Thursday, 15 April 2010

The Evolution and Destruction of the 'Fact'

An earlier debate I had led to the human understanding of eyesight. It is now an established fact that we see objects because light travels from a light source, in waves, reflects off the object to be picked up by our retinas, which then turn it into a code for our brain. However, this ‘fact’ has not been around forever.

Naturally, the first recorded theorising over how the eyes worked was in ancient Greece. Although there were different schools of thought, (notably the emission theory and the intromission theory) the established ‘fact’ was that the eye had some kind of inner light source, that allowed it to interact with objects. They also believed that sight was done entirely in the eye, not in the brain.

Fast forward a thousand or so years and al-Haytham is making better stabs at the truth. For one, he argued that light was entering the eye, not leaving it and being intercepted or such. He also recognised that the eye was not alone in its involvement with sight, but that the brain played a major part. The dominant flaw in his work (which we recognise now) was that he taught that light was interpreted in the lens (and sent to the brain), whereas now we know it happens in the retina.

The point of the above was not a full blown history of sight. There are many improvements, theories and other experiments that have led to a much better understanding of how an eye works, including its limits. But what it proves is that the ‘fact’ is not a constant thing. No doubt the Greek philosophers thought they had it almost cracked but, although they did not live to see it, al-Haytham tore down their theory. Their ‘facts’ became fiction. But even al-Haythem, brilliant as he was for his work a thousand years ago, was flawed, and some of his ‘facts’ have been disproved by modern science.

But they also show something else. The Greeks thinking about eyes, even if they were mostly wrong, was that first step. Al-Haytham’s work was the next. We are now at the stage where we understand the eye quite well, it’s the bit afterwards we don’t quite get. Just because we now say the retina sends the information not the lens does not mean al-Haytham’s work is pointless, to be discarded. His ‘facts’ have evolved, through many stages, into what we now believe. And we are not entirely there either; we haven’t set that most factual ‘fact’ possible. In the future, maybe the far future, we will understand the entire process, and by that time we will look upon the ‘facts’ of the 21st century and scoff. But without it, we’d still be thinking we sent out invisible feelers, or not bothering to think at all.

If you want to see the destruction of facts in action, look at a rock. Your mind tells you, your senses tell you, that it is solid. You can pick it up; you can see that it is solid. No doubt you can hit it against something and the sound will tell you so. But physics tells us otherwise. All the matter in the universe is mostly empty space. That rock in front of you is, by definition, hollow.

I find that mind blowing, although some physicists accept it in their stride (and no doubt there are people who deny it completely). This rock, that hurts if it hits me, that I can feel and see as solid, is mostly empty space. Electrons (which we do not fully understand) orbiting a dense nucleus (which we do not fully understand), at insane distances in comparison to their size. If a nucleus was the size of a marble, the electron would be half a kilometre away. The nucleus is not the size of a marble, in ‘fact’ it would take 20 million full hydrogen atoms to fill the size of this dash -. And rocks are considerably larger than that and, granted, not made out of hydrogen atoms but out of compounds that are a fair bit larger, but not even one of them would begin to register to our eyes. So we perceive the rock as solid, whilst simultaneously knowing that it is mostly empty space. Science has torn down a fact that has been built into us from birth.

A more every day ‘fact’ (let’s face it, a rock still hurts when it hits you, whether you know it is hollow or not) that we have destroyed is that we lose most heat through our head. This was drilled into me as a child and I, sensibly, wore a hat in cold weather and if ever I was getting cold it was my head I protected first (although there were often other clothes involved, for the sake of decency). But then scientists Rachel Vreeman and Aaron Carroll come along and tell us this is not so. No more heat is lost through our head than through anywhere else. A hat still helps, because it’s still covering an area where heat can be lost from, but it’s not like wrapping yourself in a flexible radiator. Looking at it now it looks obvious; if so much heat is lost through our head, why does losing your trousers make you feel so much colder? But it was an established fact before, and now it is a myth.
The moral is that not everything we think of as a ‘fact’ is true, even ones that have held steadfastly against the test of time. And as scientists delve deeper into the realms of quantum mechanics (and as Richard Feynman said, if you think you understand quantum mechanics, you don’t understand quantum mechanics) we can expect to see more and more ‘facts’ brought into the fiction section. But never forget, without those first flawed facts, we wouldn’t understand anything today.

1 comment:

  1. I think your post illustrates three different sources of error in human belief. I'm going to take them out of order, so I can talk about the second a bit more.

    The belief that most of the body's heat is lost through the head is a sort of accepted wisdom. It has the sound of science about it, and a certain plausibility (heat rises, heads are in an exposed position...). Maybe it started with some genuine, but incorrect, research. Perhaps it's a corruption of the possible fact that if you're already wearing other clothes it's better to put something on your head rather than, say, put on another jacket.
    The beliefs tend to circulate round, until someone puts in the effort to debunk them. Then they may die away, or they may continue regardless.

    The story of our understanding of the eye is somewhat different. The Greeks, the Arabs, and more modern scientists, all attempted to understand it with the best resources at their disposal. And they all improved on the understanding of those that came before.

    The discoveries of particle and quantum physics challenge us in a different way. What makes quantum physics so hard to understand is that it is so counter-intuitive and so different to our everyday experience. You perceive a rock as solid, and for all practical purposes this is a fact. In a similar way, newtonian laws of motion are technically completely wrong, but in practice are perfectly good.

    However when we go down to the micro, or up to the macro level, we find out intuitions no longer apply. What we have are careful observations and the "unreasonable effectiveness" of mathematics. The great search in physics at the moment is for a grand theory that unifies the micro-world of quantum physics with the macro-world of gravity. Until then, we're left with two realms with different 'facts' which are at the same time both incompatible and fantastically accurate. From the perspective of an ordinary person, it is probably best to simply accept that different facts, that may contradict one-another and our own perceptions or experience, hold true in different domains.

    On another note, while it's true that we don't fully understand electrons or nuclei, we do understand them incredibly well. We can describe their behaviour with extraordinary accuracy using just the equations of the standard model. The only things missing from the model are some exotic things and gravity (which sounds important, but is so weak it barely affect electrons). For me, one of the most surprising things about quantum mechanics, that for such an abstract theory, it's been so strongly verified experimentally. Probably we understand electrons better than most things in the universe; better than the eye, for example.