Accelerated charges radiate

We are bathed in electromagnetic radiation such as sunlight and radio waves. All such radiation comes from accelerating charges; for example, radio waves are emitted by charges moving up and down a vertical wire!

This phenomenon is common in particle physics where accelerating particles is our job!

The highlighted electron (red)- which is accelerating because it is going round in a curve - has emitted a photon which has travelled a small way before 'materialising’ into a positron-electron pair in the electric field of a nucleus. The electron that emitted the photon, having lost energy, spirals up characteristically. (Electrons and positrons are easily recognized in a bubble chamber because of this spiralling tendency; for more details, click here.)

Another example of accelerating charges radiating is known as synchrotron radiation; here the acceleration is produced by a magnetic field. For accelerator physicists, this kind of radiation is a nuisance because it reduces the energy of the particles they are trying to accelerate.

However, for biologists, this radiation, often referred to as 'synchrotron radiation’, is useful: they can use it to study the structure of complex organic molecules. What you might call a spin-off of particle physics!

For more details about this picture, click here.