Part 2
Quantum Mechanics and Dissidents
By Eric Dennis

Click here for Part 1.

[ObjectiveScience.com] The failure of Little's "theory of elementary waves" (TEW), must not be taken to support the sophistry connected with the standard interpretation of quantum mechanics, from the idea that entities lose their attributes until we observe them to the supposed victory of indeterminism in physics. 

In fact, a politically disinclined group of dissidents--including Einstein, Schrodinger, David Bohm, and John Bell--maintained their commitment to realism against the idealist and positivist tendencies of the physics establishment [11].

There is a misconception, of some currency, that Bell's results close the door on all realist versions of quantum mechanics. This is ironic because these very results were motivated by Bell's surprise and profound appreciation upon discovering such a version already in the literature. This was David Bohm's completion of an idea that started with Louis de Broglie. It has emerged as a powerful and precise alternative to the fuzziness of standard theory. 

The de Broglie-Bohm (dBB) theory is the most straightforward way of including real particles, with continuous trajectories and well-defined velocities, into the mathematical framework of quantum mechanics. Bohm showed, with real particles, how measurement processes may be put on the same footing as all other physical processes, reproducing quantum predictions while obviating any notion of observer-created reality, indeterminism, probability-as-fundamental, or "wavefunction collapse.'' 

Specifically, dBB retains the mathematical base of quantum mechanics, the Schrodinger equation involving a complex-valued wavefunction over (configuration) space, but further supposes the existence of real point-particles distinct from the wavefunction itself. The one extra mathematical postulate of dBB is that the momenta of these particles at any point in (configuration) space are given by the gradient of the wavefunction's phase at that point. 

That alone is the price of clarity for quantum mechanics. 

Probability in dBB emerges just as in classical statistical mechanics, as an expression of our lack of knowledge of initial positions for the particles, not as a metaphysical primary--and it emerges in just the way necessary to reproduce quantum predictions [12].

As a quintessential example, consider the double slit experiment, in which particles are separately launched from a source toward a pair of slits and then detected on a photographic screen behind. Although one observes distinct, point-like spots on the screen, their distribution over the screen recalls the interference pattern of a wave passing through the two slits, not that of particles traveling on straight lines from source to slits to screen. In dBB, this is easily understandable: the Schrodinger wave does indeed pass through both slits and generates an interference pattern on the screen. And this wave influences the particles, causing their trajectories to curve in a precise way that yields exactly the observed distribution of spots on the screen [13].

Despite its virtues, dBB should not necessarily be considered a complete theory. Indeed it explicitly involves instantaneous interaction between entangled particles, a physically dubious prediction. 

As occurs frequently in physics--e.g. in Newton's action-at-distance theory of gravity, the divergence of Maxwell fields around point-particles, the renormalization of quantum field theories, the black hole singularities of general relativity--such a prediction suggests an approximation is being made, underneath which lies an as-yet unknown physical mechanism. Here, the mechanism is associated with the extremely fast influences propagated between particles. It should be emphasized that the faster-than-light character of these influences is necessitated by experimental results in light of Bell's inequality. Unfortunately, there is no current data known to indicate the nature of the mechanism. One tact would be to increase the temporal precision of the Bell-type experiments and thus improve bounds on signal propagation speed, and perhaps even determine it exactly. Currently it is known with reasonable certainty, that this speed is at least 10,000 times the speed of light [14].

As to the current philosophical state of physicists, I am optimistic. While reactions to the dissidents, Bohm in particular, had been almost maniacal in the past, to the point that it was considered impolite by many even to mention the name of this Nobel-caliber physicist in such a connection, the last two decades have brought major changes. Bohm is now part of the pantheon, when before prominent physicists had asserted that it is impossible even to formulate an alternative to the orthodox "Copenhagen'' interpretation of quantum mechanics. Indeed, there now seems to be increasing support among physicists for exorcising the notion of observer-created reality from the foundations of physical science.

Thanks to Travis Norsen for helpful comments and discussion.
 

About the Author:

Eric Dennis received a B.S. in physics (1998) from Caltech and M.S. in physics from UC Santa Barbara (2000). He is currently a visiting graduate student at Princeton, where his work involves numerical simulation of quantum systems via a novel algorithm motivated by Bohm's version of quantum mechanics. Past areas of research have included quantum computation theory (topological error-correcting codes) and experimental condensed matter physics (electron spin coherence in semiconductors).
 

References:

[11] For example:

"Any serious consideration of a physical theory must take into account the distinction between the objective reality, which is independent of any theory, and the physical concepts with which the theory operates. These concepts are intended to correspond with the objective reality, and by means of these concepts we picture this reality to ourselves." from Einstein, Podolsky, Rosen, Phys. Rev., vol. 47, pp. 777 (1935).

"For example, would it be possible for us to choose the natural laws... in accordance with our tastes...? The fact that we cannot actually do this shows that these laws have an objective content, in the sense that they represent some kind of necessity that is independent of our wills and of the way in which we think about things." D. Bohm, Causality and Chance in Modern Physics, pp. 165, Harper (1961).

Bell advocates a "programme for restoring objectivity" to physical theory, which "will not be intrinsically ambiguous and approximate.... Rather it should again become possible to say of a system not that such and such may be observed to be so but that such and such be so." in "Subject and Object," Speakable and Unspeakable in Quantum Mechanics.

[12] It should be noted, this additional postulate of dBB would replace the wavefunction collapse postulate of quantum mechanics, which latter renders probability as metaphysical.

[13] See http://www.math.rutgers.edu/~oldstein/quote.html for further information on dBB. Bohm's original papers are: D. Bohm, Phys. Rev., vol. 85, pp. 166 (1952); vol. 85, pp. 180 (1952)

[14] This holds in the frame of the cosmic microwave background radiation, see V. Scarani et al in quant-ph/0007008 at http://xxx.lanl.gov.