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Using constructor theory to explain free will

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https://fqxi.org/community/articles/display/230

EXCERPT: . . . But according to fundamental physics, you didn’t actually make a choice. Your fate was encoded in the initial conditions of the universe—mysteriously fine-tuned so that life, you, and this article could arise. You’re shackled by the same physical laws as the universe in which you evolved; so there’s no such thing as truly ’free’ will.

Some scientists just don’t buy this standard story, however. At a time when we’re debating whether super intelligent machines will one day take over the planet, the question of what it means to be human is increasingly pressing. Many argue that free will is a precondition to being an autonomous and morally responsible agent. If free will could be shown to be an integral part of how nature works, rather than a social invention, that would definitely be a boost for human dignity.

Taking a step to rescue free will is Sara Imari Walker, a theoretical physicist and astrobiologist at Arizona Sate University, in Tempe. She says the notion that intelligent beings only have the illusion of influencing events in the unfolding universe through their choices, "agitates" her. With a grant of over $70,000 from FQXi, she is trying to come up with a theoretical framework, based on constructor theory, to explain how sophisticated observers can use knowledge to construct their own future, while still obeying the laws of physics.

[...] Making artificial elements is one way that people tamper with the natural physical order. However, the fundamental role of observers, intelligent or otherwise, on constructing reality has long been a sticking point in physics. [...] Walker believes it is time to take observers seriously—and that understanding information lies at the heart of the matter. [...] To develop her ideas, she needed a ’meta theory’ that can encompass all physical theories, and in which the roles of the observer and information can be illuminated.

Enter constructor theory: Proposed in 2012 by David Deutsch, a quantum physicist at the University of Oxford, UK, constructor theory strives to fully explain the physical world by stating only which transformations are possible, which are not—and why. Entities that have the ability to carry out such transformations accurately and repeatedly are called "constructors." A kettle connected to power, for instance, is a constructor that can carry out the task of heating water given a sufficient amount of energy.

A crucial aspect of constructor theory is that it takes information to be fundamentally physical—determined by physical laws—rather than an abstract, mathematical concept. Chiara Marletto, a quantum physicist at Oxford who developed the theory with Deutsch, and is Walker’s co-investigator, says it is already proving useful. For example, she and Deutsch recently used the theory to describe information processing in a way that unifies the classical world of macroscopic objects and the quantum realm, without needing to ascribe magical status to human consciousness to explain why it disrupts quantum systems through observation. "It’s basically a new way to formulate the laws of physics," explains Marletto.

The pair of physicists achieved this unification by stating that a characteristic trait of an object containing information is that it has certain physical properties that can be copied. [...] In the classical word, all properties of physical systems can, in principle, be copied to arbitrarily high accuracy [...] By contrast, quantum physicists already know that in the quantum world, it is impossible to copy or clone a quantum state. [...]

Marletto and Deutsch showed that, using solely the principles of constructor theory, including this constraint on copying in quantum systems, it is possible to derive all of the qualitative properties of quantum systems, including the notorious fact that an observer measuring a generic quantum state will inevitably disturb it. This shows explicitly that a simple constraint on copying information can help solve the puzzle of how observers (which are usually taken to be nothing more than simple detectors, in the framework) disrupt quantum systems by monitoring them.

Now, Walker and Marletto want to move up in scale and investigate more sophisticated observers. They believe that constructor theory has the right tools to do this because information is also crucial in biological systems [...] "Knowledge, in constructor theory, is defined as a particular type of information that can cause itself to remain embodied in physical systems," explains Marletto. This is Walker and Marletto’s starting point for developing what they call "causal mechanics." Their idea goes like this: Before life existed on Earth, the laws of physics could have triggered a chain of increasingly complex transformations, such as molecular reactions, carried out by increasingly advanced constructors. A simple cell, for instance, is a constructor that needs information in the form of DNA to carry out specific tasks. It also needs to be able to copy that knowledge and pass it on to new cells. "In this constructor-theoretic sense, knowledge is key to resiliency—a characteristic property of life," says Marletto.

Like cells, Walker notes, intelligent observers have the power to use information to cause transformations. The reason that traditional physics can’t account for this is that it is only concerned with micro states—the lowest levels of description you can think of—and what happens to them over time. At any instant, the configuration of atoms in your body is a micro state, while your body is a macro state. Physics assumes that the future of your body can be calculated by just evolving all those individual atoms forward in time.

But biology is far more complex than this simple picture allows. Atoms can group into molecules that only interact in specific ways with other molecules. And macro states seem to be able to influence individual particles.[...] As evolution shows, biological systems are getting even more complex over time. Walker believes that is because this complicated interplay between different sub-systems using information opens up more possible states and trajectories for living systems to take than traditional physics allows for—potentially giving rise to emergent properties [...] Emergence could explain how qualities such as specialized senses, intelligence and even consciousness evolved, says Walker. More controversially, she argues that nature can not only give rise to free will in this manner, it should favor the emergence of free will. Her line of thinking is that it may well be a principle of nature to create as many physical states and paths as possible. "If people can act as individual agents,"—with free will—"this will create more possibilities," says Walker.

But how do you actually show that this is how nature works? Walker intends to use computer models, known as cellular automata...

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