• Question: Why does the electromagnetic spectrum end at gamma waves and radio waves? Shouldn't it be infinate?

    Asked by bridget to Amy, Drew, Sara on 23 Jun 2011.
    • Photo: Drew Rae

      Drew Rae answered on 23 Jun 2011:

      Hi Bridget. I’ve been trying to find out the answer to this for you, but with not a lot of luck. as you go up the spectrum, frequency increases and the energy of the photons increases. Is there a limit to how much energy a photon can have? I can’t find a straight answer – there may be one that Sara can point out.

      In any case, by definition the electromagnetic spectrum ends at gamma waves, because the “gamma wave” part of the spectrum is open ended. Anything above a certain energy (below a certain wavelength) gets called a gamma ray. They cover quite a large range of energies, so we really should break them up into a couple of different names at least.

    • Photo: Amy MacQueen

      Amy MacQueen answered on 23 Jun 2011:

      Hi Bridget,

      I think it is because this is just what we are calling the longest and shortest waves we can measure at the moment although technically the long wavelength limit is the size of the universe itself and the short wavelength limit is generally thought to be the vicinity of the Planck length.

      But I think that you are right in principle the spectrum is infinite and continuous! 🙂

Comments

  • Photo: bridget

    bridget commented on :

    Wait. . . what’s the planck length?

  • Photo: Amy

    Amy commented on :

    The Planck length is 1.616252(81)×10−35 metres.
    Its a unit of length defined from the three fundamental physical constants: the speed of light in a vacuum, Planck’s constant, and the gravitational constant! 🙂

  • Photo: bridget

    bridget commented on :

    Thanks- I guess it’s beyond GCSE. So can gamma waves just not be detected after this point, or do they actually stop?

  • Photo: Amy

    Amy commented on :

    You get into quantum uncertainty if you go below this Planck length and then into probabilities of where something is – ie you can’t really measure a wave thats smaller than the Planck length…but it could be there!

  • Photo: Amy

    Amy commented on :

    Okay I have redone my comment after a little chat with my friend who is a phycisist!! He gave me a lot of help! 🙂 There isn’t a limit to the size of the wavelength theoretically but there are practical issues involved. The shorter the wavelength of the light, the more energy it has so to go to really short wavelengths you need loads of energy. Gamma rays have been detected from space with wavelengths as short as 3×10(-17) and they think there will be some as short as 3×10(-23). this doesnt really come close to a planck length which is 1.616×10(-35) but at distances shorter than a planck length quantum uncertainty effects mean that it’s impossible to tell the difference between two different points in space…