Light is the fastest thing in our Universe, but we can slow it down. Or it can slow itself down depending on where it travels.
This photo of car headlights streaming by was taken in Belfort, France and combines 8 photos, each lasting for 30 seconds. Image Credit: Thomas Bresson, https://www.flickr.com/people/36519414@N00
Light travels at 186,000 miles per second (or, about 670 million miles per hour) in a vacuum. The laws of physics dictate that nothing moves faster in the Universe and scientists have never found anything that’s broken that rule.
Light can, however, travel slower. When light travels through something other that a vacuum, a.k.a. total emptiness, it slows down due to its interaction with atoms and molecules. When light moves through air, like in our atmosphere, it slows down just a tiny bit. If it goes through water, it will drop down to about 500 million miles per hour. Every medium or material that light passes through will affect how quickly it moves differently. In fact, researchers can manipulate this fact to make light move slower than a person riding a bike.