Paul Ehrenfest

“ With the aid of process we can send to each other signals with superluminal velocity in all direction. Would this mean "to telegraph into the past" for an observer who is conveniently moving with respect to them? – With a simplicity and clarity, which should have prohibited any further misunderstanding, Einstein showed: [7] Yes. Despite of editorial warning from W. Wien [8] , v. Ignatowsky published his opposite opinion that is evidently wrong. ”

“ Event is the cause of . This conclusion from the existence of superluminal velocities, is exactly the one alluded to by Einstein (l.c.) , and for which it was recently coined the slogan "to telegraph into the past". ”

“ Ignatowsky, Ann. d. Phys. 33, 607, 1910. ↑ The graphical representation in the Minkowskian -plane admits to conveniently overview the state of facts. The fundamental coordinate system , is chosen from the standpoint of observer . is the "world-line" of observer as protocoled by . is the epitome of all world-points being simultaneous with world-point from the standpoint of . ”