Attractive and repulsive light force

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Discussion Overview

The discussion revolves around the nature of attractive and repulsive forces between photons as described in a scientific article. Participants explore the implications of these forces, questioning the underlying mechanisms and their relation to established concepts in physics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses confusion about the existence of attractive and repulsive forces between photons, noting that photons have no charge or mass, which complicates the understanding of such forces.
  • Another participant mentions radiation pressure as a force resulting from photon momentum, but highlights that the article claims the forces discussed are not due to radiation pressure, suggesting a need to consult the original journal article for clarity.
  • A third participant agrees on the lack of clarity in the article, pointing out that the described force differs from effects observed in laser tweezers, which involve induced dipoles, and notes the absence of detailed modeling in the article.
  • A fourth participant provides an abstract from the original paper, explaining that the optical force, termed ‘optical bonding force’, arises from the coupling of guided lightwaves in nanoscale devices and exhibits bipolar behavior based on the relative phase of the lightwaves. They suggest that this effect is classical and not related to the intrinsic properties of photons.

Areas of Agreement / Disagreement

Participants express uncertainty regarding the mechanisms behind the forces described in the article. While some agree that the article lacks clarity, there is no consensus on the nature of the forces or their implications.

Contextual Notes

The discussion highlights limitations in the article's explanations, including the absence of detailed modeling and the need for further investigation into the mechanisms of the optical forces mentioned.

junglebeast
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http://www.sciencedaily.com/releases/2009/07/090713131556.htm

I'm confused...photons have no charge and no mass. This article seems to say there is an attractive and repulsive force between photons, but that can't be electromagnetic and it can't be gravity..so what are they talking about?
 
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Well, there is a radiation pressure from light. Photons still have a momentum despite not having any mass and the transfer of the momentum will result in a force. But the article specifically states that these forces are not the product of radiation pressure so I think one would need to read the journal article to find out the specific mechanism.
 
I agree- the article is not exactly clear. It is claimed the force is a different effect from laser tweezers (which is casued by induced dipoles), but no information about their model is presented in that website.
 
Here is the full abstract of this paper:

State-of-the-art advances in nanoscale optomechanics allow light to be guided in free-standing waveguides or resonators1,2. In closely spaced devices, the coupling between the guided lightwaves gives rise to an optical force known as the ‘optical bonding force’3–6. Indeed, attractive optical force has been observed in substrate coupled devices7. According to recent theoretical predictions3, the optical force should show bipolar behaviour depending on the relative phase between in-plane coupled lightwaves. So far, such an in-plane optical force has not been measured. Here, we experimentally demonstrate a bipolar optical force between planarly coupled nanophotonic waveguides. Both attractive and repulsive optical forces are obtained. The sign of the force can be switched reversibly by tuning the relative phase of the interacting lightwaves. This highly engineerable force of bipolar nature could be used as the operation principle for a new class of planar light force devices and circuits on a CMOS-compatible platform.

So it definitely appears that (i) this is a guided EM wave (ii) it is then similar to Casimir effect of bounded wave (iii) it is analogous to the "bonding" and "antibonding" state that we get in chemical bonds that depends on the phase of the wavefunction.

Reading the paper quickly, it definitely appears that this is a purely classical effect. It has nothing to do with a photon having attractive or repulsive force.

Zz.
 

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