Seeing atoms at last - Eric Rogers' 1979 Christmas Lectures 6/6

Through indirect means, we are able to observe atoms that are otherwise invisible to the naked eye.

Watch all the lectures in this series here: https://youtube.com/playlist?list=PLbnrZHfNEDZzOq1zfje2o8Y_nIrHmdtbX&si=Q6s4EbX1BAGz-KlO
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This was recorded on 6 Dec 1979.

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This year marks 200 years of the Royal Institution Christmas Lectures — a world famous series showcasing science, curiosity, and mind-blowing demos, and started by the legendary Michael Faraday himself.

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From the 1979 programme notes:
A steady fusion chain reaction for power stations has yet to be achieved, but it is the hope of the future: fusion energy for our great-great-great-grandchildren – in addition to sunshine, which is also produced by nuclear fusion in the Sun's ultra-hot core.

A gang of lasers offers a promising avenue to the necessary high temperature. We cannot show such a gang in action, but we will show a small laser demonstrating its 'bite'.

In an earlier lecture, you saw light making double-talk: it is a storm of waves or a shower of bullets – it switches between those two behaviours according to the questions we ask or the measurements we try to make. Now see that solid bullets of matter also give double-talk.

High-speed electrons, which certainly behave as bullets, can also show wave properties – if we ask them. Shoot a stream of electrons through a thin crystal of carbon and we see a pattern formed on the receiving screen. Compare that with the pattern made by X-rays shot through a crystal or visible light shot through the woven cloth. The higher the voltage used in the electron gun, the faster the electrons and the smaller the pattern, the shorter the electrons' wavelength.

Larger things, neutrons, nuclei, even atoms, can show wave patterns like that. With still larger bullets the wavelength is utterly too short to make a noticeable pattern, but for all we know it is still there.

In Lecture V we sketched a nuclear atom model and poured some doubts on it. Now we can make a better model, better because it fits with more experimental knowledge and better because it is more fruitful – it makes more successful predictions. The new model has a tiny massive nucleus with a positive electric charge, just as before – until we try to look inside that nucleus; then we may find waves there also.

And yet you have our promise from Lecture I: You shall see atoms. You shall see the atoms of the sharp point of a tungsten needle – now that you are prepared to understand the method. It is indirect, yet we hope, now in conclusion, that you will each be able to boast I have seen atoms.

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About the 1979 CHRISTMAS LECTURES
Except for clever suggestions, our knowledge of atoms is very young compared with our older scientific knowledge. Some of it is a few centuries old but much of it is only one century old at most. There are two reasons for that late development. First: since atoms are (as we now know) far too small to be seen, all our experimental gathering of knowledge has to be indirect. Although we now know a great deal about atoms, and about the still smaller parts of atoms, we still have to describe them by imaginative pictures which we call models.

Second: even to build such knowledge indirectly, new apparatus had to be developed, such as vacuum pumps and electronic supplies for high voltage. The aid of a vast new technology was needed.

Nowadays when one learns what has been discovered about atoms one has to learn by hearsay, one has to accept the indirect methods and swallow the picturing by imaginative models. Then a keen listener must long for some experimental support or illustrations. That is what these lectures will offer in their 'circus of experiments'. The circus cannot cover all our new knowledge of atoms but it will, we trust, give visitors a feeling of friendly first-hand acquaintance, a contribution of confidence and understanding as well as a delight in seeing experiments.

Find out more about the CHRISTMAS LECTURES here: https://www.rigb.org/christmas-lectures

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