Chuck Darwin<p>A handful of mini-revolutions have already occurred. </p><p>One came in the mid-2000s,<br>when Ruth <a href="https://c.im/tags/Britto" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>Britto</span></a>, Freddy <a href="https://c.im/tags/Cachazo" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>Cachazo</span></a>, Bo <a href="https://c.im/tags/Feng" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>Feng</span></a> and Edward <a href="https://c.im/tags/Witten" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>Witten</span></a> discovered the “<a href="https://c.im/tags/recursion" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>recursion</span></a> <a href="https://c.im/tags/relations" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>relations</span></a>,” <br>equations that let physicists condense hundreds of pages of Feynman diagrams to mere lines.</p><p>Around the same time, Arkani-Hamed joined the hunt for a new conceptual perspective on particle physics, <br>after a couple of thought experiments led him to doubt that space and time are truly well-founded physical concepts. </p><p>Several years later, he and Trnka discovered the amplituhedron.</p><p>The amplituhedron is a curvy shape whose contours encode the number and orientation of particles involved in an interaction. </p><p>Its volume gives the amplitude for that interaction to occur. </p><p>This volume equals the sum of amplitudes of all the Feynman diagrams depicting the various alternative ways the interaction could play out, <br>but in this case you calculate the answer without reference to those spatiotemporal dynamics; </p><p>all you need is the list of momentums of the particles that exist before and after the interaction.</p><p>“However the scattering happens, it’s controlled by this real structure,” <br>said Vijay Balasubramanian, a physicist at the University of Pennsylvania who studies quantum gravity. </p><p>“You don’t have to talk about space-time.”</p><p>The surprising discovery brought new people into the search. </p><p>But the amplituhedron worked only for a theory of particles that came hand in hand with exotic partner particles, <br>a simplifying balance called supersymmetry. </p><p>(Generally speaking, one quantum “theory” describes one specific set of rules for one specific set of particles. <br>As such, there are many quantum theories, some for real particles and others for fictitious ones.)</p><p>“You’re a little bit suspicious that maybe the amazing things you’re seeing have nothing to do with the real world,” said Giulio Salvatori, <br>a physicist who would later join the group.</p><p>In the following years, Arkani-Hamed’s team identified a second type of shape, <br>the “<a href="https://c.im/tags/associahedron" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>associahedron</span></a>,” that worked in a similar way. </p><p>It had flat sides, and its volume gave scattering amplitudes for the particles of a simplified quantum theory, <br>one that’s easier to study. </p><p>The particles in this theory carry a type of charge called “color” that is also carried by the quarks and gluons in real-world atomic nuclei. </p><p>(This charge has nothing to do with actual colors, but the mathematics of how charges combine to make color-neutral composite particles resembles how red, green and blue light together make white.)</p><p>The particles of this theory also lack supersymmetric partners. </p><p>The associahedron therefore represented a major step toward the real world. </p><p>But the shape gave only partial answers, producing amplitudes for only the shortest sequences of subatomic events.</p><p>Sensing a breakthrough was close, Arkani-Hamed recruited Salvatori and Hadleigh Frost at the University of Oxford, <br>young physicists who had been independently advancing the understanding of the associahedron’s strange shapes, <br>along with the mathematicians Pierre-Guy Plamondon and Hugh Thomas. </p><p>In 2019, the gang started looking for a geometrical route to all of these amplitudes.</p><p>Then the pandemic hit, <br>and the team left our space-time to work in the digital ether of Zoom. </p><p>They would emerge two years later with a second revolutionary way of doing quantum physics.</p>