5 October 2019 | New Scientist | 43The
case of the
missing quarks
They are the most fundamental particles
of matter. But do quarks even exist?
Joshua Howgego investigates
F
INNEGANS WAKE has a reputation for
being one of the most difficult novels
in the English language. Written by
James Joyce over 17 years, it blends invented
words with real phrases in grammar-defying
constructions. The final line ends mid-
sentence – only for you to realise that the
words that should come next are the ones
at the book’s beginning. Some say it is
Joyce’s attempt at recreating a dream. Others
claim that it contains no meaning at all.
It might seem odd, then, that a nonsense
word from this most ungraspable of books
should have given its name to a particle known
as the building block of reality: the quark.
In modern physics, a quark is what you would
find if you were able to take a piece of matter
and cut it in half again and again until you
could cut no more.
Quarks are as fundamental as anything
can be. But they are also exceedingly weird.
They have strange quantum properties known
as flavour and spin. They crave each other’s
company, clustering together in pairs or
triplets. And they have a special sort of charge
that comes not in the positive or negative
variety, but in colours.
And now, in a twist to rival that of any
experimental novel, it seems quarks may not
actually exist. According to tantalising new
research, they may instead be an illusion, the
product of quantum trickery we don’t yet fully
understand. Perhaps the absurdist origin
of their name is apt after all. The search
for reality’s foundations may turn out to
be as meaningless and insubstantial as a
half-remembered dream.
The hunt for matter’s most basic
constituents is millennia old. The Greek
philosopher Democritus coined a new word
to describe fundamental units of matter:
atomos meaning indivisible. While physicists
today would agree with Democritus in
principle, history has played a nasty joke on
his terminology. Our modern understanding
of atoms suggests that they are composed of>particles called electrons that orbit a nucleus
made of protons and neutrons. And those
latter two are actually made of quarks (see
“Nature’s lego bricks”, page 45).
It is tempting to think of these particles as
tiny spheres whizzing around like balls on a
snooker table, but we have long known that
particles are more enigmatic than that. The
problems began with light. For centuries,
scientists disagreed over its nature, with some
believing it was a steady stream of particles,
and others calling it a wave. With the advent of
quantum theory in the early 20th century, we
were forced to accept the evidence that light
can take on either form, depending on the
situation. The same reasoning that had been
applied to photons of light was soon extended
to all other particles. Electrons, protons,
neutrons, even quarks, can all be said to exist
as waves as well as particles.
Things only got more muddled from there.
We now know that under the right conditions,
particles can be coaxed into doing something
even weirder. Inside certain specially primed
materials, electrons can merge into a two-
dimensional sea where their individual
identity is lost.
Out of this collective behaviour, strange
particles emerge. They can be heavier than an
electron, or only have a fraction of an electron’s
charge, or have the opposite charge altogether.
Think of a football crowd doing a Mexican
wave: the stadium remains full of people, butKwark or
kwork?
When physicist Murray Gell-Mann
was looking to name a set of new
fundamental particles that came in
threes, he coined the sound “quork”
before finding the enigmatic line “three
quarks for Muster Mark!” in James
Joyce’s 1927 novel Finnegans Wake.
Since then, scientists have been divided
over how to pronounce the word. “I’ve
heard quarks pronounced to rhyme with
‘bark’ and with ‘dork’, ” says Tara Shears
at the University of Liverpool, UK. “I say
it both ways, just to be confusing!”