Fastest speed of light?

  1. Speed of light through vacuum is 299 792 458 m / s, but is slower through a denser medium like glass or water. We now know vacuum is not empty as previously thought, but has all kinds of new material in them like dark matter. Has any experiments been done to determine how fast light can be thorough a medium that has no dark matter in it? Would it be intuitively faster than the currently measured speed of light through vacuum?
  2. jcsd
  3. phinds

    phinds 8,108
    Gold Member

    Nothing is faster than universal speed limit, which as far as is currently known is also the speed of light in a vacuum
  4. Chronos

    Chronos 9,771
    Science Advisor
    Gold Member

    The speed of light is invariant under GR, which assumes no media whatsoever. What would be remarkable is detection of a slightly slower speed of light through nearly empty space.
  5. Although space is not empty, the density is very low, and has little effect on the speed of light. How do we know this? For one thing, media don't just slow down light, they disperse light, causing different colors to separate. If space were fairly dense, then we would see that the images of faraway galaxies were temporally and spatially shifted by color.
  6. Nope.The Speed Of Light Now Known Is The Fastest.Because,
    If A Particle ( Eg.Photon) Moves At The Speed Of Light ( i.e The Speed Of Light In Vaccum(299 792 458 m/s), Its Mass Would Be Zero . So Is There Anything With A Mass Of Value With A Negative Sign (eg.-12kg)?So The Speed Of Light Now Known Is The Fastest Speed That A Matter Can Attain At Its Peak.

    S.I.S ;)
  7. ZapperZ

    ZapperZ 29,652
    Staff Emeritus
    Science Advisor
    Gold Member

    This about this: if dark matter is dense enough that it affects the speed of light, we would have discovered dark matter already by now!.

    Secondly, your description of light interaction with dark matter implies that there is an electromagnetic interaction between light and dark matter. Most of the models for dark matter candidates based on what we know about dark matter has no such interaction. Dark matter's main channel of interaction is via its gravitational presence. So "your dark matter" here will be very different than what we know about dark matter.

  8. Dark matter does not affect light propagation. If it did, it wouldn't be dark.
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