monopole.boo — A Field Notebook of the Phantom Particle

I

Of the Phantom That May Not Exist

In the year of our discipline 1931, one P.A.M. Dirac — a man of letters and quanta — suggested a creature unseen.

It was not the spectre of folklore, nor the wraith of the moor; rather, it was a particle bearing only one pole of magnetism. A north without a south. A south without a north. A single, lonely lodestone fragment.

For nearly a century, every loadstone broken in twain refused to oblige. Snap a magnet, and you receive two smaller magnets. Snap those, and four. The phantom does not appear — and yet, the equations whisper that it ought to.

This little volume, dear reader, is the field journal of those who hunt it still.

II

The Symmetry Restored

Maxwell's four equations describe electricity and magnetism with such elegance that any imbalance feels a transgression.

Electric charge appears in the wild as a singular thing — an electron, lonesome, may wander. Magnetic charge does not. The fourth of Maxwell's laws, with its solemn pronouncement that the divergence of B is zero, forbids it.

Yet should a single magnetic monopole be discovered, that fourth law is overturned, and a perfect symmetry between the electric and magnetic worlds is restored. The universe, in such a case, would breathe more evenly.

Dirac showed something stranger still: the mere existence of one such phantom anywhere in creation would require all electric charge to be quantised — and quantised it most certainly is.

The phantom, then, is not merely a curiosity. It is a guarantor.

III

A Catalogue of Hauntings

From the journals of those who have laid traps, far below the soil and high above the clouds.

14 February 1982 Stanford, California
A solitary jolt of current is recorded by a superconducting loop in the laboratory of Blas Cabrera. One pole, one event, one signature. It has never been repeated. The single click is, to this day, called the Valentine's Day Monopole.
2007 — present Cumbria, England
In the laboratories of frustrated magnetism, certain crystalline materials — the spin ices — exhibit emergent excitations that behave, for all practical purposes, like monopoles within the lattice. Phantoms of phantoms.
2013 — ongoing CERN, Switzerland
The MoEDAL apparatus, an array of plastic track detectors and trapping volumes, watches every collision of the Large Hadron Collider for the singular passage of a magnetic charge. As of this writing: silence. A productive silence.
Cosmic time, immemorial The interstellar medium
Should the early universe have produced monopoles in abundance, they should still drift among the stars. They have not been caught. The sky is a vast and patient trap.

IV

The Apparatus of Detection

The hunter requires curious instruments. A pistol is of no use against an idea.

The principal device is the superconducting quantum interference detector, or SQUID — a loop chilled almost to the absolute zero of temperature, through which the passage of a single magnetic charge would induce a precise and unmistakable jump in current.

Other observatories rely upon nuclear track detectors: thin sheets of plastic that record, by chemical etching, the bruise left by a heavily charged particle plunging through. The wound, once developed, is read like a rune.

Trapping volumes — great cylinders of aluminium — are stationed at the very mouths of particle accelerators. After the collisions cease and the laboratories are darkened, these cylinders are sliced and scanned, like opening the casket to see what got in.

Each apparatus, in its way, is a glass jar awaiting a firefly that may or may not arrive.

V

A Bestiary of Theoretical Forms

The monopole, in the literature, takes more than one shape — as ghosts often do.

The Dirac Monopole: The original spectre, conjured from quantum mechanics in 1931. Point-like, of unspecified mass, and accompanied by the famous Dirac string — a mathematical filament whose unobservability is its very signature.
The 't Hooft–Polyakov Monopole: A creature emerging not from postulate but from the breaking of grand-unified symmetry. Heavy, structured, of mass perhaps a million billion times that of the proton. It is not placed in the universe; the universe makes it of necessity.
The Cosmic Monopole: A relic of the first instants of creation, supposed to be wandering the void. It would, if found, be the oldest unbroken witness to the unification epoch.
The Emergent Monopole: Not a particle at all, but a tidy collective deception of countless atomic spins inside certain crystals. It walks, it carries a charge, it obeys Coulomb's magnetic law — and yet, dismantle the crystal and it ceases to be. A ghost of a ghost.

VI

Concerning Why It Has Not Yet Appeared

A patient absence is not the same as a refusal.

One supposes the cosmic specimens to be vastly heavy — far heavier than any present collider can summon. They were perhaps born only when space-time itself was hotter than any furnace we shall ever kindle.

Inflation, that grand dilution of the early universe, would have stretched the ancient population so thin that one might wander a galaxy for an aeon and meet none.

And so the trap is laid, the candle is lit, and the watcher waits. The phantom is courteous: it does not appear merely because we wish it to.

“The successful theory which describes the world should not, in itself, predict the world's appearances. It should describe what could be, and let the world choose.”

— from a marginal note, source unknown

VII

The Reader's Charge

If you have read thus far, you are now — in some small way — an apprentice to the hunt.

Carry the question with you. Mention it at long dinners. Sketch the field lines on a napkin if the talk grows dull. The phantom is fed by attention; it is, perhaps, the only entity in physics that becomes more real the more it is discussed in good faith.

Should you wish to return to these pages by candlelight, the door is always open. The flame here will be kept lit.

— the keeper of monopole.boo