What does it matter if two brains are isomorphic, or quasi-isomorphic, or not isomorphic at all? The answer is that we have an intuitive sense that, … - Douglas Hofstadter

Perhaps the greatest contradiction in our lives, the hardest to handle, is the knowledge 'There was a time when I was not alive, and there will come a time when I am not alive.' On one level, when you 'step out of yourself' and see yourself as 'just another human being', it makes complete sense. But on another level, perhaps a deeper level, personal nonexistence makes no sense at all. All that we know is embedded inside our minds, and for all that to be absent from the universe is not comprehensible. This is a basic undeniable problem of life...

Think of a dentist who has a list of
patients, and for each patient, a list of teeth. It makes perfect sense (and
plenty of money) to hold the patient fixed and vary his teeth-but it makes
no sense at all to hold one tooth fixed and vary the patient. (Although
sometimes it makes good sense to vary the dentist ... )

that the key is not the stuff out of which brains are made, but the patterns that can come to exist inside the stuff of a brain.