A recent paper, titled Inertia from an Asymmetric Casimir Effect, discusses the universal horizons relative to an accelerating observer (Rindler space). A figure it used to demonstrate its point challenged a view I held.
I previously asked a question about Rindler space, Do apparent event horizons have Hawking radiation?. My take-away from the (very good) answers was that an the Rindler Horizon (in the above figure) emits Hawking radiation in the same way that a black hole or the cosmic horizon does. This is called Unruh radiation.
This leads me to the obvious question: Does the accelerating observer see the new Unruh radiation and the old cosmic horizon's radiation?
As you accelerate to the right, then you replace the cosmic horizon to you left with a new horizon, closer to you. Radiation thus appears out of nowhere, but does that mean that the existing radiation from the prior horizon disappears?
EDITED, new material follows:
In my first version of this question I referenced both the CMB and cosmic horizon radiation. These are two different things, but I treated them as the same thing. The question was answered for the CMB - it remains just as the light from any galaxy would.
I've reformulated this so it can be about the Rindler Horizon's radiation versus radiation from the original cosmic horizon. To illustrate this, I made my own version of Figure 1 above, with more detail for the old versus new horizon. Here:
- Cosmic horizon - horizon according to an inertial observer
- Cosmic horizon prime - horizon according to an accelerating observer with same position and velocity as the inertial one
This corresponds to Figure 1, since his surface labeled "COSMIC HORIZON" is the rightmost part of the horizon that remains the same for the accelerating observer as well as the inertial observer. His "RINDLER HORIZON" on the left is only the new horizon, leaving out the old horizon, which I have included.
If we say that $O$ just started accelerating, then what do we expect? Logical possibilities include:
- Sees Hawking radiation from both horizons
- Sees Hawking radiation from old horizon, which transforms into the characteristic of the new horizon over time
- Instantly sees Hawking radiation from new horizon
I'm also not sure if I've drawn the new horizon correctly. I would think that you couldn't "reveal" any galaxy beyond the cosmic horizon at the rightmost point, but to $O$, its dark-energy acceleration is less than to the inertial observer. Maybe I should have just moved the horizon to the right instead of shrinking it? I'm not sure, but I think the paper assumed no change in the cosmic horizon Hawking radiation from the right.