Study resolves century-long debate over how to describe electromagnetic momentum density in matter

Dec 29, 2011

(PhysOrg.com) -- Researchers from the NIST Center for Nanoscale Science and Technology and the University of British Columbia have shown that the interaction between a light pulse and a light-absorbing object, including the momentum transfer and resulting movement of the object, can be calculated for any positive index of refraction using a few, well-established physical principles combined with a new model for mass transfer from light to matter.

This work creates a foundation for understanding in metamaterials, artificially tailored materials of intense interest in and microwave engineering that can have negative indices of refraction, and have potential applications in , lithography, optical sensing, high gain antennas, and stealth radar coatings.

Light carries momentum and can transfer momentum to matter via . However, for the past century, there has been an ongoing debate over the correct form of the electromagnetic momentum density in matter. In the “Minkowski formulation,” the momentum density is proportional to the ; in direct contrast, the “Abraham formulation” finds it to be inversely proportional. While light is known to carry mass, a detailed model for mass transfer from light to a medium that absorbs light had not been formulated to date.

The researchers propose a set of postulates for light-matter interaction that encompass: a) the Maxwell equations, which govern classical electromagnetic behavior; b) a generalized Lorentz force law, which describes the force felt by matter in the presence of an electromagnetic field; c) a model for electromagnetic mass density transfer to an absorbing medium; and d) the Abraham formulation of momentum density. Using both closed-form calculations and numerical simulations of the interaction between an electromagnetic pulse and a test slab, the researchers demonstrated that their postulates yield results that are consistent with conservation of energy, mass, momentum, and center-of-mass velocity at all times.

They further showed that satisfaction of the last two conservation laws unambiguously identifies the Abraham form as the true form of momentum density in a positive-index medium. In addition to the theoretical significance of these results and the implications for metamaterials, the results will enable more accurate modeling of light-matter interaction at the nanoscale and open new routes to optical control of nano-mechanical systems incorporating light absorbing materials.

Explore further: Experiment with speeding ions verifies relativistic time dilation to new level of precision

More information: Revisiting the Balazs thought experiment in the presence of loss: electromagnetic-pulse-induced displacement of a positive-index slab having arbitrary complex permittivity and permeability, K. J. Chau and H. J. Lezec, Applied Physics A 105, 267-281 (2011).

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Isaacsname
not rated yet Dec 29, 2011
What is the Balazs thought experiment ? I cannot find much online...
Callippo
1 / 5 (4) Dec 29, 2011
unambiguously identifies the Abraham form as the true form of momentum density in a positive-index medium
Nice, but the experiments say exactly the opposite http://dx.doi.org...0.12.018 http://focus.aps....v22/st20 http://prl.aps.or.../e070401
While light is known to carry mass
How the photons can be massless after then?
Callippo
1.8 / 5 (5) Dec 29, 2011
What is the Balazs thought experiment ? I cannot find much online...
Over a half-century ago (1953), Balazs proposed a thought experiment to deduce the form of electromagnetic momentum in a transparent and loss - less slab by imposing conservation of global momentum and system center- of-mass velocity after a pulse has traveled through the slab.
Isaacsname
not rated yet Dec 29, 2011
So they counteracted the displacement of the mass due to earth's movement to measure the effect of energy traveling through the medium ?

" How the photons can be massless after then ? "

I thought they were considered mass-less until they interact with something by exerting radiation pressure....*scratches head*...
Benni
1.6 / 5 (7) Dec 29, 2011

" How the photons can be massless after then ? "

I thought they were considered mass-less until they interact with something by exerting radiation pressure....*scratches head*...


I don't think photons have ever been assumed to be massless, they simply have no "rest mass" because photons can only exist at light speed. The "rest mass" of a phton is zero, but it's mass at light speed is not zero. Gravitational lensing proves this when we observe light bends in the presence of a strong gravitational field.

Additionally, if photons were massless then black holes could not form because there is no mass for gravity to act upon to prevent the escape of photons from the highest point of gravitational attraction at the surface of the BH.

Learned this in my second semester college physics course.
Noumenon
3.8 / 5 (75) Dec 29, 2011
Photon's are considered to be massless. However all forms of energy have a 'mass equivalence'. For a photon this mass equivalency depends on it's frequency.
rawa1
1 / 5 (4) Dec 29, 2011
Photon's are considered to be massless. However all forms of energy have a 'mass equivalence'. For a photon this mass equivalency depends on it's frequency.
But relativists are claiming, the photons transfer just momentum, but no mass..
Noumenon
3.8 / 5 (75) Dec 29, 2011
Photon's are considered to be massless. However all forms of energy have a 'mass equivalence'. For a photon this mass equivalency depends on it's frequency.
But relativists are claiming, the photons transfer just momentum, but no mass..


You mean no rest mass (?). It transfers energy, p=hv/c, so it must transfer an energy mass-equivalency.
Benni
2 / 5 (7) Dec 29, 2011
Photon's are considered to be massless.


Only at "rest" because photons cannot exist at "rest", therefore "rest mass" is zero, however at light speed photons have mass, black holes prove this. Black holes prove this because light (or any other frequency of electro-magnetism) cannot generate enough escape velocity to free itself from the surface gravity of that body.

This also proves gravity is not a component of electro-magnetism, or the gravity of a body that prevents electro-magnetism from reaching "escape velocity" would prevent gravity from emerging from the surface of that body to create an accretion disc from which mass falls onto the surface of the BH.
Noumenon
3.8 / 5 (76) Dec 29, 2011
Only at "rest" because photons cannot exist at "rest", therefore "rest mass" is zero, however at light speed photons have mass, black holes prove this. Black holes prove this because light (or any other frequency of electro-magnetism) cannot generate enough escape velocity to free itself from the surface gravity of that body. - Benni


It's not necessary to say that 'photons have mass', in general relativity, because any form of energy in this theory is effected by and causes gravitiation,.. even pressure (which ultimately causes BH to form).

Photons have energy that is proportional to their frequency,.. they have a 'mass-equivelancy' via e=mc^2 if you like, but are massless themselves.
Noumenon
3.8 / 5 (76) Dec 29, 2011
This also proves gravity is not a component of electro-magnetism, or the gravity of a body that prevents electro-magnetism from reaching "escape velocity" would prevent gravity from emerging from the surface of that body to create an accretion disc from which mass falls onto the surface of the BH. - Benni


I don't know of anyone saying that gravity is a component of electromagnetism. The error you are making I think, is that you assume that gravitation requires a constantly propagating force. The gravitation field is static,.. unless something causes it to propagate, like a orbiting neutron star binary, or some galactic collision, in which case it propagates at c. In general relativity, gravitation it is a static curvature of space-time.
Noumenon
3.8 / 5 (75) Dec 29, 2011
You seemed to have made the same error in the link below, when you said,..

Earth's orbit does not follow the 8.3 light minute "retardation image" of the sun, it follows an arc of 8.3 light minutes beyond that


I think you meant "non-retardation image" above,. i.e. it follows as if gravitation is instantaneous. I have responded to this below.

http://www.physor...mic.html
Noumenon
3.8 / 5 (76) Dec 29, 2011
OK, so FrankHerbert rates me a 1. Would you care to tell me where I am wrong then Frank? (I'm guess you won't).
Benni
1.7 / 5 (6) Dec 29, 2011
You seemed to have made the same error in the link below, when you said,..

Earth's orbit does not follow the 8.3 light minute "retardation image" of the sun, it follows an arc of 8.3 light minutes beyond that


I think you meant "non-retardation image" above,. i.e. it follows as if gravitation is instantaneous. I have responded to this below.


You said the same thing I said, you simply shortened my statement, there's nothing contradictory between your synopsis of my statement & the way you correctly understood what I intended. And again, satellite tracking data proves Earth's orbit tracks the actual location of the Sun, not the 8.3 light minute retarded visible image. I make no attempt to explain what on the face appears to be superluminol phenomena as we know "information" (propagation?) cannot exceed light speed. I'll look at your link later when I have more time....
Callippo
1.8 / 5 (10) Dec 29, 2011
The general relativity has nothing very much to say about photons, because it doesn't recognize quantization and photons are quantum artifacts, not relativistic ones. In AWT the photons are solitons of transverse waves of light formed with inhomogeneities of vacuum environment and they're forming dual supersymmetric counterparts of neutrinos (solitons of longitudinal gravitational waves, which are superluminal). Like all solitons of transverse waves the photons are actually moving slowly, than the speed of light, the more slowly, the higher their wavelength is. In addition, they exhibit their own gravity, the more, the more energetic they're are. The lowest mass photons are photons of CMBR, they're spreading like waves as they're not distinguishable from CMBR background. The photons of longer wavelengths are dispersed with CMBR, they're unstable and they're behaving like tachyons. It enables them to escape from black holes in limited extent (Hawking radiation).
Is it OK for everybody?
Benni
2.1 / 5 (7) Dec 29, 2011
@Noumenon: OK, I looked at your other post. I think we're at about the same level of understanding. My personal simplifified view is swinging a ball on a string around my head, my head is the sun. The string is in constant contact betwween my body & the ball, & the string represents the unbroken line of gravity shared between the bodies of Earth & Sun, however "information" transferred along that "string" probably occurs at light speed.

Visualize this: If in the course of swinging the string attached ball around my head & something hits that string, the string will vibrate sending pulses along that string to the two bodies, these pulses are "information" which do not interfere with the connection previously established between the two bodies. An asteroid could be visualized as something hitting the gravitational string between Earth & Sun, it would add a brief "gravity pulse" between the two bodies then subside, generating that information at light speed, or maybe even less.
Telekinetic
3 / 5 (4) Dec 29, 2011
@Callippo
Can you elucidate the difference between AWT and Wilhelm Reich's interpretation of the aether?
Callippo
1.6 / 5 (7) Dec 29, 2011
Can you elucidate the difference between AWT and Wilhelm Reich's interpretation of the aether?

My aether is substantially stronger model.

http://www.aether...ther.jpg
indio007
1 / 5 (1) Dec 29, 2011
Pretty ballsy saying this resolves the debate on which formulation is more correct Abraham or Minkowski.

This recent (March 2011) paper says it don't matter because they are "different separations of the same momentum"
http://arxiv.org/...54v1.pdf

This dissertation thinks that neither is completely correct
"While we have presented arguments in
favor of the interpretation of the Abraham momentum as the momentum of the eld,
our simplied analyses lead us to the conclusion that neither the Abraham nor the
Minkowski expressions for momentum give the recoil momentum of a particle in a
dispersive dielectric medium."
http://repository...tion.pdf

I guess it will stay unresolved for another 100 years.

Callippo
1.6 / 5 (7) Dec 29, 2011
Here you can see, how the glass fiber moves when the light is pushed into it. Light is stream of massive particles, so it behaves like the stream of water sprinkling from garden hose.

http://physics.ap...v22/st20
ClevorTrever
5 / 5 (3) Dec 30, 2011
"While light is known to carry mass"

HANG YOUR HEAD IN SHAME.
Callippo
1 / 5 (3) Jan 02, 2012
"While light is known to carry mass" HANG YOUR HEAD IN SHAME. (upvoted with aaaaaaaaa and Isaacsname)...
Of course it is, you just don't understand physics. The zero rest mass of photon doesn't imply zero mass of photon.
vacuum-mechanics
1 / 5 (3) Jan 05, 2012
Someone may doubt why light (wave) has no rest mass; it is easy to understand if we accept it as the vibration of some physical medium. Think analogy of a pulse of sound wave (that could be heard by ear in the same way as light could be detected by eye) which also has no rest mass. The reason is because no rest mass means no sound wave!