In the popular science fiction film The Matrix, reality as perceived by humans in the future is actually not real but a virtual, simulated world created by machines to subdue and control the human race. The film plays with the strange idea that we humans may have become an integral part of a purely fictional computed reality and that we exist inside a computer simulation.
Surprisingly, a number of serious scientists have recently suggested an even more far-fetched theory along the lines of The Matrix: they claim that everything in our universe is just the output of a giant digital computer - including us humans.
Such ideas and suggestions may be appropriate for Hollywood movies, but how can this be a serious scientific approach?
The supporting arguments for such counter-intuitive theories come from modern quantum physics. Dr Seth Lloyd, a professor at the Massachusetts Institute of Technology in Boston and one of the inventors of quantum computers, thinks of atoms as containers of bits of information. For example the charge of a particle may be positive or negative. This can be considered as equivalent to digital values like one or zero. Whenever two atoms interact, they may or may not change the value of their bits from one to zero or vice versa (for example change the positive to negative charge). According to quantum theory these properties only change in discrete quanta, not in fractions of quanta. Therefore, this changing of bits caused by the interaction of atomic or nuclear forces can be considered as a form of digital computation.
That covers the 'hardware' of the universe, the underlying particles that perform the computations. Is there an equivalent to 'software' as well in our universe? Yes, according to Lloyd, there is. The software or 'program' that runs the actual digital universe is simply the laws of physics dictating the way atoms interact with each other.
So far, so good, but what does the universe actually compute? The answer is again simple and straight forward: it is the universe itself. The universe is constantly computing each particle's new state and hence continually evolving according to the laws of physics and will do so until the end of time and along the way it is creating the expanding universe as we know it. The number of computational steps the universe has already executed/calculated since the big bang has been estimated to be approximately 10,120 steps in total so far; that would be - give or take - 1,020 to 1,030 steps/computations for each atom in the universe on average.
Stephen Wolfram, another quantum physicist and the famous inventor of the Mathematica program, goes even further with this idea. In a recent speech given at a major science conference earlier this year he conceptualised our universe to be basically just a specific example of actually a relatively simple type of computing device, a so-called cellular automata.