Wiki article on Unruh radiation

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Wikki says the following with respect to Unruh effect:

The Unruh effect could only be seen when the Rindler horizon is visible. If a refrigerated accelerating wall is placed between the particle and the horizon, at fixed Rindler coordinate \rho_0, the thermal boundary condition for the field theory at \rho_0 is the temperature of the wall. By making the positive \rho side of the wall colder, the extension of the wall's state to \rho>\rho_0 is also cold. In particular, there is no thermal radiation from the acceleration of the surface of the Earth, nor for a detector accelerating in a circle[citation needed], because under these circumstances there is no Rindler horizon in the field of view.
I'm not at all sure it's accurate though.

I seem to be getting myself more confused as I try to think about this, starting with the issue of whether the temperature of a classical fluid in an Einsten's elevator should actually be uniform with height or not.
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I'm not at all sure it's accurate though.
That's a wise policy to have with respect to Wikipedia articles. 😉

First, to say the the Rindler horizon is "visible" is a missatement, since by definition no light or any other signal from the horizon can reach an observer above the horizon. At any rate, there is certainly nothing in the standard derivation of the Unruh effect that says anything about where the observer is relative to their Rindler horizon.

Second, the standard derivation of the Unruh effect assumes that the quantum field starts out in the state that an inertial observer would see as the vacuum state. Obviously this condition can't be met if you put something like a "refrigerated accelerating wall" between the observer and their Rindler horizon.

So I would say that the quoted language is indeed not accurate.

For what it's worth, it looks like the most current version of this Wiki article (as of the date of this post) no longer has this confusing language:


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