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The Sciences

Four Surprises in Planck's New Map of the Cosmos


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By now you've probably heard about the amazing new cosmic snapshot from the European Space Agency's Planck spacecraft. It is one of those scientific achievements so mind-boggling that you have to spend a bit of time with it to truly appreciate what you are seeing. This is relic radiation from when the universe was 370,000 years old, still all aglow from the Big Bang. The radiation has been traveling 13.8 billion years since then, across ever-expanding stretches of space, before landing in Planck's detectors. Then it took a tremendous feat of imagination and insight to translate that noisy signal into a comprehensible map of what the universe looked like in its infancy.


Lopsided universe: Planck's new skymap shows that one half of the microwave background is brighter than the other, and the universe has a large cold spot. Credit: ESA and the Planck Collaboration So let's step back for a moment, look at how this image came to be, and consider some of the more surprising details hidden within it.The map started out as static. Planck didn't just turn on its microwave cameras and take this picture. Planck's detectors pull in 9 different microwave bands, at frequencies ranging from 30 gigaherz to 857 gigahertz. Most of the radiation it picks up is noise: spurious signals from the detectors themselves, emission from within our galaxy, emission from all the other objects beyond our galaxy. Planck scientists had to remove all of that to unmask the extremely faint background signal of the "cosmic microwave background"--the afterglow of the big bang that you see in the picture. (If you have an old-style TV around, you can tune it to an empty UHF station and watch the static flickering on the screen. TV static is, in part, the noise of the cosmic microwave background.) Human brains cannot make sense of all the data from Planck. If this kind of research seems almost beyond human comprehension--it is. The spacecraft has made a trillion observations of a billion points on the sky, looking at each pixel in this image an average of 1,000 times. In order to make sense of all those data points, and to weed out the noise I just described, Planck scientists had to rely on a series of computer simulations. Most of these were done on a Cray XE6 supercomputer known as the Hopper, located at Lawrence Berkeley National Laboratory. Those simulations made it possible to mimic and subtract the unwanted signals from foreground objects and from within the detectors. According to NASA, the current cosmic snapshot required 10 million processor-hours of time on the Hopper--time spent looking at a fake universe, in essence, in order to make sense of the real one. The universe is darker, lighter, slower, and older than we thought. Strange as it may sound, Planck shows that the universe contains both more ordinary visible matter (4.9 percent of the total mass) and more dark matter (26.8 percent) than previously estimated. The loser in the new cosmic census is dark energy, now estimated at 68.3 percent, down from 73.8 percent in the earlier estimate. That doesn't change the fundamental picture of the universe, but it does show the importance of recognizing false certainty. Those earlier numbers looked very precise, but turned out to contain bigger unknowns in them than the impressive looking decimal points would indicate. Put it all together and we get a new picture that the universe is just a hair under 13.8 billion years old--about 100 million years older than previously estimated--and expanding a little more slowly than thought. Those who have been following cosmology research for a long time will recall that the cosmic expansion rate was once the subject of heated, intensely personal disputes; the two sides disagreed by a factor of two. Now we know the answer (67.15 kilometers/second/megaparsec, in case you are counting) to within 2 percent.


What we're made of: A breakdown of the composition of the universe based on earlier data (left) and based on the new Planck results (right). Credit: Planck/ESA. The universe is lopsided. This is certainly the biggest surprise buried within the Planck news. Ever since Albert Einstein created the first truly physical model of the universe in 1917, scientists have adhered to the "cosmological principle" that overall the universe looks the same in all locations, and in all directions. There is a lot of local variation of course (a galaxy here, a cluster there) but on the whole the universe should be the same everywhere because the physical laws governing its formation and expansion operate the same way everywhere. Except--that is not what Planck sees. The cosmic microwave background is distinctly stronger in one half of the sky than in the other. There is also a large "cold" spot where the effective temperature of the microwaves is below average. Current theory cannot account for either of these features. They are brand new mysteries to be solved. But the fact that there are mysteries within this incredible cosmic map is not unexpected. The unexpected thing is that such a map is possible. And that certainly counts as the fifth and most wonderful surprise of all.

Follow me on Twitter: @coreyspowell

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