46 | New Scientist | 5 October 2019
Joshua Howgego is a features
editor at New Scientist specialising
in the physical sciencesWhat everyone agrees on is that it breaks
new ground. Whereas ’t Hooft’s model
couldn’t explain exotic, high-spin particles,
Komargodski’s model does just that. “The
picture [it paints] is completely different,”
says Georgi. Instead of a three-dimensional
cluster of quarks jostling for position, it says
that the high spin pulls the baryon into a two-
dimensional pancake of quantum foam, out of
which emerges the quark with fractional spin.Reality’s shaky foundations
It is very much like the way Mexican waves
emerge in a stadium, or quasiparticles appear
from a collection of electrons. In other words,
it implies that the quarks in these particles
aren’t fundamental at all, but a consequence
of the quantum foam’s behaviour. “It’s like a
new state of matter, or a new state of quark,”
says Komargodski. We have always known that
quarks are intensely strange beasts, almost
inexplicable in everyday terms. “But Zohar’s
quasiparticles are completely different, they’re
nutty,” says Georgi.
They may also be extremely useful. When
’t Hooft developed his simplification in the
1970s, no one was worried about its failure to
calculate the properties of high-spin baryons
like the delta++. That is because they tend toexist only in exotic environments like the
super-pressurised interior of neutron stars.
But today, neutron stars are at the centre of one
of the hottest areas of physics: gravitational
wave astronomy.
Over the past few years, the LIGO
collaboration has detected the gravitational
waves created when colossal objects in space
collide, including instances of a black hole
gobbling up a neutron star. These signals have
given us a new window on the cosmos, but the
glass is a little frosted. We can’t deduce much
about neutron stars from signals apart from
their mass, principally because we have no
theory with which to describe the intensely
pressurised matter they are made from.
Or at least we didn’t until now. “What Zohar
has proposed is extremely exciting because it
is relevant in these stars,” says Mannque Rho
at the Institute of Theoretical Physics in Paris,
France. He is trying to develop Komargodski’s
work into a tool that could be used with
gravitational wave signals to produce an
equation describing more about the neutron
stars, including their diameter and density.
The practical applications are only part
of the story. Komargodski’s work also raises
profound questions about the nature of
quarks. If there are circumstances under
which quarks seem to be emergent ratherthan fundamental, does that mean that all
quarks are little more than abstractions?
If so, what is reality really made of?
Perhaps surprisingly, Komargodski himself
still thinks quarks are real, fundamental
objects. He likens the situation to the odd
behaviour of electrons: although there
are some situations in which they take on
weird properties, that doesn’t mean we need
to bin the concept of electrons entirely. “But
everybody has their own opinion,” he says.
Rho sees it differently. “The fundamental
nature of the quark essentially loses its
meaning in a highly correlated system like
dense matter,” he says. “Quarks are not
fundamental any more, I think.” Perhaps this
shouldn’t come as a surprise. Most physicists
think that the standard model of particle
physics doesn’t capture the full truth about
reality, not least because we don’t know why
it is like it is. Quarks may represent another
rung on the ladder of reality, but we haven’t
reached the bottom yet. We may be right back
at the beginning. ❚