Editing Tachyon (section)

=== Mass ===
{{Main|Mass#Tachyonic particles and imaginary (complex) mass|Tachyonic field}}

In a [[Lorentz invariant]] theory, the same formulas that apply to ordinary slower-than-light particles (sometimes called bradyons in discussions of tachyons) must also apply to tachyons. In particular, the [[energy–momentum relation]]:
:<math>E^2 = (pc)^2+ (mc^2)^2 \;</math>
(where '''p''' is the relativistic [[momentum]] of the bradyon and '''m''' is its [[rest mass]]) should still apply, along with the formula for the total energy of a particle:
:<math>E = \frac{mc^2}{\sqrt{1 - \frac{v^2}{c^2}}}.</math>
This equation shows that the total energy of a particle (bradyon or tachyon) contains a contribution from its rest mass (the "rest mass–energy") and a contribution from its motion, the kinetic energy. When '''<math> v </math>''' (the particle's velocity) is larger than '''<math> c </math>''' (the speed of light), the [[Fraction|denominator]] in the equation for the energy is [[imaginary number|imaginary]], as the value under the square root is negative. Because the total [[energy]] of the particle must be [[real number|real]] (and not a [[Complex number|complex]] or imaginary number) in order to have any practical meaning as a measurement, the numerator must ''also'' be imaginary (i.e. the rest mass ''m'' must be imaginary, as a pure imaginary number divided by another pure imaginary number is a real number).

In some modern formulations of the theory, the mass of tachyons is regarded as real.<ref name=":0" /><ref name=":1" /><ref name=":2" />