Whether you're flying on a spacecraft or just hopping around in your backyard, the speed of light is pretty impressive. It can travel 7.5 times around the Earth in just one second, and it's so fast that the term "light-year" has been used to describe hugely long distances in our Universe.
Nevertheless, for many people, the question of why light travels at c still seems like a mystery. The most straightforward explanation is that the speed of light is relative to a specific observer, and this is in agreement with the principle of relativity. But why is that?
The answer to this question lies in the bending of light when it enters a medium with different density. When light enters a medium with lower density, it will bend toward the center of the medium, because the slower parts of the light wave move less than the faster parts. This is the same principle that causes a wave in water to curve up as it moves away from the shore.
Scientists can exploit this property of light by using ultrashort pulses of laser light. Various techniques for creating these pulses allow scientists to peer into the depths of molecules and atoms, or even watch chemical reactions as they happen. However, these experiments typically take a few milliseconds or femtoseconds (one billionth of a second) to achieve, which limits the usefulness of their results. Now, researchers have achieved a new record for the shortest pulse of laser light: 53 attoseconds, or a tenth of the width of an electron. This is a record breaking achievement, and it will greatly enhance research that requires measuring the positions of particles within atoms and molecules.