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Wave or Particle?

  1. Aug 13, 2005 #1
    Wave or Particle??

    Is light a wave or particles.
    If it is made up of particles, then light cannot have frequencies, can it?
    OR
    If it is a wave then how can it be affected by gravity? :confused:
     
  2. jcsd
  3. Aug 13, 2005 #2

    ZapperZ

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    It is only either a particle or a wave if we insist on using our classical dichotomy of something that must be either one or the other. The QM description of light contains no such thing. It has only ONE single, consistent description of light that can describe ALL the observed phenomena, both classical "wave-like" and classical "particle-like".

    If you think a photon cannot have any "frequency", then you need to figure out how one actually MEASURES such frequency in the first place (i.e. can you easily measure the "frequency" of a single photon, or do you actually need a bunch of them? Or what about the oscillation frequency of the E-field carried by a single photon?).

    Zz.
     
  4. Aug 13, 2005 #3
    And can you tell me one more thing. What does the term 'infinite energy of a photon' mean. Is it that photons have never-ending energy (If so, HOW?) or is it that energy in a photon never gets converted so it continues to move.
     
  5. Aug 13, 2005 #4

    ZapperZ

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    I cannot tell you what it is if you do not put the question in its proper context. If you have read this somewhere, it is important that you make an accurate citation on the source.

    Zz.
     
    Last edited: Aug 13, 2005
  6. Aug 13, 2005 #5

    rbj

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    ZZ sorta said this, but i would simply add that light has wave-like properties in some contexts and particle-like properties in others (and the tasks of physicists are to observe and learn when it's the one or other). it is neither only a wave nor only a particle.
     
  7. Aug 13, 2005 #6
    Can you elaborate on this?

    I haven't yet studied quantum physics, but to my knowledge we don't really know for sure what light actually is, only that sometimes it behaves like particles and sometimes it behaves like waves.
     
  8. Aug 14, 2005 #7

    ZapperZ

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    That would be very strange, don't you think, that we don't know something, but we literally are using it intimately to study everything from materials properties, to DNA to medical purposes (see Synchrotron light source).

    I think I've written about this so many times, I am hesitant to want to repeat everything. Suffice to say that the "particles" and "waves" that we so insist is a result of our classical world. There's no such division in QM. EVERY, and I mean EVERY, single observation of light (and particles that have wave-like properties) has a consistent description in QM. Photons producing wavelike interference? Sure... there's a reference to the Marcella paper somewhere in PF that painfully derives the single and double slit interference using photons.

    Zz.
     
  9. Aug 14, 2005 #8
    Classical Physics had the same doubts you have in this post.Quantum theory is the answer to all your doubts.QT is the best knowledge about particle behaviour that we possess.As per quantum Mechanics , particle is spread like a wave in space.The position of this particle is approximised using a wavefunction. Wave-particle duality was first proposed by DeBroglie, the the wavelength associated with a particle decreases with mass , only noticeable in small atomic particles.Light doesnot show the wave-particle duality simultaneously though it possesses it at any instant you observe it.If the instrument being used has dimensions comaparable to the wavelength of light , light shows particle nature and if instrument has dimensions way larger than the wavelength , we study the light as a wave / an EM-ray.It all depends ont he way we observe it.

    BJ
     
  10. Aug 16, 2005 #9
    Its both wave and particle. All matter has an associated matter field and thus a matter wave, first proposed by de Broglie. So when you want to consider its frequncies and wavelength one must consider it to be a wave. When considering it bending due to gravity one must consider it to be a particle.

    Light should be considered as quanta (packets) of energy not a continuous wave like a sine curve. Maybe that will help you grasp the concept of light being both wave and particle.
     
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