In particle physics, subatomic particles not only build all matter, they are also conceived as ‘carriers’ or ‘mediators’ [1] of nature's fundamental forces and related energies, with the possible exception of gravitation [2] . All subatomic particles, whether representing forces or matter, exhibit wave properties (oscillations and interference) along with their particle nature (properties occur only as discrete values, not as continua). Mass and energy are expressions of the same thing in the high-energy environment of particle physics, where forces and energies are many orders of magnitude higher than in classical physics. Ever deeper structures of matter and forces have been uncovered, and we don’t know for sure whether the presently known smallest particles are truly fundamental [3] . These and other strange phenomena, observed in experiments, provide a glimpse of the fantastically complex quantum world and the mysteries of physical reality [4] .
Major historic discoveries
More on particle detectors and accelerators
In line with the particle view of radiation, the interaction of particles can be interpreted as being brought about, i.e. 'mediated', by emission of a 'force carrier' (e.g., a photon) from one interacting particle (e.g., an electron) and absorption by another interacting particle (e.g., a proton).
Three of four fundamental forces have been assigned mediating particles identified in particle accelerator experiments: the weak force is mediated by the W and Z bosons, the electromagnetic force by the photon, and the strong force by the gluon. No partical has been found for the fourth fundamental force, the familiar yet mysterious gravitation. However, gravitational waves have been observed for the first time in September 2015 by the LIGO and Virgo interferometers which allow the identification on Earth of incredibly small vibrations (of a few nanometer amplitude) in the fabric of spacetime caused by the collision of distant super-massive cosmic bodies.
Most subatomic particles observed in accelerator experiments are composites made up of relatively few elementary particles (see Standard model ). To separate atoms in a molecule, just a few eV are required to overcome the binding energy of the valence electrons, but energies of MeV-magnitude are required to split off protons or neutrons from the nucleus. To further probe the structure of these particles, TeV-energies are needed, while today’s most powerful particle accelerator (LHC) just reaches 2 × 7 TeV. We don’t know whether at still higher energies new ‘elementary’ particles would appear.
The particle concept best describes phenomena at the smallest scale, such as observed at high energies in large accelerators. For phenomena observable at much lower energy levels (e.g., light and radio), the wave concept is used. Quantum mechanics accommodate both concepts and, when supplemented with principles of the classical field, even lead to a third, still more fundamental concept, the quantum field. The standard model encompasses quantum mechanics and special relativity, but not general relativity, which describes gravitation. Attempts to reconcile the standard model with general relativity led, inter alia, to the string, loop quantum gravity, and M theories, based, inter alia, on concepts of strings, spin, and supersymmetry. So far, all concepts and theories failed to explain reality at the most fundamental level; they provide, however, fantastically complex mathematic models that may trigger intriguing philosophical thoughts about the role of mathematics in nature.