Three progressively heavier copies of each type of matter particle exist, and no one knows why. A new paper by Steven Weinberg takes a stab at explaining the pattern. From a report: Electrons and two types of quarks, dubbed “up” and “down,” mix in various ways to produce every atom in existence. But puzzlingly, this family of matter particles — the up quark, down quark and electron — is not the only one. Physicists have discovered that they make up the first of three successive “generations” of particles, each heavier than the last. The second- and third-generation particles transform into their lighter counterparts too quickly to form exotic cats, but they otherwise behave identically. It’s as if the laws of nature were composed in triplicate. “We don’t know why,” said Heather Logan, a particle physicist at Carleton University. In the 1970s, when physicists first worked out the Standard Model of particle physics — the still-reigning set of equations describing the known elementary particles and their interactions — they sought some deep principle that would explain why three generations of each type of matter particle exist. No one cracked the code, and the question was largely set aside.
Now, though, the Nobel Prize-winning physicist Steven Weinberg, one of the architects of the Standard Model, has revived the old puzzle. Weinberg, who is 86 and a professor at the University of Texas, Austin, argued in a recent paper in the journal Physical Review D that an intriguing pattern in the particles’ masses could lead the way forward. “Weinberg’s paper is a bit of lightning in the dark,” said Anthony Zee, a theoretical physicist at the University of California, Santa Barbara. “All of a sudden a titan in the field is suddenly working again on these problems.” “I’m very happy to see that he thinks it’s important to revisit this problem,” said Mu-Chun Chen, a physicist at the University of California, Irvine. Many theorists are ready to give up, she said, but “we should still be optimistic.”
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