*Edit Reason: new links added*)

https://fqxi.org/community/articles/display/232

EXCERPT: Markus Mueller could mistakenly be accused of being a supreme individualist. After all, the quantum physicist’s radical new take on reality seems to suggest that the world we see emerges from our observations. He admits that it’s a tough idea for people to wrap their heads around, or for him to articulate: "No one’s even made up a science fiction story that would roughly explain it," Mueller says. "Our theory says that only observations are fundamentally ’real’."

[...] Quantum theory already forces physicists to take the role of the observer seriously. For example, before we measure a quantum system, it can hold contradictory properties, such as being in two different energy states. When we observe it, we force the system to assume a particular state, inherently tying the act of observing into reality itself. Mueller and Michael Cuffaro argue that they are just following these hints to their logical end. Their aim is to develop a framework to describe reality without assuming the existence of ordinary objects with properties, governed by physical laws. But how do you set about the ambitious task of constructing a universe, without any building blocks or instructions for how to assemble it?

"Mathematically when you ask, ’What if there are no laws of nature?’ that’s like asking ’What if all you have is mathematics itself? Can that give you something that allows you to predict what you’ll see—that is, some probabilities of observations, without assuming anything else?’," says Mueller. "That was my starting point."

There was already mathematics in place to help the pair of researchers to do this. The field of "algorithmic probability" is already employed by those working on artificial intelligence and machine learning. It describes the probability of an observation occurring over a whole range of possibilities, and programmers use it to create robots that can ’learn’ from observations of their environment and make decisions about what action to take based on past outcomes.

Using this mathematical framework, Mueller has derived a coherent description of reality from nothing more than descriptions of sets of observations, made one after another. [...] Mueller postulates that what happens next depends on its algorithmic probability—conditioned on what has been observed in the past. This process, he argues, can forge reality itself. Future observations that don’t fit in with what we’ve seen in the past—perhaps worlds with five or six dimensions—are thrown out because their likelihood is so much smaller than us continuing to observe a world with three spatial dimensions. Observations consistent with what we’ve seen in the past, those that fit into a description of the world in the usual sense, with regular laws—these are the most likely. Hence we get an ’emergent world’ from our observations.

"It turns out that algorithmic probability is a very useful notion," says Mueller. Physical laws and regularities emerge in the same way that robots eventually learn to give the right answers. "Laws tend to stabilise and you see regularities around you and this world with these laws of nature," Mueller explains. "It’s the same kind of mathematical origin of both."

Renato Renner, a theoretical physicist based at ETH Zurich, in Switzerland, notes that there is a long history in physics of trying to formulate theories from a first-person perspective. But unlike most attempts, Mueller has succeeded in developing "a well-defined theory within which non-trivial results can be derived," says Renner. "This is very remarkable!" In a rough sense, Renner says, Mueller has provided a quantitative version of Occam’s razor: it assigns high probabilities to possible future events that have a simple explanation.

As well as explaining why there are laws of nature at all, Mueller’s approach can also resolve some notoriously difficult puzzles in cosmology and quantum theory. (MORE - details)

EXCERPT: Markus Mueller could mistakenly be accused of being a supreme individualist. After all, the quantum physicist’s radical new take on reality seems to suggest that the world we see emerges from our observations. He admits that it’s a tough idea for people to wrap their heads around, or for him to articulate: "No one’s even made up a science fiction story that would roughly explain it," Mueller says. "Our theory says that only observations are fundamentally ’real’."

[...] Quantum theory already forces physicists to take the role of the observer seriously. For example, before we measure a quantum system, it can hold contradictory properties, such as being in two different energy states. When we observe it, we force the system to assume a particular state, inherently tying the act of observing into reality itself. Mueller and Michael Cuffaro argue that they are just following these hints to their logical end. Their aim is to develop a framework to describe reality without assuming the existence of ordinary objects with properties, governed by physical laws. But how do you set about the ambitious task of constructing a universe, without any building blocks or instructions for how to assemble it?

"Mathematically when you ask, ’What if there are no laws of nature?’ that’s like asking ’What if all you have is mathematics itself? Can that give you something that allows you to predict what you’ll see—that is, some probabilities of observations, without assuming anything else?’," says Mueller. "That was my starting point."

There was already mathematics in place to help the pair of researchers to do this. The field of "algorithmic probability" is already employed by those working on artificial intelligence and machine learning. It describes the probability of an observation occurring over a whole range of possibilities, and programmers use it to create robots that can ’learn’ from observations of their environment and make decisions about what action to take based on past outcomes.

Using this mathematical framework, Mueller has derived a coherent description of reality from nothing more than descriptions of sets of observations, made one after another. [...] Mueller postulates that what happens next depends on its algorithmic probability—conditioned on what has been observed in the past. This process, he argues, can forge reality itself. Future observations that don’t fit in with what we’ve seen in the past—perhaps worlds with five or six dimensions—are thrown out because their likelihood is so much smaller than us continuing to observe a world with three spatial dimensions. Observations consistent with what we’ve seen in the past, those that fit into a description of the world in the usual sense, with regular laws—these are the most likely. Hence we get an ’emergent world’ from our observations.

"It turns out that algorithmic probability is a very useful notion," says Mueller. Physical laws and regularities emerge in the same way that robots eventually learn to give the right answers. "Laws tend to stabilise and you see regularities around you and this world with these laws of nature," Mueller explains. "It’s the same kind of mathematical origin of both."

Renato Renner, a theoretical physicist based at ETH Zurich, in Switzerland, notes that there is a long history in physics of trying to formulate theories from a first-person perspective. But unlike most attempts, Mueller has succeeded in developing "a well-defined theory within which non-trivial results can be derived," says Renner. "This is very remarkable!" In a rough sense, Renner says, Mueller has provided a quantitative version of Occam’s razor: it assigns high probabilities to possible future events that have a simple explanation.

As well as explaining why there are laws of nature at all, Mueller’s approach can also resolve some notoriously difficult puzzles in cosmology and quantum theory. (MORE - details)