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Are there gaps between the rays coming from the sun?

  1. Mar 17, 2015 #1
    Hi! I have a question regarding the radiation coming from the sun. It might seem stupid to some people but I would really like to know how this works.

    When you see images of the sun's rays reaching the earth for example on this image from wikipedia (see attached image).

    The rays are almost always depicted as lines with gaps between them. So is this just for illustrational purposes or are there actually gaps between the rays?

    I don’t fully understand the processes behind solar fusion, but if you chose to see the energy exiting a fusion reaction in the sun heading for earth as a photon/particle being shot away, then there must be a finite amount of photons for each reaction which would indicate that there must be spaces between the photons without “sunlight”?

    And what happens if we chose to view the light as waves? There are a lot of different wavelengths comming from the sun but the wavelengths wouldn’t affect the size of the wave, just the length right? The size of both the electric and magnetic part of the wave is determined by the amplitude of the wave right? And in that case it should also be finite which could mean that there are holes/gaps in the radiation? And if this is the case, how big are these gaps, any way to put a number on it?

    So In other words what I’m wondering is: If you have an extremely small light sensor and move it around a bit (but with the same angle of incidence to the sun) on a sunny day – will there be places where the intensity of the sunlight is much lower or maybe even zero? Or are the waves overlapping in such a way that the light density is 100% even all over the place?
     

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  3. Mar 17, 2015 #2

    Orodruin

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    No, this is not the way waves work. Rays are merely illustrative and showing the direction of propagation of the light.
     
  4. Mar 17, 2015 #3

    wabbit

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    The picture of rays is as you suspected just a picture, there are no gaps - and if you move a detector the illumination will be more or less uniform - this is true even if your sensor is smaller than the wavelength of the light you are detecting, or if you use a lens to magnify the image.
     
  5. Mar 17, 2015 #4
    But why? The amount of waves/photons created in a fusion reaction should is limited right? Combined with a limited size of each wave/photon – how can there not be gaps?

    And a follow-up question: If you google for example “why is it colder in winter than summer” a lot of the answers you find looks something like this:

    “Its to do with angle of the sun. When the sun is high in the sky its radiation is concentrated over a small surface area. When its low in the sky the same amount of radiation is spread over a much larger area, so its much less concentrated and therefore less energy.“

    But if there are no gaps in the irradiation, then that would mean that this is completely wrong. Because if you again look at the Wikipedia image and imagine that a surface is tilted 90° on the north pole, it would with this explanation receive exactly the same amount of irradiation as a surface with 0° tilt positioned on the equator right? And as those of us who live far north of the equator knows from experience – that is obviously not the case. So what is the correct answer? Is the ONLY reason behind why it is colder in the winter/at northern latitudes that there is more atmosphere that the sun needs to pass though? Is the whole concept of “radiation spread over a larger area” false?
     
  6. Mar 17, 2015 #5

    Orodruin

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    Photons are not little balls. Furthermore, things like sunlight are very very classical and it is not a matter of producing a certain number of photons (classical fields are essentially what is called coherent quantum states that do not have a fixed number of photons in them).

    No it does not mean that it is wrong. It simply means that there is a certain amount of energy per transversal area. A tilted area represents less transversal area and therefore less energy per unit area than an area which is orthogonal to the direction of propagation.
     
  7. Mar 17, 2015 #6

    DaveC426913

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    Because of the density of photon flux.

    If you painted a panel of wood with a coat of yellow paint a foot thick, would you expect to see gaps?

    It's a little more complicated than that. Photons are bosons, which means, unlike fermionic atoms, there is no limit on how many can occupy the same volume of space.
     
  8. Mar 17, 2015 #7

    wabbit

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    One more things : if you dim the light a lot, you can detect the photons as individual dots on a detector plate - but these dots are randomly distributed, they will be as likely to be detected at one point than at any other. So even in a situation where you can see a non uniform result, it is still uniform on average. There are no gaps in the plate where no photon will be detected after a while.
    And if you wait long enough, the dots will gradually cover the plate uniformly again. Still no gaps.

    Edit : even in that case, the photon are not little balls, a photon detected at a certain spot wasn't "aimed at that spot", it just happened that the detector there was the one to record it, could just easily have been another detector doing so.
     
    Last edited: Mar 17, 2015
  9. Mar 17, 2015 #8
    But aren’t you sort of now saying that there are gaps? But that the gaps are so randomly distributed that over time the rays can be seen as uniform without any gaps? And if time was frozen, at least in weak light, there would be gaps?
     
  10. Mar 17, 2015 #9
    Not sure I understand that analogy. I personally wouldn’t see the gaps since the gaps are too small for my eyes to detect but surely every layer of paint doesn’t cover 100% of the space it is painted on, so yes there would be gaps..
     
  11. Mar 17, 2015 #10
    I understand that if you tilt a surface away from the direction of the sunlight the energy per area unit will decrease. And that is what I’m saying – this explanation doesn’t work when explaining why it is colder in the winter than summer, because a 90° surface on the North Pole is just as orthogonal to the direction of propagation as a 0° surface is on the equator! (well maybe it can explain why the ground on the north pole which isnt orthogonal to the sunlight is colder, but not for example a solar panel or a house façade)
     
  12. Mar 17, 2015 #11

    Orodruin

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    Yes, but you cannot think so locally. If you put a 90 degree surface somewhere on the North Pole, it will cast a shadow on the rest of the North Pole and no energy will be deposited there and when the energy is averaged over a reasonably large region (as temperature tends to do) you will have less energy per surface area.
     
  13. Mar 17, 2015 #12
    So do you agree with me then that if we imagine a completely naked earth with no trees or obstructions. One solar panel 0° on the equator and one 90° on the North pole. Any explanation to why they are producing different amounts of electricity that involves the angle of the sun somehow spreading out the light intensity would be 100% wrong? And this would simply be a matter of different atmospheric thicknesses?
     
  14. Mar 17, 2015 #13

    wabbit

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    No i wasn t saying that. I said if you have an array of detectors and a very low flux, only one detector will "see a photon" at one time. But photons are nothing like classical particles, see previous comments.

    Another way to see the same situation is : forget about photons, take a low intensity plane wave. The properties of the detectors are such that each one has a low probability of "detecting the wave" at a given time, so you will see successive localized detection events at one detector then another etc. Does that mean that the wave is localized ? No, not anymore than the photons i was talking about are localized. The locality is a property of the detection process, not of the wave or of the photons.


    Edit : at some point, interpreting what is "really happening" is just that : interpretation. The physics says what you detect, not "what is really truly there". And this applies to what I said above : it is an interpretation, nothing more.
    But I don't see how your gap interpretation can be correct, it just doesn't match the observations (uniform illumination, etc.)
     
    Last edited: Mar 17, 2015
  15. Mar 17, 2015 #14
    I don’t know anything about advanced quantum physics stuff but is it the same sort of crap with photons as with electrons; “You can never fully determine where an electron is, it’s only a matter of probability bla bla” ? Would it for example ever be possible to take a picture of a photon and use it as evidence of its location at a specific time in a court of law? :) or are we dealing with something so fundamentally strange that it doesn’t even follow a humans logical thinking of either a gap exists or no gap exists?
     
  16. Mar 17, 2015 #15

    wabbit

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    Yes I suppose it's all the same crap and bla bla, sorry I brought this up.
     
  17. Mar 17, 2015 #16

    DaveC426913

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    If the paint were a foot thick, there would be no straight line of sight, at any scale, between your eye and the wood. Somewhere in that foot, one - or more likely many, many -atoms would block your sight of the wood.

    Remember how I said there's no limit to how many photons can occupy a volume of space? Imagine the layer of paint being made of particles that can physically overlap each other. The layer could be zero thickness, and yet any location on it would be so densely crowded with particles that no wood would be visible.

    You're right, this is a terrible analogy.
     
  18. Mar 17, 2015 #17

    Orodruin

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    Most analogies are terrible ...
     
  19. Mar 17, 2015 #18

    DaveC426913

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    I am trying to avoid describing what happens if the sun could be dimmed until just a few photons emitted per second. I believe that, as Petahanks suspects, there would indeed be very large gaps (the photons would be emitted in random directions, meaning an entire array of detectors would detect nothing, except at a few points).

    I'm just not sure it's that simple. Photons don't really act like particles all the time; they'll spread as a wavefront, depending on what tools you use to measure them. But I don't have the words to answer the question properly.
     
  20. Mar 17, 2015 #19

    Orodruin

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    Depending on the specifics, you would likely have a continuous probability to measure a photon at any location on a sphere around the source. The actual detection would be discrete, just as in experiments that work with low intensity light.
     
  21. Mar 17, 2015 #20

    russ_watters

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    Since photon flux is photons per unit area, you could also (if you wanted to) calculate how many photons there are in a cubic meter of sunlight. Even though they aren't little balls or point particles, you could still calculate an average spacing. That might satisfy the OP.

    The issue may take on more relevance for looking at distant stars/galaxies, where the "gaps" can be on the order of thousands of km between photons.

    http://hubblesite.org/newscenter/archive/releases/2004/07/text/
     
    Last edited: Mar 17, 2015
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