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[troll science]: Unruh particle shower on a centrifuge (mander.xyz)
submitted 9 months ago by to c/science_memes@mander.xyz
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inspired by https://lemmy.world/post/39777765

Unruh effect should work for any acceleration, including centripetal acceleration of a James Bond-style killer centrifuge/amusement ride. The "thermal bath" experienced by such an observer is composed mainly of photons, but also some elementary particles, in proportion to quantum field coupling strengths or something, coming in as a "particle shower" from the direction of the Rindler event horizon - namely down. The accelerated observer can capture these particles for use later. Did I get it all correct?

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[–] 6 points 9 months ago* (5 children)

good meme!

by the equivalence principle, even earth's 1g gravitational field should already lead to some Unruh radiation for us, so you don't even need a centrifuge!

but your centrifuge is interesting. from the PoV of someone at rest angular momentum needs to be conserved so as you get fatter the rotation must slow down as @herrpfad@feddit.org said. but from the troll's PoV why should they slow down? it's a thermal spectrum, and acceleration is radially inward, so why should there be a retrograde force? (like, what makes the retrograde direction more special then prograde?)

i think the resolution is you don't get exactly Unruh radiation (because your acceleration isn't actually constant (its rotating)), but how exactly that affects the mode functions i have no idea

also let's tag @surrealpartisan@lemmy.world

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  • [–] [S] 4 points 9 months ago (3 children)

    Another complication is that even if the centrifuge slows down as it gets heavier, you can recover most of that mechanical energy when you hop off the centrifuge with your now full jar. Then you can boost it back up almost up to full speed. So I'm not sure exactly at what point you input energy into the system to instantiate the particles. When they hit the belljar bottom transversely maybe? Is this some kind of Maxwell's Demon situation where you need to close the jar before the particles fall back out?

    Also good to mention Earth! Logically, if Hawking radiation works for black holes it seems as if it would also work for any star or planet! But I've never seen this mentioned anywhere.

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  • [–] 2 points 9 months ago (2 children)

    So I did a bit more reading. It seems like acceleration alone is not enough for invoking equivalence principle and saying we have Unruh radiation. If it was enough, non-blackholes objects would Hawking radiate like both of us were suspecting. Apparently physicists are quite confident only blackholes can Hawking radiate.

    There is another picture that may work better for us. Instead of thinking of Unruh radiation (which would require doing serious QFT in curved spcetime calculations), we can think of the radiation coming from ripples popping up near the horizon (the black hole horizon for Hawking, the Rindler horizon for Unruh).

    In this picture you absolutely need a horizon to get radiation. So on the centrifuge you won't feel any radiation 🤷‍♂️

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  • [–] [S] 2 points 9 months ago (1 child)

    physicists are quite confident only blackholes can Hawking radiate

    Good to know! I was starting to get worried :D

    you absolutely need a horizon to get radiation

    Does the particle need to travel all the way from the horizon to reach you? How long does that take? The horizon still exists on the centrifuge, if only for a moment, shifting slightly from one instant to the next. In principle, at any moment you could detach from the centrifuge and fire 10g rocket thrusters in a straight line instead. In that first instant there is no way to tell the difference between the two.

    I say this because in the linked paper, the "acceleration" experienced by the positrons was the bouncing off the atomic nuclei in the silicon crystal, which takes place over the space of a few angstroms, or at most within the 3.5mm size of the crystal, in the time given by the speed of 178GeV positrons (+Lorenz contraction). This instant was sufficient to claim Unruh effects were occurring.

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  • [–] 2 points 9 months ago

    Technically it's not really a horizon if it "opens up" allowing you to observe events from the inside afterwards. But of course in any realistic setting (including that experiment) it will open up eventually, so no horizon. But nature doesn't know that it will open up, so maybe it should behave like a horizon until nature knows, resulting in a criteria like you said. I think the criteria is loosely equivalent to saying "the acceleration must change the speed by almost c", so your centrifuge probably wouldn't lead to radiation.

    But I really am not sure about any of this. The right way to do this is to actually calculate the mode function. One day when I'm better with QFT and all these stuff I'll try to do it.

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