Superluminal travel in Einstein's universe November 27, 2015 by Geraint Lewis The story of the drawn-out development of Albert Einstein's revolutionary rewrite of the laws of gravity has been told many times, but over the past 100 years it has given us extreme stars and black holes, expanding universes and gravitational mirages. Einstein also ensured you will never get lost, enabling the technology that helps your phone find your location with pinpoint accuracy! Read more at: http://phys.org/news/2015-11-dont-superluminal-einstein-universe.html#jCp
Some interesting extracts: After E = mc², the fact that nothing can move faster than light is probably the most common fact known about Einstein's special theory of relativity. So just what can superluminal motion actual mean? Let's begin with what Einstein was actually saying about racing a light beam. To Einstein, the race takes place "locally", such as in a laboratory, where you start a particle with mass and a light beam off at the same time. In this case, the light beam always gets ahead. But in his special theory, the details of space and time are the same everywhere. More technically, the union of the two – known as spacetime – is flat, and we can compare the speed of a particle in the laboratory to a light ray somewhere off in the universe. Things get messier in the general theory, as the presence of gravity ensures that the curvature of spacetime here is different to spacetime over there, and it is not possible to uniquely compare the speed of the particle in your laboratory to a light ray off in the distant universe. The only sensible comparison you can make is in your laboratory, and here the light ray still always wins. The same is true in the curved spacetime of the warp drive. If your traveller in the warp bubble tries to race a particle and a light beam together, the light beam will always win. An observer watching the bubble go by would calculate the light beam to be travelling faster than any light ray they create in their own laboratory. But this is not a problem, as it really makes no sense to compare velocities "there" with velocities "here". It is precisely this reason that cosmologists are happy to talk about galaxies receding from us faster than the speed of light due to the expansion of the universe. Read more at: http://phys.org/news/2015-11-dont-superluminal-einstein-universe.html#jCp
