Basil Hiley Memorial Symposium

Monday 30 Jun 2025, 09:00 → 18:00 Europe/London

Room 505 Department of Mathematics (University College London )

Peter Van Reeth (Dept. Physics and Astronomy University College London), Chamkaur Ghag, Peter Barker (University College London)

 

This memorial symposium is a celebration of the scientific life and achievements of Basil Hiley who passed away on the 25^th of January.

We expect that the variety of speakers and attendants will reflect Basil’s interests and research in the foundations of quantum mechanics. The symposium will cover most aspects of Basil’s work and aspirations through presentations by close colleagues and the next generation of physicists.

Philosophical implications of Basil’s research with David Bohm will be discussed alongside the mathematical aspects of quantum mechanics including the algebraic and symplectic approach. Discussions and presentations will also extend to the theoretical and experimental applications of his ideas in atomic and solid state physics.

1 Introduction

Speakers: Prof. Chamkaur Ghag, Prof. Peter Barker (UCL), Peter Van Reeth (Dept. Physics and Astronomy University College London)

2 Excursions in configuration space: travelling with de Broglie and Bohm.

I'll briefly review the work I carried out at Birkbeck in the late 1970s (published with Basil Hiley), and later at the Institut Henri Poincaré and the University of Portsmouth. These detailed and novel numerical calculations enabled a clear visualisation of how de Broglie–Bohm (deBB) quantum theory can account for single-particle quantum interference, quantum tunnelling, and quantum spin measurement in terms of well-defined, deterministic motions in space and time.

However, the essential features of de Broglie’s and Bohm’s new description of nature are not fully captured within single-particle quantum mechanics.

The radical nature of the ontology implied by deBB theory only becomes evident in many-particle phenomena, where the wave function is irreducibly defined on configuration space. I will illustrate how deBB theory accounts for nonlocal two-particle quantum effects, such as:

1. the destruction of interference in the two-slit experiment during which-slit detection, and
2. the “bunching” behaviour observed in Hong–Ou–Mandel-type phenomena.

These implications are indeed radical for our conception of reality, as they highlight the fundamental role of configuration space.

Speaker: Prof. Chris Dewdney (University of Portsmouth)

3 A Severe Gravitational Constraint on Practical Quantum Computing in Rational Quantum Mechanics

A Severe Gravitational Constraint on Practical Quantum
Computing in Rational Quantum Mechanics
By
Tim Palmer
Department of Physics. University of Oxford

It is often argued that the continuum should not play a vital role in fundamental theories of physics; yet it does in quantum mechanics (QM) through QM's dependence on complex Hilbert Space. Here we propose an ansatz for discretising Hilbert Space and provide an explicit information-theoretic representation of the qubit state as a length L bit string. QM is the singular limit of this ansatz at 𝐿 = ∞. With finite L, wavefunction collapse corresponds to a reduction in the information-theoretic content of the quantum state at a rate of at least one bit per unit Planck time 𝑡$_p$.Relating 𝐿 × 𝑡$_p$ to the collapse timescale in gravitised quantum mechanics, a quantitative estimate 𝐿 ≈ 10$^{193}$ is made for a typical qubit in a quantum computer. It is thus predicted that the quantum speed-up of algorithms with an exponential advantage over their classical counterparts (such as Shor's), will have saturated in quantum computations which utilise more than 𝑙𝑜𝑔$_2$ 𝐿 ≈ 640 logical entangled qubits. This prediction should be verifiable in the coming 5-10 years. If verified, the practical utility of quantum computers for applications such as decryption will be severely limited by the finite nature of the laws of physics. More positively, it is proposed that quantum computers will provide an important resource for developing and testing future theories which seek to synthesise quantum and gravitational physics within a finite framework.

Speaker: Prof. Tim Palmer (University of Oxford)

4 Boundaries, Gauge Fields and Clifford Algebras

The importance of Clifford Algebras in fundamental physics was one of Basil Hiley's major insights. In this talk I will discuss the geometry of the Dirac equation, and how this is made clearer by the use of Clifford Algebras. I will discuss the differences between the Dirac and Schrödinger equations, and I will suggest ways in which the links between the Dirac equation and Cohomology allow for topological nonlocality in quantum theory.

Speaker: Dr Calum Robson (London School of Economics)

11:00 Coffee Break

5 From Quantum in Pictures to Quantum AI

Speaker: Prof. Bob Coecke (Quantinuum Oxford)

6 Quantum physics in novel material´s research: Diffusive, ballistic and quantum transport properties

In order to honor Basil Hiley the presentation will commence with three general premises: 1. All is process, 2. We are part of nature and 3.Three world experiments are currently underway. I will explore how these premises may relate to Basil Hiley´s research and connect to quantum physics.
Then the focus will shift to a design principle for novel electronic materials which I term the “inverse Bauhaus-principle”: function follows form. Examples are quantum transport phenomena that depend on the local environment as given by geometry, or on global properties as given by topology.
Finally: How can we develop science further? In view of global challenges (third premise) it appears essential to facilitate a universal interdisciplinary dialogue. Physics experts may play a pioneering role in developing formats, methods and interfaces for universal interdisciplinary exchange as physics research is based on metrology and concepts involving processes at all scales.

Speaker: Prof. Saskia Fischer (Humboldt-Universität Berlin)

7 Bohmian mechanics: a legitimate hydrodynamic picture for quantum mechanics, and beyond

In brief, we can say that what we now know as Bohmian mechanics arose as a suitable response, from David Bohm, to Von Neumann’s theorem about the impossibility of hidden variable theories. Perhaps due to its misunderstood simplicity and elegance, it had to be revisited and given the form of an emergent theory from a deeper quantum stochastic description. Whatever the case, an ontology around it immediately appeared to explain the quantum world, which has brought more problems to this approach than benefit. If, however, we leave aside these complicated issues and we pragmatically focus on what Bohmian mechanics really says and what it does not, we discover a different perspective to think, understand, and explain that quantum world, which has nothing to do with hidden variables, with notions closer to the former Madelung (quantum) hydrodynamics.
That is an issue that I gladly had the chance to talk about on many occasions with Basil Hiley, and which constitutes the central point of this talk. More specifically, along the talk we are going to see and discuss how, when Bohmian mechanics is put on the level of other quantum representations (i.e., as another legitimate representation with its own transformations that allow us to go from one to another), one can obtain deeper physical insights on quantum interference and coherence, the so-called Bohmian trajectories become an indirect measurable quantity (as evidenced by the renowned concept of weak measurement) and hence they have nothing of “surreal”, or there is a tight connection with optics even though Schrödinger’s equation is a diffusion-type equation rather than a wave equation in strict sense.

Speaker: Prof. Angel Sanz (Universidad Complutense de Madrid)

13:05 Lunch

8 by Zoom

Speaker: Prof. Maurice DeGosson (Universität Wien)

9 Quantum Implications: A Philosophical Introduction to Bohm and Hiley

What does quantum theory teach us about the nature of reality? This was one of the key questions which motivated David Bohm and which he explored together with Basil Hiley as they worked together in Birkbeck College for thirty years beginning in the early 1960s. It also motivated Basil Hiley as he continued their research program for more than thirty years after Bohm died in 1992. Bohm first tackled the question in the light of the usual ‘Copenhagen’ interpretation in his 1951 book Quantum theory. He emphasized the undivided wholeness of the universe at the quantum level and explored the idea that quantum properties ought to be seen as opposing potentialities which actualize relative to a context, rather than as pre-existing well-defined properties of things that we reveal in an experiment. Bohm’s 1952 ‘hidden variables’ interpretation provided a more complete hypothetical picture of quantum reality and was important as a counterexample to many of the claims of the supporters of the usual interpretation (including Bohm’s own 1951 claims). It also opened up a deeper view of the nature of (in)determinism in physics which Bohm explicated in his 1957 book Causality and Chance in Modern Physics.
In the early 1960s Bohm, together with Hiley, changed his views radically. Instead of focusing on the ‘furniture’ of the world (e.g. particles and fields) they began to discuss the ‘structure’ of the world, suggesting that quantum theory and relativity imply that there exists a deeper ‘implicate’ order where movement and wholeness prevail and from which the familiar ‘explicate order’ of particles and fields, along with space and time unfold. In a series of articles, they also began to examine the nonlocality of Bohm’s 1952 ‘hidden variable’ theory in the implicate order framework. A further idea was to propose that the quantum field in the 1952 theory is not an ordinary physical field but should be understood as carrying active information. These ideas were also used by Bohm, Hiley and myself to tackle broader philosophical issues, such as the relation of mind and matter, which I will briefly describe in this talk.
https://philpeople.org/profiles/paavo-pylkkanen

Speaker: Dr Paavo Pylkkänen (University of Helsinki)

10 The Legacy of Basil Hiley, as seen in the work of his last student

Speaker: Dr Peter T. J. Bradshaw (University College London)

15:50 Coffee

11 Towards a Bohm velocity measurement in Matter-Wave Interferometry experiments

At UCL, our group had the great privilege of working closely with Basil Hiley in the pursuit of experiments exploring the foundations of quantum theory. Among the many projects we undertook, one held a particularly special place for all of us: the experimental observation of the Bohm velocity. This was a long-standing dream of Basil’s, to see the ideas he and David Bohm developed put to the test in the laboratory.

In this talk, I will briefly discuss some of the theoretical and experimental approaches we developed together over the years. One such theoretical approach involves encoding phase information, specifically the Bohm velocity, into the wavefunction using Stimulated Raman Adiabatic Passage (STIRAP), and accessing it via post-selected measurements in matter-wave experiments. This enables the interference patterns at the detector to reveal information about the Bohm velocity itself.

I will also briefly review other experimental work pursued by our group that is not directly related to this topic, though many aspects overlap with the Bohm velocity project. Together, these efforts represent a significant part of our research with Basil, and our ongoing attempt to bring foundational quantum ideas into the laboratory.

Speaker: Dr Vincenzo Monachello (University College London)

12 From Quantum Discussions with Basil and David Bohm in the 1960s and 70s. (By Zoom)

When Basil Hiley and I were both on the faculty at Birkbeck College London, he in physics and I in mathematics, in the late 1960s, we began to have frequent (weekly?) discussions, often joined by David Bohm, on the foundations of quantum mechanics, most particularly on the puzzling phenomenon of the collapse of the wave-function upon measurement. On Basil’s side, the discussions eventually led to his broad-ranging book with Bohm:

The Undivided Universe: An Ontological Interpretation of Quantum Theory.

This was a great achievement, but my own interests in general relativity eventually took me in a different direction, where the curious way in which nature allows the basic principle of general relativity—namely the Galilei-Einstein Principle of equivalence between a local gravitational field and an accelerating coordinate frame—is made consistent with quantum theory, this leading to a very different view of the collapse of the quantum wave-function.

Speaker: Prof. Roger Penrose (University of Oxford)