The most successful scientific theory ever that gives us the most accurate predictions in all of science is quantum field theory. It says that particles and forces arise out of fields. When the fields vibrate, we observe those vibrations in the form of particles. Particles are made up of two kinds of fields, fermions and bosons. Bosons make up force fields. An example would be the Higgs field, which gives particles matter. Fermions make up the objects of matter that you and I are made of.
There are basically only three kinds of matter particles and three forces that you and I are made up of. Protons and neutrons, which make up the nucleus of atoms, and orbiting electrons, are the three matter particles. Then there are the three forces in the Standard Model: the strong and the weak nuclear force and electromagnetism. The strong force binds the nucleus of atoms together (and the quarks that make up protons and neutrons), the weak force allows interaction with neutrinos and are carried by W and Z bosons, and electromagnetism binds electrons with the nucleus.
Then there's gravity, for which we use the General Theory of Relativity to describe. Gravity is a very weak force and is very simple: everything pulls on everything else. It could be said that gravity isn't really a force per se, but is rather the curvature of spacetime. Regardless, it's just easier to describe it as a force. There are two other generations of fermions but they decay rather quickly and aren't particularly relevant for describing the stuff that you and I are made of and interact with.
So that makes up everything you experience in your everyday lives, without exception. When we combine all this knowledge into a single theory, we get what is called Core Theory. It was developed and named by Nobel Laureate Frank Wilczek. And there's an equation that describes Core Theory:
Within this equation lies the physics of everyday human experience: eating, exercising, sleeping, dreaming, using a computer, driving a car, flying an airplane, reproducing, making decisions, meditating — everything you've ever done, ever seen, or ever will do (so long as you don't travel into a black hole), and every scientific experiment that has been performed is fundamentally described by, and compatible with, this equation. There are no exceptions.
The key word above is fundamentally. That means that whatever you experience yourself doing or seeing in your everyday life is going to be either reduced to and explained by, or emerges from, the fermions and bosons described by this equation. But this means there are consequences to this equation. As all-encompassing as Core Theory is, what it restricts is perhaps the most important.
One of its consequences is that psychic phenomena like telekinesis is ruled out. There are no forces or particles that your mind can produce that can bend spoons or move objects. In other words, we don't need to test the claims of every self-proclaimed psychic and mentalist. Core Theory unambiguously rules out such abilities. There's no way for there to be forces that can produce the kinds of effects mentalists claim they can cause. There's no room with in Core Theory to allow that. It isn't that we don't know of possible forces that might still exist "out there" waiting to be discovered that can allow spoon bending with one's mind, rather it's that we know all the relevant particles and forces and how they interact that are involved with the physics of everyday human experience, which telekinesis would be a part of. Any new force or particle that exists would be far too weakly interacting with the atoms that make up spoons or you and I to be able to effect them in any way like the mentalists claim they can do. This is why no psychic phenomena has ever been able to be demonstrated under any competent scientific scrutiny.
How confident can we be about this?
crossing symmetry gives us further assurance. Crossing symmetry says that if one field can interact with another one, the second field can produce particles of the first one. This means that if there were a new particle or force that could interact with the stuff that we're made of, it would be able to be created by the annihilation of a particle and its antiparticle, due to the fact that in quantum field theory every particle has an antiparticle with an opposite charge. More simply: if a new particle can interact with ordinary particles, then that particle can be created in high energy collisions. We've tested collisions of particles and their antiparticles with enormous energies and no new particles or forces were found. This rules out all possible new particles and forces that can interact with people, animals, or inanimate objects made of atoms that is in any way noticeable or detectable.
Many people will want to insist that there's still something "out there" that can rescue the possibility of psychic and spiritual phenomena, but their hopes will be futile: all possible routes are shut off. Rather than respond dispiritingly, we should rejoice in such a triumphant intellectual achievement: The laws of physics underlying everyday life are completely known.
Given the truth of Core Theory, which every experiment every done is compatible with, there are further consequences for one's worldview. And that is, in what worldview are the reality and consequences of Core Theory most compatible with? Naturalism or theism? I'm going to argue that naturalism is by far more compatible with Core Theory than theism is. But first we must consider those consequences once again.
If all particles and forces that can have any effect on the atoms that make up your body are already accounted for within Core Theory, and no other ones are possible, then this also means any non-metaphoric account of the soul is ruled out as well. This includes any account of a soul involved in substance dualism, as well as any account of a soul from Thomistic metaphysics based on formal causes. Why? Because any non-physical thing that can have any effect on the atoms that make your body are unambiguously ruled out. That's the most relevant consequence of Core Theory.
No Cartesian soul—or whatever else you wanted to call it by—that existed under any framework of substance dualism, as well as any non-physical thing like a formal cause, could effect the body in any way that's required by these versions of the soul. Everything involved with all of your behavior, including all of your decision making, is fundamentally physical and compatible with Core Theory which leaves no room for a soul. And if there's no soul of any kind, that's what we'd expect on naturalism and not on theism, since theism entails a non-physical dimension that can have causal effects on the physical world, namely, god, but also one's soul. And all the major religions of the world posit a non-physical dimension that has causal impact on the world. If this is ruled out, it makes those religions and the gods that exist within them at the very least substantially less probable, and at the very most completely falsified.
So we can argue:
1. Any non-metaphoric version of a soul requires a force that has to be able to effect the atoms that make up your body (lest our bodies and behavior be fundamentally explained purely physically)
2. Core Theory rules out any possibility of particles or forces not already accounted for within it that can have any effect on things made of atoms (like people).
3. Core Theory is true.
4. Therefore, no non-metaphoric versions of a soul that have effectiveness on things made of atoms exist.
5. Naturalism entails that there be no souls that have effectiveness on things made of atoms.
6. Almost every version of theism does claim human beings have such souls, including every major religion.
7. Therefore, the probability of Core Theory and naturalism is greater than the probability of Core Theory and theism. All things being equal, this makes naturalism more likely than theism.
In other words, the probability of Core Theory being true on naturalism is greater than the probability of Core Theory being true on theism. It's more expected. This is thus an evidential argument, not a logical argument. Where CT=Core Theory, N=naturalism, and T=theism:
Pr(CT ⋀ N) > (CT ⋀ T)
Or more simply:
Pr(CT & N) > (CT & T)
So what can the soul-believing theist do?
Not much. They can deny the truth of Core Theory or its implications. But that will be a very difficult battle. I can even grant that there's a soul force "out there" for the sake of argument, but it will have to be too weakly interacting to have any effect on human behavior. They can insist there's some unknown layers if reality more fundamental than that which we can detect that explains the soul's interaction with the body. But again, they would have to be too weakly interacting to effect human behavior, and as such, it would be explanatorily impotent.
Any soul that exists would have to be epiphenomenal: causally impotent in the same way the naturalist will view the mental. Naturalism is the view that the physical exists (the spatiotemporal world) and if the mental exists it is explained by the physical. A naturalist can technically be a platonic realist but will agree that numbers have no causal effectiveness. But a causally impotent soul is almost worthless, as almost every version of theism—certainly every popular version, insists that our soul explain human behavior to some degree, ie. it has causally effectiveness on the human body.
One can believe in a god of course and not believe in a soul. Nothing about theism necessitates that humans have a soul. There's no reason why a god couldn't create a purely physical universe. But since most religions and most versions of theism posit a human soul, this argument from Core Theory severely hampers their plausibility. At the very least it forces any logical theist to think of a soul as a metaphor, or an epiphenomenon.
Objections to Core Theory's claim that the laws of physics underlying everyday life are completely known were mostly handled by Sean Carroll on his blog. He's one of the biggest proponents of the consequences from Core Theory, and was the inspiration of this argument. I highly recommend you read his post before making an objection, as it will likely be answered.
One common rebuttal will object to the theory's truth by saying it doesn't explain dark matter or energy, which make up 95% of the universe (!). What's important here is the notion of a theory's domain of applicability. Since we don't have a theory of everything, all of our existing theories apply to certain domains. Newtonian physics applies to objects with relatively low speeds. Where it breaks down at high speeds you need special relativity to take over. Where special relativity breaks down, like with accelerating frames and strong gravitational fields, general relativity takes over. This is the theory's domain of applicability. Theories are correct in their domain of applicability, but not outside their domain. Core Theory's domain of applicability is the everyday life humans experience on earth, including everything we've ever done and experienced. It doesn't apply to events inside black holes, or on extremely large scales where dark matter and energy are relevant. Those domains are outside of reach of the everyday human experiences, so they aren't relevant. Dark matter and dark energy are two weak to affect us in our everyday experiences. The human soul—if we had one—would fit into the domain of everyday life.
Another objection perhaps more relevant is that Core Theory doesn't explain consciousness. But whatever consciousness is and is ultimately explained by is going to have to be compatible with Core Theory. Or else quantum field theory, the best tested scientific theory ever, is in correct. But we have no good reason to suspect that. No explanation of consciousness that involves a soul or mind that has any influence on the atoms that make up your brain or body is allowed. Consciousness is most likely an epiphenomenon that's an emergent property of particular complex physical processes. In other words, the mental is explained by the physical, which is exactly what naturalism posits. Such a view is compatible with Core Theory.
So what do you think?
Does this argument work? Does it demonstrate a greater probability of naturalism over theism? Does theism have a hard time explaining this? And are theists forced to think of the soul only as a metaphor or an epiphenomenon because of this? Are religions like Christianity, Judaism, and Islam ruled out, or at least made extremely less probable?
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