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Richard Feynman at 100 - Nature May 2018
Paul Halpern celebrates the oeuvre of the brilliant, unconventional scientist.
physics  quantum-mechanics  Richard-Feynman  people  biography  NatureJournal 
may 2018 by pierredv
The geometry that could reveal the true nature of space-time | New Scientist issue 3136, 29 Jul 2017
"The discovery of an exquisite geometric structure is forcing a radical rethink of reality, and could clear the way to a quantum theory of gravity"

[Andrew Hodges, one of Penrose’s colleagues at Oxford] "showed that the various terms used in the BCFW method could be interpreted as the volumes of tetrahedrons in twistor space, and that summing them up led to the volume of a polyhedron."

"So why invoke virtual particles at all? ... The first is that dealing with them rather than with fields makes the maths more tractable. The other great advantage is that they help physicists visualise everything as the well-defined interactions between point-like particles, as opposed to the hazy goings-on between particles and fields. This fits nicely with the intuitive principle of locality, which holds that only things in the same spot in space and time can interact. Finally, the technique also helps enforce the principle of unitarity, which says that the probability of all outcomes should add up to 1."

Gluon interactions seemed to complex, but "In 1986, Stephen Parke and Tomasz Taylor from Fermilab near Batavia, Illinois, used Feynman diagrams and supercomputers to calculate the likelihoods of different outcomes for interactions involving a total of six gluons. A few months later, they made an educated guess at a one-line formula to calculate the same thing. It was spot on. More than 200 Feynman diagrams and many pages of algebra had been reduced to one equation, and the researchers had no idea why."

"In 2005, Ruth Britto, Freddy Cachazo, Bo Feng and Edward Witten [BCFW] were able to calculate scattering amplitudes without recourse to a single virtual particle and derived the equation Parke and Taylor had intuited for that six-gluon interaction"

[Nima Arkani-Hamed and his team at IAS] "arrived at a mind-boggling conclusion: the scattering amplitude calculated with the BCFW technique corresponds beautifully to the volume of a new mathematical object. They gave a name to this multi-dimensional concatenation of polyhedrons: the amplituhedron."

"It may transform physics, too ... because the amplituhedron does not embody unitarity and locality, those core principles baked into reality as described by Feynman diagrams. ... If so, locality is not a fundamental feature of space-time but an emergent one."
NewScientist  geometry  physics  gravity  field-theory  quantum-mechanics  twistors  Roger-Penrose  Richard-Feynman  Ed-Witten  maths 
december 2017 by pierredv

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