A photon maze gives Feynman's path integral its first direct test
A single-photon experiment combined 5 propagator measurements across 1,419,857 possible paths to test directly the path integral proposed in 1948. Elsewhere in fundamental physics, a theoretical study set the first limits on all 132 coefficients through which Lorentz symmetry might break; an oxygen–oxygen collision simulation put the equilibrated component ahead above 20 particles, and a photon-gas experiment captured critical scaling near condensation.
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A sum over possible paths
Shi-Liang Zhu and colleagues at South China Normal University sent single photons through a maze of mirrors, lenses and crystals. They measured and multiplied 5 propagators along the route, constructing a path integral that covered 1,419,857 distinct trajectories. The peer-reviewed experiment in Science Advances directly tested the formulation Feynman proposed in 1948 for the first time. Its main difficulty was preventing noise accumulated through repeated multiplication from overwhelming the signal.[1]
132 bounds on Lorentz symmetry
Jay Tasson of Carleton College and colleagues calculated the first experimental bounds on all 132 coefficients in the standard model extension that could violate Lorentz symmetry. Combining proton and neutron measurements in rotating helium and potassium atoms with electron experiments using torsion pendulums, they found no anomalous signal but narrowed the ranges where one might still hide. The peer-reviewed calculation in Physical Review Letters covers protons, neutrons and electrons, rather than every particle species.[2]
Two systems at the edge of equilibrium
Tetsufumi Hirano and Naoya Ito at Sophia University modelled oxygen–oxygen collisions at 5.36 TeV at the Large Hadron Collider. The equilibrated core became dominant above 20 charged particles, yet about 30 per cent of hadrons still came from the non-equilibrated corona in the most central collisions; these fractions are model outputs rather than direct measurements. In a separate experiment, researchers at the University of Bonn, Heidelberg University and UNAM brought a two-dimensional photon gas close to Bose–Einstein condensation and obtained a critical exponent of 0.52(3), the first direct test in photons of a distinct critical-scaling class predicted for an almost non-interacting Bose gas.[3], [4]
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