Professor John Wheeler was a giant among physicists and a perfect
gentleman among scholars. He had a profound impact not only on all
those who were associated with him, but also on many generations of
physicists who follow his paths. He will always be in our collective
memories.
It was only a few years ago when many of his associates celebrated his
90th birthday with a symposium on "Science and Ultimate Reality" at
Princeton. About a year before the celebration, Wheeler in his
typical way wrote an article in the New York Times about the glory of
quantum physics and the mystery of its physical origin. In an
interview conducted by the Dennis Overbye of the New York Times,
Professor Wheeler said gleefully that he suffered a minor heart attack
just a year ago and that was a good thing because the mishap reminded
him that time was running short and he had better hurry up to solve
the problem of tomorrow. His youthful enthusiasm for solving
fundamental problems held no reservations even at his 'tender' age of
90.
I first met Professor Wheeler in the fall of 1960 when I was an
undergraduate at Princeton. He guided me to use Regge Calculus to
exhibit the structure of a wormhole as my senior thesis. Later in
graduate school he guided me to study the stability of superheavy
nuclei and introduced me to his idea of toroidal nuclei.
Wheeler's class teaching was in the style of the old masters. He
would come to the class often without notes, and would begin his
gentle and deliberate narration step by step from memory, writing down
the concepts and formulas in detail and explaining the thinking that
was needed at each step, as if he was thinking aloud. In the process,
we students could observe how a great mind was at work, as if pulling
out the thread of the silk continuously from a cocoon. On a few
occasions, he might get stuck in the middle of the narration, and
would stop in front of the blackboard. We students would wait eagerly
to see how he would resolve the difficult points in question. A short
pause later, he would resume and march on to get the key concepts
across. He was well known for drawing pictorial representations of
objects that were informative, complex, and often with philosophical
implications. His pictorial depiction of the Participatory Universe
and its participating observers by the letter U (or perhaps it is the
first letter of his initial J), with an eye at the end, is legendary!
Wheeler believed in the simplicity of nature. He reminded us often
that once the solution of a physics problem became known, one would
not but marvel at the simplicity of the solution and would hit oneself
regretfully why such a solution did not present itself earlier in the
first place. Wheeler's high regard for the simplicity of nature led
him to explore the possibility that the whole universe consisted of a
single electron. Indeed, no picture would be simpler if the whole
universe consisted of a single electron, with all other particles as
composite entities of electrons and positrons. Wheeler examined the
consequences of such a picture as hard as he could until late 1940's,
with the development of the model of poly-electrons, bound states of
composite objects of many electrons and positrons. He reluctantly gave
up this simple single-electron description of the universe when many
elementary particles were discovered. However, as we now know, it was
this picture of a single electron world line, winding itself up and
down in time to give rise to electrons and positrons, that led to
Feynman's space-time picture of particles and antiparticles. Feynman
won the Nobel Prize in Physics in 1965.
Wheeler's belief in the simplicity of nature led him to search for a
description of mass and charge that was free of singularities. In the
1950's, he constructed the singularity-free description of a mass that
was a gravitational-electromagnetic entity (geon). He also
constructed the singularity-free wormhole solution of a mass and a
charge to represent a "mass without mass", and a "charge without
charge". Wheeler was initially perturbed by the solution of an
inevitable gravitational collapse, and he examined the hydrodynamics
of gravitational collapse with many of his students, only to come to
the conclusion that there was no escape from gravitational collapse
for a very massive object.. Hence, he adopted the term 'black hole'
to represent a gravitationally collapsed object.
Wheeler's belief in the simplicity of nature extended also to his
search for answers to fundamental questions such as "Why the
quantum?", "How come existence?", and "How come physical
laws?"
Nothing would be simpler if the physical laws arose by themselves from
"nothing". Hence he proposed the simplest of these
possibilities, "it
from bit", in which the laws of nature could emerge from the
primordial chaos of binary bits perhaps as a result of quantum
uncertainty. Out of an ensemble of universes, a universe with a
successful evolution would leave behind participating observers to
record the evolution. In this way, the physical laws arose from no
law and out of nothing. Were Taoist Masters Lao Tsu and Chuang Tsu
alive today, they would look approvingly at Wheeler's Participatory
Universe with great favor!
As reported by Kip Thorne, Feynman said of Wheeler. ''Some people
think Wheeler's gotten crazy in his later years, but he's always been
crazy.'' Wheeler had an inventive mind that accepted no boundaries.
He was always curious about the world around him, from the vast
expanse of the universe down to the most basic and inner question of
man's existence. He always told his students that "no question is
stupid enough not to be an interesting question". Wheeler liked to
tell us the story of a battleship (in a dead-silent environment) in
enemy waters in which a stupid seaman's answer of flushing off an
enemy mine by blowing from the mouth turned out to lead to the
solution of blowing by the water hose --- a tentative solution led to
other better and better solutions. Wheeler's daring spirit to make
new and unconventional proposals left a very deep impression on his
students. He argued that it was only through daring supposition and
the ability to abstract the most complicated subject to come up with a
few words, a few lines, that may eventually bring out the promising
lines of approach. No supposition is silly enough to be dismissed
right away. Just by trying out one way, another promising method may
follow. Examples are best illustrated by his pursuit of the
one-electron universe that led to development of the space-time
concept, and the search for singularity-free solutions that led to the
inevitability of the gravitational collapse and black holes.
Among other things, Wheeler's "black hole", "wormhole",
"geons",
"quantum foams", "mass without mass", "charge without
charge", "law
without law", "it from bit", "Planck length",
"superheavy nuclei",
"neutron drip line" have become part of physics vocabulary.
In nuclear physics, Professor Wheeler made many important
contributions. Wheeler was the first to propose the collective motion
description for the nuclear structure of Be and C in 1937. It was
indeed a pity that when the Nobel Prize in Physics was awarded in 1975
for the discovery of the nuclear collective motion, Wheeler was not
included as one of the honorees. Soon after the discovery of nuclear
fission, the classic paper of Bohr and Wheeler in 1939 laid the
foundation for the dynamics of the nuclear fission process. His
papers with Hill, with Ford, and with Griffin in 1950's provided the
ground work for the dynamics and scattering of nuclear systems.
Wheeler was the first to propose superheavy nuclei and toroidal
nuclei. He introduced the S matrix which was later taken up by
Heisenberg. He was the first to study the solution of the
Schroedinger equation by the phase-amplitude method. His
contributions to gravitation physics are well-known. In his later
years, he turned to examine the foundation of quantum mechanics and
the question of existence which also led to significant impact. His
famous statements, "How come existence?", "it from bit",
"delayed-choice experiment", and "the participatory
universe" ... are very well-known.
Professor Wheeler's love for science was profound and contagious. He
inspired many generations of physicists. Wheeler declared
categorically that the greatest discovery is yet to come. It is such
a sweeping pronouncement that has driven many bright minds working
through thick and thin to search for new discoveries to reveal nature
as it is. In the process, we all benefit from the fruits of their
continuous search. At the end, whether the discovery will be the
greatest or not will not matter. It is the spirit of pursuit that is
the essence of the quest.
Wheeler's First Moral Principle says, 'never do a calculation without
knowing the answer.' He urged his students to make first an estimate
before every evaluation and to try a simple physical argument before
every derivation. A right guess will reinforce intuition while a
wrong guess will bring new insights. This way of developing intuition
should indeed be a guiding principle for all serious students of
physics.
Among his many admirable personal qualities, Wheeler held his students
in high regards and encouraged them to reach great heights of
achievement. He had an uncanny ability to get the best out of his
students. Many were the times when he encouraged his students to take
up assignments that later would be pivotal in the development of their
careers. In 1962, while Kip Thorne was a graduate student, Wheeler
was lecturing on General Relativity. On many occasions when Wheeler
was away, he would ask Kip Thorne, a second-year graduate student, to
substitute for him to teach the General Relativity class. We all now
know what an outstanding physicist Kip Thorne has later turned out to
be. When John Toll was a graduate student, Wheeler asked John Toll to
take up an important administrative assignment in Project Matterhorn.
John Toll later held many important positions in many educational and
scientific organizations. Wheeler's ability to nourish the
development of his students gave an extra dimension to his impact as a
mentor.
Wheeler had genuine concern for the welfare of his students. From
time to time, he would write letters to his students to provide a note
of encouragement. In the early 1970's, he wanted to get in touch with
one of his students, Bei-Lok Hu (now at Maryland), but he did not know
his whereabouts. He wrote 5 letters and sent them out
simultaneously to
five locations in order that his message would reach him. Few other
mentors would try as hard and would be as concerned about their
students.
Wheeler held warm friendship for his students both when they were
working under him and afterward. In my student days, he often invited
his students to tea in his Princeton home near the Institute for
Advanced Study. In even earlier years when Einstein was still living,
sometimes his Sunday tea party might include Einstein as a special
guest. During the summer, he would stay at his cottage in Maine and
would often invite his students to visit him. I visited Wheeler once
in early 1970's at his Maine cottage. His cottage was on a small
island by the sea, connected to the shore by a causeway. Around noon,
he looked at his watch and stopped working on our physics problem. He
changed to a swimming suit, opened the screened door and took a dip to
swim just outside his cottage. His warmth and friendship provide a
role model for his students -- to treat others with respect and
sincerity. Later when my three children went to study at Princeton
and came to see him, he would receive them with warmth and kind words
of encouragement.
Wheeler was productive and kept on publishing even in his 90's. His
inquisitive spirit was an inspiration for all his students. He sat
and listened to all the scientific talks in the Symposium at Princeton
to honor his 90th birthday all the way through -- for many hours on
end, without showing any sign of being bored or tired. It is not
surprising that his students have a good example to follow and
continue to be productive in making scientific contributions. We all
hope that we can be scientifically productive even in our old age.
We remember Professor Wheeler's inquisitive spirit. We remember his kindness, his encouragement, and his warm friendship. We remember the many wonderful pieces of physics treasure that he left for us. By his enthusiastic participation, he greatly enriched the Universe. He was one of the most honorable members of the Participatory Universe. He will always be in our collective memories.