Light is all around us, but how much do you really know about the photons speeding past you? There’s more to light than meets the eye. Here are eight enlightening facts about photons:
1. Photons can produce shock waves in water or air, similar to sonic booms.
Nothing can travel faster than the speed of light in a vacuum. However, light slows down in air, water, glass and other materials as photons interact with atoms, which has some interesting consequences.
The highest-energy gamma rays from space hit Earth’s atmosphere moving faster than the speed of light in air. These photons produce shock waves in the air, much like a sonic boom, but the effect is to make more photons instead of sound. Observatories like VERITAS in Arizona look for those secondary photons, which are known as Cherenkov radiation. Nuclear reactors also exhibit Cherenkov light in the water surrounding the nuclear fuel.
2. Most types of light are invisible to our eyes.
Colors are our brains’ way of interpreting the wavelength of light: how far the light travels before the wave pattern repeats itself. But the colors we see—called “visible” or “optical” light—are only a small sample of the total electromagnetic spectrum.
Red is the longest wavelength light we see, but stretch the waves more and you get infrared, microwaves (including the stuff you cook with) and radio waves. Wavelengths shorter than violet span ultraviolet, X-rays and gamma rays. Wavelength is also a stand-in for energy: The long wavelengths of radio light have low energy, and the short-wavelength gamma rays have the highest energy, a major reason they’re so dangerous to living tissue.
3. Scientists can perform measurements on single photons.
Light is made of particles called photons, bundles of the electromagnetic field that carry a specific amount of energy. With sufficiently sensitive experiments, you can count photons or even perform measurements on a single one. Researchers have even frozen light temporarily.
But don’t think of photons like they are pool balls. They’re also wave-like: they can interfere with each other to produce patterns of light and darkness. The photon model was one of the first triumphs of quantum physics; later work showed that electrons and other particles of matter also have wave-like properties.