— James Clerk Maxwell (1831 – 1879), Electricity and Magnetism, 1873.
It’s extremely improbable that when we come to understand
the true nature of electrolysis we shall retain in any form the theory of
molecular charges, for then we shall have obtained a secure basis on which to
form a true theory of electric currents and so become independent of these
provisional theories.
— James Clerk Maxwell (1831 – 1879).
Our generation has produced many volumes about recondite,
abstruse, and occult causes and wonders, and in all of them amber and jet are
represented as attracting chaff; but never a proof from experiments, never a
demonstration do you find.
— William Gilbert (1540-1603), De Magnete
[All About Magnets], 1600.
Of course, if electrons were waves, there would be no
difficulty. We think we understand the regular reflection of light and X-rays —
and we should understand the reflection of electrons as well, if only electrons
were waves instead of particles. This observation, though true, does not seem a
particularly valuable one. It is rather as if one were to see a rabbit climbing
a tree, and one were to say, ‘Well that is a rather strange thing for a rabbit
to be doing, but after all there is nothing to get excited about. Cats climb
trees — so that, if the rabbit were only a cat, we would understand its
behaviour perfectly’. Of course, the explanation might be that what we took to
be a rabbit was actually not a rabbit at all, but was actually a cat. Is it
possible that we are mistaken about electrons? Is it possible that we have been
wrong all this time in supposing that they are particles, and that actually
they are waves?
— Clinton Joseph Davisson (1881 – 1958), Franklin
Institute Journal, 205, 597.
I have already indicated that as soon as e is known it
becomes possible to find with the same precision which has been attained in its
determination the exact number of molecules in a given weight of any substance,
the absolute weight of any atom or molecule, the average kinetic energy of
agitation of an atom or molecule at any temperature, and a considerable number
of important molecular and radioactive constants. In addition, it has recently
been found that practically all of the important radiation constants like the
wave-lengths of X-rays, Planck’s h, the Stefan-Boltzmann constant [sigma], the
Wien constant c [c-subscript-2] etc., depend for their most reliable evaluation
upon the value of e. In a word, e is coming to be regarded, not only as the
most fundamental of physical or chemical constants, but also one of the most
supreme importance for the solution of the numerical problems of modern
physics.
— Robert Andrews Millikan (1868 – 1954), The
Electron, Phoenix Science Books, 1963, facsimile of the 1917 edition, 114 –
115.
On the wave side of its nature the electron is a widely
extended entity which in a sense occupies the whole region in which it might be
found. An electron is like an able guerrilla leader who occupies a wide area
with rumours of his presence, but when he strikes, he strikes with his whole
force. No analogy is perfect, and though the analogy between light and
electrons even extends to this curious duality of wave and particle, it breaks
down in the end.
Electrons are essentially different from light. They are
acted on by electric and magnetic forces, and react on the bodies which cause
these forces. Light does not, it only affects matter when it actually hits it;
there is no action at a distance. Further, the electronic waves are a trifle
less real than those of light. No one, it is true, has ever actually observed
the frequency of visible light, but that of a very long wireless [radio] wave
can be directly followed and the difference must be only one of degree.
Now as far as we know at present the frequency of electron waves is quite unobservable; it is always the
wave-length which we find. Possibly
one could observe differences of frequency under very special conditions, but
the absolute values seem to have no significance except as mathematical
symbols. Different values can be assigned to this frequency and the calculated
results still agree with experiment. Again, the fluctuating quantities or
“displacements” in the light wave have a definite physical meaning, namely,
electric and magnetic intensities. No one has observed the corresponding
quantity in the electronic wave. Indeed, in the most successful forms of the
theory, it is not even a real number.
Only the intensity of the wave has a physical meaning,
namely the chance that an electron will appear at the place in question. The
two views of electrons, as particle and as wave, are parables, each enshrining
a part of the truth. Whether between them they include all that we need to
know, as some physicists believe, or whether there are not other aspects still
undreamed of, is for the future to decide.
— Sir George Paget Thomson (1892 – 1975), Address before the Royal Institution,
4th December 1931.
You have, in entering novelty, to use what you know. You
would not be able to make meaningful mistakes without analogy. You would not be
able to try things out, the failure of which was interesting. You start
thinking by the use of analogy. Analogy is not the criterion of truth; it is an
instrument of creation, and the sign of the effort of human minds to cope with
something novel, something fresh, something unexpected. Analogies play, in the
relation between sciences, a very great part, sometimes a harmful one; and they
also play a decisive role in what little there is that natural science can
teach of general use in general human experience.
One of the great things of this century is how illuminating
and relevant the experience of the quantum theory, of complementarity, has
been; how wide the scope of those analogies; I think for our children it will
be better understood. What am I speaking of? The uncertainty in the position of
an electron can be very small, the uncertainty in its momentum can be very
small, but no experiment, no situation can be devised which makes them both
very small at the same time. This means that the physicist, or anybody else,
has some choice as to what he is going to look at in a system, what he is going
to realise. Is he going to realise a positioned electron or an electron which
has a well-defined velocity and wavelength? He can do one or the other but they
are complementary in the sense that there is no piece of equipment which will
do both for him. He cannot realise them both together; one says that they are
complementary situations.
But life is full of that. We all know it in the relations
between our acts and our introspection, our thinking about our acts. Hamlet has
said it better than Planck’s constant. We know it in the difference between,
the inherent ability fully to combine, the ideals of love and the ideals of
justice. They are just about two different things; balance between them, yes,
but fulfilment of both simultaneously, I think we know that that is not
possible. We know it in the difference between a piece of knowledge, a piece of
equipment, or a man regarded on the one hand as an instrument and on the other
hand as an end or a purpose or an object; the difference between the inevitable
and universal transience of events and their eternal and timeless quality. This
is part of life; and it is simply a rich set of analogies to the rather sharply
defined, nonambiguous, straightforward complementarity that one found in the
heart of the atom.
— Julius Robert Oppenheimer (1904 – 1967), On the Theory of Electrons and
Protons, Physical Review, 35 (1930),
562 ff.
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