Physics bridges the differences between microscopic and
macroscopic, gaseous and solid, applied and fundamental, but at the
same time appreciates a distinction between experimental and
theoretical research. There has always been a dynamic interaction -
even a healthy rivalry - between these different areas of physics
research. Often, experiments lead the way, as demonstrated recently by
such spectacular discoveries as high temperature superconductivity or
the quantum Hall effect, in which, to a certain extent, the facts
precede the theory. On the other hand, theory may anticipate
experimental facts: abstract reasoning can reveal new links by
connecting apparently unrelated pieces of data through new
concepts. Think of a milestone such as the successful "standard
model" of the fundamental interactions. This model gives a
unified description of (a) the strong interaction which is ultimately
responsible for the great diversity of stable nuclei; (b) the weak
interaction which leads to the instability of various nuclei through
radioactive decay; (c) the familiar electromagnetic force, with it's
overwhelming variety of applications which tends to dominate our
present way of life, at least at the everyday level. This standard
model, which describes the properties of the most fundamental forms of
matter successfully at least to the extent that we have been able to
verify this experimentally, is based upon three central dogmas of
contemporary physics: Einstein's theory of relativity, the postulates
of quantum mechanics, and an important symmetry principle called gauge
invariance. Experimental investigation of the smallest ingredients
such as quarks, electrons, light particles (photons) and
"heavy" particles (such as W- and Z-bosons) requires
gigantic "microscopes" known as particle accelerators. These
cost a fortune and are therefore found in only a few places throughout
the world. Therefore this field has reached an advanced state of
"internationalization", which is not restricted solely to
communication or "exchange" of ideas, but implies the total
integration of experimental work. However, despite this advanced
"task distribution and concentration", which guarantees an
unusually economical approach, this fundamental area of research has
come under pressure because it is so expensive.
Everyone is familiar a magnet, most electrical devices contain
at least one. The earth itself is a somewhat larger magnet. A bar
magnet has a north and a south pole. If we break the magnet in two
pieces, what we have left is not a separate north and south pole, but
rather two smaller magnets, each of which has its own north and south
pole. We may continue this process all the way down to a microscopic
scale, without ever being able to isolate a north or south
pole. Apparently there are no particles occurring in nature with a
magnetic (north or south) charge, in contrast with the case of
electrical charges. In the end all magnetic phenomena we know of are a
caused by currents - i.e. the motion of electric charges. A magnet is
made up of microscopic magnetic dipoles which are nothing more than
minuscule electrical current loops on a molecular or atomic
scale. There is no such thing as a magnetic monopole, full
stop. That is, unless...
Back in 1931, Dirac published a famous argument which accounted for
the crucial experimental fact that electrical charge only occurs in
whole multiples of the electron charge, based on the existence of a
magnetic monopole. His article concluded with the statement that
"One would be surprised if nature would not have made use of this
possibility". The hunt for the monopole was on. However, nothing
was found...
Despite the lack of encouragement from the
experimental side, numerous great minds continued the stubborn pursuit
of this hypothetical particle. The following episode illustrates the
unpredictability of the fundamental (im)possibilities in physics. In
1974 Gerard 't Hooft and the Russian theoretician Sasha Polyakov (now
at the Institute for Advanced Studies in Princeton) discovered that
further unification of different interactions, in accordance with the
successful principle of symmetry (gauge invariance) which forms the
basis of the weel established standard model, necessarily
implied the existence of magnetic monopoles. Good Heavens! The hunting
season reopened, with an extended toolkit which included accelerators,
and even satellites to collect moon rocks. Sure enough, the discovery
of the particle was claimed twice ofcourse leading great
commotion. But alas, both claims turned out to be false.
Further theoretical research brought numerous exotic properties of these
monopoles to light. One of these was discovered by the young Russian theoretician
Valery Rubakov. He demonstrated that monopoles should produce a dramatic
instability of protons and neutrons, implying an instability of all common
forms of matter. Monopoles would devour matter at an unimaginable rate,
and the corresponding energy would be spewed in the form of extremely light
particles. I remember one summer afternoon at that time, when we sat with
a number of driven but peace-loving researchers on the terrace of the CERN
laboratory in Geneva. On the table in front of us lay the first, rough
draft of the preprint of Rubakov's work, which someone had got hold of
through his contacts, in which this sensational claim was made public.
It was a virtuoso article, containing impressive calculations, carried
out with - by Russian standards - remarkable clarity. Absolutely convincing,
in fact. We realised that here, not for the first time, in a world full
of far-reaching abstractions, a new, gigantic - albeit extremely hypothetical
- source of energy was revealed. Carried away by this speculative discovery,
we amused ourselves with "Gedanken Experiments" and "back
of envelope" calculations. If these monopoles really existed, where
are they? Nobody has detected them, after all. Are they too rare perhaps?
Or too heavy? The theory predicts an immense mass of 0.01 milligrams per
particle, which is gigantic compared to the mass of a hydrogen atom, which
weighs just 0.000 000 000 000 000 001 milligrams. An elementary particle
with a mass comparable to that of a microbe is too heavy to be created
in even the most costly accelerator. Are monopoles perhaps hidden in ordinary
matter? Or do they form very strongly bound, magnetically neutral pairs
with antipoles? Suppose that they fly freely through space, could we attract
them with a gigantic magnet? Suppose we manage to "catch" one
and lock it up in a magnetic cage, together with a substantial heap of
rubbish: Would it indeed swallow the garbage and could this provide the
ultimate solution to our pollution problem? Or were we on the verge of
giving birth to a new, even more destructive type of BOMB, in view of the
unimaginable amount of energy released when matter decays through a monopole?
Could it be a possible explanation for the Bermuda Triangle? It looked
as though a new horizon was opening up for what insiders would call "curiosity-driven
technology". At this point I should probably fulfil an important moral
duty, and raise my finger warning for the dangers conceivably hidden in
what is supposed to be pure and innocent research into magnetic monopoles.
Today's sweet dreams may well become tomorrow's nightmares. While a great
social debate about the would be "blessings" of physics to society
flourished, backstage new doors for science were opening up. "The
world has not yet come to an end, but we are working on it", quipped
Wim Kan. Indeed, in a God-fearing nation like ours, "value-free"
physics is perceived as the Devil's henchman. People who devote their lives
to the question of how nature works, whether they do so using high-tech
instruments, laptop computers or pencil and paper, run the risk of being
typecast as power-hungry Dr. Strangeloves, preferably seated in a wheelchair,
who want to bend the universe to their will. But I digress...
Well, I think I have made it clear that the theory made steady progress,
but unfortunately not on the basis of facts. Or not yet, at any rate. People
delved diligently into other aspects of the monopole question. At one point,
convincing arguments from Moscow and Harvard claimed that these (anti)monopoles
would be created in huge quantities at a very early stage of the universe's
existence. Because of its rapid expansion, these extremely massive particles
would "not have had the time" to find and annihilate each other.
In short, monopoles, even if they are not the most predominant form of
matter in our universe (food for those in search of dark matter, perhaps),
would still completely disrupt extremely successful cosmological calculations
such as the computation of the abundance of helium in the universe. It
appeared that we could not have it both ways; we would have to throw either
the successful Big Bang theory of the universe or the successful unification
theories of elementary particles overboard. It was a meeting of extremes.
Were the smallest particles going to be in charge of the cosmos, or had
the lessons from the universe killed off a central paradigm of particle
physics? As these things tend to, the situation cooled down a little; the
extremes got together, and a thrilling new idea was born. While it was
difficult to escape from the accursed monopoles within the standard Big
Bang scenario, further study of their creation made it clear that the universe
might have gone through a phase of exponential expansion in a very early
stage. This "inflationary" phase lasted for a very short time
according to our present-day timescales, but at that time it was very long:
many times longer than the lifespan of the universe. According to this
view, the number of monopoles per unit volume was reduced exponentially
to a number of the order of one in our universe. Acceptable, thus. `Have
these scientists really nothing better to do than to kill one fiction with
another ?' I hear you asking in amazement. Compared with this, Don Quixote
looks like a first class pragmatist. Actually an interesting footnote to
the development described above is that the idea of inflation went on to
live a life of its own - independent of the monopole question. In particular,
Alan Guth showed that the proposed inflation itself eliminated a number
of long-standing, relatively annoying shortcomings of the standard Big
Bang model. In fact, it enriched the model, bringing it considerably closer
in line with certain experimental facts.
Apart from a theory of non-existent particles (`to be or not to be' remains
the question), the monopoles also appear to turn up in the theory of "nothing",
i.e. the description of empty space, or the vacuum. In physics (quantum
mechanics) this term is used to refer to the state of lowest energy - the
ground state. One would imagine that in a theory of particles the lowest
state would always correspond with a state in which no particles are present.
However, this is not entirely correct; sometimes it may be that a certain
type of particle "condenses" in order to lower the energy still
further. Water forms a vapour at high temperature and normal pressure,
but when the temperature is lowered below boiling point it will spontaneously
condense to a fluid state with much greater density. This illustrates how
the ground state, the state of minimal (free) energy, can change as a function
of the temperature. If we're talking about empty space, "fish"
for example would probably refer to a situation without fish or plants,
but not one without water. A powerful statement about the nature of a vacuum
was made by John Archibald Wheeler: "No point is more central than
this, that empty space is not empty. It is the seat of the most violent
physics." When monopoles failed to show up in our detectors, the monopole
freaks had to ask themselves whether they might be hidden in the ground
state. One sector of the standard model in particular, which describes
the strong interactions, became the target of their activity. In this sector,
dubbed "quantum chromodynamics", another sort of fairly elusive
particles, known as quarks, play a leading role. Their status is
also somewhat dubious, since they do not occur as free particles, but are
permanently confined within what are called hadrons, such as the
protons and neutrons which make up all our atomic nuclei.
What we see are thus protons, and from the properties of these protons
we can indirectly deduce that in fact they contain three quarks. Why do
quarks always assemble in threes (or with an antiquark) in a hadron? Because
of a law against assemblies of less than three quarks. This remarkable
property can be blamed on the "repressive tolerance" of the surrounding
vacuum, which is described by people like Nambu, Mandelstam and 't Hooft
as follows: the quarks have what is known as a certain "colour"
electric charge. The vacuum is a superfluid made up of "colour"
monopoles and antimonopoles, a magnetic superconductor in which the monopoles
can move without resistance. Moving magnetic charges create electrical
fields. When we put a quark charge in the vacuum, the colour electrical
fields are cancelled out by the coherent movement of monopoles, to the
extent this is possible. The total electrical field produced by the quark
charge is squeezed into a narrow tube, and that tube can end only with
an antiquark. A single quark would drag an endlessly long cylinder of field
energy behind it, which would mean that the corresponding physical state
would have infinite energy. Such states are not found in nature. This also
applies to every state which a colour combination of quarks contains which
is not neutral (white) in colour. The result, if we pull a quark-antiquark
pair apart, is reminiscent of the story of the magnet. At some point, a
new quark-antiquark pair will be spontaneously created, and the fluxtube
which bound the original pair will break in two. Thus, whenever we try
to break the hadron into quark pieces, the end product will once again
be a number of hadrons. Hence there appears to be a natural limit to our
urge to isolate increasingly smaller building-blocks of matter. The enigmatic
monopole vacuum forms a connecting link between the quarks and their hadronic
manifestation.
With this brief "case history", I have tried to illustrate the
fact that developments in basic science can be capricious and unpredictable.
They are constantly exciting for those involved in the field, who find
themselves unexpectedly confronted with unimaginable vistas while maybe
standing at the edge of an abyss. Managers and policy-makers want to be
able to plan things properly: to set concrete goals and hold interim evaluations;
they want flow charts and rock-hard criteria; advisory committees, panel
discussions, councils; visits, accurate reports, strategy meetings at windy
seaside resorts or in nature reserves. No cost or effort is saved to divide
the limited resources fairly. Science acts as a main job supplier to the
bureaucracy. However it remains pretty much true that Mother Nature does
not strip herself bare for a halfpenny, and she appears to be immune to
both political instinct and managerial enthusiasm. She rather responds
to patience and persistence, of which basic science is after all the cultural
expression. As for those monopoles, maybe we are on the wrong track, but
perhaps.....