[INTRO MUSIC] What if I told you
were a hologram? Or maybe I'm getting
ahead of myself. In my quest to become better
acquainted with reality, I decided to get the
perspective of someone who devoted their life to
discovering the true nature of the universe. Leonard Susskind is one of
the founders of string theory and Scientific America's
bad boy of physics. I'm a professor of physics
at Stanford University. And I think about physics. CRAIG: Like many
physicists, Susskind spends his days
trying to understand how the universe works. But physicists
don't always agree. And about 40 years
ago, a major battle began in the physics community
that lasted for decades. And winning the battle
required rethinking the very nature of reality CRAIG: There are two
prevailing theories, the theory of relativity
and then quantum mechanics, that seem to be at
odds with each other. Well, Yeah, they do seem to
be at odds with each other, and always had from the get go. But they can't be at
odds with each other, because they're both true. We've got to make them fit. We've got to make
them fit together. CRAIG: So in 1915,
Albert Einstein published his general
relativity theory, which explains how gravity
and space-time work. And quantum mechanics was
developed a few years later by these people. LEONARD SUSSKIND: You
know, quantum mechanics is about very, very
small and light things which are so delicate that
any way that you touch them or any way that you
observe them, they change. Relativity is about gravity. Gravity is about
very heavy objects. MATT: So relativity
is great at explaining the motions of big things,
like stars and planets, but not so good at tiny
things, like particles. CRAIG: Yes. And physicists are always on
the lookout for one theory that explains everything. But in the day to day life of
a cosmologist or a particle physicist, you're usually
dealing with very big things or very small things. So for the time being
two theories was OK. That is, until a young physicist
who was studying black holes had a brilliant idea that
screwed everything up. LEONARD SUSSKIND:
Stephen Hawking put his finger on
a very important, what's called a paradox. A paradox means something which
apparently looks contradictory. What he recognized
is that things that fall into a black
hole are lost completely. They're lost, and they
can never come out. On the other hand,
quantum mechanics says, and this is one of its very,
very basic ingredients, that nothing can
ever really be lost. Information, the
distinctions between things, can't really be lost. But what does he
mean by information? I mean, I lose
information all the time. I can't remember
where I parked my car, my dog ate my book report. That's a little different. When Susskind talks
about information, he's referring to
the distinctions between the fundamental
particles that make up the atoms in our bodies
and the rest of the universe. For instance, I could take
this book and burn it. Hey, I'm not
finished with that. I'm not going to burn it. But if I did, you wouldn't
be able to read it, because it would be a
pile of ash and smoke. However, from a
physics perspective, the atoms that make
up the paper and ink in the letters and
the tragic love story would still be there and could,
theoretically, be recombined if we had the right tools. In fact, I think
of it as more basic than any of the other
principles of physics. The most basic
principle of physics is that distinctions
never disappear. Now, take that same book,
toss it in a black hole, and you've got
yourself a problem. According to Hawking,
all that information is irretrievably lost. Why is that, exactly? Well, it has something to do
with what Hawking discovered about black holes. Well, maybe we should explain
what a black hole is first. Go for it. A black hole is a
region of space composed of super densely packed matter. Because of it's mind-boggling
density, it's pull of gravity is so strong that nearby planets
and stars can get sucked in. And nothing, not even
light, can escape once it's gone beyond the
black hole's event horizon. So it's a point of
no return, in a sense. It's a point of no return
in which when anything falls through it, it simply
cannot get out, because in a sense space is
moving inward at faster than the speed of light. So in 1974. Stephen Hawking basically said
that all matter and information that goes into a black
hole is lost forever. And I guess Susskind
wasn't too happy about this. No way. He actually wrote
a book about it. The Black Hole War, My
Battle with Stephen Hawking to Make the World Safe
for Quantum Mechanics. Yeah. Right. Could you describe
this battle, and why it was a war you felt it
was necessary to fight? Well, as I said, Stephen was
basically a gravity physicist, a general relativist. And he believed
in the principles of general relativity. Nothing else mattered. I was always a
quantum physicist. And when Stephen said that
it looks like black holes, because they lose
information into them, violate the principles
of quantum mechanics, I and a couple of my friends,
in particular a physicist by the name of Gerard 't Hooft,
a very famous Dutch physicist, said, no, that can't be right. And we didn't know
why he was wrong, but we knew he was wrong. He held his ground. We held our ground. But eventually, we began
to make sense of in what way Hawking was wrong. It's a basic
principle of the way we think of classical
physics, that a thing can only be in one place. If it's here, it's not there. If it's there, it's not here. What was going on is
that, in some funny sense, quantum mechanics
was requiring that it could be in the sense in
two places at the same time. What? How is that even possible? Yeah, what's he talking about? We begin to get the idea,
in particular, 't Hooft and myself, that what was
going on on the horizon of a black hole was
similar to a hologram. That the surface
of the black hole, the horizon of the black hole,
was like a photographic film. And what fell into
the black hole was like the image created,
a three-dimensional image created. CRAIG: So their idea
was that any matter that falls into a black hole
remains trapped inside. But at the same
time, an exact copy is perfectly preserved
on the horizon. This by itself was a
revolutionary idea. But Susskind and his
crew soon realized that the holographic principle
doesn't necessarily only apply to black holes. Once we understood
that what was inside falling into the black
hole, inside the black hole, was a kind of projection
of the horizon, we began to understand
the idea was more general, that the entire three
dimensionality of space is a projection of a
very distant horizon that surrounds us. And not the horizon
of a black hole, it's the horizon of the universe. And instead of being
on the outside of it, like we would be if there
was a black hole here, we were on the inside of it. And so you could say that
we on the inside of it are a projection of this
film-like thing that's on the boundary of the universe. So while we stand here
in The Good Stuff studio, and while you watch this
video at home, or at work, or in prison awaiting trial,
whatever you're doing, we are actually projections
of equivalent versions of ourselves that live on the
outer surface of the universe. Whatever happens here,
happens there, and vice versa and vice universa. So I'm a hologram? This isn't real? Oh my god. Is the real me just
a battery that's powering a universe-wide
simulation? No, Matt, you're
not in the Matrix. There is no spoon. It's just that you're here,
and you're sort of over there as well. Well, if we're here and also
there, are we the projection, or is the outer
surface the projection? Which one's reality? Are we on the inside
of the universe, or have we actually been in the
outer surface this whole time? That's your choice. You decide. But the mathematics
says they're equivalent. I feel like I'm here Yeah, but so does your
image on the boundary. It's also saying, I
feel like I'm here. Oh, man. Right, right. But the mathematics doesn't care
which way you think about it. It says there's an equivalence. That's about all we can say. Physicists do not
like the word reality. We may talk about
it all the time. But when it comes
down to it, we really don't want to say this is
reality and that's not reality. There are mathematical
connections between things. And that's got to be it, because
we don't have insight enough to be able to tell
which is reality. That's pretty wild. It is pretty wild. And not surprisingly, the idea
of the holographic principle was initially met with
a bit of skepticism. This was a wild idea at first. Nobody really accepted it. I think for the most part the
reaction of our colleagues were, those guys used
to be smart guys. I think they've
lost their marbles. The world is a hologram? That's too crazy. Eventually, the idea got put
into a very, very precise form by a young Argentinian physicist
by the name of Juan Maldecena. Juan Maldecena is now one of the
great physicists of the world, maybe the greatest
physicist of the world. It's now gone from being
a wild-eyed conjecture to being an every-day
working tool of physics. After Juan Maldecena's
mathematical realization of the holographic principle,
Hawking conceded defeat. He admitted that he was
wrong about information being lost in a black hole, calling it
his biggest blunder in science. So how does Susskind
feel about Hawking after he admitted he was wrong? All of these ideas were
put in place as a response to a very, very deep question
Stephen Hawking asked. He was incredibly
perceptive to see that there was this tension there. And all of the ideas
of modern physics that are exciting
all of us now trace right back to his question. So to say he was just
wrong is a pale reflection of what really happened. So does Stephen Hawking
now fully support the holographic principle? As far as I can tell
he supports these ideas. But that's kind of irrelevant,
because the rest of the physics community does. You know, we get old. Steven gets old. I get old. At some point it doesn't
matter what he or I think. OK, so the physics
community generally accepts this is a
plausible theory. That's all well and good, Craig. But how can something so
insane-sounding be true? Well, maybe you just
don't understand it. I don't understand it. Well, why is this stuff
so hard to understand? When people ask me
about these things, I always give the same answer. Our neural wiring, the
thing that we inherited from our ancestors,
and I don't mean our ancestors our
grandparents, I mean, you know, the worms in the muck. Through evolution, the neural
wiring that we inherited was not built for
quantum mechanics. It was not built for
higher dimensions. It was not built for thinking
about curved space-time. It was built for
classical physics. It was built for
rocks and stones and all the ordinary objects. And it was built for
three dimensional space. And that's not quite
good enough for us to be able to visualize
and internalize the ideas of quantum mechanics
and general relativity and so forth. So instead, what do we do? We use mathematics. Eventually, in time we
develop intuitions out of the abstract mathematics. We get better at it. And we begin to think that way. But that can be
extremely frustrating when trying to explain
to the outside world. The outside world
by and large has not had that experience of
going through the rewiring process of converting
their minds into something that can
deal with 5 dimensions, 10 dimensions, or the quantum
mechanical uncertainty principle, or whatever
it happens to be. And so the best we can do is
to use analogies, metaphors. And the holographic
principle is a metaphor. The way I've described
it in terms of a hologram is not precise. It's not exactly accurate. It's close. It captures some of the ideas. But there is a whole raft
of mathematics behind it that I can't easily
transfer to you. Yeah. I should've paid more
attention in math class. Well, it wouldn't
have been enough. Yeah. I know what you mean. Like, even learning
about relativity, just learning about
how time works and how time is a dimension, it
took me a while to fully grasp. No, you would get it. You would get it if you
took a couple years. I mean, I don't know what your
level of mathematics is, but-- I was good in high school. That's good enough. If you were good in
mathematics in high school, then within a year
or two of effort these ideas could be conveyed. Yeah. But to do so in my living room
here in an hour, all we can do is try to use metaphors
and analogies. Right. So it's possible that
after a few years of rigorous
mathematical training, we could potentially
understand these principles. Still, Susskind admits
that not everyone will be able to understand,
or even want to. And that's OK. In my experience there's
a lot of people out there who understand that they
can't understand it, and are very glad
that somebody can. There's also people
who are very resentful. They're resentful. They think there
is a conspiracy, a conspiracy that the priesthood
of science is hiding something. Can you tell them no? Can you tell them? No, no, no. We're not hiding anything. We want more than
anything else that people should listen to us, and
understand what we're saying. But we're stuck with this
obstacle of mathematics. So if you want to
understand the universe beyond the basic stuff
that we can see and touch, you gotta learn the math. Right. But it's also OK if you don't
know the math, because there are people out there
who have devoted their lives and
years of research to understanding this stuff. And they're doing
a pretty good job. Science is a constantly
evolving field. But there is plenty
that they do know. And they're getting better and
better at making predictions. So what did Susskind
think is in store for the future of physics
and our understanding of the universe? Yeah, I think this
holographic idea is permanent in the
vocabulary of physicists. It's in the textbooks. It's going to stay
in the textbooks. But how the whole story
is going to play out, the universe, how
quantum mechanics fits together with
gravity and so forth, I think there's only one
thing that's certain, that there will be surprises. Some of them will
come from experiments. Some of them will come
from giant telescopes. And some of them will come from
mathematical and theoretical thinking about how
things fit together. And I think one
can be pretty sure that anybody who thinks that
they have the final answer now is smokin' something bad. Or maybe they should be
smoking something better. Ha-ha-ha. Don't do drugs, kids. But I think
there's every reason to believe that the future
will hold surprises. So for me to sit here and to
predict how physics will evolve in the next century or so
is a total waste of time, because I'll be wrong. Good answer. So there's still a
lot to be discovered. But there's no way to
know how our understanding of the universe is going
to change in the future. And, as we've learned
throughout the episode, it's hard to even know
what's happening right now. So what are we supposed to do? Well, I guess we
just have to trust that there are people out there
who are diligently working to figure out how our world
works, where we come from, and where we're going. And at the same time, we
have to be a little cautious dealing with people who claim
to have all the answers. Great summation, Craig. Thank you. Pretty nice day out. Want to go outside and
throw the football around? That's some classical physics
I can wrap my head around. Let's go buddy. Hey, guys, wait for me. Thanks for watching our Seeing
Isn't Believing playlist. If you, or the other you on the
outer surface of the universe, liked this video, consider
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you can get a cool perk. Go long, Craig! Longer. Even longer. Don't stop. It's going to be a bomber. [MUSIC PLAYING]
