The discovery of neurons has had an enormous significance in human history. What is even more important is that of the gap between neuron and neuron, which we have called the synapse, because this is the first time in history that we begin to get an insight into how the brain might accumulate memories, by gradual increase of the density of neurotransmitters in the synapses: this is the very beginning of our knowledge of the mind.
Of course, well before this time, philosophers had a jolly good time inventing the mind in various ways because their strength is that they can work in total ignorance of any experimental facts. I have my own names for the various schools. The patron saint of the escapists, which tried to by-pass the sensible world was Plato, of whom an Oxford philosopher once said at a meeting that he was an important philosopher because he had made important mistakes.
The armchair philosophers, led by the great Emmanuel Kant, dreamt that they could understand the world and the mind by pure thought, suitably doctored, on the grounds that the traffic rules for thinking that they invented were self-evident. There is, of course, a large group of bad philosophers (BP school), of which the less said the better. Shining exceptions are, in my lifetime, the great Ludwig Wittgenstein, numerous Oxford philosophers that nourished my mind and, in the eighteenth century, my hero David Hume (1711–1776).
David Hume was an important member of the Scottish Enlightenment, an empiricist sceptical philosopher who, being an atheist, did not, like Kant, believe in absolutes but tried always to justify his assertions empirically. He was not only a philosopher but also a historian and economist.
And here we have a huge problem. Modern philosophers prefer to be self-contained, trying to derive their theories from some rules of thought rather than experience. This was not the way Hume’s mind worked. If the word scientist had existed then (which it did not until 1853 when William Whewell coined it), he would perhaps have called himself a natural scientist, and it is in this way that he must be read. He had a programme for understanding the nature of the mind, starting from its skill at handling repetitions, the basis of learning. And he then went on to find reasons for such ability that anticipate Darwinian ideas. But because he lacked the results of Darwin and Ramón y Cajal that we discussed in the earlier article titled ‘The most important discovery in human history,’ the completion of his programme had to remain conjectural, although eventually his ideas were triumphally justified by the later experimental results.
Hume started with an observation that would now be called psychological rather than philosophical. If we see that the sun heats the stone and that this happens every time the sun covers it, he remarked that the mind proceeds from the statement the sun heats the stone to a more powerful one: the sun is the cause of the stone heating (effect). This means that we pass from the single instance, the sun heats the stone, to the mental expectation, after repeated experiences, that the sun will always heat the stone. Hume called this mental expectation a custom or habit.
Hume noticed that when we say ‘a causes b’ this relation is neither a logical necessity nor it is observable. That it is not a logical necessity is easy to accept because you could imagine a world in which the stone and its environment were so hot that the sun actually cools them. Moreover, it was clear to him that the projection from past regularities to future ones could not be justified, except as a propensity of the mind.
The question of non-observability, on the other hand, is not obvious and, if you are puzzled, dozens of philosophers of the BP school are totally with you. Let me try: when you say ‘a causes b’ this is not the statement of a fact but of an expectation and an expectation is not a world event but a mind event. In another way: ‘a causes b’ is a statement like ‘here is a relation between a and b’ and a relation can never be established by a single event. If you see John kissing Jane that does not mean that they are ‘in a relationship.’ They could be actors rehearsing, or the fortunate John might have won a tombola whose prize it was the kiss of a pretty girl. It is only if you see John and Jane repeatedly going through affectionate acts that you can surmise that they are ‘an item,’ that they are ‘in a relationship.’
The fact that Hume called our mental expectation custom or habit caused tremendous trouble for many philosophers, not all, I am afraid of the BP persuasion. The causal expectation was equated with trivial customs, like reading a newspaper at breakfast. But if they had read Hume properly, they would have noticed that Hume called the custom or habit ‘the great guide of human life.’ Even more, it was ‘essential for the preservation of the species’ and when we read this we realize that Hume was going well beyond the usual task of a philosopher: he was not satisfied with the ‘how’ but with the ‘why’ for which he had a truly Darwinian insight. Being able to use causal statements is nothing else than learning, and surely the ability to learn is a positive asset in the Darwinian struggle for life.
But Hume was able to move towards an understanding of a serious philosophical conundrum. We know that daffodils are not ‘really’ yellow, that we perceive this because of the nature of our eye that could well have been like a that of a cat, unable to distinguish colour. And if we doubt the colour of daffodils, we can as well doubt all our other perceptions, some philosophers claimed. But Hume wrote that nature had given us an instinct ‘which carries forward the thought in a correspondent course to that which she has established among external objects,’ which, if he had known Darwin, would have explained by saying that seeing a lion and perceiving it as a lamb would have been totally deleterious.
We must now correlate Hume’s truncated programme with the results and theories discussed in the earlier article ‘The Most Important Discovery In Human History.
Hume insisted in the need of frequent repetition in order to establish a causal relation. When an input a, such as heat, goes through a synapse, a neural path is created to the site that represents the event b (burn). Frequent repetition will increase the density of neurotransmitters in the synapses and thus establish the neural path corresponding to a causal relation. This is a process of learning, and learning is a positive feature in the struggle for life. Thus, evolution has favoured the existence of a large neural network of about 100 million neurons in the human brain and of a large number of connections between them through synapses, about a 1000 per neuron.
We must now understand how this neural network allows the mind to parallel the external world, as Hume claimed. When the human child is born, very few synapses exist. But after birth, they are created at the extraordinary rate of 2 000 000 a second. This means that every minute detail of the child’s world is stored and learned so that a vast number of causal relations are created that map the corresponding world events.
It is important to recognize that causal relations can only be created between events that have been recorded while the brain’s neural network was established. Therefore, causality can only be valid for events belonging to the macroworld and not for others, like elementary particles, that never appeared as the inputs that the brain received after birth: our mothers encouraged us to play with balls but never with electrons or quarks. It would thus be wrong to expect that causality be valid within quantum mechanics: this was Einstein’s error.
This article is based on Simon Altmann’s book, “Einstein’s Quantum Error: An approach to Rationality,” 2018. List price £58.99, available at 50 % discount through www.cambridgescholars.com quoting the code MADRAS50.
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