The unique universe

Three decades ago, talk of other universes was not seen by most physicists to be part of science. Most research in theoretical physics and cosmology concerned observable FEs in our universe and most papers and seminars referred to experimental results. However, since then there has been a gradual shift, during which it first became acceptable to work on theories that described not only our universe, but other possible universes, universes with less or more dimensions, or universes with different kinds of particles and forces. In the last few years, we have moved further away from theories of our one universe, as these other worlds went from being logically possible to hypothetically actual. It is now common to hear about the multiverse – a quantum cosmology that takes for granted that the visible universe that we see around us is just one of a vast or infinite number of universes.