First photograph of light as both a particle and wave

[Greg Bernhardt]

I think this is really neat! Anyone with thoughts about it?

(Phys.org)—Light behaves both as a particle and as a wave. Since the days of Einstein, scientists have been trying to directly observe both of these aspects of light at the same time. Now, scientists at EPFL have succeeded in capturing the first-ever snapshot of this dual behavior.

http://phys.org/news/2015-03-particle.html

 

[kq6up]

In reference to this article:

http://phys.org/news/2015-03-particle.html

I don't understand how this is any different than using a photographic emulsion to capture a diffraction pattern. Since my understanding of the photochemical process that reduces Silver Halides requires two photons over a certain decay time to reduce a silver atom in a Silver Halide crystal lattice. Therefore the principle seems to work the same. Any thoughts guys/gals?

Chris

 

[jedishrfu]

Pretty cool!

 

[Jazzdude]

As far as I understand, they're looking at a many photon state and they're measuring the semiclassical classical field interaction together with discrete momentum transfer. I don't see how that would allow for their bold claims or in fact be any different from observing the Compton effect while measuring the classical EM field.

So no surprises for me as a theorist. But maybe someone can enlighten me or point me to the experimental aspects that I'm missing.

 

[mfb]

an experiment with a clever twist: using electrons to image light

How revolutionary! Okay, all eyes and all photographic devices ever evolved/built use electrons...
Fine, they used free electrons, that is not so common.

I do not see anything fundamentally new here. Every diffraction pattern hitting a sufficiently sensitive detector does the same, just with bound electrons instead of free electrons.

 

[ellipsis]

The power of marketing: replace

"capturing a photographic emulsion, and deriving a computer-generated image from those results based on mathematical models"

to

"First photograph of light as both a particle and a wave!"

and you become successful. Nobody calls you out on it because few people are confident enough on the subject matter to do so.

 

[tijana]

Absolutely beautiful.
Now this pic in primary schools.

 

[atyy]

http://www.nature.com/ncomms/2015/150302/ncomms7407/full/ncomms7407.html
Simultaneous observation of the quantization and the interference pattern of a plasmonic near-field
L Piazza, T.T.A. Lummen, E Quiñonez, Y Murooka, B.W. Reed,B Barwick & F Carbone
Nature Communications 6, 6407
Surface plasmon polaritons can confine electromagnetic fields in subwavelength spaces and are of interest for photonics, optical data storage devices and biosensing applications. In analogy to photons, they exhibit wave–particle duality, whose different aspects have recently been observed in separate tailored experiments. Here we demonstrate the ability of ultrafast transmission electron microscopy to simultaneously image both the spatial interference and the quantization of such confined plasmonic fields. Our experiments are accomplished by spatiotemporally overlapping electron and light pulses on a single nanowire suspended on a graphene film. The resulting energy exchange between single electrons and the quanta of the photoinduced near-field is imaged synchronously with its spatial interference pattern. This methodology enables the control and visualization of plasmonic fields at the nanoscale, providing a promising tool for understanding the fundamental properties of confined electromagnetic fields and the development of advanced photonic circuits.

 

[TrickyDicky]

So much for the Complementarity principle.

 

[Ranvir]

It might be a good time to point out that light, or for that matter any quantum mechanical entity, is neither a particle nor a wave they just follow equations which, in a classical sense, are attributed to waves and particles. It's time we stop publicizing interesting experiments like this in a pseudo-scientific fashion and throw some 'light' on the the real quantum physics for the masses.

 

[elierd jay]

I think this is really neat! Anyone with thoughts about it?
http://phys.org/news/2015-03-particle.html

View attachment 79827

does it follows pattern?

 

[Shri13]

Hi this pic looks cool, but I am still learning high school physics and very curious to learn. Can anyone elaborate the pic please?
How is that pic taken?
What are those bulges which looks like waves?
How is this pic showing both particle as well as wave nature simultaneously? (Means how I can see both natures in these pic)

Sorry if I am poking my nose in the experts thread

Thank you in advance.

 

[elierd jay]

Hi this pic looks cool, but I am still learning high school physics and very curious to learn. Can anyone elaborate the pic please?
How is that pic taken?
What are those bulges which looks like waves?
How is this pic showing both particle as well as wave nature simultaneously? (Means how I can see both natures in these pic)

Sorry if I am poking my nose in the experts thread

Thank you in advance.

me nether, still first year college. ... the evidences of light as a wave-particle are explained by refraction or reflection of light into a medium. also light has the property almost of the electron, that's why scientist use electron to identify if light has particle property, if light is not a particle there would be no effect. by proving the wave property of light, scientist provide a thin slit where light can pass, so that light will be as a thin sheet of ray and it form diffraction phenomenon and is describe as the interference of wave according to Huygens Fresnel principle. as you can see on the image, the blue part rises, this is because there is an encounter between light and electron, if two balls hit each other there will be a change of direction, depending on the forces of each ball. hope my explanation helps... well the color tells the us the energy...

 

[tijana]

Hi this pic looks cool, but I am still learning high school physics and very curious to learn. Can anyone elaborate the pic please?
How is that pic taken?
What are those bulges which looks like waves?
How is this pic showing both particle as well as wave nature simultaneously? (Means how I can see both natures in these pic)

Sorry if I am poking my nose in the experts thread

Thank you in advance.

As I see it I am not an expert also. It is just like you through rock in the pond. So you see the waves it produce it.

 

[Mabel]

It might be a good time to point out that light, or for that matter any quantum mechanical entity, is neither a particle nor a wave they just follow equations which, in a classical sense, are attributed to waves and particles. It's time we stop publicizing interesting experiments like this in a pseudo-scientific fashion and throw some 'light' on the the real quantum physics for the masses.

I question your basic concept that light is neither a particle or a wave. Since we DO see photons behaving as particles in bubble changers in pair production. This is NOT an equation. It is experimental OBSERVATION. As for wave, I leave that to someone else.

 

[phinds]

I question your basic concept that light is neither a particle or a wave.

Then you should continue your studies until you get to the part where this is explained. Light ACTS like a particle and ACTS like a wave but it is neither one. It is a quantum object.

 

[Gort]

The argument on the nature of light is part of the argument - can we ever determine the true "nature" of nature? Physics develops models which explain observation. If the model closely matches observation (under particular circumstances or initial conditions), then it's a good model. Wave theory is a good model of light (under certain circumstances). Particle physics (of which photons form a part) is a good model, too. So what is "light"? Physics cannot answer that question! To get into models a bit deeper, consider Quantum Field Theory. The wave nature of light is part of that theory. QFT considers all of nature as excitations of "fields". What, exactly, are "fields"? No one knows! But the mathematics works well enough that QFT can accurately describe much of nature. What about Quantum Electrodynamics (QED)? For a long time, Feynman was convinced that photons and electrons (and their interactions) are explained only in terms of particles taking different paths in space and time (and summing those paths). That works well, too - so well that the electromagnetic fine structure constant is predicted by QED to within 10^-8 of the observed value. So are photons particles? Do some photons travel at less than c, others at greater than c, and not in a straight line in space-time? At least that's what QED says, and it makes accurate predictions! So is light just a particle of "energy"? No one knows! Physics can't even define "particle" or define "energy" (even though QFT starts with describing a system by the Lagrangian - the difference between kinetic and potential energy). So all of this simply says - physics doesn't provide answers into the true nature of reality. Physics provides mathematical models to describe observation. That's all. IMHO.

 

[Derek Potter]

In reference to this article:

http://phys.org/news/2015-03-particle.html

I don't understand how this is any different than using a photographic emulsion to capture a diffraction pattern. Since my understanding of the photochemical process that reduces Silver Halides requires two photons over a certain decay time to reduce a silver atom in a Silver Halide crystal lattice. Therefore the principle seems to work the same. Any thoughts guys/gals?

Chris

I don't think silver halide photography needs two photons but even if it did you could pre-expose the film so that a good number of grains only needed one more photon. So I agree except that it's even simpler than you say

 

[Derek Potter]

Then you should continue your studies until you get to the part where this is explained. Light ACTS like a particle and ACTS like a wave but it is neither one. It is a quantum object.

If it looks like a duck, swims like a duck, and quacks like a duck, then it probably is a duck.

 

[Gort]

I would add "and has the DNA of a duck..." But ducks are not "fundamental" - they are (presumably) composed of many fundamental "things" or "entities". While it is easy to define macro objects (they 'are' because we say they 'are'), it is not so easy to define the true nature of fundamental entities. I can't even call those entities particles, waves, fields, energy, or anything else, because we simply don't know.

 

[Derek Potter]

I would add "and has the DNA of a duck..." But ducks are not "fundamental" - they are (presumably) composed of many fundamental "things" or "entities". While it is easy to define macro objects (they 'are' because we say they 'are'), it is not so easy to define the true nature of fundamental entities. I can't even call those entities particles, waves, fields, energy, or anything else, because we simply don't know.

In that case it can't be a quantum object either as we have no macro concept of such things. "Quantum object" becomes a catch-all for "ducking" the question

 

[Gort]

I agree. I wouldn't call light a wave, a particle, a quantum object, or even a duck. Because that would imply we somehow understand it. We don't. Continue to call it "light". Or a wave if we're doing optics. Or a photon if we're doing spectroscopy. But be clear - we don't understand its 'true' nature (if it even has one).

 

[tijana]

The main problem is we are talking about QM but at the end we have to do classical physics experiments in order to explain it to another person. That is a trouble.

 

[Derek Potter]

The main problem is we are talking about QM but at the end we have to do classical physics experiments in order to explain it to another person. That is a trouble.

I don't see why it's a trouble. It means there is continuity between QM and classical. That should be encouraging.

 

[Gort]

Point well taken. That, perhaps, is our limitation and why we may not get answers to the fundamental nature of reality. We can, of course, devise experiments which try to get at the QM nature of things. We can measure QM tunneling across a superconducting Josephson junction, but we're really measuring the current through an ammeter. And we infer (through a model) that a complex order parameter field (field theory) and Cooper pairs (particle physics) are responsible. We can even use these results to build SQUIDs - to measure magnetic fields. All the while not knowing what the basic building blocks of the SQUID really are - or even what a "magnetic field" really is.

So we, as macro beings, can use a lot of physics without understanding the real nature of things. And we don't have to, either. But I was taught that's the goal of physics - to understand nature. Her true reality. I've now changed my view. We model nature. Perhaps (with a big Maybe) if we were quantum beings (instead of classical ones) and lived in 10, 11, or 20 dimensions (instead of 4) we might be able to devise experiments which would get answers to the fundamental questions.

I guess that's my pet peeve. When physics papers say that "particles are composed of strings" or "the Big Bang happened 13.7 billion years ago", or...etc. Every paper should start out with "Our model predicts..." and it should be made clear that it's a model.

 

[tijana]

Encouraging enough yes. Even conservative like Plank had to introduce quanta in order to explain experiments,although he was concentrated to "small" problem.

Changing your way of thinking is hard, even a small step.Lots of stumble in this area ( A.Einstein and many others).
Even today after 100 years we see that changing or "enlightenment " of mind maybe is waiting for evolution of mankind. Although I would not go that far now.

 

[mfb]

That works well, too - so well that the electromagnetic fine structure constant is predicted by QED to within 10^-8 of the observed value.

The value of the fine structure constant is not predicted at all. It is a purely experimental value. Different measurement methods agree with incredible precision, however.

 

[Derek Potter]

So we, as macro beings, can use a lot of physics without understanding the real nature of things.

We happen to be born with a tendency to make sense of the world in a certain way. When this inherited "common sense" breaks down, we create abstract models. No-one is claiming any metaphysical insight into Ultimate Reality, it is sufficient to say that a concept which works satisfactorily must refer, directly or indirectly, to something that exists. An entity *is* that which is described by its attributes. A child may describe an elephant as a big animal with a trunk and so it is; and I'll stick with photons being real particles which display wave-like characteristics due to QM.

Not that I wish to be polemical about it of course

 

[Gort]

The value of the fine structure constant is not predicted at all. It is a purely experimental value. Different measurement methods agree with incredible precision, however.

I hope this isn't getting too far off-topic (from the wave-particle duality question). There's a course offered by the Institute for Theoretical Physics in Zurich - entitled "Particle Physics Phenomenology 1". Chapter 6 deals with tests of QED. See http://www.itp.phys.ethz.ch/education/hs10/ppp1/PPP1_6.pdf . It says the "precision tests of the theory [QED] which usually consist in the measurement of the electromagnetic fine structure constant α in different systems. Experimental results are compared with theoretical predictions. The validation process requires very high precision in both measurements and theoretical calculations. QED is then confirmed to the extent that these measurements of α from different physical sources agree with each other. The most stringent test of QED is given by the measurement of the electron magnetic moment."

So I believe QED does make predictions. It's based on multiple QED loops. But I only bring this up to show there are multiple ways to get "nearly correct" answers. None is necessarily right or wrong. But I hate it when someone says "Light is BOTH waves and particles - it's been photographed!" Hogwash.

 

[mfb]

The theory predictions are just the relation between the fine-structure constant and the measured quantity. Theory alone cannot make any prediction for the value.

QED is then confirmed to the extent that these measurements of α from different physical sources agree with each other.

This is the important part.

 

[Gort]

Agreed. Good point.

 

[Science2020]

neat...

 

[bhobba]

I guess that's my pet peeve. When physics papers say that "particles are composed of strings" or "the Big Bang happened 13.7 billion years ago", or...etc. Every paper should start out with "Our model predicts..." and it should be made clear that it's a model.

I think that's more or less assumed.

Things like 'understand', 'reality' etc etc are all basically big question marks in philosophy that no consensus has ever been reached.

Physics bypasses all that with a bit of common sense. Reality is what our models describe. Understanding is we have a model that's supported by experiment. Good old Euclidean geometry is the template. Points and lines are its primitives - their definitions don't really mean much in a rigorous sense - points are supposed to have position and no size - lines length but no breath - such don't really exist - but as the theory is developed and applied you get a feel for what they mean. But the theory can't define it exactly - its a primitive of the theory. The same with QM. A primitive is an observation - you can't rigorously define it in the theory in a practical way - you can abstractly and advanced texts do - but applying it requires a bit of intuition - like point and lines in Euclidean geometry do.

There are extremists like Penrose that think the math is literally the reality - but most don't go that far - it simply describes it leaving what reality is up in the air because more simply isn't required.

Thanks
Bill

 

[Gort]

Reality is what our models describe.
Bill

I would submit that "Observation is what our models describe". Reality is the Holy Grail. This thread started from an article which described an "experiment able to capture both natures of light". That implies that light HAS two natures. That's simply not true, or at least misleading. I don't know the "nature of light" and I don't think the researchers reporting this experiment do, either.
Perhaps we, as physicists, understand the subtleties. But perhaps not. And the lay public is even more susceptible to blindly believe grandiose statements of "fact" by the scientific community.

 

[Derek Potter]

The experiment doesn't demonstrate anything about the nature of light anyway. That's the province of particle phycics. It just demonstrates that light is subject to QM like everything else.