[Physics] Light, being a probability wave, carries energy; does an electron wave also carry energy? If so, how

electronsquantum mechanicsvisible-lightwave-particle-duality

The entity "light" behaves as a wave & particle.

The wave is actually probability wave . That is, to every point in a light wave we can attach a numerical probability that a photon can be detected in any small volume centred on that point.
Resnick, Halliday, Walker – Principles of Physics.

  • Now, the light wave transports energy & momentum. Doesn't also an electron wave carry energy & momentum? If so, how?

  • A light wave propagates the energy in its field components. But how does an electron wave do this if it does so?

  • Unlike light, electron-waves are not made by electric or magnetic fields. But then the question arises: if light wave carries away energy, why doesn't a matter wave do the same?

Best Answer

"The wave is actually probability in the sense that it assigns probability to the space coordinates of detecting photon at a certain time."

No, the emergence of the classical EM wave from the quantum wavefunction of the photon is not trivial, because a classical EM wave is made up of many photons. In particular, it is not the case that the classical EM wave is the wavefunction of a photon. (Even more particular, it is difficult to even speak of the wavefunction of a photon, since photons usually arise in a quantum field theoretic ("second-quantized") description where the notion of wavefunction does not exist (but is, if you insist on something comparable, replaced by a wavefunctional))

Also, do not speak of "the electron wave". While an electron - like all quantum objects - carries wave-like properties and can be described by a wavefunction (which is not a function as you might imagine it if we incorporate its spin in the sense that it does not take values in the real or complex numbers), it isn't a wave in any classical sense, and also still carries particle-like properties. It is a quantum object, neither fully wave nor fully particle at any time.

Nevertheless, all quantum objects (and hence all things you might decsribe as "matter waves") of course carry energy - the energy that is in their rest mass and the energy that is in their momentum, though the energy of any given quantum state may not be well-defined, but "smeared out" over a range of energies.

To ask how physical objects carry the properties they do is, deep down, not sensible. How does a classical particle carry momentum? By having mass and velocity! But how does it carry mass and velocity? By...um...moving and stuff. How does it move? Um... You get the idea. "Why/How" is a question that can be asked infinitely many times, but only answered finitely many before you hit a point where the only answer is because it seems that way.

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