How many of you atheists believe in the Big Bang Theory?

[HappySkeptic]

Personally, what I have an issue with is the use of the Doppler effect (DE) to explain the redshift; in other words, I don't get why the redshift necessarily implies that there's a DE involved.

A Star's photosphere has a blackbody spectrum that indicates its temperature, and a galaxy contains stars of a range of temperatures that will be some averaged blackbody curve.

But, redshifts are about spectral lines, not about blackbody curves (except for the very faintest far-away galaxies, where spectral lines can't be measured).  Atomic absorption and emission lines exist from absorption or emission (respectively) of photons from gas above the stellar photosphere, or from interstellar gas.  

Emission wavelengths from ionized atomic hydrogen and oxygen can be seen in galaxy spectra, and it is these spectral lines that we measure the redshift on.  We know their wavelength in a rest-frame.  Those are determined by the laws of physics.  Only the relativistic doppler shift will cause them to shift (gravitational redshift isn't a thing, as the gas isn't on the edge of a black hole).

Here's what I have been wondering about: the redshift in question stems from the cosmic background microwave radiation (CBMR), which is essentially photons, so let's consider Planck's equation (or "relation") for photon energy (E=hf, where E is the energy, f is frequency, and h is Planck's constant); basically, when there's less energy, there's a redshift, and we can see that from this formula since red is a lower frequency than blue; what if this is the real reason for that redshift we observe from CBMR?

The CMBR is a completely different thing.  CMBR is radiation left over from when the universe first became transparent to photons, that has been redshifted by the expansion of the universe.  It is blackbody radiation that used to be hot.

Many references will explain that the CMBR is "cold" now because the universe has expanded, but this is equivalent to there being a relativistic Doppler shift.  There is no "new" mechanism happening.  The CMBR will indeed "cool" as the universe gets older, but that is because we will be seeing it from farther away and receding faster as the universe gets older.