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Features The Big Question

What if there was no ?

Cosmologist Anna Ijjas is developing a startling new idea about the origins of everything

EFLECTING on the question of what favour of cosmic expansion based on his suspicious of this extrapolation, and it is God was doing before creation, Saint observation of the motions of distant galaxies, to do with quantum theory. By the time the RAugustine is said to have quipped: the case was settled. The expansion theory big bang entered the popular lexicon, the “He was preparing hell for those who pry into implied that the cold, vast we see rules governing the subatomic realm were mysteries.” Apparently the idea of hell doesn’t today had once been a tiny, hot patch of pretty clear, albeit extremely strange. Among scare today’s scientists. As a matter of fact, space. Keep going further back, assuming other things, they say that particles can pop many of us are trying to understand how the same laws apply, and the hot patch into and out of existence all the time, as long our universe came to be. shrinks to a pinpoint containing an ultra-high as they don’t stick around too long. This You might think that the universe started concentration of energy. This hypothetical constant fizz is important at small scales with a big bang. Ten years ago, that is what I state came to be dubbed the big bang. But there such as the big bang, when the universe was thought too. But then I came to realise that the is no evidence that this simple extrapolation the size of a pinpoint. Whatever this speck issue is far from settled. Pursuing this question is valid or that the universe began this way. contained would have been constantly and prompted me to change the tack of my career Nevertheless, it has become the standard randomly fluctuating in energy so that, as and become a cosmologist, even though I had view, so ingrained that many of us learned space expanded, those differences should just completed a PhD in the philosophy of about it as children, as I did. have been spread out, resulting in huge quantum . What I have discovered since There is one very good reason to be imbalances in the amount of energy in then supports a radically new response to the different parts of the universe. But here’s question that irked Augustine – what came the thing: we see no such imbalance. before the beginning? The answer, thrillingly, Although matter in the universe randomly may be that there never was a big bang, but coalesces in clumps that we call galaxies, instead a universe with no beginning or end, “There never when we look at the universe on the repeatedly bouncing from an epoch of largest scales, the distribution of all forms contraction to expansion, and back again. was a big bang, of matter is remarkably smooth over space. In the 1920s, the Russian Alexander This uniformity calls for an explanation. Friedmann and the Belgian priest and but instead a Furthermore, those same quantum astronomer George Lemaître independently fluctuations at the big bang ought to have proposed that the universe was expanding. universe with caused space to twist, curve and warp. As Extrapolating backwards in time, Lemaître the universe expanded, these deformations reasoned that it ought to have started off as a no beginning would have expanded too, and would small “primeval atom”. When Edwin Hubble produce wild distortions in the path of provided compelling empirical evidence in or end” light travelling across the cosmos. Yet >

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190817_F_Before the big bang.indd 42 12/08/2019 14:14 RUBY FRESSEN RUBY

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190817_F_Before the big bang.indd 43 12/08/2019 14:14 astronomers see no trace of these distortions. “The current phase The majority of cosmologists and In the early 1980s, theoretical astrophysicists today tend to neglect these , , Andreas Albrecht of the universe issues. But ever since I first heard about these and introduced an idea problems, I haven’t been able to ignore them. designed to resolve the big bang theory’s expanding will My original plan was to explore ways of fixing problems. They proposed that just moments , but then something else happened after the big bang, the universe underwent end and it will that changed my mind. a brief epoch of extremely rapid expansion, enter a new A generic feature of inflation, again due to known as inflation. Their concept was that quantum fluctuations, is that there should be inflation would stretch the universe so quickly contracting phase” small distortions in the fabric of space-time that any twists, curves and warps in the fabric wherever inflation ends that evolve to become of space-time would be ironed out and the a curious phenomenon known as primordial distribution of all matter smoothed. gravitational waves. These aren’t the same But inflation creates problems of its ripples in space-time spotted by the LIGO own. For example, it requires a hypothetical collaboration in 2015, which are usually field called the inflaton. This needs to have substantial inflation, those same troublesome created by colliding black holes. Primordial switched on at just the right time and with quantum fluctuations take over and prevent gravitational waves have much larger just the right strength – and remained nearly inflation from ending, except perhaps in a wavelengths – so large that the only way constant over time – in order to account few rare patches of space. In those regions, to detect them is by their imprint on the for the smoothness of the universe. In the cosmological properties differ randomly cosmic microwave background radiation. big‑bang scenario, this is unlikely to have and unpredictably. Instead of the uniform This radiation pattern is sometimes called occurred, because the strength of the inflaton universe we see, the outcome of inflation the baby picture of the universe because field would differ in different regions of space is that space is ultimately divided into an it provides an image of what the universe due to large quantum fluctuations. As a result, infinite number of patches with an infinite looked like when it was about 400,000 years it is more likely to have no inflation or not variety of different properties. This old. This might sound old, but if applied to a enough to smooth the universe, or inflation uncontrollable diversity is called the human life, it would correspond to a picture that would lead to a universe different from inflationary , an ensemble in taken of a day‑old baby. what we observe. which any number of different The European Space Agency’s Planck What is more, in places where there is are possible and yet nothing is probable. satellite had long been mapping this radiation

Neither bang nor bounce? Think the universe must have had a beginning? Physicists are not short of far-out ideas

STEADY STATE THE NO-BOUNDARY think the no-boundary are thought to be the We know from observations PROPOSAL proposal is flawed and came fundamental components that the universe is expanding, The physicists Stephen up with an alternative, using of matter. so it may seem logical to Hawking and James Hartle similar mathematical tools. conclude that it expanded thought rather differently. They They propose that our universe CHANGE OF PHASE from a single point. But there suggested that as you go back could be the mirror image of Some physicists think that is another way to think about it, in time towards the big bang, another. This antiuniverse space-time itself must be made as proposed by cosmologist and things get smaller and would extend backwards in of tiny, atom-like particles. Fred Hoyle in 1948. If new smaller, the three time before the big bang, One implication, according to matter is continually created of space and one of time would getting bigger as it does so, Daniele Oriti, a physicist at the as space expands, then each essentially transform into and would be dominated by Max Planck Institute for new region of space would four dimensions of space. antimatter. Gravitational Physics in Germany, look the same. Under this view, This means that the universe is that just as atoms can organise there need not be a beginning had no time boundary to it and GAS themselves into a solid, liquid or an end to the universe. the question of a beginning, Inspired by , or gas, particles of space-time Hoyle coined the phrase or of what came before the at Harvard can coalesce into different big bang in derisory reference big bang, is meaningless. University and Robert phases. Maybe the beginning to astronomer George Brandenberger at McGill of the universe was the point Lemaître’s ideas on THE ANTIMATTER UNIVERSE University in Canada proposed these particles condensed. expansion, but the joke Latham Boyle and Neil Turok that the current universe As to what things were like was on him when the term at the Perimeter Institute for emerged from a hot, dense gas before that point – who can say. was picked up. in Canada of excited superstrings, which Joshua Howgego

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190817_F_Before the big bang.indd 44 12/08/2019 14:14 in exhaustive detail, with the goal of finding The Simons evidence of primordial gravitational waves. Observatory But in 2013, the researchers behind it in the Atacama announced that they had failed to find them desert will hunt at the expected level. When I heard this news, for primordial I realised that this meant the simplest versions gravitational of inflationary theory were eliminated. I felt waves that inflation was losing its appeal as a simple explanation of what happened after the big bang, so I chose to abandon my initial plan and explore a different approach to cosmology. The idea I decided to pursue was first put forward by the same Steinhardt who co‑proposed inflation. He pointed out that there was a logical alternative to the big bang. It could be that our universe began not by bursting forth from nothing, but after a previous universe slowly contracted down to a small patch of space and then

bounced, whereupon it began to expand BRIAN KEATING, UC SAN DIEGO as we observe it today. The main appeal of this scenario was the long phase of ultra-slow contraction before It is even possible to imagine a cyclic the bounce. Just as inflation required a special “We could be universe with no beginning or end. Each form of energy (the inflaton field) to drive living in a period of ultra-slow contraction would rapid expansion, ultra-slow contraction erase any fine details of the previous cycles requires a special form of energy that cyclic universe and bring the universe to the bounce point exerts extraordinarily high pressure. The with the same conditions as it had the cycle high pressure slows contraction by resisting with bounces before. As a result, all the features of the compression and, at the same time, tends universe would be the same on average to smooth out any irregularities in the every 100 billion during each cycle, including the temperature, distribution of energy and in the fabric years or so” the concentration of dark matter, ordinary of space-time. But, unlike an inflationary matter and dark energy, and the number of phase, a slowly contracting phase doesn’t observable stars and galaxies. In other words, require special starting conditions. It can if you had lived on a planet like Earth in the be triggered in various ways, for example, cycle before our own, you would observe by decaying dark energy. I am modelling the evolution of the universe roughly the same basic properties of the And there was another perk: in a slowly to search for novel distinctive signatures universe as we do. contracting, cold universe, quantum of the contraction-and-bounce process. One This, in turn, leads to a dramatic prediction: fluctuations remain small at all times. That prediction is that the ultra-slow contraction the current phase of the universe in which means the outcome of the bouncing scenario doesn’t produce detectable primordial its expansion rate is slowly accelerating will is definite, unlike the messy multiverse gravitational waves. This is in agreement with come to an end and the universe will enter produced by wild quantum fluctuations the Planck data and subsequent observations. a new contracting phase. It will then head during inflation. More sensitive experiments are under towards a new bounce and new phase of Missing from the scenario was evidence construction, such as the Simons Observatory expansion. Consequently, the dark energy that a bounce with these properties was in the Atacama desert of Chile and the that is driving the current accelerated actually possible. Last year, I published the LiteBIRD satellite to be launched within a expansion must decay away, which may first theoretical account of how a bounce decade by Japan’s space agency. If they detect be detectable in future experiments. could happen. Simply put, I describe a primordial gravitational waves, the idea of This, together with the search for primordial putative source of energy that halts the slow contraction must be wrong. I am often gravitational waves, means it may soon be contraction and smoothly reverses it to asked if it worries me that my idea could be possible for us to know if the universe really expansion long before the universe shrinks eliminated by a single experiment. But to me did begin with a bang. My guess is that the to the point where effects this is what real science is all about. I wouldn’t story is a little more circular. ❚ are important. A universe that emerged from want it any other way. such a bounce would have exactly the smooth If we do see signs of a bounce, however, the distribution of energy and flat untwisted implications would be profound. A natural Anna Ijjas is a group leader at the geometry of space-time that we observe. extension of the concept is that we could Max Planck Institute for Today, together with Steinhardt and be living in a cyclic universe with bounces Gravitational Physics in Germany Frans Pretorius at , occurring every 100 billion years or so.

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