Physicists from Trinity College Dublin's School of Physics and the CRANN Institute, Trinity College, have discovered a new form of light, which will impact our understanding of the fundamental nature of light.
One of the measurable characteristics of a beam of light is known as angular momentum. Until now, it was thought that in all forms of light the angular momentum would be a multiple of Planck's constant (the physical constant that sets the scale of quantum effects).
Now, recent PhD graduate Kyle Ballantine and Professor Paul Eastham, both from Trinity College Dublin's School of Physics, along with Professor John Donegan from CRANN, have demonstrated a new form of light where the angular momentum of each photon (a particle of visible light) takes only half of this value. This difference, though small, is profound. These results were recently published in the online journal Science Advances.
Commenting on their work, Assistant Professor Paul Eastham said: "We're interested in finding out how we can change the way light behaves, and how that could be useful. What I think is so exciting about this result is that even this fundamental property of light, that physicists have always thought was fixed, can be changed."
Professor John Donegan said: "My research focuses on nanophotonics, which is the study of the behaviour of light on the nanometer scale. A beam of light is characterised by its colour or wavelength and a less familiar quantity known as angular momentum. Angular momentum measures how much something is rotating. For a beam of light, although travelling in a straight line it can also be rotating around its own axis. So when light from the mirror hits your eye in the morning, every photon twists your eye a little, one way or another."
"Our discovery will have real impacts for the study of light waves in areas such as secure optical communications."
Professor Stefano Sanvito, Director of CRANN, said: "The topic of light has always been one of interest to physicists, while also being documented as one of the areas of physics that is best understood. This discovery is a breakthrough for the world of physics and science alike. I am delighted to once again see CRANN and Physics in Trinity producing fundamental scientific research that challenges our understanding of light."
To make this discovery, the team involved used an effect discovered in the same institution almost 200 years before. In the 1830s, mathematician William Rowan Hamilton and physicist Humphrey Lloyd found that, upon passing through certain crystals, a ray of light became a hollow cylinder. The team used this phenomenon to generate beams of light with a screw-like structure.
Analysing these beams within the theory of quantum mechanics they predicted that the angular momentum of the photon would be half-integer, and devised an experiment to test their prediction. Using a specially constructed device they were able to measure the flow of angular momentum in a beam of light. They were also able, for the first time, to measure the variations in this flow caused by quantum effects. The experiments revealed a tiny shift, one-half of Planck's constant, in the angular momentum of each photon.
Theoretical physicists since the 1980s have speculated how quantum mechanics works for particles that are free to move in only two of the three dimensions of space. They discovered that this would enable strange new possibilities, including particles whose quantum numbers were fractions of those expected. This work shows, for the first time, that these speculations can be realised with light.
Explore further:
Leiden physicists entangle four rotating photons
More information:
K. E. Ballantine et al. There are many ways to spin a photon: Half-quantization of a total optical angular momentum, Science Advances (2016). DOI: 10.1126/sciadv.1501748

proxeiroakaount
3.3 / 5 (8) May 17, 2016I'll wait for a reproduction of their results by other scientists as well, since I'm kind of old and thus being somehow conservative, prone to think this idea is not even wrong...
emolgidou
4.3 / 5 (11) May 17, 2016compose
May 17, 2016compose
May 17, 2016Hyperfuzzy
1 / 5 (12) May 17, 2016Whydening Gyre
5 / 5 (15) May 17, 2016in most conversations, photons DO exist. Usually implied as a smallest measurable grouping of energy in the EM spectrum.
ChiefFartingDog
May 17, 2016compose
May 17, 2016Whydening Gyre
5 / 5 (8) May 17, 2016okay. I was gonna say "That we don't exist", but realized upon "quote"ing the comment i/ts was a link to a joke I found was kinda funny...;-) I gather compose did, too...;-)
That said, I suppose after string theory, we'll have to come up with a "dot" theory...
Whydening Gyre
5 / 5 (11) May 17, 2016CFD,
Your alias reminds me of the old joke about a little indian boy asking his grandfather how parents decided on a child's name. After explaining that the child was named for the first thing a father sees after the child is born.
He then questioned the boy - "Why do you ask, Two Dogs Fucking?"
:-)
Cave_Man
3.7 / 5 (6) May 17, 2016Da Schneib
4.3 / 5 (11) May 17, 2016I will be very interested to see where this leads.
This is actually pretty groundbreaking, and I expect that when it starts to catch on, it's going to make some pretty big waves in physics.
Da Schneib
4.3 / 5 (6) May 17, 2016ħ = h/2π
and can take on half-integer values for fermions and integer values for bosons.
Da Schneib
4.4 / 5 (7) May 18, 2016SA apparently thinks this is pretty important too. They don't make many articles open access. Congratulations to them for seeing the probable importance of this discovery. This may be the most important discovery in physics I have personally been aware of when it happened in my lifetime.
compose
May 18, 2016Da Schneib
4.5 / 5 (8) May 18, 2016Maybe you forgot.
compose
May 18, 2016Da Schneib
4.6 / 5 (9) May 18, 2016This is a specious claim immune to evidence and ignorant of the foundations of quantum mechanics, not to mention the results of experiment. I'll take the SM any day over your ethereal speculations.
compose
May 18, 2016Ojorf
4.5 / 5 (8) May 18, 2016So what exactly is your point?
Da Schneib
4.6 / 5 (9) May 18, 2016Da Schneib
4.2 / 5 (10) May 18, 2016compose
May 18, 2016Mimath224
4.4 / 5 (7) May 18, 2016compose
May 18, 2016MalleusConspiratori
2.5 / 5 (13) May 18, 2016You beat me to it! lol That's not one you get beaten to the punch on everyday.
ChiefFartingDog
May 18, 2016Whydening Gyre
5 / 5 (7) May 18, 2016Causality driven - by what the wave (and the particle points in it) was doing/experiencing immediately prior. It's a reaction, not a prior knowledge.
Da Schneib
5 / 5 (5) May 18, 2016Direct photon-photon interactions are not possible, since photons have no charge. The theory behind these interactions is that one or both of the photons is energetic enough to temporarily form a particle pair that almost instantly annihilate to reform the photon; if, during this brief instant, another photon interacts with one of the pair, or (much more rare) is itself undergoing such a process at the same time as the interaction, then the processes that can happen are governed by the combined energy of the photons.
[contd]
Da Schneib
5 / 5 (6) May 18, 2016Outputs consistent with electron-positron pair interaction with a colliding photon have been observed since 1934; in modern extremely high energy accelerators, a wide variety of particles have been produced, consistent with higher-order lepton and quark pairs interacting either with the other photon or with a pair it has produced.
The particular interaction(s) possible depend upon the energies of the two photons.
In the interaction you're talking about, the photons must be above 1.022 MeV in their combined energy; and in fact, at least one of them must itself be above 1.022 MeV to temporarily form an electron-positron pair. The probing photon then interacts with one of the pair before it can annihilate with its partner, scattering it away.
[contd]
Da Schneib
5 / 5 (6) May 18, 2016Whether this happens or not is a matter of pure chance; if neither photon is energetic enough to form a temporary pair it will not happen at all, and the two photons will not scatter or interact even if they pass through the same point at the same time. They are bosons, and are not prohibited from doing so as fermions are by Pauli exclusion. And even if one photon is energetic enough to form a pair, there is no assurance that it will do so when the other photon is passing through its location.
Thus, this is not a matter of "knowing" that a fermion pair *will* be created; it is a matter of a fermion pair *happening to be* created at just the right time to interact with an impinging photon. Whether it *can* happen depends on there being enough energy in one or both photons to *happen to* create a pair at that moment, and also of it *happening to* do so.
[contd]
Da Schneib
5 / 5 (6) May 18, 2016With that understanding in hand, let's proceed to your question:Neutrinos are not EM. They are leptons, of extremely small (possibly zero, but probably not) mass. Since they cannot be detected except very rarely, it would be extremely difficult to observe such an interaction, and in fact as far as I know it has not been proven to occur due to this difficulty. It is, however, possible; but you must also keep in mind that neutrinos interact only in the weak force (and possibly gravitationally, but that is an open question), so that makes this even more difficult:
[contd]
Da Schneib
5 / 5 (6) May 18, 2016The weak force is weak and slow, and weak charge is not carried by photons, so the only possibility is of two photons, both creating neutrino pairs at the same moment that they are coincident, and the two neutrino pairs happening to interact in the weak force in the extremely limited time available, both of which are extremely improbable making this an enormously extremely improbable event which is almost impossible to detect in the first place. This is why there are no experimental reports of it. It is very nearly impossible, piling all these extreme improbabilities atop one another.
[contd]
Da Schneib
5 / 5 (6) May 18, 2016Well, photon-photon interactions are possible, as I have outlined above, but they conserve all quantities and there is no need for them in order to explain the results above, in the article we are commenting on.
You also should not use "result in certain point Particles" in this context; the photons are also point particles. What you mean is whether bosons of sufficient energy can form temporary fermion pairs, and whether members of those pairs can then interact with other particles, and this can happen, but the pairs are always a particle and its antiparticle, in order to obey all the conservation laws, and if they do not happen to interact with another particle, they will recombine to form the original gamma photon.
I hope that answers your question.
Whydening Gyre
5 / 5 (9) May 18, 2016MM,
I am flattered you would include me in your request. However, Da Schneib is eminently more informed than I on these matters...:-)
And I noticed, he has prepared a pretty complete (and lengthy...) series of technical comments for you, that I would not have even come close to presenting. (I followed along for a while, but then my ADHD kicked in...) Mine would be more a visual of an artsy fluidic nature without the esoteric jargon to back it up.
So, in summation -
Yeah, what HE said...
Whydening Gyre
5 / 5 (9) May 18, 2016They DO change identity as they pass thru matter - nuetrino "flavoring", remember? (Was in an article a month or so back, bout changes as they left the sun)
You would think so. Specially considering that their density would probably be higher in matter dominated localities. (More "flavors" interacting)
And my responses were even ruffer...:-)
Mimath224
5 / 5 (5) May 18, 2016Mimath224
5 / 5 (5) May 18, 2016I've tried to give my 'intuition' a math feel and you might be be able to come up with something more appropriate. Thanks in advance.
@Whydening Gyre Ha!, understood but thanks for your time anyway.
To both, have a good day.
Da Schneib
5 / 5 (6) May 18, 2016I'll look at other points in your two posts shortly; right now I'm kinda burnt out from various RL phenomena.
Whydening Gyre
5 / 5 (9) May 18, 2016MM,
Einstein once said the only valuable thing is intuition.
There is something about spin and orientation that I feel is important, too. I lay awake at night (after scouring these conversations) trying to visualize the symmetry of it - in 3d.
Thanks for the input on your intuition. It's provided me some additional "variables" and controls, to add in to my visualizations.
I know, I know... Too Garrett Lissi-ish....:-)
Mimath224
5 / 5 (5) May 19, 2016Da Schneib
5 / 5 (3) May 19, 2016You go on to discuss, I think only as an analogy, quaternions and spinors. Then you introduce time as a factor, implying that the development of these quaternion and spinor functions over time determines what products emerge from these photon-photon interactions.
I think what's going on here is that you're wondering if there could be some other factor that somehow determines what happens in photon-photon interactions.
[contd]
Da Schneib
5 / 5 (3) May 19, 2016I doubt this, just as I doubt that there is any particular factor other than blind chance that determines when a neutron chooses to decay; such factors have been looked for since we first discovered radioactivity and determined that decay is a random event. This isn't just us throwing up our hands and saying "It's random," detailed statistical analysis supports this determination. And the same is true of other decays, including those of both heavy quarks to lighter ones down to the lightest up quark combination, two ups and a down forming a proton, and the same for the leptons, with the heavier ones decaying in a chain ending with neutrinos and electrons. These decays, and their probabilities, are fairly well characterized in the CKM and PMNS matrices for quarks and leptons, respectively.
[contd]
Da Schneib
5 / 5 (3) May 19, 2016The probabilities in photon-photon interactions are controlled by just such random chances; that is, how often photons experience pair production and subsequent annihilation back to the original photon as they propagate. This is further influenced by the energy of the photons, which governs what pairs it is possible for them to form. A photon below 1.022 MeV is incapable of forming any pair at all since its energy is insufficient to form two electrons, the lightest particles we know of. As we increase the energy of the photons, we pass thresholds where it becomes successively possible to form quark pairs, muon pairs, and so forth. However, it is not certain that above these thresholds if a pair is produced it will only be these newly allowed particles; lighter pairs may be formed as well, and the distribution is still random among which possible pair will be produced in a given interaction.
[contd]
Da Schneib
5 / 5 (3) May 19, 2016Topping all of this off is the fact (again shown by statistics) that when a Heisenberg-conjugate parameter is determined, its complementary parameter gets a random value. To demonstrate this, think of the three-polarizers experiment: after the second polarizer, the values of the spins on the original axis measured in the first polarizer, and about to be measured again in the third, is random; in the original form, with the polarizers oriented 0-π/4-0 (or if you prefer, 0°-45°-0°), you get a 50%-50% probability distribution at the third polarizer. This is very strong evidence of true randomization.
I don't think that spin state (or your postulated quanternion-like or spinor-like parameter) has anything to do with what particles are produced; assuming there is any relevance at all, I would expect it to affect the momenta of the particles produced, not their nature.
So I hope that answers your question.
MRBlizzard
5 / 5 (3) May 19, 2016A couple of observations / questions:
1. How dark is the night sky in 1/2 ħ photons? Could E/T be talking on this ultra quiet band. (What does the sun look like?)
2. Two dimensional phenomenon yield 1/2 ħ photons. Could three dimensional phenomenon yield 1/3 ħ fundamental particles, quarks? While understanding the difference between photons and static fundamental particles, one can still call on analogs, indeed mathematical analogs, "Is the electron a photon with toroidal topology? ", J.G. Williamson et al., Annales de la Fondation Louis de Broglie, Volume 22, no.2, 133 (1997) , and argue (perhaps, poorly) that confined quarks, are not entirely within Minkowski space, and could be affected by higher space/time (10d string?) physics as the material.
Da Schneib
5 / 5 (3) May 19, 2016For example, in spaces of odd dimensionality, the thing we call "axes of rotation" point in directions that are defined in the space; but in spaces of even dimensionality they need not and at least some of them do not. The trivial example is a space of dimension two: in this space, rotations in the only available direction, the x-y plane, have an axis that points in the z direction, which does not exist in the 2D space.
[contd]
Da Schneib
5 / 5 (3) May 19, 2016In SRT in 4D spacetime, we find that three of the six axes of rotation point in such directions: the x-t, y-t, and z-t planes have axes that point in directions that do not exist in the 4D manifold; but the x-y, x-z, and y-z planes all have axes that point, respectively, in the z, y, and x directions, as they do in the 3D space of Galilean-Newtonian physics.
Da Schneib
5 / 5 (3) May 19, 2016No. At least not according to the evidence presented in the paper we are discussing. What we might find later now that we're looking remains to be seen.
[contd]
Da Schneib
5 / 5 (3) May 19, 2016Be very careful here. Photons are fundamental particles too just as W and Z and gluons (and hypothetically, gravitons) are. The fact they are bosons doesn't make them other than fundamental particles in quantum physics. And this is highlighted by the W and Z particles which have mass and cannot move at the speed of light.
[contd]
Da Schneib
5 / 5 (3) May 19, 2016I'll have to have a careful look at this; I have seen this argued elsewhere in much less sophisticated terms. Hopefully there is a version of this paper available on arXiv.
My initial reaction is, no, but that's certainly not definitive; let me look at the paper and reactions to it and I might have something more to say.
Da Schneib
5 / 5 (3) May 19, 2016https://www.physi....614799/
BTW, this is the same paper I've seen linked elsewhere. As Loren says, it's not enough to duplicate part of the experimental results, for a coherent and consistent theoretical result one must duplicate all of them, and trivially, this hypothesis does not duplicate electron results above 100GeV that have been well known for a long time.
MRBlizzard
5 / 5 (3) May 19, 2016A couple of observations / questions:
1. How dark is the night sky in 1/2 ħ photons? Could E/T be talking on this ultra quiet band. (What does the sun look like?)
2. Two dimensional phenomenon yield 1/2 ħ photons. Could three dimensional phenomenon yield 1/3 ħ fundamental particles, quarks? While understanding the difference between photons and static fundamental particles, one can still call on analogs, indeed mathematical analogs, "Is the electron a photon with toroidal topology? ", J.G. Williamson et al., Annales de la Fondation Louis de Broglie, Volume 22, no.2, 133 (1997) , and argue (perhaps, poorly) that confined quarks, are not entirely within Minkowski space, and could be affected by higher space/time (10d string?) physics as the material.
Mimath224
5 / 5 (3) May 19, 2016Da Schneib
5 / 5 (1) May 19, 2016Sorry, guy, they apparently are now randomly deleting comments for no particular reason. I'll try and see if I can remember it and post later.
I also gave you a 5 for a good question; that also seems to have disappeared. Here it is back again in the meanwhile.
Hey @physorg, get your act together. You're blowin' it. If you need someone to help fix your site and figure out why you keep losing stuff I might be talked into it over the weekend, but be prepared to pay for my time.
Whydening Gyre
5 / 5 (5) May 19, 2016Just needed a refresh...
Da Schneib
5 / 5 (1) May 19, 2016Whydening Gyre
5 / 5 (6) May 20, 2016MM, apologies for Intrusion in converse with DS.
I agree on the rotation aspect of your "intuition". I had a pretty decent visual after your input last nite. Something bout 2 different direction spins (1/2 and 1/3) and... maintenance of orthogonality..(?)
You are way ahead of me on the "formulation" aspect, I suspect, so let me know, too...:-)
Da Schneib
5 / 5 (4) May 20, 2016Whydening Gyre
5 / 5 (5) May 20, 2016LOL... Okay...:-)
Mimath224
5 / 5 (3) May 20, 2016On the QM level..(cont)
Mimath224
5 / 5 (2) May 20, 2016Whydening Gyre
5 / 5 (6) May 20, 2016spin within spin.
Whydening Gyre
5 / 5 (6) May 20, 2016Solid truth.
Was not aware of EM FSC. Will delve...
Fractalization of a sort...
BE the quantum, Grasshopper...:-)
Looking forward to your more defined explanation to DS.
BTW - Did MA and was gymnast as a youth. At 62 - not so much...:-)
Whydening Gyre
5 / 5 (5) May 20, 2016That was meant to say - I understand and will apply it in my 'visualizations'. Thanks.
Mimath224
5 / 5 (3) May 20, 2016'Fractalization of a sort...
BE the quantum, Grasshopper...:-)
...BTW - Did MA and was gymnast as a youth. At 62 - not so much...:-)'
Ha! yeah, right on. I was a track athlete in my younger years (sprint), Shot, Javelin and the like. At 73 still teaching MA.
' Looking forward to your more defined explanation to DS.' This is proving difficult because other events have taken over at present but will definitely do it at some point. It's important that I get it right so that DS is not confused. i.e. spent yesterday evening trying to using vector scalar & cross product as the base for a quaternion explanation of my thoughts (first real terms = 0) but now, I'm not quite sure if that's the appropriate route. Perhaps using q =1 so that sine and cosine might be best. Ha! by the time I finish, this thread will probably be closed...(@Da Schneib maybe send you a private message...is that okay?)
Da Schneib
5 / 5 (3) May 20, 2016Mimath224
5 / 5 (2) May 21, 2016Mimath224
5 / 5 (1) May 21, 2016Let's say the photon direction is x (horizontal) so SAM in the (y(vertical),z) plane interacts with a spiral phase material (excuse my lack of correct terminology) so that a helical beam with OAM is produced. The extra degree of freedom might be in the (x,y) plane so as maintain the direction. I thinking that this would produce a kind of 'tumble' effect. I am not suggesting a full 'tumble', but a fractional one might just offset OAM & SAM enough to produce effects detectable by improved techniques. I have ignored the (x,z) plane...cont
Mimath224
5 / 5 (2) May 21, 2016Layman's rubbish eh? Ha!
Benni
3.3 / 5 (7) May 21, 2016Electro-magnetic waves do not exist at "less than c", a violation of the Mass/Energy Equivalence Principle of Special Relativity better known as: E=mc².
Measurements of c in high gravitational fields is better calculated taking into account the Shapiro Effect by the following equation:
Deflection= GMK/c²ln(R)........ as opposed to 4GM/c²R
Observations of apparent significant deflection suggests that the deflection of light by massive objects can be significant, no proofs have been shown that deflection actually slows photon velocity but only that there is resulting increased trajectory of the flight-path resulting in bent photons producing an observed lagging effect of time due to the angle of observation, thus the curvature of deflected (gravitationally lensed) starlight has a longer flight-path compared to non-deflected starlight from the same distance of the source to the observer.
Mimath224
5 / 5 (3) May 21, 2016Read my brackets too '(as when passing through different mediums)' DEFRACTION, the index water 1.33, diamond 2.42, That is, index =c/(v medium).
The rest of your post talks about SR/GR and the topic here is at quantum level. So you are off topic too.
Mike_Massen
3 / 5 (6) May 22, 2016(also heard this from those who can't do Math :/)
Although its true re special relativity a photon instantly connects one orbital/energy state change to another since time is not relevant for a photon ie Null geodesic etc..
I do see you haven't seen the evidence directly (blind ?) or haven't made the math/physics connection re the functioning of the most pertinent example indirectly (not blind ?) & leapt off into nether regions not connected practically with cause/effect extremely well described by Math & the immense consistency within Physics ?
There are many you tube videos (& great sound btw) that covers the issue of quantum mechanics very well indeed - from introductions, equivalent integer like concepts to complex vector fields etc.
I highly recommend you at least listen to them, even without the benefit of photons ;-)
Phys1
5 / 5 (3) May 22, 2016Nobel Laureate Lamb took this position. I agreed with this until 2 years ago. Now I am convinced that a photon is, like an electron, an object with wave-particle duality.
This is not correct. There are lifetimes (and photon band widths) associated with transitions. There is no such thing as an instantaneous transition.
Mike_Massen
1.8 / 5 (5) May 22, 2016ie To fully appreciate it needs to be from the photon's IRF - time is; non-existent, irrelevant, meaningless or our interpretation re its basis isn't yet understood, relevant math:-
https://en.wikipe...lativity
Tangentially similar to conundrum observed as electron "moves" between orbitals re photon emission/absorption - it effectively traverses space instantly, its maybe a spooky aspect which also has math to describe it & somewhat related to:-
https://en.wikipe...ary_time
Also like the wider view of the phenomenological aspects of the conundrum re Pauli's exclusion principle in respect of electrons - implying there's only one in the whole universe ;-)
Phys1
5 / 5 (1) May 23, 2016An atomic transition is not instantaneous.
Any statement that it is, is wrong.
Mike_Massen
2.6 / 5 (5) May 23, 2016Note, I did refer to photon from *its* IRF, are you saying Special Relativity (SR) as applied to the photon & Null Geodesic (NG) not relevant in respect of my post responding to HyperFuzzy & the link for audience's consideration ?
ie. Where was I wrong re the 2 sentences relevant to the issue in my last post & especially in reference to SR & NG ?
Are you saying its not applicable or it is, can you articulate please ?
Hmm, maybe you object re my comment:- "Tangentially similar..", apologies, maybe a tad obtuse as populist qualitative opinion for wider audience :/
Since you reply, I'm interested in your specific view to quantifying in clear detail as to the complete cycle from perspective of photon's particular IRF, re my postings here:-
t1 e- delay leaving an orbital to
t2 photon emission
t3 passage of photon to another atom
t4 photon absorption to
t5 e- orbital change
Tah
Kedas
not rated yet May 23, 2016ok, from now on h=3.313 e-34 J.s
Now the next generation scientists can curse us for changing its value ;)
techieatwork
1 / 5 (1) May 23, 2016thespinSX
1 / 5 (1) May 23, 2016While you consider that, consider this:
is.gd/impotenceofchance