The fluctuations of the Speed of Light


January 20, 2015   DAILY GALAXY

By shaping the form of light pulses, scientists were able to slow down a number of photons and challenge commonly accepted facts.

Much of how we understand the way our universe is built hangs on constants—physical measurements that describe, for example, the charge and mass of the electron. These quantities are the foundation for basic theoretical equations, and they don’t change. Except, scientists just found out that the most famous constant, the speed of light, isn’t quite as constant as we thought.

When light travels through glass or water, it’s slowed down. But scientists thought that, when it flashes through a vacuum, it’s kept to the unvarying speed of 299,792,458 meters per second. New work shows that this isn’t always the case. Depending on the structure of the light, the researchers observed, photons, the basic unit of light, will travel slower.

The researchers essentially pitted differently structured photons against each other. Light is often represented as a a wave (though the whole particle/wave thing can get twisty), but that’s just an approximation, writes Andrew Grant for Science News. Think about a laser, he suggests—that structures light as a concentrated or bull’s eye–shaped beam. Or, think about how light behaves when passed through a lens—it can convenge on a point.

So, the structure of light can vary, and that’s what this experiment hinged on. Grant writes:

“The researchers produced pairs of photons and sent them on different paths toward a detector. One photon zipped straight through a fiber. The other photon went through a pair of devices that manipulated the structure of the light and then switched it back. Had structure not mattered, the two photons would have arrived at the same time. But that didn’t happen. Measurements revealed that the structured light consistently arrived several micrometers late per meter of distance traveled.”


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