The First Law of Thermodynamics
The law of conservation of energy states that the total energy of any isolated system (for which energy and matter transfer through the system boundary are not possible) is constant; energy can be transformed from one form to another, but can be neither created nor destroyed.
All matter is energy slowed down.
E=mc2
Inside a closed system (e.g. the Universe) that which is must have always been. Something cannot come from nothing. Something cannot become nothing. All things are energy. That energy changes form as conditions change.
From a psychological standpoint, there is no "I". The "I", or "Ego" in Latin, is a fictional construct created by the brain as a defense mechanism for the body. "I" really don't exist. Consciousness interprets the Universe through the illusion created by the brain in my body (5 senses).
Therefor, in a sense, I have always been. Bodies come and go as all systems deteriorate in the cycle of life. I think of our brain as a radio that is tuned to pick up consciousness. If my radio breaks or the power goes out the radio signal is still there.