My most recent post, “Living in a Computer Simulation,” elicited some insightful comments from a reader skeptical of the possibility of mind uploading. Here is his argument with my own brief response to it below.
My comment concerns a reductive physicalist theory of the mind, which is the view that all mental states and properties of the mind will eventually be explained by scientific accounts of physiological processes and states … Basically, my argument is that for this view of the mind, mind uploading into a computer is completely impractical due to accumulation of errors.
In order to replicate the functioning of a “specific” human mind within a computer, one needs to replicate the functioning of all parts of that specific brain within the computer. [In fact, the whole human body needs to be represented because the mind is a product of all sensations of all parts of the body coalescing within the brain. But, for the sake of argument, let’s just consider replicating only the brain.] In order to represent a specific human brain in the computer, each neuron in the brain would need a digital or analog representation, instantiated in hardware, software or a combination of the two. Unless this representation is an exact biological copy (clone), it will have some inherent “error” associated with it. So, let’s do a sort of “error analysis” (admittedly non-rigorous).
Suppose that the initial conditions of the mind being uploaded are implanted in the computer with no errors (which is highly unlikely in its own right). When the computer executes its simulation, it starts with that initial condition and then “marches in time”. The action potential duration for a single firing of a neuron is on the order of one millisecond, which implies that the computer time step would need to be no larger than that (and probably much smaller or else additional computational errors are induced). So the computer would be recalculating the state of the brain at least 1,000 times per second as it marches in time (and probably more like 10,000 times per second).
Since the computer representation of the brain is not perfect, errors will accumulate. For example, suppose that the computer representation of one neuron was only 90% accurate. After that neuron “fired”, its interaction with connected neurons would have roughly a 10% error. Now consider that the human brain has roughly 86 billion neurons, each with multiple connections to other neurons. The computer does not know which of those 86 billion neurons are needed at each time step, so all would need to be included in each calculation. One can see that 10% errors in the functioning of individual neurons within the millisecond duration will quickly accumulate to produce a completely erroneous representation of the functioning of the brain a short time after the computer started its simulation. The resulting “mind” that gets created in that computer would probably bear no similarity to the original human mind (or to probably any “human” mind). It would probably be “fuzzy” and unable to function.
Would 99% accuracy in the representation of a neuron be any better? Not really. 99.9% accuracy? Still no good. 86 billion neurons is a large number (and remember, the computer is recalculating the entire brain state 1,000 to 10,000 times per second). In order for accumulated errors to not overwhelm the simulation of the brain in the computer, the accuracy in representing each neuron would need to be extremely high and the amount of information needing to be stored for each of the 86 billion neurons would be huge, leading to an impractical data storage and retrieval problem. The only practical “computer” would be a biological clone, which is not the topic here.
Consequently, if one believes in a reductive physicalist theory of the mind, then uploading the specific mind of an individual human into a computer is, for all intents and purposes, impossible.
Let me say briefly that I wouldn’t call mind uploading impossible, as many experts (Ray Kurzweil, Marvin Minsky, Randal A. Koene, Nick Bostrom, Michio Kaku, and others) attest to its possibility. And even skeptics like Kenneth Miller don’t reject the idea in principle. My view is that, with enough time for future innovation, something like it is almost inevitable. Of course we may not have that time.