William East: Exploring the places where gravity breaks

When two black holes collide, they do more than rearrange matter. They shake the universe.

The tremors that ripple outward from these cosmic collisions are gravitational waves — distortions in spacetime predicted by Albert Einstein more than a century ago, but only detected for the first time in 2015, when the Laser Interferometer Gravitational-Wave Observatory (LIGO) captured the signal from a pair of merging black holes. For physicists, it marked the birth of a new kind of astronomy.

For William East, now a faculty member at Perimeter Institute, it marked the opening of a frontier he was yearning to explore.

“In a sense it was just the beginning,” East says. “That was like the first event. And now we’re seeing more than a hundred of these black holes merging. And we expect to see many more in the future.”

East studies strong gravity, in which objects move at speeds close to the speed of light, spacetime itself becomes dynamic, and Einstein’s equations must be solved in their most extreme forms.

“We want to understand the dynamics of spacetime itself,” East explains. “When you start thinking about black holes and what happens when two of them merge and how they create gravitational waves, you really have to think about spacetime as being dynamical.”

Although gravitational waves are now being observed regularly, they still hold many mysteries. The signals detected by LIGO are faint, buried in noise, and shaped by physics that can’t be reproduced in labs on Earth. To interpret them, researchers rely on detailed theoretical models and large-scale computer simulations.

This is what excited East the most. Much of his research involves taking Einstein’s equations of general relativity and solving them numerically on supercomputers, simulating what happens when black holes or neutron stars orbit, merge, and collide. These simulations produce theoretical gravitational-wave signals with real data.

“One really powerful tool is just the ability to take these equations and throw them on a supercomputer,” explains East. “You can set up different situations, run the simulation, and get an answer to what happens. And even though you know every line of code and every equation that went in, you can still get surprises.”

East has helped pioneer simulations of systems that had never been modelled before, including collisions involving black holes and neutron stars on highly elongated, or eccentric, orbits. These rare systems could produce gravitational-wave signatures unlike anything LIGO has yet observed — and without theoretical templates, such signals could easily be missed.

“I want to make sure we don’t miss the big reveal by not looking in the right places or in the right ways,” East says. “It’s a completely new way of looking at the universe.”

In 2017, scientists detected gravitational waves from a pair of merging neutron stars and, for the first time, observed the same event across the electromagnetic spectrum, from radio waves to gamma rays, as telescopes around the world turned toward the same spot.

“That was also pretty spectacular,” East recalls. “Not only because we saw this gravitational wave signal from two neutron stars merging, but because the entire astronomy community pointed their telescopes in that direction and saw all these electromagnetic counterparts.”

This combination of signals, known as multi-messenger astronomy, allows physicists to learn far more than they could from any single observation method. It offers clues about how matter behaves at extreme densities, how heavy elements are formed, and even whether gravitational waves might reveal hints of new fundamental physics.

East wants to figure out whether gravitational-wave observations could probe phenomena beyond the standard model of particle physics, such as dark matter or exotic compact objects in space.

“One thing I’ve been thinking a lot about lately is if you have a very compact object that has a very strong gravitational pull but isn’t a black hole,” he says. “What are the limits that general relativity puts on the stability of those objects?”

These questions sit at the intersection of gravity, particle physics, and cosmology, and East enjoys exploring those connections. Strong gravity, he says, naturally connects different areas of physics. That breadth was a major reason he was drawn to Perimeter, first as a postdoctoral researcher in 2016 and then as faculty in 2018.

“One of the things that was really exciting about Perimeter was all the interaction between people doing research in different areas,” he says. “People talk to each other and collaborate with each other, so you can think about strong gravity both in itself and as a way to look for other new physics.”

Born in Chicago and raised in North Carolina, East showed an early interest in math and science. A formative experience came as a teenager, when he attended math camp and found himself surrounded by peers who shared his enthusiasm.

He went on to study math and physics as an undergraduate at Stanford University before earning his PhD at Princeton, becoming increasingly drawn to gravity not just as an abstract theory, but as a way to bridge mathematics to actual cosmic phenomena.  

Technology has, in many ways, finally caught up to the ideas of Einstein; East is grateful to be studying the cosmos during an era when the cosmos is unveiling itself as never before.

“It’s a new kind of astronomy,” he says. “and we’re really just getting started.”