When talking to folks about the quantum measurement problem, and its potential partial resolution by solving the set selection problem, I’ve recently been deploying three nonstandard arguments. To a large extent, these are dialectic strategies rather than unique arguments per se. That is, they are notable for me mostly because they avoid getting bogged down in some common conceptual dispute, not necessarily because they demonstrate something that doesn’t formally follow from traditional arguments. At least two of these seem new to me, in the sense that I don’t remember anyone else using them, but I strongly suspect that I’ve just appropriated them from elsewhere and forgotten. Citations to prior art are highly appreciated.
Passive quantum mechanics
There are good reasons to believe that, at the most abstract level, the practice of science doesn’t require a notion of active experiment. Rather, a completely passive observer could still in principle derive all fundamental physical theories simply by sitting around and watching. Science, at this level, is about explaining as many observations as possible starting from as minimal assumptions as possible. Abstractly we frame science as a compression algorithm that tries to find the programs with the smallest Kolmogorov complexity that reproduces observed data.… [continue reading]
I’m in search of an authoritative reference giving a foundational/information-theoretic approach to classical measurement. What abstract physical properties are necessary and sufficient?
Motivation: The Copenhagen interpretation treats the measurement process as a fundamental primitive, and this persists in most uses of quantum mechanics outside of foundations. Of course, the modern view is that the measurement process is just another physical evolution, where the state of a macroscopic apparatus is conditioned on the state of a microscopic quantum system in some basis determined by their mutual interaction Hamiltonian. The apparent nonunitary aspects of the evolution inferred by the observer arises because the measured system is coupled to the observer himself; the global evolution of the system-apparatus-observer system is formally modeled as unitary (although the philosophical meaningfulness/ontology/reality of the components of the wavefunction corresponding to different measurement outcomes is disputed).
Eventually, we’d like to be able to identify all laboratory measurements as just an anthropocentric subset of wavefunction branching events. I am very interested in finding a mathematically precise criteria for branching.Note that the branches themselves may be only precisely defined in some large-N or thermodynamic limit. a Ideally, I would like to find a property that everyone agrees must apply, at the least, to laboratory measurement processes, and (with as little change as possible) use this to find all branches — not just ones that result from laboratory measurements.… [continue reading]
[PSA: Happy 4th of July. Juno arrives at Jupiter tonight!]
This is short and worth reading:
The sharp distinction between Initial Conditions and Laws of Nature was initiated by Isaac Newton and I consider this to be one of his most important, if not the most important, accomplishment. Before Newton there was no sharp separation between the two concepts. Kepler, to whom we owe the three precise laws of planetary motion, tried to explain also the size of the planetary orbits, and their periods. After Newton's time the sharp separation of initial conditions and laws of nature was taken for granted and rarely even mentioned. Of course, the first ones are quite arbitrary and their properties are hardly parts of physics while the recognition of the latter ones are the prime purpose of our science. Whether the sharp separation of the two will stay with us permanently is, of course, as uncertain as is all future development but this question will be further discussed later. Perhaps it should be mentioned here that the permanency of the validity of our deterministic laws of nature became questionable as a result of the realization, due initially to D.
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Lots of matter interference experiments this time, because they are awesome.
We propose and analyze an all-magnetic scheme to perform a Young’s double slit experiment with a micron-sized superconducting sphere of mass
amu. We show that its center of mass could be prepared in a spatial quantum superposition state with an extent of the order of half a micrometer. The scheme is based on magnetically levitating the sphere above a superconducting chip and letting it skate through a static magnetic potential landscape where it interacts for short intervals with quantum circuits. In this way a protocol for fast quantum interferometry is passively implemented. Such a table-top earth-based quantum experiment would operate in a parameter regime where gravitational energy scales become relevant. In particular we show that the faint parameter-free gravitationally-induced decoherence collapse model, proposed by Diósi and Penrose, could be unambiguously falsified.
An extremely exciting and ambitious proposal. I have no ability to assess the technical feasibility, and my prior is that this is too hard, but the authors are solid. Their formalism and thinking is very clean, and hence quite abstracted away from the nitty gritty of the experiment.
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One of the main sources of hubris among physicists is that we think we can communicate essential ideas faster and more exactly than many others.This isn’t just a choice of compact terminology or ability to recall shared knowledge. It also has to do with a responsive throttling of the level of detail to match the listener’s ability to follow, and quick questions which allow the listener to hone in on things they don’t understand. This leads to a sense of frustration when talking to others who use different methods. Of course this sensation isn’t overwhelming evidence that our methods actually are better and function as described above, just that they are different. But come on. a Robin Hanson‘s Age of Em is an incredible written example of efficient transfer of (admittedly speculative) insights. I highly recommend it.
In places where I am trained to expect writers to insert fluff and repeat themselves — without actually clarifying — Hanson states his case concisely once, then plows through to new topics. There are several times where I think he leaps without sufficient justifications (at least given my level of background knowledge), but there is a stunning lack of fluff. The ideas are jammed in edgewise.… [continue reading]
I have blogged before about the conceptual importance of ideal, symplectic covariant quantum Brownian motion (QBM). In short: QBM is to open quantum systems as the harmonic oscillator is to closed quantum systems. Like the harmonic oscillator, (a) QBM is universal because it’s the leading-order behavior of a taylor series expansion; (b) QBM evolution has a very intuitive interpretation in terms of wavepackets evolving under classical flow; and (c) QBM is exactly solvable.
If that sounds like a diatribe up your alley, then you are in luck. I recently ranted about it here at PI. It’s just a summary of the literature; there are no new results. As always, I recommend downloading the raw video file so you can run it at arbitrary speed.
Abstract: In the study of closed quantum system, the simple harmonic oscillator is ubiquitous because all smooth potentials look quadratic locally, and exhaustively understanding it is very valuable because it is exactly solvable. Although not widely appreciated, Markovian quantum Brownian motion (QBM) plays almost exactly the same role in the study of open quantum systems. QBM is ubiquitous because it arises from only the Markov assumption and linear Lindblad operators, and it likewise has an elegant and transparent exact solution.
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Francisco Azuaje (emphasis mine):
According to American philosopher Harry FrankfurtHere’s Frankfurt’s popular essay [PDF]. a , a key difference between liars and bullshitters is that the former tend to accept that they are not telling the truth, while the latter simply do not care whether something is true or not.
Bullshitters strive to maximize personal gain through a continuing distortion of reality. If something is true and can be manipulated to achieve their selfish objectives, then good. If something is not true, who cares? All the same. These attributes make bullshitting worse than lying.
Furthermore, according to Frankfurt, it is the bullshitter’s capacity to get away with bullshitting so easily that makes them particularly dangerous. Individuals in prominent positions of authority may be punished for lying, especially if lying has serious damaging consequences. Professional and casual bullshitters at all levels of influence typically operate with freedom. Regardless of their roles in society, their exposure is not necessarily accompanied by negative legal or intellectual consequences, at least for the bullshitter…
Researchers may also be guilty of bullshitting by omission. This is the case when they do not openly challenge bullshitting positions, either in the public or academic settings. Scientists frequently wrongly assume that the public always has knowledge of well-established scientific facts.
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In a previous post of abstracts, I mentioned philosopher Josh Rosaler’s attempt to clarify the distinction between empirical and formal notions of “theoretical reduction”. Reduction is just the idea that one theory reduces to another in some limit, like Galilean kinematics reduces to special relativity in the limit of small velocities.Confusingly, philosophers use a reversed convention; they say that Galilean mechanics reduces to special relativity. a Formal reduction is when this takes the form of some mathematical limiting procedure (e.g., ), whereas empirical reduction is an explanatory statement about observations (e.g., “special relativity can explains the empirical usefulness of Galilean kinematics”).
Rosaler’s criticism, which I mostly agree with, is that folks often conflate these two. Usually this isn’t a serious problem since the holes can be patched up on the fly by a competent physicist, but sometimes it leads to serious trouble. The most egregious case, and the one that got me interested in all this, is the quantum-classical transition, and in particular the serious insufficiency of existing limits to explain the appearance of macroscopic classicality. In particular, even though this limiting procedure recovers the classical equations of motion, it fails spectacularly to recover the state space.… [continue reading]
I’m happy to announce the recent publication of a paper by Mike, Wojciech, and myself.
Motivated by the advances of quantum Darwinism and recognizing the role played by redundancy in identifying the small subset of quantum states with resilience characteristic of objective classical reality, we explore the implications of redundant records for consistent histories. The consistent histories formalism is a tool for describing sequences of events taking place in an evolving closed quantum system. A set of histories is consistent when one can reason about them using Boolean logic, i.e., when probabilities of sequences of events that define histories are additive. However, the vast majority of the sets of histories that are merely consistent are flagrantly nonclassical in other respects. This embarras de richesses (known as the set selection problem) suggests that one must go beyond consistency to identify how the classical past arises in our quantum universe. The key intuition we follow is that the records of events that define the familiar objective past are inscribed in many distinct systems, e.g., subsystems of the environment, and are accessible locally in space and time to observers.
… [continue reading]