Imagine you are dead, in which case the biological machinery that you once relied so much on is no longer functioning. Due to the conversation of energy and mass, the atoms made up this biological system won’t just miraculously vanish. Theses atoms would remain pretty much the same, unless nuclear reaction or annihilation occurs (though there’d be changes in the configuration of electrons in the process of decomposition). At this point in time, it would be silly to still consider these atoms “you”.
But what are actually “you”? How should “you” be defined?
To people around you, you are a concept they conceived in their mind based on their interaction with the being labeled “you”, and the information they have about this being. To them, you are a construct of their own ideology. This version of you sometimes reflects the rose colored lenses through which they perceive the world a lot more than how it would reflect anything about the being labeled “you”.
To yourself, on the other hand, you are what that constitutes the idea of self. Apparently you possess a body, but the body is not what you identify you with when you think about you at a deeper level. You may incline to think that you are what that controls the body, makes decision, etc, that is, the conscious mind. But let’s for a moment remember that the brain is responsible for the construction of thoughts and it governs how the mind processes, similar to how the computation performed by a Turing machine is governed by its transition function in relation to its states. So a question arises:
What determines you to be the mind A that's constructed by brain A, instead of the mind B constructed by brain B, where A ≠ B?
I shall now present to you the Theory of The Observer.