Re: Does Newtonian gravity bend light?

[Hugh Haskell <hhaskell@MINDSPRING.COM>]

> One of the textbooks on my desk says regarding predictions of GR "Gravity
> should bend light rays, an effect not predicted by Newtonian mechanics
> because light has no mass."  Yet
> <http://www.theory.caltech.edu/people/patricia/lclens.html> claims that
> Newtonian gravity bends light, just less than Einsteinian gravity does.
> What gives?
>
> Thanks,
> Larry

Interesting. What text is that? I rather think the web site you cite
is correct. I don't recall how Newton conceived of light in terms of
mass, but I think he attributed some to it so he could use momentum
conservation as part of his explanation for reflection and
refraction. I recall that his explanation required that light travel
faster in the denser medium but I don't remember the reasoning behind
that. I believe it is actually relativity that attributes no mass to
light, and the "bending" is due to the curvature of space induced by
the nearby mass.

I am sure that the general relativists on the list will be able to
give much more complete responses.

Hugh
--

Hugh Haskell
<mailto://haskell@ncssm.edu>
<mailto://hhaskell@mindspring.com>

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