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takyon writes:

http://www.sciencemag.org/news/2017/04/does-space-heat-when-you-accelerate-physicists-propose-test-controversial-idea

More than 40 years ago, a leading relativity theorist made a surprising prediction. Whereas empty space should feel immeasurably cold to any observer gliding along at a constant speed, one who is accelerating, say because he's riding a rocket, would find empty space hot. This so-called Unruh effect seemed practically impossible to measure, but now four theorists claim they have devised a doable experiment that could confirm the underlying physics. Skeptics say it will do no such thing—but for contradictory reasons.

"The hope is that this will convince skeptics that the whole thing is coherent," says Stephen Fulling, a theoretical physicist and mathematician at Texas A&M University in College Station who was not involved in the work. But Vladimir Belinski, a theorist at International Network of Centers for Relativistic Astrophysics in Pescara, Italy, says, "The Unruh effect is nonsense, it's based on a mathematical mistake."

[...] The effect is too feeble to measure directly. To see the vacuum heat to 1 K, an observer would have to accelerate 100 quadrillion times faster than the best rocket can. But Daniel Vanzella, a theorist at the University of São Paulo in São Carlos, Brazil, and colleagues argue that it should be possible to detect the key thing—the fog of photons seen by the accelerating observer—by studying light radiated by electrons. [...] Vanzella and colleagues start their analysis in the accelerating frame, where they assume the circulating electrons encounter that fog of photons. The electrons will both absorb photons from and radiate photons into the fog. Weirdly, every event in the accelerated frame in which the electrons absorb or emit a photon corresponds to an event in the lab frame in which the electrons emit a photon. The theorists use relativity theory to predict the spectrum of emitted photons in the lab frame, as they report in a paper in press at Physical Review Letters.

The Unruh effect (or Fulling–Davies–Unruh effect) "is the prediction that an accelerating observer will observe blackbody radiation where an inertial observer would observe none. In other words, the background appears to be warm from an accelerating reference frame; in layman's terms, a thermometer waved around in empty space, subtracting any other contribution to its temperature, will record a non-zero temperature. The ground state for an inertial observer is seen as in thermodynamic equilibrium with a non-zero temperature by the uniformly accelerating observer."

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