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Asked by ninjaboy to Ben, Jony, Katharine, Mark, Peter on 14 Nov 2011.
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Mark Basham answered on 13 Nov 2011:
More Tricky questions here.
When we deal with x-ray light at diamond we have to consider both parts of the wave particle duality to design the experiments. It is the wave properties of light which allow us to focus the x-ray beam, and its also the wave properties which let us understand how the light interacts with the scientific sample we are interested in.
But when we detect the light, we make use of the particle properties. So we can measure the position or energy of individual photons.
So for me light is equally a particle and a wave.
Hope this helps
Mark
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Ben Still answered on 14 Nov 2011:
Everything around us is both particle and wave, not just light. Light (photons), electrons, protons – they are particles when only they interact with each other, in-between times they are waves.
When you go to the smallest things in Nature nothing is certain, almost everything is possible. The Universe becomes a haze of possibilities; the wave like state of things. We cannot directly ‘see’ this wave like behaviour as we can only sample the haze of possibilities when we distil a particle out of the haze by interacting with it; viewing it with light (photons) or other particles.
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Jony Hudson answered on 14 Nov 2011:
Yeah, I’d agree with the others. Well, sort of.
Light is light. I know it sounds silly, but that’s what it is, and it’s not really a particle or a wave, it’s light!
The problem is, when you find something really new, you have to describe it. And the only words and concepts that you have to describe it are ones that describe things that you already know about. So when you discover something totally new like the quantum mechanical behaviour of light you’re a bit stuck because none of the words or concepts you’ve got do a good job of describing it.
This was the problem they had when they invented quantum mechanics. They had to use all of the old language to describe something that couldn’t really be described in it. So they ended up talking about daft and mysterious things like wave-particle duality and the like. It makes it sounds all weird and paradoxical, but actually it’s normal and whatever-the-opposite-of-paradoxical is. It’s just really hard to describe it with our puny human langauge!
People often say “isn’t it weird that light behaves like this?”. I’d answer “isn’t it weird that you thought something that you’d never looked at, something completely unknown and new, would behave just like all of the things you’re used to?” !!! 🙂
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Peter Williams answered on 14 Nov 2011:
I’ve answered this one here – http://ias.im/63.36
In short, both and yet neither 😉 -
Katharine Schofield answered on 14 Nov 2011:
Hi ninjaboy
I’m going to sit sqarely on the fence here and say it’s both and it’s neither. There’s been centuries of hot debate on this issue, where one camp seemed to be winning out over the other as different experiments demonstrated different properties of light. (see for example Young’s double slit experiment, the photoelectric effect, blackbody radiation etc). In the end everyone kind of had to compromise and say ok, it’s got aspects of both depending on what type of property you’re measuring.
I don’t really think that wave/particle duality concept is an especially great way to picture it. Scientists try to find ‘real world’ comparisons for things to try to explain them to people, sometimes it helps but sometimes it gets in the way. I felt much more reassured about all this when I was studying physics at uni and realised that you can write down equations which match exactly what’s observed in experiments.
I think someone mentioned in the chat room this morning that you’d been looking at the photoelectric effect? That’s a really neat way to show the quantum nature of light – that is, that the energy of the light comes in little packages (quanta). It was found that if you shine light on a metal, sometimes electrons are emitted and sometimes they’re not, even if you turn up the intensity of the light so that it’s really bright. So for example, dim blue light might cause a current to flow but a really bright red light won’t. That’s because each individual photon in the blue light has more energy than each individual photon on the red light (the bright red light simply has more photons per unit area than the dim blue light). This shows that the energy doesn’t get absorbed continuously, otherwise the electrons would eventually gather enough energy from the red light to escape. Instead, the electrons absorb a whole package (a whole quantum) of energy, and if it’s enough the electron escapes (and uses any left over as kinetic energy). If the package of energy isn’t enough, the electron absorbs it and re-emits it but can’t use it to escape. This whole idea of discrete packets as opposed to continuous values is fundamental to quantum physics, and this experiment is one of the reasons that people sometimes think of light as a particle rather than a wave.
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