About seven days after conception, something remarkable occurs in the clump of cells that will eventually become a new human being. They start to specialize. They take on characteristics that begin to hint at their ultimate fate as part of the skin, brain, muscle or any of the roughly 200 cell types that exist in people, and they start to form distinct layers.
Although scientists have studied this process in animals, and have tried to coax human embryonic stem cells into taking shape by flooding them with chemical signals, until now the process has not been successfully replicated in the lab. But researchers led by Ali Brivanlou, Robert and Harriet Heilbrunn Professor and head of the Laboratory of Stem Cell Biology and Molecular Embryology at The Rockefeller University, have done it, and it turns out that the missing ingredient is geometrical, not chemical.
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The finding comes from Morag Scrimgeour at the International Centre for Radio Astronomy Research (ICRAR) at the University of Western Australia in Perth and her colleagues. Using the Anglo-Australian Telescope, the researchers pinpointed the locations of 200,000 galaxies filling a cubic volume 3 billion light-years on a side. The survey, called the WiggleZ Dark Energy Survey, probed the structure of the universe at larger scales than any survey before it.
The researchers found that matter is distributed extremely evenly throughout the universe on extremely large distance scales, with little sign of fractal-like patterns. [5 Mind-Boggling Math Facts]
Scrimgeour explained the process that led to that conclusion. “We placed imaginary spheres around galaxies in the [WiggleZ survey] and counted the number of galaxies in the spheres,” she explained in a video. “We wanted to compare this to a random homogeneous distribution” — one in which galaxies are spread evenly throughout space —”so we generated a random distribution of points and counted the number of random galaxies inside spheres of the same size.”
The researchers then compared the number of WiggleZ galaxies inside the spheres with the number of random galaxies inside the similar spheres. When the spheres contained small volumes of space, WiggleZ galaxies were much more clumped together inside them than were the random galaxies. “But as we go to large spheres, this ratio tends to 1, which means we count the same number of Wigglez galaxies as random galaxies,” Scrimgeour said.
And that means matter is evenly distributed throughout the universe at large distance scales, and thus that the universe isn’t a fractal.
If it had been fractal-like, “it would mean our whole picture of the universe could be wrong,” Scrimgeour said. According to the accepted history of the universe, there hasn’t been enough time since the Big Bang 13.7 billion years ago for gravity to generate such large structures.
Furthermore, the assumption that matter is distributed evenly throughout the cosmos has allowed cosmologists to model the universe using Einstein’s theory of general relativity, which relates the geometry of space-time to the matter spread uniformly within it.
Turns out, both assumptions are safe.