A tachyon () or tachyonic particle is a hypothetical particle that always travels faster than light. Physicists posit that faster-than-light particles cannot exist because they are inconsistent with the known laws of physics. If such particles did exist they perhaps could be used to send signals faster than light and into the past. According to the theory of relativity this would violate causality, leading to logical paradoxes such as the grandfather paradox. The complementary particle types are called luxons (which always move at the speed of light) and bradyons (which always move slower than light); both of these particle types are known to exist.

History

Faster-than-light particles were discussed before the advent of relativity by such physicists as JJ Thomson and Arnold Sommerfeld.

In 1962 with redefined formulas for momentum and energy. Additionally, since tachyons are confined to the spacelike portion of the energy–momentum graph, they cannot slow down to subluminal (slower-than-light) speeds. In this framework, neutrinos experience Lorentz-violating oscillations and can travel faster than light at high energies. This proposal was strongly criticized.

Superluminal information

thumb|upright=1|[[Spacetime diagram showing that moving faster than light implies time travel in the context of special relativity. A spaceship departs from Earth from A to C slower than light. At B, Earth emits a tachyon, which travels faster than light but forward in time in Earth's reference frame. It reaches the spaceship at C. The spaceship then sends another tachyon back to Earth from C to D. This tachyon also travels forward in time in the spaceship's reference frame. This effectively allows Earth to send a signal from B to D, back in time.]]

If tachyons can transmit information faster than light, then, according to relativity, they violate causality, leading to logical paradoxes of the "kill your own grandfather" type. This is often illustrated with thought experiments such as the "tachyon telephone paradox"

Fields with non-canonical kinetic term

By modifying the kinetic term of the field, it is possible to produce Lorentz invariant field theories with excitations that propagate superluminally.

See also

  • Lorentz-violating neutrino oscillations
  • Retrocausality
  • Tachyonic antitelephone
  • Virtual particle
  • Wheeler–Feynman absorber theory

References

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