Viewing posts by magnunPI
* The recent detection of gravitational waves by LIGO confirms that we understand reasonably well the generation and propagation of these waves on cosmological distances. For the reason explained above, they would also have been sensitive to the full 5D structure of the space time and therefore their luminosity would have been completely different in such a 5D setup.
* Even if one were to brush this off as some sort of new physics (e.g. inspired by open string theory), gravity must know about the extra dimensions. Again, we know with excellent precision that the force of gravity in the solar system falls off as 1/r^2 and therefore it is 3+1 dimensional. It is possible to have a model of gravity which is 4D at small distances but sensitive to the full 5D space at large distances (see the Dvali-Gabadadze-Porrati model) but this means that the universe behaves in a completely standard way until the acceleration era. This is not what the author has in mind and comes with its own inconsistencies (ghosts etc) which have not been solved.
Models of this type were studied extensively in the late 90s/early 2000s under the guise of braneworlds (see e.g. the Randall-Sundrum model), but the extra dimensions were compact in order to prevent the existence of low-mass Kaluza-Klein modes. The size of this extra dimension would have to be microscopic, of the order of inverse TeV in order to avoid this problem.
continuation of First Peer-Review
continuation of First Peer Review: