[Advaita-l] The mystery element in the Quantum Theory

[Sriram Sankaranarayanan]

Namaste Sri Shrinivas Ji

 Experimental variations A and B, their results are fairly common. Can you
give me some reference for set ups C and D ( both 1,2)?

Thanks and regards,
 Sriram

Hamsah Soham

On Wed, Mar 22, 2017 at 7:35 AM Shrinivas Gadkari via Advaita-l <
advaita-l at lists.advaita-vedanta.org> wrote:

> Namaste,
> Few weeks ago there was a thread on quantum theory and consciousness.Here
> is a write up that tries to capture the mystery element in theQuantum
> theory - as I understand it.
> Regards,Shrinivas Gadkari
> --------------------------------------------------------------------
> The mystery element in the Quantum Theory
> -----------------------------------------
>
> To clearly bring out the mystery element in the quantum theory that
> has puzzled the foremost of the physicists, consider the following
> thought experiment. The experiment here is a hybrid of Feynman's
> double-slit experiment with electrons (Feynman Lectures on Physics,
> Volume 3, Chapter 1), and the Schrodinger's Cat experiment.
>
>
>
>                   |Barrier           ||
>                   |                  ||
>                   |                  ||
>                 D1|                  ||
>                    S1                ||
> Source            |                  ||
> =====             |                  || Screen - S
>                   |                  ||
>                    S2                ||
>                 D2|                  ||
>                   |                  ||
>                   |                  ||
>
> Description of the overall setup:
>
> The Source is an electron gun. Electrons emitted from the Source
> encounter a barrier before they hit the Screen.
> The barrier has two open slits S1 and S2 that allow
> electrons to pass through. Screen-S is a surface that can detect/ record
> the location of electrons when they hits the screen.
>
> D1 and D2 are two detectors that can detect if an electron passed
> through slit S1 and S2 respectively, and yet allow the electrons
> to pass.
>
> Electrons are emitted from Source at a very slow rate, say one
> electron every second. An electron emitted from the Source passes
> through the barrier B2 with slits S1 and S2, and then hits the screen-S.
> The position of where the electron hit the screen is recorded on S
> can be "read" off after the experiment.
>
> Experiment Variation A:
> -----------------------
> Setup A: Detectors D1 and D2 are switched off. We conduct the
> experiment for a long time, firing one electron per second. After the
> experiment, we "read" the Screen-S to analyze the locations where the
> electrons hit the screen.
>
> Result A: We see an interference pattern on the screen. There are
> some areas where electrons arrive more frequently (bright strips),
> while there are some areas which are avoided by electrons (dark strips).
>
> Explanation: For every electron that reached screen (not all electrons
> fired by the Source reach the Screen due to presence of the barrier),
> there were two possible paths that the electron could have taken:
> Path-1: Source - S1 - S.
> Path-2: Source - S2 - S.
> In absence of any information about which path the electron took, we have
> to consider the possibilities that the electron may have traveled both
> the paths, and add the complex valued exponentials that represent
> the evolution of phase of the electron in each of the of paths. When we
> add complex valued exponentials in this way for the two paths, there are
> locations on the screen where the complex exponentials cancel each other,
> and there are locations where the complex exponentials boost each other.
> The magnitude of the final complex valued sum of the two exponentials
> represents the probability that the electron may be detected at that
> position. The locations where the two exponentials cancel each other
> have a negligible probability for electrons to hit the screen - these are
> the dark strips in the interference pattern, while locations where the
> exponentials boost each other have a larger probability of electrons
> hitting the screen - these are the bright strips in the interference
> pattern.
>
> Experiment Variation B:
> -----------------------
> Setup: Detectors D1 and D2 are switched on and record the path each
> electron took (Path1: S0-S1-S, or Path 2: S0-S2-S), and these
> results are available to be analyzed by the experimenter . We conduct
> the experiment for a long time, firing one electron per second. After
> the experiment, we "read" the Screen to analyze at what locations the
> electrons hit the screen.
>
> Result: We see NO interference pattern on the screen. The bright and
> dark strip pattern us not observed.
>
> Explanation: Now again there are same two possible paths that an electron
> can take (Path1: S0-S1-S, or Path 2: S0-S2-S).
> However, now that we have information about which path an electron takes,
> we have to account for the two paths differently. The electron may have
> taken path Source-S1-S OR Source-S2-S, but not BOTH the paths together.
> So we again compute the complex valued exponentials that represent the
> evolution of the phase of the electron on each path. However, we now
> compute the magnitude of each complex exponential SEPERATELY, and
> THEN ADD the magnitudes. That is we use a completely different mathematical
> procedure to compute the probability of detecting an electron at a specific
> location on the Screen. Now the possibility of complex exponentials
> canceling each other does not exit. We now have a more uniformly spread
> distribution of electrons - no very dark strips or much brighter strips
> - that is, no interference pattern. So our conclusion is: By observing
> which slit the electron passed through we have destroyed the interference
> pattern.
>
> Experiment Variation C:
> -----------------------
> Setup C: Detectors D1 and D2 are switched on, they detect if an electron
> passed through slit S1 or S2, BUT DO NOT KEEP A RECORD of this detection.
> So physically they behave exactly as in set up B, but there is no way for
> ANYONE to retrieve the record of detection.
>
> Result C: We see again an interference pattern on the screen. There are
> some areas which electrons arrive more frequently (bright strips),
> while there are some areas which are avoided by electrons (dark strips).
>
> Explanation:
> We are in principle back to variation A of the experiment. In absence
> of any record from the detectors D1 and D2, we have to again admit the
> possibility that the electron may have traveled both the paths. So
> following the explanation A, we FIRST ADD the complex valued exponentials
> and THEN compute the magnitude of the complex valued sum. This results in
> the dark and bright strips - interference pattern.
>
> Our Conclusion: It not the physical procedure of the operation of detectors
> D1, and D2, that destroys/ disturbs the interference pattern. It is the
> AVAILABILITY of the results of detection that destroy/ disturb the
> interference pattern.
>
>
> Experiment Variation D:
> -----------------------
> Setup D: Detectors D1 and D2 are switched on, they detect if an electron
> passed through slit S1 or S2. However, this time, the data from detectors
> is "carefully" recorded on a memory device M. By "carefully", we mean:
> "outside the device M, there is absolutely no trace of the outcome of the
> detection process". We conduct the experiment for a long time. After the
> experiment we do not immediately "read" the pattern recorded on the screen.
> We detach both the memory device M, and screen S from the setup. Now
> consider the following two options:
>
> Option D1: After the experiment, we DESTROY the memory device M, and THEN
> read the screen S.
>
> Option D2: We keep the memory device M INTACT, and then read
> the screen S.
>
> Result: For Case D1, a interference pattern is observed on the screen,
> while for Case D2, there is no interference pattern.
>
> Explanation: The electron pattern on the screen is not completely
> determined at the time of this experiment. The pattern on the
> screen is a superposition of two possible states: "State with interference
> pattern" and "State without interference pattern". For case D2, when memory
> device M is kept intact, the dual state pattern collapses to single
> state pattern with no interference, when the screen is read.
> For the case D1, when memory device M is destroyed, at this instant the
> dual state pattern collapses to a single state pattern with interference.
> This is what we observe when the screen is read.
>
> Conclusion: Outcome of any physical event is (in general) not
> deterministic.
> It is a superposition of possible outcomes. The exact outcome that is
> finally presented to an observer (by nature) depends on how much
> information
> pertaining to details of the physical event is known to the observer or is
> in principle accessible to the observer.
>
>
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-- 
Sriram Sankaranarayanan
PhD Candidate,
Center for Systems Science and Engineering|Latrobe 302
Johns Hopkins University.
Ph: +1 (443) 713 6818
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