Questions about measurement devices in the double slit experiment

  • #1

Main Question or Discussion Point

How did you find PF?: Google

Is it true that the devices that quantify which slit do NOT produce wave collapse unless they actually record the light measurements rather than just detect them without recording?
 

Answers and Replies

  • #2
PeroK
Science Advisor
Homework Helper
Insights Author
Gold Member
12,317
5,117
How did you find PF?: Google

Is it true that the devices that quantify which slit do NOT produce wave collapse unless they actually record the light measurements rather than just detect them without recording?
:welcome:

What might "detect without recording" mean?
 
  • #3
DrChinese
Science Advisor
Gold Member
7,243
1,053
Is it true that the devices that quantify which slit do NOT produce wave collapse unless they actually record the light measurements rather than just detect them without recording?
It is possible to place polarizers over each of the 2 slits. In cases where the slits are aligned perpendicular, there will be no interference. And yet there is nothing being recorded in any fashion to indicate which slit the light goes through, even though in principle that is possible.

http://sciencedemonstrations.fas.harvard.edu/files/science-demonstrations/files/single_photon_paper.pdf

Is that the scenario you are envisioning?
 
  • #4
EPR
Gold Member
153
25
How did you find PF?: Google

Is it true that the devices that quantify which slit do NOT produce wave collapse unless they actually record the light measurements rather than just detect them without recording?


You can record which slit they went through and in that case there would be no interference pattern.
 
  • #5
4
2
It is possible to place polarizers over each of the 2 slits. In cases where the slits are aligned perpendicular, there will be no interference. And yet there is nothing being recorded in any fashion to indicate which slit the light goes through, even though in principle that is possible.

http://sciencedemonstrations.fas.harvard.edu/files/science-demonstrations/files/single_photon_paper.pdf

Is that the scenario you are envisioning?
When they launch the particle, where do they aim specifically?
 
  • #6
PeroK
Science Advisor
Homework Helper
Insights Author
Gold Member
12,317
5,117
When they launch the particle, where do they aim specifically?
At the slits! Where else?
 
  • #7
Nugatory
Mentor
12,614
5,165
When they launch the particle, where do they aim specifically?
The slits are close enough together that they're both equally likely to be hit. It's possible to do the experiment with the slits more widely separated (which has the effect of weakening the interference pattern and making it asymmetrical) but that just complicates the calculation without introducing any new physics.
 
  • #8
Cato
Gold Member
44
6
I have a similar and (maybe the same?) question as UnderstandingQT. If you fire electrons toward the two slits, and you have electron detectors at each slit that are turned off, then you will get an interference pattern. If you turn the detectors on and observe the results, you will not get an interference pattern. If you turn the detectors on but do not observe or record the results, will you get an interference pattern? The question, of course is trying to sort out whether the interference pattern vanishes because 1) a conscious observer was aware of which slit the electron passed through or 2) whether the mere physical process that permitted detection of the electron caused the electron to behave as a particle. Surely this obvious high-school level question has been definitively settled.

Sorry, Understanding QT, if this is not what you were getting at.
 
  • #9
Nugatory
Mentor
12,614
5,165
If you turn the detectors on but do not observe or record the results, will you get an interference pattern?
No. It's the interaction with the detectors that makes the difference.

This was definitively settled many decades ago. Unfortunately by then the idea that a conscious observer was involved had made it into the popular imagination where it lives on as a sort of urban legend, one of those things that everyone has "just heard somewhere"

A pretty good layman friendly reference is David Lindley's book "Where did the weirdness go?"
 
Last edited:
  • #10
Cato
Gold Member
44
6
Thank you! So all the talk about the importance of "observation" is mistaken. Nice to have that that settled.
 
  • #11
EPR
Gold Member
153
25
If someone were able to explain single/definite outcomes(why certain outcomes and not others), he'd surely have gotten a Nobel prize.
 

Related Threads on Questions about measurement devices in the double slit experiment

Replies
18
Views
9K
Replies
2
Views
897
Replies
3
Views
2K
Replies
3
Views
2K
Replies
42
Views
5K
Replies
21
Views
3K
Replies
1
Views
1K
Replies
5
Views
727
Top