Wednesday, September 17, 2008

Anti crackpot blog and falsifyability

There is a new blog dealing with crackpots in HEP. It probably grew out of the recent hype about LHC being the doomsday machine. I left a comment to the first post that I would like to pull out of the comment threat so I reproduce it here:

You would like to add that I think that criteria for good science are unfortunately slightly more complicated than just asking for "falsifyability".

This notion comes from the (pre war) neo-positivist school of thought with Karl Popper being one of the major figures. It is a tremendous progress after realising that strictly speaking you will never be able to prove empirical statements like "all ravens are black" (the classic example) by looking only at a finite subsample of all ravens.

This is how far the education of a typical physicist in philosophy of science goes.

Unfortunately, falsifyability is not a good criterium either from the standpoint of logic at least: The thing is that non-trivial scientific statemens are much more complex than a simple "all ravens are black". When you say such a thing (or write it in a paper), there are many qualifyers that go with it, at least implicitly. You have to know what exactly "raven" means, what exatly you call "black" and not "dark grey", you have to say how you measure the color and that might come with a theory of itself that makes sure your measuring aparatus acutally measures color (as for example percieved by the eye).

Speaking in terms of formal logic, all these presuppositions are connected to the "all ravens are black" by a long long chain of "and"s.

Now imagine you observe a white raven (after having seen a million black ravens). At least you would be tempted to further investigate whether that bird is really a raven or was painted white. It's typically not the first reaction to throw away the "black ravens" theory if it had a lot of support before. Often the reaction is that you rather fiddle with the presuppositions of your theory (for example by changing slightly the definition of what you call 'raven').

The "all ravens are black" part is somewhat protected after receiving some positive evidence for some time and you rather add bits and pieces to the silent background theory before giving up the big statements.

Thus we have to agree that it's not that easy to falsify even simple statments like "all ravens are black" that easily. Furthermore, this is not what happens in science (historically speaking)! You could probably still find an ether theory where the ether is dragged along by the earth in its orbit around the sun and that has many more very unusual properties that is not ruled out empirically. Still nobody in her right mind believes in it since relativity is some much more successful!

All this is much better explained in Thomas Kuhn's "Structure of Scientific Revolutions" and I urge everybody with a slight interst in these matters to read this classic. He argues much more for the consensus of the scientific community to be the relevant criterium (which might be a self referential criterium for science consiracy theorists).

I believe that naive following this wrong criterium of "falsifyability" has gotten beyond the standard model theory in a lot of trouble in the public perception. I would attribute a lot of this to trying to follow the wrong criterium.


Anonymous said...

How about "all swans are white"? This was certainly believed in Europe before certain land masses were investigated by Europeans.

Robert said...

Ahm, yes. What do you want to imply with this?

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