Outlook the Dark Universe

OUTLOOK THE DARK UNIVERSE

29 September 2016 / Vol 537 / Issue No 7622

29 September 2016 Supplement to Nature OUTLOOK Research journals ll the matter that has ever been detected accounts for a mere 4.9% of the Universe. Most of the cosmos CONTENTS is the dark universe: a mix of dark matter (26.8%) Aand dark energy (68.3%), both of which have so far proved S194 DARK MATTER impenetrable puzzles. What’s the matter? THE DARK The existence of dark matter has been inferred from the Physicists are narrowing down the UNIVERSE motion of stars since the 1930s, but its nature remains a possibilities for dark-matter particles Produced with support from: Physics of the unknown mystery. The dark-matter particle posited by the most popular S198 ASTRONOMY Cover art: Daniel Stolle theory has not been shown to exist — if it is to make an Revealing the unseen Universe appearance, it may be now or never. The search is narrowing A graphical guide to exploring the Editorial and the possibilities are dwindling; physicists may soon have Universe Herb Brody to move on to alternative explanations (see page S194). Michelle Grayson Explaining dark energy is even tougher. The discovery S200 Q&A Richard Hodson Cosmic cartographer Jenny Rooke of the accelerating expansion of the Universe in 1998 George Smoot discusses the big Art & Design called for a driving force that opposes the pull of gravity discovery of last year: gravitational Mohamed Ashour (S205). At the heart of attempts to characterize this energy waves Andrea Duffy is a deceptively simple question: is dark energy constant? Wesley Fernandes S201 DARK ENERGY Finding out will require looking back in time, to the birth Wojtek Urbanek Staring into darkness Production of the Universe (S201). The quest to explain why the expansion Matthew Carey The ability to detect neutrinos and gravitational waves of the Universe is accelerating Ian Pope should provide new ways of observing and exploring the Karl Smart hitherto unseen Universe (S198). Indeed, the feeling among S205 Q&A Illuminated Universe Sponsorship both Nobel prizewinners and young scientists at the 66th Reya Silao Brian Schmidt talks about the search Yvette Smith Lindau Nobel Laureate Meeting in June was that physicists for dark energy are on the cusp of a new era in astronomy (S200). Marketing S206 RESEARCH Alan Abery There is much more left to learn about the dark universe (S206). It falls to the next generation of physicists, some of 4 big questions Project Manager The most pressing puzzles waiting to Anastasia Panoutsou whom give their predictions for future research in this Outlook, be solved Art Director to build on the ideas of their Nobel-winning peers. But it is Kelly Buckheit Krause clear that the dark universe will not give up its secrets lightly. Publisher We are pleased to acknowledge the financial support of RELATED ARTICLES Richard Hughes Mars, Incorporated in producing this Outlook. As always, S207 High-energy neutrino astrophysics Editorial Director, F. Halzen Partnership Media Nature has sole responsibility for all editorial content. Stephen Pincock S213 Is dark energy really a mystery? Editor-in-Chief Richard Hodson E. Bianchi, C. Rovelli & R. Kolb Philip Campbell Supplements editor S215 Properties of galaxies reproduced by a hydrodynamic simulation

Nature Outlooks are sponsored supplements that aim to stimulate All featured articles will be freely available for 6 months. M. Vogelsberger et al. interest and debate around a subject of interest to the sponsor, SUBSCRIPTIONS AND CUSTOMER SERVICES S221 The moment of truth for WIMP dark while satisfying the editorial values of Nature and our readers’ Site licences (www.nature.com/libraries/site_licences): Americas, expectations. The boundaries of sponsor involvement are clearly [email protected]; Asia-Pacific, http://nature.asia/ matter delineated in the Nature Outlook Editorial guidelines available at jp-contact; Australia/New Zealand, [email protected]; G. Bertone go.nature.com/e4dwzw Europe/ROW, [email protected]; India, npgindia@nature. CITING THE OUTLOOK com. Personal subscriptions: UK/Europe/ROW, subscriptions@ A geometric measure of dark energy Cite as a supplement to Nature, for example, Nature Vol. XXX, nature.com; USA/Canada/Latin America, subscriptions@ S226 No. XXXX Suppl., Sxx–Sxx (2016). us.nature.com; Japan, http://nature.asia/jp-contact; China, http:// with pairs of galaxies VISIT THE OUTLOOK ONLINE nature.asia/china-subscribe; Korea, www.natureasia.com/ko-kr/ C. Marinoni & A. Buzzi The Nature Outlook The Dark Universe supplement can be found at subscribe. http://www.nature.com/nature/outlook/dark-universe CUSTOMER SERVICES S229 Nearby galaxies as pointers to a It features all newly commissioned content as well as a selection of [email protected] relevant previously published material. Copyright © 2016 Macmillan Publishers Ltd. All rights reserved. better theory of cosmic evolution P. J. E. Peebles & A. Nusser