I've always found the brain in a jar theory quite appealing, albeit somewhat disturbing. The basic idea is that we cannot prove or disprove that we wouldn't be some kind of brain-like mass floating in a jar or a vat, while being fed reactive external stimuli that renders a world to us while we really exist in a higher metalevel. Basically it boils down into "reality is a simulation", for example ála Matrix in popular culture. I do believe reality is subjective regardless of whether such a meta-transition simulation exists or not. I might even argue that our own brains are our own recursive simulation, not just in its conventional definition. There are a number of psychological experiments that show that our own brains fill in gaps in our reality and extrapolate our senses, such as the phantom limb and patterns in chaos.
What has always bugged me though, is what could possibly be the purpose of such higher layer simulations? I think most implicitly assume that this higher metalevel reality obeys the same laws of physics, and even social structures, as our human society. Therefore, we usually imagine some human scientist cruelly experimenting on a sentient mass, in order to find out whatever phenomena they're studying. Really though, I think this assumption would be likely false - if reality really was or is a simulation, I think it's non-sense to assume it'd obey e.g. the same laws of physics as ours. Things could be pretty wacky out there.
However, let's assume for a second that this higher metalevel of reality does follow our rules and norms. It's an intriguing thought experiment to try think of "realistic" scenarios why this then would happen.
I fancy one such idea of my own, somewhat ambitiously dubbed Interdimensional Job Interview. Suppose we do live in this higher metalevel, and we do have some say in our interactions there-in. We're in the line applying for say, a government job on planet Splorg for our species Z'cthun. We signed consent that we subject ourselves to a though-process interview, simulating our actions on planet Earth under controlled environment in order to assess our suitability for the job. Stuff like psychologists might do these day for companies - psychological profiling, just more sophisticated. Or twisted. Whatever, too late to question now, we signed consent and an essential part of the profiling is that we cannot be aware of our own testing environment.
It'd be kinda funny to then be pulled the plug eventually, and have our report splurted on our face: "Sorry Zr. (gender-pronoun of my choosing for my supposed personality Futz'gn Z'cthun-Norg), it appears that you pose too great desire to develop delusional greater purposes where none lie, thus you could possibly endanger our institution should you work for us. I'll therefore have to let you go this time, but we'll stay in touch. Thanks for applying, please take a free pen on your way out." Wouldn't that just be lovely.
As for our currently potentially on-going simulation, the question is somewhat relevant to a potentially lower metalevel. We can play around with the idea in principle, and should, as it is relevant for us to question: what should we be simulating, just because we seem to be able to simulate our own species in vitro? Might we eventually become the monsters, under whose shadow some of us fear of living in?
