Two new studies to be published in the European Physical Journal D demonstrate that the speed of light is variable in real space. Textbook explanations of the speed of light assume that light travels in a vacuum, but space is not a vacuum. … It is not expected that the small variation in the speed of light which has been found will affect the universally accepted theories of particle physics and quantum mechanics to a large extent. However, the studies are proof that the speed of light may be variable, and shows that the mathematical treatments that have long been...