Accelerating light beams in curved space

[beecee]

https://phys.org/news/2018-01-space.html

By shining a laser along the inside shell of an incandescent light bulb, physicists have performed the first experimental demonstration of an accelerating light beam in curved space. Rather than moving along a geodesic trajectory (the shortest path on a curved surface), the accelerating beam bends away from the geodesic trajectory as a result of its acceleration.

Read more at: https://phys.org/news/2018-01-space.html#jCp

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the paper: 

https://journals.aps.org/prx/abstract/10.1103/PhysRevX.8.011001

Observation of Accelerating Wave Packets in Curved Space

 

ABSTRACT

We present the first experimental observation of accelerating beams in curved space. More specifically, we demonstrate, experimentally and theoretically, shape-preserving accelerating beams propagating on spherical surfaces: closed-form solutions of the wave equation manifesting nongeodesic self-similar evolution. Unlike accelerating beams in flat space, these wave packets change their acceleration trajectory due to the interplay between interference effects and the space curvature, and they focus and defocus periodically due to the spatial curvature of the medium in which they propagate.

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OK, a couple of questions....Firstly the article: What do they actually mean by "accelerating light beam"?? Is this more a reference to the coordinate speed of light? Secondly, what do they actually mean by "bends away from the geodesic trajectory"??

 

With regards to the paper, I believe they are rather sloppy with reference to the three highlighted phrases. Should they not be referring to spacetime? Any other comment? 

[mathematic]

4 hours ago, beecee said:

https://phys.org/news/2018-01-space.html

By shining a laser along the inside shell of an incandescent light bulb, physicists have performed the first experimental demonstration of an accelerating light beam in curved space. Rather than moving along a geodesic trajectory (the shortest path on a curved surface), the accelerating beam bends away from the geodesic trajectory as a result of its acceleration.

Read more at: https://phys.org/news/2018-01-space.html#jCp

::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

 

the paper: 

https://journals.aps.org/prx/abstract/10.1103/PhysRevX.8.011001

Observation of Accelerating Wave Packets in Curved Space

 

ABSTRACT

We present the first experimental observation of accelerating beams in curved space. More specifically, we demonstrate, experimentally and theoretically, shape-preserving accelerating beams propagating on spherical surfaces: closed-form solutions of the wave equation manifesting nongeodesic self-similar evolution. Unlike accelerating beams in flat space, these wave packets change their acceleration trajectory due to the interplay between interference effects and the space curvature, and they focus and defocus periodically due to the spatial curvature of the medium in which they propagate.

<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

 

OK, a couple of questions....Firstly the article: What do they actually mean by "accelerating light beam"?? Is this more a reference to the coordinate speed of light? Secondly, what do they actually mean by "bends away from the geodesic trajectory"??

 

With regards to the paper, I believe they are rather sloppy with reference to the three highlighted phrases. Should they not be referring to spacetime? Any other comment? 

Acceleration refers to a change in direction, not speed. 

Space versus space-time?  I don't think it is relevant here.