Rene Descartes is best known for his quote “I think, therefore I am,” which is at the core of his dualist philosophy. He argued for a theory of existence, where consciousness is a separate entity from the human brain. Essentially using logic to prove the existence of a ‘soul’. Since then other philosophers have challenged the logic that he used, and they in turn have been challenged.
Sean M. Carroll, a physicist at the California Institute of Technology discusses the improbability of a soul based upon an examination of physics in a post on his blog, Cosmic Variance, titled “Physics and the Immortality of the Soul”
He starts out by using an example to demonstrate the applicability of rigorous thought to seemingly impossible to prove theories.
By these standards, there is no controlled, experimentally verifiable information regarding whether the Moon is made of green cheese. Sure, we can take spectra of light reflecting from the Moon, and even send astronauts up there and bring samples back for analysis. But that’s only scratching the surface, as it were. What if the Moon is almost all green cheese, but is covered with a layer of dust a few meters thick? Can you really say that you know this isn’t true? Until you have actually examined every single cubic centimeter of the Moon’s interior, you don’t really have experimentally verifiable information, do you? So maybe agnosticism on the green-cheese issue is warranted.
Needless to say, no-one would suggest that the moon is actually made of green cheese. This is because we can apply our knowledge of how the universe is structured and it’s components interact to dismiss the idea without much effort.
The idea of a soul or extra-biological soul or consciousness can be approached in a similar manner. No matter what beliefs a person has about the dualist nature of life, it must be admitted that the human brain and body are comprised of a large number of atoms interacting in various configurations. This leaves us with the questions – what form would a soul take, what is it’s composition, and how does it interact with the matter of our physical composition? The existence of these particles or energy would require a shake-up of everything that is currently known about physics.
How is the spirit energy supposed to interact with us? Here is the equation that tells us how electrons behave in the everyday world:
Dont’ worry about the details; it’s the fact that the equation exists that matters, not its particular form. It’s the Dirac equation — the two terms on the left are roughly the velocity of the electron and its inertia — coupled to electromagnetism and gravity, the two terms on the right.
As far as every experiment ever done is concerned, this equation is the correct description of how electrons behave at everyday energies. It’s not a complete description; we haven’t included the weak nuclear force, or couplings to hypothetical particles like the Higgs boson. But that’s okay, since those are only important at high energies and/or short distances, very far from the regime of relevance to the human brain.
If you believe in an immaterial soul that interacts with our bodies, you need to believe that this equation is not right, even at everyday energies. There needs to be a new term (at minimum) on the right, representing how the soul interacts with electrons. (If that term doesn’t exist, electrons will just go on their way as if there weren’t any soul at all, and then what’s the point?) So any respectable scientist who took this idea seriously would be asking — what form does that interaction take? Is it local in spacetime? Does the soul respect gauge invariance and Lorentz invariance? Does the soul have a Hamiltonian? Do the interactions preserve unitarity and conservation of information?
The problem with ignoring this, is that the equation works. Not only is there no need to add another term to the equation, the equations works as it stands, Adding something new would mean that everything we know is wrong.
We can argue the concept of life after death and the existence or absence of the soul. We can debate the effect of these differing scenarios on individual morals and politics. However, Carroll’s questions about how such a force could interact with our existing atomic structure need to be addressed if any realist discussion of any part of us that could possibly live on after death is to occur.
Physics is not my field, but I am familiar enough with biology and chemistry at the atomic level to understand the gist of his arguments. It is quite reasonable to suggest that there is no evidence to verify Descartes ideas, in fact quite the opposite is true. It is time to drop the concept of dualism and live with realism.