The Big Bang theory assumes that the current state of the universe must have arisen from an earlier state of extremely high temperature and of an extremely small volume which rapidly expanded and cooled down in an explosion-like manner, which is why it is called the Big Bang theory. This explosion would have left a characteristic background radiation (CMB), that should be present in all of the universe, since all of the universe was part of the process. This was first verified by the COBE project in 1992, which did a similar map of the universe, but in a much lower resolution
WMAP did a high-resolution scan at the same frequency range, in five frequency bands from 23 to 94 Ghz. The new data is more precise, but remains consistent with the COBE data. The group has submitted a peer-reviewed paper analysing the basic results. This paper outlines all the basic methods followed.
An important point of the paper is that the calculated power spectrum is a complete representation of the data only if the Cosmic Microwave Background radiation (CMB) anisotropy is Gaussian1. Anisotropy here means that the CMB does not have a constant value over the whole sky , but it varies. The fact is that there is no guaranteed test that would assure us that the distribution of values is Gaussian. However the authors report results that indicate with high certainty that the distribution is indeed Gaussian.. One critical assumption is that all the observed fluctuations are because of (Gaussian) fluctuations in the gravitational potential.
One interesting thing to note is that the results indicate both a polarization and a large variability in the cosmic map. This comes at odds with the generally held assumption by Hubble that the universe is isotropic and homogeneous. This assumption has to be true in order for his law (that states that a star's distance from any other star is proportional to its relative speed) to hold in all cases. However if the universe is completely homogeneous then where did all the clumps of matter come from in the first place. The WMAP data (as well as the COBE data before) shows that the universe was not completely homogeneous even at the first moment of its existence. In general physicists regard the anisotropy as large enough to allow matter to form clusters in a very long time, but not so large as to be of significant effect with Hubble's law.
In fact Hubble's law did not seem to hold, as some very distant objects seem to be moving much slower than they should have. It seemed that only a repelling force that operated over long distances could explain this data, so dark energy was introduced.
This repelling force actually accellerates the universe's expansion rather. Previously it was assumed that at large distances only gravity would be doing any work and thus, even though the universe would be expanding gravity would reduce its expansion rate or even stop expansion completely, possibly even causing the collapse of the universe into a Big Crunch. If the group's interpretation of the data is correct and assuming that of all the known forces only gravity would have an effect at large distances, the universe is expanding at an ever increasing rate, fuelled by the force provided by dark energy.2
Dark matter was another thing, introduced for a different but similar reason. It seemed that some galactic formations did not have enough mass to be held together. They would have needed to have a great amount of extra mass in order for their component galaxies to remain locked into a cluster. This matter's nature was deemed unknown and was called dark matter. This matter is also necessary in order to make the universe 'flat', so that parallel light beams will never intersect. The group also managed to use its data to characterise the type of this matter, if it exists, limiting it to low-temperature ranges (only Cold Dark Matter is possible)
The group claims that their data has a cosmological interpretation that supports the existence of both dark energy and dark matter in extremely high quantities, according to their
calculations. The model that best fits the data assumes a flat universe with a baryon function of 0.044, a matter fraction of 0.27 and a 0.73 fraction of dark energy.
Another important outcome of this research was the determenation of a more exact number of the age of the universe, estimated to 13.7 +/- 0.2 billion years. The previous estimate was between 12 and 15 billion years.
Finally, the group has published a companion paper describing the data's
implications to inflation theory. Inflation theory aims to explain the apparently faster expansion of the universe at its earliest stages of development. This is also related to the fact that their data shows the existence of stars at an extremely early age of the universe. It seems that stars started to form much earlier than cosmologists had previously thought.
The above results are mostly verifications and refinements of currently more or less accepted cosmological theories and observation. These results are expected to be much more refined in the future as the group will be able to calibrate the instrument with larger precision and also be ableo filter out more noise, simply because of increased observation time.
One of the most surprising results however, concerns what the data shows hapenned shortly after the big bang. At the initial stages of atom formation the universe was still quite hot and there were no atoms yet, just nuclei and electrons, otherwise viewed as hydrogen in an ionized state. After the universe cooled down and the electrons and protons combined into atoms this ionization should have disappeared. However the group has ascertained that ionization reappeared after the cooling down event, possibly because of massive photonic emissions.
The study is extremely interesting and its implications profound. You are urged to read the introductory paper and the
parameter paper. The latter is quite long but it explains things clearly enough. The group does make a number of assumptions, which could be of critical importance, but their work is clearly defined and when viewed within the scope of the assumptions it seems infallible. Compared to studies where conclusions are drawn only from observations of a few stars whose age and distance can only be approximately known, such a study is much more rigorous and has to be taken seriously.
1: A Gaussian is a smooth function with a single peak. In this context we are using a gaussian to describe a random process. A gaussian random process is described by a gaussian distribution (another name for the curve). The process in this case is the observed intensity of background radiation. A gaussian has interesting properties as a distribution, such as the fact that adding together events that are described by infinitely many non-gaussian distributions results in an overall gaussian distribution. This page talks in a lot more detail about what the guassian is and why it so special. It also discusses the tests made to see if your data obeys a gaussian distribution or not and thus would be useful towards an understanding of the gaussian conformity paper published by the group.
2: I am also unsure whether the dark energy referred to in this work relates to quintessence or the the energy spoken of in Parker, L. & Raval, A. A new look at the accelerating universe. Physical Review Letters 86, 749 - 752 (2001)., which is an alternative model for an accelerating universe.