A 33-year-old physicist is leading an attempt to rewrite the laws of our universe as a hologram projected on the sky. The ‘next Einstein’ tag sells magazines; the physics is more interesting, still unproven, and has Indian fingerprints on it.
Sabrina Gonzalez Pasterski has been called the next Einstein since she was a doctoral student, and she has spent years wishing people would stop. The label resurfaced on the cover of New Scientist on 31 October, attached to a question about whether her holographic theory justifies it. The fair answer is that nobody knows yet, including her. What can be said is that the research programme she leads is one of the more original attempts to solve the oldest unsolved problem in fundamental physics, and that it deserves to be understood on its own terms.
Two theories that will not shake hands
Modern physics stands on two pillars. General relativity describes gravity as the bending of space and time, and governs planets, black holes and the expanding cosmos. Quantum mechanics describes particles and forces at the smallest scales. Each has passed every experimental test set for it. Yet they contradict one another where both should apply, such as inside a black hole or at the first instant of the universe. A theory of quantum gravity that reconciles them has eluded physicists for close to a century.
One of the most productive clues is the holographic principle, proposed in the 1990s by Gerard ‘t Hooft and Leonard Susskind. It suggests that everything happening inside a region of space can be fully described by information stored on its boundary, much as a flat hologram encodes a three-dimensional image. In 1997 Juan Maldacena gave the idea a precise mathematical form, showing that a universe with gravity can be exactly equivalent to a quantum theory without gravity living on its edge.
There is a catch. Maldacena’s result works for a universe with a particular curved shape, known as anti-de Sitter space, which behaves like a box with walls. The universe we inhabit is not like that. To a good approximation on the scales that matter for particle collisions and gravitational waves, it is flat and has no walls.
Where the sky comes in
Celestial holography is the attempt to make holography work for a flat universe. Its starting point is almost poetic. Light and gravitational waves that travel outward for ever end up, in a mathematical sense, on a sphere at infinity, the same celestial sphere on which the stars appear to sit when one looks up at night. The proposal is that the physics of the four-dimensional universe can be recast as a two-dimensional theory living on that sphere.
The idea grew out of work at Harvard by Andrew Strominger and his students, Pasterski among them. They uncovered an unexpected three-way link between results that had been studied separately for decades: theorems describing very low-energy particles, hidden symmetries of space-time far from any source, and the memory effect, a permanent distortion left behind when a gravitational wave passes. In 2015 Pasterski, Strominger and Alexander Zhiboedov identified a new variety, the spin memory effect. The symmetries turned out to match those of two-dimensional theories that physicists already know how to handle.
Since 2021 Pasterski has been on the faculty of the Perimeter Institute for Theoretical Physics in Canada, where she founded and leads the Celestial Holography Initiative.
The person behind the label
The biography explains the publicity. Born in Chicago to a Cuban-American family, she built a single-engine aircraft as a teenager and flew it herself at 16. She graduated from the Massachusetts Institute of Technology with a perfect grade point average and took her doctorate at Harvard.
Her view of the Einstein comparison has shifted from irritation to weary tolerance. She told the Spanish newspaper El País in September that the label used to embarrass her and that she has stopped fighting it; in a French interview this month she called it absurd. That is the correct scientific instinct. Einstein’s standing rests on predictions that were tested and confirmed. Celestial holography has not reached that stage.
What would count as proof
The framework is, for now, a mathematical dictionary under construction. Its practitioners can translate certain calculations about particle scattering into the language of the celestial sphere, and the translations have revealed patterns that were invisible before. But no one has written down the complete two-dimensional theory, and nothing so far establishes that the approach describes the real universe.
There are possible points of contact with observation. The memory effect is a genuine prediction of general relativity that gravitational-wave observatories may eventually detect as their sensitivity improves. Pasterski has also discussed treating particle detectors as boundaries within the framework. These are opportunities, not results, and sceptics note that elegant mathematics has misled fundamental physics before.
An Indian thread
Indian theorists have made substantial contributions to the foundations on which celestial holography stands. Ashoke Sen and Alok Laddha, among others, have produced influential results on the low-energy theorems and on how gravitational memory emerges from them, work that is cited throughout the field. Research groups in Bengaluru, Chennai, Mumbai and elsewhere are active in the area, and it is a staple of string theory meetings held in the country.
There is an experimental connection too. LIGO-India, the gravitational-wave observatory under construction in Hingoli district of Maharashtra, will join the international detector network. A larger and more sensitive network improves the prospects of one day measuring gravitational memory directly.
A fair verdict
For students, the Pasterski story carries a better lesson than genius worship. Her career shows deep technical training, a willingness to pursue an unfashionable problem and candour about what is not yet known. For everyone else, the right posture is interested patience. Celestial holography may turn out to be a key to quantum gravity, a useful calculational tool, or a beautiful dead end. Finding out which is how physics works, and it rarely makes anyone the next anybody.
