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Chuck Darwin<a href="https://c.im/tags/Figueiredo" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#Figueiredo</a> sensed the need for some new magic firsthand during the waning months of the pandemic. She was struggling with a task that has challenged physicists for more than 50 years: predicting what will happen when quantum particles collide. In the late 1940s, it took a yearslong effort by three of the brightest minds of the post-war era — Julian <a href="https://c.im/tags/Schwinger" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#Schwinger</a>, Sin-Itiro <a href="https://c.im/tags/Tomonaga" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#Tomonaga</a> and Richard <a href="https://c.im/tags/Feynman" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#Feynman</a> — to solve the problem for electrically charged particles. Their eventual success would win them a Nobel Prize. Feynman’s scheme was the most visual, so it came to dominate the way physicists think about the quantum world.When two quantum particles come together, anything can happen. They might merge into one, split into many, disappear or any sequence of the above. And what will actually happen is, in some sense, a combination of all these and many other possibilities. Feynman diagrams keep track of what might happen by stringing together lines representing particles’ trajectories through space-time. Each diagram captures one possible sequence of subatomic events and gives an equation for a number, called an “amplitude,” that represents the odds of that sequence taking place. Add up enough amplitudes, physicists believe, and you get stones, buildings, trees and people. “Almost everything in the world is a concatenation of that stuff happening over and over again,” Arkani-Hamed said. “Just good old-fashioned things bouncing off each other.”There’s a puzzling tension inherent in these amplitudes — one that has vexed generations of quantum physicists going back to Feynman and Schwinger themselves. One might spend hours at a chalkboard sketching Byzantine particle trajectories and evaluating fearsome formulas only to find that terms cancel out and complicated expressions melt away to leave behind extremely simple answers — in a classic example, literally the number 1.“The degree of effort required is tremendous,” Bourjaily said. “And every single time, the prediction you make mocks you with its simplicity.”Figueiredo had been wrestling with the strangeness of the situation when she attended a talk by <a href="https://c.im/tags/Arkani" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#Arkani</a>-<a href="https://c.im/tags/Hamed" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#Hamed</a>, a leading theoretical physicist at the IAS who has spent years seeking a new way of getting the answers without Feynman diagrams. She found her way to a series of his lectures on YouTube, in which he showed how — in special cases — one could jump straight to the amplitude of a certain outcome of a particle collision without worrying about how the particles moved through space.Arkani-Hamed’s shortcuts, which involved reverse-engineering answers that satisfy certain fundamental logical requirements, confirmed Figueiredo’s suspicions that alternative methods were out there. “By asking for these very simple things you could just get the answer. That was definitely striking,” she said.She began to regularly make the half-hour walk from Princeton’s campus to the IAS to work with Arkani-Hamed, a force of nature who runs on Diet Coke and an inexhaustible enthusiasm for physics.Arkani-Hamed and his collaborators aspire to bring about a conceptual revolution of the sort that rocked physics in the late 1700s. Joseph-Louis <a href="https://c.im/tags/Lagrange" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#Lagrange</a> didn’t discover any forces or laws of nature, but every physicist knows his name. He showed that you could predict the future without laboriously calculating actions and equal-and-opposite reactions in the style of Isaac Newton. Instead, Lagrange learned to predict the path an object will follow by considering the energies that different paths require and identifying the easiest path. Lagrange’s method, despite seeming like a mere mathematical convenience at the time, loosened the straitjacket of Newton’s mechanistic view of the universe as a sequence of falling dominos. Two centuries later, Lagrange’s approach provided Feynman with a more flexible framework that could accommodate the radical randomness of quantum mechanics.Now many amplitudes researchers hope a reformulation of quantum physics will set the stage for the next physics revolution, a theory of quantum gravity and the origin of space-time.

Chuck DarwinIn the fall of 2022, a Princeton University graduate student named <a href="https://c.im/tags/Carolina" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#Carolina</a> <a href="https://c.im/tags/Figueiredo" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#Figueiredo</a> stumbled onto a massive coincidence. She calculated that collisions involving three different types of subatomic particles would all produce the same wreckage. “They are very different [particle] theories. There’s no reason for them to be connected,” Figueiredo said.The coincidence soon revealed itself to be a conspiracy: The theories describing the three types of particles were, when viewed from the right perspective, essentially one. The conspiracy, Figueiredo and her colleagues realized, stems from the existence of a hidden structure, one that could potentially simplify the complex business of understanding what’s going on at the base level of reality.For nearly two decades, Figueiredo’s doctoral advisor, <a href="https://c.im/tags/Nima" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#Nima</a> <a href="https://c.im/tags/Arkani" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#Arkani</a>-<a href="https://c.im/tags/Hamed" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#Hamed</a> has been leading a hunt for a new way of doing physics. Many physicists believe they’ve reached the end of the road when it comes to conceptualizing reality in terms of quantum events that play out in space and time. Such language can’t easily describe the beginning of the universe, for instance, when the space-time fabric likely didn’t exist in its current form. Arkani-Hamed therefore suspects that the usual notion of quantum particles moving and interacting in space-time is an approximation of deeper, more abstract concepts, which, if found, could serve as a better language for talking about quantum gravity and the origin of the universe.A major development came in 2013, when Arkani-Hamed and his student at the time, <a href="https://c.im/tags/Jaroslav" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#Jaroslav</a> <a href="https://c.im/tags/Trnka" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#Trnka</a>, discovered a jewel-like geometric object that forecasts the outcome of certain particle interactions. They called the object the “<a href="https://c.im/tags/amplituhedron" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#amplituhedron</a>.” However, the object didn’t apply to the particles of the real world. So Arkani-Hamed and his colleagues sought more such objects that wouldFigueiredo’s conspiracy is another manifestation of abstract geometric structure that seems to underlie particle physics.“The overall program is inching closer to Nima’s long-term dream of space-time and quantum mechanics emerging from a new set of principles,” said Sebastian Mizera, a physicist who studies amplitudes at the Institute for Advanced Study in Princeton, New Jersey, but was not involved in the recent work.Like the amplituhedron, the new geometrical method, known as “<a href="https://c.im/tags/surfaceology" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#surfaceology</a>,” streamlines quantum physics by sidestepping the traditional approach, which is to track the countless ways particles can move through space-time using “Feynman diagrams.” These depictions of particles’ possible collisions and trajectories translate into complicated equations. With surfaceology, physicists can get the same result more directly.“It provides a natural framework, or a bookkeeping mechanism, to assemble very large numbers of Feynman diagrams,” said <a href="https://c.im/tags/Marcus" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#Marcus</a> <a href="https://c.im/tags/Spradlin" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#Spradlin</a>, a physicist at Brown University who has been picking up the new tools of surfaceology. “There’s an exponential compactification in information.”Unlike the amplituhedron, which required exotic particles to provide a balance known as supersymmetry, surfaceology applies to more realistic, nonsupersymmetric particles. “It’s completely agnostic. It couldn’t care less about supersymmetry,” Spradlin said. “For some people, me included, I think that’s really been quite a surprise.”The question now is whether this new, more primitive geometric approach to particle physics will allow theoretical physicists to slip the confines of space and time altogether.“We needed to find some magic, and maybe this is it,” said <a href="https://c.im/tags/Jacob" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#Jacob</a> <a href="https://c.im/tags/Bourjaily" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#Bourjaily</a>, a physicist at Pennsylvania State University. “Whether it’s going to get rid of space-time, I don’t know. But it’s the first time I’ve seen a door.”<a href="https://www.quantamagazine.org/physicists-reveal-a-quantum-geometry-that-exists-outside-of-space-and-time-20240925/" rel="nofollow noopener noreferrer" translate="no" target="_blank">https://www.quantamagazine.org/physicists-reveal-a-quantum-geometry-that-exists-outside-of-space-and-time-20240925/</a>

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