Almost everything in the universe has a physics principal that explains it. However a tachyon would destroy everything we know about our universe and the physics behind it.
A tachyon is a particle that travels faster than the speed of light. In doing so the particle would travel backwards in time.
So what happens when something travels faster than light? Well in terms of its physical effects, your mass would rapidly increase until it reached the speed of light where your mass would then be infinite the same would happen to the energy required to move you. All this happens in according to the equation E=mc^2. Visually, you would experience the doppler effect. As you approached the speed of light everything in front of you would start to get a blue tint and start to condense into one single point.
So why does this magic particle break the laws of physics? Well first off its energy and mass would be larger than infinity as discussed earlier. Also as this trahyon travels faster than the speed of light, time actually goes backwards. The discovery of one of these particles would automatically prove the existence of parallel universes.
Consider this: a trachyon emitter and receiver are placed on both the earth and mars. The scientists at the station on earth shoot a particle at mars, which, when received, the scientists on mars shoot a particle back to earth. Because this particle losses 2 minutes in time as it travels, the scientist on earth get a response particle from the moon 4 minutes before they shoot their particle at mars. So lets say that the emitter malfunctioned when the other particle was received so that a particle was never sent to mars. The particle still arrived at earth, but the first particle that started the chain was never fired, how can this be? Obviously there must be an alternate universe where the particle was sent from earth so that the chain was started.
All this might be a bit confusing, and rightfully so, the existence of this tachyon particle is in fact impossible according to today's physics.