[ExI] widely, although not universally, believed

[Damien Broderick]

http://en.wikipedia.org/wiki/Unruh_effect

Although Unruh's prediction that an accelerating detector would see a 
thermal bath is not controversial, the interpretation of the transitions 
in the detector in the non-accelerating frame are. It is widely, 
although not universally, believed that each transition in the detector 
is accompanied by the emission of a particle, and that this particle 
will propagate to infinity and be seen as Unruh radiation.

The existence of Unruh radiation is not universally accepted. Some claim 
that it has already been observed,[7] while others claims that it is not 
emitted at all.[8] While the skeptics accept that an accelerating object 
thermalises at the Unruh temperature, they do not believe that this 
leads to the emission of photons, arguing that the emission and 
absorption rates of the accelerating particle are balanced.

[I was very disheartened by this, because I thought for a couple of 
minutes that I might have found an unexpected source for the cosmic 
background radiation, especially in a still-accelerating cosmos]