First of all there is matter - and,remarkably enough, all matter is the same. The matter of which the stars are made is known to be the same as the matter on the earth. The character of the light that is emitted by those stars gives a kind of fingerprint by which we can tell that there are the same kinds of atoms there as the earth. The same kinds of atoms appear to be in living creatures as in non-living creatures; frogs are made of the same 'goup' as rocks, only in different arrangements. So that makes our problem simpler; we have nothing but atoms, all the same, everywhere. The atoms all seem to be made from the same general constitution. They have a nucleus, and around the nucleus there are electrons. We can make a list of the parts of the world that we think we know about. First there are the electrons, which are the particles on the outside of the atom. Then there are the nuclei; but those are understood today as being themselves made up of two other things which are called neutrons and protons - two particles. We have to see the stars, and the atoms, and they emit light, and the light itself is described by particles which are called photons. (Then Professor R.Feynman have listed some other particles).
With these particles that I have listed, all of the low energy phenomena, in fact all ordinary phenomena that happen everywhere in the Universe, so far as we know, can be explained. There are exceptions, when here and there some very high energy particle does something, and in the laboratory we have been able to do some peculiar things. But if we leave out these special cases, all ordinary phenomena can be explained by the actions and the motions of particles.
For example, life itself is supposedly understandable in principle from the movements of atoms, and those atoms are made out of neutrons,protons, and electrons. I must immediately say that when we state that we understand it in principle, we only mean that we think that, if we could figure everything out, we would find that there is nothing new in physics which needs to be discovered in order to understand the phenomena of life.
Another instance, the fact that the stars emit energy, solar energy or stellar energy, is presumably also understood in terms of nuclear reactions among these particles. All kinds of details of the way atoms behave are accurately described with this kind of model, at least as far as we know at present. In fact, I can say that in the range of phenomena today, so far as I know there are no phenomena that we are sure cannot be explained this way, or even that there is deep mystery about.
This was not always possible. There is, for instance, a phenomenon called super-conductivity, which means that metals conduct electricity without resistance at low temperatures. It was not at first obvious that this was a consequence of the known laws. Now that it has been thought through carefully enough, it is seen in fact to be fully explainable in terms of our present knowledge. There are other phenomena, such as extra-sensory perception, which cannot be explained by our knowledge of physics. However, that phenomenon has not been well established, and we cannot guarantee that ti is there. If it could be demonstrated, of course, that would prove that physics is complete, and it is therefore extremely interesting to physicists whether it is right or wrong. Many experiments exist which show that it does not work. The same goes for astrological influences. If it were true that the stars could affect the day that it was good to go to the dentist - in America we have that kind of astrology - then physics theory would be proved wrong, because there is no mechanism understandable in principle from the behavior of particles which would make this work. That is the reason that there is some scepticism among scientists with regard to those ideas.
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1. The Law of Gravitation, an example of Physical Law
2. The Relation of Mathematics to Physics
3. The Great Conservation Principle
4. Symmetry in Physical Law
5. The Distinction of Past and Future
6. Probability and Uncertainty - the Quantum Mechanical View of Nature
7. Seeking New Law
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