Cosmologists claim to have found evidence that yet another fundamental constant of nature, called mu, may have changed over the last 12 billion years. If confirmed, the result could force some physicists to radically rethink their theories. It would also provide support for string theory, which predicts extra spatial dimensions. This is not the first time fundamental constants have been accused of changing over the lifetime of the universe. Most famously, there was controversy over the fine structure constant, alpha (α), which governs how light and electrons interact. Some physicists claimed it is changing while others said it was not (see “Speed of light may have changed recently”). The ratio of a proton’s mass to that of an electron, known as mu, is among the most mysterious of constants. There is no explanation for why the proton’s mass should be 1836 times that of the electron.
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