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I know that masses on their own don't produce Unruh radiation outside of black holes which produce a similar effect known as Hawking radiation. However, what if some observer hovers above the Earth and fires the rocket engines to prevent from going closer to the surface?Does that create Unruh radiation or no or would the Unruh radiation be affected by Earth's gravitational field and would some of the Unruh particles from acceleration fall onto the Earth? What if an observer is on an asteroid that is hovered above the Earth using rocket boosters, would the entire asteroid experience Unruh radiation or just the observer?

Níckolas Alves
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MiltonTheMeme
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No, one does not observe Unruh radiation when hovering close to a planet or star. The existence of Unruh and Hawking radiations is closely related to the existence of a horizon, which is not present in the case of a planet or similar body. Due to the absence of the horizon, the quantum state of the quantum fields ends up not being a thermal state for stationary observers (this state is known as the Boulware vacuum).

Níckolas Alves
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  • https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.130.221502 this interpretation of Hawking radiation (that it requires an event horizon) has recently been questioned. For some reason A LOT of pop science articles were written about this paper. Not sure how it's been taken by the broader community since the publication. – AXensen Mar 09 '24 at 19:14
  • Isn't there Unruh radiation from accelerating?So wouldn't hovering above a planet mean Unruh Radiation where the hovering happens due to rocket boosters and not due to the ground exerting a normal force. What if someone accelerates to space from the surface of the Earth? Does that create Unruh Radiation? – MiltonTheMeme Mar 09 '24 at 19:25
  • @AXensen I'm aware of that paper. As I mentioned in other posts in this site (and other people agreed and had even stronger positions than mine), I believe it is wrong. The author's implicitly assume a horizon in their calculations when they choose a particular vacuum state – Níckolas Alves Mar 09 '24 at 20:31
  • @MiltonTheMeme If one accelerates away from the Earth without standing at a fixed distance (like in a rocket decolating), I think (but I am not sure) they will observe Unruh radiation. However, it is well-known that a stationary observer outside a non-collapsed body will not observe Hawking radiation---it doesn't matter if the hovering is due to rocket boosters or the normal force. – Níckolas Alves Mar 09 '24 at 20:33
  • @AXensen See this, this, and this – Níckolas Alves Mar 09 '24 at 20:36
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    @NíckolasAlves thanks. I found it odd that they were still considering a Swarzschild metric, but the most important conclusion of their paper is about non-Swarzschild metrics. "Taken at face value, our local approach could imply that also mass configurations without a global event horizon would radiate and eventually decay." Like... maybe check on a non-Swarzschild metric before you make this suggestion. Also weird how much pop science coverage went toward this rather dubious claim. – AXensen Mar 09 '24 at 21:07