This is the F word for cosmology - Fractals, from New Scientist in March 2007, possibly the most elegant theory of everything I have ever read - its four pages well worth reading:
http://www.humpjones.com/pdf/IsTheUn...wScientist.pdf
Written across the sky is a secret, a hidden blueprint detailing the original designof the universe itself. The spread of matter throughout space follows a pattern laid out at the beginning of time and scaled up to incredible proportions by nearly 14 billion years of cosmic expansion. Today that pattern is gradually being decoded by analysing maps of the distribution of the stars, and what has been uncovered could shake modern cosmology to its foundations.
Cosmology is founded on the assumption that when you look at the universe at the vastest scales, matter is spread more or less evenly throughout space. Cosmologists call this a "smooth" structure. But a small band of researchers, led by statistical physicist Luciano Pietronero of the University of Rome and the Institute of Complex Systems, Italy, argues that this assumption is at odds with what we can see. Instead they claim that the galaxies form a structure that isn't smooth at all: some parts of it have lots of matter, others don't, but the matter always falls into the same patterns, in large and small versions, at whatever scale
you look. In other words, the universe is fractal.
It is a controversial view, and one that sparked an intense debate over a decade ago. Since then, astronomers have surveyed ever-greater numbers of galaxies, taking larger and larger samples of the universe. Now the biggest galaxy survey ever and a brand new map of the universe's dark matter are adding fuel to the fire. At stake is far more than the way galaxies cluster. A fractal universe could undermine cosmology's most
basic assumptions. "All of the observations we make depend to a greater or lesser extent on the idea that the universe is homogeneous," says David Hogg of New York University, who leads a team of physicists
that disputes Pietronero's view.
This idea that matter is spread more or less evenly throughout the universe is embodied in Einstein's cosmological principle. Einstein formulated it after publishing his general theory of relativity, which describes
how the distribution of mass bends space-time and creates gravity. It allows cosmologists to use the equations of general relativity to describe the geometry of the whole universe. As a result it has led to a
picture of a universe expanding uniformly from the big bang and in which cosmological measurements have defined meanings.
Fractals allow Pietronero to paint a very different sort of picture - one in which the irregular distribution of matter that we see around us never evens out into a smooth structure, but repeats itself at ever grander
scales. Fractals are familiar enough: we see them in the branching of trees, the curves of coastlines, lungs, turbulence and clouds. No matter what scale you look at them, fractal patterns look the same. Think of
broccoli: a tiny branch looks much the same as the whole vegetable. Zoom in or zoom out, the structure looks the same - exquisitely detailed, never smooth. Fractals can be beautiful to look at, but when it comes to
galaxies it may be a subversive kind of beauty.
Certainly the universe does not look smooth. Some regions contain clusters of matter; others are virtually empty. Hundreds of billions of stars group together to form galaxies, and galaxies congregate in clusters.
Clusters assemble into colossal structures called superclusters that can stretch out for 100 million light years and look uncannily like fractal patterns (see Diagram). Even superclusters string together in long filaments and sheets that stretch like ghostly cobwebs across an otherwise empty sky. The Sloan Great Wall, for example, which was discovered in 2003, spans more than a billion light years. These filaments and sheets seem to encircle huge voids of empty space. The voids range from 100 to 400 million light years in diameter, making the whole assemblage appear as an immense, glowing lattice punctuated by wells of darkness.
No one disputes that the universe is far from smooth on relatively small scales - by which cosmologists mean thousands of light years. But Hogg's team is convinced that if you zoom further out, smoothness reigns.
"When you're looking at the size scales of galaxies, groups of galaxies, clusters, superclusters and filaments, it looks like a fractal," says Hogg. "But once you get larger than all of that, then it starts to look
homogeneous."
What has convinced him is his team's analysis of the latest data from the Sloan Digital Sky Survey, the largest 3D map of the galactic universe so far. His team insists that the map is proof of smoothness. The
fractal camp, however, are sceptical. In fact, they say the Sloan observations confirm what they've been claiming all along. It might appear to be deadlock, but at least with the Sloan survey the two sides can agree what they're disagreeing about. For years Pietronero and his team argued that the statistical methods mainstream cosmologists were using to establish homogeneity were flawed because they start off by assuming that matter is evenly spread. The team was mostly ignored until 2004, when Hogg and astrophysicist Daniel Eisenstein of the University of Arizona in Tucson spent a summer in Paris with Pietronero's colleagues,
cosmologists Francesco Sylos Labini of the Enrico Fermi Centre and the Institute for Complex Systems, Rome, and Michael Joyce of the Pierre and Marie Curie University, Paris. "We argued every day about fractals," Hogg says. "Those battles raged over lunch and coffee and finally convinced us by the end of our visit that we should be doing the analysis as they say." When they returned to the US, Hogg and Eisenstein applied the fractal team's methods to a sample of 55,000 luminous red galaxies mapped by Sloan. They found that the galaxies do form a fractal pattern, but as they looked at bigger and bigger scales, the pattern appeared to disintegrate and smooth out at just over 200 million light years - a scale far larger than most cosmologists had expected.
But Pietronero and Sylos Labini are not convinced. Instead, they believe that if astronomers could continue to zoom out and look at even larger scales, they would find more clustering. They suspect that the apparent
smoothness at 200 million light years is not real, but rather an illusion created by statistical effects due to the limited range of the Sloan survey. Hogg's team, though, insist that their evidence of homogeneity is statistically significant. "I think the result really is secure," says Hogg. "I would stake my scientific reputation on that." Even if the result is real, mainstream cosmologists still have a huge problem on their hands. The fact that the fractal patterning extends to far bigger scales than anyone had expected means that there must be far bigger structures than anyone expected - structures that are even bigger than superclusters. The fractal team argues that the standard model cannot explain the existence of these galactic giants. "If you look at the galaxy data, you can see enormous objects hundreds of millions of light years across, stuff that's really huge," says Pietronero. "This is a huge problem. You're going to have to change the story very radically." The usual story runs something like this. In the tiny fluctuations of the nascent universe, matter began to
collect in denser regions, setting off a chain reaction of gravitational collapse that has given us the large-scale structure we see today. Gravity has worked from the bottom up, building galaxies first, then collecting
galaxies into clusters, then clusters into superclusters and so forth. But while the matter has been clumping together, the universe has been expanding, and thus a battle has ensued: gravity versus expansion.
