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Universe may be 4 billion years older -- possible solution to dark energy enigma

Originally posted on sciy.org by Ron Anastasia on Mon 28 Jan 2008 02:13 PM PST  



Universe may be 4 billion years older E-mail to a Friend
Tuesday, 29 January 2008
University of Canterbury

Revisiting the foundations of cosmology has led Dr David Wiltshire (Physics and Astronomy) to an exciting discovery that could solve the “biggest problem” in cosmology — dark energy.

Working on old ideas of Albert Einstein’s theory of general relativity and putting them together with the many observations of the universe that were not available in Einstein’s lifetime, Dr Wiltshire claims to offer a solution to the enigma of dark energy, while also resolving key observational anomalies.

“Dark energy is the largest contribution — 76 per cent — to the content of the universe in our present standard cosmology. It is postulated as a smooth energy in the vacuum of space, which makes the expansion of the universe want to accelerate,” Dr Wiltshire said. “But why such stuff should exist, with a particular tiny density, is a complete mystery."

Galaxies do appear to be moving away from each other and at an ever-increasing rate. But Dr Wiltshire claims such “acceleration” is an illusion, due to us misinterpreting observations based in galaxies, where space is not expanding. Clusters of galaxies are spread in filaments and bubbles around huge voids. Most of the volume of the universe, where space is expanding, is in empty voids. Once variations within this uneven distribution are taken into account, he says, we don't need exotic dark energy.

Dr Wiltshire’s latest research, published in New Journal of Physics, Physical Review Letters, and Astrophysical Journal Letters, focuses on solving for an average of the lumpy distribution of matter in the universe as it evolved, rather than a smooth distribution assumed 80-90 years ago by Einstein, Friedman and Lemaître, whose models are still the standard cosmological models today.

“The first models were based on a very simple approximation where the universe is uniformly smooth and featureless, evolving the same way in all directions. Looking at the huge numbers of observations such as supernovae distances, cosmic microwave background radiation fluctuations and galaxy clustering statistics, and thinking about the many anomalies standard dark energy does not solve, I thought we had to be much more careful in the way we interpret the observations,” Dr Wiltshire said.

He said that the present universe was very lumpy and that galaxies were not uniformly distributed with huge voids hundreds of millions of light-years across.

The standard model of the universe could not explain why those voids were there. “That got me started. Many ideas and models for dealing with inhomogeneities had been put forward but there was an essential point people were missing – they didn’t take into account where the observer was in the universe.”

Long before galaxies formed, matter was smoothly distributed and clock rates were the same everywhere. Now that it was “lumpy”, it was necessary to account for where the observer was when calibrating cosmic clocks.

A common analogy is that space curves around a massive object - just as a rubber sheet on a trampoline will stretch around a heavy cannon ball - and time slows down there.

“The flat edge of the rubber sheet is the reference point for our clocks. It is only the space beyond this flat edge that is expanding. Clock rates and the curvature of space can both vary gradually as you move across an expanding void.”

And, since mass slows down time, the clocks of observers in voids, where most of the empty space in the universe is, will appear to be ticking faster than the clocks of observers in galaxies.

It was this last feature, he said, that explained why dark energy was unnecessary.

Every parameter in cosmology had been recalibrated, starting with the age of the universe, which is 14.7 billion years old — one billion years more than currently accepted — as seen by an observer in a galaxy. But an observer in a void would see a universe more than 18 billion years old on average. This may help to explain why early galaxies often look older than structure formation models seem to allow.

Dr Wiltshire described his solution as radically conservative: “If I’m right, this will completely change the way we view the universe, but not the underlying physics." 



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