By Marcelo Gleiser
Well, it's not quite the Big Bang machine, but it gets awful close to it. A couple of days ago, physicists from around the world working together at the European Center for Nuclear Research (CERN) got their giant particle accelerator to collide protons against protons at speeds close to the speed of light.
The Large Hadron Collider (LHC), the biggest machine ever built in the history of civilization, consists of a circular tunnel 17 miles in circumference buried about 300 feet underground. Bundles of protons were made to race clockwise and anticlockwise and to collide head-on through the action of incredibly powerful magnets.
The collisions literally transform energy into matter, following the famous E=mc2 formula: the energy of motion of the colliding protons morphs into a myriad of different particles. This is why physicists are always trying to increase the energy of the colliding particles: the more kinetic energy (energy of motion) the heavier the particles that can be created by the collision.
The LHC made the news because it broke the current energy record, reaching an amazing 7 trillion electron volts, equivalent to the energy stored in the mass of 7,000 protons. Its competitor, the Tevatron machine at Fermilab, a laboratory near Chicago, can reach about a trillion electron volts.
Excluding possible advanced alien civilizations with a similar curiosity for the composition of matter, such energies were reached only once in history, at times a trillionth of a second after the Big Bang. Hence the qualifier of "awful close" to the moment time started ticking away, some 13.7 billion years ago.
You may wonder if reaching such energies is worth 16 years of work and $10 billion. Countless Ph.D. theses, whole careers were devoted to the construction of the LHC in the hope that when data stars coming out, some very deep secrets will be revealed. (And there are many technological milestones as well.) The list of longed-for discoveries is extensive. Here are a few of the most important ones, from less to more speculative:
1. Finding the elusive Higgs boson, the particle that is supposed to explain why all other particles -- like the familiar electrons and the less familiar quarks -- have the masses they have. (We still won't know how the Higgs got its mass, but that's another story...) If the Higgs is found, theories that have been proposed some forty years ago will be vindicated. Given the energies achieved by the LHC when it becomes fully operational (it may take a few years), something has to be found. Of course, it's always possible that it may not be the Higgs, a much more interesting possibility. (Although the Scottish physicist Peter Higgs will be sorely disappointed.)
2. Finding dark matter particles. Dark matter, as the name says, is matter that doesn't produce light. Some ordinary matter, that is, matter made of atoms like us and stars, can also be dark: you or I don't shine in the visible. However, dark matter amounts to about 23% of the cosmic matter, some six times more than ordinary mater, shining or dark. We know it exists because it tugs gravitationally on matter that does shine, like galaxies. The LHC may find a leading candidate for dark matter. If it does, it will also be confirming the hypothetical supersymmetry, a symmetry that doubles the number of particles that exist, proposed some 35 years ago.
3. Extra dimensions. Unified theories of Nature, that is, mathematical formulations that try to demonstrate that the four forces that act on matter particles are actually manifestations of a single force -- the "unified field" -- work better in more than the ordinary three spatial dimensions. Superstring theory, the leading candidate for a unified theory of Nature, makes sense when formulated in nine or sometimes ten spatial dimensions. The LHC can't find traces of such dimensions, which would only be visible in an accelerator the size of the solar system. (The bigger the accelerator, the higher the energies it can reach.) However, some spinoffs of string theory suggest that maybe there are only a few extra dimensions, and that they can be large enough to be found at the LHC.
Of the three items above, there is little doubt that item 1, the Higgs, or something like it, will be found. Items 2 and 3 are riskier, and opinions vary. Thousands of physicists are convinced that supersymmetry exists and that it produces not only dark matter particles but also allows for superstrings (the "super" in superstrings comes from supersymmetry) to exist as well. For reasons I explain in my forthcoming book, I belong to the group of skeptics that is not convinced of the existence of supersymmetry and much less of superstrings. And this after publishing some 40 papers on the topic. The excitement of a machine like the LHC is that it can be used -- at least to a certain extent -- to discriminate between fact and fiction, between hypotheses and reality. This is what science is all about, when it works as it should.
However, it's important to remember that we shouldn't dictate how Nature works. Science is a narrative we construct to describe what we measure in the natural world. Of course, we should be free to imagine the world and pursue ideas beyond what we can measure, as far as it is reasonable to do so. On the other hand, we should also know when to stop and abandon what may only be a flight of fancy. Nature is what it is and we do what we can to catch up with it.
categories: Science and Culture