Which slit/way at time of observation or passing slits?

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Discussion Overview

The discussion revolves around the timing of the "which-slit" decision in a single particle double-slit experiment, specifically whether this decision is made at the moment of observation or when the photon encounters the slits. Participants explore implications of these timings on the nature of photons and their properties.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that the which-slit decision is made at the time of observation, suggesting that the particle is detected as if it traveled through one slit, despite potentially passing through both.
  • Others question whether a photon possesses defined properties such as energy, size, frequency, or amplitude before detection, raising doubts about how these attributes manifest in the context of the experiment.
  • One participant wonders if a photon that goes through both slits has its energy or other properties halved, or if only the probability is distributed across the paths.
  • Another viewpoint suggests that the experimental setup influences whether the particle is considered to travel via both or one path.
  • A later reply introduces the idea that rather than the photon needing to know the questions posed by observers, it is the observers who must understand the context of their measurements and the nature of quantum behavior.

Areas of Agreement / Disagreement

Participants express differing views on when the which-slit decision is made, with no consensus reached on the timing or implications of this decision. The discussion remains unresolved with multiple competing perspectives.

Contextual Notes

Participants acknowledge the complexity of defining properties of photons before detection and the role of experimental context in determining the behavior of particles, but these aspects remain open to interpretation.

San K
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in a single particle, double slit experiment

is there any way/experiment/argument that can tell if

the which-slit decision/finalization is made at the time A or time B below:

A) when the photon is observed (by a telescope etc), say a few microsecond after it has passed through the slits
or
B) when the photon encounters the slits
 
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I'm not sure how experiments could confirm this one way or another but I believe the which slit "decision" is made when the particle is observed. In fact, the particle never travels through just one slit, it's just detected as if it did.

Here's a nice article about this
http://www.mathblog.ellerman.org/2011/11/a-common-qm-fallacy/
 
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Joncon said:
I'm not sure how experiments could confirm this one way or another but I believe the which slit "decision" is made when the particle is observed. In fact, the particle never travels through just one slit, it's just detected as if it did.

Here's a nice article about this
http://www.mathblog.ellerman.org/2011/11/a-common-qm-fallacy/

well said and good link, thanks Joncon.

I wonder if a photon goes through both slits does its energy/size/frequency/amplitude halve? (In the two new wavefronts that emerge from the two slits)

or is it that just the probability gets "distributed"?

for example in mach zender when we block one path, we still record the photon with same energy, if it went through both paths then a layman would expect "half of the original photon energy" to be detected.
 
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San K said:
I wonder if a photon goes through both slits does its energy/size/frequency/amplitude halve? (In the two new wavefronts that emerge from the two slits)

How could we ever know? Does a photon actually HAVE an energy/size/frequency/amplitude before it's detected?

It would seem to be an incredibly inefficient way for the universe to operate, if it had to split the photon up into an infinite number of parts (corresponding to the infinite number of paths it could take) and then join them all back together when it's detected!
 
It seems the photon carries "memories/states/factors" for both interference and non-interference at all times prior to detection/collapse.
 
The context of the experimental set-up determines whether the particle travels via both or one path. (Or so I believe)
 
Here's another way to think about it-- rather than imagining that the photon has to wait to know what questions we are asking before it can decide what to be, just recognize that physics is our way of, in essence, communicating with nature. So it is not the photon that needs to know what question we are asking, before it can answer-- it is we who need to know, when we receive an answer, what question we were asking that some detection is the answer to. To me, the way quantum behavior depends on the apparatus is a clear indicator of the role that our analysis approach is playing in the outcomes of quantum mechanics.
 

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