Laser and Mirror Thought Experiment

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Discussion Overview

The discussion revolves around a thought experiment involving a laser and a mirror, specifically addressing how light emitted from a laser can be seen in a mirror when the laser emits a line of photons parallel to the mirror. Participants explore the properties of light, the behavior of electromagnetic radiation, and the visibility of laser beams.

Discussion Character

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

Main Points Raised

  • One participant questions how photons emitted in a line can be seen in the mirror, seeking clarification on the mechanism of reflection and visibility.
  • Another participant asserts that a laser emits light as electromagnetic radiation rather than a stream of photons, emphasizing the interaction of light with the mirror.
  • There is a discussion about the necessity of quantum mechanical calculations for understanding photon behavior, with some arguing it is unnecessary for this scenario.
  • Concerns are raised about how electromagnetic radiation emitted from the laser travels to the mirror, with a focus on the directionality of light waves.
  • Participants clarify that photons are packets of energy associated with electromagnetic waves, but caution against oversimplifying their behavior without proper context.
  • One participant expresses appreciation for the clarification regarding the visibility of laser beams in a vacuum.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the nature of light emission and visibility in this scenario. There are competing views on the necessity of discussing photons versus electromagnetic radiation, and the discussion remains unresolved regarding the specifics of how light interacts with the mirror.

Contextual Notes

Some limitations include assumptions about the visibility of laser beams in different environments and the complexity of light behavior that may not be fully addressed in the discussion.

ChrisisC
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I have a thought experiment that i need a answer to. In my experiment, I am in a bathroom with a mirror along one wall. I also have a laser that emits a single file line of photons. The laser is attached to the ceiling and emits a line of photons parallel to the mirror. What property of light makes it so i can see the photons in the mirror? A normal laser that doesn't emit just a single file of photons can be seen reflected in a mirror while it's pointed parallel to the mirror. So how is this possible? How do the photons get out of the line if the laser and reflect off the mirror to my retina? How do the photons go in a different direction than the laser is emitting them? I hope i presented my question in a answerable manner, and please excuse my lack of knowledge.
 
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ChrisisC said:
I also have a laser that emits a single file line of photons.
There is no such thing. A laser doesn't emit a stream of photons, whether "in single file" or not, it emits light, which is to say electromagnetic radiation. The light interacts with and is scattered by the mirror, and you see the scattered light.

Photons only come into the picture if you do detailed quantum mechanical calculations (which are completely unnecessary for this problem) of exactly how the light is scattered by the mirror.
 
Nugatory said:
There is no such thing. A laser doesn't emit a stream of photons, whether "in single file" or not, it emits light, which is to say electromagnetic radiation. The light interacts with and is scattered by the mirror, and you see the scattered light.

Photons only come into the picture if you do detailed quantum mechanical calculations (which are completely unnecessary for this problem) of exactly how the light is scattered by the mirror.

Precisely my question, HOW does the EM radiation get emitted from the laser and actually travel to he mirror to be reflected? Wouldn't the light wave be traveling parallel to the mirror? The light wave would have to hit the mirror, meaning it's not parallel to the mirror anymore, right?
 
ChrisisC said:
HOW does the EM radiation get emitted from the laser and actually travel to he mirror to be reflected?
It gets scattered or reflected off something else first. A laser beam in vacuum is not visible.

ChrisisC said:
And aren't photons EM radiation? photons are individual packets of energy of a EM wave, right?
Yes, but they don't behave the way you describe. To correctly describe photons you need to use QFT.

But as @Nugatory says, that is unnecessary for this problem. All you need to do is say that your laser beam is well collimated and then talk about the scattering of the beam. There is no need to bring in photons
 
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Dale said:
It gets scattered or reflected off something else first. A laser beam in vacuum is not visible.

Ah, that's a very valuable piece of information I was not aware of. Thank you!
 
ChrisisC said:
Ah, that's a very valuable piece of information I was not aware of. Thank you!
Excellent! Glad to help
 

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