It must be true. I heard it on the Internet.

So you hear some claim on the Internet -- say, vaccines will make you grow a second head -- and you're not sure if it's true. What do you do?

This is not a trivial question. The greatest strength of the 'net is that it gives everyone a voice, and the greatest weakness of the 'net is that it gives everyone a voice. Because not everyone has a good grasp of reality, any claim, no matter how ridiculous, will have its supporters online somewhere. If you have no familiarity with a topic and stumble on some crackpot's website about it, you might not know what they're saying is baloney.

At Lifehacker, Alan Henry wrote an outstanding article about all this. And I don't just say this because he quoted me extensively in it, though of course there is that. He also talked with David McRaney from You Are Not So Smart who also has excellent advice, and then wrapped it all up in a readable and IMO very important article on how to make sure the Internet isn't duping you.

The most important thing I have to say on this is: just because you're smart doesn't mean you're right. This is an incredibly common fallacy, and one I see a lot. In many cases, the opposite is true, especially when it comes to closely-held beliefs. Smart people hear a claim and decide to check up on it, and then fall victim to the bias of only reading articles that support their pre-existing belief. It's maddening, but well-documented, and leads to things like outbreaks of vaccine-preventable diseases in places where people are better educated on average. Like Boulder.

In the Lifehacker interview I recommended following the scientific consensus as a default position. Why? Because when scientists agree on something, it's almost always because there is overwhelming evidence to support it, research indicating it's correct, and vast amounts of experience going into accepting that conclusion. That doesn't mean it's always right 100% of the time, of course, but that's the way to bet. Also, it makes a lot more sense to go with the consensus of people who have experience in a topic versus the opinions of people who don't.

And like I said, that should be your default position, not your entrenched one. There should always be some room for doubt, some allowance for data not yet seen, evidence not yet collected.

But there are times when that room is small indeed. I can list lots and lots and LOTS of topics where that's the case.

So go read the article at Lifehacker, and remember that even though you're smart -- hey, you're reading Bad Astronomy, so that's self-evident -- you might be wrong.

But of course, you already knew that.