Does a stationary charge in a gravitational field emit radiation?

[yuiop]

In post #34 I tried to answer the 10 questions in terms of the Gron and Naess paper. The papper does not explicitly answer all the questions and I will try to explain why I think that paper implies the answers I gave. In this quote "It has been shown that, as measured by an observer that is not falling freely, a freely falling charge radiates.. " they clearly state the motion of the observer and this implies they think the status of the observer is important as far as whether or not they will observe radiation from a charged particle. On the other hand it might just mean it is easy to analyse the case for a observer that is not free falling and they do not know what the answer is for the case of an observer that is free falling.

Next, they state "No generalization to curved spacetime has been made, but since the above result shows that it does not matter for the radiated effect whether a charge is accelerated by gravitational or normal forces in flat spacetime, we will assume that this also holds..". This suggests to me that they think a charged particle only radiates if it's velocity is changing over time in an absolute sense. Clearly if an observer is falling towards a charged particle that is stationary in a gravitational field, the particle will appear to be accelerating towards the free falling observer, but it does not radiate according to Gron and Naess because this is not absolute acceleration of the particle relative to the gravitational field. The stationary charge is accelerating as measured by an accelerometer and appears to be accelerating according to a free falling observer, but its location relative to the gravitational field is not changing over time so it does not radiate (as far as any observer is concerned).

We could also argue in the context of this paper that the location of an orbiting charged particle is continually changing relative to the gravitational field, so the orbiting particle radiates and spirals inwards despite the fact that an attached accelerometer would not show the particle to be accelerating. Basically charged particles do not care what a co-moving accelerometer shows, when they decide whether to radiate or not. The Gron & Maess paper does not directly confront the issue of whether a co-accelerating observer will see an accelerating charg as radiating or not. However, the http://arxiv.org/abs/physics/0506049" does directly address this issue and they state that a co-accelerating observer will not see the charged particle as radiating due to the formation of an event horizon seen by the accelerating observer. In this much these two papers seem to agree, but it would seem that some of the papers mentioned in this thread disagree about some aspects of the observed behavior of an accelerated charged particle. I agree with heldervalez, that some clarification is needed and a start would be confront, rather than avoid, the 10 questions I listed in post #35.

 

[heldervelez]

after searching mathpages I found this
https://www.physicsforums.com/archive/index.php/t-230660.html"
(note the posts by atyy)

 

[solitonion]

If my memory serves, the classic paper on this topic is by Cecil and Bryce Dewitt titled "Falling Charges".

 

[bcrowell]

If my memory serves, the classic paper on this topic is by Cecil and Bryce Dewitt titled "Falling Charges".

Hmm...here is the reference I found: C. Morette-DeWitt and B.S. DeWitt, "Falling Charges," Physics, 1,3-20 (1964)

But all I can find for the journal "Physics" is this http://physics.aps.org/about , which doesn't date back to 1964.

 

[solitonion]

Try this

link:http://www.physics.princeton.edu/~mcdonald/examples/EM/dewitt_physics_1_3_64.pdf"

 

[atyy]

If my memory serves, the classic paper on this topic is by Cecil and Bryce Dewitt titled "Falling Charges".

Hmm...here is the reference I found: C. Morette-DeWitt and B.S. DeWitt, "Falling Charges," Physics, 1,3-20 (1964)

But all I can find for the journal "Physics" is this http://physics.aps.org/about , which doesn't date back to 1964.

Wow, good memory! This paper is discussed in section 1.10 of the Poisson reference in post #11.

 

[solitonion]

Wow, good memory! This paper is discussed in section 1.10 of the Poisson reference in post #11.

I am working on the self-force problem with Poisson as my supervisor. That certainly helps ;)

 

[bcrowell]

Cool, thanks for pointing us to the paper, solitonion!

I'm predisposed to like the paper it because it seems to agree with my opinion that the e.p. is okay, but just can't be applied in the way you'd naively expect ("failure of naive applications of the equivalence principle"). They seem to give the same picture as some of the more recent references, of the electric field falling, but not rigidly.

It's cool that they start off by saying explicitly that "the forces involved are far too small to be detected experimentally." Always nice when a theorist gives you a reality check like that. If I'm understanding the paper correctly, then the violation of even the naive e.p. (expressed as fractional difference in acceleration between charged and uncharged objects) is incredibly small. They're actually calculating everything in the low-velocity limit, but in the low-velocity limit you get ridiculously small violations of the e.p. If I go ahead and apply their low-v calculation inappropriately to a high-v situation, I find that a particle with mass m and charge q, orbiting near the event horizon of a black hole of mass M, is $kq^2/GMm$ in SI units. For an electron orbiting a 10-solar-mass black hole, it's 10^-19. For an object with a mass of 1 kg and a charge of 1 C, it's 10^-11.

EDIT: It's odd that it depends on $q^2/m$ rather than q/m. That means that it doesn't predict the same motion for two objects considered as one big object.

 

[Demystifier]

Someone may find this useful too
http://xxx.lanl.gov/abs/gr-qc/9909035

 

[heldervelez]

Misconceptions on radiation

Tanks Demystifier:
the abstract is very important and I will reproduce it here (my bolds):

"A local observer can measure only the values of fields at the point of his own position. By exploring the coordinate transformation between two Fermi frames, it is shown that two observers, having the same instantaneous position and velocity, will observe the same values of covariant fields at their common instantaneous position, even if they have different instantaneous accelerations. In particular, this implies that in classical physics the notion of radiation is observer independent, contrary to the conclusion of some existing papers. A "freely" falling charge in curved spacetime does not move along a geodesic and therefore radiates. The essential feature of the Unruh effect is the fact that it is based on a noninstantaneous measurement, which may also be viewed as a source of effective noncovariance of measured quantities. The particle concept in Minkowski spacetime is clarified. It is argued that the particle concept in general spacetime does not depend on the observer and that there exists a preferred coordinate frame with respect to which the particle number should be defined."

yet another interesting paper:
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19680009569_1968009569.pdf"
where Willis E. Lamb and Marlan O. Scully (1968)
"A misconception which most physicists acquire in their
formative years is that the photoelectric effect requires
the quantization of the electromagnetic field for its explanation."
and conclued :
"In conclusion, we understand the photoeffect as being
the result of a classical field falling on a quantized atomic
electron. The introduction of the photon concept is
neither logically implied by nor necessary for the
explanation of the photoelectric effect"

--------------------
IMO Electrostactic Field (EF) can not be 'composed' of photons, and ultimately only the Electrostactic field is the radiative component of a particle.
I mean: The energy of a particle and its associated field are in balance: the more energy in the Field (expands at 'c' speed, as time goes by, since particle creation) the less in the particle (no free lunch at physics, pls).

The existence of other effects (Magnetic field, radiaton energy) are dependent on observer motion (velocity/acceleration).

Then I say, IMO, that it is a misconception the statement:
"Does a charged particle ... radiate, from the point of view of an observer that ...?"

The observer does not see 'the particle' but only the previously radiated field.

There is no way of an observer state of motion dictate the past state of radiation of a particle.
IMO the particle continously radiate a classical field (and also photons, a quanta of energy, from time to time).
The quantization of energy as a Photon is dictated not by any light intrinsic property but because the emitters and receivers are resonators.

This is only my opinion of course. Using this approach I do not have to deal with paradoxes.

 

[atyy]

yet another interesting paper:
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19680009569_1968009569.pdf"
where Willis E. Lamb and Marlan O. Scully (1968)
"A misconception which most physicists acquire in their
formative years is that the photoelectric effect requires
the quantization of the electromagnetic field for its explanation."
and conclued :
"In conclusion, we understand the photoeffect as being
the result of a classical field falling on a quantized atomic
electron. The introduction of the photon concept is
neither logically implied by nor necessary for the
explanation of the photoelectric effect"

Is the photon required to explain the Lamb shift?

 

[conway]

Is the photon required to explain the Lamb shift?

Probably not. In the Wikipedia article on the Lamb shift, the word "photon" does not appear in the derivation.

Admittedly, it seems that the technique of "virtual photons" may be used in one particular calcuation of the Lamb shift, just as "photons" are sometimes used in calculations involving the photoelectric effect. That doesn't mean they are needed.

 

[atyy]

Probably not. In the Wikipedia article on the Lamb shift, the word "photon" does not appear in the derivation.

Admittedly, it seems that the technique of "virtual photons" may be used in one particular calcuation of the Lamb shift, just as "photons" are sometimes used in calculations involving the photoelectric effect. That doesn't mean they are needed.

Well by "photon", I mean does the electromagnetic field have to be treated quantum mechanically, such that in its free state its excitations are quanta called photons?

 

[heldervelez]

Well by "photon", I mean does the electromagnetic field have to be treated quantum mechanically, such that in its free state its excitations are quanta called photons?

IMO, the quantum mechanical ease the math but it is not mandatory.
The underlying reality belongs to the 'analog world' but as it is constrained to a set of definite constraints imposed by energy and 'geometry' we perceive/measure a 'digital world'.
Like Music/Sound and 'Vinil' and CD.

 

[bcrowell]

yet another interesting paper:
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19680009569_1968009569.pdf"
where Willis E. Lamb and Marlan O. Scully (1968)

Note that it's not a published paper, it's an internal report. I wouldn't be surprised if the reason it was never published is that referees found problems with it. This is typical of the kind of thing cranks obsess over. They find some statement by a respected scientist and try to use it to promote the idea that all of modern physics is wrong. We've seen the same thing here recently with Einstein's 1924 paper "On the Aether," which is another darling of the kooks.

 

[atyy]

Note that it's not a published paper, it's an internal report. I wouldn't be surprised if the reason it was never published is that referees found problems with it. This is typical of the kind of thing cranks obsess over. They find some statement by a respected scientist and try to use it to promote the idea that all of modern physics is wrong. We've seen the same thing here recently with Einstein's 1924 paper "On the Aether," which is another darling of the kooks.

Try p24, 25 of http://books.google.com/books?id=5t0tm0FB1CsC&dq=quantum+challenge&source=gbs_navlinks_s

Also p24 of http://books.google.com/books?id=1-nhz2Ek-X8C&dq=quantum+optics+chiao&source=gbs_navlinks_s

 

[Bob S]

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19680009569_1968009569.pdf"
where Willis E. Lamb and Marlan O. Scully (1968)
"A misconception which most physicists acquire in their
formative years is that the photoelectric effect requires
the quantization of the electromagnetic field for its explanation."
and conclued :
"In conclusion, we understand the photoeffect as being
the result of a classical field falling on a quantized atomic
electron. The introduction of the photon concept is
neither logically implied by nor necessary for the
explanation of the photoelectric effect"
.

Willis Lamb won the Nobel Prize in physics for correctly calculating the QED underlying the 21-cm (1420-MHz) hyperfine structure line in hydrogen.
Bob S

 

[conway]

Try p24, 25 of http://books.google.com/books?id=5t0tm0FB1CsC&dq=quantum+challenge&source=gbs_navlinks_s

Also p24 of http://books.google.com/books?id=1-nhz2Ek-X8C&dq=quantum+optics+chiao&source=gbs_navlinks_s

Will the kookery never end??

 

[atyy]

Will the kookery never end??

Only when the Lamb is kooked.

 

[bcrowell]

Willis Lamb won the Nobel Prize in physics for correctly calculating the QED underlying the 21-cm (1420-MHz) hyperfine structure line in hydrogen.
Bob S

And Nobel Prize winners can write bad papers too :-) I've started a thread in the Quantum Physics forum giving my explanation of why I think the paper is wrong (and why it presumably never made it into a peer-reviewed journal).

[EDIT] Note that my #50 is not using the word "kooks" to refer to Einstein and Lamb. It's using the word "kooks" to refer to people who covet these papers by great physicists as holy relics in their quest to prove that the entire structure of modern physics is one big lie. (I think there is a difference between Einstein's "On the Aether" and Lamb's "The Photoelectric Effect Without Photons." The Einstein paper is interesting and, as far as I can tell, correct, but has been wildly misinterpreted by the kooks. The Lamb paper is just wrong, IMO.)

 

[heldervelez]

quantization results of electronic orbits beeing resonances, which is why radiation is emitted or absorbed in quanta not because that is their nature.
a semiclassical analisys is sufficient to explain the photoelectric effect and also the http://en.wikipedia.org/wiki/Hanbury_Brown_and_Twiss_effect#Wave_mechanics"
-----------------
The energy of a particle and its associated field are in balance because one is the source of the other.
As the field (electro/gravito) expands at 'c' speed, as time goes by, since particle creation, the energy content of the field can only increase continually.
At expense of what? Any numbers?
Am I misleaded?
-----------------

 

[sylas]

quantization results of electronic orbits beeing resonances, which is why radiation is emitted or absorbed in quanta not because that is their nature.
a semiclassical analisys is sufficient to explain the photoelectric effect and also the http://en.wikipedia.org/wiki/Hanbury_Brown_and_Twiss_effect#Wave_mechanics"
-----------------
The energy of a particle and its associated field are in balance because one is the source of the other.
As the field (electro/gravito) expands at 'c' speed, as time goes by, since particle creation, the energy content of the field can only increase continually.
At expense of what? Any numbers?
Am I misleaded?

Yes, you do seem to be mislead. Quantization is in the nature of the thing, that shows up in all aspects of the behaviour of light and radiation; it is definitely not merely a side effect of quantized orbits of atoms.

 

[conway]

quantization results of electronic orbits beeing resonances, which is why radiation is emitted or absorbed in quanta not because that is their nature.
a semiclassical analisys is sufficient to explain the photoelectric effect and also the http://en.wikipedia.org/wiki/Hanbury_Brown_and_Twiss_effect#Wave_mechanics"
-----------------

I'm going to agree with what you've said here. My inclination is that any natural phenomenon involving thermal light can be explained with a semiclassical treatment. And probably laser light as well.

 

[heldervelez]

Yes, you do seem to be mislead. Quantization is in the nature of the thing, that shows up in all aspects of the behaviour of light and radiation; it is definitely not merely a side effect of quantized orbits of atoms.

Mr. Sylas: I do like to discuss the reasoning behind physical statements.
I will be convinced if there exists (or devise) an experiment where the resonant nature of emitter and absorver is absent, or first principles.

 

[sylas]

Mr. Sylas: I do like to discuss the reasoning behind physical statements.
I will be convinced if there exists (or devise) an experiment where the resonant nature of emitter and absorver is absent, or first principles.

The quantum nature of radiation is now well established basic physics, based on far more than only the photoelectric effect.

I was only just recently looking at some lecture notes for Physics 313: Modern Physics at Rutgers, where this reference and explanation was provided:

So what would give us a proof? The study of statistical properties of photons:

"Although surely the correct description of the electromagnetic field is a quantum one, just as surely the vast majority of optical phenomena are equally well described by a semiclassical theory, with atoms quantized but with a classical field. ... The first experimental example of a manifestly quantum or nonclassical field was provided in 1977 with observation of photon anti-bunching for the fluorescent light from a single atom (PRL 39, 691 (1977))"

-- H.J. Kimble, Physica Scripta T76, 127 (1998).​

The title of the Kimble reference is "Strong interactions of single atoms and photons in cavity QED". The instructor also recommends as excellent reading on this subject: G. Greenstein and A.G. Zajonc, “The Quantum Challenge” (Jones and Bartlett Publishers, 2005).

In brief, it should be no surprise that the semi-classical approach works, even though it is not actually a fully correct representation of the nature of light. It is an error to confuse the continued usefulness of classical methods with an claim about the real nature of light being adequately described with the classical accounts.

Cheers -- sylas

 

[atyy]

The instructor also recommends as excellent reading on this subject: G. Greenstein and A.G. Zajonc, “The Quantum Challenge” (Jones and Bartlett Publishers, 2005).

This is the same reference I gave in post #51. The reference states that quantization of the electromagnetic field is not necessary to explain the photoelectric effect (there's a caveat to this, but it's not relevant at this point).

 

[bcrowell]

This is the same reference I gave in post #51. The reference states that quantization of the electromagnetic field is not necessary to explain the photoelectric effect (there's a caveat to this, but it's not relevant at this point).

I've started a thread about this in the quantum physics forum. The problem with the Scully-Lamb model is that it violates conservation of energy.

I wasn't able to access anything via the link in your #51, but I was able to find the book on amazon, which let me see certain pages. However, I was unable to see the page where they give their reference [1]. Do you have the actual book, and is reference [1] the internal report that's been floating around? I was able to access the pages where they present the idea, and it's basically just a summary of the internal report. They ignore the same issue Scully and Lamb ignore, which is that the hybrid model violates conservation of energy.

 

[atyy]

IDo you have the actual book, and is reference [1] the internal report that's been floating around?

I haven't got the book, was browsing at Borders some time ago which is when I came across their discussion.

 

[bcrowell]

I haven't got the book, was browsing at Borders some time ago which is when I came across their discussion.

It's funny trying to access this information through "keyholes" like amazon and google books. Although I couldn't access the book through google books at home, I am able to access it through google books here at work. Right after the section on the photoelectric effect, they have a section called "anticoincidences," which makes essentially the same point I'm making. Anyway, the Quantum Physics forum is really the right place to continue this discussion.