It is common knowledge that when light from a single source passes through two parallel slits, before falling on a flat screen, one does not see uniform illumination in the middle of the screen, fading off at the edges. One sees interference fringes, the Fresnel fringes as we call them, of light and dark lines. This shows that light has some of the properties of waves. But we also know that light behaves as if it were composed of quanta of energy – discrete particles which cannot be divided. The distribution of radiation given off by a hot body only makes sense if this is so. And the quantum mechanics tries to explain how the behaviour of electrons in the structure of atoms depends on this. But how can a single quantum of light pass through two slits, and form the interference fringes on the other side? The wave mechanics may say there is a wave of 50% probability that a quantum will pass through one slit rather than the other; and it makes sense to say there is 100% probability of it passing through one or the other. But it is nonsense to say there is a wave of probability that a single quantum will pass through both slits. Common sense breaks down at this point; and all we can say is that light displays some of the properties of waves, and some of the properties of particles. Maybe further research will reveal a simpler vision of elementary matter; or maybe the mystery will deepen and become even more incomprehensible. I suppose it is best to keep an open mind. But one thing eminent writers of popular science, like Sir James Jeans and Professor Eddington, have always stressed, is that science may tell you how the world started; it will never tell you why the world started. It will never tell you the purpose of life, or explain the beauty of music. Yet these are exactly the questions that the public seem to think the latest research will reveal. I fear they will find that science has feet of clay.
And of course scientists, like other people, are often limited people. Few can write decent English, or explain in simple language what they are doing. Few have that rapport with non-scientists, which shows they can easily rise above their subject. Take Heisenberg himself. He was head of the Nazi atomic energy establishment during the War. He was protected from harassment on Himler’s direct orders; so presumably he was a Jew. But he either failed to see the need to flee Germany while there was time, or failed to have the moral fibre to stand up to Hitler. After the War, he claimed he had de-railed German atomic research; but the truth of that assertion is likely to remain shrouded in mystery until the day of judgement. He failed, as we religious people would say, to see the writing on the wall, let alone understand it. The same could be said of Science as a whole. As technology progressively intrudes into every facet of our lives, it systematically prevents contact between man and man, which is the fabric that keeps communities alive. But do you ever hear a scientist utter a word of caution? Or do you ever hear a scientist propose a sensible Rule for limiting research, where its moral questions worry many ordinary people?