It is known that if a point charge accelerates, it produces electromagnetic radiation. This radiation has both energy and momentum. It is usually assumed that they come from the energy and momentum of the charged particle, damping the motion.

The history of attempts to calculate this radiation reaction (also known as radiation damping) dates to Lorentz in 1892. Major contributions were then made by many well-known physicists including Plank, Abraham, von Laue, Born, Schott, Pauli, Dirac, and Landau.

According to Maxwell’s equations, the electric field at the actual point where the point particle is is infinite. Hence the force on that point particle should also be infinite.

Various methods have been used to renormalize away this infinity. This leads to the well-established Lorentz-Abraham-Dirac equation.

A particle obeying this equation may accelerate forever with no external force or accelerate before any force is applied. There is also the quantum version of radiation damping. Ironically, this is one of the few phenomena where the quantum version occurs at lower energies than the classical one.

Physicists are actively searching for this effect. This requires `colliding’ very high energy electrons and powerful laser beams, a challenge as the biggest particle accelerators are not situated near the most powerful lasers. However, firing lasers into plasmas will produce high-energy electrons, which can then interact with the laser beam. This only requires a powerful laser. Current results show that quantum radiation reaction does exist.

The alternative approach is to consider many charged particles, where each particle responds to the fields of all the other charged particles, but not itself. This approach was abandoned since it was assumed that this would not conserve energy and momentum.

Dr. Gratus states: “The controversial implication of this result is that there need not be classical radiation reaction at all. We may therefore consider the discovery of quantum radiation reaction as like the discovery of Pluto, which was found following predictions based on discrepancies in the motion of Neptune. Corrected calculations showed there were no discrepancies. Similarly, radiation reaction was predicted, found, and then shown not to be needed.”

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