Of all our learning of the natural world we have come up with many universal constants. How things interact and such. Whos to say we couldn't make a computer program with these laws in a space and let it go. Disregarding the fact that the memory and computation speed of the computer would be enormous. But wouldn't you be able to learn from this and play around with it until we discover new things out there. And if the program didn't end up like our universe then we know we would be missing many parts.