Consistency of Bohmian mechanics

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Discussion Overview

The discussion revolves around the consistency of Bohmian mechanics in the context of a free particle described by a Gaussian wave function. Participants explore the implications of quantum measurement on the particle's position and how Bohmian mechanics reconciles with quantum mechanics, particularly regarding the behavior of the particle post-measurement.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant presents a scenario involving a free particle with a Gaussian wave function and questions how Bohmian mechanics accounts for the particle's position after a quantum measurement, noting a contradiction with quantum predictions.
  • Another participant suggests that during measurement, the Hamiltonian is more complex than simply ##p^2/2##, implying that the Bohmian equations may not apply directly during this time.
  • Several participants express interest in calculations to support the graphical representations of the wave function and Bohmian trajectories, with some emphasizing the intuitive understanding conveyed by drawings.
  • There is a discussion about the nature of the branches resulting from a position measurement, with one participant asserting that a realistic measurement leads to a finite number of branches rather than infinitely many.
  • Concerns are raised about the implications of the "forbidden region" where the particle cannot cross, with participants debating the probability of finding the particle in that region according to quantum mechanics.
  • One participant argues that the wave function after collapse should resemble a Gaussian centered at the measured position, challenging the depiction of multiple Gaussians in Bohmian mechanics.
  • Another participant clarifies that while the forbidden region is unlikely to be crossed, it does not eliminate the possibility of finding the particle there, suggesting that the probability is negligibly small.
  • There is a contention regarding the interpretation of the wave function post-collapse, with differing views on whether it can be considered a superposition of Gaussians or if it should collapse to a single Gaussian.

Areas of Agreement / Disagreement

Participants express differing views on the implications of Bohmian mechanics versus quantum mechanics, particularly regarding the behavior of particles post-measurement and the nature of wave function collapse. There is no clear consensus on how these concepts reconcile.

Contextual Notes

Limitations in the discussion include assumptions about the nature of measurements, the complexity of the Hamiltonian during measurement, and the interpretation of wave function collapse in both Bohmian mechanics and quantum mechanics.

  • #91
vanhees71 said:
I don't know that Hamiltonian. And also you again changed the setup. Now we have an infinitely thin filter. What is this filter supposed to do?
It is a piece of metal with a hole in it. Idealized to be infinitely thin; otherwise I'd need to model the interaction of the electrons with the metal. I don't know of any discussion of an experiments with slits where the latter is done; hence the idealization. Then all the complicated stuff happens instantaneously and can be summarized by the projection. At least this is done in informal discussions when blending out partial beams (in Stern-Gerlach experiments, say).
vanhees71 said:
If the filter is not moving, why should the Hamiltonian be time dependent?
You were claiming that the filters change the Hamiltonian:
vanhees71 said:
if you have two slits having an effect on the particles to be measured you modify the dynamics, i.e., the Hamiltonian and thus change the probabilities compared to the situation of freely moving particles.
I was just trying to understand what you mean. Surely away from the filters the Hamiltonian is the free Hamiltonian, so the only way I could give meaning to your claim was to assume that you thought that the Hamiltonian is time-dependent with three constant pieces before, during and after the passage through the slit.
vanhees71 said:
I still do not know, which experiment you really have in mind.
A very simple experiment. I have a source of electrons, two close and parallel (in this post only one) sheets of metal both with a big hole, and a screen parallel to the plates at the end. I want to know the probability that an electron emitted by the source is detected by the screen. Under the usual idealizations and the standard collapse assumption, this probability is given by the formula of Thors10 from post #65, with characteristic functions specified by the positions of the holes.
 
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  • #92
PeterDonis said:
Thread reopened. Two overly argumentative posters have been thread banned and some overly argumentative posts have been deleted.
I hope that Thors10 is not banned from posting in this thread, since he is the originator of the thread, and the current discussion needs his active participation:
A. Neumaier said:
This is precisely what the formula of @Thors10 quoted in post #82 does. Thus it is his intended setup. The only questionable thing in his description is that he claims he can do it by repeatedly measuring a single particle twice with a single detector. So I inquired about that.
 

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