Adam Brown

As understood by Beck and Stephen Hawking, it's just a weird fact about black holes perhaps, but we now understand it as a strong indication of what we call the holographic principle.

The holographic principle has been a powerful idea in quantum gravity, and it's the following.

So if you took a non-gravitational system in which you ignored gravity, like the pile of hard drives, the information storage would scale like the volume, as we discussed, whereas in fact it scales like the area.

So, or another way to say that is if you take a three-dimensional, three plus one dimensional theory in which you have both quantum mechanics and gravity.

The information storage scales like R-squared rather than R-cubed, i.e.

it scales as though you had a non-gravitational system in one fewer dimension.

So if you had a two-dimensional theory in which there was no gravity, the information stored in a given region would also scale like R-squared, because the information would be just the two-dimensional volume, as in the area.

So in other words, it's at least as far as information density, the information capacity is concerned, a gravitational theory in three dimensions is like a non-gravitational theory in two dimensions.

Or more generally, a gravitational theory in n dimensions is like a non-gravitational theory in n-1 dimensions.

So that is...

a big hint that forms the basis of the holographic principle.

It's like gravity eats information.

There's less information than you thought there was, than you naively thought there was, if you didn't include information.

And so the holographic principle says that maybe that's not just a neat observation.

Maybe, in fact, is the case.

that for some quantum gravitational theories, there is another theory that is exactly equivalent to it in one fewer dimension.

And so this led to Maldacena's ADS-CFT correspondence, the Gate Gravity Duality, which was the most cited paper in ING theoretical physics.

ever, I think, maybe, at this stage.

And in the late 90s, he wrote down, he took that as a hint, and it wrote down an exact, we believe, an exact duality between a particular theory of quantum gravity, some particular flavour of string theory, and a non-gravitational theory that lives on the boundary of that space.

Well, this was a very influential paper, as I said, and really becomes a tremendous theoretical laboratory for trying to understand the connection between gravity and quantum mechanics.