We come from the future

# What the Hell Are Tachyons?

Tachyons cause a lot of problems in movies with starships, but they also cause problems for people in real life. Specifically, they cause problems for students of relativity and string theorists. Learn about the ins and outs of tachyons, and why they need extra dimensions.

Whenever the Borg come jumping out of a wormhole in space, go ahead and blame tachyons. Whenever temporal distortions mean an older version of you has come back to scold the younger version of you, blame tachyons. Whenever an ancient vessel gets a boost across a galaxy, and re-starts an ancient war, blame tachyons. If you noticed that all of those things had a little something to do with time distortions, you are on to something.

Tachyons are particles that have mass, but travel faster than light. As most of us have heard from a fellow named Albert, nothing travels faster than light. In fact, only massless particles, like photons, travel at light speed at all. This is why tachyons are generally confined to episodes of Star Trek and thought experiments regarding whether, if you're late, you can use tachyons to send a signal back in time to warn yourself not to be late, and arrive on time, thereby never having sent the signal in the first place.

Before we dismiss tachyons as an annoyance to both philosophy students and Star Fleet captains, let's take a look at the problems they pose for string theorists. To travel at slower-than-light speeds, particles have to have a positive mass. To go at light speed, they need to have no mass. So when they go faster-than-light, they should have negative mass. That's a tough concept to picture, and it's about to get tougher.

The relationship between energy and mass is defined by Einstein as E = mc2. In string theory, all the particles in the universe are made up of strings that vibrate at different frequencies. The mass of a particle depends on the way the string is vibrating, but the energy level of the vibration doesn't just give us the mass of a particle, it gives us the squared mass of the particle. The vibrational energy of tachyons gives us a squared mass that is negative. Math students know this is impossible. There is no real number that anyone can square to make a negative number. Math students use the imaginary number i to signify the square root of negative one, but that's not something that can translate into the physical world.