Cold Fusion Theory: A Brief History
by Julian Schwinger
Nobel laureate Julian Schwingers talk at
the Fourth International Conference on Cold Fusion, ICCF4, Maui,
Hawaii, December 1994. Because Julian was not able to attend ICCF4,
his presentation was read to an evening session by Eugene Mallove.
This was the second talk that Schwinger had delivered to a cold
fusion conference, the first having been in Salt Lake City in March
1990 at the First Annual Conference on Cold Fusion. Ed.
As Polonious might have said: "Neither a true-believer
nor a disbeliever be." From the very beginning in a radio broadcast
on the evening of March 23, 1989, I have asked myself not whether
Pons and Fleischmann are rightbut whether a mechanism can
be identified that will produce nuclear energy by manipulations
at the atomicthe chemicallevel. Of course, the acceptance
of that interpretation of their data is needed as a working hypothesis,
in order to have quantitative tests of proposed mechanisms.
As a long-time nuclear physicist, the knee jerk reaction
to the idea of a D-D reaction without significant neutron production
brought in words like 4He and Mössbauer effect. I tried, without
success, to contact Pons and Fleischmann, to the point of sending
a letter to the Los Angeles Times, which was garbled in the editing
process. Finally, with the help of a friend, contact was made in
the early part of April and I went to Salt Lake City.
There, I was assured that they knew about 4He, and
was shown a peak in a spectroscopic read-out which, I was told,
was 4He. Soon after my return to Los Angeles, references to 4He
disappeared, to resurface only relatively recently. I do not have
to, but shall, remind you of the two fundamental problems that the
acceptance, of Pons and Fleischmanns excess heat as nuclear
in origin, entails.
1. What accounts for the absence of particles that
are familiar in ordinary hot fusion, such as the neutrons of D +
--> n + 3He and the high energy y-ray of D + D--> y + 4He?
Very early in my thinking I added the conventional reaction p +
D--> y + 3He. Why? Mostly because it would also be there. One
cannot produce heavy water without some contamination by light water.
2. Hot fusion relies on achieving enough kinetic energy
to overcome the Coulomb repulsion between like charges. How then
can cold fusion, operating far below those levels, ever achieve
fusion? Incidentally, I have read, and heard, that my solution to
the Coulomb barrier problem is to forget it! Not even an absent-minded
professor (which I am not) would go that far. Critics should learn
to operate within the bounds of sanity.
My first attempt at publication, for the record, was
a total disaster. "Cold Fusion: A Hypothesis" was written
to suggest several critical experiments, which is the function of
hypothesis. The masked reviewers, to a person, ignored that, and
complained that I had not proved the underlying assumptions. Has
the knowledge that physics is an experimental science been totally
The paper was submitted, in August 1989, to Physical
Review Letters. I anticipated that PRL would have some difficulty
with what had become a very controversial subject, but I felt an
obligation to give them the first chance. What I had not expectedas
I wrote in my subsequent letter of resignation from the American
Physical Societywas contempt.
"Hypothesis" was eventually published, after
protracted delays, in a 1990 issue of a German periodical. Does
it have any significance in 1993? I cite the following excerpts:
"... this cold fusion process (of P & F) is not powered
by a DD reaction. Rather it is an HD reaction, which feeds on the
small contamination of D20 by H20 and:
"The HD reaction p + d --> 3He does not have
an accompanying y-ray; the excess energy is taken up by the metallic
lattice of Pd alloyed with D." And finally:
"... concerning the oft repeated demand for a
control experiment using H20, one should note the possibility of
a converse effect of the HD reaction: Through the natural presence
of D20 in ordinary water, such control experiments might produce
an otherwise puzzling amount of heat."
A following paper, entitled "Nuclear Energy in
an Atomic Lattice, 1," was sent directly to another German
periodical, in November of 1989. As of today, the only memorable
part is a quotation from Joseph Priestly:
"In this business, more is owed to what we call
chancethat is, to the observation of events arising from unknown
causes-than to any preconceived theory."
The editor thought it necessary to add a total disclaimer
of responsibility, ending with: "We leave the final judgment
to our readers." In my naiveté I had thought that was
always so. When part 2 of the paper was submitted, it was simply
rejected. The fix was in.
I gave a talk with the same title"Nuclear
Energy in an Atomic Lattice"at Salt Lake City in March
of 1990. The HD hypothesisof the dominance of the pd reactionhas
the pragmatic advantage of suppressing neutron production at the
level of excess heat generation.
But, to quote from that lecture: "... a well
trained hot fusioneer will instantly object that there must also
be a 5.5 MeV y-ray. He will not fail to point out that no such radiation
has been observed. Indeed."
"But consider the circumstances of cold fusion.
At very low energies of relative motion, the proton and deuteron
of the HD reaction are in an s-state, one of zero orbital angular
momentum, and therefore of positive orbital parity. The intrinsic
parities of proton, deuteron, and 3He are also positive. Then, the
usually dominant electric dipole radiationwhich requires a
parity changeis forbidden."
In the last month of 1990, I went to Tokyo. The occasion
was the 100th anniversary of the birth of a famous Japanese physicist,
perhaps most familiar for his part in the Klein-Nishima formula
for Compton scattering. On a day that, to my surprise, I found uncomfortably
close to another infamous day, I delivered a lecture on: "Cold
Fusion Does It Have a Future?" The abstract reads:
"The case against the reality of cold fusion
is outlined. It is based on preconceptions inherited from experience
with hot fusion. That cold fusion refers to a different regime is
emphasized. The new regime is characterized by intermittency in
the production of excess heat, tritium, and neutrons. A scenario
is sketched, based on the hypothesis that small segments of the
lattice can absorb released nuclear energy."
I pick up the last sentence of the abstract with this
quotation from the text:
"If the g-rays demanded by the hot fusioneers
are greatly suppressed, what agency does carry off the excess energy
in the various reactions? One must look for something that is characteristic
of cold fusion, something that does not exist in the plasma regime
of hot fusion. The obvious answer is: the lattice in which the deuterium
Imagine then, that a small, but macroscopic piece
of the lattice absorbs the excess energy of the HD or DD reaction.
I advance the idea of the lattice playing a vital role as a hypothesis.
Intermittency is the hallmark of cold fusion... Does the lattice
hypothesis have a natural explanation for intermittency? A close
approach to saturation loading is required for effective fusion
to take place. But, surely, the loading of deuterium into the palladium
lattice does not occur with perfect spatial uniformity. There are
fluctuations. It may happen that a microscopically largeif
macroscopically smallregion attains a state of such lattice
uniformity that it can function collectively in absorbing the excess
nuclear energy that is released in an act of fusion. And that energy
can initiate a chain reaction as the vibrations of the excited ions
bring them into closer proximity. So begins a burst. In the course
of time, the increasing number of vacancies in the lattice will
bring about a shut-down of the burst. The start-up of the next burst
is an independent affair. (This picture is not inconsistent with
the observation of extensive cracking after long runs.)
What answer did I give, just three years ago to "Does
cold fusion have a future?" I said: "I have little hope
for it in Europe and the United Statesthe West. It is to the
East, and, specifically, to Japan that I turn."
Inspired by good soba and sushi, I dashed off a short
addendum that Progress of Theoretical Physics received in January
and published in April of 1991. The abstract of "Nuclear Energy
in an Atomic Lattice-Causal Order" is:
"The extremely small penetrability of the Coulomb
barrier is generally adduced to dismiss the possibility of low energy
(cold) fusion. The existence of other mechanisms that could invalidate
this logic is pointed out."
Here are excerpts. "... Implicit in this line
of thought (of negligible penetrability) is the apparently self-evident
causality assignment that has the release into the surrounding environment,
of energy at the nuclear level, occur after the penetration of the
Coulomb barrier. One would hardly question that time sequence when
the environment is the vacuum. But does it necessarily apply to
the surrounding ionic lattice? Another reading is possible, one
in which the causal order is reversed. Why? Because, in contrast
with the vacuum, the lattice is a dynamical system, capable of storing
and exchanging energy.
"The initial stage of the new mechanism can be
described as an energy fluctuation, within the uniform lattice segment,
that takes energy at the nuclear level from a pd or dd pair and
transfers it to the rest of the lattice, leaving the pair in a virtual
state of negative energy....
"For the final stage ... consider the pd example
where there is a stable bound state: 3He. If the energy of the virtual
state nearly coincides with that of 3He, a resonant situation exists,
leading to amplification, rather than Coulomb barrier suppression.
"It would seem that two mechanisms are available
... But are they not extreme examples of mechanisms that in general
possess no particular causal order?"
The last lecture on cold fusion was deliveredtwicein
the Fall of 1991, to celebrate the birthdays of former students,
one of whom is at MIT, a hotbed of hot fusioneers. The cover title,
"A Progress Report," injects a bit of my own nostalgia.
Not long after the simultaneous arrival of myself at Berkeley and
World War II, Robert Oppenheimer gave a lecture with that title.
As he explained, it meant only that time had elapsed. That also
applied to the first part of my birthday lectures"Energy
Transfer in Cold Fusion"with one exception:
I turn from "missing" radiation to Coulomb
repulsion, and quote:
"... treatments of nuclear fusion between positively
charged particles (usually) represent the reaction rate as the product
of two factors. The first factor is a barrier penetration probability.
It refers entirely to the electric forces of repulsion. The second
factor is an intrinsic nuclear reaction rate. It refers entirely
to nuclear forces. This representation ... may be true enough under
the circumstances of hot fusion. But, in very low energy cold fusion
one deals essentially with a single state, or wave function, all
parts of which are coherent. It is not possible to totally isolate
the effect of the electric forces from that of the nuclear forces:
The correct treatment of cold fusion will be free of the collision-dominated
mentality of the hot fusioneers."
To speak of transferring energy to the lattice is
to invoke lattice excitations, or phonons. At about the time of
the Salt Lake City meeting, or shortly after, I became dissatisfied
with my treatment, and began to reconstruct phonon theory. A note
entitled "Phonon Representations" was submitted to the
Proceedings of the National Academy of Sciences in June of 1990.
The abstract reads:
"The gap between the nonlocalized lattice phonon
description and the localized Einstein oscillator treatment is filled
by transforming the phonon Hamiltonian back to particle variables.
The particle-coordinate, normalized wave function for the phonon
vacuum state is exhibited."
A month later, I submitted a second note with the
title "Phonon Dynamics." The abstract reads:
"An atomic lattice in its ground state is excited
by the rapid displacement and release of an atomic constituent.
The time dependence of the energy transfer to other constituents
The third and last note is called "Phonon Greens
Function." Its abstract is:
"The concepts of source and quantum action principle
are used to produce the phonon Greens function appropriate
for an initial phonon vacuum state. An application to the Mössbauer
effect is presented."
I remind you that the Mössbauer effect refers
to "an excited nucleus of an atom, imbedded in a lattice, (that)
decays with the emission of a g-ray," thereby transferring
momentum to the lattice. "There is a certain probability ...
that the phonon spectrum of the lattice will remain unexcited, as
evidenced by the absence, in the g-ray energy, of the red-shift
associated with recoil energy."
A casual explanation of the Mössbauer effect
has it that the recoil momentum is transferred to the lattice as
a whole so that the recoil energy, varying inversely with the mass
of the entire lattice, is extravagantly small. As Pauli would say,
even to God, "Das ist falsch!" The spontaneous decay of
a single excited atom in the lattice is a localized event, the consequences
of which flow at finite speed, out into three dimensional space,
weakening as they travel. This is a microscopic event, with no dependence
on macroscopic parameters such as the total mass of the lattice.
Unmentioned in the abstract, but of far greater importance,
is another situation. To quote: "What happens if the momentum
impulse ... is applied, not to one, but all lattice sites?"
The reader is invited to "recall that the lattice geometry
is not absolute, but relative to the position of the center of mass
for the entire system. Thus the injected energy can be read as the
kinetic energy transferred to the lattice as a whole." More
of this shortly.
"I note here the interesting possibility that
the 3He produced in the pd fusion reaction may undergo a secondary
reaction with another deuteron of the lattice, yielding 5Li (an
excited state of 5Li lies close by). The latter is unstable against
disintegration into a proton and 4He. Thus, protons are not consumed
in the overall reaction, which generates 4He."
To this I add, as of some time in 1992, that observations
of 4He, with insufficient numbers to account for total heat generated,
are consistent with the preceding suggestion. The initial pd reaction
produces heat, but no 4He. The secondary reaction generates heat
and 4He. There may be more total heat than can be accounted for
by 4He production. The smaller the ratio of secondary to primary
rates, the more the 4He production will be incapable of accounting
for the heat generation.
The second part of "A Progress Report" is
entitled "Energy Transport in Sonoluminescence." What
is that? The text begins with:
"The suggestion that nuclear energy could be
transferred to an atomic lattice is usually dismissed ... because
of the great disparity between atomic and nuclear energy scales;
of the order 107, say. It is, therefore, of great psychological
importance that one can point to a phenomenon in which the transfer
of energy between different scales involves (an) amplification of
about eleven orders of magnitude."
"It all began with the sea trials, in 1894, of
the destroyer HMS Daring. The onset, at high speeds, of severe propeller
vibrations led to the suggestion that bubbles were forming and collapsingthe
phenomenon of cavitation. Some 23 years later, during World War
I, Lord Rayleigh, no less, was brought in to study the problem.
He agreed that cavitation, with its accompanying production of pressure,
turbulence, and heat, was the culprit. And, of course, he devised
a theory of cavitation. But, there, he seems to have fallen into
the same error as did Isaac Newton, who, in his theory of sound,
assumed isothermal conditions. As Laplace pointed out in 1816, under
circumstances of rapid change, adiabatic conditions are more appropriate.
"During World War I, the growing need to detect
enemy submarines led to the development of what was then called
(by the British, anyway) subaqueous sound-ranging. The consequent
improvement in strong acoustic sources found no scientific applications
until 1927. It was then discovered that, when a high intensity sound
field produced cavitation in water, hydrogen peroxide was formed.
Some five years later came a conjecture that, if cavitation could
produce such large chemical energies, it might also generate visible
light. This was confirmed in 1934, thereby initiating the subject
of sonoluminescence (SL). I should, however, qualify the initial
discovery as that of incoherent SL, for, as cavitation noise attests,
bubbles are randomly and uncontrollably created and destroyed.
"The first hint of coherent SL occurred in 1970
when SL was observed without accompanying cavitation noise. This
indicates that circumstances exist in which bubbles are stable.
But not until 1990 was it demonstrated that an SL stream of light
could be produced by a single stable cavity.
"Ordinarily, a cavity in liquid is unstable.
But it can be stabilized by the alternating cycles of compression
and expansion that an acoustic field produces, provided that sonic
amplitudes and frequencies are properly chosen. The study of coherent
SL, now under way at UCLA under the direction of Professor Seth
Putterman, has yielded some remarkable results.
"What, to the naked eye, appears as a steady,
dim blue light, a photomultiplier reveals to be a clock-like sequence
of pulses in step with the sonic period, which is of the order of
10-4 seconds. Each pulse contains about 105 photons, which are emitted
in less than 50 picoseconds, that is, in about 10-11 seconds.
"When I first heard about coherent SL (my term),
some months ago (June 1991), my immediate reaction was: This is
the dynamical Casimir effect. The static Casimir effect, as usually
presented, is a short range, non-classical attractive force between
parallel conducting plates situated in a vacuum. Related effects
appear for other geometries, and for dielectric bodies instead of
"A bubble in water is a hole in a dielectric
medium. Under the influence of an oscillating acoustical field,
the bubble expands and contracts, with an intrinsic time scale that
may be considerably shorter than that of the acoustical field. The
accelerated motions of the dielectrical material create a time-dependent
dynamical electromagnetic field, which is a source of radiation.
Owing to the large fractional change in bubble dimensions that may
occur, the relation between field and source could be highly nonlinear,
resulting in substantial frequency amplification.
The mechanisms that have been suggested for cold fusion
and sonoluminescence are quite different. (So I wrote in 1991.)
But they both depend significantly on nonlinear effects. Put in
that light, the failures of naive intuition are understandable.
So ends my Progress Report."
In the more than two years that have elapsed since
the birthday lectures, I have concentrated on the theory of coherent
sonoluminescence. Why? Because, of the two physical processes that
naive intuition rejects, it is coherent SL that exists beyond doubt.
(No, Mr. Taubes, not even you could cry fraud. Too many people have
seen the light.) With the advantage of reproducible data, under
variable circumstances, constructing a convincing theory for coherent
SL should be, by far, the simpler. That, in turn, should supply
analogies for theory construction in a domain that is characterized
experimentally by "irreproducibility and uncontrollable emission
My gut feeling about the Casimir effect, in a dynamical
role, first needed some brushing up in the static domain, which
I had not thought about for 15 years. My progress in doing that,
along with needed simplifications, is recorded in four notes, published
in 1992. Two of them share the title "Casimir Energy for Dielectrics."
Each note acknowledges the stimulation provided by the phenomenon
of coherent SL. I give only this brief excerpt concerning the action
"What the static and dynamic Casimir effects
share is the reference to the quantum probability amplitude for
the preservation of the photon vacuum state: (exponential of iWo).
That the vacuum persistence probability is less than one, in a dynamical
situation where photons can be emitted, is expressed by a nonzero
imaginary part of Wo: ... In a static situation where Wo is real,
the shift in phase associated with a time lapse, ... identifies
E, the energy of the system..."
In the latter part of 1992, and in 1993, five papers
were submitted under the cover title "Casimir Light."
The individual ones are called, successively: "A Glimpse;"
"The Source;" "Photon Pairs;" "Pieces of
the Action," and "Field Pressure." The first three
notes adopted the over-simplification that the bubble collapsethe
source of radiant energyis instantaneous. "Pieces of
the Action" begins "to remove the more egregious aspects
of that treatment." The abstract reads:
"A more realistic dynamics for the collapsing
dielectric fluid are introduced in stages by adding contributions
to the Lagrangian that forms the action. The elements are kinetic
energy, Casimir potential energy, air pressure potential energy,
and electromagnetic coupling to the moving dielectric. There are
successful tests of partial collapse time and of minimum radius."
This paper ends with a veiled question:
"If, as it would seem, a mechanism exists that
transfers kinetic energy of a macroscopic body into energy of microscopic
entities, could there not bein different circumstancesa
mechanism that transfers energy of microscopic entities into kinetic
energy of a macroscopic body?" What, in 1991, seemed to be
only a pairing of two intuitively improbable phenomena ("The
mechanisms that have been suggested for cold fusion and sonoluminescence
are quite different."), now emerges as related ways of transferring
energy between macroscopic and microscopic objects.
"Casimir Light: Field Pressure" begins with
a question: "How does a macroscopic, classical, hydromechanical
system, driven by a macroscopic acoustical force, generate an astonishingly
short time scale and an accompanying high electromagnetic frequency,
one that is at the atomic level?"
In response, "I offer the hypothesis that light
plays a fundamental role in the mechanism. Provocatively put, the
collapse of the cavity is slowed abruptly by the pressure of the
light that is created by the abrupt slowing of the collapse."
The hypothesis becomes more quantitative with this
supplement: "The conditions for light emission are at hand
when the fluid kinetic energy becomes independent of t (time) for
a short time interval, and that similar remarks apply immediately
after the emission act. In effect, one is picking out the circumstances
for spontaneous radiation, from a coherent state of definite energy,
to another such state of definite, lower energy.
"The equation of motionalong with the conservation
lawsthat is supplied by the action principle, leads to a picture
of what happens during abrupt slowing. Just before that begins,
there is no significant field ... Then the field strength rises
rapidly in the vacuum region, giving a positive value to the (outward
pressure).... the slowing has begun. That process will cease when
the field, flowing at the speed of light toward the outer dielectric
region, has produced the countering pressure."
The somewhat mysterious initial hypothesis has emerged
clarified, as an unusual example of a familiar factspontaneous
emission of radiation by an electric system is a single indivisible
act that obeys the laws of energy and momentum conservation."
Now, finally, returning to the 1991 "Causal Order"
note, for the example of the reaction
p + d --> 3He + lattice energy,
one also recognizes this as a single, indivisible act.
So ends this Progress Report.