Why don't the Slits collapse the wave function?

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Discussion Overview

The discussion centers on the phenomenon of wave function collapse in the context of the double-slit experiment, particularly addressing why the interaction with the slits does not collapse the wave function until a measurement is made. Participants explore the nature of interactions between particles and slits versus measurement devices, delving into concepts of phase coherence and the implications for interference patterns.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants question how interaction with the slits does not collapse the wave function, suggesting that bouncing off the sides of the slit could be considered an interaction.
  • Others propose that the critical issue is the path taken by the particle, with superposition playing a role in the observed interference pattern.
  • One participant describes the wave function as a corkscrew representing momentum, indicating that measuring position results in losing the interference pattern.
  • Another viewpoint suggests that the slits do not have internal degrees of freedom, which preserves phase coherence and allows for interference, while measurement devices do affect phase coherence.
  • Some participants argue that the slits serve merely to spatially separate trajectories, and the nature of measurement devices is what distinguishes their interaction with particles.
  • A participant expresses confusion about the terminology used, seeking clarification on their understanding of wave function collapse in relation to the double slit.
  • There is a challenge to the correctness of a participant's understanding of wave function collapse, indicating a lack of consensus on this interpretation.

Areas of Agreement / Disagreement

Participants express differing views on the nature of interactions with the slits versus measurement devices, with no consensus reached on the specifics of wave function collapse in this context. Some agree on the importance of phase coherence, while others challenge interpretations of the double slit’s role.

Contextual Notes

Participants note the complexity of the concepts involved, including the implications of internal degrees of freedom and phase coherence, which may not be fully resolved within the discussion.

  • #91
DrChinese said:
There is a way to learn which slit the photon pass through without absorbing it. If you put a polarizer in front (or behind) each slit, and the polarizers are crossed (at 90 degrees apart as to their relative orientation), then the photon passes through. Because of the polarizer, you know which slit it passed through (or could learn later); therefore there is no interference pattern.

I can see two situations here. If we send toward the slits a circular polarized photon, then each component of linear polarization would pass through each slit and then re-combine. The interference pattern would still be there.
If we sent a linearly polarized photon with either horizontal or vertical polarization, then we would know which slit it went through. Every photon that lands on the screen would be coming from the slit that corresponds to its initial polarization. In this case I guess the interference pattern would be destroyed. But I also think that 50% of the time the photon would be absorbed by the polarizer film in the slit with crossed polarization. If you use a polarizer that works by reflection, in that case you could absorb the photon after being reflected. So I don't know if this would qualify as a non-absorption detection experiment. It would also be equivalent to putting any obstacle in front of one of the slits. What you are detecting is the photon that doesn't make it through and not the one that does.
Well Dr. Chinese you got me thinking for a while. This is an interesting modification of the double-slit experiment and I had fun thinking about it.
 

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