This article is a pretty good overview of some of the wilder theories at the edge of physics, where cosmology and particle physics meet each other. You’ll read things like:
These theoretical universes range from vast bubbles far, far away to hyperdimensional sheets hovering right in front of one’s nose.
Strings that get entangled in space early on can be stretched out by cosmic expansion to become hyperdimensional “branes.” A brane may, in Greene’s words, resemble “a gargantuan flag whose surface extends indefinitely.”
I can attest that you need a lot more than undergraduate physics for any of this to make sense – although in my coursework I did once cite a paper titled “Towards a naturally small cosmological constant through branes in 6D supergravity.” That didn’t mean I understood it.
Anyway, there is a little bit of this article that’s not too difficult to grasp, although you risk spraining your mind when you do so. Consider the fact that computers are already pretty good at simulating a lot of physical, chemical and biological systems, in a basic sort of way. Also that the amount of computing power available for a fixed cost is increasing exponentially with time (i.e. a computer bought today is twice as powerful as one bought roughly eighteen months ago for the same price), meaning that our capacity to run these simulations is also growing extremely fast. It seems reasonable to suppose that some time before too long, it will be feasible to create computer simulations of intelligent beings, along with simulated worlds for them to live in. We then have to ask: would these simulated beings believe themselves to exist in some sort of objective reality? There would be nothing stopping us from programming them to believe such a thing. We therefore have to consider the possibility that our own reality is merely a simulation being run by some higher intelligence (that would solve the God thing, huh?).
But, it doesn’t stop there. What with the continuing fall in the cost of computing power, in time the capacity and facility to run these simulations would become available to governments, large companies, universities, research groups, eventually even individuals. It is likely that there wouldn’t be just a few simulated realities being processed inside computers – there would be very many of them. Given a universe in which the majority of experienced realities are in fact simulations being run inside computers, we have to accept that the most probable state of any experienced reality is that it’s actually a simulation – and that goes for ours as well. The article puts it like this:
Nauseatingly claustrophobic and difficult to disprove, the simulated multiverse may be more a philosophical curiosity than a scientific hypothesis, but it’s hard to get out of your head.
And leaves it at that. I just wonder, though. Is it possible to design an experiment that would test whether our reality is in fact a simulation? I mean, you’ve got Bell test experiments, that can be used to show that “local hidden variable” theories do not explain quantum mechanical interactions. I would never have though it possible that something defined as hidden could be shown not to exist by an experiment, but it’s sufficiently easy that I did it in a lab about seven years ago. Get to work, science folk!