Strings, Symmetry, and the Shape of Space: The Physics of Shiraz Minwalla

An alum of Princeton and Harvard, Shiraz Minwalla returned home to Mumbai to tackle the fundamental physics questions that animate him.

When Shiraz Minwalla talks about physics, he cannot contain his excitement. 

His hands are in constant motion as he speaks, demonstrating the push-and-pull of electromagnetic forces and mimicking particle collisions with his fists.

Shiraz Minwalla (Credit: IAP)

On a video call from his native Mumbai, Minwalla’s arms blur into chaotic pixels when he talks excitedly about the fundamental questions he’s trying to answer as a professor at the city’s Tata Institute of Fundamental Research (TIFR). He’s equally enthusiastic when teaching classes or delivering public talks on physics.

“I just love this work,” he explains. “It’s what I’ve always wanted to do.” 

Big questions, big excitement: Black holes, entropy, and the mystery of information

Black hole entropy is the topic Minwalla is most animated about these days. He wants to understand exactly what happens inside a black hole—how many microscopic configurations it can have. To an outside observer, the event horizon of a black hole is a smooth and featureless sphere. However, physics tells us that an enormous amount of information must be encoded on or beneath this inescapable boundary. But where is that information—and what can it tell us? 

A breakthrough in the 1990s came when physicists using string theory were able to explain the entropy of certain black holes by counting the number of ways strings and other objects could be arranged at a quantum level. This approach worked for some special, highly symmetrical black holes—but not for more general ones (i.e. the kinds likely to actually exist in space). 

Minwalla has spent years building upon these ideas, using a powerful version of quantum field theory known as 𝒩=4 super Yang-Mills theory. Back in 2005, Minwalla and collaborators — including Suvrvat Raju and Juan Maldacena—introduced a quantity called the superconformal index. He used this index in hopes of matching calculations in this quantum field theory with the expected entropy of black holes. 

That’s complicated work—so complicated that the numbers just didn’t add up. That mismatch persisted for years. But “about six or seven years ago, people made progress in doing the calculation," Minwalla said. “We'd missed some elements."

Enter the grey galaxies: What black holes might tell us about quantum gravity

Minwalla has recently returned to the problem with the aim of fully resolving the discrepancy. His recent work has unveiled potential new structures called “grey galaxies,” which might help account for the missing entropy. 

In one of his recent papers, he and co-authors proposed that these solutions might account for the missing entropy in the superconformal index. “We claim to see evidence for these grey galaxy solutions — the supersymmetric versions — in the index," he said.

These results suggest that a light-speed disk of Hawking radiation particles may orbit some black holes. By understanding the quantum features that may “dress” the otherwise naked black hole, Minwalla hopes to crack the code of black hole microstates — and, in doing so, potentially unlock a more complete picture of how gravity and quantum mechanics fit together.

That happy marriage of quantum mechanics and gravity is the holy grail of much theoretical physics research, whether in subfields of quantum gravity, string theory, quantum field theory or other areas. 

“It could be wrong,” he says of his theory, “but it’s still very exciting.”

From Mumbai to the Ivy League—and back again

Minwalla’s zeal for science, and his gleeful willingness to be wrong, have guided him since his childhood in Mumbai during the 1970s and 1980s. Despite his family’s limited resources, Minwalla said he received a “world-class education” at the Indian Institute of Technology in Kanpur, India. 

P.K. Kelkar Library of the Indian Institute of Technology, Kanpur. (Credit: IIT-K)

“Somehow, this very poor country organized their resources to give me this fantastic education," he recalls.

During his 20s he moved to the United States to study under some of the most renowned minds in physics, first as a graduate student at Princeton University, where he earned his PhD, and then as a fellow and faculty member at Harvard. At these institutions he found himself engaging in lunchtime conversations with string theory luminaries like Ed Witten and Andrew Strominger. He later became a member of the Harvard Society of Fellows, and split his time between the United States and India; he finally returned to Mumbai full-time in 2006, driven by a sense of duty and gratitude toward the country that first nurtured his love for science.

Now in his 50s, Minwalla’s enthusiasm for science borders on giddiness. During a 2019 TEDx talk about quantum gravity, he darts around the stage, speaking directly to young audience members, gesturing with gusto to accentuate his points. 

“I've always enjoyed dealing with young people," he says. “Their questions are completely genuine."

Minwalla says the curiosity of young people—and their energy—fuel his own seemingly endless supply of enthusiasm for his line of work.

“Since we became human, people have looked up at the sky and wondered: What is all that? Where did we come from? Where are we going? Why are we here? When I can understand something about the structure that I did not know before—and perhaps nobody knew before—that’s a good day at work.”

Colin Hunter is a science communicator, filmmaker, and contributor to FirstPrinciples. He previously led the communications teams at the Perimeter Institute for Theoretical Physics and the Institute for Quantum Computing (IQC) at the University of Waterloo.