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Old Jun 18th 2019, 07:15 PM   #1
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Unruh radiation

Does Unruh radiation imply that in an accelerating frame virtual particles become real or detectable?
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Old Jun 18th 2019, 07:34 PM   #2
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Originally Posted by wavesearcher View Post
Does Unruh radiation imply that in an accelerating frame virtual particles become real or detectable?
First, thank you. I knew of the concept that the vacuum states would oscillate differently but I did not know that this effect had a name. It is an interesting effect.

As to virtual particles, they are virtual... which means that they exist only in an exchange between two interacting particles. (Such as a photon being exchanged between two electrons.) If the intermediate particle is detected then, by definition, it is not a virtual particle. The Unruh effect does not change the particles in the interaction so virtual particles in one coordinate system are going to be virtual particles in the accelerated frame as well. What the acceleration changes is the kinetic energy of the particles involved. Or perhaps more pertinent to your question, the oscillators that make up the vacuum.

-Dan
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Old Jun 19th 2019, 05:07 PM   #3
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Talking Unruh effet vs Unruh radiation

1.There is nothing “virtual” in nature. The so called “virtual particle” might be a kind of method of description by some people. One obvious example is machinery drawing. Something might be a dash line in the front view, but it might be a solid line in the top view…etc.
2.I got the Unruh effect equation in web, I don’t know if I got the correct one, (I am not so specialized in thermodynamics): kT = ha/2πc. It seems that the Unruh question can be focused on “if there is temperature there is electromagnetic radiation”. Electromagnetic radiation such as atom emitting photon, Cherenkov effect (some points about this is in Woody’s thread “black hole image” in the lounge column) and charge moving accelerated (charge conservation), etc, actually have electromagnetic interaction as the background. More profound, the two sides of the Unruh effect equation are both affairs in 3D space while electromagnetic interaction is beyond that, I think. So in my humble opinion, Unruh effect does not equal to Unruh radiation.
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Old Jun 19th 2019, 07:29 PM   #4
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effect vs radiation

Yes I should have said Unruh effect. A similar phenomena is Hawking radiation.
The Unruh effect is often stated as follows: An accelerating observer in empty space will detect particles on a particle detector while an observer in an inertial frame will not.
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Old Jun 19th 2019, 10:14 PM   #5
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Originally Posted by neila9876 View Post
1.There is nothing “virtual” in nature. The so called “virtual particle” might be a kind of method of description by some people.
Ummmm... Sorry, but there are virtual particles. See this article. (Scroll down to "Feynman diagrams.")

Virtual particles are defined as particles that are not observed. You could talk about vacuum fluctuations but I prefer Feynman diagrams for the concept. When two electrons interact by the electromagnetic force they exchange a photon. This photon has no clearly defined energy so it's a little hard to work with conceptually. (When massive particles are involved as the exchange particle their masses aren't even specified.) Fortunately none of this has an effect on the actual calculation...We end up integrating over the momentum of the photon so a specific momentum for the photon disappears from the result.

But if we do detect it, the photon never makes it to the other electron! At this point we get the collapsing of the wavefunction, or whatever you like to call it. Then it becomes a "real" particle, not a virtual one, and all of its properties start making sense again.

-Dan
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Old Jun 19th 2019, 10:20 PM   #6
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Originally Posted by wavesearcher View Post
Yes I should have said Unruh effect. A similar phenomena is Hawking radiation.
The Unruh effect is often stated as follows: An accelerating observer in empty space will detect particles on a particle detector while an observer in an inertial frame will not.
Yes. If the observer is traveling (s)he will notice particles popping up out of the vacuum. The vacuum isn't really empty... it's "filled" with all possible particle fields. Any and all of them would react to the acceleration of the observer to "heat up" a bit, due to the field oscillators apparently having more energy and different particles (not just photons) will be seen to pop out of the vacuum. The effect is predicted but apparently it hasn't been measured so it's status is unknown.

Beyond that my understanding of the effect is basic. Without going through the calculations (!) I'm out of my depth.

-Dan
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Old Jun 20th 2019, 03:06 AM   #7
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@Dan:
Ah...good definition (of "virtual particle")...it deserves to observe for ten thousand years by people in this cosmos...No bad...
@wavesearcher:
Oh...we are talking about Hawking effect/radiation in the lounge column too, coincidence?............I always say that if people understand what QM is talking from the very beginning, from the simplest equation, it might be a good thing...
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