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Particle physics when light wave expands infinitely

  1. Jun 23, 2009 #1
    What happens to the particulate nature of light as a light expands outward infinitely from a single point light source. Pretty much all light in the universe does that, except only where lensing takes place to create a non-divergent beam of light ... although I think such a thing is a near impossibility (low-divergence happens though - the result of lensing).

    Consider one photon expanding radially from a single point light source. It only exhibits particulate nature when it is absorbed, yes? And there is a specific location where this absorption takes place, yes?

    In otherwords, consider the following scenario:

    Say you have an array of digital telescopes side by side focused on a low light source like from a extra-solar planet. That planet will reflect light as a wave as it moves through space, expanding radially as it goes so that only one photon/second should reach the telescope array, but since light is particulate in nature upon absorption only one telescope out of the entire array will see the photon.

    We know that because upon absorption it has both a finite location and fixed energy.

    Which brings me back to my questions ... all light waves in the universe gets infinitely thin over time as they radiate radially from a point source ... so when absorbed as a photon:

    1) Is it focused at the average center of the wave, regardless the size of the wave? Or is it a random location of the photon within the wave envelope - if so what would determine that location?
    2) If a digital telescope array is too small to absorb the photon's entire wave diameter, will the wave bend around the array and then continue it's path, even if the array is centered on the middle of the photon's wave? It seems this must happen because the array has to be large enough to intercept the entire wave, because as light moves it's not particulate in nature unless an entire photon's worth of energy is absorbed and a partial wave can NOT be converted to a low energy photon (ie. a single photon energy is fixed and constant for a given frequency).

    I assume the answer to the first is that the location of the photon upon absorption would be centered. The second question is I think the more difficult one ... and the more interesting.

  2. jcsd
  3. Jun 23, 2009 #2


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    An individual photon does NOT expand. When talk about "light waves expanding infinitely" you are either talking about many different photons moving from a central starting point or the "wave function" of a single photon which indicates the probability that photon will be found at a specific point.
  4. Jun 24, 2009 #3
    What you say sounds different than what I remember from my physics class 20 years ago, which is not surprising ... lost in translation perhaps, or muddied by time. What you say is much easier to grasp.

    I thought each individual photon behaved literally as a wave when moving through space ... not that it remains a discrete particle of energy when flying through space and is only part of a wave of particles. The wave function, you say, is the probability of where it is likely to be in relation to the other particles of the wave? Gee that almost seems intuitively obvious when compared to the weird way I previously understood the wave phenomena of individual photons.

    Your clarification makes light seem not as weird. But it is still very weird - where it's speed seems fixed to the observer and not to the source (though I know even that isn't an entirely accurate statement).

    I do want to understand this though ... so the wave-probability you speak of ... does this mean the probability of a photon's location, if graphed with respect to a point in time, is roughly congruent to the detected frequency of the light?

    And does that mean the along it's axis a single photon travels in a perfectly straight line?

    Thanks in advance for the info!
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