In brief, the problem(s) with BICEP2:
Foreground, foreground, foreground.
- Background VS Foreground. To see the CMB one needs to understand and eliminate all foreground sources of microwave radiation. This means everything else in the universe, in particular emissions from our own galaxy. For much more detail see ("Toward an Understanding of Foreground Emission in the BICEP2 Region" Raphael Flauger, J. Colin Hill, David N. Spergel).
- The BICEP2 team relied on a presentation graphic prepared by the PLANCK team which seemed to characterize the foreground dust emissions. BICEP2 then computationally subtracted this image of the foreground dust from their data to arrive at a measurement. It could be said this is partially the fault of the PLANCK team for not sharing the raw data openly at the time. They are very open about their data products in the long run.
- The open question is did the BICEP2 team properly remove the foreground. If not, then their observation proves nothing. If so, then their leaders will end up getting a Nobel prize along with Alan Guth.
- Only the PLANCK collaboration with it's great resources can confirm or invalidate BICEP2's results. Only they have the resources to accurately measure the foreground, and computationally subtract it from their image to get the actual CMB. In science observation rules supreme.
The situation is summed up nicely by Nature's headline... no evidence for or against gravitational waves.
I hope the BICEP2 teams result is confirmed. It's really not looking good right now.