The universe might be fractal, say scientists

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London, June 25 : A new study of nearly a million galaxies has suggested that the matter in the universe is arranged in a fractal pattern.

According to a report in New Scientist, nearly all physicists agree that on relatively small scales, the distribution of the universe is fractal-like.

Hundreds of billions of stars grouping together to form galaxies, galaxies clump together to form clusters, and clusters amass into superclusters.

The point of contention, however, is what happens at even larger scales.

According to most physicists, this Russian doll-style clustering comes to an end and the universe, on large scales, becomes homogeneous.

But a small team of physicists, including Francesco Sylos Labini of the Enrico Fermi Centre in Rome and Luciano Pietronero of the University of Rome argue that the data shows the opposite: the universe continues to look fractal as far out as our telescopes can see.

The best data for looking at the galaxy distribution comes from the Sloan Digital Sky Survey (SDSS), which is constructing the largest 3D map of the universe. When completed, it will map the positions of about a million galaxies and quasars.

When SDSS data was released in 2004, physicists David Hogg of New York University and Daniel Eisenstein of the University of Arizona, both in the US, published an analysis of 55,000 luminous red galaxies suggesting that the fractal pattern smoothed out at scales over 200 million light years.

But Sylos Labini and Pietronero were not convinced.

They believed that the apparent smoothing was an illusion caused by weak statistics. The smoothing seemed to occur at the largest scales the survey was capable of studying, where there were too few large regions to be able to reliably compare their densities, they said.

Only a bigger map could resolve the debate.

Now, SDSS has released its sixth round of data, which plots the locations of roughly 800,000 galaxies and 100,000 quasars, bright objects powered by violent supermassive black holes.

According to their latest paper, Labini and Pietronero, along with physicists Nikolay Vasilyev and Yurij Baryshev of St Petersburg State University in Russia, argue that the new data shows that the galaxies exhibit an explicitly fractal pattern up to a scale of about 100 million light years.

The researchers determined that if the universe does become homogeneous at some point, it has to be on a scale larger than a staggering 300 million light years across.

That's because even at that scale, they still observe large fluctuations in the matter distribution.

Most cosmologists interpret such fluctuations as being no more significant than small waves on the surface of the sea, but Sylos Labini and colleagues have said that these are more like tsunamis.


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