- #1
svnaras
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I'm a novice at this quantum business and was just trying to understand the single slit diffraction experiment and when an electron's position is getting measured in particular.
Given my understanding it looks like the electron's position gets measured twice. Once when it is just about to pass through the slit and the second time when it hits the screen.
As I see it from the source to the single slit the electron's waveform has a hugespread (including all possible coordinates). However, when it gets to the slit it can pass through only if its waveform is much smaller (of the width of the slit). So at that particular moment doesn't the electron's huge waveform collapse to either one that is within the slit's width or somewhere else (in which case it doesn't pass through the slit).
And because of the reduction in the bandwidth of the position waveform its conjugate momentum waveform acquires a huge spread and this makes it go in any direction after it passes through the slit giving rise to the diffraction pattern. Is this right? Please correct me if I'm wrong because this seems to be quite crucial to understanding what measurement is.
But frustratingly I've never seen anyone attribute the passing through of the slit as a measurement process. Only when it impinges on the phosphor screen do people say a measurement is performed (and sometimes only when a conscious being sees the phosphor screen).
As an analogy consider polarised light (along the horizontal direction) with a polarizer at angle 45`. When the photon gets near the polarizer a measurement is made of its polarization (ie. the wavefunction collapses into its components along 45' and its perpendicular). Now with some probability the photon passes through the polarizer.
I see the above situation similar to an electron passing through the slit. And I consider that a measurement is being made of either quantity. This way I don't see an issue of there being a need for an observer in order to collapse the function. It appears that anything that constrains the free form of an entity's wavefunction (that is a change of co-ordinate in co-ordinate space needs to be performed) constitutes a measurement. Is this correct?
Given my understanding it looks like the electron's position gets measured twice. Once when it is just about to pass through the slit and the second time when it hits the screen.
As I see it from the source to the single slit the electron's waveform has a hugespread (including all possible coordinates). However, when it gets to the slit it can pass through only if its waveform is much smaller (of the width of the slit). So at that particular moment doesn't the electron's huge waveform collapse to either one that is within the slit's width or somewhere else (in which case it doesn't pass through the slit).
And because of the reduction in the bandwidth of the position waveform its conjugate momentum waveform acquires a huge spread and this makes it go in any direction after it passes through the slit giving rise to the diffraction pattern. Is this right? Please correct me if I'm wrong because this seems to be quite crucial to understanding what measurement is.
But frustratingly I've never seen anyone attribute the passing through of the slit as a measurement process. Only when it impinges on the phosphor screen do people say a measurement is performed (and sometimes only when a conscious being sees the phosphor screen).
As an analogy consider polarised light (along the horizontal direction) with a polarizer at angle 45`. When the photon gets near the polarizer a measurement is made of its polarization (ie. the wavefunction collapses into its components along 45' and its perpendicular). Now with some probability the photon passes through the polarizer.
I see the above situation similar to an electron passing through the slit. And I consider that a measurement is being made of either quantity. This way I don't see an issue of there being a need for an observer in order to collapse the function. It appears that anything that constrains the free form of an entity's wavefunction (that is a change of co-ordinate in co-ordinate space needs to be performed) constitutes a measurement. Is this correct?