**Imaginary Mass**

A hypothetical particle with imaginary rest mass would always travel faster than the speed of light. Such particles are called tachyons. There is no confirmed existence of tachyons.

If the rest mass is imaginary this implies that the denominator is imaginary since the total energy is an observable and thus must be real; therefore the quantity under the square root must be negative, which can only happen if *v* is greater than *c*. As noted by Gregory Benford *et al.,* among others, special relativity implies that tachyons, if they existed, could be used to communicate backwards in time (see Tachyonic antitelephone article). Since time travel is considered to be non-physical, tachyons are believed by physicists either to not exist, or else to be incapable of interacting with normal matter.

In quantum field theory, imaginary mass would induce tachyon condensation.

Read more about this topic: Exotic Matter

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### Famous quotes containing the words mass and/or imaginary:

“No atomic physicist has to worry, people will always want to kill other people on a *mass* scale. Sure, he’s got the fridge full of sausages and spring water.”

—William Burroughs (b. 1914)

“Avarice, the spur of industry, is so obstinate a passion, and works its way through so many real dangers and difficulties, that it is not likely to be scared by an *imaginary* danger, which is so small that it scarcely admits of calculation.”

—David Hume (1711–1776)