In a fitting irony, the static that once bothered scientists trying to tune in to the universe has turned out to be an incredibly rich source of information about it. Probing these signals over the past 40 years—known as the cosmic microwave background (CMB) radiation—scientists have dug out cosmological secrets that have revolutionized the field. Next, European scientists will spy on the relic photons with instruments of unprecedented detail, when they launch the Planck satellite in early 2009.
But the Planck mission won’t be about putting the proverbial “one more number after the decimal.” For the first time, it will probe the dynamics of the early inflationary universe. By sifting through the details of how the temperature of the early universe varied slightly in different directions, the many different models of inflation—the furious exponential expansion of space that took place around 10–35 second after the big bang—can be put to the test, as each makes its own unique predictions. The satellite will also look for evidence of primordial gravity waves, providing theorists with more data to apply to their ideas. And it will more accurately measure the densities of ordinary matter, dark matter and dark energy that occur in puzzling proportions in the universe (5, 23 and 72 percent, respectively).
After years of planning, construction and testing, “smiles are on all faces,” says Jean-Michel Lamarre of the Paris Observatory, the instrument scientist for one of the satellite’s two onboard specialized cameras called the High-Frequency Instrument. (The other is the Low-Frequency Instrument.) About the size of a family car, the Planck satellite will launch from French Guiana in tandem with the European Space Agency’s Herschel Space Observatory. It should begin returning data in the summer and has a mission lifetime of 21 months.
The European Space Agency began planning the Planck mission in 1992, when NASA’s Cosmic Background Explorer (COBE) satellite began sending back data on anisotropies in the CMB—subtle but definite fluctuations in the remnant background heat of the universe (–270.42 degrees Celsius, or 2.73 degrees above absolute zero). Evident at only 10 parts per million, these energy density fluctuations ultimately led to the development of structure in the universe—galaxy clusters and large voids between them—and their measurement uncorked a stream of findings about the big bang.
In 2003 the field took another leap forward when the Wilkinson Microwave Anisotropy Probe (WMAP) satellite looked at the CMB with 45 times more sensitivity. It gave scientists accurate measurements of the age of the universe (13.73 billion years), its rate of expansion (70.1 kilometers per second per megaparsec, where a megaparsec is 3.26 million light-years), and the proportions of the stuff making up the universe. WMAP confirmed the leading theory in cosmology, so-called lambda-CDM (cold dark matter), which is a universe governed by Einstein’s theory of general relativity and dominated by gravity-repelling dark energy.
The Planck satellite will measure the fluctuations of the CMB to two parts per million, which is about three times better than WMAP did. And its two sophisticated cameras will gather light from nine frequency channels (WMAP had five, in a limited range) with noise lower by an order of magnitude.
“Planck will tell us fundamentally new things, complementary to WMAP,” says Oliver Zahn of Lawrence Berkeley National Laboratory, who has been elbow-deep in the calculations that will turn Planck’s raw data into cosmological parameters. “I’ll be surprised if Planck is not as surprising as WMAP and the Hubble Space Telescope have been.” WMAP can measure less than 10 percent of the information contained in the CMB temperature anisotropies and only a tiny fraction in the directional deviations of the CMB’s polarization (the bearing of its electric and magnetic fields as it propagates through space). In contrast, Planck’s full-sky view will measure essentially all the temperature information and a significant part of the polarization data.
The most exciting results could come from the so-called B modes of the polarization data, which have never been measured. The strength of the gravity waves predicted to be generated by the universe’s inflationary phase determines the amplitudes of these B modes, so measuring them can pinpoint the best among competing models of inflation. Planck could, then, provide proof that the universe went through an inflationary phase and indicate the scale of the energy that drove it. “Of all the exciting science that we will do, this is the most exciting possible measurement of all,” says Jan Tauber, the European Space Agency’s chair of the Planck science team. And, as always, the best thing to come from Planck could be completely unexpected.
Note: This article was originally printed with the title, "Deeper into the Void".