If the Matrix left you with the niggling fear that we might indeed be living in a computer generated universe staged by a malevolent artificial intelligence using the human race as an energy farm, help is at hand.
Silas Beane of the University of Bonn, Germany, and his colleagues contend that a simulation of the universe, no matter how complex, would still have constraints which would reveal it.
All we have to do to identify what these constraints would be is to build our own simulation of the universe, which is close to what many researchers are trying to do on an incredibly miniscule scale.
Computer simulations have been run to recreate quantum chromodynamics - the theory that describes the nuclear forced that binds quarks and gluons into protons and neutrons, which then bind to form atomic nuclei.
It is believed that simulating physics on this fundamental level is equivalent, more or less, to simulating the workings of the universe itself.
The idea that we might be living in an artificial reality constructed by something higher than ourselves has been a recurring philosophical hypothesis for centuries. Plato's Allegory of the Cave, Descartes' evil demon, Putnam's brain in a vat -- these are all variants of justifications for solipsism, a philosophical idea that says it's impossible to know with any certainty whether the world as we experience it is "real" or a simulation projected by some external entity. Keanu Reeves' character Neo in The Matrix opts for a dose of reality when he chooses to take the red pill, but figuring out whether our universe is "real" or not is a touch more complicated than that.
It shouldn't be surprising that simulating the universe would take up a lot of processing power, since the universe is exceedingly large (and then some). Currently, if we wanted to simulate quantum chromodynamics -- the rules which give rise to the strong nuclear force, which binds protons and neutrons together in atomic nuclei -- we can only manage it on the scale of femtometres (millionths of a nanometre). That's not even close to the level of detail needed for even the smallest microorganisms, let alone planets, stars and galaxies.
What we do know, though, is that when we create such a simulator, there's some kind of underlying lattice that holds everything together like a kind of framework. Think of it as the smallest scale at which a simulator runs -- like the way a grid divides up the playable space in a chess game. You can't move a piece less than one grid space.
If we were living in a simulator, we'd expect to find evidence of that lattice if we looked close enough to the edges of the observable universe -- and that's what Silas Beane from the University of Bonn and colleagues have calculated, in a paper published in arXiv. As cosmic particles fly through the universe, they lose energy and change direction and spread out across a spectrum of energy values. There's a known limit to how much energy those particles have, though, and Beane and his colleagues have calculated that this seemingly arbitrary cliff in the spectrum is consistent with the kind of boundary that you'd find if there was an underlying lattice governing the limits of a simulator. It should also, if present, scatter the particles in a certain way as they come up against it, and we should be able to investigate whether that's the case.
If such an investigation does look consistent with a simulator lattice, then that could mean several things. It could show us that there's a boundary out there consistent with Beane et al's hypothesis, and it works a bit like the one we'd expect if we were living inside a simulator based on the same principles as one we would also build. It could be, though, that we're incorrectly interpreting evidence of certain fundamental laws we are as yet unfamiliar with. It could even be that this isn't evidence at all for a simulator, as a real lattice might work in a different way to how we would envision it.
Frankly, we don't know yet. It's a bit like sitting really close to the TV when you're a kid and being able to pick out all the pixels -- we just have to hope the universe doesn't have a retina display ( via dailymail.co.uk ).