photo effect
When light shines onto a metal, it can knock electrons out of the metal's atoms. This is the photoelectric effect, and its properties - how does the number and energy of the electrons depend on the frequency and intensity of the light? - can only be explained ...
Perimeter Institute for Theoretical Physics
Privately funded institute for basic research in theoretical physics, located in Waterloo, Canada. Currently, the main areas of research are quantum computing, the foundations of quantum theory, and quantum gravity. Perimeter Institute ...
perihelion
For a planet or other heavenly body orbiting the sun on an elliptic orbit, that point of the orbit closest to the sun. In the context of general relativity, the perihelion is of great interest as that theory predicts a slight motion of this point around the ...
perihelion advance, relativistic
For planetary orbits, there is a small difference between the predictions of Newtonian gravity and general relativity. For instance, in Newton's theory, the orbital curve of a lonely planet orbiting a star is an ellipse. In general relativity, it is a kind of ...
Pauli exclusion principle
Basic principle of quantum theory stating that no two fermions can be in exactly the same state - for instance: no two fermions with identical properties can be at the same location. Formulated by the physicist Wolfgang Pauli. Electrons are fermions, and ...
path integrals
Synonym: Sum over histories. A technique for performing calculations in quantum theory. Roughly speaking, the probability for a certain outcome (for instance, a particle reaching location A at time t) is calculated by performing a sum over all possible ways ...
particle physics
The branch of physics that deals with particles that are, to the best of today's knowledge, not made up of more fundamental sub-units, for instance with electrons, quarks or neutrinos. Also included is the study of some species of particles that do have more ...
particle accelerator
The most important experimental technique of particle physics: accelerating electrically charged particles with the help of electric forces, make them collide with each other and, from the result of the collision, draw conclusions about the properties of ...
