Effects of a moving mirror on a ray of light

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Discussion Overview

The discussion revolves around the effects of a moving mirror on the path of a ray of light, particularly focusing on scenarios where the mirror moves at subluminal speeds. Participants explore theoretical implications, potential experiments, and the relationship between the angle of incidence and reflection in different reference frames.

Discussion Character

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

Main Points Raised

  • Some participants propose that if a mirror moves at subluminal speeds, the reflected dot on a wall will gradually move up over time.
  • Others argue that if the mirror is moving at subluminal speeds from the beginning, the reflected dot will remain fixed, although it may be higher than when the mirror is stationary.
  • A participant mentions that momentum is transferred to the light beam, resulting in a Doppler shift upon reflection.
  • Some suggest that the angle of reflection may change due to the motion of the mirror, particularly when considering different reference frames.
  • One participant introduces the concept of different frames of reference, indicating that the angle of light at the mirror differs depending on whether the mirror or the light source is considered to be in motion.
  • Another participant draws an analogy between moving mirrors and the techniques used by tennis players to control the direction of a ball.
  • A later reply discusses a paper that presents a relativistic treatment of light reflecting from a uniformly moving mirror, suggesting that the momentum change of each photon is perpendicular to the mirror's surface.
  • Some participants assert that if there were a significant effect from the mirror's motion, it would be observable in everyday reflections.
  • One participant posits that an ideal mirror, which exchanges momentum only along the y-axis, would not be affected by movement along the x-axis, likening it to a collision with a frictionless surface.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the effects of a moving mirror on light reflection, with no consensus reached on the outcomes or implications of the scenarios discussed.

Contextual Notes

Some discussions involve assumptions about the ideal nature of the mirror and the conditions under which the effects are analyzed, including the treatment of momentum and reference frames.

  • #31
yrjosmiel said:
So far, after taking into account the contraction of the distance of the light source and the wall, I concluded that there is indeed no difference in where the laser dot will land on the wall.

If I do have any remaining questions: should I do an experiment to confirm this conclusion or would that be a waste of time and resources?
This open-access paper presents some relevant considerations:
Classical dynamics of a moving mirror due to radiation pressure
 
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  • #32
reflection rule is in approxation that mirror is massive enough. Compton effect should be active for high energy photon and mirror.
 
  • #33
My understanding that the speed of light is slower in a medium is not because the light actually travels at a slower speed, but because the light interacts with the various particles of the medium which takes time. doesn't the mirror absorb the light than readmit it? wouldn't the mirror have at least traveled a short distance during this time? Wouldn't this cause the dot to be slightly lower?
 
  • #34
Justin Hunt said:
My understanding that the speed of light is slower in a medium is not because the light actually travels at a slower speed, but because the light interacts with the various particles of the medium which takes time. doesn't the mirror absorb the light than readmit it? wouldn't the mirror have at least traveled a short distance during this time? Wouldn't this cause the dot to be slightly lower?
The initial question and all the answers have been assuming an ideal mirror, one that is of zero thickness and reflects 100% of the incident light.
 

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