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Does space resist the passage of light?

  1. May 17, 2009 #1
    Please excuse my naive use of algebra.

    [tex]R_{s}=c\frac{\phi_1 \phi_2}{r^2}[/tex]

    I have concocted this equation in an attempt to show that the stuff of which space is made resists the passage of light.
    I wonder how more experienced members of this forum would interpret the equation?
    R_s is the resistivity of space, c is the speed of light in a vacuum, ø is the flux of light in a location and r^2 is distance.

    Does this make any sense at all?
  2. jcsd
  3. May 17, 2009 #2


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    No, it doesn't make any sense at all. It is just a bunch of terms you pulled out of the air and stuck together. It has no meaning. The very idea you based it on has no meaning either - the speed of light in free space is based on Maxwell's equations: http://en.wikipedia.org/wiki/Speed_of_light#Light_in_free_space
  4. May 17, 2009 #3
    Thank you, for your quick reply.

    It is not the velocity but the power of light which I think may encounter resistance as it moves through space. The velocity of light is constant across distance, its power is not.
    It is the reduction of power that I am trying to describe.

    Any better?
  5. May 17, 2009 #4
    I doubt the above equation has any equation has meaning, either, and if it did... A lot more information would be required to show that it does.. I don't even think "impedance of free space" is a (known) real property of free space (?)

    But, I think saying "the speed of light in free space is based on Maxwell's equations" isn't right either.... The actual speed of light in vacuum isn't based on anything known.. It is just measured "property" of the universe, based on something we don't really understand fully. Right?
    Last edited: May 17, 2009
  6. May 17, 2009 #5

    Doc Al

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    Perhaps you're trying to describe the inverse square law, which shows how the intensity (but not the total power) from a point source drops off with distance? See http://hyperphysics.phy-astr.gsu.edu/HBASE/vision/isql.html#c1"
    Last edited by a moderator: Apr 24, 2017
  7. May 17, 2009 #6
    I was going to ask a question related to this actually, why is the speed of light what it is?

    Even if metres and seconds are some arbitrary human concoction that doesn't change the fact that the speed of light is a a certain thing. I have heard the weak anthropic principle, saying that 'if the speed of light were different the universe would be different and we wouldn't be here to ask that question', but i think it is a weak answer to a cool question...
  8. May 17, 2009 #7
    I think the speed of light as its known is based on the energy of a photon and its wavelength:

    [tex]E = hc[/tex][tex]/[/tex][tex]\lambda[/tex]

    [tex]c = E\lambda/h[/tex]

    On another note wouldn't the equation above allow for super luminous (FTL) photons where E is greater. So when it comes to virtual particles c is truely a barrier that can be tunneled?

  9. May 17, 2009 #8
    The speed of light in a vacuum is constant everywhere in any inertial system, but we do not know what specifically determines this velocity. Nevertheless, we have named two "constants", the permeability of free space u0, and the permittivity of free space e0, and have via their placement in Maxwell's equations defined them as
    1/sqrt(u0e0) = 2.99792458 m/s (speed of light in vacuum), and
    sqrt(u0/e0) = 376.7254 ohms (the impedance of free space).
  10. May 17, 2009 #9


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    That makes even less sense.

    Start this way: show how what you are proposing is actually consistent quantitatively with what we have observed now. After all, we have a huge range of laser power as it is already.

    And just in case you missed it, the https://www.physicsforums.com/showthread.php?t=5374" that you agreed to already allow for very little leeway for personal unverified theory.

    Last edited by a moderator: Apr 24, 2017
  11. May 17, 2009 #10
    Shouldn't the real question be: What determines the mass of a photon? Given the realtionship of engery, wavelength and the Planck's constant leaves only one answer for c.

    But as I noted earlier c could change by a photon tunneling with more mass (engery) since its wavelength is fixed.

    Last edited: May 17, 2009
  12. May 17, 2009 #11


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    Well, the impedance of free space is just [itex]Z_0=1/\epsilon_0 \mu_0[/itex] and is about 377 Ohm. It is certainly a "real property" in that it has real, measurable effects. However, it is obviously just a reactive impedance, there is no power loss (meaning free space can sort of be thought of as a lossless transmission line with an impedance of 377 ohms).
    A good example of this is an antenna which can be thought of as a device that matches the impedance of an electrical circuit to that of free space in order to maximize power transfer.

    There are also other -more subtle- effects. One interesting example is that if you try to study quantum mechanical effects of macroscopic electrical circuits you will find that the impedance of free space is effectively shunting your circuit which in turn leads to a "leakage" and therefore decoherence. Nowadays we've learned to design our circuits to minimize this effects, but if no precautions are taken the measured shunting impedance works out to be about 100 Ohms just as one would expect(the exact value predicted by theory is Z0 divided by pi).
  13. May 17, 2009 #12


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    E(x) = E(0)e − x / R

    I used to love to think about it. Then someone said it was crackpottery. I had to give it up.

    Then I discovered http://en.wikipedia.org/wiki/Quantum_foam" [Broken].

    I decided that light traveling through free space might be sapped by the mechanism of creating said foam, as a function of the cosmological constant; each wavelength giving up a minute amount of energy, unhindered in velocity, but forever weakening.

    Supposedly, http://www.cfa.harvard.edu/~sblondin/publications/timedilation/timedilation.pdf" [Broken] written a couple of years ago put the final nail in the tired light coffin, which made me quite happy as I very seldom spend much time on my outlandish ideas of which I have very little background in the first place.
    Last edited by a moderator: May 4, 2017
  14. May 17, 2009 #13


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    When you come up with an equation make sure that at least the units are the same on both sides. This doesn't seem to be the case with your equation therefore it must be wrong.
  15. May 17, 2009 #14
    Yes, sorry. I can see that I was being 'overly speculative'.
    Last edited by a moderator: Apr 24, 2017
  16. May 17, 2009 #15


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    Shouldn't that be [itex]\sqrt{\mu_0/\epsilon_0}[/itex] to get the units of an impedance?
  17. May 18, 2009 #16


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    Indeed it should :redface:
    I guess I was thinking of [itex] 1/\epsilon_o c_0 [/itex] when I wrote down the equation above.
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