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\noindent{\er Louis Michel, IHES, 91440 Bures sur Yvette, France,\quad
michel@ihes.fr}\hb
Lecture given at Goslar (Germany) on July 16, 1996 \hb 
to close the ceremony of the Wigner medal award. \hb
{\ninerm published: p.36--44 in {\ninesl Group 21, Physical Applications and 
Mathematical Aspects of Geometry, Groups and Algebras}, vol. 1, editors 
H.-D. Doebner, P. Nattermann, W. Scherer,  World Scientific (1997).}
\vskip 2cm
\centerline{\bf WIGNER Memorial Lecture}
\medskip
\centerline{by Louis Michel \ninerm (Wigner medalist 1984)}
\bigskip
Born on November 17, 1902, Eugene Wigner died on January 1, 1995. Since 
his death, this is the first Wigner medal award ceremony. It is befitting 
to commemorate this very great physicist now. Unfortunately his 
lifelong friend, Edward Teller, has not been able to come, but he did 
send some recollections which will be read later.

An excellent way, may be the best, to commemorate a scientist is to 
publish a collection of his works. The first volume of the Complete  
Scientific Works of Eugene Wigner [1] appeared more than three years 
ago, the eighth and last volume will appear probably next year. These 
volumes include unpublished papers from the Manhattan project and many 
scattered philosophical papers on the nature, the meaning and the role of 
science. Some of the latter had already been gathered by Wigner in 
``Symmetries and Reflections'' [2]. 

Wigner's complete works are so vast and so deep that an eight-day 
colloquium whould be necessary for a real memorial. In a half-hour lecture 
I can only speak about one domain of his activity and that only briefly.
At this XXI International Colloquium on Group Theoretical Methods in 
Physics, I have of course chosen to speak about Wigner's work on symmetry in 
physics. He wrote about sixty papers on this topic, but I have time only to 
speak about some of them. I am sure that every one of you has read, 
and probably studied, his book on ``Group theory''[3].

However one cannot commemorate a scientist without speaking about
the man himself. Happily Wigner has done this for us in 1988, and the 
resulting book {\sl The recollections of Eugene P. Wigner as told to Andrew 
Szanton} [4] is marvellous. Reading it, Wigner appears before you, speaking 
to you, telling you about his life (with delicate discretion regarding his 
private life), his science, his philosophical and political ideas. Yes, his 
scientific judgements were sharp, but his legendary politeness was genuine. 
What struck me most was his immense generosity towards colleagues and younger 
physicists. One of the greatest surprises of my life was to find my name 
among the four persons to whom ``{\sl He wishes to record his deep indebteness}'' 
in the preface of the English edition of his Group Theory book. J. von 
Neumann had already died. Later V. Bargmann received the first Wigner 
medal. The only other survivor is Arthur Wightman who has worked 
tremenduously hard editing Wigner's collected works and was his colleague at 
Princeton University for forty years. It is a pity that Arthur could not
give this Memorial Lecture.

For me Wigner has been a model in science: a complete physicist, drawing, 
when necessary, from his deep mathematical culture. Let me read to you what 
was written for his sixtieth birthday, by some of his Princeton colleagues 
[5]~: ``{\sl A characteristic feature of Wigner's way of working is its 
down-to-earth quality. There are many young men who, their head bulging 
with information on Hilbert spaces, have come to him with an idea, only to 
have him try it out first on $2\times2$ matrices. (It usually helped.) 
Another aspect of this down-to-earth quality is his great respect for, 
and knowledge of, facts. If one comes to discuss a crystal with him, it 
is a good bet that he will be able to give off hand its density, 
structure, thermal conductivity, and the slow neutron cross sections of 
its elements. Moreover the stuff he is thinking about probably has the 
right color.}''

After graduating in chemical engineering in Berlin and the publication of 
his first three papers, including his thesis, Wigner returned to Budapest, 
to work in a Mauthner brothers' tannery (his father had worked all his 
life in it and became a director). He had subscribed to the Zeitschrift 
f\"ur Physik, and was studying it at night, when he could. As he told us 
in a long, published interview [6], he missed the first Heisenberg paper 
on quantum mechanics [7], but read and understood immediately the Born 
and Jordan paper ``Zur Quantenmechanik''[8]. In 1925, invited as an 
assistant by Weissenberg (a well known crystallographer who followed 
Polanyi's advice) in Berlin he became a physicist. He continued to publish 
important work in chemistry with M. Pol\'anyi [9] but started to use 
symmetry in quantum mechanical systems: first the general methodology [10], 
the parity quantum number [11], the atomic spectra (with von Neumann) [12], 
the diatomic molecules (with Witmer) [13], to which must be 
added the work with Jordan [14] on the second quantization of fermion 
fields, the introduction of the ``Vierbein'' for gravitating spinors in
general relativity [15], two other papers with von Neumann (one showed the 
possible existence of a state with discrete eigenvalue inside the interval 
of a continuous spectrum [16], the other studied the changes of atomic level 
structure in adiabatic transformations [17]), two papers on statistics and the 
paper [18] establishing the group theoretical study of the vibrations of 
molecules; indeed the treatment of the symmetry of this classical linear 
problem is similar to that for bounded quantum states of finite systems. 
Such an activity in four years! But they were also exceptional years for 
physics in general. The Jordan and Wigner paper [14] was submitted 
on January 26, 1928 (exactly 24 days after Dirac's paper on his equation); 
they used Clifford algebra for building the representation of the 
anticommutation rules (they were very near to finding the equation for the 
spinning electron!) and proved the uniqueness of the representation 
(this applies also to the Dirac equation). 

``{\sl There was a great reluctance among physicists toward accepting group 
theoretical arguments and the group theoretical point of view}'' wrote Wigner 
in the preface of the English edition of his book; he added 
``{\sl the recognition that almost all rules of spectroscopy  follow from 
the symmetry of the problem is the most remarkable result.}'' The book 
has had a much bigger impact. It is the first place where, for the rotation 
group, the matrix elements of the operators which decompose the Kronecker 
(=tensor) product  of two irreducible representations into the direct sum 
of irreducible representations are computed and systematically studied. 
As Wigner said much later, in a conference to the American 
Mathematical Society [19], they ``{\sl were also called Clebsch-Gordan 
coefficients (though the reason for this is mysterious to me), or vector 
coupling coefficients, which is the name I prefer}''. In the English 
version of the book, he presented them in the symmetrical and covariant form 
called 3-$j$ coefficients, see also [20]. He had already extended them 
[21] to the ``simply reducible groups'' [22]. That started a whole 
industry in theoretical physics; in chapter 27 of the English version of 
his book, Wigner gave an interesting geometrical interpretation of the 
3-$j$ and 6-$j$ (=Racah) symbols and their classical limit.

In his book, Wigner emphasized an original point of view: in quantum 
mechanics, the action of the symmetry group $G$ on the projective space 
of rays (of vector states) can be embedded in a linear unitary projective 
representation of $G$ on the Hilbert space of vector states (he gave the 
proof even for infinite dimension). As you know, for $SO_3$ this 
corresponds to using the representations of its universal covering group
(i.e. $SU_2$); so it leads to the concept of half-integer spin.
In 1937 Wigner solved the same problem for the Poincar\'e group [23]. That 
paper is one of the scientific landmarks. Using some not yet published von 
Neumann's results, it is the first paper giving complete families 
of unitary infinite dimensional representations of a non semi-simple, non 
compact Lie group; moreover this paper also deals with the projective 
representations! In physics it is the foundation of the quantum relativistic 
kinematics of elementary particles.

Two German editions of Weyl's book [24] had appeared before the first edition 
of Wigner's book. These two excellent books are still necessary 
readings for understanding symmetry in quantum physics. Weyl's book has 
a wider mathematical point of view (but does not study projective 
representations) and deals with a broader domain of physics. The 
emphasis is different in the two books and their overlap is relatively 
small. A very weak point in Weyl's book is time reversal. In 1932 
Wigner wrote the fundamental paper on time reversal in quantum physics [25]. 
For physicists outside the Wigner's school of thought it took a long time 
to understand and use this symmetry. One had indeed to tame a new tool 
necessary for this symmetry: the antiunitary operators. Chapter 26 of the 
English version of Wigner's book calls {\sl corepresentations} the extension 
of unitary representations with antiunitary operators and teaches us how 
useful they are. The following year Wigner published two simple and elegant 
papers on antiunitary operators  [26]; the projective corepresentations 
of the full Poincar\'e group were dealt with in [27].

Let us return to 1930: after well-know papers with  Weisskopf on linewidth 
in spectra, Wigner wrote important papers on chemical physics and conceived 
his quantum mechanical phase space distribution function [28] (one of 
his great inventions). In 1932, when the neutron was discovered, Wigner 
immediatly studied this particle [29] and the nuclear forces, without
ignoring other important problems, e.g. studying with Jordan and von Neumann
the role of Jordan algebras in quantum mechanics and the determination of 
the exceptional Jordan algebras [30]. Since Wigner worked for thirty 
more years in nuclear physics, it is outside the scope of this lecture 
to review his related work. I shall mention only three papers. In 1937 the 
one [31] on supermultiplets; it is a formal $SU_4$ invariance treating spins 
and isospins on an equal footing. This abstract approximate symmetry was 
useful for the study of light nuclei. In the sixties it was a surprise to 
discover that it was also valid for heavier nuclei; and in 1964 the symmetry 
was extended to $SU_6$ independently by Sakita, G\"ursey and Radicati, 
Gell-Mann, followed by many physicists. The title of the second one [32],  
with  Eisenbud, summarizes perfectly the content of this basic paper:
``Invariant forms of interaction between nuclear particles''. The third 
paper I choose, [33], is an excellent review of isospin, very rich in 
physics, one which appeared at the right time, viz. that of the 1958 
Feynman, Gell-Mann paper [34]. 

From 1932 on, Wigner was not only pioneering in nuclear physics, but also in 
solid state physics! In this domain, his work and those of his three 
students Seitz, Herring, Bardeen (in chronological order) have had a 
tremendous impact. The first paper is on metallic sodium [35]; this crystal 
contains one atom per fundamental cell of the body centered cubic space group 
$G=Im\bar3m$. The authors consider, for the first time in solid state physics,
the Vorono{\"\i} cell (generally called, because of that paper, Wigner-Seitz 
cell by physicists); they do note that for any $G$-invariant function and on 
any face of the cell, the normal component of the gradient vanishes and that 
the cell can be inscribed in a sphere (i.e. its 24 vertices lie on a sphere). 
Then they show that it is a good physical approximation to replace the 
computation of the valence electron wave function in the crystal by the
corresponding boundary problem inside this sphere, for the Schr\"odinger 
equation with the Coulomb potential of the ion $Na^+$. They solve the 
problem including the effect of Pauli principle and obtain good values for 
the size of the cell, the binding energy by atom (yielding the heat of
vaporisation) and the compressibility coefficient. This paper is a great 
classic. In the papers [36],[37] two predictions were made; respectively, 
the existence of electron crystals (they were first observed in 1981 on 
the surface of superfluid helium) and the existence of a metallic hydrogen 
phase at a pressure greater than .25 millions of atmospheres (it may 
have been discovered this year at Livermore).
In his thesis Seitz constructed the unitary irreducible representations 
of the space groups; for each space group $G$ there is a continuous 
infinity of such representations, labelled by the wave vectors $\vec k$ 
of the Brillouin zone and a finite valued index (labelling the different 
irreducible, ``allowed'' representations of the little space group $G_k$).

The 1936 paper [38], with Bouckaert and Smoluchowsky, is one of the most 
often quoted; indeed it is the fundamental paper for the application of group 
theory to the quantum physics of crystals although he solved only some 
aspects of the very general problem it described. Let us quote from the 
introduction: \hb
``{\sl Thus far the group theory of the Brillouin zone is not different from 
the group theory of any other system. But while in atoms, molecules, etc., 
the characteristic values of (1)} [= the eigenvalues of the Schr\"odinger 
equation for bound states] {\sl are well separated, the characteristic 
values of (1) for a crystal form a continuous manifold...} [for 
instance the energy E is a function over the Brillouin zone.]....\hb
{\sl Thus a certain topology for the representations must exist and 
it will be shown that part of this topology is independent of the 
special Brillouin zone......} ''\hb 
And the last sentence of the introduction is: \hb
``{\sl The investigation of the ``topology'' of representations will be 
essentially the subject of this paper, from the mathematical point of 
view}.'' Indeed, after laying the method for studying the symmetry of 
energy bands, the authors showed how to obtain the compatibility 
conditions. The paper announced Herring's thesis [39] which studied the 
contacts between band branches imposed by time reversal invariance as well 
as the possible accidental degeneracies. This grandiose program has been
forgotten by many solid state physicists: those of them who use only the 
finite Born-von Karman groups, with a finite set of points for the Brillouin 
zone (passing to the continuous limit, when it can be done, is very 
deceptive because the topology is different). J. Zak and I are presently 
completing this aspect of Wigner's program: its predictions are rich and 
harmonious.

In August 1939, just before the start of the big crisis that we call 
``second world war'', Szil\'ard and Wigner suggested to Einstein to 
write a letter to president Roosevelt about the possibility of making 
nuclear bombs. After two mathematical papers on groups [40], [21] and a
few others in nuclear physics (including [32]), there are between 1942 
and 1946 no scientific publications from the outstanding theoretical 
physicist whom we commemorate. During that time he was 
an  exceptional engineer planning in detail a new kind of 
industrial plants: the neutron chain reactors. He had to fight with 
``professional engineers'' as it is clear in [1]V (a typical incident 
is told by Wigner in [6]). The basic physics of that work is given in [3]c.
After the first nuclear bomb test at Alamogordo, Szil\'ard and Wigner 
started a petition for using the bomb only in an uninhabitated place of 
our planet.

At the end of the war Wigner came back to Princeton. From that time on
symmetry in physics was no longer one of his main interests in physics. Thus it 
is very unfair to him to restrict a memorial lecture to this subject. However, 
I cannot end the lecture here without quoting some later important and very 
original works of Wigner in this field. The literature on relativistic wave 
equations was very extensive but partly unsatisfactory without the 1947
contribution of Bargmann and Wigner [41]. At the same time Wigner [42]
considered the equations for particles with infinite spin (corresponding 
to some unitary representations of the Poincar\'e group which seem
pathological for physics); I wish also to mention a subsequent paper [43]
with a similar title, which is a good review of relativistic wave 
equations and contains some approach to 
general relativity. The relations between the latter theory and quantum 
mechanics are also studied in [44] and will be one of the subjects of 
reflections by the older Wigner. Ref [41] led Newton and Wigner to clarify 
very much in [45] the problem of localisability of relativistic particles 
in quantum theory. 

In 1952, the ``three W's paper'' (Wick, Wightman, Wigner) [46] introduced what 
we call now the {\sl superselection rule}, a new concept which shocked many 
physicists at that time, but that cannot be ignored when we are interested 
in the foundation of quantum theory. I cannot refrain from giving you an 
excerpt from the footnote 9 of that paper: {\sl That $C$ is an exact 
symmetry property is moreover still far from proved. The disturbing 
possibility remains that $C$ and $P$ are both only approximate and $CP$ 
is the only exact symmetry law}. A remarkable prophecy which was 
realized within four years! However a tiny violation of $CP$ was found 
in 1964....In a little known work, Wigner proved the conservation with 
time of superselection rules. It was popularized later by the same trio 
[47]. I wish also to mention the contribution of Wigner [48] to what has 
become known as ``Bell's inequalities'' and if I had to answer the impossible 
question (already asked me here) ``which Wigner paper is a summary of 
his teaching on symmetry in physics?'', I would suggest ref. [49]. The 
domain of Wigner's activity I reviewed, corresponds mainly to vol. I of the 
``Collected works''; this volume also contains two analyses by B. Judd and 
G. Mackey.

It is impossible for me to end this lecture without mentioning the 
creation by Wigner of a new tool for studying many physical phenomena:
{\ Random matrices} [50]. A whole industry in theoretical physics has 
been built on the use of them in different domains. 

Wigner has been one of the outstanding physicists of modern times.
His influence is tremendous and will last. Many of us here, owe him much 
scientifically. I suggest to conclude this memorial lecture by a moment
of silence that each of us may use for his own commemoration.
\bigskip 
\noindent
{\bf References}:
\item {[1]} Collected works of Eugene Paul Wigner, vol. I = A biographical 
sketch. Applied group theory. The mathematical papers. II = Nuclear 
Physics. III = Particles and Fields. Foundations of Quantum Mechanics.
IV Physical chemistry. Solid State Physics. V = Nuclear Energy. 
VI Philosophical reflections and Syntheses. To appear VIII = Civil Defense.
and VII. Springer-Verlag.
\item {[2]} E.P. Wigner in {\sl Symmetries and Reflections}, 
Indiana University Press (1967), paper back edition: MIT Press (1970),
reprint edition: Ox Bow, Woodbridge, Conn. (1979).
\item {[3]} a) E.P. Wigner {\sl Gruppentheorie und ihre Anwendung auf die 
Quantummechanik der Atomspektren}, F. Vieweg and Sohn, Braunschweig (1931),
{\sl Group Theory and its application to the quantum mechanics 
of atomic spectra}, Academic Press (1959), expanded and improved edition 
from the translation (by J.J. Griffin) of the German edition. We will 
often mention this reference as Wigner's book. But, besides [2], Wigner 
has also published the books: b)  with L. Einsenbud, {\sl Nuclear 
structure}, Princeton University Press (1958), c) with A.M. Weinberg 
{\sl The Physical Theory of Neutron Chain Reactors}, University of 
Chicago Press (1958).   
\item {[4]} {\sl The recollections of Eugene P. Wigner as told to} Andrew 
Szanton, Plenum Press (1992)
\item {[5]} V. Bargmann, M.L. Goldberger, S.B. Treiman, J.A. Wheeler, 
A. Wightman, To Eugene Paul Wigner on his sixtieth birthday, Rev. Mod. Phys.
{\bf34} p. 587 (1962).
\item {[6]} M.G. Doncel, L. Michel, J. Six, Interview de Eugene P. Wigner sur 
sa vie scientifique, Archives Internationales d'Histoire des Sciences
{\bf34} (1984) 177-217. This long interview of Wigner was done in two 
parts, one in French and one in English. It contains several informations 
not given in [4].
\item {[7]} W. Heisenberg, \"Uber die quantentheoretische Umdeutung 
kinematischer und mechanischer Beziehungen, Z. Phys. {\bf33} (1925) 879--893.
\item {[8]} M. Born, P. Jordan, Zur Quantenmechanik, Z. Phys. {\bf34} (1925) 
858-888.
\item {[9]} M. Polanyi, E. Wigner, Z. Phys. Chem. {\bf139} (1928) 439.
\item {[10]} E. Wigner, \"Uber nichtkombinirende Terme in der neueren 
Quantentheorie, Z. Phys. {\bf40} (1927) 492--500 and 883--892.
\item {[11]} E. Wigner, Einige Folgerungen aus der Schr\"odingerschen Theorie 
f\"ur die Termstrukturen, Z Phys.{\bf43} (1927) 624--652. 
\item {[12]} J. v. Neumann, E. Wigner, Zur Erkl\"arung einiger Eigenschaften 
der Spektren aus der Quantenmechanik des Drehelektrons, Z. Phys. I. {\bf47} 
(1928) 203--220; II. {\bf49} (1928) 73--94; III. {\bf51} (1928) 
844--858. 
\item {[13]} E. Wigner, E.E. Witmer, \"Uber die Struktur des zweiatomigen 
Molekulspektrum nach den Quantenmechanik, Z. Phys. {\bf51} (1928) 859--886.
\item {[14]} P. Jordan, E. Wigner, \"Uber das Paulische \"Aquivalenzverbot,
Z. Phys. {\bf47} (1928) 631--651. 
\item {[15]} E. Wigner, Eine Bemerkung zu Einsteins neuer Formulierung des 
allegemeinen Relati\-vit\"ats-prinzips, Z Phys. {\bf53} (1929) 592--596. 
\item {[16]} J. v. Neumann, E. Wigner, \"Uber merkw\"urdige diskrete 
Eigenworte, Physik Z. {\bf30} (1929) 465--467.
\item {[17]} J. v. Neumann, E. Wigner, \"Uber das Verhalten von Eigenwerten 
bei adiabatischen Prozessen, Physik Z. {\bf30} (1929) 467--470.
\item {[18]} E. Wigner, \"Uber die elastischen Eigenschwingungen symmetrischer 
Systeme, Nachr. Ges. Wiss. G\"ottingen Math.-Phys. Kl. (1930) 133-146.
\item {[19]} E.P. Wigner, Symmetry principles in old and new physics, 
Bull. Amer. Math. Soc. {\bf74} (1968) 793-815.
\item {[20]} E. Wigner, On the matrices which reduce the Kronecker product 
of representations of S. R. groups, p. 89--133 in {\sl Quantum Theory of 
Angular momentum}, edit. L.C. Biedenharn and H. Van Dam, Academic Press 
(1965). This book reprints [11], [21].
\item {[21]} E. P. Wigner, On representations of certain finite groups,
Amer. J. Math., {\bf63} (1941) 57--63.
\item {[22]} E. Wigner, a) Condition that the irreducible representations of 
a group, considered as representations of a subgroup, do not contain any 
representation of the subgroup more that once, p. 131--136 in {\sl 
Spectroscopic and group theoretical methods in Physics. Racah volume 
memorial}, edit. F. Bloch {\it et al}, North-Holland Publ. (1968); 
b) Restriction of irreducible representations of groups to a subgroup, Proc. 
Roy. Soc. Lond. A. {\bf322} (1971) 181--189; c) with F.E. Goldrich,
Condition that all irreducible representations of a compact Lie group,
if restricted to a subgroup, contain no representation more that once,
Can. J. Math. XXIV (1972) 432-438.
\item {[23]} E. Wigner, On unitary representations of the inhomogeneous 
Lorentz group, Annals Math. {\bf40} (1939) 149--204. Wigner quotes the 
less complete and less rigourous paper of E. Majorana (N. Cim. {\bf9} (1932) 
335) on the representations of the Lie algebra of the Poincar\'e group. 
It is remarkable that 
part of this Wigner's paper is purely algebraic. I was very  interested 
by the beginning of the ``{\sl Acknowledgement. The subject of this paper 
was suggested to me as early as 1928 by P.A.M. Dirac who realized even 
at that date the connection of representations with quantum mechanical 
equations. I am greatly indebted to him also for mainly fruitful 
conversations about this subject, especially during the years 1934/35, 
the outgrowth of which the present paper is}''. I had the occasion to talk at 
length with each of them in the early seventies, but neither could 
remember these conversations. In [6] Wigner told that his paper was 
refused by Amer. J. Math. but in 1980 he received a telephone call from 
this review congratulating him to have published one of the 25 most often 
quoted papers in mathematics since the beginning of the century!
\item {[24]} Hermann Weyl, Gruppentheorie und Quantenmechanik, S. Hirzel, 
Leipzig, 1928, 2. Auflage, umgearbeitet 1931, English tranlation, 
Dutton (1932) reprinted by Dover in 1949. This book quotes the ref. [10] 
and [14] but not [12].     
\item {[25]} E. Wigner, \"Uber die Operation der Zeitumkehr in der 
Quantenmechanik, Nachr. Ges. Wiss. G\"ottingen Math.-Phys. Kl. (1932) 546--559.
\item {[26]} E.P. Wigner, J. Math. Phys. {\bf1} (1960) p. 409--413: Normal 
form of antiunitary operators; p. 414--416: Phenomenological distinction
between unitary and antiunitary symmetry operators. 
\item {[27]} E.P. Wigner, Unitary Representations of the Inhomogeneous 
Lorentz Group Including Reflections, p. 37--80 in  Group Theoretical 
Concepts and Methods in Elementary Particle Physics., edit. F. G\"ursey,
Gordon and Breach (1964). Wightman and I knew of this Wigner's work for more 
than ten years before; it defines what is often quoted as ``Wigner types''.
\item {[28]} E. Wigner, On the quantum correction for thermodynamic 
equilibrium, Phys. Rev. {\bf40} (1932) 749.
\item {[29]} E. Wigner, Beitr\"age zur Theorie des Neutrons, Math. 
Naturw. Anz. Ungar. Akad. Wiss. {\bf49} (1932) 142.
\item {[30]} P. Jordan, J. v. Neumann, E. Wigner, On an algebraic 
generalisation of the quantum mechanic formalism, Annals Math. {\bf35}
(1934) 29.
\item {[31]} E. Wigner, On the consequence of the symmetry of the nuclear 
Hamiltonian on the spectroscopy of nuclei., Phys. Rev. {\bf51} (1937) 
106--119. 
\item {[32]} L. Eisenbud and E.P. Wigner, Proc. Natl. Acad. Sci. U.S. 
{\bf27} (1941) 281.
\item {[33]} E.P. Wigner, Isotopic spin: a quantum number for nuclei, p. 
67--91, chap IV of Proceed. Robert A. Welch Foundation Conferences on 
Chemical research, I. The structure of the nucleus.
\item {[34]} R.P. Feyman and M. Gell-Mann, Theory of Fermi interaction,
Phys. Rev. {\bf109} (1958) 193--198.
\item {[35]} E. Wigner and F. Seitz, On the constitution of metallic 
sodium, Phys. Rev. {\bf43} (1933) 804--810, II. {\bf46} (1934) 509.
\item {[36]} E. Wigner, On the interactions of electrons in metals,
Phys. Rev. {\bf46} (1934) 1002--1011.
\item {[37]} E. Wigner and H.B. Huntington, On the possibility of 
metallic modification of hydrogen, J. Chem. Phys. {\bf3} (1935) 764--770. 
\item {[38]} L.P. Bouckaert, R. Smoluchowsky, E. Wigner, Theory of 
Brillouin zones and Symmetry Properties of Wave functions in Crystals.
Phys. Rev. {\bf50} (1936) 58--67
\item {[39]} C. Herring, Phys. Rev. {\bf52} (1937) a) Effect of Time 
reversal symmetry on energy bands of crystals, p. 361--365; b) Accidental 
degeneracy in the Energy bands of Crystals, p. 365--373.
\item {[40]} J. v. Neumann, E.P. Wigner, Minimally almost periodic groups, 
Annals Math. {\bf41} (1940) 746--750.
\item {[41]} V. Bargmann and E.P. Wigner, Group theoretical discussion 
of relativistic wave equations, Proc. Natl. Acad. Sci. U.S. {\bf34}
(1948) 211--223.
\item {[42]} E. Wigner, \"Uber relativistische Wellengleichungen, Z. Phys.
(1948) 665.
\item {[43]} E. Wigner, Relativistic invariance of quantum mechanical 
equations, Helv. Phys. Acta Suppl. {\bf4} (1956) 210--226.
\item {[44]} E. Wigner, Relativistic invariance and quantum phenomena,
Rev. Mod. Phys. {\bf29} (1957) 255--268.
\item {[45]} T.D. Newton and E.P. Wigner, Localized states for 
elementary systems, Rev. Mod. Phys. {\bf21} (1949) 400--406.
\item {[46]} G.C. Wick, A.S. Wightman and E.P. Wigner, The intrinsic 
parity of elementary particles, Phys. Rev. 88 (1952) 101--105.
\item {[47]} G.C. Wick, A.S. Wightman and E.P. Wigner, Superselection 
rule for charge, Phys. Rev. {\bf D1} (1970) 3267--3269.
\item {[48]} E.P. Wigner, On hidden variables and quantum mechanical 
probabilities, Amer. J. Phys. {\bf38} (1970) 1005.
\item {[49]} R.M.F. Houtappel, H. Van Dam and E. Wigner, The conceptual 
basis and use of the geometric invariance principles, Rev. Mod. Phys. 
{\bf37} (1965) 595--632.
\item {[50]} E.P. Wigner, Random matrices in physics, SIAM Rev. {\bf9}
(1967) 1--22. That is a 30 year old review by Wigner himself!
 
\bye