Today, the Wilkenson Microwave Anisotropy Probe won the prestigious Gruber Cosmology Prize for "observations and analyses of ancient light have provided the unprecedentedly rigorous measurements of the age, content, geometry, and origin of the universe that now comprise the Standard Cosmological Model." This experiment eliminated a collection of theories about how the universe began, and left the Inflationary Big Bang theory standing alone. (More specifically, it left the Lambda Cold Dark Matter Inflationary Big Bang Theory standing alone.)
This award mentions WMAP's principal investigator Charles Bennett explicitly, and is shared amongst the WMAP science team members.
In 2003, WMAP was also awarded Science Magazine's Breakthrough of the Year. It is an experiment that measures the fluctuations in the cosmic microwave background radiation (CMBR), and by doing so, it is gathering data from the early universe -- when it was 380,000 years old. Looking at the CMBR is studying the light left over from the Big Bang, which has the same structure as it did shortly after the universe began.
The CMBR is the oldest light in the universe. Early on, the universe contained a hot plasma that was opaque to light, but when everything cooled to the point where atoms began to form (an event that is misnamed recombination), the universe became transparent to light. As the plasma cleared up, the light suffered its last scattering, and has traveled on unmolested ever since.
By studying this light, we can get a picture of what the universe looked like at the time of last scattering, right after the universe cooled enough that the plasma cleared. The fluctuations in that light tell us where the dense points were in the early universe that caused the gravitational collapses that clustered into galaxies. We can get the relative composition and age of the universe. Most notably, we can tell that the universe is inflationary.
Inflation occurred just after the Big Bang, when the universe expanded at an enormous rate. You can see this represented on the horn shaped diagram below, where time is along the axis of the horn, and the horn represents the space-like properties of the universe. The inflationary period is shown at the far left, where the radius of the horn grows quickly with respect to the time axis along the center of the horn.
The place on the left side of the graph where the horn stops getting wider is where the inflationary epoch ended. The physics between that end and the time of last scatter is pretty simple, so we can use the CMBR data to trace the events in our universe back until 10-32 seconds after the big bang. The temperature fluctuations in the light can tell us about the density profile of the early universe which can tell us something about how galaxies formed. Because we can measure this light, we know quite a lot about the content and structure of the universe.
So what does WMAP tell us?
The universe is 13.73 billion years old, plus or minus 120 million years. We know the age of the universe accurate to within the age of the dinosaurs.
The universe is inflationary. That is to say, of all the self-consistent cosmological theories we have, the ones that include inflation get the CMBR predictions right. We cannot say for sure that inflation is right, but we can rule out all of the theories that get the CMBR wrong -- and the inflationary models are the ones left standing.
The universe is flat and highly uniform. WMAP nailed down the curvature of the universe to within 1% of Euclidean flat. That doesn't mean the universe is shaped like a latke -- it means that Euclidean geometry is pretty good on a large scale. Also, ordinary atoms make up 4.6% of the universe.
The universe is dominated by dark energy. Dark energy makes up 72.1% of the universe, to within 1.5%. This means that universal expansion is speeding up -- we are undergoing a gentle inflation, so to speak. The universe will not collapse back down into a point as some theories predict.
The pie charts come from fitting the CMBR to cosmological models, and shows the composition of the universe at the time of last scatter as well as today. This is where dark matter and dark energy come from -- we see their effects in our measurements. Neutrinos and photons lose energy as the universe expands, so their energy density decreases. Atoms and dark matter become less dense over time as the universe gets bigger. The dark energy density doesn't appear to decrease very much. Although dark energy didn't contribute much to the universe when it was young, as the universe aged, it became dominated by dark energy -- which accelerates the universe's expansion. That acceleration is depicted in the timeline diagram above where you can see the bell curving outward as the diagram approaches contemporary time.
Nature was kind to us in that the CMBR light is so promordial that it gives us a picture of what the very early universe looks like. WMAP did a fantastic job in mapping the anisotropy (it superceded COBE), and the Planck satellite is now taking similar data.
Congratulations to Professor Bennett and the WMAP science team! (And my darling mr. rb137.)
Included in this award are:
Chris Barnes, Rachel Bean, Olivier Doré, Joanna Dunkley, Benjamin M. Gold, Michael Greason, Mark Halpern, Robert Hill, Gary F. Hinshaw, Norman Jarosik, Alan Kogut, Eiichiro Komatsu, David Larson, Michele Limon, Stephan S. Meyer, Michael R. Nolta, Nils Odegard, Lyman Page, Hiranya V. Peiris, Kendrick Smith, David N. Spergel, Greg S. Tucker, Licia Verde, Janet L. Weiland, Edward Wollack, and Edward L. (Ned) Wright.