Curved
Space
Physicists
have demonstrated accelerating light beams on flat surfaces, where acceleration
has caused the beams to follow curved trajectories. However, a new experiment
has pushed the boundaries of what’s possible to demonstrate in a lab. For the
first time in an experiment, physicists have demonstrated an accelerating
light beam in curved space. Instead of traveling along a geodesic
trajectory (the shortest path on a curved surface) it bends away from this
trajectory due to the acceleration.
The
study, published in the journal Physical Review X, “opens the doors to a new avenue of
study in the field of accelerating beams. Thus far, accelerating beams were
studied only in a medium with a flat geometry, such as flat free space or slab
waveguides. In the current work, optical beams follow curved trajectories in a
curved medium,” according to Anatoly Patsyk, a physicist from the Israeli
Institute of Technology.
Completed by
physicists at Israel Institute of Technology, Harvard University, and the
Harvard-Smithsonian Center for Astrophysics, the success of the experiment will
increase research potential for further lab-based studies of phenomena like
gravitational lensing. By performing these expeirments in a lab, scientists
will be able to study such phenomena which stem from Einstein’s general theory of
relativity in a controlled setting.

The
accelerating light beam propagates on a non-geodesic trajectory, rather than the
geodesic trajectory taken by a non-accelerating beam. Credit: Patsyk et al.
©2018 American Physical Society
General
Relativity
The team
first caused a laser beam to accelerate by reflecting the beam off a spatial
light modulator, which is a device used to modulate amplitude, phase, or
polarize light waves. Bouncing the beam off this device imprints a specific
wavefront on the beam, creating one that accelerates while keeping its shape. The
team then pointed the accelerating laser along the inside of an incandescent
light bulb painted in such a way that the light both scattered and was visible
to the researchers.
The team
observed that when moving along the inside of the bulb, the beam’s trajectory
breaks apart from the geodesic line. When they compared this movement to a beam
that was not accelerating, they found that when it was not accelerating, the
beam would follow the line.
The research
could be a starting point for future research into phenomena that fall
within Einstein’s
general theory of relativity. Patsyk stated that “Einstein’s equations of
general relativity determine, among other issues, the evolution of
electromagnetic waves in curved space. It turns out that the evolution of
electromagnetic waves in curved space according to Einstein’s equations is
equivalent to the propagation of electromagnetic waves in a material medium
described by the electric and magnetic susceptibilities that are allowed to
vary in space.”

(a) Experimental
setup, (b) propagation of the green beam inside of the red shell of an
incandescent light bulb, and (c) photograph of the lobes of the accelerating
beam. Credit: Patsyk et al. ©2018 American Physical Society
Patsyk went
on to say that this foundation gives “rise to the emulating effects such as
gravitational lensing and Einstein’s rings, gravitational blue shift or red
shift, which we have studied in the past, and much more.”
In other
words, the techniques innovated through this experiment could help physicists more effectively study phenomena like
gravitational lensing. The team is also exploring whether plasmonic beams
(those that have plasma oscillations instead of light) could also be
accelerated in curved space.
Article was
originally published on Futurism.
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