As ‘Big Questions’ I would like to name those which are fundamental to the physical understanding of our Universe, such as: Why is the Universe made of matter rather than antimatter? What is the nature of Dark Matter, and of Dark Energy? Is there a preferred reference frame to the Universe? How are the forces of nature, including gravity, unified?
For decades, the primary experimental tools for addressing such Big Questions were large particle accelerators. However, scaling of these facilities to higher energies and larger sizes has become increasingly difficult and expensive—and may soon be impossible.
The conjecture I would like to discuss is: What can we learn from small-scale, low-cost terrestrial experiments in which subtle signs of new physics are sought through extreme sensitivity and precision?
Searches for tiny deviations from “ordinary” physical laws can be interpreted as tests of the very structure of the physical world. Examples might include the braking of symmetries like time reversal symmetry, or the search for a variation of the fundamental constants of nature like fine stricture constant or searches for a deviatipn from the 1/r law for the gravitational potential.
Great question Jörg,
Although we must sometimes beware, in our questions, of implicit 'cognitive bias' - the questions we ask are not always necessary legitimate (e.g. 'how are the forces of nature unified' - well, there is no proof to begin with that they are unified, see e.g. Marcelo Gleiser , who ascribes the search for a GUT of physics to a subconscious slant stemming from our monotheistic culture) or may be mere semantics (matter /antimatter - the real question is really that of the underlying symmetry modes)
This being said - we can learn a huge amount from low energy experiments. The issues are always the same though - first, incontrovertible experimental results can be and shall be interpreted very differently by different teams and 2- in low energy experimentation, accuracy and repeatability issues crop up more forcefully than at high energies ....
Low energy physics is still chock-full of controversial results for which definite, final explanations remain elusive. High energy physics, with its huge budgets, is meant as further aids towards solutions. We could not wholly forgo HE though - a recent case in point being Higgs, a question that could only be settled by the deployment of HE
This is indeed an excellent question. I have some examples which could be relevant to investigations into dark matter, dark energy, cosmology and astrobiology. Neutrinos have a tiny yet non-zero mass, evident from their flavour oscillations. However, we still do not know whether their mass hierarchy is inverted or normal and we don't have a good fix on the absolute masses of the mass eigenstates. One way of determining the mass scale would be a sensitive experiment operating at low energy which uses the mutual annihilation of pairs of nonrelativistic neutrinos mediated by leptons of the same flavour. For instance, annihilation could excite an electron orbiting an atom, closely followed by the spontaneous emission of a photon of measurable wavelength and hence energy. This interaction is essentially the time reversal of the photoneutrino process but, since the neutrinos would be nonrelativistic, the annihilation/excitation energy would be well-defined and informative. More precise meaurements of neutrino flavour oscillations could also establish the existence of sterile neutrinos - which may be an important component of dark matter in galaxy clusters. I am not saying these experiments would be easy to conduct, but they are at the opposite end of the energy scale to the (still) very well-funded particle colliders. You can assess for yourself their potential importance to the 'Big Questions' by following the link provided below:
http://www.scirp.org/journal/PaperInformation.aspx?PaperID=41504
Relatively low cost satellite based experiments such as WMAP
and PLANCK are used to constrain new physics models. Specially
dark matter and dark energy models. Typically apart from
measuring the temperature of microwave background radiation,
these facilities also measure delta T, these are the small fluctuations
in the temperature of CMBR as a function of angle. When
fluctuations are plotted the graph shows a major peak and a few
smaller peaks. Anslysis of positions and heights of the first
few peaks can give useful information regarding dark matter
and dark energy.
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