Talk:Unruh effect

Direction of the Radiation
The direction of the Unruh radiation is often overlooked, but when it is mentioned it is usually assumed that it comes at the accelerating observer from in front. This cannot be the case if it is supposed to be the analogue of Hawking Radiation via the Equivalence Principle, for if this was so the radiation would have to be perceived as coming from behind the accelerating observer !

Can anyone confirm that Unruh radiation should (if it exists) be detected by an accelerating observer as coming from behind his direction of motion.... —Preceding unsigned comment added by 212.85.28.67 (talk) 13:56, 21 June 2009 (UTC)
 * I am disappointed that nine years have passed without any answer to this question appearing within the article. Is it not known?


 * My impression from reading various sources is that accelerating observers are expected to observe Unruh radiation coming at them from all directions. Is this radiation indistinguishable from Hawking-like radiation emitted from the Rindler event horizon?  I can see how it would be true for emitted particles of non-zero rest mass, since such particles would follow trajectories that eventually would return them to the event horizon.  The accelerating observer would encounter both outgoing and in-falling radiated particles.  But that would not be the case for photons, and (if true) that would violate the equivalence.73.162.77.84 (talk) 06:20, 17 June 2018 (UTC)


 * This is a question has gone long unanswered here which is a testament I think to the difficulty of the question even among seasoned physicists who themselves get tied in knots over things like this. Anyway... To finally answer: Unruh radiation is described by a thermal equilibrium bath such that the radiation flux is locally zero. You, or your thermometer, heat up because the small volume around you seems filled with omni-directional radiation. It's an oven. This bath however is distinguishable from normal kind of thermal bath constructed from a black box. If we heated up a black box and stuck you inside, you could translate around the box and measure the same temperature. This however cannot be done with Unruh radiation as the temperature of the bath varies as you translate around the coordinate system. This should sound very strange because a thermal bath should be by definition in equilibrium, thus it would normally be contradictory for there to be a "temperature gradient" without the accompanying flux of heat. Or in other words, the hot region should warm up the cooler regions, and it would in a normal thermodynamic system like an oven, but it doesn't here because the thermal bath made by Unruh radiation very specifically arises from the vacuum state observed under acceleration. This article published in Nature goes over the details. https://www.nature.com/articles/s41467-019-10962-y


 * I hope this is helpful to any who stumble upon this talk page. - Andrew S. 2601:500:4380:9AB2:645B:507A:EF82:100F (talk) 09:43, 5 February 2022 (UTC)

(random heading)
(Inserted by random ... said: Rursus (bork²) 10:52, 20 February 2009 (UTC))

Question: The last sentence, about testing the effect, mentions accelerating a particle to 10^26 m/s^2. How does that work? The only way I can figure is to keep oscillating its speed, since after the first second of uniform acceleration it would exceed lightspeed.


 * The acceleration is measured in the rest frame of the accelerating particle. Measured from an inertial frame, the acceleration would get smaller and smaller as the apparent mass of the particle increses with speed. If you have access to a physics library, check out the section on "hyperbolic motion" in Misner, Thorne and Wheeler's Gravitation; you can also look at Rindler's book Relativity: Special, General and Cosmological (renamed simply Relativity for the second edition). I would also recomend Taylor and Wheeler's Special Relativity. &mdash; Miguel 21:41, 2004 Dec 9 (UTC)


 * If I don't mix things up, we are talking about very short periods of accelaration, e.g. by using the electromagnetic field of laser light: http://www.slac.stanford.edu/slac/media-info/20000605/chen.html --Pjacobi 21:07, 9 Dec 2004 (UTC)


 * Edits Those last two "anon" edits (23 Oct 2005) were by me. Login-related Wikiglitches ( : ErkDemon 20:13, 23 October 2005 (UTC)

I have a feeling this article would be really interesting if it was written in English. --61.214.155.14 04:41, 18 August 2006 (UTC)


 * This is as close to English as it's really possible to get. The first paragraph of the overview gives a pretty good layman's overview, and the rest of the introduction adds on detail incrementally. I can't completely follow the final parts of it, but I seriously doubt there's _any_ way to explain the detailed mechanism that doesn't require me to learn about the terms being used. The qualitative effect is covered in the first paragraph ("if you accelerate, it looks like space is filled with a warm gas instead of empty"), with no additional explanation needed.


 * If you can think of a better way this should be organized, by all means propose it here. --Christopher Thomas 05:09, 18 August 2006 (UTC)

What is "k"? "T" might be temperature, and "c" light celerity, "&pi;" some times means the relation between radius ant its circumference, but what is "k"? Coronellian 19:09, 16 August 2007 (UTC)

I though this article means that the minimum temperature on hearth is 4&times;10&minus;20 K, not 0 K. It is likely the sincrotron radiation, but only at 9.8 m/s2. Coronellian 19:17, 16 August 2007 (UTC)

Controversy
The existence of Unruh radiation is not universally accepted. Its status ranges from claims that it has already been observed, to claims that it is not emitted (although the sceptics accept that an accelerating observer thermalises at the Unruh temperature they do not accept that this leads to the emission of real photons. arguing that the emission and absorption rates are balanced in their model and, they claim, probably more generally).


 * The controversy about emission is actually an old one--- does a uniformly accelerated charge radiate? The radiation reaction force is proportional to da/dt, so if a is constant, there is no radiation. But boundary effects make a big difference, and so the controversy.


 * The Unruh effect itself, though, doesn't care about outgoing photons. It only cares that the detector responds as if in a thermal bath. On that count, the sources you cite don't have any controversy, and as far as I know, nobody else does either. So I think it would be better to make this comment on "radiation reaction", or something.Likebox (talk) 12:14, 30 January 2008 (UTC)
 * Unruh radiation redirects to Unruh effect -- a distinction this section clearly makes -- so it is an issue for this article. End of story. --Michael C. Price talk 12:26, 30 January 2008 (UTC)


 * Ok, then I'll put it in, but try to be careful with the distinction.Likebox (talk) 14:48, 30 January 2008 (UTC)
 * I'm clear about the distinction. Let's make sure about the article.  Thanks for reinserting it.  If the sceptics are right then this has big implications for Hawking radiation... --Michael C. Price talk 21:13, 30 January 2008 (UTC)


 * I get your drift, but it's just the Unruh effect that's needed for the Hawking radiation, not the Unruh radiation. That's why I wanted to be so careful to make the distinction. You don't need to radiate real photons to infinity in the Rindler case to get the real photons coming out of the black hole. The big difference is that if you redshift in the Rindler metric, the redshift factor goes to 0 as rho->infinity, meaning that by the time you get to infinite rho the equilibrium state is zero temperature. This doesn't mean that Unruh radiation doesn't exist--- I haven't figured that out. I don't know if it does or doesn't I mean. There's other wedges and boundary conditions and I get confused. But in the Hawking case, When you match up the local observer temperature which you know from the local near-horizon Unruh effect to the far-observer temperature by redshifting, the redshift factor asymptotes to a finite value. So if the black hole has a vacuum state which matches to the Unruh vacuum near the horizon, it's got to be hot at infinity, while the Rindler space at infinity is cold no matter what. I'm still confused about the Rindler radiation thing though.Likebox (talk) 22:34, 30 January 2008 (UTC)


 * The article should be written to reflect this (non-violent) controversy. See reflecting controverse below. ... said: Rursus (bork²) 10:51, 20 February 2009 (UTC)

Complete Derivation of Unruh Effect?
Hello, dear webmaster,

I am very interested in the Unruh effect. Can you show me the detail derivation of Unruh effect? Is quantum mechanics needed in the derivation? The article says that accelerated observer will observe temperature. Can I also say that temperature will cause acceleration? I am very curious. Thank you very much.

Sincerely, Wanchung Hu —Preceding unsigned comment added by Wanchung Hu (talk • contribs) 07:56, 6 November 2008 (UTC)

Reflecting the controverse properly
The article starts as be the 'Unruh effect' a scientific truth. Then it walks on gladly, but in the section Experimental Observation of the Unruh effect it suddenly occurs that nobody have observed it! (What a revelation!) The intro should therefore mention 'Unruh effect' as theoretical or hypothetical, and have a final sentence claiming that it hasn't been observed (yet). Furthermore, each mention of 'Unruh effect' should avoid "is", "has" and instead use "would be", "would have" and similar verb forms indicating "hypotheticality" (nice word, ehh ... ?) of the effect. ... said: Rursus (bork²) 11:00, 20 February 2009 (UTC)


 * I got it wrong: truth is that the claimed observations made are under discussion. I'll edit the article according to this. It is still hypothetical. ... said: Rursus (bork²) 11:10, 20 February 2009 (UTC)


 * Now I've made many edits in order to distinguish between the theory of the Unruh effect, that most certainly exists, and the Unruh effect, that may exist. Most of them are in the history marked as "conjunctive", the verb form to use for hypotheses and unattested theories. ... said: Rursus (bork²) 11:19, 20 February 2009 (UTC)


 * The lede labeled the effect as both hypothetical and a prediction which is a bit redundant and somewhat misleading. As the effect (if not the radiation) is expected by everyone, it seems to be more than hypothetical, so I've removed that term. The lede goes on to make it clear that it's not yet observed, so this should cause no misunderstanding. Cutelyaware (talk) 10:12, 14 February 2017 (UTC)

Circular motion and horizons
I have a hard time believing that we really need a Rindler horizon to see Unruh radiation. The article claims that circular motion does not radiate, because there is no associated horizon, but this claim is not referenced and the only paper supporting it I can find has been withdrawn.--Michael C. Price talk 18:21, 18 April 2009 (UTC)

A counter theory paper for references balance.
The following paper shows only a transient Unruh effect theory, and not a steady state solution, like a thermometer getting free-energy by accelerating in a vacuum, breaking the conservation law for energy surrounding the thermometer and thrust matter, where it is claimed:

E--Thermometer--System =  E--Kinetic--Relativistic--Energy  +  Unruh--Vacuum--Energy.

X LoneRubberDragon (talk) 06:21, 16 July 2009 (UTC)

http://www.citebase.org/fulltext?format=application%2Fpdf&identifier=oai%3AarXiv.org%3Agr-qc%2F0611062

NAME [Where is the Unruh Effect? New Insights from Exact Solutions of Uniformly Accelerated Detectors]

ABSTRACT [Using non-perturbative results obtained recently for an uniformly accelerated Unruh-DeWitt de- tector, we discover a very different scenario in the dynamical evolution of the detector’s internal degree of freedom after the coupling with a quantum field is turned on. From a calculation of the evolution of the reduced density matrix of the detector, we find that the Unruh effect as originally derived from time-dependent perturbation theory is existent only in transient and under very special limiting conditions. In particular, the detector at late times never sees an exact Boltzmann distri- bution over the energy eigenstates of the free detector, and in the range of parameters of realistic processes no Unruh temperature can be identified.]

An additional apparent problem with the Unruh effect cited for supporting Hawking Radiation, is that a universe filled with matter accelerating and decelerating, would slowly gain this Unruh free-energy, with the bath of thermal photons seen in a steady state acceleration versus Heisenberg Uncertainty bound transient Unruh effect, or even non existent Unruh effect. LoneRubberDragon (talk) 07:00, 16 July 2009 (UTC)

One more observation, wouldn't this also make all gravitating objects with an acceleration frame, bathed in such Unruh vacuum virtual photons, raining from (the sky?) / (the ground?) / (isotropically?) that an observer is being accelerated into? That is, in normal observation from planets, stars, white dwarfs, and neutron stars, as classical examples, since Einstein Equivalence Special Relativity definitively shows that a stationary gravitational well accelerator observer, and vacuum zero-gravity accelerator observer are both identical? LoneRubberDragon (talk) 07:00, 16 July 2009 (UTC)

LoneRubberDragon

Does the Unruh effect mean any observer on the surface of an atmosphere-less planet would detect radiation?
And as such, the planet will evaporate after all as a black hole does?--MathFacts (talk) 17:21, 10 February 2010 (UTC)
 * I would have thought so, but a number of experts assert the contrary. --Michael C. Price talk 11:11, 8 October 2010 (UTC)

Merge discussion
I propose that the Unruh temperature article should be merged into this article, as it is too short and it would be better on this article. Armbrust Talk  Contribs  08:50, 10 September 2010 (UTC)

Is the source of the force and the radiation the same?
Is it possible that the radiation is created by whatever force is maintaining the acceleration of the detector rather than emerging spontaneously from the vacuum? JRSpriggs (talk) 10:41, 8 October 2010 (UTC)
 * I think it amounts to the same thing - i.e. it is a matter of interpretation. --Michael C. Price talk 11:14, 8 October 2010 (UTC)

Tajmar effect
I think something should be said on this: http://www.physorg.com/news/2011-07-gyroscope-unexplained-due-inertia.html in the article — Preceding unsigned comment added by 83.100.194.186 (talk) 08:43, 27 July 2011 (UTC)

Can the value-of-acceleration be More than the Speed-of-Light?
In the formula for Unruh temperature, derived by William Unruh in 1976, if we insert the minimum temperature of the unverse, i.e. the temperature of cosmic-microwave-radiation 3 degree Kelvin, then the value of acceleration we get from the formula is of the order ten raised to twenty meters per seconds squared. Now, my question is, when the maximum-speed of any object is limited to the speed-of-light, i.e. three-times ten-raised-to-eight meters-pre-second, then how any object can get accelerated to the speed of ten-raised-to-twenty meters-per-second in one second? Some authors have attempted to propose thermodynamic-explanation for gravity, in which they use this Unruh-temperature-explanation to get acceleration of particles, and then compare it with Newton's formula; so if the formula used, to get the value of acceleration, is not correct, then the thermodynamic-explanatin for gravity would loose its base. Therefore, i request the experts to clarify this question. The same question applies to the similar formula for Hawking-Temperature also. Hasmukh K. Tank 123.201.19.157 (talk) 15:17, 23 January 2013 (UTC)

How the Rate Of Acceleration can be More than the Speed Of Light
Some authors have tried to use Unruh effect to derive force from temperature to explain origin of gravity. According to the formula of Unruh-effect, even one degree Kelvin temperature can cause acceleration of the order of ten-raised-to-twenty meters-per-seconds-square. This value is ten-raised-to-twelve-times more than the speed-of-light. How the rate of acceleration can be more than the speed-of-light? So the validity of the formula is questionable. I had put this question in this talk-page which some-one has deleted; which implies that this question is adversely affecting to some researchers. They should be bold enough human beings to face the questions. Hasmukh K. Tank 123.201.19.157 (talk) 12:44, 24 January 2013 (UTC)

Thanks :)
Just wanted to say thanks after reading this for such a clearly written article. The understanding it has of the sticking points for lay readers and the simple clarifications it makes eg of a vacuum are greatly appreciated LookingGlass (talk) 17:27, 8 January 2014 (UTC)

Unruh effect and the Big Bang - the Unruh Big Bang
Old universes become emptier, sparse and chaotic. Various chunks of them run into each other some at faster than light speeds, and that generates relativistic heat at Big Bang levels. — Preceding unsigned comment added by 2A02:587:4113:1F00:2C98:51C7:9539:215A (talk) 07:46, 12 January 2017 (UTC)
 * not correctly mentioned

The universe is acceleratingly expanding, so if we pick a random point inside it, that point will have a surrounding horizon sphere of superluminal expansion (each random universal point, sees a different observable universe) which shrinks by time. The event horizon of these spheres shrink and emit Unruh radiation until gradually reach the Big Bang values. (some unanswered questions... Do these "horizon spheres" reach point size, or do we have Big Bang before that event? The universal homogeneity of energy is an indication that "horizon points, or near points" are reached.)
 * Each random universal point, sees a different observable universe, the event horizon of which shrinks due to the accelerating expansion of the universe. Each of these event horizons emits Unruh radiation of increasing energy, until each visible universe becomes a point with its Unruh radiation at Big Bang levels.


 * The Unruh effect during Big Bang is an issue in cosmology, because each superluminally expanding point generates it.

During Big Bang the amount of energy is huge and it does matter. It is a known issue in cosmology/cosmogony to be answered.

Some user-comments might be erroneous in detail, but not necessarily about their core notion mentioned in the title. So keep them. — Preceding unsigned comment added by 2A02:587:411A:D340:B1CD:5E5B:5D0B:33E4 (talk) 16:34, 7 May 2020 (UTC)

You claim: The Unruh effect is the prediction that an accelerating observer will observe blackbody radiation where an inertial observer would observe none
At extremely high energies and close interactions, the components of observer A pass through the components of the observer B. The only observer is the wave function of the universe, thus ANY change has a global impact, which is puny at low energy levels and/or afar interactions especially for some "supposedy" inertial observer. NO INERTIAL OBSERVER actually exists if we are extremely strict (messing a part of the universe messes all other parts, maybe a puny bit, but it messes them).

WE CANNOT SOLVE THE CONTRIBUTION OF THE UNRUH RADIATION DURING THE BIG BANG IF YOU HIDE ISSUES! — Preceding unsigned comment added by 2a02:2149:8246:3f00:91c3:5e93:f262:d995 (talk) 03:43, 30 October 2020 (UTC)

Controversy over WHERE the accelerating observer detects the radiation
There are three main hypothesis (nowhere is the fourth)
 * 1) everywhere in his/her body
 * 2) Imagine the noninertial observer being a point surrounded by a sphere of subluminal expansion around him/her (because we know that the universe expands). According to that view only at his/her causal horizon (where his/her subluminal sphere ends and afar from it the universe expands superluminally in reference  to him/her. Actually for the noninertial observer, we don't have a causal subluminal expansion sphere, but an ovoid (not an ellipsoid). At the front of the causal ovoid (which isn't a sphere because the observer is noninertial) there is more heat than the average void temperature, and at the back less heat than the average void temperature. The overall temperature is the same but biasedly shared according to the distortion of the subluminal causal ovoid. In everyday life, that effect is negligible because most noninertial observers move a lot slower than the speed of light and the universe doesn't explode/expand superluminally in small/near regions. During the Big Bang the Unruh effect isn't negligible, because superluminal expansion happens in very small regions (and not afar galaxies).
 * 3) Option two is correct, but option one also but not due to the Unruh effect but because the noninertial body becomes itself slightly distorted in an ovoid-like manner, and that causes two types of heat: 1. negligible internal friction due to the negligible deformation, 2. negligible friction with spacetime itself, because the noninertial observer distorts his mapping of spacetime and thus the energy of the void isn't the same everywhere inside him/her/it but it has a void interpretation bias, and that distortion moves through spacetime (it's not static), and that moving ovoid spatiotemporal distortion causes some negligible friction (which during the Big Bang is ginormous... we have to calculate it...).  — Preceding unsigned comment added by 2A02:2149:8246:3F00:91C3:5E93:F262:D995 (talk) 03:30, 30 October 2020 (UTC)

Secondary problem we didn't mention
A different virtual sphere of subluminal expansion surrounds each arbitrary observer (a spheres for the inertial observer and an ovoid for the noninertial).

Problems: Our universe is acceleratingly expanding, thus the size of the "sphere of subluminal expansion" of each observer isn't static in size but its size changes.

If the universe expanded with a constant acceleration, the sphere of subluminal expansion surrounding each arbitrary observer would have been of fixed size, but that's NOT the case in our universe (Nobel Prize data).

That fact complicates even more the Unruh calculation. — Preceding unsigned comment added by 2a02:2149:8246:3f00:91c3:5e93:f262:d995 (talk) 03:43, 30 October 2020 (UTC)

Hawking temperature
Should there not be a 8pi instead of 2pi in the Hawking temperature. If 2pi please show source of derivation, publication for example.

ChrisCalif (talk) 23:34, 21 May 2021 (UTC)

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