Occam’s Razor, Space Invaders, and Lizard People
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Occam’s Razor, Space Invaders, and Lizard People
“Reports that say that something hasn't happened are always interesting to me, because as we know, there are known knowns; there are things we know we know. We also know there are known unknowns; that is to say, we know there are some things we do not know. But there are also unknown unknowns—the ones we don't know we don't know. […] The absence of evidence is not evidence of absence, or vice versa.”
—Donald Rumsfeld
There may never be a better quote than this to capture the implications of decision-making under uncertainty. Donald Rumsfeld was the secretary of defense under George Bush Jr. from 2001 until 2006. Rumsfeld gave this answer when he was asked whether the United States had information about Saddam Hussein selling weapons of mass destruction to terrorist groups. We constantly face decisions that are shrouded in uncertainty, with bigger and smaller consequences. For Rumsfeld and Bush’s government, their decision was, of course, catastrophically massive.
When faced with uncertainty or a shortage of data, we might come up with all sorts of different hypotheses. But how can we choose among different ones? Is it more likely that someone is hiding weapons of mass destruction or not? Is your spouse cheating on you? Is there some secret conspiracy controlling a large part of humanity? We need a rule to help us figure this out.