Questions at the bottom, so please read through before you jump to conclusions and an answer:
While reading through the following three things, I had an interesting thought - just how closely are these three related, anyway?
Cosmic microwave background radiation
The Unruh effect is where an accelerating observer will observe black-body radiation whereas an inertial observer sees none. Put simply, to an accelerating observer, the vacuum around an inertial observer appears to contain particles in thermal equilibrium i.e. "a warm gas."
Reading this made me think of the edge of the observable universe. Interestingly, under comoving coordinates, it states:
Then I considered this possibility: What if the CMBR isn't echos of the Big Bang, but rather, simply Unruh effect from the edge of the universe (if not the most distant 5 to 30%) that's moving away fast enough, up to c, that we see it as background radiation?A comoving observer is the only observer that will perceive the universe, including the cosmic microwave background radiation, to be isotropic. Non-comoving observers will see regions of the sky systematically blue-shifted or red-shifted. Thus isotropy, particularly isotropy of the cosmic microwave background radiation, defines a special local frame of reference called the comoving frame.
I also thought of the blue/red shifting, and devised a simple experiment: Accelerate a probe as fast as possible to see if it detects a measurable blue-shifting of the CMBR in the direction of travel, and a measurable red-shifing behind it. If so, the CMBR is indeed echoes of something.
If not, however, if there's no doppler shift, then the CMBR may very well simply be the Unruh effect of the most distance edges of our observable universe receeding from us close to, and up to c.
How sensitive are our instruments? Is Hubble sensitive enough to detect a doppler difference in the CMBR from the varying relative velocities it'll achieve every six months given Earth's orbit around the sun? Is there another instrument out there sensitive enough to detect/reject any shift?