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Dark energy and fate of the Universe

Science China Press


For millennia, human beings have been pondering two ultimate questions: "Where do we come from?" and "Where are we going?" Over that time, these questions have spurred theological and philosophical debate. Thanks to the rapid development of modern cosmology in the past three decades, scientists nowadays have obtained some important clues to answer these questions. The standard "inflation + hot big bang" framework has been developed to explain the origin of the Universe. However, to forecast the destiny of the Universe, researchers have realized that the nature of dark energy is key.

In the absence of a consensus on what dark energy is, a phenomenological description of the equation-of-state parameter w--the ratio of pressure and density of dark energy--provides an important means for investigating dark energy dynamics. Properties of dark energy will decide the ultimate fate of the Universe. In particular, if w<-1 at some time in the future, dark energy density will grow to infinity in finite time, and its gravitational repulsion will tear apart all the objects in the Universe. This "big rip" (or "cosmic doomsday") scenario is the major focus of the paper. "We want to infer from the current data what the worst fate would be for the Universe", said the authors.


One of the more intriguing questions is: "If a doomsday exists, how far are we from it?" After constraining the MZ parameter space via a Markov Chain Monte Carlo method, the authors found that by using the current observational data tBR - t0 = 103.5 Gyr for the best-fit result, and tBR - t0 = 16.7 Gyr at the 95.4% confidence level (CL) lower limit. Here tBR denotes the time of the big rip, and t0 denotes the present day. "In other words, at worst (95.4% CL), the time remaining before the Universe ends in a big rip is 16.7 Gyr", said the authors.




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