Hi everybody! I am (like many) very fascinated by the cosmic microwave background, but there are many aspects of it that I do not understand yet. I'm currently in 4th semester of my physics studies, and just starting quantum physics now. Some of those questions might be stupid or (mis)leaded by the interpretation of the information I read, but I think that asking them might help me clarify a few things. :) I've numbered the questions so that it is easier to answer: 1. The CMB is often -if not always- presented as an almost isotopic background "glow" dating from around 400000 years after the Big Bang. How is it possible that we are still able to observe the photons that could escape at the time of photon decoupling? I read that their wavelengths were stretched by the expansion of the universe, therefore they are in the microwave range today. But what I don't get is: when the photons were freed, why didn't they simply escape at (nearly) the speed of light, so faster than matter, which I guess would mean that they would be far away now? Probably a thinking mistake from me, possibly because I treat photons as particles and not as EM waves here. 2. The shape of the CMB map we have is spherical. Did that observation come from observing the sky in all directions? Can we approximate the size of the sphere at the time when the light could escape? Can we say "where" the Big Bang happened, relatively to the position of the galaxies today? Is the last question senseful? :) 3. Why are we able to map the radiation of this precise time of our universe and not other periods afterwards? Is it because the energy emitted at other times was weaker and the wavelengths have been stretched so much that there is quasi zero observable energy (according to Planck's relation, energy is inversely proportional to wavelength)? Will the CMB become virtually unobservable in some distant time because the wavelength will keep on stretching as long as the universe expands? 4. About this page: http://thecmb.org/ (3D model of the CMB) Do the (slight) anisotropy correspond to the model of the universe as we observe it today? Can we even compare? When you switch the channel (bottom left button) to GHz, there appears to be an equator separating the sphere. What does that show and why does it look so anisotropic then? I think that answers to those basic questions would already give me a better understanding of how to consider the CMB... Thanks a lot in advance for your answers, I'm looking forward to reading you! Julien.