It's funny that you ask this question because I was just thinking about that yesterday. I posted something about it on the Crazy Stoned Idea Thread in the Experiences forum. When I was a kid I got this idea that maybe I had just been created a second earlier and all my memories had been implanted into my mind. I thought maybe all the past didn't really exist or maybe the reality I percieved wasn't actually real.

I had this idea before I had seen any movies about memory implantation or virtual reality. When I saw Blade Runner, I loved it. Part of the reason I liked it so much was because of the androids (they call them replicants in the movie) and the fake memories that they give them. The replicants only live a few years, so they ease them into their lives by giving them the fake memories. By the end of the movie, you are not sure if maybe the Deckard character, the main character whose job it is to hunt down and kill escaped replicants, is maybe himself a replicant. It is a great movie.

One of the things about these kinds of questions is that you will probably never know for sure the answer. It's more of a philosophical than practical question. From a practical point of view, you have to live your life like the past is real and that reality as you experience it is real.

It's the difference between subjective reality and objective reality. Subjective reality is the reality that you personally experience. Objective reality is the reality they way it actually is, independent of how you experience it. So maybe the objective reality is that the universe was formed in a Big Bang 15 billion years ago and has played out since then according to the laws of physics, or maybe the universe was created a second ago and all your memories were implanted into you, or maybe the universe is the dream of some super stoned alien, or maybe it is all just a virtual reality program or hologram. But your subjective reality is that you were born, you lived your life to thie point, you have your memories and the experinces that you have every day --- from a practival point of view, you have to live based on that subjective reality. But that doesn't mean it's not interesting to speculate about the nature of the objective reality!

Another intersting question is if the universe was just formed and your memories implanted, what is the purpose? Who did the implanting and why? Are they trying to trick you? Is it some kind of test? If you ask too many questions will they just erase your mind? Be careful!