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Distance between photons?

  1. Mar 30, 2010 #1
    What is the distance between two photons in a ray of light?
  2. jcsd
  3. Mar 30, 2010 #2
    Photons are bosons, which means that you can have as many photons in the same state as you want. This means that an arbitrary number of photons can be in the exact same place, moving in the exact same direction with the same polarization.

    In a laser, we try stack as many photons on top of each other in as small a space as we can. The density of photons that we get depends mostly on the technical limitations of the laser.
  4. Mar 30, 2010 #3
    ok, when light travels in a ray of light, isn't there some distance between them, otherwise I guess it wouldn't be quanta. Or when a laser is beamed towards the moon for measurement, the light disparses, so distance would increase. In an experiment done with a single photon counting CCD camera, the distance between the photons was 2km (http://ophelia.princeton.edu/~page/single_photon.html"). Is it wave related?
    Last edited by a moderator: Apr 24, 2017
  5. Mar 30, 2010 #4
    A laser disperses because of the motion of a single photon* not because photons bump into each other. Photons can pass right through each other and lie on top of each other without feeling each other at all (they only interact through gravity as far as we can tell)

    * a laser disperses because a single photon is a wave... it also has a definite position - those are very vague statements, do not ponder them for too long, they will drive you mad unless you learn more about them
  6. Mar 30, 2010 #5
    I wasn't suggesting they would bump into each other. I just wanted to have an idea what the distance, definite positions, between these single waves are in a normal ray of light or a laser beam. Thus when light "travels", and before the distances get bigger when they disperse.
  7. Mar 30, 2010 #6
    The point LukeD is trying to make, is that if you have a strong enough beam e.g. laser light, there is zero distance between them - they overlap. You can in principle even have what "looks" like a single photon, that actually is 2 photons overlapping completely - just twice as "strong".
  8. Mar 30, 2010 #7


    Staff: Mentor

    Again, as LukeD said they are bosons so not only can there be 0 distance between them they can also be in otherwise completely identical states of polarization momentum etc.
  9. Apr 2, 2010 #8
    Is there such a thing as "bosonized", like in the sense of "ionized", where matter can become more charged?
  10. Apr 2, 2010 #9


    User Avatar

    Staff: Mentor

    Getting back to your original question, it's possible to find a number that would be the distance between photons, if photons really were pointlike objects traveling along the beam, like a stream of tiny bullets. But you need some information about the beam to start with. Let's say for example that:

    1. The beam has a power of 5.0 milliwatts (typical for a handheld laser pointer).

    2. The beam's cross-section is circular, with a radius of 1.0 millimeter.

    3. The light has a wavelength of 670 nanometers.

    From the first two, you can calculate the energy density (joules per cubic meter) inside the beam. From the third, you can calculate the energy (joules) per photon. Using these two numbers, you can find the average distance between photons.
    Last edited: Apr 2, 2010
  11. Apr 2, 2010 #10


    Staff: Mentor

    Not really. Although you can annihilate matter with antimatter and turn it into light and therefore bosons.
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