18 posts tagged universe
A 10-dimensional theory of gravity makes the same predictions as standard quantum physics in fewer dimensions
A team of physicists has provided some of the clearest evidence yet that our universe could be just one big projection. In 1997, theoretical physicist Juan Maldacena proposed that an audacious model of the Universe in which gravity arises from infinitesimally thin, vibrating strings could be reinterpreted in terms of well-established physics. The mathematically intricate world of strings, which exist in nine dimensions of space plus one of time, would be merely a hologram: the real action would play out in a simpler, flatter cosmos where there is no gravity. Maldacena’s idea thrilled physicists because it offered a way to put the popular but still unproven theory of strings on solid footing—and because it solved apparent inconsistencies between quantum physics and Einstein’s theory of gravity. It provided physicists with a mathematical Rosetta stone, a “duality,” that allowed them to translate back and forth between the two languages, and solve problems in one model that seemed intractable in the other and vice versa. But although the validity of Maldacena’s ideas has pretty much been taken for granted ever since, a rigorous proof has been elusive. In two papers posted on the arXiv repository, Yoshifumi Hyakutake of Ibaraki University in Japan and his colleagues now provide, if not an actual proof, at least compelling evidence that Maldacena’s conjecture is true.
If different wavelengths of light experience spacetime differently, the big bang may never have happened
What if the universe had no beginning, and time stretched back infinitely without a big bang to start things off? That’s one possible consequence of an idea called “rainbow gravity,” so-named because it posits that gravity’s effects on spacetime are felt differently by different wavelengths of light, aka different colors in the rainbow. Rainbow gravity was first proposed 10 years ago as a possible step toward repairing the rifts between the theories of general relativity (covering the very big) and quantum mechanics (concerning the realm of the very small). The idea is not a complete theory for describing quantum effects on gravity, and is not widely accepted. Nevertheless, physicists have now applied the concept to the question of how the universe began, and found that if rainbow gravity is correct, spacetime may have a drastically different origin story than the widely accepted picture of the big bang.
What is the purpose of the Universe? Here is one possible answer.
The more we learn about the universe, the more we discover just how diverse all its planets, stars, nebulae and unexplained chunks of matter really are. So what is all this matter doing in our universe, other than just floating in space? Well, it just so happens that there is a theory that gives a kind of raison d’etre to our universe and all the objects flying through it. If true, it would mean that our universe is nothing more than a black hole generator, or a means to produce as many baby universes as possible. To learn more, we spoke to the man who came up with the idea. It’s called the theory of Cosmological Natural Selection and it was conjured by Lee Smolin, a researcher at the Perimeter Institute for Theoretical Physics and and an adjunct professor of physics at the University of Waterloo. (via What is the purpose of the Universe? Here is one possible answer.)
Has the cosmos existed forever, or did something bring it into existence? Time to grapple with the universe’s greatest mystery AS BIG questions go, it’s hard to beat. Has the universe existed forever? Over the years, some of the greatest minds in physics have argued that no matter how far back in time you go, the universe has always been here. Others have argued that the opposite must be true - something must have happened to bring the cosmos into existence. With both sides claiming that observations support their view, until recently an answer seemed as distant as ever. However, earlier this year, cosmologists Alex Vilenkin and Audrey Mithani claimed to have settled the debate. They have uncovered reasons why the universe cannot have existed forever. Yet what nature grudgingly gives with one hand, it takes back with the other - even though the universe has a beginning, its origins may be lost in the mists of time. Modern cosmology began in 1916 when Einstein applied his newly formulated theory of gravity, general relativity, to the biggest gravitating mass he could think of: the entire universe. Like Newton, Einstein favoured an unchanging universe - a universe that had existed forever and therefore had no beginning. To achieve this, Einstein realised that the gravity pulling together all the matter in the universe had to be countered by a weird cosmic repulsion of empty space. Einstein’s static universe was unfortunately unstable. As the English physicist Arthur Eddington pointed out, such a universe was balanced on a knife-edge between runaway expansion and runaway contraction. A further blow came in 1929 when American astronomer Edwin Hubble observed that galaxies were flying apart from each other like pieces of cosmic shrapnel. The conclusion was that the universe was expanding. Yet if the universe was expanding, an unavoidable consequence must be that it had been smaller in the past. Imagine rewinding that expansion back to a time when everything was compressed into the tiniest of volumes. This was the big bang.
The universe may grow like a giant brain, according to a new computer simulation. The results, published Nov. 16 in the journal Nature’s Scientific Reports, suggest that some undiscovered, fundamental laws may govern the growth of systems large and small, from the electrical firing between brain cells and growth of social networks to the expansion of galaxies. “Natural growth dynamics are the same for different real networks, like the Internet or the brain or social networks,” said study co-author Dmitri Krioukov, a physicist at the University of California San Diego. The new study suggests a single fundamental law of nature may govern these networks, said physicist Kevin Bassler of the University of Houston, who was not involved in the study. [ What’s That? Your Physics Questions Answered ] “At first blush they seem to be quite different systems, the question is, is there some kind of controlling laws can describe them?” he told LiveScience. By raising this question, “their work really makes a pretty important contribution,” he said. (via Universe may grow like a giant brain - Technology & science - Science - LiveScience | NBC News)