Presentation Speech by Professor Ivar Waller, member of the Nobel Committee for Physics

Your Majesty, Your Royal Highnesses, Ladies
and Gentlemen.

The electrons of an atom move according to the laws of quantum
mechanics established in 1925 and the next following years. For
the hydrogen atom, which has only one electron and consequently
is the simplest atom to investigate theoretically, the
calculation of the motion of the electron in the electric field
of the nucleus led to results of such accuracy that 20 years
elapsed until any error of the theory could be found
experimentally. This occurred, however, in 1947 when Lamb and his
collaborator Retherford discovered that some energy levels of
hydrogen which should coincide theoretically were in fact
somewhat shifted relative to each other.

One important result of the work of this year's Nobel Prize
winners Sinitiro Tomonaga, Julian Schwinger and Richard Feynman
was the explanation of the Lamb-shift. Their work is, however,
much more general and of deep general significance to physics. It
has explained and also predicted several important phenomena. It
is the continuation of some investigations performed in the late
1920's in order to find the general quantum mechanical laws
according to which the atoms and in particular the electrons give
rise to electromagnetic fields, e.g. emit light, and are
influenced by such fields. By applying quantum mechanics not only
to matter but also to the electromagnetic field Dirac, Heisenberg, and Pauli managed in those
years to formulate a theory, called quantum electrodynamics,
which contains the quantum mechanical laws for the interaction of
charged particles, in particular electrons, and the
electromagnetic field. It satisfies the important condition of
being in agreement with the theory or relativity.

It was soon realized, however, that this theory had serious
defects. When one tried to calculate a quantity of such
importance as the contribution to the mass of an electron
originating in its interaction with the electromagnetic field an
infinite and therefore useless result was obtained. A similar
difficulty occurred for the charge of the electron.

Because of the fundamental importance of having a more useful
quantum electrodynamics many theoretical physicists tried during
the 1930's to over come those difficulties. Some indications were
forthcoming how this should be accomplished. It lasted, however,
until the 1940's for decisive progress to be made.

A new area was then initiated by investigations first performed
by Tomonaga. His work was primarily related to the demands
imposed by the theory of relativity. In a paper published in 1943
and in later work published together with his collaborators,
Tomonaga managed to give a new formulation of quantum
electrodynamics and other similar theories, which marked an
important progress.

Definite progress was only made as a consequence of the discovery
of the Lamb-shift mentioned earlier. When this discovery was
discussed at a conference the idea was accepted that the new
effect could be explained by quantum electrodynamics provided the
proper interpretation was given to this theory. The correctness
of this idea was supported by a provisional calculation of the
Lamb - shift which was published by Bethe shortly after the
conference.

As soon as Tomonaga knew about the Lamb experiment and Bethe's
paper he realized that an essential step to be taken was to
substitute the experimental mass for the fictive mechanical mass
which appeared in the equations of quantum electrodynamics and to
perform a similar renormalization of the electric charge. The
compensating terms which had then to be introduced in the
equations should cancel the infinities. Tomonaga managed to carry
out this difficult program on the basis of his earlier
investigations mentioned above. He deduced further a correct
formula for the Lamb-shift which was found to give results in
good agreement with the measurements.

Almost simultaneously with the discovery of the Lamb-shift
another peculiarity was found by Kusch and his collaborator Foley, which
made it clear that the magnetic moment of the electron is
somewhat larger than had been assumed before. Using the method of
renormalization which he also developed Schwinger was able to
prove that a small anomalous contribution should be added to the
value of the magnetic moment accepted until then. His calculation
agreed with the experiments. Schwinger's calculation was indeed
earlier than and very important for the proper interpretation of
these measurements.

Schwinger had developed the formalism of the new quantum
electrodynamics in several fundamental papers using partially
methods similar to those of Tomonaga. He has also made this
formalism more useful for practical calculations.

Feynman used more radical methods for solving the problems of
quantum electrodynamics. He created a new formalism which he made
very useful for practical calculations by introducing a graphical
interpretation called Feynman diagrams, which have become an
important feature of modern physics. In the description used by
Feynman the electromagnetic field did not any more appear
explicitly. His description has been very valuable in elementary
particle physics where it is necessary to consider besides the
electromagnetic also other interactions.

When considering the truth of quantum electrodynamics in its new
form one has first of all to realize the extraordinary success of
this theory in giving results in agreement with the experiments.
For the Lamb-shift and for the anomalous part of the magnetic
moment of the electron the agreement is within some parts in one
hundred thousand respectively in a million and no disagreement
has yet been found. Quantum electrodynamics is indeed one of the
most accurate of all the theories of physics. Further evidence in
this respect is given by the applications of the theory to the
positronium atom and to the mu-particle. The new formalism has
also been very important for other parts of physics in particular
elementary- particle physics, but also solid-state physics,
nuclear physics and statistical mechanics.

Professor Tomonaga has unfortunately been prevented by an
accident from receiving his prize here in Stockholm. It will be
presented to him by intermediary of the ambassador of Sweden in
Tokyo, and it is accompanied by the congratulations of the Royal
Academy of Science.

Professor Schwinger and Professor Feynman.
By introducing new ideas and methods into an old theory you have,
together with Professor Tomonaga, created a new and most
successful quantum electrodynamics, which occupies a central
position in physics. This theory has been unique in stimulating
modern research. You have yourself contributed to the extension
of its methods to other fields of physics where it has also been
essential for recent progress.

On behalf of the Royal Academy of Science I congratulate you on
your work and ask you to receive your Nobel Prize from the hands
of His Majesty the King.

From *Nobel Lectures, Physics 1963-1970*, Elsevier Publishing Company, Amsterdam, 1972

Copyright © The Nobel Foundation 1965

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