The fundamental act of an experimental physicist is that of measurement. By measuring a quantity (the mass of a particle, the intensity of a laser beam etc) and comparing the result to the predictions of a theory, the validity of the theory can be tested. In this manner, human knowledge is enlarged!
Collaborations: Certain branches of Physics, notably Particle Physics and Astronomy (the experimental side of Astrophysics and Cosmology) involve extremely expensive facilities: particle accelerators and space telescopes for example. This has led to the formation of international collaborations, through which the money and manpower required to build and run such facilities may be provided by a number of different countries.
In Particle Physics, the major international collaborations are:
- CERN, located on the French-Swiss border near Geneva. Its main facilities are LEP, the Large Electron Positron collider (now dismantled) and the LHC, or Large Hadron Collider (under construction).
- DESY, located in Hamburg, Germany. Its main facility is HERA, which collides electrons and protons.
- SLAC, located near Palo Alto, USA. Its main facility is PEP-II, which collides electrons and positrons.
- Fermilab], located near Chicago, USA. Its main facility is the Tevatron, which collides protons and antiprotons.
- Brookhaven National Lab], located on Long Island, USA. Its main facility is the Relativistic Heavy Ion Collider, which collides heavy ions such as Au (it is the first heavy ion collider) and protons.
Many other particle accelerators exist.
Spectroscopy is an important tool used by physicists.