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

Astronomy says light slows down.

  1. Feb 14, 2004 #1
    "Astronomy" says light slows down.........

    Does the response to a question about gravitational lensing on page 72 of the March issue of "Astronomy" agree with other statements on this forum about the absolute nature of light speed?

    The question asked by "Astronomy" reader Tom Schmidt: "I noticed the photo of Einstein's Cross on page 47 in the November 2003 issue shows four images. Why aren't there many more, even a circle of images because the light from the source would be going in all directions?"

    Paul Schechter of the Massachusetts Institute of Technology replied (edited to present only the relevant passage):

    "........... In the gravitational case, the gravity of the lensing galaxy acts like the index of refraction of air. It slows down the light as it travels past the galaxy. If the quasar (which we take to be pointlike) aligns sufficiently closely with the galaxy, a second image appears. If the quasar aligns very closely, we get four images........"
     
  2. jcsd
  3. May 18, 2004 #2
    meddyn,

    Sorry no-one has answered you yet.

    Dr. Einstein addresses this point in Relativity. While SR rests on the constancy of c, GR supersedes this. Dr. Einstein defends himself along these lines:

    Dr. Einstein then goes on to dicsuss the relationship between electrostatic principles and electrodynamic principles in order to show that it is quite normal for one valid theoretical construct to be superseded by a more general one. He ends this discussion thus:

    So, your question is a valid step in the process of relating SR to GR. Whether you choose to take the next step toward accepting both GR and SR is up to you.

    Hope this helps!
     
    Last edited by a moderator: May 18, 2004
  4. May 18, 2004 #3
    couldn't you simply look at it like the velocity of c is constant but the gravitational fields creates space-time curvature which means the light has farther to travel along a certain path?
     
  5. May 18, 2004 #4
    Yes. That's what Einstein is saying.
     
  6. May 18, 2004 #5

    turin

    User Avatar
    Homework Helper

    That is one of my favorite Einstein pseudo-quotes.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?