Faster-than-light: Encyclopedia II - Faster-than-light - Tachyons

Faster-than-light - Tachyons

In special relativity, while it is impossible to accelerate an object to the speed of light, or for a massive object to move at the speed of light, it is not impossible for an object to exist which always moves faster than light. The hypothetical elementary particles that have this property are called tachyons. Their existence has neither been proven nor disproven.

Tachyons are not structurally stable. The equations of relativity do allow faster than light travel, since the equations are symmetric about the velocity 'c', the speed of light. However, any particle which is moving faster and faster, at velocities less than 'c', ends up with more and more kinetic energy. This is true even in the classical model, but with special relativity, as the velocity approaches 'c', the energy goes to infinity.

Once the velocity crosses 'c', the energy has no place to go but down. In other words, a particle with mass moving at any speed above 'c' will lose energy when its velocity goes up even further. Put another way, such a particle will speed up when it loses energy.

Everything that moves causes a change in the structure of the fabric of space. This change in the structure of the fabric of space causes the formation of gravitational ripples (waves), which carry away energy. In most cases, the change is negligible. However, for a particle with mass moving above 'c', even a tiny loss of energy is troublesome. As mentioned above, it actually increases the velocity, causing more energy loss, which increases the velocity further. This positive feedback loop causes the particle to soon reach infinite velocity. In effect, the particle vanishes.

This structural instability of tachyons is a significant limitation to their practical value, if they do indeed exist.

Adapted from the Wikipedia article "Tachyons", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki