Two studies of vacuums suggest that the speed of light in a vacuum might fluctuate, pointing the way to a quantum mechanical explanation for why the speed of light and other so-called constants are what they are.
Malcolm Denemark/Florida Today/AP
Where did the speed of light in a vacuum come from? Why is it 299,792,458 meters per second and not some other figure?
The simple answer is that, since 1983, science has defined a meter by the speed of light: one meter equals the distance light travels in one 299,792,458th of a second. But that doesn't really answer our question. It's just the physics equivalent of saying, "Because I said so."
Unfortunately, the deeper answer has been equally unsatisfying: The speed of light in a vacuum, according to physics textbooks, just is. It's a constant, one of those numbers that defines the universe. That's the physics equivalent of saying, "Because the cosmos said so."
Or did it? A pair of studies suggest that this universal constant might not be so constant after all. In the first study, Marcel Urban from the University of Paris-Sud and his team found that the speed of light in a vacuum varies ever so slightly.
This happens because what we think of as nothing isn't really nothing. Even if you were to create a perfect vacuum, at the quantum level it would still be populated with pairs of tiny "virtual" particles that flash in and out of existence and whose energy values fluctuate. As a consequence of these fluctuations, the speed of a photon passing through a vacuum varies, about 50 quintillionths of a second per square meter.
That may not sound like much, but it's enough to point the way toward a new underlying physics.