New Directions in the Foundations of Physics Conference
(and a reply)
Today I will continue to talk about the New Directions conference. My plans changed after all the slides were posted online (this is a very nice initiative and I urge the organizers to make it permanent) and I'll present them all to give a birds' eye view of the conference and have a convenient reference for the future. One thing to recognize about this conference is the extremely generous time slot allocation for the talks and discussions which allows to go beyond actual results and leads to in depth exploration of motivation.
Without ado, here were the presentations:
Reinhard Werner: Is an Ontological Commitment at the Quantum Level Helpful for Physics
"After a brief introduction I will describe the operational approach to quantum mechanics, which aims to systematize a minimal pragmatic approach to the empirically relevant intersection of various interpretations. This minimal interpretation is signal-local and does not suffer from a measurement problem. This is then contrasted with Bohmian Mechanics, which sacrifices locality for a classical mode of description, even at the microscopic level. I will argue that the added elements have a somewhat spooky claim to reality, as they are unconnected to empirical fact as a matter of principle."
Michael Esfeld: The Measurement Problem and the Primitive Ontology of Quantum Physics.
"In this talk, I will argue that an ontology of matter arranged in physical space (known as a primitive ontology) is a necessary condition to avoid the measurement problem of quantum physics. To turn this necessary condition into a sufficient one, a dynamics is needed that excludes superpositions of matter in space, but includes entanglement. I use the de Broglie-Bohm theory to illustrate how these conditions can be satisfied. The main part of the talk then consists in sketching out a minimal primitive ontology of quantum physics in terms of matter points that are individuated only by the spatial relations in which they stand. The quantum state—including parameters such as a wave-function, spin, energy, mass, etc.—comes in only through its dynamical role for the evolution of the configuration of matter points. It is not mandatory to conceive that state as a physical reality that exists over and above the configuration of matter points."
Gilles Brassard: Parallel Lives: Why Quantum Mechanics is a Local Realistic Theory After All.
"Most physicists take it for granted that the experimental violation of Bell's inequality provides evidence that our universe is nonlocal. However, this is not the case! Indeed, I shall describe a toy universe (not meant to describe our world) in which Bell's (CHSH) inequality is maximally violated, yet this world is purely local. Then, I shall present mathematical requirements for quantum mechanics itself to be local. It turns out that these requirements cannot be satisfied if we take the universal wavefunction as a complete representation of reality, even if we admit the existence of the multiverse. Nevertheless, I shall present a solution to this conundrum with a framework that provides a simple local-realistic description of quantum mechanics. In particular, one can recover the whole (even if entangled) from the description of the parts, in sharp contrast with the standard formalism of quantum mechanics."
Chris Fuchs: What QBism Learns from the Bell Inequality Violations.
"In QBism, a 4-dimensional Hilbert space is a 4-dimensional Hilbert space and should be treated with the full apparatus of quantum theory. It makes no difference whether one insists on thinking of the number 4 as the unique integer 4 or instead as the composite 2 x 2. That is, breaking a system into components, whether within a single atom or within an experiment across Lake Geneva (as in a Bell experiment), changes nothing about this fundamental edict. The same can be said of any composite integer pq, whether p=2 and q=2Avogadro's number, or anything else. The game of quantum mechanics is to be consistent with its use all the way through and not get cheap about it when a problem seems to involve other observers, i.e., quantum systems with particularly big Hilbert spaces."
Samson Abramsky: Contextuality: At the Borders of Paradox.
"Contextuality can be understood as arising where we have a family of data which is locally consistent, but globally inconsistent. From this point of view, it can be seen as a pervasive phenomenon, arising not only in quantum mechanics, but in many other areas. There are also remarkably direct connections to logical paradoxes. One can say that contextual phenomena, which we must accept as key features of our picture of physical reality, lie at the very borders of paradox, but do not cross those borders.
On the qualitative level, we show how a hierarchy of strengths of contextuality emerges naturally in a sheaf-theoretic language, and how the ‘All-versus-Nothing’ arguments which have played an important role in quantum foundations are witnessed by sheaf cohomology as obstructions to global sections. On the quantitative level, we show that all Bell inequalities, for a very general notion of contextuality scenarios, arise uniformly from logical consistency conditions."
Dagomir Kaszlikowski: The Triangle Principle: A New Approach to Non-Contextuality and Local Realism.
"In my talk I will introduce the ‘triangle principle,’ which is a new approach to quantum contextuality and violations of Bell inequalities. This approach recovers all known bipartite Bell inequalities, state dependent non-contextual inequalities, predicts new such inequalities as well as various monogamy relations between them. I will also show that the triangle principle allows one to perform an experimental test to distinguish between quantum and classical correlations without using the notion of probability. I will finish my talk with a few remarks about the philosophical consequences of the triangle principle."
Dan Greenberger: Why We Are Having Such Trouble Hooking Up Gravity to Quantum Theory.
"Besides the more obvious problems (non-linearity, etc.) in trying to connect relativity to gravity, my own feeling is that there is a more subtle reason that poisons the whole enterprise.
While energy plays an important dynamical role in quantum theory, mass enters as a mere parameter in our theories, even though it physically plays a dynamical role. (I don't mean internal symmetries, I am talking about space-time). For example, when a proton and electron are brought together, they form an H atom, whose mass includes the binding energy. But the individual masses don't change. The new mass is put in by hand, but should automatically change with the interaction.
Similarly, proper time is determined geometrically in classical relativity, but physically it also plays a much more complicated role in quantum theory. Both these concepts should play a dynamical role, and in fact should be canonically conjugate variables, and obey an uncertainty principle. I believe this is needed for the self-consistency of the theory, and it constitutes a necessary first step if the theories are to be consistently conjoined."
Sabine Hossenfelder: Analog Duality.
I will discuss a new duality between strongly coupled and weakly coupled condensed matter systems. It can be obtained by combining the gauge-gravity duality with analog gravity. In my talk I will explain how one arrives at the new duality, what it can be good for, and what questions this finding raises.
Mile Gu: Quantum Simplicity: Can Quantum Theory Better Isolate the Causes of Natural Phenomena?
"We understand complex phenomena around us though predictive models — algorithms that generate future predictions when given relevant past information. Each model encapsulates a way of understanding future expectations through past observations. In the spirit of Occam’s razor, the better we isolate the causes of what we observe, the greater our understanding. This philosophy privileges the simpler models; should two models make identical predictions, the one that requires less input information is preferred.
Yet, for almost all stochastic processes, even the provably optimal classical models waste information. The amount of input information they demand exceeds the amount of predictive information they output. In this presentation, I outline how we can systematically construct quantum models that break this classical bound, and that the system of minimal entropy that simulates such processes must necessarily harness quantum dynamics.
I will discuss the potential consequences of these findings to complexity theory, where the minimal amount of causes to model a phenomenon is often used as an intrinsic measure of its structure of complexity. I show, by comparing the simplest classical models with even simpler quantum models on a range of stochastic systems, that the quantum generalization of this measure can have drastically different qualitative behaviour. Thus many observed phenomena could be significantly simpler than classically possible should quantum effects be involved, and existing notions of structure and complexity may ultimately depend on the type of information theory we use."
Joe Henson: How Causal is Quantum Mechanics?
"I will discuss some attempts restore a meaningful notion of ‘locality,’ meaning lack of superluminal causal influence, to quantum theory (QT) after Bell's theorem, in particular ‘denial of independence of settings,’ ‘denial of the reality of distant outcomes,’ and ‘denial of ontological separability.’ I will point out a common problem with these attempts, and use this discussion to frame and motivate a new question: *what aspects* of the notion of causality can be maintained when dealing with QT?
If time allows, I will describe an emerging program to answer this question. Rather than imposing an answer on quantum theory, this program first delves into the details of QT in order to understand what analogies to the standard ‘Reichenbachian’ idea of causation can be made, and what aspects of this package of ideas must be given up. I will argue that this fledgling program holds the promise of a genuinely new — and useful — understanding of quantum theory."
From all this one sees the great diversity of the foundations community and the fact that no one challenges the existing points of view more than the community itself. Last time I offered in good faith Lubos a chance to present his point of view. Apparently I was mistaken in my assumption of how he would respond. Here was his reply:
On number 1 Lubos gave a lengthy reply later despite not having the time. Each interpretation in quantum mechanics has strengths and weaknesses and is easy to find faults in any of them. Challenging Matt's answers was the easy way out. Responding to the faults of the traditional point of view is much harder and I would have asked Lubos different questions related to his stance on quantum mechanics. I know his position is weakest around the measurement problem where he used handwaving in the past.
For numbers 2 and 3 I want to point out that in science the size of the followers counts for nothing even if you are the Pope and claim to speak with God. The Sun does not move around the Earth regardless of how many people believe it.
Number 4 on spreading pseudoscience is plainly absurd. The quality of the readership is more important than quantity. I do not want to build a readership around false ideas like global warming is not real. On topics other than quantum mechanics, sometimes me and Lubos talk about the same things, like: 1+2+3+... = -1/12 My presentations have more in-depth information (like introducing the outstanding lectures of Mr. Bender) and I presented the idea with more rigor. On quantum mechanics topics TRF does not even come close to my blog. Quantum mechanics is best expressed in the language of sheaves, category theory, algebraic topology, non-commutative geometry. I have yet to see any meaningful in depth discussion about them on TRF. But perhaps this is not the focus of TRF and the focus is on high energy physics. Has anyone seen any presentation of the modern developments of gauge theory like the Seiberg-Witten gauge theory there? Topics like 1+2+3+...=-1/12 are cheap shots introduced for expedience reasons and I know I am guilty of this because sometimes I do not have the proper time to put into my blog. However I strive for the real in depth explanations of genuine value.
On Number 5 my answer is that it was my job is to ask hard questions and create opportunities for presenting the opposing points of view and I believe I have done that. Sure, I agreed with Matt that pursuing questions of interpretations is a worthwhile scientific activity and Lubos earlier criticism of Matt for this reason is baseless. As of today there is no consensus in the community of experts dedicating their careers pursuing those kinds of questions.