Tag Archives: Real Life

Doubt, Science, and Magical Creatures


I grew up in a Jewish household, so I didn't have Santa Claus to doubt - but I did have the tooth fairy.

It was hard for me to believe that a magical being I had never seen somehow knew whenever any child lost their tooth, snuck into their house unobserved without setting off the alarms, for unknown reasons took the tooth, and for even less fathomable reasons left a dollar and a note in my mom's handwriting.

On the other hand, the alternative hypothesis was no less disturbing: my parents were lying to me.

Of course I had to know which of these terrible things was true. So one night, when my parents were out (though I was still young enough to have a babysitter), I noticed that my tooth was coming out and decided that this would be...

A Perfect Opportunity for an Experiment.

I reasoned that if my parents didn't know about the tooth, they wouldn't be able to fake a tooth fairy appearance. I would find a dollar and note under my pillow if, but only if, the tooth fairy were real.

I solemnly told the babysitter, "I lost my tooth, but don't tell Mom and Dad. It's important - it's science!" Then at the end of the night I went to my bedroom, put the tooth under the pillow, and went to sleep. The next morning, I woke up and looked under my pillow. The tooth was gone, and in place there was a dollar and a note from the "tooth fairy."

This could have been the end of the story. I could have decided that I'd performed an experiment that would come out one way if the tooth fairy were real, and a different way if the tooth fairy were not. But I was more skeptical than that. I thought, "What's more likely? That a magical creature took my tooth? Or that the babysitter told my parents?"

I was furious the possibility of such an egregious violation of experimental protocol, and never trusted that babysitter in the lab again.

An Improvement in Experimental Design

The next time, I was more careful. I understood that the flaw in the previous experiment had been failure to adequately conceal the information from my parents. So the next time I lost a tooth, I told no one. As soon as I felt it coming loose in my mouth, I ducked into the bathroom, ran it under the tap to clean it, wrapped it in a tissue, stuck it in my pocket, and went about my day as if nothing had happened. That night, when no one was around to see, I put the tooth under my pillow before I went to sleep.

In the morning, I looked under the pillow. No note. No dollar. Just that tooth. I grabbed the incriminating evidence and burst into my parents bedroom, demanding to know:

"If, as you say, there is a tooth fairy, then how do you explain THIS?!"

What can we learn from this?

The basic idea of the experiment was ideal. It was testing a binary hypothesis, and was expected to perfectly distinguish between the two possibilities. However, if I had known then what I know now about rationality, I could have done better.

As soon as my first experiment produced an unexpected positive result, just by learning that fact, I knew why it had happened, and what I needed to fix in the experiment to produce strong evidence. Prior to the first experiment would have been a perfect opportunity to apply the "Internal Simulator," as CFAR calls it - imagining in advance getting each of the two possible results, and what I think afterwards - do I think the experiment worked? Do I wish I'd done something differently? - in order to give myself the opportunity to correct those errors in advance instead of performing a costly experiment (I had a limited number of baby teeth!) to find them.

Cross-posted at Less Wrong.

Sharks are Forever

Back in the 5th or 6th grade my science teacher was telling the class about sharks. She said something about how sharks are an example of a perfected product of evolution, and that some sharks have been around basically unchanged for thousands of years. I'm now quite sure that she meant, some species of shark. But at the time, I thought:

If she meant "species," surely she would have said "species." Therefore, if she didn't, by modus tollens, she must mean that some individual sharks have been around for thousands of years. Unchanging. Undying. All-consuming.

I'm sure that this was like many subtle childhood misunderstandings, insofar as it didn't affect my day-to-day life very much. I don't interact with elderly sharks very often. I've never had to take a shark's vital readings, or card a shark at a bar. There's basically nothing in my life where I would need to know how old a shark is. Until Freshman year of college, that is.

In Freshman Lab (non-Johnnies can think of it as intro biology), my tutor (professor) Mr. K made some point about aging - in particular, about how animals that reproduce sexually instead of by cell division don't destroy the original in the process of making copies. He noted that it seems like all such animals have a natural aging process. They only get so old before they start declining with age, and they can only age so long before they die. But I had the perfect counterexample.

"Excuse me," I said, "but what about sharks?"

"Well, what about sharks?" responded Mr. K.

"We all know that sharks are immortal, right?"