The common theory of perception is based on the philosophy that there is an external world that is real to which we react - however that is an Aristotlean (look him up you stupid lazy kids) dictatorship which is imposed on the masses who reside inside the educational system and have come wired up to it like humans wired up to the matrix.
In reality, considering the state of perception it is perfectly possible to perceive virtually anything, and believe any construct or effect that arises from the actions which inevitably arise as consequences of those perceptions.
In other words: what you believe, you become.
It goes ever deeper than this, but you really do have to take the initiative and step outside of the box of your conventional thinking if you want to experience it for yourself.
External perception: "There's something out there.. it is real. I should conform to that something at all times."
Theoretically this means that anything is possible, but it does not mean that there will be no challenges.