"The problem is, we discovered how to control the human brain in totally arbitrary ways, build and grow new ones, squish them together, etc etc, but we also discovered how to make new physical laws, teleport things, make matter at a distance, etc etc.  And we were fighting secret military battles while we did it.  So now we can't quite tell which one we are doing, for sure: giving your brain an exotic light show, or actually making that exotic light show around you.  Still, the park is broken into two categories: unbelievable experiences of the mind, and provable experiences of reality that your mind will never believe is real.  The first question is, what do you need to experience to know that the physical things, which are actually real, aren't one of the neurological tricks?"