# Re: [asa] Fw: Pilot-wave theory

From: George Murphy <GMURPHY10@neo.rr.com>
Date: Sun Jun 21 2009 - 22:12:58 EDT

Purely on the history - & that pre-Bohm.

De Broglie discussed these ideas in Non-Linear Wave Mechanics: A Causal Interpretation (Elsevier, 1960) - which, in spite of the date of publication, picks up on ideas he'd been developing ~ 35 years later. He discusses some of the history in this book. The basic idea is that the linear Schroedinger eqn is an approximation to a non-linear eqn in which particles would be represented by regions of very high concentrations of field amplitudes, similar to the way in which Einstein & co-workers later worked out the equations of motion for a particle in general relativity. As de Broglie describes the history, he did not feel prepared at the 1927 Solvay Conference to present this theory in any detail, and so offered there a truncated version in which the non-linear region of such a future theory is described simply by a particle which is "guided" by the solutions of the linear equation - this a "pilot wave" theory. This wave never intended to be anything more than a provisional suggestion. Since his ideas didn't receive much suppport, & since he didn't see how to develop the more complete theory, he went along with, & taught, the consensus Copenhagen intepretation for some years. In the 1950s, partly because of Bohm's related ideas, he returned to the earlier concept.

De Broglie discusses this here in connection with the "second solution" of the Schrodinger equation. Here's what that means for a free particle. The usual wave function in such a case is simply a plane wave, psi = exp [i(p.x-Et)/2*pi*h]. But it's easy to show that U = psi/sqrt[x - Vt], with V = p/m the velocity of the corresponding classical particle, is also a solution, albeit a singular one that blows up at the location of the particle (r = Vt).

Shalom
George

----- Original Message -----
From: philtill@aol.com
To: wjp@swcp.com ; randyisaac@comcast.net
Cc: asa@calvin.edu
Sent: Sunday, June 21, 2009 3:54 PM
Subject: Re: [asa] Fw: Pilot-wave theory

I think this article is muddled on its physics history. As I recall, it wasn't de Broglie who proposed the pilot wave -- that was David Bohm. de Broglie's contribution was to argue that particles with mass should have a wave nature, just as massless light (being a wave) has a particle nature. So it is true that de Broglie was interested in the wave behavior of quantum mechanics, but as far as I know de Broglie never proposed that the particles are a separate entity from a wave that exists to "pilot" them about. That came much later from David Bohm.

I never liked Bohm's pilot wave concept because it requires the existence of two entities where only one is needed. As far as I know, the pilot wave has no function except to appear at the proper time and push particles around. It is immeasurable and is discerned (supposedly) only through the fact that the particles behave a certain way. The particles meanwhile have no ability to get where thy are going unless the wave shows up and pushes them. This seems to be a very inelegant theory, IMO. It is substituting awkwardness for the usual abstraction of QM, and is that really a good thing? I prefer the abstraction because we have good reason to expect abstraction in the fundamental reality of nature, and also to expect elegance. Furthermore, the pilot wave idea doesn't so lve the non-locality of QM (the violation of Bell's inequality); the pilot wave still needs to behave non-locally with information passing between its parts faster than light, so what good does it do? In the final analysis, isn't it still abstract?

Phil

-----Original Message-----
From: Bill Powers <wjp@swcp.com>
To: Randy Isaac <randyisaac@comcast.net>
Cc: asa@calvin.edu
Sent: Sun, Jun 21, 2009 9:49 am
Subject: Re: [asa] Fw: Pilot-wave theory

Randy:

Can you provide us with more information as to the critical experiment that Valentini suggests?

BTW, Roland Omnes provides another approach to QM, as a description of histories, following on Griffith's work, that would also avoid a lot of these paradoxes.

He has an interesting take on the direction of time also, associated with decoherence and the dissipation of the entangled states.

thanks,

bill

On Sun, 21 Jun 2009, Randy Isaac wrote:

> Do any of you folks knowledgeable about quantum mechanics have a perspective on de Broglie's pilot-wave theory as advocated by Valentini?
> I'm not20much of an autograph collector but I do cherish an autograph I obtained from Louis de Broglie when I met him after a lecture he gave in Paris in 1971. So my reasons for wishing him success are highly unscientific!
>
> Here are a few paragraphs from the latest issue of Science.
>
> Randy
>
> Science 19 June 2009:
> Vol. 324. no. 5934, pp. 1512 - 1513
> DOI: 10.1126/science.324_1512
>
>
> News Focus
> Physics:
> Is Quantum Mechanics Tried, True, Wildly Successful, and Wrong?
> Tim Folger*
>
> A skeptical physicist charges that his field has been wandering in a philosophical wilderness for 80 years. The good news: He thinks he knows the way out.
> Antony Valentini has never been happy with quantum mechanics. Sure, it's the most powerful and accurate scientific theory ever devised. Yes, its bizarre predictions about the behavior of atoms and all other particles have been confirmed many times over with multi-decimal-place exactitude. True, technologies derived from quantum mechanics may account for 30% of the gross national product of the United States. So what's not to like?
>
> Valentini, a theoretical physicist at Imperial College London (ICL) and the co-author of a forthcoming book on the early history of quantum mechanics, believes that short ly after the theory's birth some 80 years ago, a cadre of influential scientists led quantum physics down a philosophical blind alley. As a result of that wrong turn, Valentini says, the field wound up burdened with paradoxical dualities, inexplicable long-distance connections between particles, and a pragmatic "shut up and calculate" mentality that stifled attempts to probe what it all means. But there is an alternative, Valentini says: a long-abandoned "road not taken" that could get physics back on track. And unlike other proposed remedies to quantum weirdness, he adds, there's a possible experiment to test whether this one is right.
>
> "There isn't a more insightful or knowledgeable critic in the whole field of quantum theory," says Lee Smolin, a theoretical physicist at the Perimeter Institute for Theoretical Physics in Waterloo, Canada. Smolin, who researches a subfield known as quantum gravity, has long held that current quantum theory is incomplete at best.
>
> In a book to be published later this year by Cambridge University Press, Valentini and co-author Guido Bacciagaluppi, a philosopher of physics at the University of Aberdeen in the United Kingdom, reassess a pivotal and contentious meeting at which 29 physics luminaries-including Louis de Broglie, Niels Bohr, Werner Heisenberg, Erwin SchrÃ¶dinger, and Albert Einstein-butted brains over how to make sense of quantum theory.
>
> The book, Quantum Theory at the Crossroads, includes the first English20translation of the proceedings of the historic 1927 Solvay conference. The gathering was the fifth in an ongoing series of invitation-only conferences in Brussels, Belgium, launched in 1911 by the Belgian industrialist Ernest Solvay. At the meeting, blandly titled "Electrons and Photons," attendees grappled with issues that were-and remain-among the most perplexing ever addressed by physicists. Quantum mechanics confounds commonsense notions of reality, and the physicists in Brussels disagreed sharply about the meaning of the theory they had created.
>
>
> ....
>
> The proceedings do, however, contain 24 pages of discussion of a rival interpretation by de Broglie. Unlike Bohr, who viewed the quantum wave equation describing a particle as a mathematical abstraction, de Broglie thought such waves were real-he called them pilot waves. In de Broglie's picture, particles never exist in more than one place at the same time. All the mysterious properties of quantum theory are explained by pilot waves guiding particles along their trajectories. In the two-slit experiment, for example, each particle passes through only one slit. The pilot wave, however, goes through both slits at once and influences where the particle strikes the screen. There is no inexplicable wave collapse triggered by observation. Instead, Valentini says, "the total pilot wave, for the particle and the detectors considered as a single system, evolves so as to yield an apparent collapse."
>
>=2 0Bohr, Heisenberg, and their supporters at the Solvay conference were unimpressed. The details of the particle trajectories were unobservable, and Bohr insisted that physicists shouldn't traffic in hidden, unmeasurable entities. "De Broglie wasn't happy with the Copenhagen interpretation," says Valentini, "but he gave up trying to argue about it."
>
> Bohr and Heisenberg's vision of quantum theory prevailed; de Broglie's languished. David Bohm, a prominent American physicist, rediscovered de Broglie's work in the early 1950s and expanded on it. But Bohm's work, like de Broglie's, failed to attract much support, because it could not be distinguished experimentally from conventional quantum mechanics.
>
> The past decade has seen renewed interest in understanding the foundations of quantum mechanics, and physicists have devised several competing interpretations of the theory (Science, 25 June 2004, p. 1896). Valentini has been in the thick of this quantum renaissance. In the early 1990s, as a graduate student studying with the late Dennis Sciama, a cosmologist who also mentored Stephen Hawking, he learned about the work of de Broglie and Bohm and became convinced that it had the potential to resolve all the mysterious paradoxes of quantum mechanics. He has spent most of his career almost single-handedly building on their work.
>
> ...
>
> Confirmation of Valentini's idea would be one of the biggest advances in physics in decades. The Planck sp acecraft, launched in May by the European Space Agency (Science, 1 May, p. 584), will take a closer look at CMB and could conceivably find evidence supporting Valentini's predictions.
>
> "One of the most attractive features of Antony's proposals is that they're testable," says David Wallace, a philosopher of physics at the University of Oxford in the United Kingdom. "If tomorrow there is some experiment that Antony's theory gets right and quantum mechanics gets wrong, then end of story."
>
> Valentini knows he faces steep odds. "Maybe in 200 years people will look back and say the time wasn't right to reexamine the foundations of quantum mechanics," he says. "Or it might be that they'll say, 'My God, it opened up a whole new world.' We can't tell. One thing is certain: We won't find out if we don't try."
>

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Received on Sun Jun 21 22:14:29 2009

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