Understanding of light momentum: Researchers shine a light on 150-year old mystery

Researchers shine a light on 150-year old mystery
Kenneth Chau is an associate professor of engineering at UBC's Okanagan campus. Credit: UBC Okanagan

The idea that light has momentum is not new, but the exact nature of how light interacts with matter has remained a mystery for close to 150 years. New research from UBC's Okanagan campus, recently published in Nature Communications, may have uncovered the key to one of the darkest secrets of light.

Johannes Kepler, famed German astronomer and mathematician, first suggested in 1619 that pressure from sunlight could be responsible for a comet's tail always pointing away from the Sun, says study co-author and UBC Okanagan engineering professor Kenneth Chau. It wasn't until 1873 that James Clerk Maxwell predicted that this was due to the residing within the electromagnetic fields of itself.

"Until now, we hadn't determined how this momentum is converted into force or movement," says Chau. "Because the amount of momentum carried by light is very small, we haven't had equipment sensitive enough to solve this."

Now, technology has caught up and Chau, with his international research team from Slovenia and Brazil, are shedding light on this mystery.

To measure these extremely weak interactions between light photons, the team constructed a special fitted with acoustic sensors and heat shielding to keep interference and background noise to a minimum. They then shot laser pulses at the mirror and used the sound sensors to detect as they moved across the surface of the mirror, like watching ripples on a pond.

"We can't directly measure photon momentum, so our approach was to detect its effect on a mirror by 'listening' to the elastic waves that traveled through it," says Chau. "We were able to trace the features of those waves back to the momentum residing in the light pulse itself, which opens the door to finally defining and modelling how light momentum exists inside materials."

The discovery is important in advancing our fundamental understanding of light, but Chau also points to practical applications of radiation pressure.

"Imagine travelling to distant stars on interstellar yachts powered by solar sails," says Chau. "Or perhaps, here on Earth, developing optical tweezers that could assemble microscopic machines."

"We're not there yet, but the discovery in this work is an important step and I'm excited to see where it takes us next."


Explore further

Transfer of atomic mass with a photon solves the momentum paradox of light

More information: Tomaž Požar et al, Isolated detection of elastic waves driven by the momentum of light, Nature Communications (2018). DOI: 10.1038/s41467-018-05706-3
Journal information: Nature Communications

Citation: Understanding of light momentum: Researchers shine a light on 150-year old mystery (2018, August 21) retrieved 19 September 2019 from https://phys.org/news/2018-08-momentum-year-mystery.html
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Aug 21, 2018
Zero information content.

Aug 21, 2018
Well apart from new tech being able to measure photon momentum more precisely.
What more did you want?

Aug 21, 2018
This comment has been removed by a moderator.

Aug 21, 2018
Among other things, the momentum, or "momentum", of light has supposedly already been described be "relativity". We are told that every prediction by "relativity" has been proved. Now we are told the momentum has never really been measured to see if it agrees with "relativity"!
And consider, at the base of it all, no one has yet tried to explain why light would have the same apparent speed with respect to all inertial observers. What construct describes light knowing before it even reaches an observer, what speed the observer is moving at, to adjust its appearance. Note, f there was no absolute zero, light should see the observer moving at any speed, the fact that light provides only one number indicates there is a universal basis that light uses the gauge the speed of an observer.

Aug 21, 2018
It's hard to see the connection between the actual research question explored in the paper itself, q.v., and the abstract question posed (and resolved) by Maxwell et al. There is no 150 year 'mystery' in view by the authors, rather the intricate photo-mechanical phenomena posed by momentum-transfer by PULSES of light.

Aug 21, 2018
And there is a facet non one talks about.
Light is an oscillating electromagnetic field. The electrostatic field gives rise to the magnetic field. But the magnetic field gives rise to the electrostatic field. But the electrostatic field the magnetic field gives rise to is the very electrostatic field that is giving rise to the magnetic field. The model of light has it giving rise to itself. There is no other instance in physics in which an entity is described as giving rise to itself, meaning that it has no existence apart from its behavior. Water can change temperature and be water, metal can change shape and be metal. They come into being, they are described by physics as essentially having an independent existence, physics says they continue without having to act upon themselves. Light, though, gives rise to itself in physical models. It is described as its own source. No one tries to explain how this is accomplished in any form of physics.

Aug 21, 2018
Among other things, the momentum, or "momentum", of light has supposedly already been described be "relativity". We are told that every prediction by "relativity" has been proved.


Almost every tested prediction has (ultimately) further confirmed the theory; not every prediction has been proven.

Aug 21, 2018
Pardon me. It's a matter of definition, Planck spent an entire life. Each charge center responds to the changing field, every center! They create an entirely new set, duh. So design it and stop with the Easter Egg hunt.

Aug 21, 2018
Silly science. They have the wrong momentum. Light(EM) transfers torque. It gives the absorber a twist. An electric field is not positive or negative. It's left handed and right handed. Absorption is a left twist, then a right twist. Light is also an area acceleration, not a velocity. A perpendicular acceleration.


Aug 21, 2018
Silly science. They have the wrong momentum. Light(EM) transfers torque. It gives the absorber a twist. An electric field is not positive or negative. It's left handed and right handed. Absorption is a left twist, then a right twist. Light is also an area acceleration, not a velocity. A perpendicular acceleration.


Chill

Aug 21, 2018
And there is a facet non one talks about.
Light is an oscillating electromagnetic field. The electrostatic field gives rise to the magnetic field. But the magnetic field gives rise to the electrostatic field. . . Light, though, gives rise to itself in physical models.


Quantum field theory (and QED in particular) has done a phenomenally good job of describing the electrodynamic nature of electrons and photons, how they interact, and how to calculate the probabilities of their behavior.

Aug 21, 2018
And there is a facet non one talks about.
Light is an oscillating electromagnetic field. The electrostatic field gives rise to the magnetic field. But the magnetic field gives rise to the electrostatic field. . . Light, though, gives rise to itself in physical models.


Quantum field theory (and QED in particular) has done a phenomenally good job of describing the electrodynamic nature of electrons and photons, how they interact, and how to calculate the probabilities of their behavior.

chill, i'm juz say'n; sing point sources in a 4D space, Lambda = T, within a unit-less space, i.e. defined attributes per point. meh

Aug 21, 2018
And there is a facet non one talks about.
Light is an oscillating electromagnetic field. The electrostatic field gives rise to the magnetic field. But the magnetic field gives rise to the electrostatic field. . . Light, though, gives rise to itself in physical models.


Quantum field theory (and QED in particular) has done a phenomenally good job of describing the electrodynamic nature of electrons and photons, how they interact, and how to calculate the probabilities of their behavior.

chill, i'm juz say'n; sing point sources in a 4D space, Lambda = T, within a unit-less space, i.e. defined attributes per point. meh

You know, it's been awhile, the cat is dead. Thought you should know that. There are no particles! Only field centers!!! .. its only a summation of spheres; reducible, mathematically to a single relative point for any charge, i.e. Center:Accumulator;Clock;add as much memory as required: Initial Set!! Use Coulomb, Maxwell; or just E(r);

Aug 21, 2018
The force is strong with the nutters tonight.

Aug 21, 2018
The electrostatic field gives rise to the magnetic field...

Erm...I think you failed in introductory electronics course somewhere.

Aug 21, 2018
The electrostatic field gives rise to the magnetic field...

Erm...I think you failed in introductory electronics course somewhere.


.....because he was copying from you on exams.

Aug 21, 2018
The electrostatic field gives rise to the magnetic field...

Erm...I think you failed in introductory electronics course somewhere.


That's a bit harsh, Antialias, I was taught the same idea back in the sixties:

A changing electric field produces a changing magnetic field.
The changing magnetic field produces a changing electric field.
And so on ad infinitum.

It sort of explains why light doesn't require an aether but doesn't address any quantum issues.

Julianpenrod is just very out of date.

Aug 22, 2018
A changing electric field produces a changing magnetic field.

A changing electric field is not an electroSTATIC field. It's an electroDYNAMIC field.
There's a reason why it's called electrodynamics.

Aug 22, 2018
A changing electric field produces a changing magnetic field.

A changing electric field is not an electroSTATIC field. It's an electroDYNAMIC field.
There's a reason why it's called electrodynamics.

OK! a boo boo is made; but still, it boils down to spherical electric fields and their updates; sorry i was thinking about a cpu program, i.e state defines all! Only the centers exists! A changing magnetic field is produced by an E field with a moving center! I'm trying not to be redundant. I say spherical because these are equal potential surface of a unique center! If ya don't know what the centers are doing, ya don't know what ya doing.

Aug 22, 2018
A changing electric field produces a changing magnetic field.

A changing electric field is not an electroSTATIC field. It's an electroDYNAMIC field.
There's a reason why it's called electrodynamics.

OK! a boo boo is made; but still, it boils down to spherical electric fields and their updates; sorry i was thinking about a cpu program, i.e state defines all! Only the centers exists! A changing magnetic field is produced by an E field with a moving center! I'm trying not to be redundant. I say spherical because these are equal potential surface of a unique center! If ya don't know what the centers are doing, ya don't know what ya doing.

Everything plus the kitchen sink. now go play. Light?

Aug 22, 2018
The bigger boo-boo is that you don't understand that light is the EM wave. It is not the E part or the M part - so it doesn't "give rise to itself" in any sense.
E and M fields are descriptions of two aspects of it. They are not separate entities.

Aug 22, 2018
The bigger boo-boo is that you don't understand that light is the EM wave. It is not the E part or the M part - so it doesn't "give rise to itself" in any sense.
E and M fields are descriptions of two aspects of it. They are not separate entities.

It's a sinusoidal update of a single charge; updates due to the motion of the center. Should I say it again?

The field has an origin, the change in the field has an origin, the field only changes if the center changes. Ok produce s Spherical field! Move it around. Does the field change, can you see that the field change is difficult to do backward?

Aug 22, 2018
The bigger boo-boo is that you don't understand that light is the EM wave. It is not the E part or the M part - so it doesn't "give rise to itself" in any sense.
E and M fields are descriptions of two aspects of it. They are not separate entities.

It's a sinusoidal update of a single charge; updates due to the motion of the center. Should I say it again?

The field has an origin, the change in the field has an origin, the field only changes if the center changes. Ok produce s Spherical field! Move it around. Does the field change, can you see that the field change is difficult to do backward?

What you originated by moving the sphere around was a set of equal potential Spheres moving away from the center, each update updates the center, LIGHT!

These centers been here forever, think about how much info is in each unique spherical E field!

Aug 23, 2018
It's a sinusoidal update of a single charge

Light is not charged.
updates due to the motion of the center. Should I say it again?

You can say it as often as you lie - but it doesn't make it sound any less stupid.

Hint: That light is often drawn as a wavy thing does not mean there is motion around anything. Light moves in a straight line (it can't do anything else). The wave is just to illustrate the cyclic nature of the E and M fields involved.

The field has an origin, the change in the field has an origin, the field only changes if the center changes. Ok produce s Spherical field! Move it around. Does the field change, can you see that the field change is difficult to do backward?

This part doesn't make sense on so many levels
Syntactically
Semantically
Logically

Unless you bother to actually start learning some stuff (like starting in first grade), you shouldn't even bother posting on the net. It's doing you no good.

Aug 23, 2018
The field has an origin, the change in the field has an origin, the field only changes if the center changes. Ok produce s Spherical field! Move it around. Does the field change, can you see that the field change is difficult to do backward?
erm...
whut????

Aug 23, 2018
It's a sinusoidal update of a single charge

Light is not charged.
updates due to the motion of the center. Should I say it again?

You can say it as often as you lie - but it doesn't make it sound any less stupid.

Hint: That light is often drawn as a wavy thing does not mean there is motion around anything. Light moves in a straight line (it can't do anything else). The wave is just to illustrate the cyclic nature of the E and M fields involved.

The field has an origin, the change in the field has an origin, the field only changes if the center changes. Ok produce s Spherical field! Move it around. Does the field change, can you see that the field change is difficult to do backward?

This part doesn't make sense on so many levels
Syntactically
Semantically
Logically

Unless you bother to actually start learning some stuff (like starting in first grade), you shouldn't even bother posting on the net. It's doing you no good.

meh

Aug 23, 2018
Illuminate me!

Aug 23, 2018
Illuminate me!

Naw, you stay with the non-causal QM; I pick causality. Want to race to understanding, enlightenment? You guys use 'nonsense' like it's axiomatic!

Aug 25, 2018
@ Hyperfuzzball
It would have been much more civilised of you if you had just explained the differences between the 2 words/concepts, instead of taking on the nasty behaviours and superiority complex of the Evil Axis that is Captain Stinky, tgoO1923 and aa_P and a few others. Nobody in their right mind appreciates a wise-ass.

Aug 25, 2018
@ Hyperfuzzball
It would have been much more civilised of you if you had just explained the differences between the 2 words/concepts, instead of taking on the nasty behaviours and superiority complex of the Evil Axis that is Captain Stinky, tgoO1923 and aa_P and a few others. Nobody in their right mind appreciates a wise-ass.

Sorry, I simply post the obvious, if offended, OK; but, relax. You'll right; my code idea needs more work!

Aug 26, 2018
This comment has been removed by a moderator.

Aug 26, 2018
This comment has been removed by a moderator.

Aug 26, 2018
This comment has been removed by a moderator.

Aug 26, 2018
It would have been much more civilised of you if you had just explained the differences between the 2 words/concepts, instead of taking on the nasty behaviours and superiority complex of the Evil Axis that is Captain Stinky, tgoO1923 and aa_P and a few others. Nobody in their right mind appreciates a wise-ass
Wassamatter obamasocks, nothing sufficiently ignorant to say in this thread?

Old trolls never die they just rot as usual.

Aug 26, 2018
From many aspects it's apparent, that vacuum not only physically exists, but it even resembles behavior of water surface rather closely. For example, at small distance scales it exhibits "Brownian noise" which blurs all close observations with so-called "quantum uncertainty". Whole the existence of photons is also https://i.imgur.com/Esex2Lj.gif and many other things, which laymen may not be aware of, because establishment of mainstream physics censors and covers these connections before them - but they still exist.

Vacuum and Empty are two different things.

Sep 06, 2018
@ Hyperfuzzball
It would have been much more civilised of you if you had just explained the differences between the 2 words/concepts, instead of taking on the nasty behaviours and superiority complex of the Evil Axis that is Captain Stinky, tgoO1923 and aa_P and a few others. Nobody in their right mind appreciates a wise-ass.

You need a joint!

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