down, and so you never actually reach it. If
to wait for time equals infinity to see something actually
fall into a black hole, that's if you're the person
on the outside watching right. If you're the person jumping
into the black hole, then you don't experience any of that.
And just like in relativity, your experience of time depends
on who you are, where you are, and how fast

(25:09):
you're going. And so in this case, you just fall
right in, you pass through the event horizon, you head
towards the singularity. And so people are wondering, like, what's
going on? How can everything be smeared on the outside
of the black hole and also be inside the black hole?
How is that possible? You're saying, it depends on who
you ask, right, Like to us on the outside and
far from a black hole, hopefully things gets mirrored on

(25:31):
the surface of the black hole the event horizon. But
you're saying to the person falling in. They just fall
right in, but at time infinity for us. Yeah, that's
exactly right. We see them fall in only a time
equals infinity. But they see themselves fall in, you know,
very normally and very naturally. And these two things contradict
each other, and so often in relativity you have people

(25:52):
having different accounts of the same situation and both being correct.
And that's possible in scenarios where there's like no causal
link between the events, they have a timelike relationship, for example.
But here it's hard to understand, you know, how the
black hole actually accumulates stuff, whether there are actually are
things inside the black hole. And it goes to this

(26:12):
question of like the black hole information, right, we talked
about how if you put something into a black hole,
then it's information is inside the black hole, like you
throw a banana in there. Where does its energy go,
Where does this entropy go, where does its quantum information go?
And people are trying to understand, like what happens when
these black holes evaporate. Is everything actually on the surface

(26:34):
of the black hole and so it never really fell in,
and so it's information wasn't lost or was it inside
the black hole actually? And when the black hole evaporates,
its information is somehow lost, So it's important whether it's
actually gone inside the black hole or not. And then
can you still slip on the banana? Though? If it's
on the surface of the black hole, that's really the
important question. I mean, that's what this whole thing, because well,

(26:58):
I mean, if you're going to do a cartoon on
the surface of a black hole, you want to make
it physically accurate, right, And every cartoon has got to
have somebody slipping on a banana. And so I appreciate
your desire here to do physically accurate black hole surface cartoons.
Thank you comedy, Yeah, and then you laugh about it
at the end of time. But I think what you're
saying is that there's this kind of paradox, right, Like

(27:18):
we think things splat on the surface, and but someone
according to the people going in, they go inside. And
so there's this kind of idea that maybe you know,
once you go inside, you're just like on a to
the surface of the black hole. Yeah, that was sort
of the start of the puzzle, Like how do you
reconcile these two things? They seem like fundamentally very different things.
And hawking and this other guy, Beckenstein. We're working on

(27:39):
this and trying to understand, like where is the information
in a black hole? How does it actually work? And
they were working on this one day and they were
calculating how much information can be encoded inside a black hole.
That we're working on these calculations of black hole entropy.
Thinking about black holes is like thermodynamic objects with temperatures
that really and all this stuff. And one day they

(28:00):
arrived at this equation, and this equation told them that
the amount of information inside a black hole doesn't depend
on the volume of the black hole. It depends on
the area of the surface of the black hole. So
like it doesn't depend on the radius cube, that depends
on the radius squared. And that's kind of interesting. That's
the suggestion. It says, like, m the maximum information you

(28:22):
can store in a black hole depends on the area
of its surface, not on its volume. That suggests that
maybe actually these are just two dimensional objects, Like a
black hole is just a two dimensional object. But we
see it grow, right, don't we see a growth? Doesn't
that mean that it has volume to it? It could
be a two dimensional object embedded in our three D world, right,

(28:43):
Like the surface of a sphere technically is a two
D object. It's embedded in a three dimensional universe that
has a radius. It can move around in three dimensions,
but it's actually a two D object, like an infinitely
thin sheet of paper would also be a two D object.
So that's where this idea of a holographic universe hologrammic
hologrammic holographic principle of a holographic universe, meaning the university's

(29:06):
a hologram. So you're saying to the black hole could
be a two dimensional object in our three D world,
So how do we go from there to the whole university.
We didn't yet. First were trying to understand the interior
of a black hole, and the first step was to think, well,
maybe the interior of the black hole is a hologram, right,
maybe there is no interior. So if you are that

(29:27):
person that fell into the black hole and you think
you're on the inside of the black hole, you're actually
not actually still on the surface, but the whole surface
of the black hole has enough information to encode what
feels like a three D internal volume. So first, before
we go to the whole universe, people thought maybe the
two D surface of a black hole is a hologram

(29:49):
that projects the three D interior. So then what happens
is the black hole grows. The whole inside stays on
the surfacen't but it grows with the black hole. Oh man,
you can't think about that. You can't change the parameters.
This only works for a single thing falling into a
black hole. It gets much more complicated as soon as
you add like something else to a black hole. You know,

(30:10):
for example, if you throw a banana into a black hole,
then in principle, it never actually enters the event horizon.
It's smeared across the surface forever, right, And that's what
we're talking about now. If somebody behind you throws in
an apple, everything changes because that apple will now change
the shape of the event horizon. The event horizon will
actually grow out to meet that apple as the apple

(30:31):
falls in, and it will absorb the banana. So it's
a totally different scenario. You're now like tossing in multiple
things into the black hole. Not even something we're capable
of thinking about carefully, but that that is what's happening
right now in the universe, right, Like black holes are
constantly sucking stuff in things are constantly falling into and
they're constantly growing, So why would we think that that's

(30:51):
what's going on. Then yes, that is definitely what's happening
in the universe. And we see black holes actually growing,
and so we don't know what's going on there. If
you're the banana and and you're like smeared across the
black hole surface, and then somebody else throws in an
apple and increases the size the event horizon, it increases
the surface area, and now that surface area, in theory,

(31:12):
should be capable of describing a larger internal volume. There
is nothing actually inside the black hole in this picture.
Inside the black hole, there's no space, there's nothing. There
isn't anything in there that's not three D space that
you can move around in. There's just this weird surface
that has mathematically encoded onto it enough information to describe

(31:32):
a three D space. So the banana the apple feel
like they're in a normal three D space inside the
black hole, but they're still smeared across the edge of it.
All right. So then thinking about black holes and what
happens at the surface is what sort of led us
to this idea of a universe as a hologram, like,
are you saying that we're a universe imprinted on the
surface of a black hole, or are you saying that

(31:53):
just thinking about black holes let us to think, like, oh,
maybe the whole thing is imprinted somewhere else. Yes, exactly,
this idea from black holes let us to think more
carefully about the relationships between three D spaces and two
D spaces. And there was a bunch of guys working
on string theory, and string theory is really really difficult.
It's really hard to do any sort of calculation in
string theory, and sometimes when a problem is too difficult,

(32:17):
you look for like a mathematical trick to make it easier.
There's this idea that you can have a three dimensional
universe encoded on a two dimensional space, and some folks
realize that if you did that with string theory, it
might solve some mathematical problems, like if it's too difficult
to do a calculation in two dimensions, well, what if
it's actually a three dimensional universe. Then you can do
the calculation there. And so people were playing around with

(32:39):
that and realizing, oh, you can play the same game
not just with a black hole, but with string theory.
And so maybe you can describe the entire three dimensional
universe that has strings in it has a two dimensional
service and that would make some calculations easier to do
and other calculations actually harder to do. But they sort
of projected this whole idea onto the universe. And you know,

(33:01):
that's a really fun moment in science when you like
build a tool over here and you're like, oh, this
is cool. This solves this problem, and then you turn
around you're like a whole lot of second, maybe I
could do this to everything, you know, maybe I can
make it two thirds easier, so I'll have to do
as much math. Yeah, And so there was this really
big important result by a guy at the Institute for
Advanced Studies in Princeton, where that collection of smart folks

(33:25):
over there called a D S c F T, which
you can google if you're interested in more details about it,
or maybe we'll do a podcast episode about that. But
it give us this vision that maybe the entire universe
can be described in terms of being a three D
illusion of a two dimensional surface somewhere. All right, Well,
I have two questions for this three three dimensional problem.

(33:47):
I guess the first one is where did the third
dimension go? Like how is it being encoded in this
to the surface? And two could we ever tell the
difference that whether or not we are in a hologram
or not. So let's get into these questions, but first
let's take another quick break. All right, I know here's

(34:16):
my favorite question in these episodes. What does it all mean? Man?
Like if we're actually if our three D universe is
actually imprinted on it to the surface somewhere, like where
did the third dimension go? Is it just an illusion?
Is it actually there? You you mentioned like maybe it's
encoded in some quantum fields? Can you talk more about that?
Like how does how would that encode a whole dimension? Yes?

(34:38):
So think about space, right, do you think about spaces emptiness?
But we actually know that space isn't just empty, that
everywhere in the universe space has these things and that
we call quantum fields. And what is a quantum field? Well,
it's just like a number at every point in space.
For example, you know, there's the electromagnetic field and anywhere

(34:59):
you go in the universe, so you can ask what's
the strength of the electromagnetic field here, what's the strength
of it over there? It's something that has like a
value at every point in space, and the E M
field is actually more complicated because that's more than just
a value. It has like multiple values for every point
in space. But that doesn't matter. So this is something
which is sort of like added to space. You know.

(35:19):
It's like if instead of just having a city with
an address, where we have a house at every location.
Now inside that house you have a number like how
much is that house worth? Right, So that's like another
piece of information at every point in space. It's encoded
into this quantum field. But there's lots of quantum fields,
though you're saying this like extra information is encoded in

(35:42):
all the fields, or like there's one quantum field for
basically the Z direction. Yes, there's a special quantum field,
because if you just have a quantum field, you can
have like arbitrary random values and that doesn't give you
like a dimension. Instead, if you have a special quantum
field that follows certain rules, these are called formal field theories.
If you have a quantum field which looks the same

(36:04):
if you zoom in really really close or if you
zoom out really really far, if it tends to follow
the same rules. But things that are zoomed in really
really close don't interact very well with things that are
zoomed out really really far. Then the mathematical structure of
that quantum field theory has some symmetries to it which
allow things to behave exactly as if there was a

(36:25):
third dimension. Like if things that are zoomed in really
really small don't interact with things that are like really
zoomed out in this quantum field theory, then it's sort
of like things passing by each other in that other dimension.
And you know, if there's a scale that you can
like zoom in and zoom out, then it's sort of
like there's another direction there in this quantum field. And

(36:46):
so this is like a way to encode something into
the quantum field by adding a bunch of rules for
how it behaves, and those rules essentially make it as
if it was exactly like a dimension. Kind of feel
like maybe you're trying to pull a fast one on
your dear yor Daniel, I am, I feel like trying
to You're trying to paint an illusion here. I feel

(37:06):
like maybe you're saying that there maybe are three dimensions,
but one of them you don't want to call it
a dimension, you know what I mean, Like, maybe it
feels like maybe it's just like a technicality about the
naming of it, But if it acts and looks like
a dimension, why not just call it at the nmdion.
I got nothing against calling it a dimension, but it
is different from the other two, right, And our program

(37:26):
here not just on this podcast, but as humans trying
to scratch out the nature of the universe, is to
figure out the nature of the universe, and so if
it turns out that to the dimensions are different from
the third dimension, then that's quite interesting. And so we'd
be fascinated to discover, for example, that our universe was
actually one dimensions with like two weird projected dimensions instead

(37:48):
of being three dimensions, or if you were like, you know,
a three dimensional surface in a four dimensional space. I
think I would definitely want to know that. You know,
it doesn't change how you live your life necessarily, or
whether you should buy insurance. Yes, definitely buy insurance, but
it changes I think, our concept of the nature of reality.
So I definitely want to know. Even if mathematically the

(38:10):
two things are totally equivalent, physically, it means that one
of these dimensions is not the same as the other two, right,
But is it not the same in that fundamental of
a way or is it just different in a sort
of like notation mathematically way. No, I think it's fundamentally different,
because that would mean that space itself is two dimensions.

(38:31):
And remember one of our goals here is to understand
the nature of space, and so space itself is two dimensions.
But then it has these properties, you know, these properties
which allowed to do things that three dimensional space would do.
Then that's different from living in three dimensional space. Yeah,
I feel like you're trying to pull a Pluto here
on the up and down dimension or something. It's like,
it's technically a dimensionoid out a dimension. It's a dwarf dimension. Yeah, exactly.

(38:56):
But you know, some of these calculations, these string theory calculations,
are harder to do in a certain number of dimensions,
and they make more sense in fuel or in more dimensions.
And so if the sort of fundamental theory of everything
turns out to only work in two dimensions and not
in three, then also sort of tells you something about
the nature of the universe itself. You know, the universe

(39:17):
pervers the two dimensional description. I mean, in theory. You
could describe the universe in terms of any number of
dimensions you want, but we're looking for the most compact,
the simplest, the most natural description that we hope reveals
not just the way we are thinking about things, but
the actual structure of the physical universe outside our minds.
And I guess it also sort of depends on where
you define a space, right, like space. If you define

(39:39):
space as only the two dimensions you like, then yeah,
there's it's only a two the space. But if you
maybe define spaces these two dimensions plus this extra you know,
value of the quantum field, then you know, maybe that
is what space is quote unquote hm, that's definitely what
our experience of space is, right, Either space is naturally
three dimensional or it's two dimensions with this extra wiggle

(40:02):
room in it that allows us to experience it as
if it was three dimensions. I mean, it sounds to
me like your question is sort of like saying, isn't
the hologram actually a three D object? Like, well, no,
it's not really there, you know, like it really is
just a two D surface baseball card. Isn't actually three dimensions?
And you might say, well, it doesn't look any different
if you couldn't actually tell, what would it matter? Well,

(40:24):
it matters to me because I want to know the truth. Man,
What does it all mean? All right? Well, let's get
into the last question here, which is, um, how would
we even tell if we are in a two D
or three D universe? Right? Like, if the difference is
so small or subtle or kind of sort of like, uh,
you know complex, will we ever be able to, you know,

(40:45):
devise an experiment to tell us whether we are two
D or three D. Well, we're not sure, but there
are some folks out there who have some really fun
ideas for figuring out if we actually live on a
two D surface. And the idea is that a two
D surface with a projection and it's three D surface
would actually be different because there would be different quantum fluctuations,

(41:05):
Like we're talking about a quantum field generating this third dimension, right,
and so we would definitely be sensitive to like the
way these fields fluctuate and quantum fields fluctuate differently in
two dimensions and in three dimensions. We had a whole
fun podcast episode about the nature of two D objects.
You should go check that out. But things move differently

(41:26):
in two dimensions and in three dimensions, and so they
fluctuate differently, and so we can see like quantum fluctuations
from the very very beginning of the universe. Quantum fluctuations
you normally think of like oh, this electron went left
instead right, and nobody really cares that, nobody can ever
see them. But in the very beginning of the universe,
those fluctuations dictated like how things happened, and they got

(41:47):
blown up into real measurable effects. So if there was
a two D world, we would see different quantum fluctuations
than in a three D world, and we might be
able to see hints of that in remnants of the
early universe, or I see because that the when the
universe was born, you're saying, at the Big Bang, you know,
with things were so compact and hot and small and
dance that quantum fluctuations were a big deal. And so

(42:11):
as the universe blew up. If there was actually only
two dimensions, then we would see something funny going on
right now instid of the universe around us. And because
this bonus dimension is responsible for making the third dimension
and affecting how gravity works in this three dimensional world,
we should be able to see it in gravitational wave detectors. Basically,
the bottom line is that if we live in a

(42:33):
two dimensional world with a funny bonus dimension, we should
be able to see a weird sort of like noise
in gravitational wave detectors that you wouldn't otherwise see. This
noise would be like an extra fuzz or a unique
kind of fuzz that comes from the two D surface
instead of being in a three D world. But I
think you're saying You're not saying that there's like one
dimension that's fake. You're saying that, you know what I mean, Like,

(42:55):
it's not like Z is fake. It's more like X,
Y and Z actually mapped to a B in the
a little bit and something bonus called C. You want
to see flat gravitational ways, for example, you would see
some weird mathematical or some weird dependency on the on
the gravitational waves. Yeah, exactly. The idea is if all
the three dimensions are not the same, if two of

(43:16):
them are actual dimensions and one of them is just
a bonus, then there are different rules for those dimensions.
And when it comes to things like quantum mechanics and so,
they have different impacts on things like gravitational waves, and
we should be able to see if there's like two
dimensions of noise in the gravitational waves or three dimensions
of quantum noise in the gravitational waves. That was the idea.

(43:36):
At least. There's this guy for me, that Craig Hogan,
who said in two thousand and eight that he had
a prediction for what he thought these gravitational wave detectors
should see if we actually lived in a holographic universe,
if we lived in a two D world projected into
three D by our minds, then we should see this
extra fuzz in these experiments from these gravitational wave detectors.

(43:59):
So that was his diction in two thousand and eight.
So we've actually seen gravitation of waves now with the
Lego experiments, and so have we seen this noise? Is
there evidence for a holographic universe? So that was sort
of a moment of excitement because he sent his prediction.
He's like, here's what you should see. You should see
this kind of fuzz if you look at your data.
And then they sent it back some data and it

(44:21):
looked just like the fuzz he predicted. And so for
a moment, people were like, what, hold on a second,
did Hogan just proved that we live in a hologram?
But then it turns out, you know, he might have
seen that plot already. He might have known in advance
the kind of noise that they were seeing. What it
might have been a postdiction and not a prediction, right.

(44:41):
And you know, these gravitational wave detectors are very tricky
and have a lot of noise in them, and the
whole game is getting them to be quiet and noise
free so you can see gravitational waves. So it's not
that impressive to like find noise in a gravitational wave detector.
It's almost like the noise is the illusion, right, Like
you can project anything you want to that noise if
you do the theory right exactly. And so people did

(45:03):
some other calculations and they realize that even if he's
right that you can see it in this way, then
the size of the noise he predicts is much much
smaller than anything we're seeing. So so far, we don't
have any evidence that we're living in a holographic universe
or that the universe is a hologram. But there are
clever people out there thinking about ways to sort of
probe this and looking for clues around the edges of

(45:26):
stuff to see if we're just living on a baseball card. Well,
I hope it's a valuable one, not one of those
common cards. It's got a baseball player slipping on a
banana near a black hole. But you only think he's
slipping exactly sleeping. You have to wait till the end
of time to see him actually slip on the banana.
All right, Well, I guess once again the answer is

(45:47):
stay tuned. We think it's possible. Well, we know it's possible.
We could be in ato the sort of universe, But
I guess we don't have the instruments right now to
tell the difference, or we don't know the right way
to tell the difference. Even that's right, people are still
thinking about and coming up with ways to predict it.
And there are folks out there thinking about clever experiments
that might be sensitive to the nature of space. Is

(46:07):
it really two plus one dimensions or is it three dimensions?
We don't even know. But maybe in the future somebody
will unravel this. Somebody will figure out that it only
makes sense for it to be two plus one or
one of these listeners out there will come up with
a really awesome experiment to probe the very nature of
space and time. And in the meantime, I guess you
should watch out for those three the snacks, because you

(46:27):
are still three dimensions as far as everyone else. That's right.
Just toss them in the black hole and watch for
infinity as they very slowly fall in. It's the long
term die there you go. All right, Well, we hope
you enjoyed that and it didn't what flattened your mind, Daniel.
I hope it doesn't change the nature of your experience
in this universe, because that third dimension is pretty fun.

(46:48):
I like being able to step over puddles rather than
having to walk through them or go around them. So
let's all savor and enjoy that third dimension at least
while we know it's real. Well, we hope you enjoyed that.
Thanks for joining us, see you, and thanks for listening,

(47:08):
and remember that. Daniel and Jorge Explain the Universe is
a production of I Heart Radio. For more podcast from
my Heart Radio, visit the I Heart Radio Apple Apple Podcasts,
or wherever you listen to your favorite shows.