• Somebody dropped a burning cigarette and accidentally set the tree on fire.
• The government tested a secret weapon, which accidentally set the tree on fire.

Which one of these two explanations is the better one, and why is it better? Many would probably say that the first explanation is the more reasonable one, but why is it more reasonable? The second explanation could be correct as well! Maybe there is a secret weapons program, and we don’t know about it! Could it be that the first explanation, with somebody dropping a burning cigarette, is too “normal” to be true? There just has to be more to it, right?

Well, as a matter of fact, the first explanation is indeed the better one and is more likely to be correct. The reason is, that it is the simpler explanation, and it is based on fewer assumptions. Remember, you should always go with the simplest possible explanation. The second explanation, the secret weapons program, is a conspiracy theory and requires several assumptions. You have to assume that such a weapons programs indeed exists in the first place, you have to assume that the government was able to keep it secret, you have to assume that they tested the weapon, you have to assume that the weapon hit the tree and that it was able to set the tree on fire. There are simply too many assumptions that can not be verified. The person dropping a cigarette requires far fewer assumptions and is therefore to be preferred.

This is called “Ockham’s Razor”, named after 13th century philosopher William of Ockham. To put it in easier words – don’t make the issue more complicated then necessary. Go with the simplest explanation that explains the observations. Do not look for complicated explanations, even if these explanations are more “exciting” or “interesting”.

It is now July 2009, and 40 years after the first moon landing. A moon landing, which, according to some people, never took place. Yes, there are some folks out there who claim that the moon landing is a conspiracy, it never happened! All the pictures and films of the moon landing, in their view, were made inside a studio. The rocket did start, for all the world to see, but the astronauts were only placed into an orbit around the earth, and never really went to the moon. In the meantime, filming started in a studio on earth. After several days the astronauts returned from their orbit and their space capsule landed inside the ocean to be picked up.

There are countless other examples of conspiracy theories, here are some examples:

• The Chemtrails conspiracy: This conspiracy started back in 1996. You have already noticed that high flying airplanes make condensation trails of water vapor, which are nothing more than clouds. If you remember your chemistry, the burning of fuel (or any organic substance) produces carbon dioxide gas and water. Now, conspiracy theorists claim, that these condensation trails are in reality some chemical or biological agent, which the government sprays on the population – for whatever reason. Of course the governments refuted these claims, but for conspiracy theorists, this is even more evidence that they have something to hide.
• The 9/11 conspiracy: This one states that the 9/11 attacks were an “inside job” and that the US government itself was responsible for it. The conspiracy theorists came up with many “proofs” all of which turned out to be wrong.
• Global warming conspiracy theory: Global warming is not really taking place, or CO2 is not responsible for it – it’s all a lie.
• Princess Diana: She died in a traffic accident in 1996. Conspiracy theorists say that she was assassinated.
• And there are many more, of course.

What do all of these conspiracy theories have in common?

• One of these characteristics is that all of them violate Ockham’s Razor. They are not the simplest possible explanation for the events.
  Now – what is the simplest explanation? The simplest explanation is the one which is based on the fewest assumptions. Don’t forget, assumptions have not yet been proven right or wrong, so they are an uncertainty factor.
• Conspiracy theories are also resistant to falsification. Conspiracy theorists will follow the theory no matter how strong the proof against the theory is. For example, if you try to convince a conspiracy theorist by showing some proof, then the person will simply say that the proof is fake. To them the conspiracy has become a dogma. Scientific theories, on the contrary, are falsifiable.
• They are ignoring counter evidence. Conspiracy theorists are ignoring the enormous number of proofs of the contrary. In that sense, there is a very strong bias in favor of the theory.

Why so many people still adhere to conspiracy theories, despite so much contradicting evidence, that is a mystery to me. And the funny thing is, that no amount of evidence will convince these people of the contrary. If you show them evidence, photographs, sound recordings, whatever, they will consider everything a fake. Trying to convince conspiracy theorists won’t work, the more you convince them, the more they become convinced that the person who tries to convince them is part of the conspiracy.

Now, why did I choose to talk about this topic? I regularly meet students who are absolutely convinced that the moon landing never took place (they saw a TV documentary), or they think that the Vatican is involved in a conspiracy (they read Dan Brown’s book DaVinci Code). The issue was topped a few months ago when a group of two students did their Theory of Knowledge Presentation on the 9/11 conspiracy. They claimed that the attacks on the World Trade Center were an “inside job” by the US government, and not by terrorists. The students tried to apply Ockham’s Razor to the 9/11 conspiracy and said: “The simplest and easiest explanation for the 9/11 attacks is, that it was a conspiracy! This explains everything!”.

Wrong. It is not the simplest explanation, because it is based on so many assumptions, assumptions that can not be verified. The two students showed some videos from YouTube, which presented some “proofs” for the conspiracy. What they (or the videos) overlooked is, that there are many more reasonable explanations that speak against a conspiracy.

So, what’s the take home message? Go for the simplest explanation, it is usually the correct one, even if the explanation does not sound very exciting.

I want to conclude with a quote from Sir Karl Popper:

Whenever a theory appears to you as the only possible one, take this as a sign that you have neither understood the theory nor the problem which it was intended to solve.