I wouldn't believe it even if you proved it to me!

The "Brain-in-a-jar" Problem

This is related to a certain type of mindset that I have encountered when debating with creationists. It happened a few times before I began to realise what was going on.

I occasionally receive emails from fundamentalists or creationists challenging me to explain this or that aspect of evolution, the age of the universe, or whatever. I try to answer to the best of my abilities, referring to what I understand of the current state of theories in those areas.

For example, recently I was asked about the age of the earth, and I explained about the various radiometric dating methods, dendrochronology, continental drift, coral and stromatolite formation, the distance to other galaxies and so on. I did my best to explain how all the various fields gave remarkably similar ages for the universe, and how the theories were open for testing by anyone with the facilities to do so. I thought I did reasonably well, for a layman (I'm a programmer, not a paleontologist).

After listening to all these different pieces of evidence, he changed tack. His argument was this :

"Ah, but can you prove that continental drift, sediment deposition, coral growth etc. has always been fairly constant? Can you prove, 100% without a doubt, that all this did not happen in the last few thousand years at a greatly increased rate?"

I have to say I was gobsmacked! He said that unless I, personally, could prove to him that the rate of decay of radioactive elements (and all the rest) has remained constant then he saw no reason to believe it, and the Biblical version of events was undamaged.

It did not matter that all the diverse lines of evidence pointed to an old Earth. If all the evidence (no matter how diverse) was somehow affected in the same way, then the Earth could easily be 6000 years old!

This is when I came up with the brain-in-a-jar argument:

Can you prove, beyond all doubt, that you are a real living person, just as you perceive yourself to be, and not a disembodied brain in a mad scientist's laboratory being fed complex stimuli?

You cannot. Is that a good reason to believe that you are just a brain in a jar?

I would say not. However, to take the thinking of some fundamentalists to it's logical extreme, it might well be a good reason to believe it. It cannot be proved false, so it must be true. Alternatively, if there is any slight possibility of error in a scientist's data (and in science, nothing is ever 100% proven - scientists always publish the known margin of error) then it is safe to assume that the theory is completely wrong (especially if it contradicts the religious facts - which, you will notice, have no margin of error).

We have to draw the line somewhere. If there is a wealth of strong evidence from a variety of different sciences supporting a theory, and little or no solid evidence to refute that theory, then should we accept the theory as being quite close to the mark? Or reject it because we can conceive of any number of far-fetched and impossible-to-prove (i.e. unscientific) hypotheses that would invalidate it were they true?

Sinking ships

In science, if one piece of solid evidence is found that refutes a particular theory, then that theory must be wrong - it can be shot down by a "magic bullet". For example, if a fossil human skull was found wedged between the teeth of a fossil T. Rex, then the theories of evolution, paleontology and many other sciences would be fatally flawed. Unfortunately, this does not seem to apply to religious beliefs - if you find a dozen good reasons to show that Noah's Flood did not happen, the true believer will simply cling onto all the remaining reasons and continue to believe regardless of any fatal flaws in that belief. If a true believer were Captain of the Titanic, the scene might have been something like this:
"Captain! We've hit an iceberg! We're sinking!"
"Nonsense, laddy. This ship is built of the finest steel."
"What's that got to do with it? We're taking on water!"
"Maybe so, but our engines are among the best in the world."
"Are you mad?!? We're going down!"
"Don't worry so - this ship is unsinkable. It says so here in the manual, and I have total faith in that."
"The ship is breaking apart! We're all going to die!"
"Balderdash. See how the Swiss-made clocks still function perfectly. And the fine oak-panelled walls - what craftsmanship. How can such a vessel sink?"
"Aiee! glub.. glub.. glub.."

(Actually, this particular sort of reasoning is more Head-In-The-Sand than Brain-In-A-Jar. There's plenty of it about. Fnord.)

You cannot prove me wrong, so I must be right. Right?

I claim that there is a tiny green elephant hovering behind your head right now. You cannot see it or touch it, but it's there. Can you prove me wrong? Does that mean I'm right?

I claim that I am God, and I created the universe ten seconds ago, with all your memories in place. Can you prove me wrong? Does that mean I'm right?

In science, there is no such thing as absolute proof. There are theories and hypotheses, and evidence to support or refute them. Nothing can be proved absolutely - you have to draw the line somewhere.

This is the Brain-In-A-Jar Problem.

(brain image from Icon Bazaar)