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First Things First: The Physics of Causality
Why do we remember the past and not the future? Untangling the connections between cause and effect, choice, and entropy.

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A devilish new framework of thermodynamics that focuses on how we observe information could help illuminate our understanding of probability and rewrite quantum theory.

Gravity's Residue
An unusual approach to unifying the laws of physics could solve Hawking's black-hole information paradox—and its predicted gravitational "memory effect" could be picked up by LIGO.

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September 16, 2019

Quantum Cybernetics
The quest for a meta-theory of quantum control that could one day explain physical systems, certain biological phenomena—and maybe even politics.
by Nathan Collins
October 1, 2015
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Gerardo Adesso and Davide Girolami
Quantum Controllers
Quantum cybernetics began, as so many interesting things do, on a Friday afternoon.

Gerardo Adesso, a physicist at the University of Nottingham, UK, recalls sitting in his office, a couple of years ago, thinking about "quantumness, in all its aspects," when his graduate student, Davide Girolami, walked in "and started talking apparent nonsense about a medical doctor who wrote a book in the 1960s."

The book, actually first published in 1956, was W. Ross Ashby’s An Introduction to Cybernetics, which outlined a framework for unifying the sciences—the classical disciplines, that is—in terms of how systems can be controlled. Ashby had not considered the quantum realm, in which subatomic particles are subjected to some very curious laws. But over half a century later, his ideas would lead Adesso, Girolami, and postdoctoral fellow Rebecca Schmidt to develop an entirely new perspective on the quantum world—research that, with the support of a $90,000 Foundational Questions Institute grant, could help change the way natural and maybe even social scientists think. The team hopes that the "meta-theory" that emerges will be able to collectively explain the behavior of physical as well as social and biological phenomena where quantum strategies play a fundamental role.

Cyber Control

To the extent it’s still in common use, the prefix "cyber" is associated with computers and the Internet. But the former was in its infancy and the latter not even conceived in 1948, when mathematician Norbert Weiner first used the word "cybernetics" to describe a new field he and colleagues were developing. Drawn from the Greek word for pilot or governor, cybernetics is a framework for analyzing any system in which information passes back and forth between any two entities, be they electrical components or members of Congress.

We have to radically
reassess what we had
believed to be the
- Gerardo Adesso
The framework is extremely useful. Core cybernetics concepts such as feedback and control have been essential to engineering and science since the days of the steam engine and the ’flyball governor’ that regulates it, says John Gough, an expert on quantum information at Aberystwyth University, UK. Today, many innovators believe that the next big technological revolution will utilize the potential of the subatomic world for building ever more powerful devices. These include quantum computers, which in principle would have capabilities that far surpass even the latest crop of their classical counterparts. (See "Quantum Computers Get Real.")

"The twenty-first century promises to be the century of quantum technology," says Gough. "My feeling is that the most profound ideas in quantum technology revolve around building quantum mechanical analogues of the flyball governor." So it makes perfect sense to try to extend the winning formula of cybernetics to the quantum realm, he says.

That brings us back to that pivotal Friday afternoon in Nottingham. In An Introduction to Cybernetics, Ashby laid out the Law of Requisite Variety, which states that to keep a system stable, a control mechanism must have at least as many states as the system does. For example, to adequately control a nuclear power plant, an automatic control system must have an appropriate response—the appropriate feedback—for every possible circumstance he or she may encounter, whether it’s normal operation, an earthquake-damaged reactor, or a complete meltdown. So the first task for Adesso, Girolami and others interested in extending cybernetics to microscopic systems is to find the quantum version of this law.

A Quantum Law of Requisite Variety?
In the search for a quantum theory of cybernetics, physicists must account for the weirdness
of the microscopic realm.

Credit: agsandrew
The trouble with extending the existing principles of cybernetics to quantum physics, however, is that things on the microscopic scale seem to defy classical logic. Take quantum entanglement, the phenomenon in which the properties of one atom or some other miniscule object are bound up in the properties of another. For example, if experimenters entangle the quantum spins—akin to the orientations of spinning balls—of two atoms, then as soon as someone measures one atom’s spin, the other’s spin is immediately determined. That kind of correlation can’t happen in the classical world—once set in motion, one ball’s spin doesn’t affect any other’s—suggesting the need for a new, quantum cybernetics to understand quantum systems.

"Developing a quantum law of requisite variety…is crucial because quantum systems can be correlated in ways which are different from classical ones," says Girolami. Once that has been achieved, the team can begin to calculate how quantum correlations contribute to the control and controllability of quantum systems.

Gough admires the team’s strategy, describing it as an "excellent opportunity" for eventually developing better quantum technologies and for bringing the ideas of quantum cybernetics to a wide audience.

"I really like the direction of quantum cybernetics, as it extends the usual notion of quantum information processing," agrees Vlatko Vedral, a physicist at the University of Oxford. Usually, quantum information processing is concerned with storing and transmitting information according to quantum mechanical laws, "but cybernetics also implies being able to use this information for self-regulation of the system." Vedral is such a fan that he recently hired Girolami as a postdoctoral researcher, in fact.

Quantum Biology

If Adesso’s team can create a solid mathematical formalism, Vedral says, it could shed light on some mysterious biological processes that appear to be using a sprinkling of quantum magic to improve efficiency. Until recently, physicists had assumed that quantum effects were too fragile to survive in the warm and wet environments of cells, let alone that they could play a crucial role in macroscopic biological systems. However, over the past decade, there has been increasing evidence that plants and some algae exploit quantum effects to speed up photosynthesis, the process for converting sunlight to energy. Some physicists have also suggested that birds use quantum entanglement to help navigate magnetic fields. (See "Quantum Biology: Making Waves in the Natural World.")

Such examples of quantum biology have already blurred the line between the quantum and classical worlds. "We have to radically reassess what we had believed to be the quantum/classical divide," Adesso says. By bringing various scientific disciplines together under one umbrella and describing them with one mathematical language, quantum cybernetics could help researchers figure out just where the cut-off truly lies. "The hope we have is that we will be able to provide compelling evidence that quantum mechanical effects cannot be ignored in a range of phenomena occurring in other disciplines," Adesso says.

So where does Adesso think this line will be drawn? Will we one day describe politics in terms of quantum cybernetics? It’s not as crazy a question as it might sound—political scientists and economists have for years known that just as quantum particles don’t always behave independently, neither do voters or stock traders. "As Davide likes to say, in 20 to 50 years we hope to give an affirmative answer to the question whether biologists and social scientists should learn quantum mechanics," says Adesso.

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Diederik Aerts and his colleagues at the VUB and elsewhere have been pursuing a not dissimilar approach (applying QM principles isomorphically to macroworld social and other issues) for a couple of decades. Just noting.

One concern. All this seems to be edging fairly close to a ToE or -- not contradictory -- something akin to empirical proof that P=NP. Or am I fundamentally misreading?

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