WHAT happened before the beginning of time is—by definition, it might be thought—metaphysics. At least one physicist, though, thinks there is nothing meta about the question at all. Roger Penrose, of Oxford University, believes that the Big Bang in which the visible universe began was not actually the beginning of everything. It was merely the latest example of a series of such bangs that renew reality when it is getting tired out. More importantly, he thinks that the pre-Big Bang past has left an imprint on the present that can be detected and analysed, and that he and a colleague in Armenia have found it. The imprint in question is in the cosmic microwave background CMB. This is a bath of radiation that fills the whole universe. It was frozen in its present form some 300,000 years after the Big Bang, and thus carries information about what the early universe was like. The CMB is almost, but not quite, uniform, and the known irregularities in it are thought to mark the seeds from which galaxies—and therefore stars and planets—grew.

Dr Penrose, though, predicts another form of irregularity—great circles in the sky where the microwave background is slightly more uniform than it should be. These, if they exist, would be fossil traces of black holes from the pre-Big Bang version of reality. And in a paper just published in arXiv.org, an online database, he claims they do indeed exist.

Once upon a timeThe Penrose version of cosmology stands in sharp distinction to received wisdom. This is that the universe popped out of nowhere about 13.7 billion years ago in a quantum fluctuation similar to the sort that constantly create short-lived virtual particles in so-called empty space. Before this particular fluctuation could disappear again, though, it underwent a process called inflation that both stabilised it and made it 1078 times bigger than it had previously been in a period of 10-32 seconds. Since then, it has expanded at a more sedate rate and will continue to do so—literally for ever.

Dr Penrose, however, sees inflation as a kludge. The main reason it was dreamed up by Alan Guth, a cosmologist at the Massachusetts Institute of Technology was to explain the extraordinary uniformity of the universe. A period of rapid inflation right at the beginning would impose such uniformity by stretching any initial irregularities so thin that they would become invisible.

As kludges go, inflation has been successful. Those of its predictions that have been tested have all been found true. But that does not mean it is right. Dr Penrose’s explanation of the uniformity is that, rather than having been created at the beginning of the universe, it is left over from the tail end of reality’s previous incarnation.

Dr Penrose’s version of events is that the universe did not come into existence at the Big Bang but instead passes through a continuous cycle of aeons. Each aeon starts off with the universe being of zero size and high uniformity. At first the universe becomes less uniform as it evolves and objects form within it. Once enough time has passed, however, all of the matter around will end up being sucked into black holes. As Stephen Hawking has demonstrated, black holes eventually evaporate in a burst of radiation. That process increases uniformity, eventually to the level the universe began with.

Thus far, Dr Penrose’s version of cosmology more or less matches the standard version. At this point, though, he introduces quite a large kludge of his own. This is the idea that when the universe becomes very old and rarefied, the particles within it lose their mass.

via The Economist.