The speed of light might not be so constant after all. A team of Scottish scientists found a way to slow down the speed of light, even in a vacuum, by changing its shape.
We already know that light can slow down in the real world, for example, if it passes through a glass of water. But light speed has been thought of as a constant when it travels through a vacuum, where no other forces or particles are thought to be acting upon it.
Researchers from the University of Glasgow and Heriot-Watt University provided the first real evidence that that's not always true. They fired two photons—tiny, particle-like bundles of light—side by side in a vacuum. But they sent one particle through a device that reshaped its structure. The reshaped particle actually traveled slower than the one left unaltered. The team published its results Thursday in the online edition of Science Express, though it had been previously available on arXiv.org.
The findings indicate that the speed of light—measured at 299,792,458 meters per second—is not an invariable constant, as scientists have believed. It is more a kind of ceiling or upper limit on the speed that light can travel, according to an article in Science News that discussed the research before it was formally published.