De Broglie theory and relativity

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Discussion Overview

The discussion revolves around the relationship between de Broglie's theory and relativity, exploring its implications for wave mechanics and quantum theory. Participants examine the validity of de Broglie's approach within relativistic frameworks, the interpretation of wave functions, and the integration of classical and quantum concepts.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants argue that de Broglie's theory can be viewed as a relativistic framework that replaces Newtonian mechanics within a single inertial frame.
  • Others question the interpretation of wave functions in relativistic contexts, suggesting that single-particle descriptions are inadequate due to the potential for particle creation and annihilation.
  • A participant raises the issue of calculating wavelength and group velocity in a frame where a particle is at rest, noting implications of zitterbewegung on these values.
  • Some participants discuss the intermixing of classical and quantum ideas as problematic, suggesting that this leads to confusion in understanding the development of quantum mechanics.
  • There is mention of alternative formulations of quantum field theory (QFT) that might align with de Broglie's ideas, particularly regarding particle dynamics.
  • Participants express skepticism about the de Broglie-Bohm interpretation, questioning its utility and the introduction of unobservable trajectories.
  • Discrepancies in the derivation of the Quantum Potential between de Broglie's work and that of Ballentine are noted, with some participants favoring de Broglie's approach.
  • One participant speculates that differences in constants may arise from the use of different units, suggesting a non-fundamental nature of certain factors.

Areas of Agreement / Disagreement

The discussion features multiple competing views, particularly regarding the interpretation of de Broglie's theory in the context of relativity and the adequacy of wave functions in relativistic quantum mechanics. No consensus is reached on these issues.

Contextual Notes

Participants highlight limitations in the classical interpretation of quantum phenomena and the challenges in reconciling de Broglie's ideas with modern quantum field theory. The discussion reflects ongoing uncertainties and assumptions regarding the applicability of various theoretical frameworks.

PhilDSP
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After suitable study I'd have to say that it is a misnomer to state that de Broglie's theory is not relativistic. But it does express relativity in such a unique way that it becomes a replacement for Newtonian mechanics within any chosen single inertial frame.

The most basic expression is covered on page 40 of "An Introduction To The Study Of Wave Mechanics". For the Lorentz group:

x = \frac{x_0 + vt_0}{\sqrt{1 - \beta^2}} \ \ \ \ \ t = \frac{t_0 + \frac{\beta}{c}x_0}{\sqrt{1 - \beta^2}} \ \ \ \ \ and \ \ \ \ \ x_0 = \frac{x - vt}{\sqrt{1 - \beta^2}} \ \ \ \ \ t_0 = \frac{t - \frac{\beta}{c}x}{\sqrt{1 - \beta^2}}

An EM or energy wave for system with reference to x_0, y_0, z_0, t_0 depends on time only through a factor cos 2\pi f_0(t_0 - \tau_0)

Switching to system x, y, z, t with \tau_0 = 0 the factor becomes cos 2\pi f_0(\frac{t - \frac{\beta}{c}x}{\sqrt{1 - \beta^2}})

Since f = \frac{f_0}{\sqrt{1 - \beta^2}} and v_{phase} = \frac{c^2}{v} = \frac{c}{\beta}

\beta = \frac{c}{v_{phase}} so that the phase factor is cos 2\pi f(t - \frac{x}{v_{phase}})

What de Broglie has done is to account for all relativistic effects on waves, and subsequently particles, within that single chosen inertial reference. There becomes no further need to consider something in a separate inertial frame. The bulk of his thesis is developed in phase space using mathematical ideas of Hamilton and Jacobi, but he carefully relates the variables in the phase space to variables in Euclidean physical space and time. The concept of a secondary inertial frame is not even especially valid then as his theory applies even to accelerating particles.

Thoughts? criticisms? comments?
 
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PhilDSP said:
Thoughts? criticisms? comments?

Jump to a frame where the particle is at rest. What's the wavelength there? What's the group velocity?

Thanks
Bill
 
In addition the naive interpretation of "wave functions" in the sense of a single-particle description is flawed for relativistic wave equations. The reason is simply that for relativistic energies it is always possible that in reactions particles get created and destroyed. That's why relativistic quantum theory is most appropriately formulated as a quantum field theory, where such creation and annihilation processes are very natural.
 
bhobba said:
Jump to a frame where the particle is at rest. What's the wavelength there? What's the group velocity?

If we give credence to zitterbewegung the particle will be at rest in that frame for an exceedingly short period of time. But then the wavelength would be infinite, group velocity zero while the phase velocity infinite.

I know you've expressed consternation at an infinite wavelength, but since there is no energy moving anyway in that case, one can interpret an infinite wavelength as an instance of non-oscillation.
 
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vanhees71 said:
In addition the naive interpretation of "wave functions" in the sense of a single-particle description is flawed for relativistic wave equations. The reason is simply that for relativistic energies it is always possible that in reactions particles get created and destroyed. That's why relativistic quantum theory is most appropriately formulated as a quantum field theory, where such creation and annihilation processes are very natural.

I suppose an alternative to QFT where those processes are modeled more in concert with DB theory would incorporate particle creation and destruction in a Hamiltonian/Jacobi framework...
 
PhilDSP said:
If we give credence to zitterbewegung the particle will be at rest in that frame for an exceedingly short period of time. But then the wavelength would be infinite, group velocity zero while the phase velocity infinite.

The problem here is the intermixing of classical and quantum ideas. That's the cause of the issue and why its just an intermediate step to fully developed QM that was realized in the transformation theory of Dirac. Once that came out there was simply no need for it.

Thanks
Bill
 
bhobba said:
The problem here is the intermixing of classical and quantum ideas. That's the cause of the issue and why its just an intermediate step to fully developed QM that was realized in the transformation theory of Dirac. Once that came out there was simply no need for it.

Fair enough. There are cases where QM concepts have found uses and new physics in the classical realm (Berry phase for example). But going the other direction and providing QM with new insights would require a truly exceptional further refinement and development of de Broglie's ideas.

Berry phase effects on electronic properties
http://journals.aps.org/rmp/abstract/10.1103/RevModPhys.82.1959
 
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PhilDSP said:
I suppose an alternative to QFT where those processes are modeled more in concert with DB theory would incorporate particle creation and destruction in a Hamiltonian/Jacobi framework...

If by DB you mean de Broglie-Bohm (pilote wave) mechanics, one must say that there seems to be no satisfying formulation of this concept for relativistic quantum theory.

I also never understood what might be attractive with the Bohm interpretation since it introduces trajectories that are not observable anyway and does not make any other predictions about Nature than (minimally interpreted) quantum theory. So what's the point to introduce complicated concepts that don't buy anything in our understanding of Nature?
 
I can't offer any insight into Bohm's interpretation. I've read his "Quantum Theory" textbook (which I'd rate quite favorably). But he didn't delve into Pilot Wave theory there. Ballentine has a nice, short summary on p. 399.

Starting on p. 394 Ballentine derives the Quantum Potential starting from the Schrödinger equation. He arrives at a different value than de Broglie.

Ballentine: \ \ \ W_Q = -\frac{h^2}{2M} \frac{\nabla^2 A}{A} \ \ \ \ \ \ de Broglie: \ \ \ F_1(x, y, z, t) = -\frac{h^2}{8 \pi^2 m} \frac{\nabla^2 a}{a}

Since de Broglie's is a covering theory which derives the Schrödinger equation as the non-relativistic limit (along with some other stipulations), I'll assume de Broglie's derivation of the Quantum Potential (ending on p. 112) is the correct one.

However, Ballentine makes a very important observation on p. 398 in further analysis where he states

"The failure of this method to yield the expected classical limit in this case is clearly due to the formation of a standing wave, which is a manifestation of the quantum-mechanical phenomenon of interference between the leftward- and rightward-reflected waves that make up ##\Psi##".
 
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  • #10
I suspect the factor of 4 * pi is due to the use of different units; thus it is not fundamental.
 

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