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Thread: What is Light made of?

  1. #1 What is Light made of? 
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    So I know that different wave lengths mean the color etc, but what are those wave lengths composed of. Like what actual form of matter reaches your eyes for example if a flashlight shines on an image and then bounces off into your eyes.

    Thanks!


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  3. #2  
    Brassica oleracea Strange's Avatar
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    Light is electromagnetic radiation. So the waves are waves in the electric and magnetic fields.


    ei incumbit probatio qui dicit, non qui negat
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    Quote Originally Posted by ScienceNoob View Post
    So I know that different wave lengths mean the color etc, but what are those wave lengths composed of. Like what actual form of matter reaches your eyes for example if a flashlight shines on an image and then bounces off into your eyes.

    Thanks!

    Light is not a form of matter. Light is composed of particles called photons. Photons differ from particles of matter because
    photons don't interact with each others, whereas particles of matter (electrons for example) do interact with each others:
    http://plus.maths.org/issue29/featur...nteraction.jpg

    Photons do interfere with each others.
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  5. #4  
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    Quote Originally Posted by ScienceNoob View Post
    So I know that different wave lengths mean the color etc, but what are those wave lengths composed of. Like what actual form of matter reaches your eyes for example if a flashlight shines on an image and then bounces off into your eyes.
    Light is not classified as "matter", it is not "made of" anything. Light is just a particular form of energy, so that is what reaches your eyes.
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    If a photon of a radio wave and a photon of an x-ray are both just one single photon, is the radio one "bigger" than the x-ray? But then, don't x-rays and other "smaller" photons have a lot more energy, or am I misunderstanding? It's hard to imagine single photons having different sizes yet still being fundamental particles.

    Is there some kind of equation relating to length and energy, like inversely proportional or something? Can there be such a thing as a high energy radio wave?
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  7. #6  
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    Quote Originally Posted by Daecon View Post
    If a photon of a radio wave and a photon of an x-ray are both just one single photon, is the radio one "bigger" than the x-ray? But then, don't x-rays and other "smaller" photons have a lot more energy, or am I misunderstanding? It's hard to imagine single photons having different sizes yet still being fundamental particles.

    Is there some kind of equation relating to length and energy, like inversely proportional or something? Can there be such a thing as a high energy radio wave?
    Different frequencies correspond to different photon energies (the energy per photon E = hf, where h is Planck's constant, and f is the frequency), and frequency is related inversely to wavelength (f = c/lambda, where c is the speed of light and lambda is the wavelength). Since the energy per photon is a function of frequency only, a radio wave photon has much less energy than that of an x-ray photon. The total energy of a stream of photons is simply the energy per photon, multiplied by the number of photons. So, yes, there can be a high energy radio wave; one only needs many, many photons. An x-ray would need far fewer to convey the same total energy.
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    Forum Professor Daecon's Avatar
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    I'm sorry, I foolishly used the wrong word, I meant to say "high energy radio photon" not radio wave, but you answered my question for me anyway. :-)

    Is there a theoretical limit to either the shortness or length of a photon? I'm presuming that a photon can't be completely "flat" otherwise that would mean it would have zero energy and therefore not exist, so there must be some minimum but non-zero limit to the least amout of energy a photon can be or have?
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  9. #8  
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    Photons have no rest mass. In other words when they are not busy being light they do not exist. They considered as pointlike particles in QM, which means they have no physical dimensions.

    The explanation on this page is engineeering style so it concerns itself with the math more than philosophy.
    Energy of Photon | PVEducation

    The miniumum energy a photon can actually have is calculated with the Planck Constant.
    Planck constant - Wikipedia, the free encyclopedia
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  10. #9  
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    Rather confusingly, even though Dan Hunter is absolutely correct that the photon is volumeless (point like), it has spin. That is, it acts like a small rotating top. This becomes extremely important in photon/atom interactions, as "spinny-ness" (in physicist speak: angular momentum) is conserved, i.e. the total amount of it in some closed system need remain fixed. This severely limits the number of available transitions in atoms, and is one of the reasons (if not the principle reason) that atoms can actually spend any time in excited states (very important for all kinds of things).
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    To jump in on this as well (assuming that the question has been effectively answered), I have a question that probably is simply answered:

    Do all "energy" signals (aforementioned Radio waves, X-Ray, Light, and so on,) consist of photons and therefore travel at that same constant light speed, or do they travel at speeds depending on other constants related to their wavelength?
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  12. #11  
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    All electromagnetic radiation (from gamma rays through to radio waves) consist of photons which travel at the speed of light.
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  13. #12  
    Forum Sophomore keeseguy's Avatar
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    Quote Originally Posted by PhDemon View Post
    All electromagnetic radiation (from gamma rays through to radio waves) consist of photons which travel at the speed of light.
    Planck refers to light as a wave and a particle (photon), how can it be both. What distinguishes the different kinds of EMF when considering them as photons?
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  14. #13  
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    Light (and everything else) is "really" neither a wave or a particle it is something that behaves as a particle at one scale and waves at another. For light the photon aspect only really becomes apparent on the small (quantum) scale, the wave nature is more apparent at larger scales. As the question was phrased in terms of photons I answered it as such. It is the energy of photons that distinguish between the different types of EMR.
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    If you want to learn more about something more interesting, get this.

    light encoded DNA filament

    there is harmonic oscillations of electrons going on in the center in the microtubules or the DNA. this is the source of electromagnetic filament that runs all through the center of polymers (see DNA molecule). the way it works is this: oscillating charges (produce) --> magnetic fields (which produce) --> electrical fields (which produce) --> electromagnetic waves in other words, light.

    evidence:

    Russian scientist Alexander Gurwitsch in 1920s connected the ultraweak electromagnetic emission of organisms to developmental processes of morphogenetic field and called them mitogenic rays. Recently it has been confirmed the intra and intercellular communication via electromagnetic emissions.

    DNA can receive light, transduce it, compute a response, and re-emit a EM signals. When information within light is received, it can be stored, computed, and transmitted holographically by DNA. There are studies that show the efficacy of using DNA for computations.

    DNA computing might replace silicon-based computer technologies!
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  16. #15  
    Genius Duck Dywyddyr's Avatar
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    Quote Originally Posted by thulium_gal View Post
    If you want to learn more about something more interesting, get this.

    light encoded DNA filament

    there is harmonic oscillations of electrons going on in the center in the microtubules or the DNA. this is the source of electromagnetic filament that runs all through the center of polymers (see DNA molecule). the way it works is this: oscillating charges (produce) --> magnetic fields (which produce) --> electrical fields (which produce) --> electromagnetic waves in other words, light.

    evidence:

    Russian scientist Alexander Gurwitsch in 1920s connected the ultraweak electromagnetic emission of organisms to developmental processes of morphogenetic field and called them mitogenic rays. Recently it has been confirmed the intra and intercellular communication via electromagnetic emissions.

    DNA can receive light, transduce it, compute a response, and re-emit a EM signals. When information within light is received, it can be stored, computed, and transmitted holographically by DNA. There are studies that show the efficacy of using DNA for computations.

    DNA computing might replace silicon-based computer technologies!
    Mostly complete woo.
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    "[Dywyddyr] makes a grumpy bastard like me seem like a happy go lucky scamp" - PhDemon
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  17. #16  
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    Quote Originally Posted by Dywyddyr View Post
    Mostly complete woo.
    which part?
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  18. #17  
    Anti-Crank AlexG's Avatar
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    The part that starts at the top and ends at the bottom.
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    Its the way nature is!
    If you dont like it, go somewhere else....
    To another universe, where the rules are simpler
    Philosophically more pleasing, more psychologically easy
    Prof Richard Feynman (1979) .....

    Das ist nicht nur nicht richtig, es ist nicht einmal falsch!"
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  19. #18  
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    it's in research and development stage at this point
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  20. #19  
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    Quote Originally Posted by PhDemon View Post
    All electromagnetic radiation (from gamma rays through to radio waves) consist of photons which travel at the speed of light.
    In a vacuum. In materials, photons travel slower, but this is independant of their energy.
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  21. #20  
    Bullshit Intolerant PhDemon's Avatar
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    My understanding was that photons ALWAYS travel at c, the apparent slower speed through media being due to absorption and re-emission by the atoms in the medium.
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  22. #21  
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    Quote Originally Posted by ajarjour View Post
    Quote Originally Posted by PhDemon View Post
    All electromagnetic radiation (from gamma rays through to radio waves) consist of photons which travel at the speed of light.
    In a vacuum.
    Yes thanks ajarjour, but we all know this when we state c. It gets tiresome to always qualify the speed of light with "in a vacuum' so it is usually unsaid but understood.
    Last edited by Chucknorium; May 17th, 2014 at 10:33 PM.
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  23. #22  
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    Quote Originally Posted by PhDemon View Post
    My understanding was that photons ALWAYS travel at c, the apparent slower speed through media being due to absorption and re-emission by the atoms in the medium.
    So this means that they travel at c inside of an atom, as well as before absorption and re-emission? What happens if an electron is jumped out of orbit, or leaves the atom - to the photon?

    Are photons even proven to exist, or are they just an accepted hypothesis?
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  24. #23  
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    Quote Originally Posted by Mayflow View Post
    Quote Originally Posted by PhDemon View Post
    My understanding was that photons ALWAYS travel at c, the apparent slower speed through media being due to absorption and re-emission by the atoms in the medium.
    So this means that they travel at c inside of an atom, as well as before absorption and re-emission? What happens if an electron is jumped out of orbit, or leaves the atom - to the photon?

    Are photons even proven to exist, or are they just an accepted hypothesis?
    Nothing in science is proven.

    All theories are mere models of reality and thus are provisional and subject to being shown incomplete or wrong by further observation. But photons are a very successful model for accounting for the observed behaviour of light and other EM radiation. Light does not travel to a significant degree inside atoms - they are too small. But certainly it travels always at c.

    What PhDemon is referring to is that the phase velocity of light travels more slowly in a medium than it does in vacuo, due to coupling of the photon's EM fields to the substance it is passing through.

    Nice animation here of phase velocity, group velocity etc. : Speed of light - Wikipedia, the free encyclopedia
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  25. #24  
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    Thanks for picking that up, I didn't see those questions thanks to my ignore list
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  26. #25  
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    Quote Originally Posted by PhDemon View Post
    Thanks for picking that up, I didn't see those questions thanks to my ignore list
    I quite understand.
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