Trade.Information

Physicist Re-Create the Conditions a Fraction of a Millisecond After the Big Bang Using Unprecedented Energy

For a research physicist, Sandra Ciocio knows all about the trials of the construction site. In recent years she’s seen 7,000 tons of sensitive equipment lowered down a 100-m shaft to prepare for a single grand experiment. The technology was groundbreaking and the schedule punishing. “It’s been deadline, deadline, deadline,” she says. “I haven’t had a holiday in five years.” But when the first real data begin to emerge this summer, the possible rewards should be worth the effort: a final explanation of one of the last puzzles of physics. “I feel like crying,” says Ciocio. “It’s like a dream come true.”

Deep beneath a tranquil patch of farmland, Ciocio and her colleagues at the European Organization for Nuclear Research, known as CERN, have built the world’s biggest and most sophisticated scientific instrument, the Large Hadron Collider, housed in a 27-kilometer tunnel that loops beneath the French-Swiss border. Using unprecedented energy, it will re-create the conditions a fraction of a millisecond after the big bang that gave birth to the cosmos 14 billion years ago. The goal: to track down a single elusive particle whose existence — if it can be proved — would fill a critical gap in our understanding of the universe.

This particular mystery has a daunting history. More than 30 years ago scientists developed an elegant series of equations, called the Standard Model, that describes the make-up of the universe in terms of the relationship between a few fundamental particles and forces. But the model has gaps. One gap is the baffling issue of mass. Why are some particles heavy while others have no mass at all? According to the leading theory, the weight of a particle depends on how it interacts with a mysterious “Higgs field” that permeates all space. So far scientists haven’t found any evidence that this field — and its associated particle, the Higgs boson — exists. They’ve been waiting for a particle collider big enough to perform the necessary experiments. The Large Hadron Collider was built to fit this bill.

The idea behind the collider is simple: get protons — positively charged particles present in every atom — going fast, crash them into each other and observe the fragments. The LHC will use superconducting magnets to guide the protons round and round the subterranean ring until they’re going almost as fast as light. The resulting collisions will release unprecedented amounts of energy (equivalent to 100,000 times the temperature at the center of the sun). With luck, they’ll also produce, among a shower of lesser particles, the long-sought Higgs boson.

The collider may also throw up clues to puzzles that arise at the strange intersection of particle physics and astronomy. To understand the cosmos, scientists must understand how it developed from those first primordial particles. “In effect, what we have is far and away the most capable microscope ever built, and the most powerful telescope ever built,” says theoretical physicist John Ellis. A central mystery is the supposed existence of invisible “dark matter,” and its counterpart “dark energy,” a strange force that seems to accelerate the expansion of the universe. Although together the dark pair make up for 96 percent of the universe, scientists know next to nothing about them — only their gravitational effects. Those grand collisions may produce undiscovered particles that account for both. The collider might also reveal yet another set of particles, the “superpartners,” needed to bolster the case for String Theory, a “theory of everything” that proposes the existence of six extra dimensions and a universe constructed of tiny vibrating strings.
All this knowledge comes with a whopping price tag: the collider will cost about euro 3 billion. Its annual energy consumption will match the entire city of Geneva’s. The 1 billion collisions taking place every second, captured and filtered by underground detectors, will generate enough data to fill 100,000 CDs a year. But ultimate knowledge is worth it, says CERN boss Robert Aymar.

It’s entirely possible that after all this money and effort the collider’s detectors will find no trace of the Higgs boson. That would still make the project worthwhile, researchers say. It would indicate beyond doubt that the Standard Model, the basis of modern physics, requires a radical rethinking. “Our theorist friends tell us to look this way or the other, but maybe Nature is telling us to look behind us,” says Tejinder Virdee, a physicist from Imperial College in London.

The Geneva experiments will keep scientists occupied for 20 years or more. “This is truly a once-in-a-generation experiment,” says Virdee, “but it will take a generation to do.” Setting up the world’s greatest experiment took more than a decade: fixing the nature of the cosmos will take a little longer.

Note for Standard Model
The Standard Model of particle physics is a theory that describes three of the four known fundamental interactions between the elementary particles that make up all matter. It unifies the electroweak theory and quantum chromodynamics into a structure denoted by the gauge groups SU(3)×SU(2)×U(1). It is a quantum field theory which is consistent with both quantum mechanics and special relativity. To date, almost all experimental tests of the three forces described by the Standard Model have agreed with its predictions. However, the Standard Model falls short of being a complete theory of fundamental interactions, primarily because of its lack of inclusion of gravity, the fourth known fundamental interaction, but also because of the eighteen numerical parameters (such as masses and coupling constants) that must be put "by hand" into the theory (rather than being derived from first principles).

In physics, the dynamics of both matter and energy in nature is presently best understood in terms of the kinematics and interactions of fundamental particles. To date, science has managed to reduce the laws which seem to govern the behavior and interaction of all types of matter and energy we are aware of, to a small core of fundamental laws and theories. A major goal of physics is to find the 'common ground' that would unite all of these into one integrated model of everything, in which all the other laws we know of would be special cases, and from which the behavior of all matter and energy can be derived (at least in principle). "Details can be worked out if the situation is simple enough for us to make an approximation, which is almost never, but often we can understand more or less what is happening." (Feynman's lectures on Physics, Vol 1. 2-7)

The standard model is a grouping of two major theories – quantum electroweak and quantum chromodynamics – which provides an internally consistent theory describing interactions between all experimentally observed particles. Technically, quantum field theory provides the mathematical framework for the standard model. The standard model describes each type of particle in terms of a mathematical field.

Note for String Theory
String theory is a still-developing mathematical approach to theoretical physics, whose original building blocks are one-dimensional extended objects called strings. Unlike the point particles in quantum field theories like the standard model of particle physics, strings interact in a way that is almost uniquely specified by mathematical self-consistency, forming an apparently valid quantum theory of gravity.

Since its birth as the dual resonance model which described the strongly interacting hadrons as strings, the term string theory has changed to include any of a group of related superstring theories and larger frameworks such as M-theory, which unite them. A shared property of all these theories is the holographic principle.

String theorists have not yet completely described these theories, nor have they determined if these theories relate to the physical universe or how. The logical coherence of the approach, however, and the fact that string theory can include all older theories of physics, have led many physicists to believe that such a connection is possible. In particular, string theory is the first candidate theory of everything, a way to describe all the known natural forces (gravitational, electromagnetic, weak and strong) and matter (quarks and leptons) in a mathematically complete system. On the other hand, many detractors criticise string theory because it has not yet provided experimentally testable predictions.

Like any other quantum theory of gravity, it is widely believed that testing the theory experimentally would be prohibitively expensive, requiring heroic feats of engineering on a solar-system scale. Although string theory, like any other scientific theory, is falsifiable in principle, critics maintain that it is unfalsifiable for the foreseeable future, and so should not be called science.

Work on string theory is made interesting because of the mathematics involved, and because of the large number of forms that the theories can take. String theory strongly suggests that spacetime has eleven dimensions, not the usual three space and one time; but the theory can easily describe universes with four observable spacetime dimensions too.

String theories include objects more general than strings, called branes. These are black-holes charged with a differential form vector potential which has more than one index, a different type of electricity and magnetism where the fundamental objects are extended. By studying certain p-branes and identifying them with D-branes, endpoints for strings, certain types of string theory are shown to be equivalent to certain types of more traditional gauge theory. Research on this equivalence has led to new insights on quantum chromodynamics, the fundamental theory of the strong nuclear force.

String theory is formulated in terms of an action principle, either the Nambu-Goto action or the Polyakov action, which describes how strings move through space and time. Like springs with no external force applied, the strings tend to shrink, thus minimizing their potential energy, but conservation of energy prevents them from disappearing, and instead they oscillate. By applying the ideas of quantum mechanics to strings it is possible to deduce the different vibrational modes of strings, and that each vibrational state appears to be a different particle. The mass of each particle, and the fashion in which it can interact, are determined by the way the string vibrates — the string can vibrate in many different modes, just like a guitar string can produce different notes. The different modes, each corresponding to a different kind of particle, make up the "spectrum" of the theory.

Strings can split and combine, which would appear as particles emitting and absorbing other particles, presumably giving rise to the known interactions between particles.

String theory includes both open strings, which have two distinct endpoints, and closed strings, where the endpoints are joined to make a complete loop. The two types of string behave in slightly different ways, yielding two different spectra. For example, in most string theories, one of the closed string modes is the graviton, and one of the open string modes is the photon. Because the two ends of an open string can always meet and connect, forming a closed string, there are no string theories without closed strings.

The earliest string model — the bosonic string, which incorporated only bosons, describes — in low enough energies — a quantum gravity theory, which also includes (if open strings are incorporated as well) gauge fields such as the photon (or, more generally, any gauge theory). However, this model has problems. Most importantly, the theory has a fundamental instability, believed to result in the decay (at least partially) of space-time itself. Additionally, as the name implies, the spectrum of particles contains only bosons, particles which, like the photon, obey particular rules of behavior. Roughly speaking, bosons are the constituents of radiation, but not of matter, which is made of fermions. Investigating how a string theory may include fermions in its spectrum led to the invention of supersymmetry, a mathematical relation between bosons and fermions. String theories which include fermionic vibrations are now known as superstring theories; several different kinds have been described, but all are now thought to be different limits of M-theory.

Some qualitative properties of quantum strings can be understood in a fairly intuitive fashion. For example, quantum strings have tension, much like regular strings made of twine; this tension is considered a fundamental parameter of the theory. The tension of a quantum string is closely related to its size. Consider a closed loop of string, left to move through space without external forces. Its tension will tend to contract it into a smaller and smaller loop. Classical intuition suggests that it might shrink to a single point, but this would violate Heisenberg's uncertainty principle. The characteristic size of the string loop will be a balance between the tension force, acting to make it small, and the uncertainty effect, which keeps it "stretched". Consequently, the minimum size of a string is related to the string tension.