Monday, November 10, 2008

Baby Science

Many people are familiar with the quantum physics paradox of Schrodinger's Cat. Briefly, a cat and a vile of poison are sealed in a box, with the release of the poison linked to the detection of radiation. The paradox says that, because of quantum mechanics, before one looks in the box, the cat exists in a state of being both alive and dead. Once the box is opened, however, in order to check the status of the cat, one sees the cat in one of the two states, not in both at the same time. This paradox is often interpreted, in lay terms, as an observer's paradox: the act of looking at the cat, in a way, forces the cat into one of the states.

That's all well and good, as far as high school physics is concerned. But are you familiar with the lesser known paradox of Schrodinger's Baby? It goes something like this: a quiet baby in a darkened room exists in a state of being both asleep and awake (ie, if the baby is quiet, you don't really care which state the baby is in). However, the act of walking into the room (or in some other way spying on the baby) forces the baby into the awake-and-waiting-to-be-picked-up state. Even if you make no noise at all.

From my own field of theoretical computer science, there exists a problem known as the Halting Problem. It says that, for certain types of computer systems, if you ask a question of a computer, you may never know the answer, because the system might take an indeterminately long time to respond. A simplistic analogy: remember calling someone on the telephone before there were answering machines? If the person answered the phone right away, you knew they were home, but if they didn't answer, how many times should you let the phone ring? If they don't answer after, say, 5 rings, you can't conclude that they're not home, because maybe they just haven't gotten to the phone yet. No matter how many times you let it ring, you can't actually conclude that they're not home, because maybe they would have answered on the next ring. The only way to be 100% sure, in fact, is to let the phone ring forever.

Which brings me to the Baby Halting Problem, in which we attempt to determine whether a baby has finished pooping. How long do you wait after the last grunt and fart before concluding that it is safe to change the diaper? No matter how long you wait, you might still be surprised by the sudden arrival of more poop once the baby is naked on the changing table. The only way to be sure is in fact to wait forever, which is supremely uncomfortable for the baby, and results in an infinite amount of poop.

The Baby Halting Problem actually has a second, less messy statement, in which we attempt to determine when a baby has been successfully rocked to sleep, as opposed to just faking it by closing his eyes and lying slack-jawed in your arms, waiting to surprise you the moment you attempt to put him down. The formalization of this alternate statement of the Baby Halting Problem is left as an exercise for the reader.


  1. LOL!!! I remember monkey was about 3 week old, all I wanted to do was sit and watch young and the restless. I swear I changed that damn diaper 4 times in 20 minutes + plus had pooping occurring on the change table. Luckily my MIL arrived when I was at the point of wanting to throw him out the window.

  2. I've no answer to any of the problems. However, from my babysitting days, I have an older child corollary. There's the Heisenberg Uncertainty Principle. That is the more you know about one variable the less you know about the other (eg. position vs. speed). The more you accurately you can hear what the child is doing, the less accurately you know what a child is doing (otherwise known as "why silence is a bad sign.").

  3. So very true! I completely screwed up on the baby halting problem this morning and went through far more diapers than I really needed to!

  4. We have been very fortunate when it comes to the first formulation of the baby halting problem, but far less so with the second.


Talk To Me!