Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Question About Light and Speed of Light

  1. Oct 21, 2012 #1
    Not really sure if this is the right location for this post, but here it goes.

    I have found myself becoming increasingly interested in light and wondering if the speed of light could be increased by some amount. If the light was charged, and released near a powerful electric field, could the velocity of light go beyond the speed of light as it is currently defined? This isn't for any homework or school assignment, just an idea I was curious about.
     
  2. jcsd
  3. Oct 22, 2012 #2

    cepheid

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Light is not charged, so it can't be accelerated by electric fields. In classical physics, light IS electric (and magnetic) fields. As far as we know, the speed of light is a universal constant.
     
  4. Oct 22, 2012 #3
    That being said, is there anyway light could become charged through an outside factor? Or is it physically impossible?
     
  5. Oct 22, 2012 #4

    cepheid

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    No, in quantum physics, light is made out of elementary particles called photons. Electric charge is a fundamental property of an elementary particle i.e. it's one of the characteristics that defines that particle. For example, electrons have a charge of -1, and protons +1. This, along with their masses, and other properties, is what *makes* them electrons (or protons) and not some other particle. So, since the electric charge is an intrinsic property of a a given particle you can't change the electric charge of a that type of particle: it is what it is. In the case of a photon, the charge is 0.
     
  6. Oct 22, 2012 #5
    Ah, I understand now. Thank you.
     
  7. Oct 22, 2012 #6

    cepheid

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    You are welcome! I edited my explanation a bit for clarity, but it seems it was unecessary, as you understood anyway.
     
  8. Oct 25, 2012 #7
    While you can't charge light and somehow pull on it using an electric field, you CAN pull on it using gravity.

    Nevertheless, even in a gravity field the speed of light is capped at C.
     
  9. Oct 25, 2012 #8
    Not quite. Gravity has no effect on photons. It appears that light bends around large masses due to space-time bending. The space is bending, not light trajectory.
     
  10. Oct 25, 2012 #9
    That's a bit of a chicken-and-egg statement. Gravity is bent space-time.
     
  11. Oct 25, 2012 #10

    Drakkith

    User Avatar

    Staff: Mentor

    If spacetime is bent, and gravity is the manifestation of this, and lights trajectory is altered because of bent spacetime, then I would say light is affected by gravity.
     
  12. Oct 25, 2012 #11
    What Feynman means, I believe, is that light always travels on geodesics, it's just that in some frames straight lines appear bent. But if I'm sitting near a massive object, I don't see light curving in some strange way. An observer far away does though.
     
  13. Oct 25, 2012 #12
    You could say the same about planets orbiting the Sun gravity has no effect on them and it's due to space-time.Or an object falling on Earth there is no such thing as gravity only space-time bending.
     
  14. Oct 26, 2012 #13
    Ok ok ok I worded it wrong. I just wanted to clarify that gravity wasn't pulling on photons, as if they have a mass or something. Yes, so gravity is bent space time, and "bent" light is a consequence of this warping. You could say that light is affected by gravity in that way, but it looks as if Lsos is talking about photons being influenced by a Newtonian view of gravity.
     
  15. Oct 26, 2012 #14

    Drakkith

    User Avatar

    Staff: Mentor

    You realize light gravitates as well right? It contributes to gravitation, just like matter does.
     
  16. Oct 26, 2012 #15
    It's an interesting idea...never thought about that. Here are some 'deeper' considerations:

    So far, as noted above already, light seems to have a universally fixed speed. While we can't currently 'charge' it electrically, also noted above, gravity does ACCELERATE it....but only by changing it's direction, not it's speed. In so far as we know, when the energy of light changes, it's frequency changes, not it's speed. [That's unique to massless entities.] And adding electric charge would appear to add energy.....?? So that might not help.

    We say mass can't be accelerated to the speed of light...but might there be some way to accelerate 'charge' to c?.....not from current theory, because all we really know about charge so far is that it seems to be associated with mass...like in an electron or an ion.

    [I checked that last comment and it seems correct:

    http://en.wikipedia.org/wiki/Electric_charge] [Broken]


    Hmmm....Charge is a 'conserved' property....Could charge be separated from an electron??...that could conserve [retain] charge, but we can't do that according to anything I know. It would no longer be an 'electron' because an electron always has charge. Could we add such separated charge 'entity' to a photon??.......one problem is it would no longer be a photon.....however you play with these ideas, current science does not go so far.
     
    Last edited by a moderator: May 6, 2017
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Question About Light and Speed of Light
Loading...