What is a ray of light made of?

Light is what allows us to understand the world we live in. Our language reflects this: after groping in the dark, we see the light and understanding dawns.

Yet light is one of those things that we don't tend to understand. If you were to zoom in on a ray of light, what would you see? Sure, light travels incredibly fast, but what is it that's doing the travelling? Many of us would struggle to explain.

It doesn't have to be that way. Light certainly has puzzled the greatest minds for centuries, but landmark discoveries made over the last 150 years have robbed light of its mystery. We actually know, more or less, what it is.

Not only do today's physicists understand the nature of light, they are learning to control it with ever-greater precision - which means light could soon be put to work in surprising new ways. That is part of the reason why the United Nations designated 2015 as the International Year of Light.

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