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I guess I am trying to understand whether the description of a quantum waves aligns to any sort of physical wave description or should it only be interpreted as a mathematical construct? By way of an example and general reference, the following links make reference to http://phy240.ahepl.org/Chp5-MatterWaves-Serway.pdf" of a book called 'Modern Physics' by Serway, Moses and Moyer. Section 5.3 provides an introduction to ‘Wave Groups & Dispersion’, while section 6.2 addresses the ‘Wavefunction for Free Particle’ and the implications of a time evolving wave equation. However, this latter section is the primary focus of this post. In Chapter-6, on the page numbered 192, is the following quote:
Based on normal mechanical waves, [itex]\Psi[/itex] would correspond to some sort of amplitude, but the inference appears to be that this concept doesn’t apply to a quantum wave. However, based on deBroglie’s hypothesis, a matter wave is often described in terms of a wave packet that has both physical momentum [itex]p=\hbar \kappa [/itex] and energy [itex]E=\hbar \omega [/itex]. However, in order to mathematically describe the wave packet many references use the idea of the superposition of continuous and infinite plane waves within a large spread of wavelengths, i.e. [k], as linked to Fourier theory. While Section 5.3 covers the basic idea, equation (6.5) in Chapter-6 states the basic dispersion relationship of deBroglie matter waves. This equation can also be cross referenced to the Wikipedia link ‘http://en.wikipedia.org/wiki/Dispersion_relation#De_Broglie_dispersion_relations"where the relationship is linked to kinetic energy, not total energy:
[tex]E= \frac {p^2}{2m}[/tex]
[tex]\omega = \frac {\hbar \kappa^2}{2m}[/tex]
However, if you read the sub-text to Figure 6.3, in Chapter-6, it appears to suggest that this equation is a source of dispersion of the composite matter wave packet, because each plane wave component, required to ‘construct’ the wave packet, travels at a different phase velocity based on the logic:
[tex]v_p = \frac {\omega}{\kappa} = \frac {\hbar \kappa}{2m}[/tex]
However, it is not clear whether these superposition waves, in isolation, have any tangible physical existence to which physical mass [m] could be attributed, as required by the equation above. Equally, alternative approaches, which are also said to align to deBroglie’s hypothesis, appear to forward a different suggestion for the phase velocity, e.g.
[tex]E=mc^2=hf= \frac {hv}{\lambda}[/tex]
[tex]\lambda = \frac {h}{m} \frac {v}{c^2}[/tex]
[tex]v_p= \frac {E}{p} = \frac {mc^2}{mv} = \frac {c^2}{v}[/tex]
So while we appear to have physical attributes linked to some sort of quantum wave description, it is unclear whether the wave description is representative of a quantum particle’s physical structure. So my first question is:
What velocity do the plane wave components of a wave packet propagate and do they have any physical inference?
In Chapter-6, there is an example (6.3) relating to the construction of a wave packet that is based on the assumption of a Gaussian distribution of an initial wave packet at (x=0) and the spread of its component wave numbers [k]. Without questioning either the assumptions or the mathematical derivation, at this stage, we arrive at an equation that appears to allow the dispersion time of a matter wave packet to be estimated, see Example 6.4, for an electron and a 1g marble, i.e.
Electron = [itex]1.7 * 10^{-15}seconds[/itex]
1g Marble = [itex]6 * 10^{16} years[/itex]
Under these examples is the quote:”
Again, I would like to try to clarify what, if any, physical interpretation can be extrapolated from these figures and the quote above in contrast to the perception that a classical free particle will simply remain localised in space in the absence of any force:
Is the quantum description only saying that the mathematically probability of the location is dispersed or is there some inference of the physical dissipation of a particle as a waveform?
How does the structural composition of the marble that is made up of quantum particles, i.e. electrons, protons and neutrons, circumvent the dispersion process that appears to affect each quantum particle in isolation?
Can the idea of the dispersion of transverse superposition of waves be extended to 3-dimensions?
Appreciate any knowledgeable insights or links to alternative references that might be thought to address these issues. Thanks.
“Notice that [itex]\Psi[/itex] itself is not a measurable quantity; however, [itex]| \Psi|^2[/itex] is measurable and is just the probability per unit length, or probability density P(x), for finding the particle at the point (x) at time (t).”
Based on normal mechanical waves, [itex]\Psi[/itex] would correspond to some sort of amplitude, but the inference appears to be that this concept doesn’t apply to a quantum wave. However, based on deBroglie’s hypothesis, a matter wave is often described in terms of a wave packet that has both physical momentum [itex]p=\hbar \kappa [/itex] and energy [itex]E=\hbar \omega [/itex]. However, in order to mathematically describe the wave packet many references use the idea of the superposition of continuous and infinite plane waves within a large spread of wavelengths, i.e. [k], as linked to Fourier theory. While Section 5.3 covers the basic idea, equation (6.5) in Chapter-6 states the basic dispersion relationship of deBroglie matter waves. This equation can also be cross referenced to the Wikipedia link ‘http://en.wikipedia.org/wiki/Dispersion_relation#De_Broglie_dispersion_relations"where the relationship is linked to kinetic energy, not total energy:
[tex]E= \frac {p^2}{2m}[/tex]
[tex]\omega = \frac {\hbar \kappa^2}{2m}[/tex]
However, if you read the sub-text to Figure 6.3, in Chapter-6, it appears to suggest that this equation is a source of dispersion of the composite matter wave packet, because each plane wave component, required to ‘construct’ the wave packet, travels at a different phase velocity based on the logic:
[tex]v_p = \frac {\omega}{\kappa} = \frac {\hbar \kappa}{2m}[/tex]
However, it is not clear whether these superposition waves, in isolation, have any tangible physical existence to which physical mass [m] could be attributed, as required by the equation above. Equally, alternative approaches, which are also said to align to deBroglie’s hypothesis, appear to forward a different suggestion for the phase velocity, e.g.
[tex]E=mc^2=hf= \frac {hv}{\lambda}[/tex]
[tex]\lambda = \frac {h}{m} \frac {v}{c^2}[/tex]
[tex]v_p= \frac {E}{p} = \frac {mc^2}{mv} = \frac {c^2}{v}[/tex]
So while we appear to have physical attributes linked to some sort of quantum wave description, it is unclear whether the wave description is representative of a quantum particle’s physical structure. So my first question is:
What velocity do the plane wave components of a wave packet propagate and do they have any physical inference?
In Chapter-6, there is an example (6.3) relating to the construction of a wave packet that is based on the assumption of a Gaussian distribution of an initial wave packet at (x=0) and the spread of its component wave numbers [k]. Without questioning either the assumptions or the mathematical derivation, at this stage, we arrive at an equation that appears to allow the dispersion time of a matter wave packet to be estimated, see Example 6.4, for an electron and a 1g marble, i.e.
Electron = [itex]1.7 * 10^{-15}seconds[/itex]
1g Marble = [itex]6 * 10^{16} years[/itex]
Under these examples is the quote:”
“The localization of an atomic electron is destroyed in a time that is very short, on a par with the time it takes the electron to complete one Bohr orbit.”
Again, I would like to try to clarify what, if any, physical interpretation can be extrapolated from these figures and the quote above in contrast to the perception that a classical free particle will simply remain localised in space in the absence of any force:
Is the quantum description only saying that the mathematically probability of the location is dispersed or is there some inference of the physical dissipation of a particle as a waveform?
How does the structural composition of the marble that is made up of quantum particles, i.e. electrons, protons and neutrons, circumvent the dispersion process that appears to affect each quantum particle in isolation?
Can the idea of the dispersion of transverse superposition of waves be extended to 3-dimensions?
Appreciate any knowledgeable insights or links to alternative references that might be thought to address these issues. Thanks.
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