Time taken to absorb neutrons,photons

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Discussion Overview

The discussion revolves around the time taken for particles, specifically photons and neutrons, to change momentum when interacting with surfaces, including bouncing and absorption processes. It also touches on the concept of particles, such as neutrinos, being at rest in reality versus theory. The scope includes theoretical considerations, conceptual clarifications, and exploratory reasoning regarding particle interactions.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions the time it takes for particles to change momentum when bouncing off or being absorbed by a surface, specifically comparing photons and particles with rest mass.
  • Another participant asserts that photons do not bounce but are absorbed and then re-emitted by atoms, suggesting a different interaction mechanism compared to particles with mass.
  • A participant states that neutrons can be at rest in reality, challenging the notion that they can only be at rest in theory.
  • There is a query about whether neutrinos can be at rest in reality, with a response indicating that if neutrinos have mass, it is theoretically possible, although none have been trapped yet.
  • Participants discuss the timescale for photons reflecting off mirrors and electrons interacting with solid surfaces, with one suggesting that the timescale for photons is comparable to the lifetime of excited atomic states.
  • Another participant mentions that the reflection of electrons can be treated classically and depends on the properties of the reflecting medium.

Areas of Agreement / Disagreement

Participants express differing views on the nature of photon interactions, with some asserting that photons do not bounce while others explore the concept of reflection. There is also a lack of consensus on the specifics of how long these interactions take, indicating ongoing debate and uncertainty.

Contextual Notes

Participants reference the lifetime of excited atomic states and the properties of reflecting media, but these concepts remain loosely defined and not fully resolved within the discussion.

kurious
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How long do particles take to change their mometum when they "bounce"
off a surface and when they are absorbed by a surface?
Do photons have a noticeably different "bounce" and absorption time to particles with rest mass?
Can a neutron have a rest mass and be at rest in reality rather than just in theory?
 
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Photons cannot ever change their speed, so they do not bounce. They are absorbed by an atom, then the atom emits a new photon in another direction.

Neutrons have zero residual (external) electronic charge, but their component quarks can interact either via the electromagnetic or strong forces with other particles. Depending upon the angles involved in the collision, I'd expect a neutron to be either be scattered by a nucleus ("bouncing"), or captured by a nucleus.

Neutrons can certainly be at rest in reality.

- Warren
 
I meant to ask: can a neutrino be at rest in reality and not just in theory?
 
kurious said:
I meant to ask: can a neutrino be at rest in reality and not just in theory?

If the neutrinos have even a small mass, the answer is yes. Nobody has trapped one, but someday it may be done.
 
Over what sort of timescale does a photon reflect off a mirror back along the direction it came from, and the same for an electron "reflected" by a solid surface.
 
As has been said, the photon doesn't reflect. It's absorbed, then a new photon is emitted. I suppose the time scale is comparable to the lifetime of an excited atomic state, something on the order of nanoseconds or less I believe. As for an electron, this can be treated clasically, and I think it depends on the properties of the reflecting medium.
 

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