I have an opinion. As a spiritualist by faith - I believe in the existence of the soul and spirit entities. I've been trying to figure out how to reconcile these things with the laws of physics, particularly quantum mechanics. Neurobiology seems to be able to explain a whole range of cognitive events and behaviors as just parts of the brain that interact with each other in this electrochemical storm we know of as consciousness. Since the brain can become non-functional and die, it is a real downer to an otherwise good life. Ever optimistic, the question becomes: how could quantum mechanics save our consciousness in some disembodied spirit existence? Well, if you're OK with some loss of cognitive precision, there is a way.
As human intelligences, we are very accustomed to our states of consciousness (joy, love, anger, curiosity, annoyance, serenity). To emphasize, those are just states of consciousness. Of course if we died and became a spirit, but couldn't remember uncle Lewie who died when we were young, but was so fun to be with when he was alive, then it just wouldn't be as blissful as all those near death experiences that people describe. Thus a spirit has to encode some memories (even if they are a bit fuzzy). It's the particular emotions that you want to recall as a spirit entity.
Quantum entanglement suggests that wave-functions might have a real existence (be part of reality) even if they are not physically detectable. This is good news. If small things like particles were made of hard spheres, there would be no wiggle room. But every quantum system has a wave-function that describes its collection of states that a particle might be detected in. The mathematics of describing a two particle quantum system is difficult; if we wanted to describe a quantum system (like a brain) with 10^26 particles, it might be impossible. Nevertheless, there is probably a naturally occurring wave-function for it anyway.
A spirit, if such a thing exists, could be thought of as an elaborate wave-function. We worry about whether or not we have free will. That's equivalent to a spirit choosing a particular state to be in (which is all about mental discipline and will power). An electron will generally fall into a particular quantum state in some random way. But a spirit might be able to resist the whimsical choice based on how it feels, and choose to do what is right (for example) instead of what is easy or convenient.
It might be impossible to prove the existence of a soul or a spirit just as it is impossible to prove the existence of a wave-function. The soul and spiritual entities would simply be more intricate patterns of wave-functions just as particle physics/atomic physics/chemistry/organic chemistry/biochemistry and biology are more intricate patterns of quantum particles.
The wave-function is a naturally occurring phenomena that makes available a bunch of states that energy (photons or other quantum particles) can occupy. Presumably, there is another naturally occurring phenomena of nature that can influence the likelihood that a particle will transition from state 1 to state 2. At the most basic level, that's you're space-time. There are probably unimagined ways (extremely advanced technology) to compel the particle to move to the state you want. We'll probably get into designer forces to overcome entropy.
