For the last nine years, my day job has been teaching high school science. People outside of education ask how I handle creationist students. Actually, it's simple: I don't challenge the premise upon which they base their life. In explaining the scientific method, I start with Descartes' evil demon hypothesis. You know Descartes, the guy responsible for the axes on graph paper? Well, this 17th century French philosopher came up with an interesting argument: how do you know anything it real? Couldn't it be that an evil demon was tricking you into thinking it was real? His answer was that he couldn't prove anything was real except himself. He was thinking; therefore, he existed.

I update this for my students, stealing a trick from someone (I can't remember whom). I replace the demon with an evil neurosurgeon. I focus on one student and tell her I will only be speaking with her for the rest of the class, as she is the only one who exists, and I am the evil neurosurgeon stimulating her brain to make her think the room and all its occupants exist. I then challenge her to prove me wrong.

Although I sometimes have to let the student consult the "voices" in her head, generally classes who have never been taught philosophy eventually come to something approximating "I think; therefore, I am." I then introduce Kantian a prioris and use existentialist ideas to establish that the materialist assumption--the world is as we perceive it and measure it--is actually a leap of faith, no more provable or disprovable than faith in a deity. Then I argue why accepting the materialist assumption has advantages and, for those who can't buy in, invoke Aristotle's idea that the mark of intelligence is the ability to consider a proposition without necessarily accepting it.

With this strategy, I've never had a problem with a single creationist student.

However, Doctor Who, with the latest episode, just challenged this line of argumentation. Spoiler alert for those who haven't seen it, but the entire episode takes place within a computer simulation. The season's big evil types, probably the Cybermen, have simulated Earth to figure out how to defeat it. Having done some mathematical simulations in my scientist days, I know how difficult it is to simulate behavior of entire systems based on independent simulations of every object and simulation of relationships between objects. As in, with today's tech, it is so complex that it's nearly impossible to tease out patterns. But, Doctor Who is science fantasy, so it's certainly not the most implausible thing ever to be on that show to imagine computers one hundred years from now would be better in the real world, so why not let the alien villains have them now?

The way the "humans" realized they were simulations was a test in which two or more independently tried to come up with random numbers. There are various tricks for a computer to get numbers that seem random, but if calculation is algorithmic, they can't truly be random. So all the characters said the same numbers.

Back to Descartes: the only way we know we are not a simulation is that we can also pass this test. So, the knowledge that I exist does indeed depend upon my ability to think, but I cannot know that I am not a simulation unless someone else exists who can also attempt to come up with a list of random numbers that are unlike mine. And I have no way of knowing they exist, because my brain might be under stimulation by an evil neurosurgeon as I lie on his operating table.

So, could I be a simulation run by evil beings of someone lying on a simulated table in a simulated neurosurgeon's office with my simulated brain being stimulated to think it is all real? You come up with a different list of random numbers than I do only because the simulated evil neurosurgeon created the image of you in my mind?

Maybe, but Occam's Razor would argue against it. As such, I better get back to the boring task of grading papers.

They exist.

Damn.