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By Root 1165 0

They hastily purged the target of oxygen contamination by heating it in hydrogen and placing it once again in a vacuum. What they did not realise was that in doing so they had changed the surface of the nickel, producing a few, large crystals at regular intervals along its surface. When they resumed firing electrons they discovered to their consternation that the electrons being scattered were fanning out from the target in a definite pattern which consisted of alternate bands of very high and very low numbers of electrons. They finally realised that since the electron beam was hitting the nickel surface at an angle, the crystals were reflecting the electrons away in a consecutive stream, whereupon the electrons were interfering with each other as if they were consecutive and out-of-phase waves, producing interference patterns in exactly the way light did. Particles could be waves after all.

The experiment that shook physics: Davisson and Germer’s electron diffraction test that went wrong. Left, the electrons are collected after they have bounced off the target. After the accident (right) the parallel refracting electron beams interfere with each other like waves, to augment or cancel each other.

In 1927 Werner Heisenberg showed that it could never be determined which phenomenon was occurring, as both were products of the instruments. Either an experiment could look for particles and find them, or it could look for waves and find them too, but not both at once.

The proof that particles are waves. This view along the axis of a beam of electrons passing through gold foil shows how the particles interact to produce the familiar ripple pattern of wave peaks and troughs.

He also noted that particles could never be observed with certainty. Either their momentum could be studied through observation of the wave form in which they travelled, or their position could be established by stopping them in flight. Each examination precluded the other. We could say where an electron was or how fast it was going, but not both. Moreover, the act of observation itself would complicate matters. In order to ‘see’the electron it would be necessary to shine a light of some kind on it. This would add to the energy of the electron and alter its state or position. In the act of observation the universe was changed. As Heisenberg said, in a statement that finally ended the speculation begun in the eighteenth century, ‘If we want to describe what happens in an atomic event, we have to realise that the word “ happens” can apply only to the observation, not to the state of affairs between the two observations.’

The investigation of electricity led to an entirely new view of the universe and of the ability of science to say anything about it. It destroyed the cause-and-effect view that had ruled since the time of Thales, in ancient Greece.

If, as Heisenberg suggested, every description of reality contains some essential and irretrievable uncertainty and the observer, in observing, modifies the phenomenon, then, as Wittgenstein said, ‘You see what you want to see.’The universe is what we say it is. However, if this is so, what is knowledge?

The medieval view of man and the universe. For a society built on the belief that the sky ruled all aspects of life, this view of the human condition was as valid then as is ours for the twentieth century.

Worlds Without End

When Einstein made the great conceptual leap that changed physics and with it the understanding of the fundamental nature of matter and the way the universe worked, he said that it came to him as if in a dream. He saw himself riding on a beam of light and concluded that if he were to do so, light would appear to be static. This concept was against all the laws of physics at the time, and it brought Einstein to the realisation that light was the one phenomenon whose speed was constant under all conditions and for all observers. This led him directly to the concept of relativity.

Einstein’s dreamlike experience is echoed by other descriptions of the same kind of event.