Fallacies in Scientific Dispute

Scientists don't know everything and they've been wrong before!

The Incomplete Knowledge Fallacy

Listen to debates about scientific problems, such as global warming or whether power lines cause cancer, and sooner or later you will hear something like, "You (meaning scientists or science) don't know everything!". The implication is, "You don't know everything, and you could be wrong about this." Of course if this statement is used indiscriminantly it really says, "You don't know everything and therefore you know nothing", and this is patent nonsense.

I am a working scientist, and let me assure you that I am acutely aware that I (and by extension, science) do not know everything. But that does not mean that I (or science) know nothing. There are very many things that we can be pretty darn sure of. Generally these things are given the honorific of "law". So we call the idea that there is no free lunch when it comes to energy the "Law of Conservation of Energy". Because this law is a summary of thousands of years of experience it doesn't have to be true, but it can never be wrong. If you find this confusing read more on laws in the basics section.

So, while it is true that I don't know what dark energy is, and I don't know how quarks create the cosmos, I do know that a perpetual motion machine is impossible because it violates the Second Law of Thermodynamics, and what this really means is that it disagrees with thousands of years of experience with the natural world.

Is this the naked arrogance of an ivory tower academic? After all, science has got things wrong before and maybe one of these high and mighty laws is wrong!

Well, no.

First, this argument is related to the Previous Error Fallacy, discussed below. Second, when it comes to the basic laws of physics, everyone is a scientist. Every time you let go of a rock, it drops. If ever this does not happen (and you are standing still on the Earth), email me immediately because either the Earth has just been pulverised or a law of physics has been violated. Either way, I'd like to know.

The Previous Error Fallacy

This fallacy, related to the Incomplete Knowledge Fallacy, asserts that previous failures imply that the possibility of current failure. While logically possible, this argument cannot be used willy-nilly because you cannot violate a law of physics. Again, Laws are based on thousands of years of experience gained by millions of people; you just don't go throwing that kind of thing out with the dirty water!