Light lnside a Hollow Sphere

Hi,

I was curious to know what would happen to light inside a hollow sphere. I remember doing a physics problem where we prove that the net force (from gravity) acted on a body inside a hollow sphere is zero. I also remember being told that light "bends" in the presence of a gravitational field.

So what I was wondering was what would happen to the light if we were to shine a flashlight inside a hollow sphere. Would the light continue in a straight line until it hits the walls of the sphere or would it "bend." If so, in which way?

Thanks,
juanucleus

(PS: Sorry if it is a repeated question, I get lost in these threads).

 

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Seeing as no-one else has had a go at this.....

Only if dead centre right?

I would say yes. The light would be slightly blue shifted in wavelength as it is falling into a gravity well, the wall the beam is directed at.

Of course others will agree or not.

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Boris2:

The gravity anywhere inside a hollow sphere IS equal to zero. This assumes that the sphere itself is not close to a massive object.

juanucleus:

The light would not bend inside the sphere since the gravity is zero. Although the light would shift, and might bend, when approaching the sphere.

Tom

 

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What you are saying then Joe is that you would not be able to walk on the interior surface of the sphere as there would be no gravity.

Gravity works on the inverse square law so the nearer you get to one part of the sphere the grav would increase and the effect of the grav from the opposite wall would decrease.

I see that the only place where the grav effects from the sphere are equal is dead centre.

Where am I going wrong here?

 

boris

Joeblow is right. Basically you apply Gauss's theorem to Newtonian gravity. Heres the math.

http://dept.physics.upenn.edu/courses/gladney/mathphys/java/sect5/subsubsection5_1_1_2.html

 

Thanks (Q) Intutition lets me down again.

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The link explained it nicely, lucky for me the were words inbetween those squiggley things.

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Thanks for the responces so far.

But if I may, Boris2, why is this a blue shift? Intuatively I would have thought it would be a red shift.

Thanks,
juanucleus

 

Well I was thinking, incorrectly as it turns out, that the gravity would increase going from the centre of the sphere towards the walls. Light can be gravitationally red/blue shifted depending on which way it is travelling within a gravity well. Redshift when moving away from a gravity source and blueshifted when falling into one.

But neither of these would happen in your sphere.

 

Unless the material were a perfect reflector, the light would not last long. It would get dimmer every time it reflected from the interior of the hollow sphere. At the speed of light it should do a lot of reflecting.