sci.physics.particle

Apologies if this is a duplicate -- I'm having some news problems.

In sci.physics Koobee Wublee wrote:
> On Feb 25, 7:47 am, Tom Roberts wrote:

>> The best model we have for the propagation of light near a massive
>> object like the sun is GR, in which the curvature of spacetime is the
>> important aspect in determining the path light follows. And it agrees
>> with measurements to part-per-million accuracy over an enormous range.

> First, derive a set of geodesic equations a massed particle traveling
> at high speed near the sun. Then, gradually reducing the mass to zero
> and increasing the speed to c, do you see a discontinuity at mass = 0
> and speed = c?

This is definitely a worthwhile exercise. I recommend that you do it.
If you get stuck, you can find the details in Lightman et al., _Problem
book in relativity and gravitation_, problem 15.9.

> As you know, the geodesic equations are independent of mass. What
> does that tell you when the model predicts a 1x deflection traveling
> at speed just a hair below c and suddenly jumps to 2x deflection at
> speed = c?

It doesn't. The model predicts a deflection proportional to 1+v^2/c^2,
which varies smoothly from the "Newtonian" value of 1 for small velocities
to 2 as v approaches c.

The moral is that before you decide that a model doesn't make sense,
you should check what the model actually predicts.

Steve Carlip