Group: sci.physics.particle
From: Koobee Wublee
Date: Tuesday, March 04, 2008 7:34 PM
Subject: Re: Why does light bend under gravity?

On Mar 4, 9:59 am, carlip-nos...@physics.ucdavis.edu wrote:
> In sci.physics Koobee Wublee wrote:

> > 2 O ~= pi + 2 u (1 + 1 / B^2)
>
> This is correct.

But according to you, Lightman gave a result below.

2 O = pi + 2 u (1 + B^2)

> > If (B^2 = 1), we have a deflection of (4 u) which is twice the
> > Newtonian result.
>
> That's right.
>
> > However, at the speed just below 1, the deflection
> > angle is higher than twice the Newtonian result.
>
> No. Now calculate the *Newtonian* prediction. You will find that,
> in your notation
>
> 2 O ~= pi + 2u/B^2

At (B = 0.99), (1 + 1 / B^2 = 2.02) which results

2 O = pi + 4.04 u

The deflected amount at lower speed of (B = 0.99) is higher than
light, and this makes sense. Deflected angle of light represents the
lowest angle of deflection.

> (If you get stuck on this, look at chapter 3 of Goldstein, _Classical
> Mechanics_.) The GR prediction is thus, as I said, (1+B^2) times the
> Newtonian one. For speeds just below c, the GR deflection is just
> below twice the Newtonian deflection; as v becomes small, the GR
> deflection approaches the Newtonian value.

If Lightman is wrong (not your typo), how about Goldstein and others?

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