WiggleZ survey confirms the big picture of the Universe

August 21, 2012
This image is a slice from a large simulation called 'GiggleZ' which complements the WiggleZ survey. It shows a snapshot of the large-scale matter distribution as studied in Morag Scrimgeour's research. Image Credit: Greg Poole, Centre for Astrophysics and Supercomputing, Swinburne University

(Phys.org) -- We know that stars group together to form galaxies, galaxies clump to make clusters and clusters gather to create structures known as superclusters. At what scale though, if at all, does this Russian doll-like structure stop? Scientists have been debating this very question for decades because clustering on large scales would be in conflict with our 'standard model' of cosmology. The current model is based on Einstein's equations assuming everything is smooth on the largest scales. If matter were instead clumpy on very large scales, then the entire model would need to be rethought.

Cosmologists agree that on 'small' scales (tens of millions of light years), matter in the Universe is highly clustered. So the '' can only hold true if the Universe transitions to an even distribution of matter (homogeneity) on larger scales, irrespective of the viewing direction. However, some scientists have recently argued that the entire Universe never becomes homogenous, and that it is clustered on all scales, much like one of Mandelbrot's famous 'fractals' (a snowflake is a good example of a ). If the Universe has properties similar to a fractal, our description of is wrong, and our understanding of things like is deeply flawed.

A comparison of large southern-hemisphere galaxy surveys. Each point is an observed galaxy, with the Earth at the centre (the surveys look like wedges since they only look in certain directions). The celestial sphere is at redshift=1, which corresponds to a distance of around 10 billion light years. WiggleZ (yellow) is one of the largest, densest galaxy surveys ever made out to this distance. Image Credit: Dr Aaron Robotham and Professor Simon Driver, ICRAR. (The other surveys shown are as follows:WiggleZ (yellow), 2dfGRS (cyan), 6dFGS (blue), GAMA (red), 2SLAQ (white), 2QZ (violet), GAMA (red) and VVDS (green).

New data from a recently completed was published last night by a from the International Centre for Radio Astronomy Research (ICRAR) and The University of Western Australia in Perth and her colleagues. This paper might finally put an end to this long running debate.

The video will load shortly
Morag Scrimgeour explains her latest result in a CAASTRO (ARC Centre of Excellence for All-sky Astrophysics) video

Using the Anglo-Australian Telescope, Ms Morag Scrimgeour has found that on distance scales larger than 350 million light years, matter is distributed extremely evenly, with little sign of fractal-like patterns.

"We used a survey called WiggleZ which contains more than 200,000 galaxies, and probes a cosmic volume of about 3 billion light years, cubed," Ms Scrimgeour explains "This makes it the largest survey ever used for this type of measurement of the large scale Universe."

This finding is extremely significant for cosmologists as it confirms that the tools being used to describe the Universe are the right tools for the job after all. Had evidence been found confirming large-scale fractals, it would have left without a working model for the Universe, sending them back to the drawing board to painstakingly adjust theories.

"Our entire understanding of the Universe, even how we interpret the light we see from stars and galaxies, would be affected if the Universe were not even on large scales. By looking at how the WiggleZ galaxies are distributed in space on scales up to 930 million light years, we find that they are very close to homogeneous, meaning there is no large-scale clustering. So we can say with a high degree of certainty that our picture of the large-scale Universe is correct," said Ms Scrimgeour.

Explore further: Aussie galaxy survey to lead to 'new physics'

More information: Morag Scrimgeour et al. “The WiggleZ Dark Energy Survey: the transition to large-scale cosmic homogeneity.” Accepted for publication in the Monthly Notices of the Royal Astronomical Society Journal, Vol 425 Issue 1 2012.

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1.4 / 5 (10) Aug 21, 2012
the answer is obvious, the scale of the fractal structure stops at the scale you are unable to observe the fractal structure anymore. thus----you will never know 'when' it stops.

this however presumes that the big-bang theory is not a comprehensive theory of the universe(s)
1 / 5 (8) Aug 21, 2012
No simulation can confirm anything, than just assumptions, which were put into its creation.
1 / 5 (4) Aug 21, 2012
"...our understanding of things like Dark Energy is deeply flawed."

You can bet on that.
5 / 5 (6) Aug 22, 2012
Oy vey, all commenters denying the new find.

@ JM: No, these observations were able to observe any fractal structure, it was the structures that stopped looking fractal. See the last figure in the video.

@ Valera: Creationists shouldn't comment on science, it is hilarious to see. These were simple observations, see the video. I doubt even "no redshift" YEC crackpots would see fractals if they keep the apparent distance in.

@ Moebius: This result tested DE cosmology and it could not be rejected. But an alternative was. '100' for DE against 0 in tests.
4.8 / 5 (5) Aug 22, 2012
Another thing to note is that large scale fractal appearance would not have meant that everything we know now is wrong (just incomplete).

It would have necessitated the addition of an extremely long range force (some sort of 'super weak gravity'). And much like the addition of gravity didn't change electrodynamics (because EM is 36 orders of magnitude stronger than gravity) such a force would not have changed the models for short range (10 million light years and below) noticeably.
1 / 5 (1) Aug 22, 2012
The brief video explains the study well. Largest volume galaxy survey ever by far.
1.5 / 5 (2) Aug 22, 2012
To me this looks like a brain network or a water ripples in the sun.
not rated yet Aug 27, 2012
Ok, I'll bite on this one.

There is no law in physics which requires that fractals be observable on *every* scale. And so homogeniety *could* be an observable state between scales, larger and smaller, where fractal patterns can be observed.

200,000 galaxies is not a very large sample. Does homogeniety appear at larger scales than this? Or do fractal patterns reappear?

I'd call this study an interesting datum, but I think we need more data to prove the point.

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