More eloquently:
Once upon a time, two Serious Minded people were in their local pub, having a few pints, and talking about the nature of the Universe.
Bill pointed out that most of what we consider "matter" is made up of empty space. The distance between a nucleus, its electrons, and the nearest adjacent atom is comparatively large; why, that barstool over there shouldn't even be considered a solid!
Joe responded, "But wait. As far as we can actually prove, that barstool might simply be a hallucination, for we're not actually seeing the barstool, we're processing electric signals in our heads generated by our optic nerves. And all they are doing is claiming certain wavelengths of light have bounced off an object. But what if the nerves are misfiring, which we all know happen quite often? So, we can't really say whether or not the barstool even exists!"
Just then, a man approached them and said, "I couldn't help but overhear you two talking. If I may, I have an experiment for you. Purely in the interest of a Deeper Understanding of the Universe."
He then proceeded to pick up the barstool and pummel both Bill and Joe squarely about the head and torso, yelling "I REFUTE IT THUSLY".
Thus endeth the Discordian Parable.
It's possible we live in sort of hyper-advanced computer simulation; it's possible we're just brains in a vat with all the sensory data we perceive being fed to us. The point, though, is that it doesn't matter. These situations are nothing more than philosophical masturbation, as we'd never be able to prove any of these ideas (and if we somehow did, it likely wouldn't matter).
Reality is whatever can raise a lump on your skull.