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By 1913, Albert Einstein had nearly completed general relativity. But a simple mistake set him on a tortured, two-year reconsideration of his theory. Today, mathematicians still grapple with the issues he confronted.
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.
A mysterious object that repeatedly bursts with ultra-powerful radio waves must live in an extreme environment — something like the one around a supermassive black hole.
It weighs as much as 780 million suns and helped to cast off the cosmic Dark Ages. But now that astronomers have found the earliest known black hole, they wonder: How could this giant have grown so big, so fast?
Physicists theorize that a new “traversable” kind of wormhole could resolve a baffling paradox and rescue information that falls into black holes.