• Question: Does light have size?

    Asked by ttturner to James, Marcus, Martin, Rob, Suzanne on 16 Mar 2012.
    • Photo: Marcus Gallagher-Jones

      Marcus Gallagher-Jones answered on 16 Mar 2012:

      Thats a tricky question though i don’t think you could consider light to have a size. The best way to think of light is by it’s wavelength. The height of a wave is not so important for lights properties but the length is. Light can take a large range of wavelengths, from the very long, radio waves which are also light can be as long as 10,000,000 metres, to the very short, X-rays can have a wavelength less than a billionth of a mm. Only a very short portion of this is actually visible to us though. Visible light ranges between 400nm (blue) to 700nm (red). These wavelengths are what you see as a rainbow when white light passes through water droplets in the air, the different wavelengths are bent, or refracted, by water by slightly different amounts allowing them to be separated.

    • Photo: Martin Zaltz Austwick

      Martin Zaltz Austwick answered on 16 Mar 2012:

      Light doesn’t really have size, but you could say the same thing about matter! Something which is “point-like” – exist at a particular point in space – is so small it may as well not exist! You can say things about where a ray of light is, but not very precisely (e.g. that it’s in a room!).

    • Photo: Suzanne McEndoo

      Suzanne McEndoo answered on 18 Mar 2012:

      It is hard to say. If you trap a particle of light between two mirrors, it will fill all the space between the mirrors, so you can kinda say that the light is as big as the distance between the mirrors.

      Of course, no mirrors are perfect, so at some point the light will escape. Because of quantum physics, there’s always a bit of uncertainty about when the light escaped, so we know it escaped between one time and another time. Because light is so fast, that means the size of the light can stretch out to really huge sizes as it escaped. On the other hand, when you detect light, it shrinks again to the size of the machine you use to detect it.

      In other words, light is weird!

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