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a heavier family, made up of the charm and strange quark on the one 
hand, and the muon and its neutrino on the other. And finally, as ex-
periments have now confirmed over the past decade or two, there is a 
third family, made of two new types of quarks, called bottom and top, 
and an accompanying heavy version of the electron called the tau par-
ticle, along with its neutrino. 
Beyond these particles, as I shall soon describe, we have every reason 
to expect that other elementary particles exist that have never been ob-
served. While these particles, which we think make up the mysterious 
dark matter that dominates the mass of our galaxy and all observed gal-
axies, may be invisible to our telescopes, our observations and theories 
nevertheless suggest that galaxies and stars could never have formed 
without the existence of dark matter. 
And at the heart of all of the forces governing the dynamical behavior of 
everything we can observe is a beautiful mathematical framework called 
gauge symmetry. All of the known forces, strong, weak, electromagnetic, 
and even gravity, possess this mathematical property, and for the three 
former examples, it is precisely this property that ensures that the theo-
ries make mathematical sense and that nasty quantum infinities disappear 
from all calculations of quantities that can be compared to experiment. 
With the exception of electromagnetism, these other symmetries re-
main completely hidden from view. The gauge symmetry of the strong 
force is hidden because confinement presumably hides the fundamental 
particles that manifest this symmetry. The gauge symmetry of the weak 
force is not manifest in the world in which we live because it is spontane-
ously broken so that the W and Z particles become extremely massive. 
The shadows on the wall of everyday life are truly merely shadows. In 
this sense, the greatest story every told, so far, has been slowly playing 
out over the more than two thousand years since Plato first imagined it 
in his analogy of the cave. 
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But as remarkable as this story is, two elephants remain in the room. 
TWo protagonists in our tale could until recently have meant that the 
key aspects of the story comprised a mere fairy tale invented by theo-
rists with overactive imaginations. 
First, the W and Z particles, postulated in 1960 to explain the weak 
interaction, almost one hundred times more massive than protons and 
neutrons, were still mere theoretical postulates, even if the indirect 
evidence for their existence was overwhelming. More than this, an in-
visible field—the Higgs field—was predicted to permeate all of space, 
masking the true nature of reality and making our existence possible 
because it spontaneously breaks the symmetry between the weak and 
the electromagnetic interactions. 
To celebrate a story that claims to describe how it is that we exist, 
but that also posits an invisible field permeating all of space, sounds 
suspiciously like a religious celebration, and not a scientific one. To 
truly ensure that our beliefs conform to the evidence of reality rather 
than how we would like reality to be, to keep science worthy of the 
name, we had to discover the Higgs field. Only then could we truly 
know if the significance of the features of our world that we hold so 
dear might be no greater than that of the features of one random ice 
crystal on a window. Or, more to the point, perhaps, no greater than 
the significance of the superconducting nature of wire in a laboratory 
versus the normal resistance of the wires in my computer. 
The experimental effort to carry out this task was no easier than that 
in developing the theory itself. In many ways it was more daunting, tak-
ing more than fifty years and involving the most difficult fabrication of 
technology that humans have ever attempted. 
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Chapter 20 
SPANKING THE VACUUM 
If anyone slaps you on the right cheek, turn to him 
the other also. 
-MATTHEW 5:39 
As the 197os ended, theorists were on top of the world, 
triumphant and exultant. With progress leading to the Standard Model 
so swift, what other new worlds were there to conquer? Dreams of a 
theory of everything, long dormant, began to rise again and not just in 
the dim recesses of the collective subconscious of theorists. 
Still, the W and Z gauge particles had never actually been observed, 
and the challenge to directly observe them was pretty daunting. Their 
masses were precisely predicted in the theory at about ninety times 
the mass of the proton. The challenge to produce these particles comes 
from a simple bit of physics. 
Einstein's fundamental equation of relativity, E = me, tells us that 
we can convert energy into mass by accelerating particles to energies of 
many times their rest mass. We can then smash them into targets to see 
what comes out. 
The problem is that the energy available to produce new particles by 
smashing other fast-moving particles into stationary targets is given by 
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what is called the center-of-mass energy. For those undaunted by an-
other formula, this turns out to be the square root of twice the product 
of the energy of the accelerated particle times the rest mass energy of the 
target particle. Imagine accelerating a particle to one hundred times the 
rest mass energy of the proton (which is about one gigaelectronvolt—
GeV). In a collision with stationary protons in a target, the center-of-
mass energy that is available to create new particles is then only about 
14 GeV. This is just slightly greater than the center-of-mass energy avail-
able in the highest-energy particle accelerator in 1972. 
To reach the energies required to produce massive particles such as 
the W or Z bosons, two opposing beams of particles must collide. In 
this case the total center-of-mass energy is simply twice the energy of 
each beam. If each colliding beams of particles has an energy of one 
hundred times the rest mass of a proton, this then yields zoo GeV of 
energy to be converted into the mass of new particles. 
Why, then, produce accelerators with stationary targets and not col-
liders? The answer is quite simple. If I am shooting a bullet at a barn 
door, I am more or less guaranteed to hit something. If I shoot a bullet 
at another incoming bullet, however, 
have to be a much better shot 
than probably anyone else alive and have a better gun than any now 
made to be guaranteed to hit it. 
This was the challenge facing experimentalists in 1976, by which time 
they took the electroweak model seriously enough that they thought it 
worth the time, effort, and money to try to test it. 
But no one knew how to build a device with the appropriate energy. 
Accelerating individual beams of particles or antiparticles to high ener-
gies had been achieved. By 1976 protons were being accelerated to Soo 
GeV, and electrons up to so GeV. At lower energies, collisions of elec-
trons and their antiparticles had successfully been carried out, and this 
is how the new particle containing the charmed quark and antiquark 
had been discovered in 1974 
Protons, having greater mass and thus more rest energy initially, 
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are easier to accelerate to high energies. In 2976 a proton accelerator at 
the European Organization for Nuclear Research (CERN) in Geneva, 
the Super Proton Synchrotron (SPS), had just been commissioned as a 
conventional fixed-target accelerator operating with a proton beam at 
goo GeV. However, another accelerator at Fermilab, near Chicago, had 
already achieved proton beams of soo GeV by the time the SPS turned 
on. In June of that year, physicists Carlo Rubbia, Peter McIntyre, and 
David Cline made a bold suggestion at a neutrino conference: convert-
ing the SPS at CERN into a machine that collided protons with their 
antiparticles—antiprotons—would allow CERN to potentially produce 
W's and Z's. 
Their bold idea was to use the same circular tunnel to accelerate pro-
tons in one direction, and antiprotons in another. Since the two par-
ticles have opposite electric charges, the same accelerating mechanism 
would have opposite effects on each particle. So a single accelerator 
could in principle produce two high-energy beams circulating in op-
posite directions. 
The logic of such a proposal was clear, but its implementation was 
not. In the first place, given the strength of the weak interaction, the pro-
duction of even a few W and Z particles would require the collision of 
hundreds of billions of protons and antiprotons. But no one had ever pro-
duced and collected enough antiprotons to make an accelerator beam. 
Next, you might imagine that with two beams traversing the same 
tunnel in opposite directions, particles would be colliding all around the 
tunnel and not in the detectors designed to measure the products of the 
collisions. However, this is far from the case. The cross section of even a 
small tunnel compared to the size of the region over which a proton and 
an antiproton might collide is so huge that the problem is quite the op-
posite. It seemed impossible to produce enough antiprotons and ensure 
that both they and the protons in the proton beam would be sufficiently 
compressed so that when the two beams were brought together, steered 
by powerful magnets, any collisions at all would be observed. 
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Convincing the CERN directorate to transform one of the world's 
most powerful accelerators, built in a circular tunnel almost eight ki-
lometers around at the French-Swiss border, into a new kind of collider 
would have been difficult for many people, but Carlo Rubbia, a bombastic 
force of nature, was up to the task. Few people who got in Rubbia's way 
were likely to be happy about it afterward. For eighteen years he jetted 
every week between CERN and Harvard, where he was a professor. His 
office was two floors down from mine, but I knew when he was in town 
because I could hear him. Moreover, Rubbia's idea was good, and in pro-
moting it he was really suggesting to CERN that the SPS move up from 
an "also-ran" machine to the most exciting accelerator in the world. As 
Sheldon Glashow said to the CERN directorate when encouraging them 
to move forward, to you want to walk, or do you want to fly?" 
Still, to fly one needs wings, and the creation of a new method to pro-
duce, store, accelerate, and focus a beam of antiprotons fell to a brilliant 
accelerator physicist at CERN, Simon van der Meer. His method was so 
clever that many physicists who first heard about it thought it violated 
some fundamental principles of thermodynamics. The properties of the 
particles in the beam would be measured at one place in the circular 
tunnel, then a signal would be sent for magnets farther down the tun-
nel to give many small kicks over time to the particles in the beam as 
they passed by, thus slightly altering the energies and momenta of any 
wayward particles so that they would eventually all get focused into a 
narrow beam. The method, called stochastic cooling, helped make sure 
particles that were wandering away from the center of the beam would 
be sent back into the middle. 
Together van der Meer and Rubbia pushed forward, and by 1981 the 
collider was working as planned, and Rubbia assembled the largest phys-
ics collaboration ever created and built a large detector capable of sort-
ing through billions of collisions of protons and antiprotons to search 
for a handful of possible W and Z particles. Rubbia's team was not the 
only one hunting for a W and a Z, however. Another detector collabora-
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tion had been assembled and was also built at CERN. Redundancy for 
such an important observation seemed appropriate. 
Unearthing a signal from the immense background in these experi-
ments was not easy. Remember that protons are made of more than 
one quark, and in a single proton-antiproton collision a lot of things 
can happen. Moreover, the W's and Z's would not be observed directly, 
but via their decays—in the case of the W, into electrons and neutrinos. 
Neutrinos would not be directly observed, either. Rather the experimen-
talists would tally up the total energy and momentum of each outgoing 
particle in a candidate event and look for large amounts of "missing en-
ergy," which would signal that a neutrino had been produced. 
By December 1982, a W candidate event had been observed by Rub-
bia and his colleagues. Rubbia was eager to publish a paper based on this 
single event, but his colleagues were more cautious, for good reason. 
Rubbia seemed to have a history of making discoveries that weren't al-
ways there. In the meantime he leaked details of the event to a number 
of colleagues around the world. 
Over the next few weeks his "UM" collaboration obtained evidence 
for five more W candidate events, and the UAI physicists designed sev-
eral far more stringent tests to ascertain with high confidence that the 
candidates were real. On January 2o, 1983, Rubbia presented a memora-
ble and masterful seminar at CERN announcing the result. The stand-
ing ovation he received made it clear that the physics community was 
convinced. A few days later Rubbia submitted a paper to the journal 
Physics Letters announcing the discovery of six W events. The W had 
been discovered with precisely the predicted mass. 
The search was not over, however. The Z remained to be seen. Its 
predicted mass was slightly higher than that of the W, and its signal was 
therefore slightly harder to obtain. Nevertheless, within a month or so 
of the W announcement, evidence for Z events began to come in from 
both experiments, and on the basis of a single clear event, on May 27 
that year Rubbia announced its discovery. 
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The gauge bosons of the electroweak model had been found. The sig-
nificance of these discoveries for solidifying the empirical basis of the 
Standard Model was underscored when, just slightly over a year after 
making the announcement, Rubbia and his accelerator colleague van 
der Meer were awarded the Nobel Prize in Physics. While the teams 
that had built and operated both the accelerator and the detectors were 
huge, few could deny that without Rubbia's drive and persistence and 
van der Meer's ingenious invention the discovery would not have been 
possible. 
One big Holy Grail now remained: the purported Higgs particle. Un-
like the W and Z bosons, the mass of the Higgs is not fixed by the the-
ory. Its couplings to matter and to the gauge bosons were predicted, as 
these couplings allow the background Higgs field that presumably exists 
in nature to break the gauge symmetry and give mass not to just the W 
and the Z, but also to electrons, muons, and quarks—indeed to all the 
fundamental particles in the Standard Model save the neutrino and the 
photon. However, neither the Higgs particle mass nor the strength of its 
self-interactions was separately determined in advance by then existing 
measurements. Only their ratio was fixed by the theory in terms of the 
measured strength of the weak interaction between known particles. 
Given conservative estimates of the possible magnitude of the Higgs 
self-interaction strength, the Higgs particle mass was conservatively es-
timated to lie within a range of 2 to 2,000 GeV. What set the upper limit 
was that, if the Higgs self-coupling is too big, then the theory becomes 
strongly interacting and many of the calculations performed using the 
simplest picture of the Higgs break down. 
Aside from their necessary role in breaking the electroweak sym-
metry and giving other elementary particles masses, these quantitative 
details were therefore largely undetermined by experiments up to that 
time—which is probably why Sheldon Glashow in the 3.98os referred to 
the Higgs as the "toilet" of modern physics. Everyone was aware of its 
necessary existence, but no one wanted to talk about the details in public. 
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That the Standard Model didn't fix in advance many of the details of 
the Higgs sector didn't dissuade many theorists from proposing models 
that "predicted" the Higgs mass based on some new theoretical ideas. 
In the early 1980s, each time accelerators increased their energies, new 
physics papers would come out predicting a Higgs would be discov-
ered when the machine was turned on. Then a new threshold would be 
reached, and nothing would be observed. To explore all the available 
parameter space to see if the Higgs existed, a radically new accelerator 
would clearly have to be built. 
I was convinced during all this time that the Higgs didn't exist. The 
spontaneous symmetry breaking of the electroweak gauge symmetry 
did certainly occur—the W and the Z exist and have mass—but adding 
a fundamental new scalar field designed by recipe specifically to per-
form this task seemed contrived to me. First, no other fundamental sca-
lar field had ever been observed to exist in nature's particle menagerie. 
Second, I felt that with all of the unknown physics yet to be discovered 
at small scales, nature would have developed a much more ingenious 
and unexpected way of breaking the gauge symmetry. Once one posits 
the Higgs particle, then the next obvious question is "Why that?" or 
more specifically "Why just the right dynamics to cause it to condense 
at that scale, and with that mass?" I thought that nature would find a 
way to break the theory in a less ad hoc fashion, and I expressed this 
conviction fairly strongly when I was interviewed for my eventual posi-
tion at the Society of Fellows at Harvard after getting my PhD. 
Let's recall now what the existence of the Higgs implies. It requires 
not just a new particle in nature but an invisible background field that 
must exist throughout all of space. It also implies that all particles—
not just the W and the Z particles but also electrons and quarks—are 
massless in the fundamental theory. These particles that interact with 
the Higgs background field then experience a kind of resistance to their 
motion that slows their travel to less than the speed of light—just as a 
swimmer in molasses will move more slowly than a swimmer in water. 
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Once they are moving at sub-light-speed, the particles behave as if they 
are massive. Those particles that interact more strongly with this back-
ground field will experience a greater resistance and will act as if they 
are more massive, just as a car that goes off the road into mud will be 
harder to push than if it were on the pavement, and to those pushing it, 
it will seem heavier. 
This is a remarkable claim about the nature of reality. Remembering 
that in superconductors the condensate that forms is a complicated state 
of bound pairs of electrons, I was skeptical that things would work out 
so much more simply and cleanly on fundamental scales in empty space. 
So how to explore such a remarkable claim? We use the central prop-
erty of quantum field theory that was exploited by Higgs himself when 
he proposed his idea. For every new field in nature, at least one new type 
of elementary particle must exist with that field. How, then, to produce 
the particles if such a background field exists throughout space? 
Simple. We spank the vacuum. 
By this I mean that if we can focus enough energy at a single point 
in space, we can excite real Higgs particles to emerge and be measured. 
One can picture this as follows. In the language of elementary particle 
physics, using Feynman diagrams, we can think of a virtual Higgs par-
ticle emerging from the background Higgs field, giving mass to other 
particles. The left diagram corresponds to particles such as quarks and 
electrons scattering off a virtual Higgs particle and being deflected, thus 
experiencing resistance to their forward motion. The right diagram rep-
resents the same effect for particles such as the W and the Z. 
We can then simply turn this picture around: 
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In this case energetic particles such as W's and Z's or quarks and/or 
antiquarks or electrons and/or positrons appear to emit virtual Higgs 
particles and recoil. If the energies of the incoming particles are large 
enough, then the emitted Higgs could be a real particle. If they aren't, 
the Higgs would be a virtual particle. 
Now remember that if the Higgs gives mass to particles, then the 
particles it interacts with most strongly will be the particles that get the 
largest masses. In turn this means that the particles most likely to spit 
out a Higgs are the incident particles with the heaviest masses. That 
means that light particles such as electrons are probably not a good bet 
to directly create Higgs particles in an accelerator. Instead we can imag-
ine creating an accelerator with enough energy so that we can create 
heavy virtual particles that will spit out Higgs particles, either virtual 
or real. 
The natural candidates are then protons. Build an accelerator or a 
collider starting with protons and accelerate them to high enough en-
ergies to produce enough virtual heavy constituents so as to produce 
Higgs particles. The Higgs particles, virtual or real, being heavy, will 
quickly decay into the lighter particles that the Higgs interacts with 
most strongly—once again either the top or bottom quarks or W's and 
Z's. These will in turn decay into other particles. 
The trick would be to consider events with the smallest number of 
outgoing particles that could be cleanly detected, then determine their 
energies and momenta precisely and see if one could reconstruct a se-
ries of events traceable to a single massive intermediate particle with the 
predicted interactions of a Higgs particle. No small task! 
These ideas were already clear as early as 1977, even before the dis-
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covery of the top quark itself (since the bottom quark had already been 
discovered, and all the other quarks came in weak pairs—up and down, 
charm and strange—clearly another quark had to exist, although it took 
until 199s to discover it, a whopping um times heavier than the proton). 
But knowing what was required and actually building a machine ca-
pable of doing the job were two different things. 
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Chapter 21 
GOTHIC CATHEDRALS OF THE 
TWENTY-FIRST CENTURY 
The price of wisdom is above rubies. 
-JOB 28:18 
Accelerating protons to high enough energies to explore 
the full range of possible Higgs masses was well beyond the capabilities 
of any machine in 1978—when all the other predictions of the elec-
troweak theory were confirmed—or in 1983 when the W and the Z had 
been discovered. An accelerator at least an order of magnitude more 
powerful than the most powerful machine then in existence was re-
quired. In short, not a collider, but a supercollider. 
The United States, which for the entire period since the end of the 
Second World War had dominated science and technology, had good 
reason to want to build such a machine. After all, CERN in Geneva 
had emerged by 1984 as the dominant particle physics laboratory in the 
world. American pride was so hurt when both the W and the Z particles 
were discovered at CERN that six days after the press conference an-
nouncing the Z discovery, the New York Times published an editorial 
titled "Europe 3, U.S. Not Even Z-Zerol 
Within a week after the Z discovery, American physicists decided to 
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cancel construction of an intermediate-scale accelerator in Long Island 
and go for broke. They would build a massive accelerator with a center-
of-mass energy almost one hundred times greater than the CERN SPS 
machine. To do so they would need new superconducting magnets, 
and so their brainchild was named the Superconducting Super Col-
lider (SSC). 
After the project was proposed by the US particle physics commu-
nity in 2983, the traditional scramble proceeded among many different 
states to get a piece of the enormous fiscal pie for its construction and 
management. After much political and scientific wrangling a site just 
south of Dallas, Texas, in Waxahachie, was chosen. Whatever the moti-
vation, Texas seemed particularly appropriate, as everything about the 
project, which was approved in 1987 by President Reagan, was supersize. 
The huge underground tunnel would have been eighty-seven kilo-
meters around, the largest tunnel ever constructed. The project would 
be twenty times bigger than any other physics project ever attempted. 
The proposed energy of collisions, with two beams each having an en-
ergy twenty thousand times the mass of the proton, would be about one 
hundred times larger than the collision energy of the machine at CERN 
that had discovered the W and the Z. Ten thousand superconducting 
magnets, each of unprecedented strength, would have been required. 
Cost overruns, lack of international cooperation, a poor US economy, 
and political machinations eventually led to SSC's demise in October 
1993. I remember the time well. I had recently moved from Yale to be-
come chair of the Physics Department at Case Western Reserve Uni-
versity, with a mandate to rebuild the department and hire twelve new 
faculty members over five years. The first year we advertised, in 1993-94, 
we received more than two hundred applications from senior scientists 
who had been employed at the SSC and who were now without a job or 
any prospects. Many of them were very senior, having left full professor-
ships at distinguished universities to spearhead the effort. It was sad, and 
more than half of those people had to leave the field altogether. 
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The anticipated cost of the project when it was canceled had risen 
from 54.4 billion at its inception in 2987 to about $12 billion in 1993. 
While this was, and still is, a large amount of money, one can debate the 
merits of killing the project. Two billion dollars had already been spent 
on it, and twenty-four kilometers of tunnel had been completed. 
The decision to kill the project was not black-and-white, but a num-
ber of things could have played a bigger role in considerations—from 
the opportunity costs of losing a fair fraction of the talented accelera-
tor physicists and particle physics experimentalists in the country to 
the many new breakthroughs that might have resulted from the expen-
ditures on high-tech development that would have contributed to our 
economy. Moreover, had the SSC been built and functioned as planned, 
we may have had answers more than a decade ago to experimental ques-
tions we are still addressing. Would knowing the answers have changed 
anything we might have done in the meantime? We'll probably never 
know. 
The $12 billion would have been spent over some ten to fifteen years 
during construction and the commencement of operations, which 
makes the cost in the range of Si billion per year. In the federal budget 
this is not a large amount. My own political views are well known, so it 
may not be surprising for me to suggest, for example, that the United 
States would have been just as secure had it cut the bloated US defense 
budget by this amount, far less than 2 percent of its total each year. More-
over, the entire cost of the SSC would have probably been comparable 
to the air-conditioning and transportation costs of the disastrous 2003 
Iraq invasion, which decreased our net security and well-being. I can't 
help referring once again to Robert Wilson's testimony before Congress 
regarding the Fermilab accelerator: "It has nothing to do directly with 
defending our country except to help make it worth defending! 
These are political questions, however, not scientific ones, and in a 
democracy, Congress, representing the public, has the right and respon-
sibility to oversee priorities for expenditures on large public projects. 
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The particle physics community, perhaps too used to a secure inflow 
of money during the Cold War, did not do an adequate job of inform-
ing the public and Congress what the project was all about. It is not 
surprising that in hard economic times the first thing to be cut would 
be something that seemed so esoteric. I wondered at the time why it 
was necessary to kill the project, rather than suspend funding until the 
economy improved or until technological developments might have re-
duced its cost. Neither the tunnel (now filling with water) nor the lab-
oratory buildings (now occupied by a chemical company) were going 
anywhere. 
Despite these developments in the United States, CERN was moving 
forward with a new machine, the Large Electron-Positron (LEP) Col-
lider, designed to explore in detail the physics of the W and the Z par-
ticles, at the urging of its newest Nobel laureate, the indomitable Carlo 
Rubbia. He became the laboratory's director in 1989, the same year the 
new machine came online. 
A twenty-seven-kilometer-long circular tunnel was dug about a 
hundred meters underground around the old SPS machine, which was 
now used to inject electrons and positrons into the bigger ring, where 
they were further accelerated to huge energies. Located on the outskirts 
of Geneva, the new machine was large enough to cross under the Jura 
Mountains into France. European nations are more familiar with build-
ing tunnels than the United States is, and when the tunnel was com-
pleted, the two ends met up to within one centimeter. Moreover CERN, 
as an international collaboration of many countries, did not significantly 
eat into the GDP of any one country. 
The new machine ran successfully for more than a decade, and after 
the demise of the SSC in the United States, the huge LEP tunnel was 
considered for the creation of a miniversion of the SSC—not quite as 
powerful but still energetic enough to explore much of the parameter 
space where the long-sought Higgs particle might exist. Some competi-
tion came from a machine at Fermilab, called the Tevatron, which had 
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been running since 1976 and in 1984 came online as the world's most 
energetic proton-antiproton machine. By 1986, the collision energy of 
protons and antiprotons circulating around the 6.s-kilometer ring of 
superconducting magnets at Fermilab was almost two thousand times 
the equivalent rest mass energy of the proton. 
As significant as this was, it was not sufficient to probe most of the 
available parameter space for the Higgs, and a discovery at the Tevatron 
would have required nature to have been kind. The Tevatron did garner 
one great success, the long-anticipated discovery, in 1995, of the mam-
moth top quark, 175 times the mass of the proton, and the most massive 
particle yet discovered in nature. 
With no clear competition therefore, within fourteen months of the 
demise of the SSC the CERN council approved the construction of a 
new machine, the Large Hadron Collider, in the LEP tunnel. Design and 
development of the machine and detectors would take some time to 
complete, so the LEP machine would continue to operate in the tunnel 
for almost another six years before having to close down for reconstruc-
tion. It would then take almost another decade to complete construc-
tion of the machine and the particle detectors to be used in the search 
for the Higgs and/or other new physics. 
That is, if a working machine and viable detectors could be con-
structed. This would be the most complicated engineering task humans 
had ever undertaken. The design specifications for superconducting 
magnets, computing facilities, and many other aspects of the machine 
and detectors called for technology far exceeding anything then avail-
able. 
Conceptual design of the machine took a full year, and another 
year later two of the main experimental detector collaboration pro-
posals were approved. The United States, with no horses in this race, 
was admitted as an "observer" state to CERN, allowing US physicists to 
become key players in detector development and design. In 1998 con-
struction of the cavern to hold one of the two major detectors, the CMS 
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detector, was delayed for six months as workers discovered fourth-
century Gallo-Roman ruins, including a villa and surrounding fields, 
on the site. 
Four and a half years later, the huge caverns that would house both 
main detectors underground were completed. Over the next two years, 
1,232 huge magnets, each fifteen meters long and weighing thirty-five 
tons, were lowered fifty meters below the surface in a special shaft and 
delivered to their final destinations using a specially designed vehicle 
that could travel in the tunnel. A year after that, the final pieces of 
each of the two large detectors were lowered into place, and at 10:28 
M., September 10, 2008, the machine officially turned on for the first 
time. 
Two weeks later, disaster struck. A short occurred in one of the mag-
net connectors, causing the associated superconducting magnet to go 
normal, releasing a huge amount of energy and resulting in mechanical 
damage and release of some of the liquid helium cooling the machine. 
The damage was extensive enough that a redesign and examination of 
every weld and connection in the LHC was required, taking more than 
a year to complete. In November of 2009 the LHC was finally turned 
back on, but because of design concerns, it was set to run at seven thou-
sand times the center-of-mass energy of the proton, instead of fourteen 
thousand. On March 19, 2010, the machine finally began running with 
colliding beams at the lower energy, and both sets of detectors began to 
record collisions with this total energy within two weeks. 
These simple timelines belie the incredible challenges of the techni-
cal feats achieved at CERN during the fifteen years since the machine 
was first proposed. If you land at Geneva airport and look outside, you 
will see gentle farmland, with mountains in the distance. Without being 
told, no one would guess that underneath that farmland lies the most 
complicated machine humans have ever constructed. Consider some of 
the characteristics of the machine, which lies at some points in meters 
below this calm and pastoral scene: 
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1. In the 3.8-meter-wide tunnel, traversing twenty-seven kilome-
ters, are two parallel beamline circles, intersecting at four points 
around the ring. Distributed around the ring are more than six-
teen hundred superconducting magnets, most weighing more 
than twenty-seven tons. The tunnel is so long that, looking down 
it, one almost cannot see its curvature: 
2. Ninety-six tons of superfluid 4I-le are used to keep the magnets 
operating at a temperature of less than two degrees above absolute 
zero, colder than the temperature of the radiation background in 
the depths of interstellar space. In total, 120 tons of liquid helium 
are utilized, cooled first by using about ten thousand tons of liquid 
nitrogen. Some forty thousand leak-tight pipe connections had 
to be made. The volume of He used makes the LHC the largest 
cryogenic facility in the world. 
3. The vacuum in the beamlines is required to be sparser than the 
vacuum in outer space experienced by the astronauts performing 
space walks outside the ISS, and ten times lower than the atmo-
spheric pressure on the Moon. The largest volume at the LHC 
pumped down to this vacuum level is nine thousand cubic me-
ters, comparable to the volume of a large cathedral. 
4. The protons accelerated around the tunnel in either direction 
move at a speed of 0.999999991 times the speed of light, or only 
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about three meters per second less than light speed. The energy 
possessed by each proton in the collision is equivalent to the en-
ergy of a flying mosquito, but compressed into a radial dimension 
one million million times smaller than a mosquito's length. 
5. Each beam of protons is bunched into 2,808 separate bunches, 
squeezed at collision points to about one-quarter the width of 
a human hair, around the ring, with 115 billion protons in each 
bunch, yielding bunch collisions every twenty-five-billionths of a 
second, with more than 600 million particle collisions per second. 
6. The computer grid designed to handle data from the LHC is the 
largest in the world. Every second the raw data generated by the 
LHC are enough to fill more than a thousand one-terabyte hard 
drives. This must be reduced considerably to be analyzed. From 
the 6 million billion proton-proton collisions analyzed in 2012 
alone, more than twenty-five thousand terabytes of data were 
processed—more than the amount of information in all the books 
ever written and corresponding to a stack of CDs about twenty 
kilometers tall. To do this, a worldwide computer grid was cre-
ated with 170 computer centers in thirty-six countries. When the 
machine is running, about seven hundred megabytes per second 
of data are produced. 
7. The requirements for the sixteen hundred magnets to produce 
beams intense enough to collide is equivalent to firing two nee-
dles from a distance of ten kilometers with such precision that 
they collide exactly halfway between the two firing positions. 
8. The alignment of the beams is so precise that account must be 
taken for the tidal variations on the ring from the gravity of the 
Moon as its position over Geneva changes, causing a variation of 
one millimeter in the circumference of the LHC each day. 
9. To produce the incredibly intense magnetic fields needed to steer 
the proton beams, a current of almost twelve thousand amps 
flows through each of the superconducting magnets, about 120 
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