Double Slit Hide and Seek

Interesting physics explained with many thought experiments and little math.
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Double Slit Hide and Seek

Post by SsDd » Tue Oct 05, 2010 12:52 am

The lecture video is embedded below.

Additionally, slides used in the lecture are embedded below, or can also be downloaded directly from here.

Questions after the lecture? Please feel free to post them in the same thread.

Click to play embedded YouTube video.


Re: Double Slit Hide and Seek

Post by LP » Wed Aug 03, 2011 7:27 am

Starting with a typical 2 slit experiment, is it possible to record the position of the photon (or perhaps an electron or other particle) at the screen without disturbing its trajectory?

If so then:
1. Then a wide area bubble chamber behind the screen could be used to determine "which slit info" after the no-interference/interference pattern has been recorded on the screen.
2. With the bubble chamber moved back away from the screen you could have time to change your mind and not record "which slit info" (block the particle before reaching the bubble chamber).

I assume #1 above is prohibited by Heisenburg, and #2 also violates cause - effect?

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Re: Double Slit Hide and Seek

Post by Chris Peterson » Wed Aug 03, 2011 1:01 pm

LP wrote:Starting with a typical 2 slit experiment, is it possible to record the position of the photon (or perhaps an electron or other particle) at the screen without disturbing its trajectory?
No. The thing is, the particle has no well defined position, and no trajectory. It is described by a probability of existing in some particular location, with a certain momentum, at some time. You can't observe it without affecting it.

Chris L Peterson
Cloudbait Observatory


Re: Double Slit Hide and Seek

Post by LP » Thu Aug 04, 2011 6:42 am

Thanks Chris. now what I'm not sure about is:

1. In reality, is it commonly believed that the particle does not really exist until it's wave function is collasped, or is quantum mechanics merely a math that describes what we are able to observe because of the low energy of our subject.

2. Is quantum entaglement analogous to :
Alice and Bob reach into a hat that they know contains a penny and a dime, and each pulls out a coin without looking at it. Alice then travels a distance from Bob. Now Bob observes the coin in his hand and instantly knows the coin Alice holds. Is this the crux of entaglement, or is there a deeper meaning to it?


Re: Double Slit Hide and Seek

Post by DG1 » Sat Jan 28, 2012 12:48 pm

Hi, I was curious to watch the lecture and hear the favored explanation by Robert J. Nemiroff.
I think he chose the explanation proposed by Drezet - that those photons that reach the detectors do not have formed interference. This is however wrong, and is not consistent with the solution of Fresnell diffraction integrals for the double slit - lens system. Check this article, where for the first time are shown the calculated probability distributions for Afshar setup in coherent (both slits open) and incoherent setups (one slit open at a time, or both open but different polarization filters are placed on the pinholes).
D. Georgiev. (2012). Quantum Histories and Quantum Complementarity. ISRN Mathematical Physics, Article ID 327278, 37 pages
There is much more in the article, just check it out. I favor the application of Feynman's sum-over-histories, which makes things quite transparent. In the book "QED: The Strange Theory of Light and Matter" Feynman made very nice footnote remark about the principle of complementarity, which is that once you sum-over-histories you do not need to rely on the principle of complementarity. You just add the corresponding quantum amplitudes contributed by different histories and you can "see" what cancels with what. Complementarity is correct, but not in the way all advocates of the Copenhagen Interpretation believe. In coherent Afshar setup there is no which way information at the images to begin with, so placing wire grid is irrelevant. This was independently proved by Tabish Qureshi in 2007, associate professor at JMI, India, who posted his work in ArXiV just a couple of months later after my first pre-print was released in PhilSci in 2006.