 In Star Trek The Next Generation, you just know that if Katharine Picard ever failed to get his T. Earl Grey hot, engineering was about to go through some sort of replication crisis. You may have heard of the so-called replication crisis, a recent string of failures to replicate the results of several important scientific studies, including many which had been more or less accepted as true by researchers in those fields. It's definitely true that many of the failures to reproduce these published, peer-reviewed, rigorous scientific findings are because they're just wrong. Even papers that have been cited thousands of times and are foundational for entire branches of successful research. Occasionally, someone tries them in some new context and discovers that their conclusions must be flawed or incomplete in some significant way. In 1984, economist Fritz Machloup started analyzing scientific knowledge as a form of capital, a sort of resource which could be harvested by research with a value that changes over time. He came to the conclusion that this sort of knowledge has a half-life, just like radioactive isotopes, a period of time which would see any given number of facts decay by half. According to Machloup, if you had a body of scientific knowledge of, say, eight facts and then waited for that half-life, four of those facts would become worthless, either superseded by new information or proven wrong. And by almost any measure, he was totally right. A 2002 paper tracked about 500 studies on cirrhosis and hepatitis of the liver published in the last half of the 20th century and found that the average half-life of the information contained in those papers was around 45 years. If that's representative, it means that of all the medical information we know today, in 45 years, a full half of it will be either proven wrong or useless. In fact, many med students are told that around half the things that they learn in med school will be obsolete by the time they graduate. Some people might hear this sort of thing and come to the conclusion that science isn't to be trusted, especially those people who were disinclined to trust scientists in the first place. Those guys told us that aches were good for us, then they were bad for us, now they're good for us again. Who cares what they say? Just eat what you like. But the thing is, among all the different methods we have for learning stuff about the universe, science is so much more successful and accurate than anything else that it would be utterly ludicrous to ignore it. I mean, there's a reason you don't have to worry about smallpox or polio anymore, while you can safely drive over bridges or watch this video. And it ain't psychics. Science is truly awesome at figuring stuff out and important to this conversation. It's not in spite of these reversals of opinion. It's not in spite of the half-life of scientific knowledge. It's because of it. It's not a bug, it's a feature. We've all known people who, despite clear evidence of the contrary, continue to believe something, either out of habit or because they have other cherished beliefs that depend on it, which they don't want to give up. Members of the Flat Earth Society, which is a real thing, can look at pictures and videos like this all day long and still vehemently assert that the Earth is a disk, not a sphere. That's just an extreme example of something that we're all guilty of to some degree. Belief perseverance is a well-established trait of human psychology, at least for the moment. The persistence of beliefs long after the expiration date on their supporting evidence has come and gone. In a well-known experiment, a psychologist will give a test subject a set of suicide notes and ask them to sort the real ones from the fake ones, then give some sort of randomized feedback about their performance, either positive or negative. If you ask the test subject how skilled they think they are at the task, they'll generally agree with that assessment, saying something like, oh yeah, I'm really good slash really bad at this sort of thing. It's then revealed that all the notes were made up, as was the performance evaluation. There is now literally no reason for someone to suspect that they're actually good at sorting fake suicide notes from real ones. But even in that situation, even with total ignorance as to their actual skill, people will still say things like, well, yeah, but if this were a real test, I'd totally be awesome at it. It's apparently very difficult for us to change our beliefs, even when the support for them totally evaporates. And this isn't even something that anyone really cares about. Our relative skill at sorting suicide notes doesn't carry any of the emotional baggage that we frequently saddle our beliefs with. There is definitely a cultural pressure to identify and define ourselves by what we believe. For many, what sort of bumper stickers you put on your car, or what gods you do or don't worship, tells them everything they need to know about what you believe, and thus who you are. That's not ideal. I mean, if what I believe is who I am, I'm not going to want to change it, even if there's a good reason to think that it might be wrong. The tighter we wind ourselves into our ideas, the harder it gets to see even very obvious problems with them. This is also true in science. There are definitely researchers who have pet theories that they absolutely refuse to give up on. Even in the light of compelling evidence to the contrary. And I'm not just talking about bad researchers either. Linus Pauling won two separate Nobel Prizes in different fields by himself, but he spent the last half of his life trumpeting the unproven health benefits of one of his discoveries, Vitamin C. He claimed that it prevented colds in the flu and even cancer, but despite the fact that the research showed that that wasn't true, it was his baby and he just couldn't let it go. So how can we avoid that sort of trap? How do we keep our egos out of our beliefs so we can let new information update them the way that science does? Well, as always, blah blah critical thinking, blah logic, blah blah rigor, standard thunk stuff. But it's easy to subvert those sorts of things when you're motivated to do so. Unfortunately, there's no silver bullet from when you want to be fooled. But there is a cute thing that I sometimes use to try and put myself in the right frame of mind to be convinced by the evidence, to open myself to the possibility that something that I believe might be in that half-life of facts that I really should be getting out of my head. It's called the litany of Tarski, named after logician Alfred Tarski, for some reason. I'm not really clear why, but that's what it's called. It's a simple formula that you can plug any potential belief into, something like Vitamin C prevents colds. If Vitamin C prevents colds, I want to believe Vitamin C prevents colds. If Vitamin C doesn't prevent colds, I want to believe Vitamin C doesn't prevent colds. Let me not become attached to beliefs I may not want. Like I said, it's not a silver bullet. It's just something I say to myself sometimes to try and disentangle my ego from what I believe. To remind myself that my beliefs are separate from who I am, that I can change any one of them and still be me. After all, changing my mind is hard enough as it is, and if I can reduce the amount of extra evidence I'd need to be convinced of the truth, that's probably a good thing. But I do take some reassurance in the fact that when I get those Facebook history notifications, I'm frequently amazed at how much my beliefs have changed over time, how much of my previous knowledge has fallen victim to its own sort of half-life. Now, if only I could get over the crippling embarrassment. Can you recall ever being inordinately attached to a belief that you later didn't want? Please leave a comment below and let me know what you think. And a quick reminder, thunk episode 100 is coming up, so if you have any questions you'd like me to answer, please leave a comment or send me an email. Thank you very much for watching. Don't forget to blah blah subscribe, blah share, and don't stop thunking.