A 7-minute guide to the relationship between quantum mechanics and black holes

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 of the computers that

we're all familiar with. It's basically copying information. You can't do that in quantum mechanics

It's called the no cloning theorem. 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

have been 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. The remarkable thing for me is an intimate relationship between black hole physics and quantum computing If we go back right to the beginning of the work on black holes in the 1970s

Jacob Bekenstein, a 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 space-time

Now, how does something store information? You need some structure, you need atoms, or something that can store bits of information

Well, it 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

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, speed of light

It's the smallest distance that we can talk about sensibly 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 to say it's a

library then you would say well it to do with how many books I can fit in the room but black Coles seem to be telling us that there something about the surface surrounding a region This is the first glimpse I think of an idea called

holography. 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. 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

a very specific model called ADS-CFT by a physicist called Maldesina, 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 Maldesina was purely mathematical

It wasn't framed in the study of black holes, although the questions ultimately seemed 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, may be in some sense true. And it seems that we're beginning to glimpse and 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

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 called quantum error correction code

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

We're catching glimpses of this theory. And that's where the research is at the moment

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