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

In the absence of light

  1. Oct 22, 2005 #1
    ...there is darkness and spacetime

    but there is still light...

    In a semi dark room there is light and i can make the shape of objects out. I turn the switch on and the room is flooded with light but what happened ??? Did the energy levels of the existing photons in the semi dark room just get boosted ???

    With that in mind...

    ...is it possible to extricate spacetime without light given that spacetime is the medium through which light travels. Is a black hole spacetime without light ???

    What does the presence of light suggest then about the relationship between spacetime and light ???

    Is spacetime merely the effect of photonic mass and gravity travelling in 3+1d ???

    Is it possible to accurately model spacetime without including the effect of light from the outset ???

    If spacetime is inflating at faster than lightspeed from the inside. How do we ever manage to see light from vast distances given the the distance needed to travel is always increasing ???

    ...just some random questions i been thinking about I hope someone can help me with
  2. jcsd
  3. Oct 22, 2005 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    No, the light bulb produces new photons in vastly greater quanities than existed in the room before you threw the switch.
    Boosting the energy of the existing photon would result in the shifting of their frequencies (they would shift to the blue end of the spectrum).
  4. Oct 23, 2005 #3
    I don't think the word 'extricate' makes sense in your sentence. A non-spinning uncharged black hole (commonly called the Schwarzschild solution) is a spacetime described by the Schwarzschild metric.

    The presence of light is nothing special really, not even that light travels at the speed c is too special. What is remarkable is the fact that there is a maximum speed for all objects in the universe. This happens to match the speed of light since the quanta of the electromagnetic field is massless and therefore moves at that speed.


    Which effect of light?

    The most accurate model of spacetime is a "4-dimensional pseudo-Riemannian manifold." One consequence of this is that it doesn't make too much sense to speak of properties of objects that aren't in your local frame; i.e. the energy-momentum of a photon that is many light-years away.
    I hope I have been of some help.
  5. Oct 23, 2005 #4
    why yes, thank you masudr...

    ...so light in no way affects spacetime given that it has no mass and gravity

    but if it did then ???

    Is light as a particle the most abundant substance in the universe or is it possibly grains of spacetime or something else ???
  6. Oct 23, 2005 #5
    thank you too Janus...

    so do we know how photons are produced from non existence to visibly physical ???
  7. Oct 23, 2005 #6


    User Avatar
    Staff Emeritus
    Science Advisor

    Light has a small effect on the curvature of space-time, because it has energy - just not very much energy compared to matter. Light is in no way necessary to have space-time.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook