Accelerating light beams in curved space

January 12, 2018 by Lisa Zyga, Phys.org feature
accelerating beams
The accelerating light beam propagates on a nongeodesic trajectory, rather than the geodesic trajectory taken by a non-accelerating beam. Credit: Patsyk et al. ©2018 American Physical Society

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.

Previously, accelerating light beams have been demonstrated on flat surfaces, on which their acceleration causes them to follow curved trajectories rather than straight lines. Extending accelerating beams to curved surfaces opens the doors to additional possibilities, such as emulating phenomena (for example, gravitational lensing) with optical devices in the lab.

The physicists, Anatoly Patsyk, Miguel A. Bandres, and Mordechai Segev at the Technion – Israel Institute of Technology, along with Rivka Bekenstein at Harvard University and the Harvard-Smithsonian Center for Astrophysics, have published a paper on the accelerating light beams in curved space in a recent issue of Physical Review X.

"This work opens the doors to a new avenue of study in the field of accelerating beams," Patsyk told Phys.org. "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."

In their experiments, the researchers first transformed an ordinary into an accelerating one by reflecting the laser beam off of a spatial light modulator. As the scientists explain, this imprints a specific wavefront upon the beam. The resulting beam is both accelerating and shape-preserving, meaning it doesn't spread out as it propagates in a curved medium, like ordinary light beams would do. The accelerating light beam is then launched into the shell of an , which was painted to scatter light and make the propagation of the beam visible.

When moving along the inside of the light bulb, the accelerating beam follows a trajectory that deviates from the geodesic line. For comparison, the researchers also launched a nonaccelerating beam inside the light bulb shell, and observed that that beam follows the geodesic line. By measuring the difference between these two trajectories, the researchers could determine the acceleration of the accelerating beam.

(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

Whereas the trajectory of an accelerating beam on a flat is determined entirely by the beam width, the new study shows that the trajectory of an accelerating beam on a spherical surface is determined by both the beam width and the curvature of the surface. As a result, an accelerating beam may change its trajectory, as well as periodically focus and defocus, due to the curvature.

The ability to accelerate along curved surfaces has a variety of potential applications, one of which is emulating general relativity phenomena.

"Einstein's equations of general relativity determine, among other issues, the evolution of electromagnetic waves in curved space," Patsyk said. "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. This is the foundation of emulating numerous phenomena known from general relativity by the propagating in a material medium, giving 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."

The results could also offer a new technique for controlling nanoparticles in blood vessels, microchannels, and other curved settings. Accelerating plasmonic beams (which are made of plasma oscillations instead of light) could potentially be used to transfer power from one area to another on a curved surface. The researchers plan to further explore these possibilities and others in the future.

"We are now investigating the propagation of light within the thinnest curved membranes possible—soap bubbles of molecular thickness," Patsyk said. "We are also studying linear and nonlinear wave phenomena, where the laser beam affects the thickness of the membrane and in return the membrane affects the propagating within it."

Explore further: Physicists turn to Maxwell’s equations for self-bending light

More information: Anatoly Patsyk et al. "Observation of Accelerating Wave Packets in Curved Space." Physical Review X. DOI: 10.1103/PhysRevX.8.011001

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42 comments

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adam_russell_9615
5 / 5 (4) Jan 12, 2018
Wouldnt light accelerate in any fiberoptic that wasnt straight?
mackita
1 / 5 (4) Jan 12, 2018
Was the accelerating light faster than normal light?
RNP
4.5 / 5 (8) Jan 12, 2018
@mackita
Acceleration refers to a change in velocity (a vector) not simply in speed. An object under acceleration may then change in direction AND/OR speed. The Earth moving under the influence of the gravitational field of the Sun is a simple example of an accelerating object whose speed is (almost) constant.
shavera
4.2 / 5 (5) Jan 12, 2018
Actually, RNP, if we really are trying to be particularly pedantic, and I only mention because the above article mentions geodesics, the Earth moving around the sun is actually the case of a non-accelerating object. Since it's in free-fall, the inertial path "forward" is actually a curved path around the sun. A better example to use of acceleration might be an electron beam being deflected by a charged ball.

I only mention because the article initially states that the inertial path for this light is already a curved path. The Geodesic it will follow is already something that, to an external observer, looks curved. What is remarkable is that the light curves *beyond* the geodesic one would expect, thus being 'accelerated.'
antialias_physorg
5 / 5 (6) Jan 12, 2018
Was the accelerating light faster than normal light?

No.
RNP
5 / 5 (2) Jan 12, 2018
@shavera
....the Earth moving around the sun is actually the case of a non-accelerating object


That is not right.

Quite simply, *by definition*, acceleration is a changing velocity. Velocity is a vector, which means it has both magnitude AND direction. Therefore any object whose velocity is changing in magnitude (speed) OR direction is being accelerated.

I'm not sure what your reference to geodesics means.
shavera
5 / 5 (4) Jan 12, 2018
In General Relativity, the way in which one measures directions changes with relationship to where you are located near mass, say. Since the way one measures distance changes, it redefines what direction is "straight" ahead. The end result is that a "straight" line, for a massive particle near a massive body, is an orbit. But since that conflicts very heavily with our notion of what "straight" means, we call these "straight" lines 'geodesics.'

Put another way: When you are in a car going around a tight turn, you may feel as if there is a 'centrifugal' force pushing you toward one side of the car. But that force, that acceleration, only arises because you're choosing a reference frame where inertia is not conserved (one that is rotating). Similarly, we could chose a reference frame where we're looking down over our solar system like in a text book. And we can draw "straight lines" through that solar system. But in order for an object to travel along those lines, it must accelerate.
shavera
5 / 5 (3) Jan 12, 2018
So I'll admit that I was maybe overzealous in saying that it's 'not' accelerating, just that it's not accelerating if you're looking from the perspective of inertial reference frames, which we usually are not (since we usually just absorb the non-inertial reference frame's force as "gravity" and treat the problem as if gravity was a real force between objects)
691Boat
5 / 5 (5) Jan 12, 2018
@Adam:
Wouldnt light accelerate in any fiberoptic that wasnt straight?

Light in fiberoptics relies on Total Internal Reflection (TIR) off the boundaries of the core to cladding. Any bounce will result in acceleration due to a change in direction, so even straight fibers have "accelerating" light traveling coaxially.
mackita
2.6 / 5 (5) Jan 12, 2018
accelerating beam follows a trajectory that deviates from the geodesic line. The researchers also launched a nonaccelerating beam inside the light bulb shell, and observed that that beam follows the geodesic line. By measuring the difference between these two trajectories they could determine the acceleration of the accelerating beam
What the researchers did was, they prepared Gaussian non-diffracting beam, which is known to keep its direction and to flow around obstacles. And they found that this beam indeed tends to keep its direction even on curved surface of bulb matte. This portion of study is solely noncontroversial. But the connection to Einstein's equations is pretty weak one, in particularly because Einstein himself found in 1908 already, that propagation of light within curved space cannot be completely modeled by refraction (it was one of his first early attempts to formulate general relativity).
mackita
2 / 5 (4) Jan 12, 2018
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
The idea of general relativity is exactly the opposite: the speed of light remains constant everywhere in it. The Einstein's field equations just prohibit it. When the light is propagating inside curved space, it doesn't accelerate. Instead of it, it changes its wavelength (red/blue shift).
mackita
1 / 5 (3) Jan 12, 2018
the researchers also launched a nonaccelerating beam inside the light bulb shell, and observed that that beam follows the geodesic line
But even if I'd accept this analogy of nonaccelerating beam with relativity, I don't understand which coincidence they wanted to demonstrate with Airy / Gauss beam, which behaves differently.
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... Extending accelerating beams to curved surfaces opens the doors to additional possibilities, such as emulating general relativity phenomena (for example, gravitational lensing) with optical devices in the lab.
Why/how they want to emulate relativistic phenomena with beam, which admittedly behaves differently? This is going over my head.
Stevepidge
1.7 / 5 (6) Jan 12, 2018
Space-time. Is illogical, it makes ZERO sense and not one of you damned fools have any idea what it means, nor can you explain it in any meaningful manner. You cannot "bend" a non physical entity called "space" and you cannot traverse "time" which DOES NOT EXIST. There is only the present and your stupid memory clinging onto memories confusing you into believing there is some "location" called the past or the future. Damn Einstein and his mythomatics for confounding physics and man for over 100 years.
mackita
1 / 5 (5) Jan 12, 2018
You cannot "bend" a non physical entity called "space" and you cannot traverse "time" which DOES NOT EXIST.
The deniers of relativity get confused in this point, as they propose an aether as a replacement for space-time which indeed suddenly DOES EXIST, despite it's just another name for the same subject. The dense aether model has therefore no problem with relativity and 4D space-time concept - it merely points to fact, this theory describes well only rather narrow slice of dimensional/energy density scale where we are living in.

As a general rule of thumb we may spot this scale by its occurrence of well defined spherical bodies: if something looks nicely round in our Universe, then the vacuum around it would fit the general relativity (and quantum mechanics) well. If something gets less symmetric and regular shape, you shouldn't apply these theories carelessly anymore as you'll face smaller or larger deviations from these theories.
Elmo_McGillicutty
not rated yet Jan 12, 2018
If your reference is under a constant change.......is the reference really changing?
Da Schneib
5 / 5 (3) Jan 12, 2018
@shavy, isn't acceleration defined for light by the geodesic of an unmodulated laser? That would be analogous to defining acceleration in an inertial frame, which can always be done by performing a local experiment to show the acceleration, according to the equivalence principle, remembering of course that under this principle acceleration is equivalent to gravity under GRT.
Da Schneib
5 / 5 (4) Jan 12, 2018
Here's a question worthy of the site: why is it correct to state that SLMs "accelerate light?" I can see from an examination of SLMs that it's demonstrated experimentally, but what's the theory behind it?
mackita
1 / 5 (3) Jan 12, 2018
@Schneib: You probably guessed it correctly: because Airy beam follows curved surfaces by its nature, it would also follow the curved surface more like massive body than the light, i.e. like body accelerating in gravity field. I'm just a bit suspicious about homological nature of this relativity analogy. For example we could compare the path of droplets dripping along curved surface with fluids adhering on this surface in different degree with the same result. Or the path of cars sliding on curved surfaces with different friction and so on. The problem with homologies is, they don't enable us to predict nothing more, than it's already considered during their formulation: they illustrate the situation but they don't explain it. Typical homology of relativity is for example the famous sliding of balls along elastic spandex fabric. Because the profile of fabric doesn't follow gravitational potential, this homology is misleading.
Eikka
not rated yet Jan 13, 2018
But that force, that acceleration, only arises because you're choosing a reference frame


Regardless of which frame of reference I choose, I still feel the pull of the seatbelts in the car.
milnik
1 / 5 (1) Jan 13, 2018
Einstein's fabric (textile) or a network of twisted and curved from time and space would come to the textile industry because it can sew up its pants, and when a mass there is lost gravitational attraction without any kind of love affair. And the poor light moves and behaves as the researchers say, which are some geodetic lines. I know what geodesic lines are on spherical surfaces, but how they look in a vacant space or in a mixture of substances that these examiners bully and subject to some "polygraph" test. It is again evidence that science does not know what photon is and how it moves through AETHER. If there is no respect for the existence of Aether, this would be the same situation as when the progeny of two sexes are expected (Einstein's married couple: space and time, only gently there are lesbians and two "warm brothers").
Whydening Gyre
not rated yet Jan 13, 2018
But that force, that acceleration, only arises because you're choosing a reference frame


Regardless of which frame of reference I choose, I still feel the pull of the seatbelts in the car.

And THAT is an effect of "acceleration"...
Da Schneib
5 / 5 (2) Jan 14, 2018
But that force, that acceleration, only arises because you're choosing a reference frame


Regardless of which frame of reference I choose, I still feel the pull of the seatbelts in the car.
Right, that's a local experiment. You can always find out if you're in an accelerated frame by a local experiment.
humy
4.3 / 5 (6) Jan 14, 2018
You cannot "bend" a non physical entity called "space"...

Err, space IS a physical entity. In what sense could space NOT be 'physical'?

torbjorn_b_g_larsson
5 / 5 (2) Jan 14, 2018
There is nothing on arxiv, too bad as the details look interesting.

There is nothing on arxiv, too bad as the details look interesting.

@mackita:
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
The idea of general relativity is exactly the opposite: the speed of light remains constant everywhere in it. The Einstein's field equations just prohibit it. When the light is propagating inside curved space, it doesn't accelerate. Instead of it, it changes its wavelength (red/blue shift).


Good points, but the purpose of these model systems is not to be equivalent analogies (material systems cannot be completely analogous to empty, curved space) but to demonstrate some analogous property (here of gravity lenses) that can be studied in the lab.
mackita
2.3 / 5 (3) Jan 14, 2018
I just like how relativity theory - which considers the path of light straight and space-time curved - gets demonstrated by model, which is doing exactly the opposite - and nobody gets even trace of suspicion, because - you know - it's about Einstein! A science!

This is the same like if Galieo would demonstrate heliocentric model by epicycles or like if spherical Earth would be demonstrated by Hollow Earth model. This example just illustrates the power of intersubjective religion and occupational blindness. BTW only schizophrenics will not get fooled by inverted mask illusion.
rrwillsj
not rated yet Jan 14, 2018
My takeaway from this article i. Since these experiments are being performed on the Earth's surface? Perhaps the 'curve' of the light beam is being caused by this planet's gravity?

Maybe it's just my limited imagination but I cannot see any other way to 'bend' a beam of light external to an apparatus. Isn't that how gravitational lensing works?

I wonder how this experiment would turn out in a micro-to-zero G orbit?

milnik
1 / 5 (3) Jan 14, 2018
@rrwillsj,
It should be known that gravity can not influence what is not matter. Here science has blinded and incomprehensible natural laws that rule in the universe.
Turning or curving a light beam can only cause magnetism, not gravity. Download this warning team that does not understand almost anything in the universe!
Da Schneib
3 / 5 (4) Jan 14, 2018
I just like how relativity theory - which considers the path of light straight and space-time curved - gets demonstrated by model, which is doing exactly the opposite - and nobody gets even trace of suspicion, because - you know - it's about Einstein! A science!
Actually, as I pointed out to @shavy, the path of an unmodulated laser is in fact a geodesic. Like most #physicscranks, you don't understand lasers, light propagation, or relativity. And your intent, as I have pointed out repeatedly, is to disrupt the conversation.
mackita
not rated yet Jan 15, 2018
The predictions of relativistic aberration and gravitational lensing belong into important successes of general relativity theory. But these predictions are based on assumption, someone can observe curved 4D space-time in more dimensions than this model assumes. The above experiments are modeling curved 4D space-time by curved 2D plane in 3D space (i.e. by classical ball on the spandex trampoline) which is standard approach - but this model assumes more spatial dimensions than general relativity is providing. It essentially observes the curvature of space-time from outside in similar way, like the quantum mechanics is doing, i.e. from extrinsic higher dimensional perspective. The ignorance of this fact introduces many paradoxes into existing physics, for example the entropic paradox of black hole or cosmological constant problem.
mackita
not rated yet Jan 15, 2018
Note that the above experiment compares the behavior of classical non-accelerating beam of light with so-called Airy beam, which is following curved space-time more closely than the light beam in similar way, like the massive bodies are following curved space-time along more curved path than the beam of normal light. This similarity is not accidental, because massive particles differ from photons by their higher content of high-dimensional scalar waves (longitudinal waves of vaccum). These waves have ability to interact with higher dimensions of space-time.

Airy beam is also special beam of light shaped by longitudinal waves (which are called evanescent waves in Maxwell theory), i.e. modes of light which propagate perpendicularly to beam direction in additional dimension. These waves are giving the beam ability to follow curved surface/space more closely, i.e. along extradimensions of its curvature from low-dimensional perspective of normal light spreading.
mackita
not rated yet Jan 15, 2018
With compare to light the path of massive bodies is shaped by gravitational force and in some stringy theories (six-dimensional conformal gravity and supergravity in particular) the gravity is actually weak six-dimensional force leaking into 4D space-time from extradimensions. These extradimensions manifests only weakly in our space by subtle quantum fluctuations, which light beam usually avoids. But the massive particles and bodies interact way more intensively with them, because they contain high-dimensional scalar waves and transverse waves revolving inside them along compacted heavily curved space-times. Therefore such a bodies follow six dimensional space-time embedded into 4D space-time. There are also ideas, that dark matter represent large scale Cassimir force (which is five-dimensional by its distance dependence) - so that behavior of dark matter is something between behavior of photons and massive particles.
mackita
not rated yet Jan 15, 2018
Note also that Airy beam cannot be prepared in other way, than by interaction of normal 4D light beam with massive particles (their refractive surfaces in particular) - so that it represents a 4D beam of energy stuffed/infected with extradimensions in smaller or larger degree. This is enabled by fact, that electromagnetic wave can undulate through fractal quantum foam forming vacuum in many nested directions/dimensions at the same moment. One would therefore expect, that the Airy beam is propagating by subluminal speed i.e. lower speed than the light, because it gets massive character by interaction/modulation by massive objects and it also has a tendency to interact more closely with them (by following curved surfaces). We already know, that polarized light is propagating more slowly than normal one (1, 2) and the Airy beam should behave similarly.
milnik
not rated yet Jan 15, 2018
@mackita,All this is evidence that neither you nor science know what light is, waves of matter, energy, magnetism, gravity, and all that is related. Just inventing additional theories to explain what you do not know about.
I have to educate you again: photon is a pair of "condensate", specially formed, as a pair, we call it "electron-positron". This "positron moves through the AETHER (without the aether, there is no movement in general), and around it a" electron "on the sinusoidal radius, and therefore it is seen as an electromagnetic wave. That your model curved the grid space time, has disowned your awareness by turning into Einstein's Fatamorgana Circle.
TechnoCreed
not rated yet Jan 15, 2018
For @Tobjorn who is looking for a link to the paper http://sci-hub.na...8.011001
mackita
not rated yet Jan 15, 2018
I have to educate you again: photon is a pair of "condensate", specially formed
Thank you - but what would that imply?
milnik
not rated yet Jan 15, 2018
This explains each complex movement and the body and particle in the universe.
Such is the situation with the Earth's spin. The center of mass of Earth and Moon moves along the ellipse (it is not Kepler's ellipse), and the Earth has two spins, its own, a rotation around its own axis, and the other one in the same magnitude, but the opposite direction, which occurs with the rotation of the Earth around this pericenter, on the sinusoidal radius . It forms the path of the Earth as a sinusoid wrapped around the Kepler ellipse. That is why the moon (and other months) have the same side facing the planet, always. This disassociates Einstein's "proof" of the cause of the precession of the perihelion of the planet (example Merkur)
Stevepidge
not rated yet Jan 15, 2018
You cannot "bend" a non physical entity called "space"...

Err, space IS a physical entity. In what sense could space NOT be 'physical'?



Tell me, what are the properties of "space". It most certainly is a mere abstraction at best. Hell, it doesn't even accurately denote location because there is no absolute reference point because it is for all intents and purposes without end. Space is not a physical entity. It might as well be 'turtles all the way down'.
Stevepidge
5 / 5 (1) Jan 15, 2018
I just like how relativity theory - which considers the path of light straight and space-time curved - gets demonstrated by model, which is doing exactly the opposite - and nobody gets even trace of suspicion, because - you know - it's about Einstein! A science!

This is the same like if Galieo would demonstrate heliocentric model by epicycles or like if spherical Earth would be demonstrated by Hollow Earth model. This example just illustrates the power of intersubjective religion and occupational blindness. BTW only schizophrenics https://www.wired...llusion/ by inverted mask illusion.


It is pointless arguing with them, they are well in the thrall of the Einstein delusion.
milnik
1 / 5 (1) Jan 16, 2018
When matter was formed, the space was formed as the place where the substance was placed and for its movement in it according to the laws of nature, and the time is merely a measure of that movement. Einstein's fantasies are a pesticide for consciousness that leads us to finding out the true causes of the phenomenon.
mackita
not rated yet Jan 16, 2018
When matter was formed, the space was formed as the place where the substance was placed
There is no evidence for it - you just invented it. Even if it would be correct, how it does invalidate relativity? Why your fantasies should be handled more seriously than the relativity?
rrwillsj
not rated yet Jan 16, 2018
m & m,
As for that Einstein 'delusion'?

I don't think it's very smart to argue with the guys who can build thermonuclear weapons.

No sirree. And my speculation of All Gravity, All the Time, Everywhere! Is even crazier than your pseudo-religious claptrap.
milnik
1 / 5 (1) Jan 16, 2018
@mackita,
you are looking for evidence for each statement. Now, when you dream of something, you must prove it either as a film or a mathematical one. And secondly, Einstein is your God who told you what time and space are there. Do you feel any clutter when you fall into that network? Especially, what do you think who formed you, did you come up with a big bang? You do not believe in any Spiritual Power, because the science wants to impose itself on it that it is the one who knows everything and claims that everything was created out of nothing. Such people, who believe in this, are really derived from nothing and do not understand anything, important for the structure of the universe.

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