two-slit newb question

[Guest dy/dx]

http://www.bottomlayer.com/bottom/reality/chap2.html#n2

 

The above site describes what I presume is the classical scenario, i.e. an electron emitter, two slits, an electron detector at each slit and a screen at the back. Several variations are presented, the following two for example:

 

1) The electron detector at each slit is kept on but the information not recorded. The back screen still indicates a wave distribution, showing that the electron detectors by themselves did not interfere with the results.

 

2) The electron detector at each slit is kept on and the information *is also recorded*, but before the back screen is examined, the detector info is erased. There is *still* a wave interference pattern on the back screen.

 

*Only* if the detector info from each slit is observed does the pattern on the back screen change from a wave to a particle distribution.

 

NOW HERE'S MY QUESTION:

 

What would happen if the detector at each slit is kept on, the info recorded, *but before reading it* you examine the back screen FIRST, THEN read the info from the detectors.

____

[Johnny5]

http://www.bottomlayer.com/bottom/reality/chap2.html#n2

 

The above site describes what I presume is the classical scenario' date=' i.e. an electron emitter, two slits, an electron detector at each slit and a screen at the back. Several variations are presented, the following two for example:

 

1) The electron detector at each slit is kept on but the information not recorded. The back screen still indicates a wave distribution, showing that the electron detectors by themselves did not interfere with the results.

 

2) The electron detector at each slit is kept on and the information *is also recorded*, but before the back screen is examined, the detector info is erased. There is *still* a wave interference pattern on the back screen.

 

*Only* if the detector info from each slit is observed does the pattern on the back screen change from a wave to a particle distribution.

 

NOW HERE'S MY QUESTION:

 

What would happen if the detector at each slit is kept on, the info recorded, *but before reading it* you examine the back screen FIRST, THEN read the info from the detectors.

____[/quote']

 

 

Are you asking about electron diffraction?

[Guest dy/dx]

<i>Are you asking about electron diffraction?</i>

 

OK, that website I mentioned is my first detailed introduction to quantum theory. If you read it, I think you will agree that it is lucid, coherent, and highly detailed. The author says that detectors at the slits do not by themselves effect the particles in any way, i.e. a wave interference pattern still occurs. The detector output has to be observed (by a human I guess) at which point a particle distribution occurs on the screen. This is a claim that is strongly refuted in a thread I have started in sci.physics, so needless to say I don't know what to believe.

 

In any case, my question is, if the author is correct, what happens if you examine the screen *first*, i.e. before reading the detector output?

 

Sorry to bring up crank websites in this forum if that's what it is.

[swansont]

The kind of detailed "which path" experiments they are describing aren't really introductory QM. I've looked at a few of the pages on the site and I'm not convinced they are describing experiments accurately.

[bascule]

OK, that website I mentioned is my first detailed introduction to quantum theory. If you read it, I think you will agree that it is lucid, coherent, and highly detailed. The author says that detectors at the slits do not by themselves effect the particles in any way, i.e. a wave interference pattern still occurs. The detector output has to be observed (by a human I guess) at which point a particle distribution occurs on the screen. This is a claim that is strongly refuted in a thread I have started in sci.physics, so needless to say I don't know what to believe.

 

You seem to be asking a "if a tree falls and no one is there to hear it does it make a sound" type question.

 

The detectors can still be present but disabled. When they are disabled the interference pattern still appears. Only when they are "switched on" and thus are detecting the "which path" information is the interference pattern destroyed. It doesn't matter if anything is actually there to observe the information being garnered... as long as the information is being garnered the interference pattern will be destroyed. The presence of an actual human is irrelevant.

[Rebel.esd]

By its very nature, in order to "detect" something a detector must interact with it, and as soon as a particle is interacted it is "compelled" to take on a definite property. So, if the detectors are off (and not influencing the particle) it can continue its happy little waltz through the haze of probability, allowing both histories to factor into its destination.