Then I logged into LambdaMOO. Almost everything I'd ever read about MOOs was about this one, so I decided to try it out, with the mindset that I was going to walk in without any preconceived notions, and see what would happen. I walked into the living room and was greeted by almost everyone there. Everyone seemed eager to help me get oriented. And as I explored the house I saw more and more things. I saw items that had been dropped by other players. I found a cat that was wandering around that I picked up and brought back to the main room. I dropped the cat off and the other occupants of the room proceeded to play with the cat.
There was no doubt in my mind that these people, while perhaps not actually fooled into thinking that they were sitting in that large house, were sharing a real experience.