(Cloos is just wrong: massless particles with energy are well known, photons are examples. Also, some previous poster was just wrong in asserting that while in QED electrons could be interpreted as positrons moving backwards in time, and Feynman diagrams included "backwards causal" components.... this was no longer true in electroweak theory. Nonsense, it is true in every such theory. However, there are ways of interpreting both QED and those other theories in ways which "save causality." To explain that in an oversimplified way, you basically, whenever a particle moves backward in time, or moves faster than light -- you could instead regard it as its antiparticle moving forward in time. Thus causality and the existence of antimatter are inextricably interlinked. Furthermore there are ways to argue that all the remaining acausal effects, arising from faster than light motion, magically cancel whenever one computes anything that actually could be measured, because then both these plain-particle and anti-particle interpretations happen and yield canceling effects. It's quite magical and is discussed in Peskin & Schroeder near the start of the book.) ===== Perhaps more interesting that my original objection about information transmission using these tachyons, is the fact that presumably we could apparently-violate conservation of energy & momentum too. That is: 1. You emit photon. 2. photon interacts with tachyon. 3. You receive photon back again. During step 2, photon mysteriously (if you did not know about tachyons) loses or gains energy and/or momentum. The thing about tachyons is they need to be invisible and incapable of interacting with normal particles, or we get paradoxes. But if they can interact with photons we can effectively "see" them... ditto gravitons... and so I don't see how they avoid paradoxes both informational and in terms of apparent conservation violations. Somebody should actually read their paper... Proc. Royal Soc. A 2012...