Choosing from a limited pool of actors

One of the themes in the book Cloud Atlas by David Mitchell is that characters can be linked across space and time. The film chose to make this concept more explicit by having the same actors portray different characters in the several stories. The idea is that although the characters are different, some underlying essence is the same. In a lighthearted way I’d like to ask “What if such a thing were true?”

Of course we have to ask, what do we mean exactly when we say that the different characters ‘are the same person’. One interpretation, and maybe the one implied by the film, would be based on re-incarnation of an immaterial soul, such as is attributed to Buddhist mythology. The same soul is born over and over again in different bodies. While such an idea is entertaining, we can dismiss it as clearly absurd nonsense.

A more scientifically possible, though highly speculative interpretation is that all the characters (and us) are living in a simulation. The individuals may die in the simulation, but the substrate of course still has a complete record of their neural pattern, and they are put back into the simulation again as different characters, but still ‘the same’. Think -REDACTED- in Surface Detail. The reasons for doing something like this are myriad and un-knowable, but to throw out a few random suggestions:

• The simulation could be a training program, designed to hone a mind by having them live out different lives.
• We could be doing it purely for entertainment, living out different lives in the same way we read different books.
• It could be a historical research project, with the researchers playing an active role by instantiating over and over again in the simulation.
• It could be a prison, designed to punish the prisoners.

The last point touches on the question, that suppose the simulation hypothesis were true, how could it be moral to leave the subjects in ignorance that they are in a simulation? Again many unknowable answers – the moral question might never have occurred to those that setup the simulation, or they might have considered it a necessary evil to achieve the goals of the simulation without the result being contaminated by meta-knowledge. Or maybe we are all volunteers. If we had knowingly agreed to have all meta-knowledge wiped before each instantiation then the moral question might not apply.

However leaving the simulation hypothesis aside, there is another more scientifically grounded sense in which different people at different times and places could really be the ‘same’ person. It is often said that ‘every individual is unique’. This may however be over-optimistic. In constructing a brain, we know that the instructions for building it are complex, but not ridiculously complex. The total amount of specifiable information must be at least contained within the number of bases of a human genome (about 3Gbases). Suppose that we develop a really detailed understanding of all the neural pathways that make a brain. We may then be in a position to say “this pathway causes this personality trait” and “this other pathway causes this different trait”. Imagine building on a psychologist’s “personality traits” profile where they try to identify someone as “open/closed, introverted/extroverted etc.”. Instead of five traits, we build one for each physically realizable neural pathway – how many are there? I don’t know, probably tens of thousands, maybe millions. But probably not too much more than that. Even though biology uses lots of self-assembly tricks while building brains there is a limit to how much can self-assemble while also still being useful. The number of effective pathways is constrained by the size of the genome. Let’s say for the sake of argument that there are 100,000 distinct traits mappable to physical brain structures. We can create a mathematical space in which each trait is represented by an orthogonal axis. Each of us would then be represented as a point on this multi-dimensional space. 100,000 is a really big dimension with plenty of room to find our own unique spot. However some factors may reduce the amount of room in practice. It is likely for instance that on many traits we would fall somewhere in the middle of a bell shaped curve. This would cause people to cluster towards the center of trait-space. In addition small differences may be practically indistinguishable for many traits, so that ‘bin size’ would be fairly large.

It is conceivable that the number of ways in which our brains are practically different is less than the number of human beings alive, or at least alive in the last thousand years. In this of course I am ignoring accumulated memories, which are undoubtedly unique. Nevertheless if we ignore memory for the moment and consider that “me today” and “me a year ago” are the same person, then in some real sense “me” and “some random person” and also the same person. They have exactly the same personality traits as I do, and would react the same way as me in every circumstance.

It has some interesting implications for memory storage vs. personality storage, the limits of human minds, and our place in the world.