Sunday, December 23, 2012

Do we live in a computer simulation? How to test the idea

The energy surface of a massless, non-interacting Wilson fermion. The continuum dispersion relation is shown as the red surface. (Credit: Silas R. Beane et al.)

The concept that we could possibly be living in a computer simulation has been suggested by science writers and others, and was formalized in a 2003 paper published in Philosophical Quarterly by Nick Bostrom, a philosophy professor at the University of Oxford.

With current limitations and trends in computing, it will be decades before researchers will be able to run even primitive simulations of the universe. But a University of Washington team has suggested tests that can be performed now, or in the near future, that could resolve the question.

Currently, supercomputers using a technique called lattice quantum chromodynamics (LQC), and starting from the fundamental physical laws that govern the universe, can simulate only a very small portion of the universe, on the scale of one 100-trillionth of a meter, a little larger than the nucleus of an atom, said Martin Savage, a UW physics professor.

Eventually though, more powerful simulations will be able to model on the scale of a molecule, then a cell and even a human being. But it will take many generations of growth in computing power to be able to simulate a large enough chunk of the universe to understand the constraints on physical processes that would indicate we are living in a computer model.

However, Savage said, there are signatures of resource constraints in present-day simulations that are likely to exist as well in simulations in the distant future, including the imprint of an underlying lattice if one is used to model the space-time continuum.

The supercomputers performing LQC calculations essentially divide space-time into a four-dimensional grid. That allows researchers to examine what is called the strong force, one of the four fundamental forces of nature and the one that binds subatomic particles called quarks and gluons together into neutrons and protons at the core of atoms. “If you make the simulations big enough, something like our universe should emerge,” Savage said. Then it would be a matter of looking for a “signature” in our universe that has an analog in the current small-scale simulations.

Savage and colleagues suggest that the signature could show up as a limitation in the energy of cosmic rays.

In a paper they have posted on arXiv, they say that the highest-energy cosmic rays would not travel along the edges of the lattice in the model but would travel diagonally, and they would not interact equally in all directions as they otherwise would be expected to do.

“This is the first testable signature of such an idea,” Savage said.

If such a concept turned out to be reality, it would raise other possibilities as well. For example, co-author Zohreh Davoudi suggests that if our universe is a simulation, then those running it could be running other simulations as well, essentially creating other universes parallel to our own.

“Then the question is, ‘Can you communicate with those other universes if they are running on the same platform?’” she said.

There are, of course, many caveats to this extrapolation. Foremost among them is the assumption that exponential growth of computers will continue into the future. Related to this is the possible existence of the technological Singularity, which could alter the curve in unpredictable ways.

And, of course, human extinction would terminate the exponential growth — or its simulation.

References: Kurzweil Accelerating Intelligence

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