New York Times science section:

In fact, if you accept a pretty reasonable assumption of Dr. Bostrom’s, it is almost a mathematical certainty that we are living in someone else’s computer simulation.

This simulation would be similar to the one in “The Matrix,” in which most humans don’t realize that their lives and their world are just illusions created in their brains while their bodies are suspended in vats of liquid. But in Dr. Bostrom’s notion of reality, you wouldn’t even have a body made of flesh. Your brain would exist only as a network of computer circuits.

I don’t quite understand the math, but basically, some think that by 2050, computers will have processing capabilities so powerful that they will rival that seen in The Matrix.  Computers, through their programmers, will be capable of creating virtual humans, possessing virtual nervous systems, living in virtual worlds, with a virtual "past" and ancestry.  Kind of like The Sims on superhyper steroids.  Endowed with artificial sentience, these "posthumans" won’t have bodies, but only the microchipped sense of having bodies.  The virtual humans will have a sense of their own selves and the world around them, just as we do.  They won’t know they are merely a flow of 1’s and 0’s.

Of course, once you comprehend that (and really, it’s not hard to do), then it’s a small step to ask: "How do we know that we’re not all ‘virtual humans’ now?"

The author of the NYT piece then wonders what happens once the virtual humans realize that they (we?) are, indeed, not real:

If simulations stop once the simulated inhabitants understand what’s going on, then I really shouldn’t be spreading Dr. Bostrom’s ideas. But if you’re still around to read this, I guess the Prime Designer is reasonably tolerant, or maybe curious to see how we react once we start figuring out the situation.

Yeah, I hope the Prime Designer is tolerant.  Let’s hope he doesn’t pull the plug.  I’m too young to be deprogrammed.