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The Quantum Agent
https://fqxi.org/community/articles/display/238

INTRO: In the cult movie classic The Matrix, the disturbingly nihilistic ’Agent Smith’—an artificially intelligent computer program who looks like an FBI agent and acts like a prison guard in a simulated reality—seems smarter and more powerful than the other agents in the system. He goes off-book to make his own decisions independent of his controller and to cunningly anticipate attacks; he can replicate himself and, just when you think he has been deleted, he sneakily reappears.

There are perhaps some eerie similarities between Agent Smith and many of the questions tossed about by quantum physicists. What properties of an agent give rise to free will, or the appearance of it? Can you make perfect copies of information? Is something really deleted when you think it is?

To a quantum physicist, an ’agent’ isn’t always of the FBI variety. It doesn’t even need to be ’intelligent’ in the way that we normally think about that word. All it needs to do is observe something, process that information, and act upon it. A simple logic gate in computing—the little switch that says "if the input is x, then do y"—is an agent. But there is still some mystery surrounding the phenomenon, particularly at small scales. Here quantum physics applies and particles can do odd things, like be in two places at once, or travel along separate paths simultaneously. Fully describing quantum-scale agents, and understanding how they might give rise to the everyday agents we see in our macroscopic ’classical’ world, is a work-in-progress.

Most of the things we typically ascribe with intelligent agency, after-all, exist in the human-scale world of classical physics, not the microscopic quantum realm. So how does that agency emerge? As University of Maryland Baltimore County physicist Sebastian Deffner puts it, "Is there some underlying physical reason why agents tend to look classical?"

A group of researchers are tackling this question from all angles as part of an FQXi grant round called ’Agency in the Physical World’—a program that has spread US$2 million amongst 24 research projects, including Deffner’s, which has been awarded over $111,000. The unifying topic for these projects: How quantum measurement might lead to the emergence of agency and (bonus points for this part) the conscious mind. Intelligence and free will, after all, are the ultimate manifestations of ’agency.’

The work is interesting not just philosophically, but should feed into efforts to make quantum computers and optimize quantum machines, which might process information in novel ways. Understanding agency is synonymous with understanding how quantum systems are controlled. "Right now, we have extremely sophisticated techniques for controlling airplanes and things like that. We have all sorts of instruments," says another FQXi grant-winner Aephraim Steinberg, a physicist at the University of Toronto, who has been awarded $138,000. "These days we want systems that control quantum devices. So we need an analogue of that." (MORE)



Quantum Dream Time
https://fqxi.org/community/articles/display/224

EXCERPT: Picture a man dreaming. On the outside, he’s totally still. But inside is a world in motion: moving, growing, changing, evolving. Could our universe be like the dreaming man—static seen from outside, but alive on the inside?

Maybe, according to a new definition of "quantum time" from Lorenzo Maccone, of the University of Pavia in Italy, Seth Lloyd at MIT in Cambridge, USA, and Vittorio Giovannetti at the Scuola Normale Superiore, in Pisa, Italy. With support from a grant of almost $50,000 from FQXi, the three physicists are reviving a long-abandoned approach to quantum mechanics. They hope their strategy may make it possible to solve one of the biggest problems in physics: the apparent incompatibility of quantum mechanics, which governs the physics of the very small, and general relativity, which describes the motion of stars and planets.

[...] The nature of time is one of those paradoxes. In the 1960s, physicists John Wheeler and Bryce DeWitt made a major push toward mathematically unifying quantum mechanics and general relativity, deriving a new version of the equation that describes the evolution of quantum systems, the Schrödinger equation, so that it also includes gravity. The problem: time drops out of the equation entirely, leaving physicists who believe that quantum theory is fundamental with a conundrum.

"Most physicists regard the quantum state as a complete description of the state of the universe," says Matthew Leifer, a quantum physicist at Chapman University, who is not involved in the project. "Then the Wheeler-DeWitt equation implies that there is no change in the state of the universe, which contradicts our everyday observations."

This notion of a timeless universe jars with our everyday experience. "It’s clearly meaningless because we see things evolving all the time!" says Maccone. Solving the conundrum may require appreciating ambiguities [...] Although time is an essential ingredient in the equations of quantum mechanics, there is no definition that’s natively quantum, says Maccone. Instead, time is whatever the clock on the lab wall says it is. That’s an "ugly" way to treat time [...] it sets the results of quantum equations on a potentially flawed foundation.

A few years ago, Giovannetti hit on a promising solution: What if he just swapped the classical clock for a quantum one? [...] In this view, the probability equations at the core of quantum mechanics are conditional on the state of the quantum clock; the approach is therefore called "conditional probability amplitudes."

Conditional probability amplitudes seem to solve Wheeler and DeWitt’s problem of vanishing time, says Maccone. An "inside" observer, correlated with the quantum clock, would see the system change over time, but someone watching from the outside could only observe the static properties of the combined systems. "The state of the universe as seen from the outside is static, but from the inside, it is not," says Maccone. Like the dreamer, the quantum system looks to be at a standstill, while it’s actually alive with action on the inside.

Though the idea was new to Giovannetti, it was actually first hatched in the early 1980s by theorists, and FQXi members, Don Page [...] and William Wootters ... So why had Giovannetti, Lloyd and Maccone never heard of it? The decades-old papers revealed that the approach had been quickly abandoned due to criticisms that, at the time, seemed fatal. But today, Maccone argues, those objections can be overcome using insights from the quantum information theory, a field which was still in its infancy when Page and Wootters’ idea was nixed. Quantum information theory has introduced new ways to think about measurement devices... (MORE - details)