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The renowned British physicist, who died at 76, left behind a riddle that could eventually lead his successors to the theory of quantum gravity.
The amount of energy infusing empty space seems too small to explain without a multiverse. But physicists have at least one alternative left to explore.
A recently proposed experiment would confirm that gravity is a quantum force.
The theoretical physicist Joe Polchinski, who died Feb. 2, left a tremendous professional and personal legacy, says a friend and collaborator.
For decades, physicists have struggled to create a quantum theory of gravity. Now an approach that dates to the 1970s is attracting newfound attention.
A complete classification could lead to a wealth of new materials and technologies. But some exotic phases continue to resist understanding.
The mother of all string theories passes a litmus test that, so far, no other candidate theory of quantum gravity has been able to match.
Edward Witten reflects on the meaning of dualities in physics and math, emergent space-time, and the pursuit of a complete description of nature.