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What movies the particles of light?

  1. Jun 28, 2009 #1
    Light travels at almost 190,000 MPH per second. Light is a particle just like dust or any other thing. What is making it travel that fast? How does light travel threw space if theres nothing to travel threw? Shouldn't that mean that sound can travel threw everything too? If light can travel threw everything except for solids then why can sound travel threw solids?
    To Dave: how is it massless if everything has mass? blackholes are so strong they can pull light in so it can't be massless,
    Thanks for informing me! That anwsers aloooooot of my questions!
     
    Last edited: Jun 28, 2009
  2. jcsd
  3. Jun 28, 2009 #2

    DaveC426913

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    No it is not a particle like any other thing.

    Light photons are bosons. Bosons are massless and always travel at the speed light.
    All matter particles such as dust are fermions, whcih cannot travel at the speed of light.

    For some intents and purposes, we can treat light in certain circumstances like it's a particle, but that does not make it a particle of matter. (In some circumstances, my laptop behaves like a boat anchor, but that does not mean it is a boat anchor.)

    The same way particles of dust and particles of rocket ships and do.

    Sound is not a physical thing; it is the transmission of vibration from molecule to molecule of a medium. The medium might be air or steel or drywall.
     
    Last edited: Jun 28, 2009
  4. Jun 28, 2009 #3

    DaveC426913

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    Everything does not have mass. Photons do not have mass.

    Black holes do not "pull" light. Black holes distort spacetime, causing it to curve back on itself. Massless photons and massive matter both follow curved spacetime.
     
  5. Jun 28, 2009 #4

    Nabeshin

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    Where do you get these ideas and the confidence to assert that they're all correct? I don't understand.

    Who said everything had mass?
    Who said black holes only attract objects with mass?
    Who said light can travel through everything except solids?
    Who said sound can't travel through solids? (To the best of my knowledge, I can hear people in the room next door!)
     
  6. Jun 28, 2009 #5

    DaveC426913

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    Certainly not Nabeshin. You misread this one. :wink:
     
  7. Jun 28, 2009 #6
    It's called inertia.

    Light-speed is merely a specified velocity (without direction). It is the fastest anything can travel, because mass slows an object down, in a sense. Light has no rest mass, so it travels at the fastest pace. It travels, like anything, with a constant speed through space. There is nothing 'mysterious' about it.
     
  8. Jun 28, 2009 #7

    DaveC426913

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    No it isn't. Inertia is a property of mass. No mass = no inertia.
     
  9. Jun 28, 2009 #8
    Poorly stated (by me), sorry. I think momentum was the word I was looking for.

    What I meant is that light doesn't have any inertia. :smile:
     
  10. Jun 28, 2009 #9

    russ_watters

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    Though he did say light can't travel through solids, which is wrong....where'd he hear that?
     
  11. Jun 29, 2009 #10

    Nabeshin

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    You're right, I got caught up in it all.

    Still I seriously think it's a valid question, where do people hear this kind of stuff?? Is it in books or magazines or is it just the reader (citizen) interpreting vague statements and combining with common sense to reach completely wrong conclusions?

    PS: Natevi, it's better to post a response rather than edit your original post... Just don't go overboard with this new found freedom.
     
  12. Jun 29, 2009 #11

    Chalnoth

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    Er, while photons are indeed bosons, this alone does not indicate that they are massless. A boson is just an integer-spin particle, and we are aware of a number of bosons which have mass (the W and Z bosons, for instance, and many atoms behave as bosons as well).

    It is fundamentally the massless property of light, not the bosonic property, that causes it to always travel at the speed of light. The two properties are not identical. The bosonic property of light (and other matter) usually only causes interesting effects at extremely low temperatures. For example, Helium-4, which is bosonic, becomes a superfluid at 2.17K, while Helium-3, which is fermionic due to the odd number of total fermions, becomes a superfluid at about 0.0025K, as it has to get cold enough that the Helium-3 atoms form pairs to become bosons.
     
  13. Jun 30, 2009 #12
    In the fine Hollywood tradition of physics:

    DUCK -- HERE COMES A PHOTON!
     
  14. Jul 1, 2009 #13
    Light can be a particle or it can be a wave, any reasonable book will explain the mechanics of it, In space light has what is called wave-particle duality. the particles travel on the wave and the wave carries the particle. This is why light can travel through space. Sound hower has entirely different mechanical properties. It needs a medium to travel through, sound is pressure pushing on e.g. air, when the air hits your ear drum the ear drum vibrates at a frequency denoted by the air hitting your eardrum...thats why sound cannot travel through space, there is no medium (be it air or water etc etc)..

    Actually light can travel through solids....otherwise we wouldnt have x-rays etc etc, its the frequency of the light that will determine what it can travel through, eg. gamma rays. If light couldnt travel through solids then how do you explain being able to make a call off your mobile....mobiles operate in the microwave spectrum.....

    If you can find a book called "x stands for unknown" auther Isaac Asimov it explains the light spectrum in very simple terms, very easy to understand. You might find it in the library, the other chapters are just as intersting too if you are interested in physics

    Hope this helps.
     
  15. Jul 1, 2009 #14

    Chalnoth

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    Actually, it's just a quantum-mechanical particle, which means it has wave-like qualities as well. It is neither a wave nor a particle in the sense of a macroscopic wave (like an ocean wave) or a macroscopic particle (like a piece of dust). It's a weird quantum thing that has properties of both (as with all quantum particles).

    Basically what this means is that if you describe a photon by using its quantum-mechanical wave function, you can accurately reproduce all of its behavior just by evolving that wavefunction forward in time (provided you also have the wavefunctions of everything it interacts with, too). There is no transition where you have to think of the particle as anything but just following the dynamics of the wavefunction.

    Anyway, that's my bit of pedantry for the time being.
     
  16. Jul 1, 2009 #15
    Light travels with v<c in transparent mediums.

    Bob_for_short.
     
  17. Jul 1, 2009 #16
    Yeah, thanks to electrons. The time it takes for electrons to absorb and emit the photon is what 'slows' the photon down. The photon still moves at speed c.
     
  18. Jul 1, 2009 #17
    Wrong. For a transparent medium there is no absorption, there is no delay due to "delayed" radiation. There is a collective effect, that is true, but it is a superposition of the incident wave and continuously oscillating and thus radiating electrons. That makes the resulting EMF velocity smaller than c. There is no de-phase phenomenon due to spontaneous absorption and delayed emission.

    Bob for short.
     
  19. Jul 1, 2009 #18
    I looked this up. Fascinating. I never new that. My apologies.
     
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