| > A blackbody is an optically thick medium in thermal equilibrium. Black body can be simulated by a cavity with small hole, so incoming light will be scattered and fully absorbed, with zero reflections. In case of CMB, light from our Visible Universe will never return back to us, because it will be too weak and too stretched. Moreover, this is really big journey for a photon, with very high probability to hit something on the way to us, so we may see a large portion of re-emitted EM radiation instead of the original light. What is the difference between black sky and black body? > Galaxies are not blackbodies (not even close), and when you average a bunch of non-blackbody spectra, you don't get a blackbody. You'll get a spectrum with all sorts of atomic and molecular features. Emission from multiple random objects can be approximated as black body radiation, even when they are not in thermal equilibrium with their surroundings. Moreover, we use statistic to distinguish between different emitters. In case of CMB, years may pass until we receive second photon from a same galaxy. Statistic doesn't work in such extreme cases, unless we will point an antenna in the same direction for a millennia or even longer. > There is actually something called the "Cosmic Infrared Background," which is caused by distant galaxies, but it's not a blackbody and it has much larger amplitude variations than the CMB (because galaxies are distributed in a clumpy way). CIB emitted mostly by stars and dust particles, which are hit by the star light, which are much closer to us than CMB emitters. We may get different picture from outside of our galaxy, or when we filter out local emitters. > Spacelike surfaces of constant coordinate time are flat, but the whole manifold is not flat. You are talking about model. Can you map your model back to physical reality, please? As I understand, you are trying to tell me that a point in the non-flat space-timecan have less or more neighbourhood points that in flat space time. In other words, wormholes or space-bubbles are possible in your imagination. > then you need to learn the basics of General Relativity. I'm too stupid to understand this great theory. I need simple explanations. |
Wrong. The universe is remarkably empty, and photons can easily travel across the entire visible universe without hitting anything.
> Emission from multiple random objects can be approximated as black body radiation
Wrong. There are very specific conditions for blackbody radiation. Other conditions give rise to different types of spectra, such as synchrotron radiation, Bremsstrahlung, etc.
You're making a lot of claims about how physics works that are simply false. Before making up your own alternate theories of physics, you should learn physics as it is presently understood.