The Large Hadron Collider (LHC) is the newest, largest and most powerful sub-atomic particle accelerator so far built. It is circular structure 27 km (17 mi) in circumference, buried 50 m to 175 m underground (the surface is mountainous, and there are four larger cavernous regions along the LHC), and straddles the French-Swiss border northwest of Geneva. The LHC is operated by the European Organization for Nuclear Research (the acronym in French is CERN), and was 15 years in the making. The purpose of this machine is to smash bits of matter into each other at speeds nearly indistinguishable from that of light, to produce evanescent globs whose ultra-high temperatures and densities are similar to the conditions one trillionth of a second after time zero for the Big Bang. The LHC has two parallel tubes along which protons are circulated in opposing directions; the positively charged protons are propelled by electric fields and kept on track by magnetic fields. At four points along the track, steering magnets guide the opposing beams to collision sites, which are surrounded by detection equipment. The LHC began operating on September 10, 2008, when beams began circulating, and it is scheduled to produce its first collisions after its official unveiling on October 21, 2008.
Why is high energy needed to study matter? Is the operation of the LHC safe? Will it precipitate Doomsday?
Matter is known to be up of particles, which are themselves known to be made up of even smaller particles, and these are bound together with increasingly strong bonds as they are more deeply embedded. For example, most of the substances we see and touch are made up of molecules, like DNA, water, and the (diatomic) oxygen and nitrogen in our atmosphere. With sufficient heat, the chemical bonds between individual atoms that make up molecules can be broken, and atoms released. A unit of energy used to understand matter is the electron volt, eV; this is the energy absorbed by an electron (a light weight, negatively charged sub-atomic particle) that is accelerated by a voltage difference of one volt, [1 eV = 1.60217646 × (10 to the -19th power) joules]. The chemical bonds of molecules require perhaps 1 eV to 15 eV to be overcome. Chemical bonds are made up of electrical interactions — overlaps, if you will — between the individual electrical fields holding atoms together.
Each atom has a nucleus with the overwhelming portion of the atomic mass, and a number of orbiting electrons. The nucleus is made up of protons (positively charged), and neutrons (no charge). The positive charge of the centrally-located protons is balanced by an equal negative charge of orbiting electrons. A proton is over 1800 times more massive than an electron, and is only ever so slightly less massive than a neutron. The electrical attraction between positive and negative charges holds the atom together. Extracting an electron from an atom can require from 5 eV to well over 1000 eV. The first electron comes off fairly easily, but then the positive nucleus has a stronger hold on the now smaller total negative charge of the remaining electrons. So, succeeding electron extractions require more and more energy. The force holding an atom together is the electromagnetic force.
A free neutron exists for about 15 minutes before it decays into a proton, electron and electron antineutrino. When the decay of a neutron occurs within an atomic nucleus, that nucleus exhibits radioactivity by the process of beta decay, the emission of mass-energy as an electron or a positron (same mass as an electron but of positive charge). The “weak force” involved in these effects acts over a very small range, no larger than the extent of a neutron, and it is much weaker than the electromagnetic force (by 10 to the 11th power), hence the name “weak.”
The nucleus of an atom is held together by the “nuclear force” or the “residual strong nuclear force.” This force is a side effect of the “strong force,” which holds quarks and gluons together to form protons and neutrons. The “residual” aspect of the strong force holds positively charged protons together in a nucleus despite their electrical repulsion, and is about 100 times stronger than intra-atomic and intra-nuclear electrical forces.
In order to observe effects governed by the weak force, one has to study naturally radioactive substances, or one has to artificially fission nuclei to extract neutrons and to induce reactions between colliding sub-nuclear particles. Often, the energy required to produce desired collisions is high because it is first necessary to overcome the electrical repulsion between colliding particles, before they can be brought sufficiently close that the short range weak force can have an effect. This may require tens to hundreds of millions of eV (one million eV is an MeV).
Similarly, to observe the action of the strong force, one must invest the colliding partners with sufficient energy to overcome repulsive electromagnetic forces, to liberate protons and neutrons from nuclei (unless using proton or neutron beams), and to overcome the integrative operation of the strong force within those protons and neutrons. This may require thousands to millions of MeV, that is to say up to trillions of eV. The LHC is designed to accelerate protons up to 7 trillion eV (7 Tev) and produce collisions of 14 TeV.
The higher the energy of the collision, the greater the range of phenomena that can be accessed. The LHC should have sufficient energy to fully test out the “standard model” of particle physics, where the material aspect of mass-energy is confined to point masses in 3D space and affected by three of the four basic forces: weak, electromagnetic and strong. Gravity is the fourth basic force. Experiments to date have verified many aspects of the standard model (which has known inaccuracies of uncertain cause). A result anticipated from the LHC is the observation of the Higgs boson, a particle predicted by the the standard model (to address the known inaccuracies). Whatever the result in this regard, reliable experimental data is key to fashioning a correct theory about the nature of matter, either by validating prior ideas and predictions, or by demonstrating that reality differs from prior conceptions, and these errors must be eliminated even at the cost of replacing the bulk of the existing theory. We’ll see.
Beyond settling the accounts of the standard model, physicists hope the LHC has sufficient energy to bring hitherto hidden phenomena to light. That would be exciting (and it would spur many careers). In particular, physicists hope to learn more about hidden dimensions and how a single theoretical model could explain the emergence of the four basic forces. At present, there is an electroweak model that describes how the electromagnetic force and the weak force emerge from a more basic unified force; and the standard model is a unification of the electroweak model and quantum chromodynamics, which latter theory describes the strong force. As yet there is no certain theoretical unification of gravity with the standard model (which unifies weak, electromagnetic and strong forces). Perhaps LHC will produce some clues.
One conception is that gravity is so exceptionally weak (especially on the atomic and nuclear scale) in our 3D view because there are “really” many more than three dimensions (11?, 22?), and gravitational energy leaks beyond our 3D into the other hidden dimensions. These hidden dimensions are curled up in ultra-small scales, well below those of sub-nuclear particles, and in turn these particles are “really” multi-dimensional strings whose multi-dimensional vibrations exhibit their mass-energy, which we observe as point masses in our restricted 3D view, analogous to the 2D profile of a shadow hinting at the 3D contours of a face. There is a vast literature on super-string theory, and there is no data. Perhaps LHC can produce some hints. One consequence of the concept of hidden dimensions is that perhaps an LHC collision would produce a quark-gluon plasma (the high energy-density goo created from the insides of smashed protons) of sufficient intensity so that the supposed gravitational energy stored along its hypothesized hidden dimensions would be compacted to the point of producing a micro black hole.
From Einstein’s general theory of relativity, it is known that a sufficiently massive concentration of matter can collapse on itself shrinking in linear scale into a “hole” in 3D space whose gravitational pull is so strong it would even prevent light from emerging, or time from proceeding. Such a black hole would have essentially curved space back into itself; any matter drifting into its vicinity could be swept into the hole, contributing to its strength and disappearing from external reality. As matter falls into a black hole, it accelerates, heats and radiates. It is from the astronomical observation of such radiation that black holes are known to exist. Astronomical black holes may be tens to hundreds of kilometers in diameter, and include masses that range from several times that of our Sun to orders of magnitude more. But micro black holes at LHC? Even if they really formed, would they survive? If we allow they may come into existence, would they be capable of swallowing matter endlessly, devouring CERN, then France, then everyone and everything else including Texas? We have rocketed along an exponential path of speculative thought. At this point there are two options: hysterical panic or rational analysis.
Of course, hysterical panic is much more fun, much less work, and much more likely to sell copy. CERN has invested considerable effort to investigate the Doomsday potential of LHC experiments, and their reports as well as those of competent independent reviewers have been published, in 2003 and 2008. Basically, there is no Doomsday potential for the simple reason that the known physics of black holes indicates that any LHC-produced black hole (itself a highly speculative conjecture) would dissipate by radiating energy away (a process called Hawking radiation, named after the famous English physicist), and that micro black holes can just as easily be produced in the Earth and its atmosphere by collisions with cosmic rays (which shower our planet continuously and have LHC-like energy), and there has been no known Doomsday effect during the last 4 billion years. This same argument can be made for the many stars in the universe, far more likely to suffer interactions with cosmic rays because they are larger and denser; many of these stars are far older than the Earth. Additionally, the accretion of matter by a stable micro black hole on Earth might be insignificant due to the small mass-energy of the micro black hole, the small scale over which its gravitational pull might be significant, and the sheer size of the Earth in comparison. Only a detailed quantitative analysis should be trusted as regards making these conclusions, and that is what CERN scientists and their reviewers produced. I choose to believe them.
The Doomsday fears for the LHC are reminiscent of the fear of burning up the entire atmosphere as a result of the first atom bomb test on July 16, 1945, at Alamogordo, New Mexico. It was thought that the radiation released by the nuclear explosion might start chain reactions in the air, and these would eventually consume the atmosphere. Hans Bethe was put to work to calculate this likelihood, and found it to be negligible. The original concern may have been based on sound physical principles, but once the actual quantities for physical effects were calculated, they were found to be insignificant. So, we can forgive hysterical panic if it is just a momentary first step to proceeding with a rational and accurate quantitative analysis. However, we must accept that for some, hysterical panic is the desired state to remain in. Can’t be helped.
High energy physics is not my specialty, so if you want more information about it and the LHC I recommend you read articles like those listed at the end of this one.
A project like the LHC absorbs a significant quantity of public funds, so it is fair to ask if it gives a reasonable return to the public good. Ultimately, that judgment will rest on one’s estimation of the value of the expansion of knowledge the LHC produces, if any; its value as a training facility for scientists and engineers young in their careers; its value as an engine of economic activity; its value as a mechanism for international cooperation; its value as an incubator of inventiveness. Physics is a subtle and absorbing activity that both soothes and exercises the mind, its best results spring from pure curiosity unhampered by commercialism or militarism. If CERN can nurture physics of that sort at the LHC, then with patience and careful management it will probably be a successful and satisfying public investment.
For More Information, See:
LHC — The Large Hadron Collider
E = MC2: Tunnel Vision, Let The Collisions Begin
Science News, Volume 174, Number 2, 19 July 2008
Large Hadron Collider
Safety of the Large Hadron Collider
MANUEL GARCIA, Jr. is a retired physicist. E-mail = firstname.lastname@example.org