Web edition: March 21, 2013
Print edition: April 20, 2013; Vol.183 #8 (p. 5)
The universe is a little older and perhaps a bit stranger than previously thought, according to the best measurements ever taken of the radiation left over from just after the Big Bang. Presented March 21 at a press conference in Paris, the data from the Planck satellite combine to form a map of the remnant glow that largely affirms scientists' theories about the universe's early history. But the results also reveal a few quirks that scientists will have to explain.
“The clarity and precision of Planck’s map is stunning,” says Richard Easther, an astrophysicist at the University of Auckland in New Zealand, who is not on the Planck team. “It’s as good as anyone could have hoped for.”
Launched by the European Space Agency in 2009, the Planck satellite scans the sky for the cosmic microwave background, radiation that dates back to about 380,000 years after the Big Bang. That radiation was originally about 2,700° Celsius but has cooled to a mere 2.7 degrees above absolute zero. Planck is essentially a supersensitive thermometer that can probe the temperature of this radiation to millionths of a degree.
That extraordinary precision allowed researchers to map tiny temperature fluctuations in the radiation across the entire sky. (The red spots in the map are about 1 part in 100,000 hotter than the average temperature, while the blue spots are slightly colder.) These subtle perturbations in the early universe eventually grew into stars and galaxies.
The image, said George Efstathiou, an astrophysicist at the University of Cambridge who presented the Planck results in Paris, "might look like a dirty rugby ball … but some cosmologists would have given up their children to get a copy of this map." Now that cosmologists do have access to the map, they can make many conclusions about how the universe has evolved.
For the most part, Planck's results align with theoretical predictions and observations from the previous microwave background probes, COBE and WMAP. The data support the theory of inflation, which posits that, around 10-30 seconds after the Big Bang, the universe briefly expanded faster than the speed of light.
“Not only is inflation continuing to look like a superb fit to the data,” says Alan Guth, the MIT physicist who proposed inflation in 1981, “but it still looks like the simplest inflationary models are the ones that fit best.”
Planck also reaffirmed previous calculations of the universe’s age and composition – with a few tweaks. Researchers who analyzed the telescope’s data announced that the universe is about 13.81 billion years old, or 80 million years older than previously thought. It contains more matter, both the ordinary kind we can see and the massive stuff we can’t, and less of the mysterious entity called dark energy than earlier observations suggested.
Planck also found several features that surprised scientists. Most notably, it reaffirms a quirky WMAP finding that one half of the sky seems to have more fluctuations than the other. Theory predicts the universe should look the same in all directions.
Efstathiou said researchers should be able to account for this lopsidedness without invoking new physics, but he left open more tantalizing possibilities, such as our universe’s being just one of many in a vast multiverse. That is music to the ears of New York University physicist Matthew Kleban, who plans to scour Planck data for evidence that our universe collided with another one in the distant past. “It’s much too early to say what [the anomalies] mean, but it looks like there is some very interesting work to be done,” he says.
The Planck data also delivered an unexpectedly low rate of expansion for the universe, a figure called the Hubble constant that describes how dark energy is increasingly stretching the fabric of space. “This is one of the most exciting parts of the data,” says Martin White, a Planck scientist at the University of California, Berkeley. “The hope would be that this is actually pointing to extra physics we’re not aware of.”
Planck has already provided enough data to keep physicists busy for years, but it is not done yet. The telescope is still making observations, and in about a year researchers will add another heap of data to the mix. “Cosmologists will be climbing a mountain to make sense of the Planck data,” Easther says.
Back Story | More matter
The universe contains more matter and less energy than previously thought, Planck measurements suggest. The data reveal that more than a quarter of the universe is made up of dark matter, strange massive particles that hold galaxies together yet do not interact with light. Another 5 percent is made up of ordinary matter, the atoms that make up stars, planets and people. Planck delivered its biggest surprise by suggesting a lower-than-expected abundance of dark energy, which stretches out empty space and causes the universe to expand at an ever-increasing rate. As a result, Planck scientists say the universe is not expanding quite as quickly as previous measurements had suggested.
Ade, P. et. al. Planck 2013 Results Papers. Posted March 21, 2013. [Go to]