• Question: In your opinion, is light a wave or a particle and why?

    Asked by lucyb to Ben, Jony, Katharine, Mark, Peter on 14 Nov 2011. This question was also asked by testtubelover.
    • Photo: Mark Basham

      Mark Basham answered on 13 Nov 2011:

      Hi lucyb

      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.

      Mark

    • Photo: Ben Still

      Ben Still answered on 14 Nov 2011:

      Everything is both, not just light. Light, electrons, protons – they are particles when 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.

    • Photo: Peter Williams

      Peter Williams answered on 14 Nov 2011:

      ben’s got there first! It’s both. that’s a real cop out isn’t it – sorry.

      and it’s not just light. electrons are also both particles and waves. look up a technique called “electron diffraction”

      the best way to understand wave/particle duality it is to think about the “Young’s slits” experiment. Then go away and do something else. Then come back a few days later and think about it again. I’m still thinking about it years after i first heard about it. Pretty much everything in the quantum world can be explained in terms of the Young’s slit experiment.

      Here’s my quick precis: the light travel from a source to a screen, but in between is a card with two slits in it. it helps if the distance between the slits is a few times the wavelength of the light. on the screen you see patterns of dark and light lines – like a barcode. this is called an interference pattern and occurs with any wave phenomena. there’s a nice picture here and a video here http://www.youtube.com/watch?v=dNx70orCPnA

      Now the wierd thing is what happens when you turn the intensity of the light down. these days we can measure the energy of an individual particle of light leaving a source – a photon. so you make the source such that it emits only one photon at a time – maybe only one a second, or minute. The photons travel one at a time to the screen, and you’d think that they would have to choose to go through one slit or the other (or none). Then after a while you add up the positions of all the photons on the screen, you would expect to see a distribution that is just the sum of individual distributions from each slit on it’s own, and no interference. But that’s not what happens – you still see an interference pattern!

      So each INDIVIDUAL PHOTON must travel through BOTH slits at the same time. How wierd is that. Remember that all of modern electronics is based on the same physics.

      For extra credit: What happens for three slits?

    • Photo: Jony Hudson

      Jony Hudson answered on 14 Nov 2011:

      Hi LucyB,

      take a look at my answer to ninjaboy:

      /subatomicn11-zone/2011/11/is-light-considered-more-of-a-particle-or-more-of-a-wave

      Jony

    • Photo: Katharine Schofield

      Katharine Schofield answered on 14 Nov 2011:

      Hi lucyb – see my answer to ninjaboy here: http://ias.im/63.45
      Katharine

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