A relativistic particle is a particle which moves with a

relativistic speed Relativistic speed refers to speed at which relativistic effects become significant to the desired accuracy of measurement of the phenomenon being observed. Relativistic effects are those discrepancies between values calculated by models consideri ...

; that is, a speed comparable to the speed of light. This is achieved by photons to the extent that effects described by special relativity are able to describe those of such particles themselves. Several approaches exist as a means of describing the motion of single and multiple relativistic particles, with a prominent example being postulations through Dirac equations of single particle motion.

Massive particle The physics technical term massive particle refers to a massful particle which has real non-zero rest mass (such as baryonic matter), the counter-part to the term massless particle. According to special relativity, the velocity of a massive particl ...

s are relativistic when their kinetic energy is comparable to or greater than the energy

mc^2

corresponding to their rest mass. In other words, a massive particle is relativistic when its total mass-energy (rest mass + kinetic energy) is at least twice its rest mass. This condition implies that the particle's speed is close to the speed of light. According to the Lorentz factor formula, this requires the particle to move at roughly 85% of the speed of light. Such relativistic particles are generated in particle accelerators, as well as naturally occurring in

cosmic radiation Cosmic rays are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the Solar System in our own ...

.An example of this is the

Oh-My-God particle The Oh-My-God particle was an ultra-high-energy cosmic ray detected on 15 October 1991 by the Fly's Eye camera in Dugway Proving Ground, Utah, U.S. It is the highest-energy cosmic ray ever observed. This particle's energy was unexpected an ...

. In

astrophysics Astrophysics is a science that employs the methods and principles of physics and chemistry in the study of astronomical objects and phenomena. As one of the founders of the discipline said, Astrophysics "seeks to ascertain the nature of the h ...

, jets of relativistic plasma are produced by the centers of active galaxies and

quasar A quasar is an extremely Luminosity, luminous active galactic nucleus (AGN). It is pronounced , and sometimes known as a quasi-stellar object, abbreviated QSO. This emission from a galaxy nucleus is powered by a supermassive black hole with a m ...

s. A charged relativistic particle crossing the interface of two media with different

dielectric constant The relative permittivity (in older texts, dielectric constant) is the permittivity of a material expressed as a ratio with the electric permittivity of a vacuum. A dielectric is an insulating material, and the dielectric constant of an insulat ...

s emits transition radiation. This is exploited in the

transition radiation detector A transition radiation detector (TRD) is a particle detector using the \gamma-dependent threshold of transition radiation in a stratified material. It contains many layers of materials with different indices of refraction. At each interface betwe ...

s of high-velocity particles.

Notes

{{Authority control Quantum mechanics Special relativity Accelerator physics

See also

Notes