Can a photon be accelerated

Can you slow down photons?

As massless particles, photons always move with the maximum possible speed, the speed of light in a vacuum. They can neither be braked nor accelerated. However, light usually propagates more slowly in matter than in a vacuum, so the speed of light is lower in matter than in a vacuum. Recently, researchers even succeeded in completely stopping a light wave in a medium and allowing it to continue running a short time later.

Even if these experiments are very exciting, it is not justified to say that the photons are slowed down. A light wave in a medium does not only consist of photons. Rather, an excitation wave moves through a medium, in which, in addition to the normal electric field strength, the polarization of the atoms also plays a role. By coupling the electric field to the atoms, the light wave moves more slowly in the medium than in a vacuum and this new wave can be quantized into slower photons similar to a free light wave. However, these light quanta are not identical to the photons in a vacuum. Therefore one cannot speak of a deceleration of the photons.

Old concept

In the past the claim was made at this point that the photons would move between the atoms at the speed of light and would be stopped by the constant absorption and emission. This explanation is often found in popular scientific papers, but it does not correspond to the facts. There is practically no absorption in transparent media.

Further questions on the topic

Are photons indivisible?

Shouldn't photons have mass according to E = mc²?

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Last change: 02/25/2007