Why we still don’t get gravity

A better understanding of gravity will allow us to know more about black holes. Photo: NASA/CXC/M.Weiss.

Gravity. It’s simple, right? Objects, the larger the better, exerting force on each other. Turns out, it’s a complex subject that we don’t quite understand yet. In the 1970s physicist Stephen Hawking declared that gravity was incompatible with quantum mechanics—laws governing how objects behave at the subatomic level. But recent research is bringing these apparently disparate views together. UBC physicist Mark Van Raamsdonk is helping to pioneer a new theoretical approach to gravity that could rewrite physics books.

What is the focus of your research?

At the macro level, Einstein’s theory of gravity gives us a set of rules that allow us to understand the movement of solar system objects or galaxies, or even the cosmological evolution of the whole universe. I study gravity in the framework of quantum mechanics—interactions at the subatomic level. At the micro level we need a different set of rules to understand what’s happening. Even though gravity is usually about large scale things, we think it is fundamentally a quantum mechanical theory, and it’s important to understand the quantum aspects.

Why take on gravity?

We’ve discovered quantum versions of most physical laws, except gravity! A better understanding of gravity utilizing quantum mechanics is essential to understand black holes and the Big Bang. We know our universe is expanding, but we believe it began as something extremely dense, where gravity would be important, even at tiny distances. Inside black holes, matter is so dense that gravity is important even at an atomic scale. In both of these situations, quantum mechanics is important to understand the physics.

You’ve described our universe as being akin to a video game.

The ‘universe’ of a video game is made of digital bits of information encoded on a two-dimensional chip. According to a new concept known as ‘holography’ our universe might be described by something like quantum bits stored on a two-dimensional chip which encodes our tri-dimensional reality. It’s like the hologram on a credit card, which shows a 3D image but is printed on a flat piece of plastic. It’s currently the most promising way to reconcile Einstein’s theory of gravity with quantum theory. Remarkably, it suggests that even ordinary space and large scale gravity might have a quantum origin in an underlying 2D description.

What do people misunderstand about your work?

My work, which exists in the context of string theory, is a very theoretical branch of physics. In many areas, you’d be able to go back and forth between theory and experiment to test your theories. With string theory and quantum gravity, it’s much more difficult to test things experimentally, so we need to rely on indirect tests and mathematical consistency. We can’t make black holes, sadly.

Silvia Moreno-Garcia
silvia.moreno-garcia@science.ubc.ca
604.827.5001