Why bad philosophy is stopping progress in physics<\/p>\n <\/a><\/p>\n His latest book, Discordance, fits into the class of conventional popular cosmology, in so far that it is an account of how our present understanding of the Universe has emerged. But it is also, with some exceptions, more historically correct than other similar books. Baggott\u2019s book is a masterpiece that combines depth with clarity and comprehensiveness with readability. It presents modern cosmology as an unfinished business, rather than as the final conclusion on what the Universe is all about.<\/p>\n Discordance does not shy away from difficult concepts, either. Modern cosmology is challenging to understand and Baggott ambitiously introduces his readers to the technical terms cosmologists use to think about the Universe. For example, he explains in detail how patterns in the cosmic microwave background<\/a> tell us about the behaviour of matter and radiation in the hot early Universe. And he reveals why cosmologists are so interested in \u2018type Ia supernovae\u2019 \u2014 the rare explosions of dying stars<\/a> that function as markers of cosmic distances and help to trace how the Universe expands.<\/p>\n \u201cThe science can be hard,\u201d Baggott admits, \u201cbut the reward for sticking with it is the glimpse it affords of the extraordinary beauty of the universe. Not just the universe as we see it, but the universe as we try to comprehend it.\u201d<\/p>\n A humbling tension<\/p>\n Discordance is essentially the story of how scientists have perceived and explained the Universe from the early twentieth century to the present. The title refers to the fact that the favoured theory of the Universe disagrees with some observations and is challenged by rival ideas. It also refers to concordance \u2014 the antonym of discordance \u2014 in so far that the currently accepted theory of the cosmos is sometimes called the concordance model.<\/p>\n How Stephen Hawking flip-flopped on whether the Universe has a beginning<\/p>\n <\/a><\/p>\n More specifically, the book focuses on the Hubble constant, the measured rate of the Universe\u2019s expansion \u2014 a key parameter in cosmology since its introduction in 1929. Incidentally, the Hubble constant is not constant. Because the inverse Hubble constant provides a rough measure of the Universe\u2019s age, the parameter\u2019s value slowly decreases as the Universe grows older. Thus, the term is a misnomer. But many astronomers and physicists still prefer this well-established terminology over the alternative, the Hubble parameter, and so does Baggott.<\/p>\n The book describes how astronomers\u2019 estimates of the Hubble constant have changed over time as observations have improved, first drastically and, over the past few decades, more modestly, albeit still markedly. Originally, the problem was a too-large value that implied that the Universe\u2019s age was less than that of Earth \u2014 an obvious difficulty. Advanced telescopes, including the Hubble Space Telescope, fuelled the development of \u2018precision cosmology\u2019 and narrowed the value down to around 70, in the awkward unit of kilometres per second per megaparsec.<\/p>\n Yet disagreements between results from different methods persist \u2014 a much-discussed conundrum known as the Hubble tension<\/a>. Reliable results estimated using the cosmic microwave background (remnant light from the early Universe) disagree with equally reliable findings from astronomical measurements using nearby galaxies. Although the two techniques\u2019 estimates for the Hubble constant are not hugely different, astronomers worry that they are distinct enough to create a serious problem. Or are they? As Baggott points out, amid the confusion, we don\u2019t know whether it is a real problem, nor whether improved measurements will solve the issue.<\/p>\n Temperature variations in the cosmic microwave background reveal the seeds of galaxies that we observe today.Credit: ESA, The Planck Collaboration\/SPL<\/p>\n In addition to the Hubble tension, the current standard cosmological model has a few other problems, of which the lack of understanding about dark matter<\/a> (if it exists) is the best known. Scientists\u2019 attempts to explain the dark energy<\/a> that \u2018blows up\u2019 the Universe and accelerates its expansion have so far failed miserably. Similarly, physicists have been unable to explain why the Universe consists almost exclusively of matter with practically no trace of antimatter<\/a>. These problems, too, are dealt with in Discordance, expertly but in less detail than the Hubble tension.<\/p>\n Given all these gaps in understanding, leading cosmologists disagree about whether some type of new physics beyond the standard model of particle physics is required to remedy what a few scientists consider a fundamental crisis. Baggott\u2019s conclusion is balanced: \u201cThe arguments in favour of new physics and the demands to rethink cosmology should not detract from the extraordinary achievements of astronomy and cosmology over the past century or so. What we are witnessing is simply the scientific enterprise at work, and this is often messy and incoherent.\u201d<\/p>\n A matter of precedence<\/p>\n","protected":false},"excerpt":{"rendered":"Discordance: The Troubled History of the Hubble Constant Jim Baggott Oxford Univ. 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