Two Questions about Photon/Electron Interaction

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In summary, Richard Feynman explains the interaction between a photon and an electron, where the electron can absorb the photon's energy and continue on for a brief period before emitting a new photon. This process can occur in atoms, where the photon's energy can be stored and the electron can be pushed further from the nucleus. The duration of the interaction is determined by chance and follows the Heisenberg uncertainty principle. The driving force behind the process is the interaction between the electromagnetic field and the electron's charge.
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Richard Feynman writes, on page 97 of his primer of quantum electrodynamics, QED: The Strange Theory of Light and Matter, about the interaction of a photon and an electron. He writes: "One way this event can happen is: a photon is absorbed by an electron, the electron continues on a bit, and a new photon comes out."

FIRST QUESTION: When Prof. Feynman says "continues on a bit," what sort of time scale is involved? Is it on the order of 10-30 to 10-15 second, or can it also be whole seconds, minutes, years or even eons?

I take it that an electron in free space cannot interact with a photon because there is no way an electron can store a photon's energy. But for an electron in an atom, the energy of the photon can be stored in the atom, i.e., with the electron being pushed a little farther from the nucleus.

SECOND QUESTION: What drives, provokes, or stimulates the process by which "a new photon comes out"?

I'm not a physicist, just an interested layman. Thanks for any guidance.
 
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The original electron obeys the usual special-relativity relationship between energy and momentum: E2 = p2c2 + m2c4. When the photon is absorbed, energy and momentum are conserved in the collision, and so the electron that emerges from the collision has greater energy E' and momentum p'. Furthermore E' and p' do not obey the above relationship. We say it is a virtual particle, and is "off the mass shell."

The virtual electron "continues on a bit." How long it does so is a matter of chance, but is approximately given by the Heisenberg uncertainty principle.

What drives the particle to decay back into a photon plus electron is the same thing that drove them to combine in the first place: the interaction between the electromagnetic field and the charge of the electron.
 
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Bill_K said:
The virtual electron "continues on a bit." How long it does so is a matter of chance, but is approximately given by the Heisenberg uncertainty principle.
Like on the order of 10-34 second?
 
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What is the difference between photon and electron interactions?

Photon and electron interactions are fundamentally different processes. Photons are particles of electromagnetic radiation, while electrons are fundamental particles with a negative charge. When photons interact with matter, they can be absorbed, reflected, or scattered, depending on the material and the properties of the photon. On the other hand, electrons can undergo a variety of interactions, including scattering, diffraction, and emission, as well as forming bonds with other atoms in chemical reactions.

How do photons and electrons interact with each other?

Photons and electrons can interact with each other in several ways. One common interaction is through the photoelectric effect, where a photon transfers its energy to an electron, causing it to be emitted from a material. Another important interaction is Compton scattering, where a photon collides with an electron, transferring some of its energy and changing its direction. Additionally, electrons and photons can interact through the process of pair production, where a high-energy photon can create an electron-positron pair.

Can photons and electrons interact with different types of materials?

Yes, photons and electrons can interact with a wide variety of materials. The specific type of interaction depends on the properties of the material and the energy of the photon or electron. For example, low-energy photons are more likely to be absorbed by materials with high atomic numbers, such as lead, while high-energy photons are more likely to be scattered by lighter materials, such as carbon. Similarly, electrons can interact differently with different materials, depending on factors such as their density and atomic structure.

How does the energy of a photon or electron affect their interactions?

The energy of a photon or electron plays a crucial role in determining the type of interaction that will occur. For photons, the energy determines their wavelength and frequency, which in turn affects how they will interact with matter. Higher energy photons can penetrate deeper into materials and cause more ionization, while lower energy photons are more likely to be absorbed. Similarly, the energy of electrons determines their velocity and how they will interact with other particles, such as atoms and molecules.

What is the significance of photon and electron interactions in everyday life?

Understanding photon and electron interactions is essential for many technological applications in our everyday lives. For example, the photoelectric effect is crucial for the functioning of solar cells, which convert the energy of photons into electricity. Compton scattering is used in medical imaging techniques such as X-rays, and pair production is important in radiation therapy for treating cancer. Additionally, electron interactions are essential in chemical reactions, which are the basis of many everyday processes, including food digestion, combustion, and energy production.

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