International workshop

21st-Century directions in
de Broglie-Bohm theory and beyond

28th August - 4th September 2010

Conference report

For a week at the end of August 2010, a disparate - or should that be desperate - collection of physicists and philosophers gathered in Valllico Sotto to discuss the meaning of a partial differential equation, and related matters. Not very exciting you might think. But the wearying, childish, relentless six-month media and internet storm which preceded it - concerning who should or should not be invited to attend - depressed many of the thousands of people that were dragged into it, almost always against their will.. the personal threats, the badly-spelled diatribes from internet psychics and telepaths, the conspiracy theories concerning precisely which of the worlds' intelligence agencies were controlling events at TTI (MI6, since you ask - and definitely not the CIA).. Not a good start, by us or them.

Which made it all the more remarkable that what followed was almost certainly the best physics conference in the world that year (not that I went to all the others, but it's probably true.). The aim was to imitate the 1927 Solvay conference - sadly with 19 fewer Nobel prize winners - and to discuss the theory of quantum mechanics first presented by French physicist Louis de Broglie at that meeting. With the considerable advantage of not having Wolfgang 'Not Even Wrong' Pauli around to make fun of us.

De Broglie-Bohm theory is a 'hidden variables' formulation of quantum mechanics initially developed by de Broglie from 1923-1927 and clarified and extended by American physicist David Bohm beginning in 1952. Just by the simple expedient of refusing to believe that particles cease to exist if you stop looking at them, it is easy to show that - contrary to popular belief - quantum mechanics can be interpreted as a dynamical theory of particle trajectories rather than as a statistical theory of observation. In such a formalism the standard paradoxes related to measurement, observation and wave function collapse (Schrödinger's cat, and so on) largely evaporate. The classical limit does not have to be presupposed and emerges from the theory in a relatively clear way. All the 'talk' is replaced by sharply-defined mathematics, it becomes possible to 'visualize' the reality of most quantum events, and - most importantly - the theory is completely consistent with the full range of QM predictive-observational data. The theory also gives rise to the possibility of new physics - and of new mathematical and philosophical ideas - and considerable emphasis was placed on this during the meeting.

One of the most common remarks by the participants, many of whom work in relative isolation, was an expression of surprise that there were all these other people out there working on topics related to de Broglie-Bohm theory. The number of scientists apparently unaware of each others' work was consistently surprising, and the meeting led to a number of new collaborations. The overall quality of the talks and of the accompanying discussions was very high - the only problem being the overall tendency to talk too much, leading to many unscheduled early afternoon sessions to fit in all the talks that people wanted to give.

We were also fortunate to enjoy the presence of many of Bohm's former friends and colleagues - including Basil Hiley, Chris Dewdney, Paavo Pylkkänen and almost, but not quite, David Peat and Georg Wikman. Their personal reminscences of Bohm - who died in 1992 - were extremely interesting.

As with all events at TTI, afternoon athletic achievements were strongly encouraged. The week kicked off with a couragous and successful bid by Lev Vaidman, Shantena Sabbadini, Wayne Myrvold, and Ilja Schmelzer - menaced by the threat of thunderstorms - to reach the summit of the giant and very vertical peak of Pizzo d'Uccello. Other expeditions traversed the Turrite di San Rocco canyon, scaled Monte Procinto and Monte Matanna, crossed the giant rock arch of Monte Forato, penetrated the depths of the Tana di Cascaltendine cave, and er.. sat around by Bagni di Lucca and Barga swimming pools eating ice cream.

Thursday saw the latest and greatest installment of the regular "Vallico Sotto against the World" football match. At the last minute we learned that Vallico's Team Captain and inpirational talisman Marco was crippled with a broken arm, and that Michele and Luca (the 2nd and 3rd best players) were similarly unable to play. Hence it was a team largely made up of balding, middle-aged reserves that took the field against the best that the Rest of the World could offer. Within minutes, the World - led by the skilful and quick Benincasa twins - were stuffing Vallico 6-0. Taking full advantage of the fact that Vallico lacked any substitutes whatever and were quickly exhausted, the World team substituted players at will every few minutes whenever they felt a bit out of breath, and continued to press home their advantage. And then, and then.. a speculative shot from the Vallichese nearly blew out the back of the net, and slowly the tiny village (average age of inhabitants: 87) began to creep back into the game. After an hour's play, the score was - unbelievably - only 11-10 to the World yet victory was within the physicists' grasp. Then, with only 5 seconds to go, the funny little Vallico guy in the white vest skipped past three defenders and equalized. The resulting tense Golden Goal period came to a sudden end when the Mysterious Stranger now playing for Vallico in the blue and red stripey shirt blasted the ball into the top corner. The humiliation of the World was complete. The Benincasas, Batelaan, Struyve, Derakhshani, Oriols, Ip, Schmelzer and Norsen skulked off, crying.. All the pretty Vallico girls looked pityingly at the inept and cowardly foreigners, and cheered the victors to the skies. Then everyone mucked in at the old village restaurant to make pizza, and everything was alright in the end, but the World boys won't forget that in a hurry..

MDT congratulates the winners of 'Vallico Sotto against the World': the Vallico reserves

The meeting concluded with some of the best talks of the week, a trip to the beautiful city of Lucca, dinner in a high mountain village, late-night fireworks, the Best Cheese in Italy (soaked in barolo, by God), and some Warre's 1991 port in the back garden.

It all seemed so far from the email I received from Guardian journalist Jonathan Margolis last April:

"Dear Mike. I was having a very nice afternoon sitting in the directors' box at Nottingham Forest with [UK Justice Secretary] Kenneth Clarke when Uri Geller called, and I thought it was such a funny combination of circumstances that.."

Conference information

Herman Batelaan, Dionigi Benincasa, Gregorio Benincasa, Andrew Bennett, Howard Burton, John Bush, Jeremy Butterfield, Murray Daw, Maaneli Derakhshani, Chris Dewdney, Christos Efthimiopoulos, Lucien Hardy, Richard Havery, Basil Hiley, Kris Krogh, Alberto Montina, Wayne Myrvold, Gillie Naaman-Marom, Hrvoje Nikolic, Travis Norsen, Xavier Oriols, Pedro Naranjo Pérez, Patrick Peter, Nelson Pinto-Neto, Enrico Prati, Paavo Pylkkänen, Anton Ramsak, Peter Riggs, Joshua Rosaler, Shantena Sabbadini, Ilja Schmelzer, Rafael Sorkin, Ward Struyve, Mike Towler, Jos Uffink, Lev Vaidman, Wouter Valentin, Antony Valentini, James Yearsley, Michael Naaman-Marom, Elaine Bennett, Mari Hirano, Glenys Dewdney, Irena Burton, Louis Burton, Emma Burton, Elina Pylkkänen, Kasper Pylkkänen, Ester Pylkkänen, Vanessa Hardy, Vivienne Hardy, Branka Ramsak, Samantha Keil, Saska Towler, Samuel Denny, Daniel Thorpe, Pui Ip.

Withdrawn participants:
Guido Bacciagaluppi, Jeffrey Bub, Maurice de Gosson, Jonathan Halliwell, Tim Maudlin, David Peat, Roger Penrose, Carlo Rovelli, Simon Saunders, Maximilian Schlosshauer, Lee Smolin, Rob Spekkens, Georg Wikman.

Official conference material

Background material and references


Introductory talks

Mike Towler
  • "21st-century directions in de Broglie-Bohm theory and beyond - an introduction" [PDF]
    • Movie: 1927 Solvay conference [MP4]
    • Movie: The central dogma of molecular biology [MP4]
Antony Valentini
  • "Introduction to current research in de Broglie-Bohm pilot-wave theory" [PDF]

Research talks

Herman Batelaan

  • "Particle diffraction from a double slit and a phase grating; can random electrodynamics provide a physical picture for the de Broglie-Bohm pilot wave?" (NOT AVAILABLE)

Andrew Bennett

  • "Lorentz-invariant relaxation to quantum thermal equilibrium" [PDF]

Howard Burton

  • "'Advice' from the Founding Director of the Perimeter Institute" [AUDIO FILE AVAILABLE]

John Bush

  • "Pilot waves and the quantum behaviour of bouncing droplets"
    [PDF of relevant paper - too many videos in talk slides.]

Maaneli Derakhshani

  • "On the phase-quantization problem in stochastic mechanics" [PDF]

Christos Efthimiopoulos

  • "The role of chaos in the de Broglie-Bohm quantum theory" [PPT]

Lucien Hardy

  • "Why we should consider situating the de Broglie-Bohm model in the context of a much more general framework for hidden variable theories?" [BLACKBOARD TALK]

Basil Hiley

  • "Moyal and Clifford algebras and the Bohm approach" [PDF]

Alberto Montina

  • "Resource cost in the classical simulation of a quantum preparation-measurement process" [PDF]

Wayne Myrvold

  • "Are corpuscle trajectories idle wheels?" [PDF]

Gillie Naaman-Marom

Hrvoje Nikolic

  • "Making Bohmian mechanics compatible with relativity and quantum field theory" [PDF]

Travis Norsen

  • "Out of this world ontology" [PPTX]

Xavier Oriols

Patrick Peter

  • "Cosmological problems and a possible non-inflationary solution in the framework of de Broglie-Bohm quantum cosmology" [PDF]

Nelson Pinto-Neto

  • "The de Broglie-Bohm interpretation of quantum cosmology" [PPT]

Enrico Prati

  • "From classical to quantum observables in mesoscopic electron systems" [NOT AVAILABLE]

Paavo Pylkkänen

  • "The philosophical relevance of Bohm's interpretation of quantum theory" [PDF]

Anton Ramsak

  • "De Broglie-Bohm analysis of entangled qubit pairs" [PDF]

Peter Riggs

  • "Testing de Broglie-Bohm theory with 21st-century technology" [PPT]

Joshua Rosaler

  • "Decoherence and the emergence of deterministic classical behaviour in de Broglie-Bohm theory" [PDF]

Ilja Schmelzer

  • "About pilot wave field theory" [PDF].

    More information here.

Rafael Sorkin

  • "A re-formulation of quantum theory in which events really do (or do not) happen." [BLACKBOARD TALK]

Ward Struyve

  • "Pilot wave theory and quantum fields" [PDF]

Mike Towler

  • "The origin of the Born rule: dynamical relaxation to quantum equilibrium" [PDF]
    • Movie: Approach to quantum equilibrium. [GIF]

Lev Vaidman

  • "Bohm vs. Everett" [PPTX]

Antony Valentini

  • "In search of a breakdown in quantum theory" [PDF]

James Yearsley

  • "Comparing solutions to the arrival time problem in de Broglie-Bohm theory and decoherent histories: What can we learn?" [PDF]

Additional volunteered talks

Brian Josephson

  • "A New Paradigm?" [MP4] (Video filmed in Cambridge)

Kris Krogh

  • "Wave World" [PPT]

Shantena Sabbadini

  • "Persistence of information in the quantum measurement problem" [PDF]

Wouter Valentin

  • "Beyond the theory / wrapping up" [PPT]


  • "Well, words fail me really! That was a stupendous conference; a real feat by Mike if I may say so: to keep so many people feeling welcome, and intellectually stimulated; and so much more than that. Truly an amazing week, and we all owe you a big debt of gratitude."

  • "It was a great privilege to be invited to the Towler Institute and to enjoy that blissful week in the beautiful surroundings with such good company, intellectual stimulation and, not least, exercise! I think you and Samantha have made a wonderful home of that delightful monastery - to hear (and see) lectures in the twelfth-century church was most exciting. I am lost in admiration for your organizational capacity and energy - the diversity of all the things you have to think about is enormous. You are playing a great part in promoting pilot wave theory among the physics community. May it flourish!"

  • "Thank you for a wonderful visit and conference. I have learned more than I can express, and made many new friends, among whom I am glad to include the Towlers. I hope to see you in [my town] soon. In the meantime, I hope you'll enjoy this adventure, the story of discovery which reminds me of what we have spent the week sharing. See you in the New World." [inscribed inside the cover of "Undaunted Courage" by Stephen Ambrose]

  • "Thanks so much for a wonderful week, with a well-organized workshop, interesting talks, lovely venue, great excursions, gorgeous food, and welcome environment. I can't believe how you're doing this all by yourselves! Take care and best wishes."

  • "Many, many thanks for organising such an excellent conference. Thank you for being such good hosts. Mike, I felt exhausted just watching you dealing with all the schedule and the many problems that must arise when such a group gather. Congratulations!"

  • "Really enjoyed the meeting in Vallico Sotto. I also enjoyed tremendously seeing your house/monastery. It is amazing what you have done with it. We were blown away with Sam's sculptures. Seeing them "in the flesh" was much better than seeing photos of them. She is really good. ... Thanks very much for a fantastic meeting. It was very satifying to see an approach to pilot wave that is fully engaged with the big problems in physics. Meetings in quantum foundations can be depressing. This was anything but."

  • "The conference was excellent in every way, both [my wife] and I thoroughly enjoyed it and wanted to convey our thanks for all the work that you did. We were particularly sorry to leave without saying goodbye to Sam as she was such good company during our "lazy" afternoons by the pool. Please give her our best wishes. Unfortunately it is wet and windy in [my town] and I have spent the day doing very boring administrative tasks for our new Applied Physics degree - with much more to do. It is a hard contrast with talking physics in the sunshine in Tuscany!"

  • "A quick note to thank you for the fantastic visit to Tuscany. I apologize for my less than graceful exit, but I think someone must have put something in my Ouzo! It was a tough day... I really enjoyed the meeting, and getting to know you and yours. Hopefully our paths will cross again before too long.. With many thanks for everything, a great meeting, and some great fun - a wonderful exclamation point on a mad summer!"

  • "I'd like to express my sincere gratitude for the wonderful week I've spent at TTI. The atmosphere surrounding the conference was just awesome. I've had the chance to talk a bit with Sam and she's told me about the difficulties you've being through in order to organise this meeting. I really appreciate what you both are doing. It's simply impressive..'s definitely very encouraging to know that there are some people out there making huge efforts to allow people meet each other (in some cases young people having the opportunity to learn techniques that are then developed at their countries), irrespective of whether financial support happens to exist."

  • "Thanks again for the kickass conference. I hope you got -- and are still getting -- some much deserved rest."

  • "I would like to congratulate you for an excellent organization of the meeting and thank you again for the acceptance of my late application. It was really fruitful for me, in particular to discuss with Basil Hiley."

  • "It was good to meet you and the others at the conference. All in all a great success, I think."

  • "I want to thank you, once more, for you hospitality sharing your house and your life with us during this week. For me, apart from a very fruitful scientific conference, it was also a wonderful and unique experience. I do also hope to be in touch with you in the future to discuss."

  • "I want to thank you again for this very enjoyable conference! It was extremely fruitful from my point of view at least."

  • "I'd like to thank you and Sam for opening up your home and organising such an interesting conference. This has been without a doubt the peak of my summer!"

  • "Thanks again for the wonderful conference."

  • "I have been impressed by your personal dedication to the goal of creating such conditions that people can get the best out of themselves and of discussing new and interesting physics. You and your family created an atmosphere which I felt very friendly from the start. I am sure that all participants will recognise owing a lot to your efforts."

  • "I keep rereading your conference report. Every time it brings a smile to my face or makes me laugh out loud. I agree it must have been the best physics conference this year -- and maybe the most fun ever. The best surprise for me was the number of friends made. Thanks to you and Sam for a fabulous time and regards to my 'niece' Saska!"

  • "The pleasure is mutual. It was the all-around best conference I've been to in my short career."

  • "I am still enjoying my memories from the wonderful, indeed amazing workshop you organized."

  • "It was lovely meeting you and Samantha, you have a wonderful place there, the conference was great, the outings spectacular, the Alpi Apuane a real discovery... what more to ask?"

  • "Thanks for the warm words and your general hospitality. That's a pretty special place you have there."

  • "Thank you very much for an excellent conference & for your tremendous hospitability! [My wife], I & the kids truly enjoyed meeting you all and seeing Vallico Sotto. And sorry for breaking the electric wall socket in Doctor's house while trying to charge my laptop 4.30 in the morning - I hope it was possible to fix!"

  • "Thanks again for the great time last week. I'm still in complete awe of the fact that you not only organized the conference, but chaired all the talks, led tours every afternoon, coordinated 3 meals a day for 50 people, emceed the football match, kept your daughter alive and your wife (mostly) happy, get a little drunk as needed, purchase and light fireworks, etc. And that you did all that 3 times already in one summer. You should find a way to bottle your energy and sell it."

  • "That is one fantastic house to chill in. I certainly envy you that!"