2nd Week Going round in circles

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Cosmology

Going round in circles

In contradiction to most cosmologists’ opinions, two scientists have found evidence that the universe may have existed for ever

Dec 2nd 2010 | from PRINT EDITION

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 time

The 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.

That thought is not entirely bonkers. The consensus among physicists is that particles began massless and got their mass subsequently from something known as the Higgs field—the search for which was one reason for building the Large Hadron Collider, a huge and powerful particle accelerator located near Geneva. Mass, then, is not thought an invariable property of matter. So Dr Penrose found himself speculating one day about how a universe in which all particles had lost their mass through some as-yet-undefined process might look. One peculiarity of massless particles is that they have to travel at the speed of light. That (as Einstein showed) means that from the particle’s point of view time stands still and space contracts to nothingness. If all particles in the universe were massless, then, the universe would look to them to be infinitely small. And an infinitely small universe is one that would undergo a Big Bang.

Uncommon sense

It is well known that fundamental physics is full of ideas that defy what humans are pleased to call common sense. Even by those standards, however, Dr Penrose’s ideas are regarded as a little eccentric by his fellow cosmologists. But they do have one virtue that gives them scientific credibility: they make a prediction. Collisions between black holes produce spherical ripples in the fabric of spacetime, in the form of gravitational waves. In the Penrose model of reality these ripples are not abolished by a new Big Bang. Images of black-hole collisions that happened before the new Bang may thus imprint themselves as concentric circular marks in the emerging cosmic microwave background.

The actual search for such cosmic circles has been carried out by Vahe Gurzadyan of the Yerevan Physics Institute in Armenia. Dr Gurzadyan analysed seven years’ worth of data from WMAP, an American satellite whose sole purpose is to measure the CMB, and also looked at data from another CMB observatory, the BOOMERanG balloon experiment in Antarctica. His verdict, arrived at after he scoured over 10,000 points on the microwave maps, is that Dr Penrose’s concentric circles are real. He says he has found a dozen sets of them—one of which is illustrated. (The visible rings in the picture have been drawn on subsequently to show where computer analysis has found circle-defining uniformity.)

This is, of course, but a single result—and supporters of inflation do not propose to give up without a fight. Amir Hajian, a physicist at Princeton, for example, says he is concerned about distortions in the WMAP data caused by the satellite spending more time mapping some parts of the sky than others. Then there is the little matter of how the masslessness comes about.

Dr Guth, meanwhile, claims that a handful of papers are published every year pointing to inconsistencies between the microwave background data and inflation, and that none has withstood the test of time. Moreover, even if the circles do hold up, they may have a cause different from the one proposed by Dr Penrose. Nevertheless, when a strange theory makes a strange prediction and that prediction proves correct, it behoves science to investigate carefully. For if what Dr Penrose and Dr Gurzadyan think they have found is true, then much of what people thought they knew about the universe is false.

Science and Technology