Gravity laser


A gravity laser, also sometimes referred to as a Gaser, Graser, or Glaser, is a hypothetical device for stimulated emission of coherent gravitational radiation, much in the same way that a standard laser produces coherent electromagnetic radiation.

Principle of function

While photons exist as excitations of a vector potential and so contain an oscillating dipole term, gravitons are a spin-2 field and so have an oscillating quadrupole term. For efficient lasing to occur, there are several conditions that must be met:
  1. There must be particles in an excited state capable of emitting radiation at the desired frequency. In a normal laser, these would be valence electrons in an excited state. For a gaser, the more straightforward analog would be a binary system of massive bodies.
  2. These particles must couple to supplied radiation, in order to provide stimulated emission. This could be possible in a gaser by a stimulated analog of the Penrose process.
  3. The particles must be in an inverted population, where more are in the excited state than the ground state. This typically requires some type of pumping, such as optical pumping.
  4. The lasing medium must be long enough for the radiation to persist and excite more of the same. In optical systems this can typically be created by mirrors, effectively making a larger optical path length. For a gaser, a large-scale, slowly spatially varying gravitational potential could act as a mirror. Alternately, a hypothetical gaser could simply be built with sufficient length to begin with.
Alternate design proposals involve free undulators akin to a free-electron laser. Several proposals involve exploiting the momentum transport properties of superconductors, where s-waves and d-waves couple distinctly to gravitational radiation.
As of 2019, there are no plans to construct a gravity laser.

Use in Science Fiction

The idea of gravity lasers has been in part popularized by science fiction works such as Earth Unaware where glasers are used as a plot device to enable planetary-scale manipulation of matter, akin to gravity guns. In other works such as Star Ocean they may be a hypothetical weapon. They are also commonly employed as a proposed mechanism for tractor beams or antigravity.