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Science

Photo First: Light Captured As Both Particle and Wave 136

Posted by samzenpus from the suitable-for-framing dept.
mpicpp sends word that scientists have succeeded in capturing the first-ever snapshot of the dual behavior of light. "It's one of those enduring Zen koans of science that we've all grown up with: Light behaves as both a particle and a wave—at the same time. Einstein taught us that, so we're all generally on board, but to actually understand what it means would require several Ph.D.s and a thorough understanding of quantum physics. What's more, scientists have never been able to devise an experiment that documents light behaving as both a wave and a particle simultaneously. Until now. That's the contention of a team of Swiss and American researchers, who say they've succeeded in capturing the first-ever snapshot of light's dual behavior. Using an advanced electron microscope – one of only two on the planet – at the EPFL labs in Switzerland, the team has generated a kind of quantum photograph of light behaving as both a particle and a wave. The experiment involves firing laser light at a microscopic metallic nanowire, causing light to travel — as a wave — back and forth along the wire. When waves traveling in opposite directions meet, they form a "standing wave" that emits light itself — as particles. By shooting a stream of electrons close to the nanowire, the researchers were able to capture an image that simultaneously demonstrates both the wave-nature and particle-nature of light. 'This experiment demonstrates that, for the first time ever, we can film quantum mechanics — and its paradoxical nature — directly,' says lead researcher Fabrizio Carbone of EPFL, on the lab's project page. The study is to be officially published this week in the journal Nature Communications."
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Photo First: Light Captured As Both Particle and Wave More

Photo First: Light Captured As Both Particle and Wave

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  • not the first time (Score:3, Insightful)

    by Ralph Siegler ( 3506871 ) on Monday March 02, 2015 @04:38PM (#49167255)
    every dual slit experiment shows light behaving as both particle and wave, because every photon only interferes with itself. Two or more photons never interfere with each other.

    • Re: (Score:3)

      by Dins ( 2538550 )
      Maybe it's me, but I thought light behaving as both a particle and a wave was a quantum state. And that quantum state exists until the system is observed and then it collapses into one of two possibilities. Looking that the picture in the link, and...I guess that's not what I was expecting. What am I missing here, physicists? Is the light particle/wave thing not a quantum thing? If it is, that picture doesn't seem like it describes both at once. It almost seems too...cartoony.

      • Re: (Score:2)

        by dj245 ( 732906 )

        Maybe it's me, but I thought light behaving as both a particle and a wave was a quantum state. And that quantum state exists until the system is observed and then it collapses into one of two possibilities. Looking that the picture in the link, and...I guess that's not what I was expecting. What am I missing here, physicists? Is the light particle/wave thing not a quantum thing? If it is, that picture doesn't seem like it describes both at once. It almost seems too...cartoony.

        From my limited understanding, it appears the photo is showing the particle while showing the effects of the wave on the wire. If light particles were rocks, we are seeing a photo of the rock sinking to the bottom of a pond at the same time we are seeing the water being disturbed by waves. In other words, we aren't seeing the light as a wave, only the wavelike effects on another object.

        • Outside the wire, the effect is on the ether.

          Yves Couder provides a macroscopic experiment that duplicates the diffraction patterns of photons self-interfering: Single Particle Diffraction and Interference at a Macroscopic Scale [hekla.ipgp.fr].

          The reason he won't go so far as to say that's what's happening on a quantum level is, that it requires an ether. And we all know that Einstein disproved the ether (actually he just came up with a, supposedly, simpler model).

          • No, Einstein did different things with each of SR and GR. Wikipedia elucidates [wikipedia.org]. The way things stood, after GR, was that there could be an ether, or not, and it didn't matter -- to GR.

            The supposed "disproving" of the ether was merely that it wasn't detected across a number of experiments. But what the "it" was also changed over time. The ether has been proposed as a solid, liquid and gas (and now pure energy, in Spring-And-Loop Theory [just-think-it.com]).

            The debate about the ether is by no means over. Nor has "it" be

      • Re:not the first time (Score:5, Informative)

        by stoborrobots ( 577882 ) on Monday March 02, 2015 @05:00PM (#49167423)

        The wave-particle duality is not a quantum superposition like you're describing (which would break down under measurement), although the caricatured manner in which we teach it might lead you believe that. It's a little more simple than that.

        In our world, we are used to two kinds of things: particles, and waves. We are used to this distinction, and describe most things in one of these manners. Sound is a wave, a billiard ball is a particle, vibrations are waves, bricks are particles. If something is a particle, it has certain properties, like position, size, and shape. If it is a wave, it has certain other properties like wavelength, frequency, and amplitude. In addition, there are some common properties like velocity and direction.

        When it came to studying light (and many other quantum stuffs), we can't directly see what it's made of. But we can take measurements of each "puff" of light, and infer its properties that way. When we do this, we notice that puffs of light have some properties which are particle-like, and some which are wave-like. So the term "particle-wave duality" became popular to describe this new material that was behaving simultaneously like a particle and a wave. It doesn't make sense to ask which one it is - a "puff" of light is neither a particle, nor a wave, but a different kind of stuff which has some properties of each.

        • " It doesn't make sense to ask which one it is - a "puff" of light is neither a particle, nor a wave, but a different kind of stuff which has some properties of each."

          But this is like the Academie Francaise outlawing certain words. It is an academic exercise. Nature, and language, is far more expressive than (some) physicists, and academicians, would have you believe.

          • Of course it's an academic exercise. Physics is academic research.

            I can't figure out your point. And I really can't figure out how it's like L'Académie française.

          • Who's outlawing any words? I think we agree - I'm suggesting we need a new word, because the words we have (wave, particle) are perfectly good but don't describe the thing we want (nature of light)...

        • Re: (Score:2)

          by bondsbw ( 888959 )

          Great response. I never thought of it that way, but it makes much more sense the way you put it.

          Light is simply different.

        • Re: (Score:3, Interesting)

          by WillgasM ( 1646719 )
          The brick is also a wave, it's just such a complex wave that it would be nearly impossible to express in those terms (it's just a sum of all its subatomic parts, after all). If we could express a brick in terms of a wave, the values would just be endless strings of numbers that make little sense to our human brains. Then, lets say we devise a way to visualize those values in a form more palatable for human consumption; you'd end up with a picture of a brick.

        • Re: (Score:2)

          by McWilde ( 643703 )

          a different kind of stuff which has some properties of each.

          Isn't the general idea that light has all the properties of each?

          • Isn't the general idea that light has all the properties of each?

            Some of the properties are mutually exclusive. For example, a wave requires a medium of transmission (such as water) but a particle doesn't (boats exist independently of water).

        • Any other particle behaves the same way. The dual slit experiment can be done with electrons instead of photons, and you get the same result. A particle IS something that shows up in one place when you try to figure out where it is, but travels as a wave until you try to detect it. That's how particles can interfere with themselves: the probability waves travel through space and determine the likelihood of the particle appearing in any place. Photons are no different from other particles in this way.

          So ligh

      • We can observe both particle and wave behavior at the same time. For example, a solid state detector system can pick up the photons from a dual slit experiment, and a famous variation is to send photon at a time to a two slit configuration. Over time the photons still land on "bright" parts of interference pattern but were detected individually as particles.

    • Re: (Score:2)

      by jandrese ( 485 )
      This. The wave particle duality is the whole point of the double slit experiment, and it is mindblowing when you go down the path that led up to that experiment.

    • every dual slit experiment shows light behaving as both particle and wave

      Yes, but not at the same time. The light behaves like a wave as it travels, and interferes with itself. Then it behaves like a particle when it illuminates the backstop. But one happens after the other. In this experiment, the light, supposedly, can be observed acting like both a wave and a particle simultaneously, not sequentially.

    • every dual slit experiment shows light behaving as both particle and wave, because every photon only interferes with itself. Two or more photons never interfere with each other.

      Uhh, yes they do? All the time? Hell, I could have laser beams from two completely independent sources and generate an interference pattern. The dual slit experiment shows absolutely nothing about the wave/particle duality of light, and is in fact absolutely completely 100% explained by classical electromagnetism. Seriously, this comment is simply dead wrong. The dual-slit experiment in it's classical form only shows that something is propagating as a wave, not anything about the particle nature (of course,

      • Wrong, it's a famous conclusion by Dirac, verified by many experiments, that even with your two lasers a photon can only interfere with itself, *two different photons never interfere with each other*.

    • every dual slit experiment shows light behaving as both particle and wave, because every photon only interferes with itself. Two or more photons never interfere with each other.

      If you want to see two photons interfering in a double slit experiment you don't have to do anything more complex that direct a laser pointer at a narrow slit. This is generally what happens in almost all double slit experiments ever performed by school kids and undergrads to demonstrate diffraction. You are talking about a special version of it to show that photons self-interfere but this does not exclude them interfering with other photons if there are some present.

      • Nope. That only demonstrates a large amount of photons self-interacting. Proven many times since Dirac first declared photons only self-interact. The only thing near to a photon-photon interaction are under certain high energy conditions where they transform into pairs of other particles first, and those interact. These conditions are not present in two-slit experiments.

  • It's the measurement (Score:5, Informative)

    by thebes ( 663586 ) on Monday March 02, 2015 @04:42PM (#49167269)

    If you attempt to measure it in the way you would measure a wave, it will present itself as a wave.

    If you attempt to measure it in the way you would measure a particle, it will present itself as a particle.

    Light doesn't choose to be a particle or a wave at any given time, the measurement we use defines the characteristics it has. Nothing more, nothing less.

    • Yup . prior to observation it is neither particle or wave . It is perhaps a string .

      • And yet, the photograph shows both!

        The "it's neither, not both" argument is sophistry, an attempt to rescue the law of non-contradiction from its clear empirical violation.

        • Re: (Score:1)

          by Anonymous Coward
          Except there is no contradiction, and experiments can be explained by a single, consistent theory of quantum mechanics. The only time a contradiction or paradox is involved is when you either assume or force classical descriptions on things. The whole wave-particle paradox is an artificial paradox, not a contradiction in observations or even modern (as of almost 100 years ago) theory, but a contradiction in people's intuitive, gut tendency to pigeonhole things.

    • Re: (Score:2, Funny)

      by Anonymous Coward
      In that case, I'm going to attempt to measure it in the way I would measure Mila Kunis.

    • Re:It's the measurement (Score:5, Insightful)

      by Anonymous Coward on Monday March 02, 2015 @05:29PM (#49167565)

      I wish physicists would stop using the word "measurement" when talking about quantum mechanics. To detect fundamental particles we have to interact with them in an intrusive or destructive way. It's not like putting a rock on a scale to measure its weight or putting a ruler to a golf ball. We don't get to keep the original particle after we're done. It's more like colliding snowballs with other snowballs to probe their properties. You destroy or transform them in the process. If this was how we conveyed the concepts, the quantum ideas would become a lot more understandable.

      • Re: (Score:2)

        by slew ( 2918 )

        I wish physicists would stop using the word "measurement" when talking about quantum mechanics. To detect fundamental particles we have to interact with them in an intrusive or destructive way. It's not like putting a rock on a scale to measure its weight or putting a ruler to a golf ball. We don't get to keep the original particle after we're done. It's more like colliding snowballs with other snowballs to probe their properties. You destroy or transform them in the process. If this was how we conveyed the concepts, the quantum ideas would become a lot more understandable.

        Well, except for that QM entanglement thing...

        It's a bit difficult to explain QM entanglement except in reference to a conserved property (say spin) and a subsequent measurement (to deduce the partial QM state in an entangled system).

        Also, I don't know if it's really possible to "understand" QM in a way that is intuitive...

        I am going to tell you what nature behaves like. If you will simply admit that maybe she does behave like this, you will find her a delightful, entrancing thing. Do not keep saying to yourself, if you can possibly avoid it, ‘but how can it be like that?’ because you will get ‘down the drain,’ into a blind alley from which nobody has yet escaped. Nobody knows how it can be like that.
        -- Richard Feynman

        I would venture to guess most of us on /. comprehend far less of QM than Mr Feynman...

        • You can explain part of quantum entanglement by comparing it to two envelopes, one containing a black card and one a red, and that opening one envelope tells you what's in the other. That's at least useful for showing why it can't carry information faster than light.

          Explaining what happens when you open the envelopes at different angles is where it gets difficult. (You turn your envelope 90 degrees before opening it, I open mine in the original orientation, and you have no idea whether I've got red or

      • I wish physicists would stop using the word "measurement" when talking about quantum mechanics....We don't get to keep the original particle after we're done.

        Actually that is not true if you go to high enough energy: have a look at this [atlas.ch]. Those four tracks coming out of the centre of the ATLAS detector at the LHC are muons, a heavy cousin of the electron. The muons are neither stopped nor destroyed by the detector but they do lose a little of their energy as they pass through it but for high energy particles this really is a very small, non-instrusive fraction of their energy. We can even use the curvature of the track in ATLAS' magnetic fields to measure the mo

      • Re: (Score:2)

        by Altrag ( 195300 )

        I don't suppose you plan on being the one to coin a new term then? Preferably one that isn't even more confusing -- especially for the physicists who've been using the term "measurement" since long before quantum mechanics was discovered.

        Aside from that, where was it ever claimed that measurements had to be non-destructive? If I want to measure the explosive power of a bomb, I sure as hell won't be recovering it after I'm done (at least not in one piece!) Or if we want to stick with high school physics,

      • Re: (Score:1)

        by Tablizer ( 95088 )

        I wish physicists would stop using the word "measurement" when talking about quantum mechanics. To detect fundamental particles we have to interact with them in an intrusive or destructive way.

        Hmmm, strangely like the Middle East.

      • Re: (Score:2)

        by thebes ( 663586 )

        Using a somewhat related example: all "measurements" we perform on macro objects are identical to those on quantum objects, but the relative scale of effects are drastically different. How do you "measure the color of grass"? Fire a few photons of different wavelengths at it, and see which photons come back. At a macro scale, we may not thing we changed the grass, but you can be sure we did. We changed the momentum of the blade of grass, the position, etc by a small but finite degree.

        You have attempted to c

  • The wave or the particle? .. i'm for the wave
  • Would someone kindly dumb down the summary a touch?

    • Re:My brain is full (Score:4, Informative)

      by youngone ( 975102 ) on Monday March 02, 2015 @04:52PM (#49167345)
      There's no way of doing that. Feynman said "I think I can safely say that nobody understands quantum mechanics". You've probably got no chance. :-)
    • A group of physicist-journalists have done an interesting experiment to show how light trapped in a tiny wave guide interacts with electrons. They then massively overhyped the results by making claims that are highly dubious at best in order to gain attention.

  • > Light Captured As Both Particle and Wave

    Well, thanks. I'm glad the universe didn't telefrag.

  • 3-D to 2-D display (Score:5, Insightful)

    by Camel Pilot ( 78781 ) on Monday March 02, 2015 @04:46PM (#49167309) Homepage Journal

    From the fine article it provides a caption to the graphic

    "The bottom "slice" of the image shows the particles, while the top image shows light as a wave""

    Looking at the graphic the top image is a 3-D display and the bottom just a color coded 2-D representation with topo lines. I see nothing in this displaying the wave aspect and particle aspect. Mistake?

    • Re: (Score:1)

      by Anonymous Coward

      Yes, the mistake was expecting real information from the popular science press.

    • Re: (Score:2)

      by mlkj ( 3794193 )

      Have a quote from the original article :

      The scientists shot a stream of electrons close to the nanowire, using them to image the standing wave of light. As the electrons interacted with the confined light on the nanowire, they either sped up or slowed down. Using the ultrafast microscope to image the position where this change in speed occurred, Carbone’s team could now visualize the standing wave, which acts as a fingerprint of the wave-nature of light.

      While this phenomenon shows the wave-like nature

      • Note: Is anyone aware of a term for photos taken with electrons (or anything that isn't photons) ?

        Electrographs?

        • Re: (Score:1)

          by Anonymous Coward

          Electron micrograph is often used.

  • Seen it b4. But not meh. (Score:3)

    by 140Mandak262Jamuna ( 970587 ) on Monday March 02, 2015 @04:59PM (#49167417) Journal
    I have seen these images so many times before. Standing waves, traveling waves, plane polarized wave entering a ferrite core and its plane of polarization turning and twisting, all in glorious 24 bit color. But all those images and animations came from Ansoft High Frequency Structure Simulator software. Not actual experimental physically observed phenomena. And not at light frequencies. Microwave wavelengths mostly. So seen it so many times before, but definitely not meh.

  • Several Ph.D.s? (Score:4, Insightful)

    by TechyImmigrant ( 175943 ) on Monday March 02, 2015 @05:03PM (#49167449) Homepage Journal

    > but to actually understand what it means would require several Ph.D.s and a thorough understanding of quantum physics

    No, just some understanding of statistics and calculus up to tensors along with an ability to know why you know something rather than just knowing things.

    When we make out relatively simple things (like quantum physics) to be complex, when in fact they are just strange we do a disservice to those who might otherwise put in the effort to understand.

    • Re: (Score:2)

      by GuB-42 ( 2483988 )

      The hard part of quantum physics is not the maths, it is the interpretation.
      We have formulas that work, you can apply them and predict the results of experiments, they can be used to design microprocessors, etc... But it is just manipulating numbers. Having a gut feeling of what it means in human terms is so much harder that even the best scientists cannot agree on an interpretation.

      There are areas like fluid dynamics where the maths are not easier, however it is easy to visualize things like air swirling a

  • This attitude pisses me off (Score:5, Interesting)

    by crioca ( 1394491 ) on Monday March 02, 2015 @05:39PM (#49167609)

    Light behaves as both a particle and a wave—at the same time. Einstein taught us that, so we're all generally on board, but to actually understand what it means would require several Ph.D.s and a thorough understanding of quantum physics

    Stop pretending physics is spooooky. It's not that difficult to understand, at least at a superficial level. And I don't have a degree, let a lone a Ph.D, but even I can explain it (again, superficially):

    Time dilation means that the faster you go, the slower time goes. If you're travelling at the speed of light in a vacuum, then the speed at which you're travelling through time is slowed infinitely. This means a photon experiences no passing of time between the moment it is created, and the moment it collides with something.

    But the speed of light is finite, so it has to travel through time to go between two points. But because from the photon's perspective it's travel is instantaneous, it can't experience that time. So a photon doesn't know where it's going to land, until it does. And so until it does land, it could have landed anywhere. So when a photon is created, it travels out in all directions, like a wave, until it lands somewhere and the wave collapses.

    The part that's hard to understand is the why.

    • If you're travelling at the speed of light in a vacuum, then the speed at which you're travelling through time is slowed infinitely.

      But wave-particle duality also applies to particles traveling slower than c, so it has nothing to do with traveling at light speed.

      • Re: (Score:2)

        by Livius ( 318358 )

        That's the interesting part, but far too many times people will try to explain quantum 'spookiness' and end up just demonstrating special relativity.

    • Superficial knowledge of science can make real knowledge next to impossible. Learning things can be quite difficult but trying to unlearn things can defeat giants.

    • Re: (Score:2)

      by slew ( 2918 )

      But the speed of light is finite, so it has to travel through time to go between two points. But because from the photon's perspective it's travel is instantaneous, it can't experience that time. So a photon doesn't know where it's going to land, until it does. And so until it does land, it could have landed anywhere. So when a photon is created, it travels out in all directions, like a wave, until it lands somewhere and the wave collapses.

      Yes, and no... another way to think of it is that from the frame of reference of the photon, it doesn't really need to "travel" at all (with infinite time dilation, comes infinite length contraction).

      It sort of brings new way to think about the phrase, no matter where you go, there you are... (Buckaroo Banzai paraphrasing Confucius)...

      Another thing to think about it is that a photon really is never really a particle or wave but simply an artifact of book-keeping energy in an electromagnetic field (or perhap

    • Unless you have an isotopic source of photons (point source) the photons will have preferential directions. Not that the probability is exactly zero for some directions, but for a flashlight style beam the chance a photon will make it through the reflector, battery, case, and perhaps part of your hand is quite low.

  • I had no idea photons were so colorful.

  • https://www.youtube.com/watch?... [youtube.com]

    What another groan worthy /. summary. It's not the standing waves that equate to photons. The only thing photonic here is the quantum exchange between the light field and the electrons used for imaging.

    And no, you don't need to have several PhDs to understand this, reading the articles at the links totally suffices.

  • Misleading summary (Score:3)

    by burtosis ( 1124179 ) on Tuesday March 03, 2015 @12:56AM (#49169471)
    It is not theoretically possible to both capture a single photon as both a wave and particle simeltaneously. What they have done is show a set of thousands (millions?) of electron photon interactions at the same instant in time arranged on 2 axis. Basically the lower and slower lumps become particles and the upper smoother lines show waves. So its neat and a first for light waves afaik but misleading as it is not a photo of a single photon.

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