A modern, secular argument for the immortality of the soul

I had meant to write this post a few weeks ago as an Easter/Passover/etc. present for my religious friends, but the first half of this quarter’s been pretty crazy. Anyway, here it is, better late than never!

We normally associate arguments for the immortality of the soul with the likes of Plato [1], Aquinas [2], and other ancient thinkers. Their proofs almost always implicitly or explicitly relied on certain religious assumptions, such as belief in a god, or at least of a kind of eternal,intangible, spiritual element to human existence. It seems impossible to argue for an immortal soul without relying on such assumptions, but that is exactly what I will attempt to do here. My argument should be just as believable for a religious person as it is for the most atheistic of atheists.

What is a soul?

That’s right Mauricio, what is all this talk of souls? Isn’t that already a religious notion? Well, it normally is. Here I will be using a somewhat different definition, with no religious or spiritual content.

The human soul

What is the essence of what we normally call a ‘soul’? It is a certain principle or thing which senses, acts, remembers, and thinks (many people, following Descartes [3], think of it as only a thinking thing). Many people think of it as being a kind of spirit, others think of it as a brain or mind. But what form it takes is not essential to what it is. If every human had a little blue baseball cap that was the source of all our thoughts and actions, we would probably call that our ‘soul’. So, since the actual form of the soul is merely accidental to it; what really defines the soul is its ability to sense, remember, cause our actions, and think.

All of these abilities and all our memories are encoded in our brains. If you really want to you can believe that there is some kind of spirit hovering around you or whatever, but the fact is that everything we do, think, say, or feel is causally reducible to some brain process. Even physical things, such as our body parts, are unnecessary parts of these abilities. One might think that you need eyes to see, but the eyes are not part of the soul, only the ability to receive impressions from the senses. Nor are our vocal chords part of the soul, but the ability to communicate. Similarly with every other part of our bodies, even the brain. Yes, the brain is where all these abilities are physically stored, and we have no way to ‘copy’ all our memories and thoughts out of our brains in practice (yet); but it should be clear to everyone that the brain is not the abilities, but it’s merely a receptacle for them.

The best analogy for this is a computer. Imagine I have Windows, or any other piece of software installed in my computer. It is clear that the computer is not the software, but it contains it. The physical hardware is what makes the software useful to me, in a sense, but the software exists independently of the hardware. Having a movie stored in a DVD may be useless without a kind of computer to read it and show me the movie through a screen, but the movie itself exists independently of the existence of any hardware capable of showing it.

Similarly, we can think of the brain as the hardware to the soul’s software. That is, the soul is a kind of algorithm. A series of stored memories, rules to receive impressions from the senses, rules to react to these senses. It may seem to us that human nature is not as deterministic as your usual computer algorithm, but it is still reducible to the same kinds of rules and principles. When my hand gets burned, I feel the pain, and I pull it away. This is a very simple example, but one can imagine how it can be extended to all kinds of human experiences. When I see a loved one catch a cab to the airport, all kinds of principles and memories cause me to feel sad, to cry, to wave goodbye; and then store the impressions of the event forever in my memory. This is a much more complicated process than anything a modern computed does, but it is still essentially reducible to a set of memories, rules, and principles for action. It is true that we do not always react in the same way to the same stimuli, our emotions and mental states have an effect, and there is perhaps some degree of randomness to some of our actions. But all of these mental states can be encoded in the algorithm of our minds, and an algorithm can even account for randomness where there is no predetermined rule for action.

Thus I take it for granted that the soul is an algorithm defined by the sum of our memories, thoughts, habits, and other principles for action.

The immortality of the soul

An algorithm can be written down as a finite list. So for any sense impression, I can write down a finite series of rules of how to react to them. For example:

  1. If you feel pain on your right hand, move your hand away from the source of the pain.
  2. Look towards the source.
  3. Remember not to put your hand on the source of pain in the future.

Obviously, these kinds of ‘sub-algorithms’ can get much longer and more complicated than that. Maybe a full characterization of a human’s algorithm would take much more storage space than the best supercomputers we have now (though I doubt this), but it should still be possible to break down the whole algorithm into a finite series of simple steps.

Now, in my example I wrote down the steps in the form of sentences, but this was not necessary. I could have written them as symbols, or anything really. Computers programs are usually written in binary due to certain physical constraints, namely that it’s very easy to encode a machine in binary, you can just put a bunch of lights, and if a light is on, it represents a 1, if it is off it is a 0. But one could represent an algorithm in any number system, and encode it in that number system in many different ways. For example, I could write a program that does the same thing in several different computer languages, and these would all be encoded differently on a computer, but the essence of the algorithm would be the same.

A piece of Napoleon's soul (probably).

Now let’s get back to souls. The essence of the soul is the algorithm itself, and this algorithm can be written in many different ways. But the algorithm exists independently of any representation of it. Think for example of the number π. We normally represent it by the sequence of decimals 3.14159… But it can also be written in binary as 11.0010010000111111… Or in any number system really. I can also write it as a sentence, and say π is the ratio between the circumference and diameter of a perfect circle. But nobody would deny that π exists independently of these representations, not only as a constant of this universe, but even independently of the universe. Mathematical constants are like eternal features of the nature of reality, and they exist independently of any human who can count 1,2,3,…; independently of any computer that has them stored in its hardware; independent of everything.

The same is true of souls. Since they can be written down as a number (even if it is an unimaginably large number), then they must exist as that number, and moreover they must have existed since always, and they must always exist. The number that would become what I call my mind today must have existed since before I was born, and will continue to exist after today and until after I die. Of course, the algorithm that is now stored in my brain is constantly changing, but similarly when I install a new program on my computer it doesn’t stop being my computer. My soul is the algorithm which I am now, and that number has always existed and will always exist. Moreover, every algorithm which I’ve ever been and every algorithm I will be in the future has also always existed. So not only am I eternal as I am today, but every form which my soul has taken, every form it will take, and every form it could conceivably take, also exist and are eternal.

The Boltzmann brain

This is of course a different kind of existing from the usual sense. When I say I exist I usually mean my physical self, not this strange, abstract algorithm. And after I die, how useful is it to me that the algorithm which I was will continue to exist? Of course, it is completely useless. I cannot take solace in a kind of continued existence after death from this eternal algorithm. But I will offer one final thought, if only for entertainment.

Have you ever heard of a Boltzmann brain? A Boltzmann brain is a hypothetical concept which we owe to physicist Ludwig Boltzmann. The idea is that there are plenty of strange things that arise from the chaotic nature of the universe. Many of them even seem to have a certain kind of order, such as the Solar System. There is also a certain phenomenon called a quantum fluctuation, which is the creation of a particle and anti-particle out of a vacuum, i.e. matter out of nothing, but a Boltzmann brain need not arise through this process. Boltzmann’s idea is that due to the chaotic nature of the Universe, at any point in space-time, there is a non-zero chance that a whole bunch of matter will randomly coincide to create a self-subsistent, self-aware being.

And since your soul is eternal, this being could be you.