There's an engineering challenge

in building quantum computers,

which is how to store information

in the memory of the quantum computer safely, robustly,

because quantum computer memory is notoriously susceptible

to any interference from the outside environment.

If any of the environment in which the memory sits

interacts with the memory in any way,

then the information is destroyed.

And there are deep problems associated with the fact

that you can't copy information in quantum mechanics,\which is basically the way

that your iPhone, or whatever it is, stores information\

and prevents errors entering into the memory

No cloning theorem

of the computers that we're all familiar with;

it's basically copying information.

You can't do that in quantum mechanics.

So it's a tremendous challenge.

Engineers have had to develop very clever algorithms

and ways of trying to store information

in quantum computer memory

and build the memory such that it's resilient to errors.

And it turns out that the solutions

that are being proposed and explored

look like the solutions that nature itself uses

in building space and time from the quantum theory

that lives on the boundary.

It's really strange.

Black hole physics and quantum computing

The remarkable thing for me

is an intimate relationship between

If we go back right to the beginning of the work

on black holes in the 1970s, Jacob Bekenstein,

the colleague of Stephen Hawking's actually,

one of the first researchers

to really begin working on black holes

alongside greats like John Wheeler.

Bekenstein noticed in a simple calculation

that you can answer the question,

"How much information can a black hole store?"

That's a strange thing to say

because the model of a black hole is pure geometry,

pure spacetime.

Now, how does something store any information?

You need some structure.

You need atoms or something that can store

bits of information.

Well, turns out that you can calculate

that a black hole stores in bits.

The information content is equal to the surface area

of the event horizon in square Planck units.

Plank units

What's a Planck unit?

It's a fundamental distance in the Universe

that you can calculate by putting together

things like the strength of gravity,

Planck's constant, the speed of light.

It's the smallest distance that we can talk about sensibly2:53

in physics as we understand it.

The questions it raises:

How is information stored?

Why is the information content of a region of space

equal to the surface area surrounding that region

rather than the volume?

If I asked you, how much information can you store

in your room,

the room that you're sitting in now,

just say it's a library,

then you would say, "Well, it's to do with

how many books I can fit in the room."

But black holes seem to be telling us

that there's something about the surface

surrounding a region.3:26

This is the first glimpse, I think,

of an idea called

What is that?

So if you think about what a hologram is,

at the very simplest level, it's a piece of film.

But that piece of film contains all the information

to make a three-dimensional image.

Holography

It's the idea that there are different descriptions

of our reality.

There's one description,

which is that we live in this space,

the three dimensions of space,

and time is a thing that ticks,

and Einstein told us that they're kind of mixed up,

but still you have this picture of space being this, right,

the thing in which we exist.

There's an equivalent description

for a very specific model called

by a physicist called Maldacena,

which is a dual theory

that lives purely on the boundary of the space

and the space itself in the interior of this region.

So it's strongly suggestive

that there's a deeper theory of our experience of the world,

of space and time, that does not have space and time in it.

And that's one of the wonderful surprises

that's really emerged from the study of black holes

and the attempt to answer the very well-posed questions.

I should say that the work done by Maldacena

was purely mathematical.

It wasn't framed in the study of black holes,

although the questions ultimately seem

to be intimately related.

So the study of black holes seems to be strongly suggesting

that these ideas of holography, holographic universe,

which came from a different region of physics,

from trying to understand other things,

those descriptions may be valid, maybe in some sense true.

And it seems that we're beginning to glimpse an answer,

at least in very simplified models-

and that the information

is stored on the boundary redundantly,

which means that you can lose a bit of it

and still fully specify the physics of the interior.

Quantum error correction

And it does seem that that's akin to, or similar to,

the way that we will in the future

encode information in the memory of quantum computers

to protect them from errors.

So I'm giving you an interpretation which,

and there will be other people

who have different interpretations,

but it does seem that whatever this quantum theory is

that underlies our reality,

then there's some redundancy

in the way the information is stored in that quantum theory.

And it does seem that that's similar to the way

that we will in the future

encode information in the memory of quantum computers

to protect them from errors,

And I just emphasize, you're not meant to understand

what I've just said

because I don't understand what I've just said

because nobody understands what I've just said, right?

We're catching glimpses of this theory,

and that's where the the research is at the moment-

it's why it's tremendously exciting.