Second the COBE DMR showed that the typical amplitude of these fluctuations was essentially independent of their physical size. That is, large length scale fluctuations, medium length, and smaller lengths all have about the same average (actually rms or absolute value as some are negative and some positive indicating slight over and under densities) variations. This is just the right (like Goldilocks) size dependence. If there were bigger amplitudes at smaller scales, the Universe would have a lot of black holes in it all around. If there were bigger amplitudes on larger scales then there would be giant aggregations of matter pulling everything towards them at high speeds due to the acceleration of gravity over the 14 billion years since the Big Bang started. This provides the basic input conditions for those studying how stars, galaxies, clusters, and so on formed.
Third the COBE DMR provides information on the primordial conditions in the even earlier Universe. For the scientists that are interested and study how the Universe is formed and ultra-high energy physical process, this provided the first look into regions where terrestrial accelerators and experiments did not reach and for some things not likely to reach. Of great interest is what the maps might tell us about Inflation. Inflation is a model of the Big Bang in which at a very early time the Universe undergoes a rapid and accelerating (increasingly rapid) expansion. This solves problems in the Big Bang (or set up appropriate conditions). The long period of acceleration provides a means to smooth out the early universe taking a small homogeneous region and expanding it to a point it is now a size larger than we can see today. That expansion would make space nearly flat (Euclidean - meaning there is little or no curvature to our three dimensional space). The expansion also dilutes nearly all initial impurities to the point that they are negligible today. The rapid, accelerating expansion would also generate fluctuations on the otherwise smooth Universe by generating small quantum fluctuations (rapid expansion) and pulling them out to astronomical scales but frozen in amplitude (accelerating expansion). This rapid, accelerating expansion must be driven by a large energy everywhere in space and at the end of inflation that energy is converted to the be the particles and energy the Universe is made of today. To make such fluctuations probably requires energies billions to trillions of times higher than any man-made accelerator being consider for construction. It is likely to be at the energy scale of the Grand Unification of forces - the energy at which basic forces all show that they are the same basic force and have frozen out to different forces in the cooler present Universe. We see signs that this might happen from experiments and theory. The CMB maps allow one to explore this region most directly.
Fourth the COBE DMR discovery of variations not only meant that a lot
of these theories are supported by the data but also indicated that further
more precise observations in terms of angular resolution (the DMR beam
size was rough 7 degrees) would have signal to see and theory to be developed.
Both theory and observations have made substantial progress in the 10 years
since the COBE DMR announcement of variations (anisotropy). It is now clear
that the CMB can provide a wealth of cosmological information and has developed
already into a powerful cosmological probe. In 2000 the MAXIMA and BOOMERANG
balloon-borne experiments and then in more detail in 2001 and the DASI
ground-based interferometer adding the showed that the spectrum of fluctuations
has features that move away from scale independence on smaller angular
scales. In particular that there were characteristic fluctuations on angular
scales of about 1 degree, 1/2 degree, and 1/3 degree. The first peak is
strongest and the next are harmonics, as in music. Following them in 2002
the Archeops balloon-borne detector mapped nearly 1/5 the sky and 12.5%
of the sky was extremely clean and provided a beautiful picture of the
sky with resolution of 1/6 degree. The location of the first peak provides
very strong evidence that the Universe is flat or nearly so - as predicted
by Inflationary models. The existence of the first, second, and third peaks
is more direct evidence of the acoustic oscillations that were predicted
(originally by Andre Sakarov) as the beginning steps before structure formation
starts fully. These are powerful confirmations of our cosmological model
and show the power of CMB observations.
But that is not all. Earlier this year the CBI experiment provided measurements on much smaller angular scale and detected power out in the regions where the higher harmonics of the acoustic oscillations are expected (1/4 degree, 1/5 degree, 1/6 degree, 1/7 degree). This power is falling in roughly the expected way due to damping and photon leakage from the fluctuations as predicted by Prof. Joe Silk and thus called Silk damping. This was followed late this fall by even more precise results from the ACBAR experiment operating from the high, dry (and cold) site at the NSF's South Pole Station. This is the same site as the DASI experiment which recently (September 2002) reported detection of CMB polarization. Theory predicts that CMB polarization must be present at about 10% of the level of CMB temperature variations (anisotropy), if our cosmological picture is correct. There is much more that can be learned for CMB polarization observations including direct information about the energy scale of Inflation process.
These are only some of the experiments and theory motivated and enabled by the COBE DMR discovery and maps (some from the data and from the substantial public support and interest). We are awaiting the first results from the first of the two following satellites: NASA's MAP (Microwave Anisotropy Probe) already taking data and expected to confirm established results including COBE DMR and to improve them with full sky coverage and thus more samples of our Universe and the ESA/NASA (European Space Agency/National Aeronautics and Space Administration) Planck Surveyor planned for launch in 2007 as a third generation CMB satellite.
Thus the COBE DMR not only made a major discovery about the Universe
but also became the pioneer in a field which is consistently making new
observations about our Universe.
It set a high standard with the quality of its observations both in terms of the input and maps and in terms of its science. Succeeding experiments have had to strive to meet and exceed this high level and as such this has spilled out into cosmology as a whole. Most cosmological experiments are now measured in comparison to Planck surveyor and held to high standards. The excitement following the announcement of the COBE DMR discovery made it more exciting and appropriate to do such experiments and for funding agencies to support them.