[THS] The hunt for the God particle

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The hunt for the God particle

We have all heard of 'dark matter'. But what about dark galaxies, dark planets - even
dark people? Ian Sample reports on the new holy grail of physics


Ian Sample
guardian.co.uk, Monday 21 June 2010

http://www.guardian.co.uk/science/2010/jun/21/higgs-boson

Can we actually see everything out there? Can we actually see everything out there?
Photograph: Nasa - Hubble Heritage Team - Es/ NASA - Hubble Heritage Team -

Durham, northern England, December 2009. The largest meeting of particle
physicists in the country is underway and James Wells, a leading theorist at Cern, the
European nuclear research organisation near Geneva, is beguiling his audience with
an idea that has all the makings of the next great revolution in science.

Massive: The Hunt for the God Particle
by Ian Sample
320pp,
Virgin Books,
£15.99

Buy Massive: The Hunt for the God Particle at the Guardian bookshop

Wells, a tall, softly-spoken 44-year-old from Tampa Bay, Florida, begins with an
uncomfortable home truth. Particle physicists have a problem, he says. They are an
anthropocentric bunch, too preoccupied with the particles and forces that impinge on
humanity. They have spent so much time unravelling mysteries such as the structure
of atoms and why the sun shines that they have neglected other avenues of inquiry.
They need to broaden their horizons, Wells says. To think beyond the world we see
and touch.

If that was the stick, next came the carrot. Our knowledge of the cosmos tells us that
the stuff around us, from plants and people to stars and planets, is made from just a
handful of elementary particles. On top of these, there is a small number of forces
that make nature run smoothly, doing things like keeping planets in their orbits and
ensuring everyday objects don't suddenly collapse into a pile of atoms. But how do
we know, asks Wells, that there isn't much more going on than this? Our knowledge
of nature and how it works is based on observations. What if we can't see
everything? What might we be missing out on? There could be a "hidden world" out
there, Wells says, where particles and forces are busily at work, all around us, but
beyond the realm of our senses.

The phrase "hidden world" sounds like a science-fiction cliche, but it simply means
that there may be more particles and forces at work in the world – and the cosmos at
large – than those we see when we look around. They are so aloof, so hidden from
our daily experience, that they go completely unnoticed.

"It would be strange if we were so special that we could feel and observe everything
that is going on out there," says Wells, who is one of a growing number of physicists
working on the hidden worlds idea. "We are lumps of clay swirling on a little blue
marble in an overwhelming vastness of universe. We have to envision that there is
more going on. There really should be additional particles and forces," he says.

Six months after his Durham lecture, Wells is back in his office at Cern. For hundreds
of scientists like him, June is turning out to be a hectic month. One of the most
important meetings in the academic calendar, the International Conference on High
Energy Physics in Paris, is only weeks away and this year is the first time that
physicists at Cern will unveil results from their shiny new machine, the $6bn Large
Hadron Collider (LHC). People are furiously writing up papers and cross-checking
data. Heads are down; blood pressure is up.

While many of his colleagues are busy writing up results from the LHC's first few
months of running, Wells is preparing another lecture, this time on using the LHC to
find evidence for a hidden world. The LHC, it turns out, is perfectly placed to be the
first instrument in history that could shed light on whether a hidden world exists.

The LHC is aptly named. The machine sits in a giant circular tunnel with a five-mile
diameter that crosses the French-Swiss border 100m beneath the Cern campus.
Inside the machine, subatomic particles, protons, are whipped up to within a whisker
of the speed of light and slammed together in head-on collisions. These orchestrated
acts of violence recreate conditions that prevailed in the first moments of the big
bang.

Physicists have a lengthy shopping list of new phenomena they want the LHC to find,
but most prominent is the Higgs boson, an elusive particle dreamt up in the 1960s
that is believed to give mass to other particles. The Higgs boson is a glittering prize in
its own right, but to Wells and many other physicists, it has an added appeal. The
Higgs particle should be influenced by what happens in the hidden world. As such, it
could act as a kind of bridge or window into the unknown world.

"The LHC will likely be the first collider in history to be able to see the Higgs boson
and so illuminate this bridge," Wells says. "We may be on the brink of discovering
new worlds by means of it."

The idea of a hidden world might sound absurd, but physicists have good reason to
believe it exists. Even with today's most advanced telescopes, astronomers can see
only 4% of what makes up our cosmic neighbourhood. The rest is invisible to us,
revealing itself only by the effects it has on the galaxies we can see. Around 70% of
the unseen universe is labelled as "dark energy", a mysterious force that drives the
expansion of the universe, making galaxies race away from us. The remaining
quarter is chalked up as "dark matter", an obscure substance that clings to galaxies
and exerts an unmistakable gravitational pull on them. The word "dark" means we
cannot see it, but it also means scientists haven't the faintest clue what it is. Last
week, British scientists reported a new analysis that suggests dark matter and dark
energy might not even exist, though other researchers reject the findings. Charles
Bennett at Johns Hopkins University in Baltimore has worked on both. "We
unequivocally stand by our results," he says.

As the Milky Way spins on its axis, our planet passes through vast stretches of dark
matter – if it does exist – without us even noticing. And though dark matter is part of
the hidden world, it is only a part. "The likely existence of dark matter suggests that
there is more stuff out there that we do not know than we do know," says Wells.

Ask physicists to speculate about a hidden world – and that is half the fun of
theoretical physics – and the possibilities of what might be lurking beyond the reach
of our senses are endless. "Once you start considering these ideas actively, there's no
theoretical reason to rule out a very interesting, dynamic and diverse dark or hidden
world," says Neal Weiner, a physicist at New York University. "It leads to all sorts of
conversations about the possibilities of dark people and dark planets. Now that is
extremely unlikely, but it's something to think about. Once you open the box, it's not
obvious where it will end."

What is more likely, according to physicists working in the field, is that the hidden
world is filled with a wispy fog of dark matter and puny dark forces that are incapable
of forming dark planets and more exotic objects like dark life. When normal planets
form, cosmic matter has to cool down and coalesce into enormous lumps of rock, but
it can only do this by losing heat. As far as we know, dark matter doesn't cool down:
if it did, we would see the heat if gives off. It would glow.

Other particles might flit in and out of existence in the hidden world, just as they do
in ours. Of all the particles physicists have found in nature – often in cosmic rays and
particle colliders like the LHC – only a tiny fraction are stable enough to form long-
lasting objects. The rest decay immediately, into lighter, more durable particles.

The uncertainty over what exists in the hidden world has done nothing to dampen
physicists' enthusiasm for the idea. John March-Russell, a theoretical physicist at
Oxford University, says proof of a hidden world could become the central plank of a
scientific revolution that rivals any in history. When Copernicus put the sun at the
centre of the solar system in the 16th century, and when Charles Darwin described
evolution in the 19th century, they both knocked humans down a peg or two. The
discovery of a hidden world would force us to reassess our place once more. The
cosmos as we know it – with all its stars and planets – might turn out to be nothing
more than a mediocre microcosm of a far richer and more complicated universe.

"Just as the Copernican revolution told us that the Earth isn't special, the same could
be true for everything that we've so far discovered," says March-Russell. "All of this
stuff around us, the stuff of our reality, is it the dominant and most complex part of
the universe? It might not be."

It's a view that Weiner shares. "If evidence for a hidden world started showing up in
experiments, you would unleash a huge amount of experimental creativity on the
problem. If we find dark forces it would be a sea-change. I don't think it's hyperbole
to say it would be one of the most important discoveries in particle physics."

Frank Wilczek is a theoretical physicist at Massachusetts Institute of Technology and
considered one of the most brilliant minds in physics. At the age of 21, he developed
a theory about the so-called "strong force" that holds the innards of atoms together.
The work was so groundbreaking he was awarded the Nobel prize in physics for it in
2004. Two years after receiving the award, Wilczek and his student at MIT, Brian
Patt, coined the phrase "Higgs portal" in a theoretical paper that fleshed out how the
Higgs boson could be used to study hidden worlds. Wilczek forgets how they came
by the name, but it means the same thing as the "bridge" Wells described earlier.
"The Higgs particle is special because it is more open to influence from the hidden
world," says Wilczek. "It might be that the Higgs decays into particles that are
invisible, in which case it will look as though it has just disappeared." This would not
leave physicists as stuck as it might seem. The LHC would register that some energy
– that wrapped up in the Higgs particle - had gone missing. The vanishing act could
be intriguing evidence, at least, that a hidden world is real.

Another possibility is that the Higgs boson collapses into particles from the hidden
world, which themselves decay back into real-world particles we are more familiar
with. This would really give scientists at the LHC something to think about. Their
detectors would flash with bursts of particles that seem to come out of nowhere. The
crucial point is that by studying how the Higgs boson behaves in the LHC, physicists
should be able to build up a picture of the particles and perhaps even forces at work
in the hidden world.

One of the most compelling aspects of the hidden world idea is that it doesn't require
physicists to tear up all the work they have already done in describing how the
universe works. "Physics has advanced so far that it's not easy to take things on in a
way that is consistent with what we already know. The hidden world idea at least
passes that test. It's easy to add all of this stuff into our existing theoretical
framework," says Wilczek.

So when is the LHC going to find this thing? The short answer is that nobody expects
the Higgs boson to be discovered any time soon. To find it physicists need a collider
that has enough energy to make the particle, but how much is enough is not clear.
They then need to find the telltale signature of the Higgs particle among the
subatomic detritus spewed out by collisions in the machine, which is a formidable
task. The last major collider at Cern, which shut down in 2000, came up empty-
handed despite a lengthy search for the particle. Another atom smasher, the
Tevatron at Fermilab near Chicago, has been hunting the Higgs particle for a while,
but is due to close within a year or so. Many physicists believe the LHC is guaranteed
to find the Higgs boson, but not for three or four years. In 1993, the American Nobel
prizewinning physicist Leon Lederman gave the Higgs boson a nickname: the God
particle, because he considered it critical to our understanding of matter. Considering
the wait, a more appropriate nickname might be the Godot particle.

Finding the Higgs boson will end one of the greatest hunts in modern physics, but as
that chapter closes, a new one will open. Wrapping up his talk in Durham in
December last year, Wells issued a rallying call. The Higgs particle could help them
get over their anthropocentric ways and open up vast new territories of hidden
worlds. "And that would only be the beginning," says Wells.

This article was amended on 22 June 2010. The original referred to Copernicus
putting the Earth at the centre of the solar system. This has been corrected.