# What does a tachyon observe?

by dynkindiagram
Tags: relativity, tachyon
P: 97
 Quote by bcrowell I found this paper, which discusses how to define FTL frames of reference. They claim to have a natural extension of the Lorentz group in 1+1 dimensions, which includes the Lorentz group as a subgroup. However, it doesn't work in 3+1 dimensions. So if you buy their reasoning, then there is no elementary argument that suffices to rule out FTL frames, but FTL frames are ruled in 3+1 dimensions. Vieira, An Introduction to the Theory of Tachyons, http://arxiv.org/abs/1112.4187
I started to read that paper, but I already have a dubt.

In 1+1 dimensions they find new transformations such that

$x^\mu x_\mu \rightarrow x'^\mu x'_\mu = - x^\mu x_\mu \, .$

It seems to me that such a trasformation do not form a soubgroup of the "generalized Lorentz transformations". Infact, given 2 of those "new" transformation $\Lambda_1$ and $\Lambda_2$:

$x^\mu x_\mu = - (\Lambda_1 x)^\mu (\Lambda_1 x)_\mu = (\Lambda_1 \Lambda_2 x)^\mu(\Lambda_1 \Lambda_2 x)_\mu \, .$

So $\Lambda_1 \Lambda_2$ is in the soubgroup of the usual Lorentz transformations.

This seems odd to me because I'd expect that composition of two "boosts", each with $v>c$, could result in another "boost" with $v>c$.

Is this an issue to me only because I'm not used to those new transformations?

Anyway I'll continue reading the paper

Ilm
P: 249
 Quote by Ilmrak Tachyons are defined to have four momenta $p^\mu p_\mu \equiv m^2< 0\,$* so if we assume $p^\nu \in ℝ$, then $|\vec p |^2 > E^2$, i.e. they travel faster then light. I think the only reason in assuming they would interact weakly with ordinary matter is that they are never been observed.
I am not saying that any particle that comes to have a negative value travels back in time. The only thing I thought could be a wrong interpretation is them traveling through hyperspace, because i/i=-1. In tachyon physics the speed of light barrier is not broken. It assums that any value greater than c makes the particle travel back in time. The velocity of the particle itself becomes negative, but there was nothing in the equations to determine the velocity that shows that it would have had a change in direction. So then if anything travels faster than c it no longer travels forward through spacetime, if it no longer travels forward through spacetime then it will never travel further than light in a given amount of time. So then if you say bah humbug something can travel FTL, then you put it into the equation and graph it, the particle still doesn't travel FTL according to the amount of distance it has covered over time. The equation just doesn't allow it.

On another note, they where predicted to have little or no interaction with matter but this was because of the mathmatics done for them. I wish I could give more sources, but I didn't learn physics on the internet. I think my only conspiricay theory is that finding this was a cover up done by the government. I think they canceled this early because they found them with little problems, and then it has created a hole in modern physics. I mean what physics experiment have they done to just suddenly say nope you can't find them and then just shut it down for it to never be reapeted? And, I think I have seen one of these before....