Wikipedia:Reference desk/Archives/Science/2023 October 16

= October 16 =

Quantum physics: what is the most photons an electron can release?
Like an electron at rest and such. 170.76.231.162 (talk) 16:24, 16 October 2023 (UTC).


 * "An electron at rest" isn't really a well-defined concept, since by the uncertainty principle an electron whose position is entirely certain would have an infinite uncertainty in momentum.
 * Electrons (like all charged particles) emit electromagnetic radiation (photons) when they accelerate or decelerate, and the name for the type of radiation depends on the context. (Some examples include synchrotron radiation, cyclotron radiation, bremsstrahlung, etc.)   The NUMBER of photons depends on the mechanism and the energy change. PianoDan (talk) 20:25, 16 October 2023 (UTC)
 * There is also the phenomenon of atomic electron transition, in which an electron in the electron cloud surrounding the nucleus of an atom "jumps" from an orbital shell to one of a lower energy level. But then the electron is not "at rest" – whatever that means – and just one photon is emitted of precisely the right energy to satisfy the conservation of energy. --Lambiam 21:27, 16 October 2023 (UTC)
 * Indeed, in such a condition as atomic orbitals or molecular orbitals, I guess I would define "at rest" as "in the ground state," and electrons at their ground state energy/in their ground state wavefunction are not going to be emitting photons at all. They could be excited by various means, such as thermal or absorbing a photon, etc., and then undergo radiative relaxation to emit a photon... but that's not generally going to happen when just at the ground state. Even something like Raman scattering still involves excitation to at least a virtual state, if not a discrete excited electronic state. --OuroborosCobra (talk) 22:11, 16 October 2023 (UTC)
 * An electron present in some system can emit a photon, constrained by conservation of energy, conservation of momentum, conservation of angular momentum and the Pauli exclusion principle. For an isolated electron, the first two can never be met simultaneously (except for a zero-energy photon), so an isolated electron cannot emit photons. An electron present in some system with an electromagnetic field can change its state to emit photons, until no transition releasing energy and satisfying the other constraints is available. In a hydrogen atom, an electron dropping down one energy level at a time, starting at infinity, could emit infinitely many photons, but the total energy of those photons will be limited to 13.6 eV. If you pump energy into the electron (or rather: system) by having it absorb photons, it can emit photons forever. PiusImpavidus (talk) 08:44, 17 October 2023 (UTC)