What we've traditionally called 'our universe' is just a tiny part of something which is infinite, so allows for many replicas of us elsewhere (in our same space-time domain, but far beyond the horizon of our observations), but even that infinite universe is just one element of an ensemble that encompasses an infinity of quite different universes. So that's the pattern adumbrated by cosmology and some versions of string theory.  What we have normally called the laws of nature are not universal laws—they're just parochial by-laws in our cosmic patch, no more than that, and a variety of quite different regimes prevail elsewhere in the ensemble.

One thing which struck me recently, and I found it a really disconcerting concept, was that once we accept all that, we get into a very deep set of questions about the nature of physical reality. That's because even in our universe, and certainly in some of the others, there'd be the potential for life to develop far beyond the level it's reached on earth today. We are probably not the culmination of evolution on earth; the time lying ahead for the earth is as long as the time it's elapsed to get from single-celled organisms to us, and so life could spread in a post-human phase far beyond the earth. In other universes there may be an even richer potentiality for life and complexity.

Now life and complexity means information-processing power; the most complex conceivable entities may not be organic life, but some sort of hyper-computers. But once you accept that our universe, or even other universes, may allow the emergence within them of immense complexity, far beyond our human brains, far beyond the kind of computers we can conceive, perhaps almost at the level of the limits that Seth Lloyd discusses for computers—then you get a rather extraordinary conclusion. These super or hyper-computers would have the capacity to simulate not just a simple part of reality, but a large fraction of an entire universe.

And then of course the question arises: if these simulations exist in far larger numbers than the universe themselves, could we be in one of them? Could we ourselves not be part of what we think of as bedrock physical reality? Could we be ideas in the mind of some supreme being, as it were, who's running a simulation? Indeed, if the simulations outnumber the universes, as they would if one universe contained many computers making many simulations, then the likelihood is that we are 'artificial life' in this sense. This concept opens up the possibility of a new kind of 'virtual time travel', because the advanced beings creating the simulation can, in effect, rerun the past. It's not a time-loop in a traditional sense: it's a reconstruction of the past, allowing advanced beings to explore their history.

All these multiverse ideas lead to a remarkable synthesis between cosmology and physics...But they also lead to the extraordinary consequence that we may not be the deepest reality, we may be a simulation. The possibility that we are creations of some supreme, or super-being, blurs the boundary between physics and idealist philosophy, between the natural and the supernatural, and between the relation of mind and multiverse and the possibility that we're in the matrix rather than the physics itself.

Once you accept the idea of the multiverse, and that some universes will have immense potentiality for complexity, it's a logical consequence that in some of those universes there will be the potential to simulate parts of themselves, and you may get sort of infinite regress, so we don't know where reality stops and where the minds and ideas take over, and we don't know what our place is in this grand ensemble of universes and simulated universes.


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