Avi Loeb

once we figure out what is missing, perhaps we'll have a full quantum gravity theory.

So it may have nothing to do with extra dimensions, the way string theory operates.

I don't know what it is, but if I had to guess, I would say it must be something that we are missing that perhaps has to do with the way gravity operates

combined with quantum mechanics, which we don't know how to marry these two things, you know, as of now.

Could it be a graviton carrying that information from... Well, that's part of the so-called semi-classical picture that we have of gravitational waves as a collection of gravitons.

We've never detected a particle of gravity, a graviton, on its own, you know, like a single particle, like we detect a single photon and a particle of light.

And so...

We can talk about gravitons, but it doesn't give us a quantum theory of gravity.

It's just a phenomenological way of approaching, in a semi-classical way, how to describe gravity.

There are other derivatives that are done in this way.

For example, Stephen Hawking decided at some point to prove a graduate student at Princeton wrong.

The graduate student's name is Jacob Bekenstein, back in 1970.

He said, well, Hawking showed that if you take two black holes, you can associate the surface area around them.

That's the event horizon.

Whatever gets inside cannot live.

It's the ultimate prison.

It's just like Las Vegas, what happens there stays there.

Hawking showed that if you take two black holes and combine them, merge them to make a bigger black hole, the surface area can only increase.

So Bekenstein said, as a student, he said, well, that reminds me of the second law of thermodynamics because maybe the entropy of the black hole is proportional to its area.

So then entropy always increases and that will explain it.