COMMUNICATION DEPARTMENT PRESS RELEASE
The director of the Max-Planck Institute for Astrophysics, today’s speaker in the “Science of the Cosmos, Science in the Cosmos” lecture series
Simon White talks in the BBVA Foundation about using simulated universes to explore the mystery of dark energy
· White is one of the leaders of Millennium, the largest ever computer simulation of cosmic structure formation, in which 300 billion particles evolve to form hundreds of millions of galaxies
· “Dark energy is our biggest challenge right now, but we need new ideas,” he affirms
· White’s work with simulations has also offered clues to unlock another mystery of modern-day cosmology: the nature of dark matter
· In view of the success of the series and the keen interest shown, the BBVA Foundation has opened a window on its website – http://www.fbbva.es – where visitors can view the lectures in the first two editions in original version (http://www.fbbva.es/TLFU/tlfu/ing/home/index.jsp) and subtitled in Spanish (http://www.fbbva.es/TLFU/tlfu/esp/home/index.jsp), with the latest talks added as they take place
Madrid, November 18, 2013.- The study of one of the deepest mysteries in modern science – the nature of dark energy – is enjoying something of a golden age. Astrophysicists are attacking the problem in two separate blocks: those whose focus is on data gathering through the ambitious international observation programs now being launched, and those working on the theories that will serve to interpret these data when they arrive. Simon White, director of the Max-Planck Institute for Astrophysics in Garching, Munich (Germany), is a member of the second group. His work involves creating virtual universes that evolve parallel to reality, but inside computers, and using them to uncover fresh clues about dark energy, a process he will explain more fully during his talk this evening in the BBVA Foundation, Madrid.
White is a speaker in the third edition of the “Science of the Cosmos, Science in the Cosmos” lecture series on cosmology and astrophysics, inaugurated in 2011, which has brought to Madrid some of the world’s leading specialists in these areas of science. Their talks can be viewed on the BBVA Foundation website http://www.fbbva.es, in original version (http://www.fbbva.es/TLFU/tlfu/ing/home/index.jsp) and subtitled (http://www.fbbva.es/TLFU/tlfu/esp/home/index.jsp).
Dark energy makes up 68% of the content of our universe, but no one yet knows what it is. Since its existence was confirmed in 1998, with the observation that the universe was expanding at a growing rate – a discovery honored with the 2011 Noble Prize – the astrophysicist community has been puzzling over its exact nature.
“The only thing we know for sure is that dark energy is what drives the accelerating expansion of the cosmos, but that’s it,” says White. “It’s our biggest challenge, but we need new ideas.”
Theorists versus observationalists
Most talk about the discovery of the universe’s expansion refers to the surprise factor. Brian Schmidt, one of its authors and now a Nobel laureate, revealed in an earlier lecture in the BBVA Foundation that he had to revise his data over and over again before deciding they were true.
But White insists, from the standpoint of a theoretical scientist, that “the discovery of dark energy was not unexpected; the models were already telling us that some cosmological constant had to exist, but the observationalists chose to ignore us.” There is always, he admits “a kind of healthy tension” between the theorist and observationalist side.
Both know, however, that they need each other. Data are obviously indispensable to describe reality, but without a theoretical framework – a hypothesis – to attach them to, we cannot understand their meaning. And it is for this reason that astrophysicists use simulations, already an essential tool for the study of the cosmos. A simulation allows hypotheses to be tested in a kind of toy universe; its results can then be compared to the real observed data to see whether they hold true or not.
The hunt for dark energy gets under way
In the hunt for dark energy, the observationalist arm is entering something of a golden age. The international BOSS project is even now measuring the distribution of one and a half million galaxies with a 2.5-meter telescope sited in New Mexico. One of its participants, the astrophysicist Francisco Prada of the Madrid-based Instituto de Física Teórica will introduce Simon White’s lecture at this evening’s event in the BBVA Foundation.
But to understand the behavior of dark energy, cosmologists have to measure the distribution of the galaxies at different points in the universe’s history, including its earliest years. And this, precisely, is the goal pursued by some even more ambitious observational programs. Among them, BOSS’s successor DESI, now under construction, with Francisco Prada of IFT at the head of the Spanish team; the DES (Dark Energy Survey), a newly inaugurated project, in which Spain also participates, using a telescope in Chile to scan 300 million galaxies over the space of five years; and the Japanese HSC, which will observe the heavens from its base in Hawaii. Meantime, the European Space Agency (ESA) and NASA are building the Euclid space telescope, to be launched in 2020. The goal of all these programs is to measure the universe’s acceleration with an unprecedented degree of accuracy and determine whether dark energy has evolved over time.
The data so far suggest not, as White explains: “On our current understanding, the acceleration responds to the cosmological constant predicted by Einstein.” And that, in a sense, is not good news for simulation runners, because it gives them no room to play. The simulation itself is a computer program in which a set of initial conditions evolve according to fixed rules; researchers can then tweak these initial conditions to see how differently things pan out. In the case of dark energy, however, it makes no sense to vary the conditions while the data say they remain constant.
Galaxies born from a computer
For this reason, White contends, the ball is currently in the court of the observationalist scientists. But this does not turn the theoreticians into no more than silent onlookers. One of the big questions relating to dark energy that simulations can address is how the galaxies are formed and evolve. And the most ambitious simulation run for this purpose, known as the Millennium project, will be the topic of White’s lecture in the BBVA Foundation.
With Millennium, a product of the international Virgo consortium in which White plays a leading role, the evolution of matter was simulated for a cosmological box of 2 billion light years each side. The astrophysicists on the team fed in over 300 billion virtual particles of matter, and set them evolving in accordance with the law – gravity – governing the large-scale behavior of matter. After over a month of calculations on the main computer in the Max Planck Society’s Supercomputing Center, the result was hundreds of galaxies, many of them with enormous black holes at their core.
“The Millennium run was an attempt to simulate the formation of the structure in a large region of the universe, with sufficient resolution to see how individual objects like our own galaxy could form,” White explains. It was the first time the formation of galaxies had been visualized across such a large region of the universe. The results of the first Millennium were published in Nature in 2005. Subsequent versions have improved resolution still further.
Clues to clearing up dark matter
White’s numerous career achievements testify to the value of simulations, of which he was an early adopter back in the 1980s.
The first important result he and his group achieved with this tool won them the 2011 Gruber Cosmology Prize. The project in question had provided essential clues to the enigma of dark matter, the dominant gravitating component of the universe today. White’s simulation indicated that one of the most favored hypotheses to explain dark matter was in fact wrong, while another idea, based around “cold dark matter” appeared to offer a much better fit with reality. Data subsequently obtained with space telescopes showed that the simulation was on the right track, and now it is generally accepted that dark matter is made of a kind of particle still unknown to science that barely interacts with the matter we know, as the cold dark matter theory predicted.
Bio notes
Simon White (Kent, United Kingdom, 1951) studied applied mathematics at the University of Cambridge, United Kingdom, and astronomy at the University of Toronto (Canada). In 1977 he obtained a doctorate in astronomy at the University of Cambridge under Donald Lynden-Bell – a famous astrophysicist, author of the theory that galaxies contain massive black holes at their center – with a thesis on the formation of galaxies. The ideas he put forward on the distribution of dark matter were borne out when the Einstein X-ray satellite began sending back detailed images of galaxy clusters. After his PhD, he worked at the universities of California at Berkeley and Arizona, then returned to Cambridge until his appointment, in 1994, as director of the prestigious Max-Planck Institute for Astrophysics in Garching, Munich (Germany).
He is a fellow of the Royal Society, the German National Academy (the Leopoldina) and the Academia Europaea, and a foreign associate member in the U.S. National Academy of Sciences. His other distinctions include the Helen B. Warner Prize of the American Astronomical Society, the Dannie Heineman Prize of the American Institute of Physics, the Gold Medal of the Royal Astronomical Society, the Max-Planck Research Prize for International Cooperation of the German Research Foundation, the European Latsis Prize of the European Science Foundation, the Max Born Prize of the German Physical Society and Institute of Physics, and the Gruber Cosmology Prize.
For further information, contact the BBVA Foundation Communication Department (+34 91 374 5210/+34 91 537 3769, ) or visit www.fbbva.es