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Three Degrees.' They were exploring, and found the uniform background radiation prior to any theory of
it. But here is what happens to this very experiment when it becomes `history':
Theoretical astronomers have predicted that if there had been an explosion billions of years ago,
cooling would have been going on ever since the event. The amount of cooling would have reduced the
original temperature of perhaps a billion degrees to 3K 3 above absolute zero.
Radioastronomers believed that if they could aim a very sensitive receiver at a blank part of the sky, a region that
appeared to be empty, it might be possible to determine whether or not the theorists were correct. This was done in
the early 197os. Two scientists at Bell Telephone Laboratories (the same place where Karl Jansky had
discovered cosmic radio waves) picked up radio
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t Information and Publication Division, Bell Laboratories, 1979.
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signals from `empty' space. After sorting out all known causes for the signals, there was still left a
signal of 3 they could not account for. Since that first experiment others have been carried out. They
always produce the same result 3 radiation.
Space is not absolutely cold. The temperature of the universe appears to he 3K. It is the exact
temperature the universe should be if it all began some 13 billion years ago, with a Big Bang. 2
We have seen another example of such rewriting of history in the case of the muon or meson,
described in Chapter 6. Two groups of workers detected the muon on the basis of cloud chamber
studies of cosmic rays, together with the Bethe Heitler energy-loss formula. History now has it that
they were actually looking for Yukawa's `meson', and mistakenly thought they had found it when in
fact they had never heard of Yukawa's conjecture. I do not mean to imply that a competent historian
of science would get things so wrong, but rather to notice the constant drift of popular history and
folklore.
Ampere, theoretician
Let it not be thought that, in a new science, experiment and observation precede theory, even if, later
on, theory will precede observation. A.-M. Ampere (1775 1836) is a fine example of a great scientist
starting out on a theoretical footing. He had primarily worked in chemistry, and produced complex
models of atoms which he used to explain and develop experimental investigations. He was not
especially successful at this, although he was one of those who, independently, about 1815, realized
what we now call Avogadro's law, that equal volumes of gases at equal temperature and pressure will
contain exactly the same number of molecules, regardless of the kind of gas. As we have already seen
in Chapter 7 above, he much admired Kant, and insisted that theoretical science was a study of
noumena behind the phenomena. We form theories about the things in themselves, the noumena,
and are thereby able to explain the phenomena. That was not exactly what Kant intended, but no
matter. Ampere was a theoretician whose moment came on September 11 1820. He saw a
demonstration by ersted that a compass needle is deflected by an electric current. Commencing on
September 20 Ampere laid out, in weekly lectures, the
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2 F.M. Bradley, The Electromagnetic Spectrum, New York, 1979, p. 100, my emphasis.
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foundations of the theory of electromagnetism. He made it up as he went along.
That, at any rate, is the story. C.W.F. Everitt points out that there must be more to it than that,
and that Ampere, having no official post-Kantian methodology of his own, wrote his work to fit. The
great theoretician experimenter of electromagnetism, James Clerk Maxwell, wrote a comparison of
Ampere and Humphry Davy's pupil Michael Faraday, praising both ` inductivist ' Faraday and
`deductivist' Ampere. He described Ampere's investigation as `one of the most brilliant achievements
in science . . . perfect in form, unassailable in accuracy . . . summed up in a formula from which all
the phenomena may be deduced', but then went on to say that whereas Faraday's papers candidly
reveal the workings of his mind,
We can scarcely believe that Ampere really discovered the law of action: by means of the experiments
which he describes. We are led to suspect what, indeed, he tells us himself, that he discovered the law
by some process he has not shewn us, and that when he had afterwards built up a perfect
demonstration he removed all traces of the scaffolding by which he had raised it.
Mary Hesse remarks, in her Structure of Scientific Inference (pp. 20If, 262), that Maxwell called Ampere the
Newton of electricity. This alludes to an alternative tradition about the nature of induction, which
goes back to Newton. He spoke of deduction from phenomena, which was an inductive process. From
the phenomena we infer propositions that describe them in a general way, and then are able, upon
reflection, to create new phenomena hitherto unthought of. That, at any rate, was Ampere's
procedure. He would usually begin one of his weekly lectures with a phenomenon, demonstrated
before the audience. Often the experiment that created the phenomenon had not existed at the end of
the lecture of the preceding week.
Invention (E)
A question posed in terms of theory and experiment is misleading because it treats theory as one
rather uniform kind of thing and experiment as another. I turn to the varieties of theory in Chapter 12.
We have seen some varieties in experiment, but there are also other relevant categories, of which
invention is one of the most important. The history of thermodynamics is a history of practical
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invention that gradually leads to theoretical analysis. One road to new technology is the elaboration of
theory and experiment which is then applied to practical problems. But there is another road, in
which the inventions proceed at their own practical pace and theory spins off on the side. The most
obvious example is the best one: the steam engine.
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