Ancient
philosophers thought wind, water, fire and earth were the most basic elements
of the cosmos, but the study of the small has since grown up. Physicists
continue to carve the known universe into particles to describe everything from
magnetism to what atoms are made of and how they remain stable. Yet striking
similarities in the world of quantum mechanics, as the study of particles and
their forces is known, has led to a one of the most important questions in modern
science: Is there a single theory that can describe everything?
"We
understand a lot about the universe up to the first few energetic microseconds,
but earlier than that our physics break down," said Mark Jackson, a
theoretical physicist at Fermilab in Batavia, Illinois. "But those first
moments are where the really interesting things happened."
If a theory
can be designed to withstand the incredible energies of the early universe as
well as incorporate
gravity, Jackson said, then a universal theory of physics could become a
reality.
Standard
frustration
The
"standard model" of physics views particles as infinitesimal points,
some of which carry basic forces. In spite of the fact that it fails to include
gravity and becomes gibberish at high energies, the time-tested theory is the
best tool scientists have for explaining physics.
"You
hear people complain about how good the standard model is," said Michael
Turner, a cosmologist at the University of Chicago. "It's an incomplete
model, and yet we can't find
flaws in it."
Turner
explained that discovering a mass-inducing particle, called the Higgs boson,
remains the next big test for the standard model. If discovered, the heavy
particle would definitively show that properties like electromagnetism and
radioactivity are really different facets of the same force.
"It's
the miracle that allows us to combine them together," Turner said of the
Higgs, which may be found someday in the collisions of particle accelerators
that "rewind" matter to the intense energies of the early universe.
Stringing
in gravity
The
stubbornness of the standard model has been too much for some physicists,
however, leading to new theories that include gravity and work at extremely
high energies.
Perhaps the
most popularized of them all is string
theory, which describes particles as strands of energy vibrating at
different "frequencies." To explain the point-like nature of
particles, string theory holds that strings are wrapped up in 10 or 11
dimensions—six to seven more than are currently recognized.
The idea is
similar to viewing a building from far away. At great distances it looks like a
point, but moving closer it appears flat and eventually as a three-dimensional
structure. Wrapped within the building are extra dimensions that become smaller
and smaller: pipes, and nooks and crannies within the pipes, the spaces between
the nooks and crannies and so on.
The inability
so far for string theory to prove up to 11 tiny dimensions exist is a hang-up
for many, but Jackson thinks some strings could have been stretched across the
universe into "superstrings"--ones large enough to detect in space today.
In spite of
a present lack of such evidence, Jackson is confident string theory will
weather the storm.
"It's
hard to imagine that the universe has two different sets of rules for physics.
When does it turn one off and the other one on?" Jackson reasoned.
"We know there is quantum mechanics and we know there is gravity, so it
seems there should be one overall theory. I'm betting my career that it's
string theory."
Supersymmetric
search
Fermilab
cosmologist Scott Dodelson also finds a unified theory logical, but doesn't
think a big departure from the standard model is required to conjure one up.
"There
are basically two approaches; one is the bottom-up, which is taking data and
fixing pieces of a theory to make it more elegant," said Fermilab
cosmologist Scott Dodelson. "The other approach is top-down, starting with
an elegant theory and working down toward the data. My chips are on the bottom-up
people wanting to get down and dirty with data."
In either
case, physicists, theorists and cosmologists alike are waiting for high-energy
experiments such as the Large Hadron Collider (LHC) in Europe to go online.
They hope to find not only the Higgs in the aftermath of colliding particles,
but also particle
"super-partners" that Dodelson described as the overweight,
hidden cousins of more familiar electrons, neutrinos and the like.
"They're
too heavy to have been seen so far," Dodelson said, adding that the
intense energies LHC-like machines may be enough to get them to "pop
out" of colliding particles. If so, the mystery of dark
matter (much of the universe's missing mass) could be solved in addition to
creating a more formidable standard model of physics.
"We
may eventually pierce the 'cloak' of dark matter and detect supersymmetric
particles in the lab," Dodelson said. "It would introduce a whole new
class of particles and create a new standard model."
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