@marcporcel
Not to rain on your parade, but a Doctorate in Metaphysics is the literal equivalent of filling out an essay and mailing in a check. There is no recognized institution that issues these. They're all pretty much "self issued".

Metaphysics is a polite term for bullshit that uses terms from physics.

What your friend is claiming as a postulate in Quantum Physics regarding a soul, is actually a type of thought experiment called an "absurdism".

You take the least likely thing to be true and begin to attack it.
In this case the thought is experiment is called "Quantum Suicide".
Here is how it goes...

John Doe was seriously depressed, and decided to end his life.
He loaded a six shooter revolver with six bullets, put the gun to his temple and pulled the trigger.
The gun failed to fire.

He did this again and again, each time the gun failed to fire.

Eventually he gave up in frustration and went to see his local Quantum Mechanic, Eve.
Eve examined the gun, finding it in working order. She pointed it at John and pulled the trigger.
The gun fired this time. John collapsed dead.
Eve had a shiny new gun.

John's ghost returned and asked what happened.
Eve explained that what really happened, is that under the many-worlds interpretation of Quantum Mechanics; at each point where he attempted suicide, time diverged.

The whole universe went in two or more different and mutually exclusive directions. In one direction John had died, in the other direction the gun failed to fire.
The direction where the gun went off, resulted in the man's death each and every time.

He was no longer aware and thus for him, it was game over.

But in an alternate reality he survived, only to try and fail, again and again.
Our John had just been incredibly lucky up to this point.
He had achieved Quantum Immortality only because he couldn't collapse his own wave function. He was "unable to observe himself" without interference.

John's ghost disappeared in a puff of logic leaving behind a very scared cat who immediately hid in the box in Eve's garage.

This explanation is a consequence of the Multi World Interpretation applied to Schrodinger's cat.
Schrodinger's cat exists as a retort to the Copenhagen interpretation of the Schrodinger wave function which is used to explain the observed phenomena of wave/particle duality.

MWI exists to solve the various time travel related paradoxes inherent in the time symmetry of all the equations we have describing the laws of physics.
Put another way, time travel is possible. Time travel is actually mandated in certain circumstances.
Yet just like the Fermi Paradox attempts to ask why we see no aliens if the Universe is abundant with life, there is a corollary paradox that says if time travel is possible at all, there should be time travelers going back in time to kill hitler every day or so. So why is Hitler still in our shared causality?

MWI says that for each quantum event a new Universe is spawned. This is a lovely theory but unless you accept creation exnihlo, then you have to ask where did the energy come from? You really ought to see the energy density of the Universe decreasing each time one of these events occurs. Yet it isn't. In fact it's increasing and it's increasing at such a rate that we may only have 20 Billion years left before the expansion of the universe is supraluminal. This would be the big rip and it's probably a bad thing.

Final thoughts...