Has the Unruh Effect ever been observed?

[lindberg]

TL;DR Summary

There are claims about the extreme difficulty of observing the Unruh effect. Others claims to have already observed it experimentally. Who is right?

A recent paper (June 2021) claims to have observed the Unruh effect: https://arxiv.org/abs/1903.00043
A more recent article (with links to the papers inside it) talks about a possible way to detect it (Barbara Soda et al., April 2022), while there are still skeptics (Anatoly Svidzinsky). Here is the article https://physicsworld.com/a/warm-glo...-seen-in-the-lab-using-accelerated-electrons/
So wait... has it been detected? If yes, why talk about possible ways to amplify it to hope future detection? If it cannot be detected, why so much talk about its possible detection?

 

[PeterDonis]

The obvious answer to your questions is: there are multiple research groups in different parts of the world doing research in this area, and they aren't aware of each other's work. This is common in scientific research.

 

[lindberg]

@PeterDonis I get what you're saying, it's an option I have thought of.
But this (the first paper) is CERN after all, not some tiny private lab... If there's anything I have retained from my school classes on writing scientific papers, it's that analyzing the state-of-the-art research is the first and most important step before even considering getting published anywhere.
Besides, even if we admit that the authors of the second paper were somehow unaware of the first one to propose a possible way to somehow observe at some moment in the future "in principle" measurable effects of the Unruh thermality (because they propose a method they hope will be implemented one day), there are at least two proof-readers / reviewers at any remotely respected journal. Those guys will for sure be aware of the research done at CERN.

 

[PeterDonis]

this (the first paper) is CERN

What makes you think that? I don't see a reference to CERN anywhere. It's the Israel Institute of Technology in Haifa.

 

[renormalize]

I don't see a reference to CERN anywhere.

The authors of https://arxiv.org/pdf/1903.00043.pdf cite the source of their experimental data (reference [32]) as https://inspirehep.net/files/635b576911b7ae90f46783fc2a48a980. This paper analyzes "channeling radiation" produced by bombarding silicon with 178 GeV positrons using the super-proton-synchrotron at CERN.

 

[lindberg]

@renormalize thanks. I could not have put it better.

 

[PeterDonis]

The authors of https://arxiv.org/pdf/1903.00043.pdf cite the source of their experimental data (reference [32]) as https://inspirehep.net/files/635b576911b7ae90f46783fc2a48a980. This paper analyzes "channeling radiation" produced by bombarding silicon with 178 GeV positrons using the super-proton-synchrotron at CERN.

That's fine, but the CERN paper does not make the claim that they are experimentally observing the Unruh effect. So the CERN paper cannot be used as a basis for a claim that experimental observations of the Unruh effect should be common knowledge among researchers in the field.

 

[renormalize]

So the CERN paper cannot be used as a basis for a claim that experimental observations of the Unruh effect should be common knowledge among researchers in the field.

Good point!

 

[lindberg]

@PeterDonis I see what you mean. Probably not as wide spread as I would have expected then. To be honest, a claim of "the first observation of Unruh thermality" seemed quite loud to me. I thought it might be of the same magnitude as (maybe) the observation of gravitational waves at LIGO. Perhaps not, my bad.

Actually, there is a paper by Rosu (1994) that cautions against reading too quickly into the experimental data to "finally observe" the Unruh effect.
https://arxiv.org/abs/gr-qc/9406012

To quote Rosu:
"Last but not least, the clear-cut aspects of Unruh effect in the realm of nonlinear (multiphoton) quantum electrodynamical effects (the case of Hawking effect is similar within the squeezing perspective) should be further studied taking into account the ‘quasi-feasibility’ of some proposed experimental schemes. As Prof. Keith McDonald recently communicated to the author, it is useful to continue looking for new ways to explore such effects. At the same time, we shouldn’t be overenthusiastic about these highly ideal effects; the nonlinear physics is extremely rich in all sorts of effects coming into play at some curious length and time scales that might be assembled from various combinations of the coefficients in some nonlinear partial differential equations, that usually enter the mathematical description of the complicated physical processes that we were writing here about."

I also keep wondering what Unruh-like effects have to say about the fate of particles in general, but I'll create a separate thread for that issue.

Thank you @Demystifier @PeterDonis @renormalize

 

[Demystifier]

I also keep wondering what Unruh-like effects have to say about the fate of particles in general, but I'll create a separate thread for that issue.

Conceptually, to understand Unruh-like effects I think it's useful to think of those "particles" as quasi-particles.

 

[lindberg]

Conceptually, to understand Unruh-like effects I think it's useful to think of those "particles" as quasi-particles.

So how can one make a distinction between a particle and a quasi-particle?
Am I made of "real particles"? Why is the ontological status of those ones different?

Two days ago I came across this paper (I think it's yours) https://www.worldscientific.com/doi/abs/10.1142/S0217732310033359
But then again, as I said, I'll write a separate post on it. I need to put my ideas together.
Thanks for your reaction.

 

[Demystifier]

So how can one make a distinction between a particle and a quasi-particle?
Am I made of "real particles"? Why is the ontological status of those ones different?

Two days ago I came across this paper (I think it's yours) https://www.worldscientific.com/doi/abs/10.1142/S0217732310033359
But then again, as I said, I'll write a separate post on it. I need to put my ideas together.
Thanks for your reaction.

Yes, it's mine. See also my https://arxiv.org/abs/2205.05986 Sec. 4.2.

 

[lindberg]

Yes, it's mine. See also my https://arxiv.org/abs/2205.05986 Sec. 4.2.

Oh, I see. You distinguish "photons" from "phonons". I am not sure I fully get it, I will need to reread it several times. But from what I have understood, your paper about Unruh-like effects can actually do away with phonons and use actuals particles.
Quote from your paper:
"This state is actually a squeezed state [73], containing an uncertain number of objective particles with an average number of objective particles being larger than zero. Thus, the interaction with the environment creates new objective particles, even when the measurement apparatus is found in the state |E0i>"

I also like your phrase about not that the world is that way (Bohmian interpretation), but that it might be. That is exactly what is bothering me and how I feel. Things just don't add up if you want to combine 1.) countable and localizable particles 2.) relativity of simultaneity. I don't even need a definite "it is like that", but some picture that makes sense and shows a "might be".

 

[Nugatory]

You distinguish "photons" from "phonons". I am not sure I fully get it, I will need to reread it several times. But from what I have understood, your paper about Unruh-like effects can actually do away with phonons (funny name, by the way, nice word-play on "phony") and use actuals particles.

The term “phonon” has been around for a very long time (early 1930s, so almost as long as QM) and the word is derived from the Greek “phonos”, meaning sound - same root as the English words “telephone” and “phonetic”.