Why electron absorbs photon costs FINITE time?

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SUMMARY

The discussion centers on the finite time required for an electron to absorb a photon, emphasizing that this process is not instantaneous. It is established that interactions in the universe, including photon absorption by electrons and phonons, take a finite amount of time to avoid issues related to infinite energies and faster-than-light causality. The key equations presented are Δt ΔE ≈ h-bar/2, which relates the time of absorption to the energy width of the excited state, and Δt Δω ≈ 1/2, which can be derived from electrical circuit principles.

PREREQUISITES
  • Understanding of quantum mechanics concepts, particularly energy states.
  • Familiarity with the Heisenberg uncertainty principle.
  • Basic knowledge of electrical circuits and their equations.
  • Awareness of photon and phonon interactions in physics.
NEXT STEPS
  • Study the Heisenberg uncertainty principle in detail.
  • Learn about energy state transitions in quantum mechanics, specifically in hydrogen atoms.
  • Explore the derivation of Δt Δω ≈ 1/2 in electrical circuits.
  • Investigate the implications of finite time processes in quantum field theory.
USEFUL FOR

Physicists, quantum mechanics students, electrical engineers, and anyone interested in the fundamental interactions of particles and energy absorption processes.

luxiaolei
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Hi,all, why electron absorb photon costs FINITE time? Not only for electron, when phonon
interact with photon(absorbs it) also costs finite time.

As I think, it should be instant, can not find any reason for finite time. Helps!

Thanks In advance!
 
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luxiaolei said:
As I think, it should be instant, can not find any reason for finite time.
Nothing in the universe is instant, everything takes a finite time.
Not very long - but still finite

Things happening instantly leads to infinite energies or faster-than-light causality problems
 
An electron absorbing a photon and moving up from a stable bound atomic state (e.g., hydrogen 1s state) to a higher unstable bound state (e.g., 2p state) requires an absorption time

1) Δt ΔE ≈ h-bar/2

where ΔE is the natural width of the 2p state.

Divide both sides by h-bar and get (using Ephoton = h-bar ω)

2) Δt Δω ≈ 1/2 for electrical circuits..

Derive Eqn 2 first for electrical circuits (doesn't require quantum mechanics), then multiply both sides by h-bar to get Eqn 1.

Bob S
 

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