Doctor Manhattan and Existence

"A live body and a dead body contain the same number of particles. Structurally, there's no discernible difference. Life and death are unquantifiable abstracts. Why should I be concerned?"

This quote was spoken by the character Doctor Manhattan from the graphic novel Watchmen. He had just witnessed a fellow ‘superhero’ fatally shoot a pregnant woman and, even though he could have, did not stop it from happening. Although he sounds completely inhuman (and in many ways is), Dr. Manhattan does make a good point. There is no structural difference between a dead body and a live body.

What he says about life and death being “unquantifiable abstracts” is very interesting. We cannot clearly calculate or measure them. How do we know we exist? There is no equation for proving that we do. True, most people argue that once our heart stops pumping blood to our organs we are dead. But what about the brain-dead? Is a person still considered alive if their brain will never function again? The amount of atoms they possess is equal to that of a normal, healthy human’s, but in essence they are vastly different.