Copyright Disclaimer Under Section 107 of the Copyright Act 1976?Fair use is a use permitted by copyright statute that might otherwise be infringing. Non-profit, educational or personal use tips the balance in favor of fair use. Unless you are in this field of investigative journalism, especially covering extremely sensitive subjects and potentially dangerous subjects as well, you simply cannot understand the complexities and difficulties involved with this work that I face every day.
Just because Cern researchers discovered the Higgs Boson particle
last year doesn't mean it's time to close up shop on the biggest
scientific instrument humanity ever created. Instead, the scientific
community has plans to upgrade and retrofit the Large Hadron Collider
with bigger, better, and more powerful systems over the next decade—like
the US LHC Accelerator Program's (LARP) new interaction region
quadrupole magnets (IRQM) that will help tease every last one of the
Higgs-Boson's secrets.
Particles
come together in one of four Interaction Regions (IR) within the Large
Hadron Collider. The number of iterations generated from each collision
(of which you want as many as possible) is known as the integrated
luminosity. Cern hopes to increase the collider's integrated luminosity
by 10x over the next decade (known as the High Luminosity LHC project),
but the process is technically challenging to say the least. Much of the
the equipment currently installed on the LHC is definitely powerful
enough for the current level of experiments conducted there, but just
won't cut it for higher-energy experiments in the future. Take the
IRQMs, for instance.
On either
immediate side of the interaction region is a quadrupole magnet
(quadrupole as in "four poles"). These devices help focus the particle
beams towards each other by generating a massive electromagnetic field.
The current generation of IRQMs are built from niobium titanium, the
Methuselah of superconducting materials, and that from which almost all
superconducting material technologies are built. Problem is, niobium
titanium isn't strong enough to endure the massive temperatures and
radiation produced by the higher energy experiments necessary for
deciphering the Higgs-Boson. And any tiny failure within the structure
of the magnet itself will nix its superconducting ability and the
torrent of protons flowing through the material will stop instantly
(this is called a "quench" and is roughly equivalent to crossing the
streams).
But the new
IRQMs from LARP are different. Dubbed the HQ02a (which stands for
something even more complicated), they're built from niobium tin. This
next-gen superconducting material is designed, as all magnets at the
LHC, to run in a helium superfluid cooled to near absolute zero. But
unlike the earlier models, the HQ02a not only operates at a much higher
magnetic field, it also features a larger aperture (120 mm vs 70mm), a
much wider operating temperature margin, and can better withstand the
IR's intense radiation levels, which is only going to increase as the
systems integrated luminosity jumps as well. In all, the HQ02a's
superconducting coils can pump out 12 tesla, that's a 50 percent
increase.
The only
problem with niobium tin is that it's so brittle. The material has a
tendency to crack under the intense strain of its electromagnetic field.
To counteract this fault, engineers at LARP developed a thick, aluminum
shell structure to help support the magnet while under load.
“This is a
major step forward in reaching our ultimate goals,” said Bruce Strauss,
LARP program manager, in a press statement. “It should not be regarded
as a single accomplishment but rather the realization of a significant
number of individual goals in the design, construction, and testing of
Nb3Sn beam-line magnets.”
There's no
word on when this specific part will be implemented, but ten years to
unlock one puny secret of the universe seems an interminable wait. [Berkeley Lab]
Millions of people in the UK and northern Europe have glimpsed the best solar eclipse in years.
A great swathe of the Earth's surface was plunged into darkness as the Moon came between us and the Sun.
From an aeroplane above the Faroe Islands, a BBC camera crew
captured startling footage of the event reaching totality at 09:41 GMT.
The deep shadow formed first in the North Atlantic and then swept up into the Arctic, ending at the North Pole. Brilliant beads
People keen to catch a glimpse of the rare phenomenon were advised not to look directly at it.
Looking directly at the Sun can cause serious harm, and skywatchers were directed to the multiple ways to catch an eclipse safely and in comfort.
The BBC's rooftop camera captured the moment darkness fell over Belfast
In all parts of the UK, the eclipse reached at least 83%, with the darkness peaking at about 09:35 GMT. The precise timing and degree of the eclipse varied with location.
For the Shetland Islands, the eclipse was at its height at
09:43 GMT and was very near total, with 97% of the Sun's disc obscured
by the Moon.
For those caught under cloudy skies, the internet was a good option to see the eclipse.
Scientific agencies had planes and even satellites gathering video to relay on the web and on television.
In the UK, the weather turned out to be slightly better than
anticipated, with clouds breaking in many places at just the right time.
London and the South East, on the other hand, just saw their grey day
get slightly gloomier.
Experiencing a genuine total eclipse required a trip north of
the British Isles - such as the flight taken by a BBC camera crew and
Stargazing Live's Liz Bonnin, above the clouds in the Faroes.
"We have a pretty spectacular view," Bonnin said. "This is extraordinary."
That footage revealed interesting features of the eclipse,
including a clear view of "Baily's beads". These are the sparkles of
light seen at the very edge of the Moon, where its rugged landscape
allows the last rays of sunlight to peak through before full
obscuration.
Few land areas were directly in the path of the Moon's
deepest shadow - its so-called umbra - and seabirds probably had the
some of the most dramatic eclipse experiences.
The period of greatest darkness - nearly three minutes -
occurred over a spot in the Norwegian Sea, a little below the Arctic
Circle, at 09:46 GMT.
The European Space Agency's Proba-2 satellite caught this view of the eclipse
Eclipse watchers in southern England
Many professional and amateur astronomers positioned themselves
in the Faroe Islands, where the capital city of Torshavn got totality
for a full two minutes, beginning just before 09:41 GMT.
And those who could not book a flight or a hotel for the
Faroes went to Svalbard, where the capital city of Longyearbyen
witnessed two and a half minutes of totality, starting shortly after
10:10 GMT. Shifting the wind
Irrespective of the cloud cover, scientists said citizens could still help them with their research.
A University of Reading team wants to learn more about how the atmosphere behaves as the Moon's shadow runs over the Earth.
Protective glasses allowed many around the UK to try and catch a glimpse
This observer, on a beach in Spain, was plunged into relative darkness but still cast a shadow
The National Eclipse Weather Experiment (NEWEx) asked people to record conditions at their locality.
Prof Giles Harrison explained: "This is the first big
partial eclipse to happen in the UK since 1999, and the next one isn't
until August 2026, so this is a once-in-a-generation opportunity.
"By observing what happens on Friday we are effectively
turning the skies of Britain into a giant weather lab, giving us a rare
chance to see what happens when you 'turn down the Sun'.
"This will give us a precious insight into how the Sun
influences the clouds and wind, as well as more obvious effects, such as
temperature.
"By improving our understanding of how the weather works,
we're better able to predict it, meaning scientists can further improve
weather forecasts."
One phenomenon the experiment hopes to investigate is the
"eclipse wind". This refers to changes in the breeze that eclipse
observers have reported as darkness falls.
Oxford University scientists, meanwhile, are using the event to try to understand how eclipses affect electricity grids.
The deep shadow will have reduced the output from solar
panels, which now supply a significant proportion of power needs right
across Europe.
The researchers will look to see how this dip in performance impacted the stability of grid networks.
Next year will have a total solar eclipse, too.
That will occur on 9 March, and will cross Sumatra, Borneo, Sulawesi, and extend out over the Pacific.
The UK will not experience a solar eclipse on this scale a
This morning Europe was lucky enough to enjoy a solar eclipse—though
only those in the Faroe Islands and Svalbard, Norway, were theoretically
able to see a full occlusion. This wonderful view from space, though,
we can all appreciate.
In fact, many parts of Europe—including London, where I'm based—were
covered in cloud as the eclipse occurred. A gray morning, then, was just
made darker and more gloomy than usual. But up in orbit, the European
Space Agency's
Proba-2 minisatellite used its SWAP imager to capture the event as the Moon passed between the Earth and Sun. The
SWAP imager records what it sees in the ultraviolet range, so it was
able to capture the corona of the Sun as the eclipse occurred.
The Large Hadron Collider (LHC) is the most audacious physics
experiment in human history. Now scientists are about to restart the
giant particle collider for a new set of experiments. Last time, they
did the almost-impossible and found the Higgs Boson. This time, they might find something even more exciting.
Back in 2008,
just nine days into its first run of experiments, there was a
significant incident at the Large Hadron Collider. A faulty electrical
connection between two magnets stopped superconducting, then melted and
caused serious mechanical damage to the facility. The accident delayed
use of the LHC for six whole months as repairs and testing was
undertaken—but it also meant that the facility ran for three years at
much lower capacity than envisioned.
Clearly the collider coped. On July 4th 2012, scientists from two
experiments at the LHC—CMS and ATLAS—announced that they had discovered
a new boson. It was the Higgs Boson;
the invisible particle that gives everything mass and, in turn, holds
the universe together. The finding was arguably the biggest scientific
finding of the decade, perhaps even more.
But all the while it was running below par. The LHC shut down for
maintenance in 2013, though, and over the past two years, engineers have beefed it up. They've upgraded the superconducting interconnections between a series of magnets on the accelerator, adding extra shunts and more powerful magnets.
The shunts provide a route through which current can escape if
high-power accidents—like the one that caused the break back in
2008—happen again, meaning it's safer to run at higher energy levels.
Just 27,000 shunts around the 16.7-mile circumference accelerator
later, the LHC is back in business. And more powerful than ever.
Absolute Power
When the LHC closed down in 2013, its highest energy experiments has
been carried out at 8 teraelectron volts (TeV). Soon, scientists at the
LHC will be able to ratchet the accelerator to an unprecedented 13TeV.
For most of us that's a fairly incomprehensible unit of energy, though,
so LHC scientists have prepared a neat analogy to help those without
degrees in particle physics. The newly refurbished LHC can create beams
of particles that carry energy to melt a tonne of copper on impact.
That's... impressive.
"The higher energy means more chance of finding new discoveries,"
explains Alan Barr, a Professor of Particle Physics at the University of
Oxford who works on the ATLAS experiment at the Large Hadron Collider.
"The LHC's higher energy can give us sensitivity to new,
as-yet-undiscovered particles."
Einstein's famed equation, E=mc2, explains that that energy
and mass are broadly equivalent, so in practice extra energy allows the
scientists to find heavier particles than before. "The kinetic energy
of the colliding particles is converted into the mass of heavier
particles, which immediately decay back into the particles with which we
are familiar," explains James Hirschauer from the Fermi National
Accelerator Laboratory who works on experiments at the LHC. "We are
hoping that we will produce heavier particles that are so far unknown —
just like we produced and discovered the Higgs boson in 2012. The energy
jump is desirable because, if a new heavy particle exists, the rate of
production of that particle will be higher at higher collision
energies." In an email, Hirschauer gave me a great example of why
increasing the rate of particle production is so important:
"We now know that we were producing Higgs bosons at the Fermilab
Tevatron (collision energy of 1.96TeV). But there were relatively few
Higgs bosons, and they were hidden by the enormous "background" of
non-Higgs collisions at the Tevatron, so we could not separate the Higgs
signal from the background in our analyses of the Tevatron data.
However, at the higher energy of the 8TeV LHC, each collision was about
30 times more likely to produce a Higgs boson than at the 2TeV Tevatron.
So in a given number of collisions, we produced about 30 times more
Higgs bosons at the LHC than at the Tevatron. [I]n case you are
wondering: People often ask, doesn't the *background* production rate
also increase with increasing collision energy? Indeed the background
rate does increase, but not as much as the production rate for a high
mass particle, so we still gain by moving to higher collision energy."
Sadly, it's not possible to simply flick a switch on the LHC and summon
13TeV on demand. Instead, the $6 billion accelerator requires a gradual
warm up before it reaches peak power. Last week, CERN researchers sent
the first test particles through the accelerator. Slowly, over the
coming weeks, they'll send more and more, each time checking the
alignment of the beams and the accelerator's ability handle them. Cern's
director general, Rolf-Dieter Heuer, has said that the LHC will be
loaded with the first proper proton beams in the next two weeks. The
accelerator should gradually ramp up to higher energies, with the
resulting collisions—which will be the most energetic ever created by
humans—due to follow near the end of May.
Dark Secrets
The results may not initially seem worth the wait. When the new
high-energy collisions begin, we'll initially see more of the same.
After all, we managed to glimpse the Higgs at 8 TeV so, as Hirschauer's
reasoning tells us, in the first instance we'll just see even more of
them at these higher energies. That might not be too exciting, but it
will help us understand the relatively new particle more precisely,
enabling more accurate measurements of its properties.
But there will likely be more. "One thing we think we might discover
are supersymmetric particles," explains Hirschauer. Super symmetrical
particles are the theoretical partners of each of the particles
explained by the Standard Model—the most elementary particles that we
know of, like quarks, leptons and bosons. While the Standard Model does a
wonderful job of explaining particle physicists, scientists admit that
it's incomplete.
Taken at face value, the Standard Model predicts that all particles
should have zero mass—but that disagrees with direct human observation
of the world around us. While the Higgs boson goes some way to
explaining why other particles have mass, it remains a mystery why it
itself also has no mass. An additional set of supersymmetric particles
that behave similar properties but have different masses, physicists
suggest, could cancel out contributions to the Higgs mass from their
Standard-Model partners—making a massless Higgs boson possible. In turn,
that would make it possible to mathematically link the Standard Model's
three forces – electromagnetism and the strong and weak nuclear forces –
and create single unified theory to explain the Universe. A theory of
everything.
"For certain supersymmetric particles, the production rate increases by
a factor of about 30 when we increase the collision energy from 8TeV to
13TeV," explains Hirschauer. "At the same time, the production rate for
the main 'background' to this supersymmetric 'signal' only increases by
a factor of about 4. So the signal-to-background ratio will increase by
a factor of about 7.5. This is a huge and very exciting gain!" In other
words, the LHC is currently the best chance we have of creating a
unified theory.
Those supersymmetric particles might not just help us to develop a
powerful equation though. They could also explain one of the most
enigmatic theories in physics: Dark Matter. "Most of the universe is
made of Dark Matter," explains Barr. "That is stuff that pulls
gravitationally on matter around it, but which doesn't interact with
light, so is invisible. But it's very hard to detect." Dark matter
theoretically accounts for up 80 per cent of the mass of the
universe—but we've never yet observed a particle with the qualities we
think it should exhibit. Perhaps unsurprisingly, then, scientists around
the world are hopeful that the new experiments at the LHC might reveal
something "It would be truly ground-breaking if we could find, in the
debris from the LHC collisions, evidence for the particle (or particles)
which are responsible for this Dark Matter," enthuses Barr. "We know
they're not made of any particle we have already found, so the terra incognita that will be explored by the LHC is really very exciting."
Perhaps
most tantalisingly, if one school of physics thinking is to be believed,
we could potentially hit the jackpot and find both at once. "Based on
our theories and the indirect evidence, these dark matter particles
[could be] the same supersymmetric particles," explains Hirschauer. "I
am personally working hard to discover dark matter particles under the
assumption that they are supersymmetric particles."
All of this is, of course, far from certain. The nature of
experimentation is that, however good your theories seem, reality can
turn out to be something entirely unexpected. That, though, could end up
being the most exciting outcome we could hope for. "On my most wildly
optimistic day, [I imagine] we will discover something—anything—that
disagrees with our current understanding of the universe," explains
Hirschauer. "Disagreement will show us how we need to refine our
theories to correctly explain the laws of nature. I promise that we will
not be disappointed if we instead discover something completely
unanticipated!"
Part of the Compact Muon Solenoid particle detector is lowered into place several hundred feet below ground.Credit COURTESY CERN
The European Organization for Nuclear Research, known as CERN,
has its offices on the outskirts of Geneva, in an area once devoted to
dairy farms and now given over to sprawl. The offices occupy several
dozen buildings, some of them in Switzerland and the remainder, a few
hundred yards away, in France. The buildings are reachable by roads with
names like Route Bohr, Route Schrödinger, and Route Curie. By the
entrance to the complex, there is a museum—nearly empty the day I
visited—that attempts to make particle physics comprehensible to the
general public. Behind that there is a park where bits of old cyclotrons
are displayed, like playground equipment from Mars.
If
you think of the sciences as a tower, with one field resting on another
until you reach, say, botany or physiology, then particle physics
represents the bottommost floor. The first key experiment was conducted
in 1909, under the direction of Ernest Rutherford. When Rutherford shot
alpha particles at a wafer-thin sheet of gold foil, a small proportion
of the particles bounced right back, a phenomenon that he described as
“almost as incredible as if you fired a fifteen-inch shell at a piece of
tissue paper and it came back to hit you.” Rutherford’s work led to the
realization that most of an atom’s mass was concentrated in a tiny
area, the nucleus. “All science is either physics or stamp-collecting,”
he is supposed to have said.
Since
Rutherford’s discovery, particle physics has provided one
extraordinary—if increasingly implausible-sounding—revelation after
another: first protons and neutrons, then antimatter, gluons, neutrinos,
and quarks. In 1967, the existence of particles to mediate the weak
force, which is responsible for radioactive decay, was theorized; in
1983, at CERN, these particles—the W and the Z—were
observed and their properties measured. In 1977, the existence of what
became known as the “top” quark was predicted; in 1995, at Fermilab, in
Illinois, it, too, was found.
And yet, for all
its triumphs, the field has been haunted by failure. The more physicists
have learned about the way matter behaves at its most fundamental
level, the more acutely they have become aware that something—a big
something—is missing from their accounts. Among the many possibilities
proposed for what’s often called “new physics” is that the universe
actually consists of tiny strands (or strings) of energy; that it
contains several dimensions beyond those that we perceive; that it is
full of mysterious particles—“sparticles”—that have yet to be detected;
that it is not a universe at all but a multiverse; and that it began not
with a bang but with a splat.
Sometime in the next few months, physicists at CERN
will finish preparations for the most ambitious particle-physics
experiment ever, which will be conducted in an apparatus modestly
referred to as the Large Hadron Collider, or L.H.C. The L.H.C. fills a
circular tunnel seventeen miles in circumference. To get from one side
of it to the other, it is necessary to drive through several towns, and
then descend three hundred feet in an elevator. Alternatively, it is
possible to ride through the tunnel in one of the dozens of bicycles CERN provides for its staff, but in that case a supply of emergency oxygen is required.
The
L.H.C. is considered the best—some would say the only—hope for testing
the theories of “new physics” against material reality. Once the
collider begins operating at full power—in early 2008, if all goes
well—nearly half the particle physicists in the world will be involved
in analyzing its four-million-megabyte-per-hour stream of data. Few
events in the history of science have had a bigger buildup. It’s been
suggested that the L.H.C. will unlock the secrets of the universe or,
barring that, prove this ambition to be hopeless.
The
L.H.C. is a kind of Babel built underground. Dozens of countries have
manufactured its components, and dozens more have lent manpower and
expertise. (Some contracts went to Russian physicists who previously
worked for the Soviet military; in this way, the collider has provided a
livelihood for scientists whose employment options might otherwise
include selling nuclear secrets.) When I ate in CERN’s
lunchroom, I heard people speaking English, French, German, and Italian,
as well as several languages that I couldn’t identify. The place was so
crowded that it took me five minutes to pay for a cup of coffee,
proving the elemental truth that man can build a superconducting
collider but not a functional cafeteria.
CERN’s
chief scientific officer, Jos Engelen, is from the Netherlands. He
serves under the director general, who is from France, and alongside the
chief financial officer, who is from Germany. I went to speak to
Engelen in his office; behind his desk a chart indicated when the
various parts of the collider are supposed to be completed. It was a
crazy quilt of multicolored blocks, with lines radiating in all
directions. Engelen greeted me with a half-ironic cheerfulness that
struck me as very Dutch. Among his responsibilities is dealing with the
frequent calls and letters CERN receives about the
possibility that the Large Hadron Collider will destroy the world. When I
asked about this, Engelen picked up a Bic pen and placed it in front of
me. “In
quantum mechanics, there is a probability that this pen will fall
through the table,” he said. “All of a sudden, it will be on the floor.
Because it can behave as a wave, it can go through; we call that the
‘tunnel effect.’ If you calculate the probability that this happens, it
is not identical to zero. It is a very small probability. But it never
happens. I’ve never seen it happen. You have never seen it happen. But
to the general public you make a casual remark, ‘It is not identical to
zero, it is very small,’ and . . . ” He shrugged.
Worries about the end of the planet have shadowed nearly every high-energy experiment. Such concerns were given a boost by Scientific American—presumably
inadvertently—in 1999. That summer, the magazine ran a letter to the
editor about Brookhaven’s Relativistic Heavy Ion Collider, then nearing
completion. The letter suggested that the Brookhaven collider might
produce a “mini black hole” that would be drawn toward the center of the
earth, thus “devouring the entire planet within minutes.” Frank
Wilczek, a physicist who would later win a Nobel Prize, wrote a response
for the magazine. Wilczek dismissed the idea of mini black holes
devouring the earth, but went on to raise a new possibility: the
collider could produce strangelets, a form of matter that some think
might exist at the center of neutron stars. In that case, he observed,
“one might be concerned about an ‘ice-9’-type transition,” wherein all
surrounding matter could be converted into strangelets and the world as
we know it would vanish. Wilczek labelled his own suggestion “not
plausible,” but the damage had been done. “BIG BANG MACHINE COULD DESTROY EARTH” ran the headline in the London Times.
Brookhaven was forced to appoint a committee to look into this and
other disaster scenarios. (The committee concluded that “we are safe
from a strangelet initiated catastrophe.”)
“I
know Frank Wilczek,” Engelen told me. “He is an order of magnitude
smarter than I am. But he was perhaps a bit naïve.” Engelen said that CERN
officials are now instructed, with respect to the L.H.C.’s
world-destroying potential, “not to say that the probability is very
small but that the probability is zero.”
I
asked Engelen how he would explain the project of particle physics to a
non-physicist, or if he thought such an explanation was even advisable.
“We simply want to know what the world is made of, and how,” he said.
“What is in here”—he rapped on his desk with his knuckles—“and how these
particles in here constitute a table.”
“Let us
start with Ernest Rutherford in the beginning of the last century,” he
went on. “Rutherford understood what an atom looks like. It is a fat,
heavy nucleus, with very light electrons orbiting around. The next step
is we discovered objects inside the nucleus, one called the proton, the
other the neutron. That is the pattern. As a next step, people started
to wonder about these protons and neutrons, whether there is structure
in there. And they started probing that. And they found that there is
structure in there. There are quarks in there. And what we want is to
reduce the world to objects that have no structure, that are points,
that are as simple as we can imagine. And then build it up from there
again.”
So far, physicists have succeeded in
observing sixteen pointlike, or fundamental, particles, a number that
increases if you count antimatter particles, or if you differentiate
among, say, the eight types of gluons. Particles in the largest group,
called fermions, in honor of Enrico Fermi, are the stuff of matter.
Fermions include electrons and quarks, which come in the
whimsical-sounding varieties up, down, charm, strange, top, and bottom.
(A hadron is a collection of quarks, or quarks and antiquarks. A proton
is a hadron composed of two up quarks and one down; a neutron consists
of two downs and one up.) Fermions also include neutrinos, which,
somewhat unnervingly, stream through our bodies at the rate of trillions
per second. “Neutrinos, they are very small,” John Updike’s poem
“Cosmic Gall” observes. “And do not interact at all.”
Hypothetically
at least, there is also a seventeenth particle, known as the Higgs. The
Higgs particle was first postulated more than forty years ago by the
Scottish physicist Peter Higgs, and has been sought—fruitlessly—at every
major collider built since then. Its discovery would have many
fantastic implications, one of which is that the void of space is not
really void but is permeated by an invisible field that acts a bit like
cosmic molasses. This Higgs field, if it exists, exerts a drag on matter
passing through it, lending mass to particles that otherwise wouldn’t
have any. Without the Higgs, physicists have no way to explain why
fundamental particles weigh anything at all, since, according to theory,
they should be massless. The fact that the Higgs is central to modern
physics even though it has never been found has prompted one Nobel
laureate to label it the rug under which the discipline sweeps its
ignorance and a second to dismiss it as the “toilet” into which physics
flushes its inconsistencies. A third Nobel winner has labelled it the
“God particle.” “We are going to make that particle,” Engelen told me. “Or we are going to show that it doesn’t exist.”
The day that I met with Engelen, I also spoke with the deputy head of CERN’s
physics department, Michael Doser. Doser is tall and lanky, with fuzzy
blondish hair and a narrow stripe of beard that runs down the middle of
his chin. His primary interest is antimatter.
“If
you think about what matter is, you end up with a very Zen-like
answer,” he told me. “If you look at what a quark is, or an electron,
the primary constituents of matter, they’re pointlike particles. They
have no spatial extent. They have a number of properties, like mass and
charge, and that’s it. In a way, they’re mathematical figments, and
they’re separated by vacuum—mathematical figments in nothing. And
antimatter is the opposite—mathematical figments with the opposite
charge.” When matter and antimatter meet, they annihilate each other in a
burst of energy. It is believed that in the Big Bang equal quantities
of matter and antimatter were produced. But this theory makes it
difficult to explain certain basic facts, like you and me and countless
galaxies. How to account for the abundance of matter in the universe,
and the shortage of antimatter, Doser told me, “is one of the most
embarrassing questions in particle physics.”
Doser began his career at CERN
in 1991, at which point most of the physicists at the organization were
working on a project known as the Large Electron-Positron Collider, or LEP. Basically, LEP
was a high-precision matter/antimatter demolition-derby track. Billions
of electrons looping around in one direction were, at discrete
intervals, made to cross paths with billions of antielectrons—or
positrons—moving the opposite way. Where the beams crossed, huge
detectors were set up to record the smashups.
The L.H.C., Doser explained, relies on much the same design, and, in fact, makes use of the tunnel originally dug for LEP.
Instead of electrons and positrons, however, the L.H.C. will send two
beams of protons circling in opposite directions. Protons are a good
deal more massive than electrons—roughly eighteen hundred times
more—which means they can carry more energy. For this reason, they are
also much harder to manage.
“Basically, what
you must have to accelerate any charged particles is a very strong
electric field,” Doser said. “And the longer you apply it the more
energy you can give them. In principle, what you’d want is an infinitely
long linear structure, in which particles just keep getting pushed
faster and faster. Now, because you can’t build an infinitely long
accelerator, you build a circular accelerator.” Every time a proton
makes a circuit around the L.H.C. tunnel, it will receive
electromagnetic nudges to make it go faster until, eventually, it is
travelling at 99.9999991 per cent of the speed of light. “It gets to a
hair below the speed of light very rapidly, and the rest of the time is
just trying to sliver down this hair.” At this pace, a proton completes
eleven thousand two hundred and forty-five circuits in a single second.
“The
more energetic the particles are, the more force you need to keep them
on orbit,” Doser went on. “They want to go straight. And so you need
very strong magnetic fields.” In the L.H.C., such strong fields are
required that they cannot be produced by conventional, or so-called
“warm,” magnets. Instead, the L.H.C. beam pipe has been encased in
superconducting magnets, cooled with superfluid helium. These magnets
are supposed to operate at minus 271.25 degrees Celsius—minus 456.25
degrees Fahrenheit—a temperature colder than that of deep space. Doser
noted that there are many hazards involved in working with such powerful
magnets; for example, if a bolt or a screw is left lying around when
they are turned on, it can fly through the apparatus like a bullet. He
recalled that as a graduate student he had once lost a wrench in a
machine this way: “It cost me a year.” Meanwhile, if any of the magnets
fail, the beams, each of which is supposed to contain something like
three hundred trillion protons, could veer off course and, in short
order, burn a hole through the collider. “That’s why people are so
nervous about starting up,” Doser said. (In fact, a few weeks after my
visit to CERN, during a test of a set of magnets known as
an “inner triplet,” a support failed, bursting a pipe and spewing
helium into the tunnel. The failure of the support, which was produced
in the United States, was attributed to a simple engineering error.) When
protons crash into each other at 99.9999991 per cent the speed of
light, the resultant mess is usually just that—the subatomic equivalent
of shattered glass and twisted metal. But stranger things can happen.
Just as it is possible to convert mass into energy—as in a nuclear
explosion—the reverse is also true: energy can be transformed into mass
according to the Einsteinian equation E=mc2 (c being
the speed of light). In this way, new particles can be produced that are
more massive than those that entered the collision in the first place.
The process might be compared to smashing two high-speed Priuses into
each other and finding that they have rematerialized as a tank.
By
now, the Higgs has been sought for so long that physicists have a
pretty clear idea of how much it must weigh. The lower bound is around
120 times more than a proton—or roughly 2 × 10¯²² grams. The upper bound
is about 210 times as much as a proton. The most powerful collider
currently in operation is Fermilab’s Tevatron, outside Chicago. The
Tevatron, which smashes protons into antiprotons, can accelerate
particles to an energy of just under a trillion electron volts, or one
TeV. (An electron volt is the amount of energy acquired by a single
electron falling through a potential difference of one volt.) So far,
the Tevatron has failed to reveal the Higgs, though physicists there are
actively looking for it. The L.H.C. will accelerate particles to seven
TeV, which means that it will be seven times as powerful as the
Tevatron. This should be more than enough energy to produce the Higgs,
if there is a Higgs to produce. It may also be enough to uncover much
more than the Higgs. Depending on how the universe is constructed, extra
dimensions, mini black holes, and the source of so-called “dark matter”
may all be revealed at CERN. Any black holes created, Doser was quick to assure me, would be entirely benign.
On my second day at CERN,
I drove out to the detector farthest from Geneva—the Compact Muon
Solenoid—which is to operate in, or really underneath, the town of
Cessy, France. Robert Cousins, a physicist visiting CERN
from the University of California at Los Angeles, had agreed to show me
around. When we met in the C.M.S. parking lot, Cousins was wearing a
bright-yellow hard hat. He handed me one to put on.
The
L.H.C. will have four main detectors, spaced at intervals around the
tunnel like beads on a bracelet. Each is being constructed by a
different team according to a different design, the theory being that
any interesting phenomena missed by one should be captured by the
others. The teams share information, but there is a certain amount of
cheerful rivalry among them. C.M.S., in particular, has been plagued by
difficulties—during excavations, the soil in Cessy proved so soupy that
the ground had to be frozen with liquid nitrogen—and before I went to
look at it a physicist who is not affiliated with the project told me
that C.M.S. was sometimes referred to as “See a Mess.”
Cousins
led me into a vast, hangarlike building where the detector was being
assembled. There was a loud clanging coming from all directions. Iron
rings several stories high were sitting on hydraulic lifts. At the far
end of the hangar, a huge shaft dropped down several hundred feet.
Cousins said that the shaft would be used to lower the detector, piece
by piece, to the level of the L.H.C. tunnel. We boarded an elevator, and
got out near the bottom. A section of the detector that had already
been lowered into place loomed up in front of us. It looked like the
underside of a rocket ship. It
is one of the paradoxes of particle physics that fundamental particles,
though pointlike and indivisible, are also generally unstable. In fact,
the heavier particles are so short-lived that even to speak of their
having an existence seems faintly ludicrous; a top quark, for example,
is estimated to last no more than 1 × 10¯²⁴ seconds. (For comparison’s
sake, 1 × 10¯²⁴ centuries comes to three millionths of a billionth of a
second.) When unstable particles break down, new, lighter particles are
produced. Some of these are likely to be unstable as well, and to break
down further. The outcome of this process is a distinctive scattering of
“decay products,” which physicists refer to as a particle’s
“signature.”
In order to “read” such a
signature, a detector has to capture all the decay products that come
flying out after a collision and measure their properties. This requires
layer after layer of detecting elements; at C.M.S., these are arranged
in the shape of an enormous jelly roll. The innermost layer, known as
the tracker, consists of some seventy-five million silicon sensors. The
next layer, which measures the energies of photons and electrons,
contains eighty thousand crystals of lead tungstate. Surrounding this
are brass-and-plastic scintillators for tracking hadrons and a
tube-shaped magnet—a superconducting solenoid—twenty feet in diameter.
Finally, there are several iron rings of increasing circumference. These
hold sensors to detect muons, which are essentially heavy electrons.
(Neutrinos can’t be measured directly, and are therefore factored in as
an absence.) All told, the Compact Muon Solenoid will weigh twenty-eight
million pounds. It will hold enough iron to reconstruct the Eiffel
Tower. Apparently, “compact” is a relative term.
Cousins
explained that the information gathered by each layer of C.M.S. would
be analyzed virtually instantaneously, and a decision made by the
detector’s computers whether to ignore the collision or to save the
results for further study by recording them on tape. “There are famous
high-energy-physics experiments that missed discoveries because they
weren’t writing them to tape,” he told me. We were walking back through
the hangar, past the giant iron rings, which were painted fire-truck
red. “This is why we try not to be too specific about which theoretical
speculations we care about. We add up all the energy, and if it’s a huge
number we write that event to tape. If on one side of the detector it’s
a not-so-huge number, but there is nothing on the other side, so it’s a
huge imbalance, we get excited about that, and we write that to tape,
too.”
Only a small fraction of the protons
zipping through C.M.S. at any given moment will actually crash into one
another. Still, this fraction represents an enormous number. When the
L.H.C. is operating at full “luminosity,” it is expected that the beams
will cross forty million times a second and that each crossing will
produce twenty collisions. C.M.S. will write fewer than .001 per cent of
the crossings to tape; even so, it will be recording six thousand per
minute, or three hundred and sixty thousand per hour, or some six
million per week. The three other main detectors at CERN
will generate similar amounts of data. There are many ways to represent a
data stream of this magnitude; one that stuck with me was in terms of
CDs. If all the L.H.C. data were burned onto disks, the stack would rise
at the rate of a mile a month.
Lodged somewhere
in this tower of information should be the signature of the Higgs, or,
really, signatures, since the particle is expected to decay in a variety
of ways. These signatures will look an awful lot like the signatures of
other unstable particles. One physicist I spoke to compared the
computational challenge of distinguishing a Higgs to finding a needle
not in one haystack but in ten. I thought it sounded more like finding a
needle in a needle factory.
Particle
physicists come in two distinct varieties, which, rather like matter
and antimatter, are very much intertwined and, at the same time,
agonistic. Experimentalists build machines. Theorists sit around and
think. “I am happy to eat Chinese dinners with theorists,” the Nobel
Prize-winning experimentalist Samuel C. C. Ting once reportedly said.
“But to spend your life doing what they tell you is a waste of time.”
“If
I occasionally neglect to cite a theorist, it’s not because I’ve
forgotten,” Leon Lederman, another Nobel-winning experimentalist, writes
in his chronicle of the search for the Higgs. “It’s probably because I
hate him.”
A few weeks after I returned from talking to the experimentalists at CERN,
I went to speak to Nima Arkani-Hamed, a theorist at Harvard.
Arkani-Hamed, who is thirty-five, has an oval face, deep-set eyes, and
dark, shoulder-length hair. The day I visited, he was dressed entirely
in black. He immediately offered me an espresso, which he made at a
little machine that spit out one cupful at a time. “I’ve been trying to
understand something about the fact that the universe is accelerating,”
he explained, erasing a double-wide blackboard covered with equations. “Often,
this kind of physics is referred to as particle physics, which I don’t
like,” Arkani-Hamed told me. “People get the mistaken impression that
what we care about is the particles. The science is characterized like:
What are things made of? What are the ultimate building blocks of
matter? I hate that. That sounds a lot like chemistry, and it’s not like
that at all. There are many, many more exciting things in nature than
some random elementary particles.
“The reason we
go to short distances isn’t to probe the building blocks of matter,” he
went on. “It’s because for four hundred years fundamental physics has
been on this trajectory of unifying seemingly disparate things. We’ve
found that, as we understand more, apparently incredibly disparate
phenomena turn out to be different aspects of a more surprising, more
beautiful answer than we could have anticipated—and often even hoped
for. This started with Newton, who realized that the force dragging the
apple down was the same force holding the moon around the earth. It
continued with the realization that electricity and magnetism are
different aspects of the same thing. Relativity told us that space and
time are different aspects of the same thing. There’s more and more
unity in our understanding of nature. And we’ve seen, especially over
the last hundred years, that the essential unity and the essential
simplicity best reveal themselves at short-distance scales. So it’s not
that we care about the particles. We care about the laws.”
Taped
to the wall of Arkani-Hamed’s office is a graph labelled “LHC
Luminosity Profile.” It shows when various phenomena—including the
Higgs—should, if they exist, be revealed. Arkani-Hamed is a frequent
visitor to CERN, and every time he goes, he told me,
“it’s like a religious experience.” To prepare for the start-up of the
collider, he has helped organize a series of dress rehearsals, called
the L.H.C. Olympics. In these exercises, one team, playing God, chooses,
out of the many models of the universe proposed by theorists, one to be
true. The team then generates the sort of data that, according to this
model, should be produced at the L.H.C. The other teams have to analyze
the data to try to arrive back at the theoretical model the numbers are
supposed to reflect. There are no winners or losers, Arkani-Hamed
explained. “But afterward some people are high-fiving each other and
other people are being consoled.” He added, “It’s an amazing blast.”
One
source of tension between experimentalists and theorists is the awkward
matter of credit. Who should get the glory when a discovery is made:
the theorist who proposed the idea, or the experimentalist who found the
evidence for it? In this context, even access to L.H.C. data is a vexed
subject; in the United States, the groups that have worked on building
the detectors will receive the raw data, but they’re not likely to share
it. Arkani-Hamed joked that in order to get at the information
theorists might have to find a “Deep Throat” who will pass them the data
in secret.
“There is a sense among many
experimentalists that theorists are a bunch of irresponsible little
spoiled brats who get to sit around all day, having all these fun ideas,
drinking espresso and goofing off, with next to no accountability,” he
said. “Meanwhile, they’re out there, nose to the grindstone, for ten
years; they’ve built this damn detector, and damn it if they’re not
going to be the ones to figure it out! And so this stuff that we’re
doing, there’s some Johnny-come-lately feeling like ‘Oh, now that it’s
all done the theorists finally want to think about how they’re going to
solve this’; it’s like there are theorists swooping in to try to take it
from them. I’m exaggerating slightly, but not much.
“It’s
a general fact about physics that the people you tend to remember are
the theorists,” he went on. “At least in the mythology, experiment plays
a less central role. And there’s a natural reason for that, because the
ultimate goal isn’t to observe things about nature; the ultimate goal
is to understand and explain things about nature. So, for that reason,
it’s a chicken-and-egg problem. But definitely you want to be the
chicken.”
Arkani-Hamed
is often called a string theorist, although he is more closely
associated with ideas like large extra dimensions—large being on the
scale of a tenth of a millimetre—and a hybrid theory known as “split
supersymmetry.” String theory posits that the universe is composed of
tiny strands of energy, which vibrate at different frequencies, creating
what appear to be different particles. In its most popular form, string
theory demands the existence of seven dimensions beyond the usual
four—three in space and one in time—that we’re familiar with.
Supersymmetry, meanwhile, which is often referred to by the acronym SUSY
(pronounced soo-see), holds that every particle has a “superpartner”
with a different spin, spin here being understood not as it is in
everyday life but as a fixed property of a particle that determines some
of its basic characteristics. Under the naming system that’s been
devised for these hypothetical superpartners, the counterpart of a quark
would be a squark, and that of a photon a photino. (The superpartner of
the as yet undiscovered Higgs would be a Higgsino.) It has been
proposed that these “superparticles” could account for the dark matter
that physicists estimate makes up nearly a quarter of the universe.
String
theory and supersymmetry are enormously compelling to theorists, so
much so that their proponents dominate the theory groups at most élite
universities. (As of 2000, at least ten thousand scientific papers on
supersymmetry, and several thousand more on string theory, had been
written.) Both aim at further unification, and both—to varying
degrees—resolve problems that have frustrated physicists for decades.
Arkani-Hamed spent nearly two hours trying to take me through the
details of just one of these—the so-called “hierarchy problem.” In the
process, he consumed four or five or six cups of espresso—even this I
lost track of. Broadly speaking, the hierarchy problem has to do with
mathematical contortions, known to physicists as “fine-tuning,” that
must be performed in order to account for the fact that gravity is so
weak compared to the other forces.
“This is not
just a little weird,” Arkani-Hamed told me. “It’s incredibly weird. The
big question that we don’t have an answer to, or that we have an answer
to but it seems absurd, is: Why do we have a macroscopic universe at
all?”
The trouble with string theory and
supersymmetry is that, at this point, they remain entirely theoretical.
The last confirmed breakthrough in particle physics was a set of
equations known as the Standard Model. Developed in the early
nineteen-seventies, the equations describe the behavior of all known
forms of matter and all known forces, with the notable exception of
gravity. Despite the model’s limitations as a fundamental theory of
nature—the hierarchy problem is just one of its many shortcomings—the
predictions it has generated have been borne out, with astonishing
precision, at one collider after another. (The Higgs would represent the
last element of the model to be confirmed.) String theory, by contrast,
has yet to provide a single prediction that could be definitively
tested. As for supersymmetry, which is generally considered a
precondition for string theory, all efforts to confirm its predictions
have so far failed: at the energy levels achieved by colliders to date,
not a trace of a squark or a photino has turned up. As Lee Smolin, a
physicist at Canada’s Perimeter Institute, observed in a recent critique
of contemporary theory, eventually “you begin to feel like Sbozo the
clown. Or Bozo the clownino. Or swhatever.”
To
theorists, the tantalizing promise of the L.H.C. is that it will,
finally, supply the evidence of “new physics” that they’ve been waiting
for. Certain patterns of missing energy, for example, would suggest the
existence of extra dimensions, as would the creation of mini black
holes. Different results—also in the form of missing energy—would
indicate the existence of squarks or other superparticles. There are
good theoretical reasons to expect these phenomena to begin to appear at
the energy level of the L.H.C., or so at least Arkani-Hamed tried to
explain to me over several more espressos. He told me that he was
completely confident the Higgs would be found at the collider: “I would
bet many, many months’ salary.” He also said that if the Higgs was the
only result, the L.H.C. would be a disappointment. “We theorists, we’re a
hard lot to please. We’ve taken things for granted for so long we say,
‘Oh, yeah, for sure you’ll discover the Higgs.’ But the things we’re
really interested in are all these major puzzles.”
Eventually,
some of Arkani-Hamed’s graduate students wandered into his office. They
had brought with them a Diet Coke, which Arkani-Hamed began to drink
out of his espresso cup, and a hundred-page paper that they—and he—were
planning to release that day. The opening sentence of the paper
declared, “With the upcoming turn-on of the Large Hadron Collider (LHC),
high energy physics is on the verge of entering its most exciting
period in a generation.” (A later sentence noted, “As the reader might
find intuitive, we can tremendously improve our scheme over the constant
approximation by including the leading order near-threshold behavior of
matrix elements.”)
In
1969, the Congressional Joint Committee on Atomic Energy held a hearing
at which the physicist Robert Wilson was called to testify. Wilson, who
had served as the chief of experimental nuclear physics for the
Manhattan Project, was at that point the head of CERN’s
main rival, Fermilab, and in charge of $250 million that Congress had
recently allocated for the lab to build a new collider. Senator John
Pastore, of Rhode Island, wanted to know the rationale behind a
government expenditure of that size. Did the collider have anything to
do with promoting “the security of the country”?
WILSON: No sir, I don’t believe so.
PASTORE: Nothing at all?
WILSON: Nothing at all.
PASTORE: It has no value in that respect?
WILSON:
It only has to do with the respect with which we regard one another,
the dignity of men, our love of culture. . . . It has to do with are we
good painters, good sculptors, great poets? I mean all the things we
really venerate in our country and are patriotic about. . . . It has
nothing to do directly with defending our country except to make it
worth defending.
Asked to explain
how their work, supported by public funds, contributes to the public
good, particle physicists often cite Wilson, or offer some variation on
his non-answer answer: the search for knowledge cannot be justified on
other grounds; its value, like the particles under study, is
irreducible.
The cost of the L.H.C. is expected
to run to more than $8 billion, and this doesn’t include the price of
the tunnel, which was originally dug for LEP. Most of the
funding is being provided by European taxpayers; Germany has
contributed the most—around twenty per cent of the total—and Britain and
France have each contributed slightly less than that. (The United
States is contributing a little more than $500 million.) Meanwhile,
physicists are already lobbying for the next generation of machines. The
plan for the International Linear Collider, which, as its name
suggests, would be built in a straight line rather than a ring, calls
for smashing electrons and positrons together at the midpoint of a
tunnel twenty miles long. According to the Web site that has been set up
for the I.L.C., the hypothetical collider’s design would allow for “an
upgrade” to a thirty-mile-long machine “during the second stage of the
project.” The even more ambitious Very Large Hadron Collider would
occupy a tunnel a hundred and forty miles in circumference.
In
principle, colliders could just keep on getting bigger—the Incredibly
Large Hadron Collider!—and commensurately more expensive. As a practical
matter, of course, there’s a limit, and it’s quite possible that limit
has already been reached. At CERN, nearly every physicist
I spoke to recalled the sad—very sad—story of the Superconducting Super
Collider. Announced with much fanfare by President Ronald Reagan in
1987, the Superconducting Super Collider was supposed to occupy a tunnel
fifty-four miles in circumference under Waxahachie, Texas. It was
designed to generate beam energies of 20 TeV, roughly three times as
high as those that will be achieved at CERN. Fourteen
miles of the tunnel had been excavated—and $2 billion spent—when, in
1993, Congress pulled the plug. “If we find more basic building blocks
of the universe, it’s not going to change the way people live” is how
Representative Martin R. Hoke, of Ohio, shrugged off his vote. As the
historian of science Peter Galison pointed out to me, it is probably no
coincidence that funding for the supercollider was cancelled almost
immediately after the fall of the Soviet Union. The “dignity of men”
defense of particle physics worked best at the height of the Cold War,
when no one, except maybe the scientists involved, entirely believed it.
Unless
funding for another collider materializes, a lot of experimentalists
will soon find themselves out of work. “Half of those guys already have
résumés in at hedge funds,” one theorist joked to me. Arguably, the
theorists’ situation is not all that much more secure; at a certain
point, speculations about the nature of the universe that can’t be put
to the test cease to be physics. The promise of the Large Hadron
Collider is thus also its great burden. A truly astonishing discovery
there—proof, say, of extra dimensions, or of something even weirder than
that, which theorists have yet to conceive of—would provide a powerful
impetus to keep particle physics going for another generation. Barring a
breakthrough, it’s hard to imagine how the project can continue. Such
an outcome would not mean that the fundamental order of the universe is
unknowable. But it might well mean that we will never know it. ♦
The CMS detector uses a huge solenoid magnet to bend the paths of particles from collisions in the LHC
The Compact Muon Solenoid (CMS) is a general-purpose detector at the Large Hadron Collider (LHC).
It has a broad physics programme ranging from studying the Standard Model (including the Higgs boson) to searching for extra dimensions and particles that could make up dark matter. Although it has the same scientific goals as the ATLAS experiment, it uses different technical solutions and a different magnet-system design.
The CMS detector is built around a huge solenoid magnet. This takes
the form of a cylindrical coil of superconducting cable that generates a
field of 4 tesla, about 100,000 times the magnetic field of the Earth.
The field is confined by a steel “yoke” that forms the bulk of the
detector’s 14,000-tonne weight.
An unusual feature of the CMS detector is that instead of being built
in-situ like the other giant detectors of the LHC experiments, it was
constructed in 15 sections at ground level before being lowered into an
underground cavern near Cessy in France and reassembled. The complete
detector is 21 metres long, 15 metres wide and 15 metres high.
The CMS experiment is one of the largest international scientific
collaborations in history, involving 4300 particle physicists,
engineers, technicians, students and support staff from 182 institutes
in 42 countries (February 2014).
