Making non-trivial predictions today for how will basic research be in subnuclear physics ten years down the line is highly non-trivial. For exactly the opposite reason that it is equally hard in several other fields of research.
Usually, in basic research long-term forecasts are complicated by the rapidity of the evolution of the field: one sits on the steeply rising slope of a curve describing our technological capabilities and amassed knowledge, and there is no way to have a glance of the summit from there. Nevertheless, the goals of the research are in most instances clear, and it is on the rapidity of the development of the proper means of investigation that one places one's riskiest wagers.
But in subnuclear physics we are in a different situation today. While the technological progress and the development of more and more sophisticated instruments has not slowed down, we have means to gauge pretty well what we will be able to do in ten years from now. One tool, although not the only one, is Moore's law -the observation that computing power doubles every two years, with direct consequences on our capability to study more collisions and dig deeper in the structure of matter. Another is the long history of progress in the energy of our particle beams (see figure on the right, from Symmetry magazine), which is obviously correlated with the discoveries we have been capable of making with them. The complication arises from the fact that we come from forty years of dullness, and we do not know in the least where we are going: the goals are much fuzzier than in any other field of basic research. Or if you will, subnuclear physics is "more fundamental" than other Sciences, and thus its boundaries and its goals are less well defined. In the last forty years the standard model of electroweak interactions, formulated by Glashow, Salam, and Weinberg toward the end of the sixties, has been confirmed to a great level of precision, and so has the theory of Quantum Chromodynamics, which explains the strong interaction binding quarks and gluons inside hadrons and nuclei. Particle physicists have been lulled into believing that the simple doubling of power of their toys would bring new wonders in sight, but unfortunately, the paradigm is shifting.
Whatever is left to discover, apart from the Higgs boson, is not contained in our pretty picture of today's organization of the subnuclear world - and guessing it is as wild a bet as any. I might be criticized for writing this, but in my opinion there is not a theory that we should marry confidently, or one which is sufficiently based on hard facts to give us guidance; I do not even see a definite theory on which to place my money with a non-ridiculous chance of winning the bet.
[To put this in perspective: four years ago I placed a 1000$ wager which said that the LHC would not discover new particles except the Higgs boson, with Jacques Distler and Gordon Watts taking me on for respectively 750$ and 250$. The fact that I had originally proposed to bet against supersymmetry alone, but was later steered toward a much broader "any new particle" stipulation before anybody accepted it, should show you that it is really hard to marry any specific theory nowadays.]
Instead, all I see is a multitude of proposed augmentations of the particle spectrum, often solely motivated by the fact that present-day experimental observations leave a corner of phase space where to stuff them. The list is long: new Z' bosons, leptophilic or leptophobic, universal or not; particles disappearing in one, two, up to seven other dimensions (for some reason even theorists do not seem to have the guts to offer two-digit numbers of extra dimensions); first, second, or third-generation leptoquarks; fourth-generation quarks and leptons; mini-black holes. And I am leaving as last item a host of supersymmetric particles, belonging to a wide variety of possible models, quite different from one another: R-parity-conserved, or R-parity-violated Susy; split or unsplit Susy; minimal or non-minimal Susy Higgs sectors; SUGRA-ready, or SUGRA-don't care models; universal, quasi-univesal, or not nearly so extended Higgs sectors; dark-matter-allowed, dark-matter-disfavoured parameter space points; funnel regions, focus points, or coannihilation zones. What a mighty mess, my friends!
Now, the fact that I am a die-hard skeptic and that I do not believe in Supersymmetry is no news, nor is it worth a post on the physics we will face in 2020. So, being unable to put together a straight face and place a cheap bet on this or that model of the new physics we will be finding in the next ten years, I hereby renounce the cheap shot -knowing that the odds that my superior vision and foreseeing get sanctified in ten years' time by a lucky coincidence are basically zero. Instead, let me take on the issue from a different perspective: where will we be on the map on the experimental point of view, in ten years' time ?
The experimental landscape in 2020
In 2020, the field of particle physics will not be as different from now as we might think. Let me give here my very own predictions for what will happen.
The Tevatron collider will by then be long gone. The CDF and DZERO collaborations will be dismantled in 2013 -a quite sad, but unavoidable, outcome. A trickling of papers describing late analyses of the huge bounty of proton-antiproton collisions acquired by CDF and DZERO until September 2012 will continue to make it through to Physical Review Letters well into the late 10's, but by 2020 even CDF die-hards like Paolo Giromini or Giorgio Bellettini will have decided it is better to retire and enjoy the warmer weather of the Tuscan coast than to wrestle over yet another anomaly or another tenth of a GeV improvement in the top quark mass measurement.
[And let me add here that I sincerely hope that Professor Giorgio Bellettini will be awarded the 2013 Nobel Prize in Physics, for the discovery of the top quark!]
The CDF experiment will become a historic endeavour cited in textbooks, to praise a successful collaboration of physicists from all around the globe which lasted well over thirty years, produced over a thousand scientific papers, and produced the discovery of the top quark. Textbooks, however, will neglect to mention the huge fights and the scientific controversies that provided the necessary core pressure and kept the experiment from imploding, but ex-collaborators (guess who) will write about it in detail, finally free to recount dozens of as-of-yet untold stories and the human dramas that took place within the flimsy walls of the trailer complex sitting east of the CDF assembly building.
Having paid tribute to the older brother, the Large Hadron Collider will be alone in the field of the high-energy frontier. In 2020 the LHC will be a mature facility, having undergone a two-phase surgery to boost its power and endow its detectors of improved capabilities to cope with the increased proton collision rate. It will still be going strong and delivering data at a fantastic pace. The CMS and ATLAS experiments, along with ALICE and LHCb, will be producing exquisite science. New physics or not -most likely, not-, the measurement of quarks, leptons, and their interactions at 14 TeV of energy will indeed dig deep in the foundations of the standard model and will let us finally understand the details of electroweak unification and the origin of mass.
If, as I believe, the Higgs boson exists and it is a unique, neutral scalar field, the LHC experiments will measure its branching fractions, its exclusive production modes, its couplings to top and bottom quarks, and they will confirm that our picture of subnuclear physics, albeit grievously incomplete, is beautifully precise. By 2020 particle physics might then be facing the spectre of foreclosure: if no new physics is seen beyond the standard model at the scale of 14 TeV, no expensive new project may be able to justify its existence. But physicists may have managed to out-run that spectre, getting close enough to completing a new project before it becomes clear that it is not scientifically justified.
So, while other experiments will make important discoveries in the course of the next ten years -particularly in the neutrino sector-, at the high-energy frontier we might be able to see zero, or at most only one new facility in the process of being built. This new machine might be a new high-energy linear collider for electrons and positrons, o a more exciting muon collider (see the proposed layout on the left). Either way, such a machine will probably not see the light of its own collisions in ten years' time. These things are complicated to design, and because of their scale and complexity they are almost impossible to put together! A muon collider at Fermilab would be a wonderful opportunity for particle physics in the United States, but I do not see it taking data in 2020.And after all I hope I am wrong. Who cares about those 1000 dollars I bet against new discoveries ? It was an insurance bet against the dullness of a desert stretching beyond the standard model all the way through to our visible horizon. No: I hope that the LHC -i.e. ATLAS and CMS, including myself together with the other 2500 collaborators in my experiment- will indeed soon stumble in a host of new particles, magically turning on our detectors as a Christmas tree. Wouldn't it be beautiful ? Just turn the master knob anti-clockwise by half a turn, increasing the beam energy from 2 to 14 TeV, and wham!, a whole new world rains from the sky in flying colours. Experimentalists will lose their sleep, theorists will go nuts, careers will be made overnight. Nobel prizes will pop up....
...Nah. Sorry, but I do not buy it. It just looks too good to be true. I think the fantastic years for particle physics were the fifties and the seventies of the XXth century. I also think that in the next ten years we will learn much more about the world, about the universe, and about fundamental science by studying astrophysics and cosmology. But on that matter, my dear readers, I feel unqualified to pontificate!
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