How Does Light Interact with Different Media According to Quantum Mechanics?

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Discussion Overview

The discussion revolves around the interaction of light with different media as described by quantum mechanics, focusing on the nature of light's behavior when transitioning from one medium to another, particularly in terms of wave-particle duality and the implications of interference.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant references Feynman's lectures, questioning how light "knows" about the denser medium and what constitutes "information" in this context.
  • Another participant argues that light does not "know" the shortest path, explaining that light exhibits both wave and ray properties, with waves propagating along all paths and only those along minimal paths interfering constructively.
  • A follow-up question arises regarding the conservation of energy when photons undergo destructive interference, prompting further clarification about the nature of photons and their self-interference.
  • It is noted that a single photon interferes with itself, and the wave function represents a probability distribution rather than a physical entity, with measurement affecting the interference pattern.
  • Clarification is provided that the square of the amplitude of the wave function gives the probability density, distinguishing between the wave and the probability it represents.

Areas of Agreement / Disagreement

Participants express differing views on the nature of light's behavior and the implications of quantum mechanics, particularly regarding the concepts of information, interference, and the interpretation of quantum phenomena. No consensus is reached on these points.

Contextual Notes

Participants discuss the implications of wave-particle duality and the interpretations of quantum mechanics, highlighting the complexity and unresolved nature of these concepts in the context of light's interaction with media.

feynmann
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In Feynman lectures, Feynman says if light goes from air to denser medium,light goes more in air and less in denser medium so that it takes shortest time to reach its destination.

My question are

How light knows that there is a denser medium ahead in its path?

Does light get information about the denser medium?

what is information?
 
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The light doesn't "know" which path/time is the shortest...The fact is that light has wave characteristics as well as ray properties. The light waves propagate along ALL paths...the waves that are traveling along paths that are not minimized will reach the point exactly out of phase and undergo destructive interference, while the waves on the minimal path will interfere constructively. So basically any light waves traveling along a path that does not represent minimal time will cancel each other out.
 
destro47 said:
The light doesn't "know" which path/time is the shortest...The fact is that light has wave characteristics as well as ray properties. The light waves propagate along ALL paths...the waves that are traveling along paths that are not minimized will reach the point exactly out of phase and undergo destructive interference, while the waves on the minimal path will interfere constructively. So basically any light waves traveling along a path that does not represent minimal time will cancel each other out.

So what happens to the energy of the photons when they destructively interfere? Doesn't this go against the law of conservation of energy?
 
mn4j said:
So what happens to the energy of the photons when they destructively interfere? Doesn't this go against the law of conservation of energy?

There's only one photon and it interferes with itself. As such, the "wave" which interferes with itself is just a probability to find the photon at a given point. The photon is either found at a point or not found at a point. The photon never splits up. But if you make a measurement along one of the paths to find out which way it went, you'll destroy the interference effect. The question of "what happens to the photon in between its emission from a source and its detection" is the subject of the so-called interpretations of quantum mechanics. i.e. quantum theory doesn't tell us anything apart from measurable phenomena.

Edit: The wave itself is not directly the probability. If you've done complex valued functions, the square of the amplitude of the wave gives the probability density.
 

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