I was going through some questions on my latest course this morning, and when answering a question on angular velocity, I was wondering how angular velocity applies to light.

If light follows a curve, how do you account for the constant speed without any acceleration? Is this just a case of mixing classical mechanics with relativity, and the equation for angular velocity just isn't applicable...can somebody explain how this is accounted for ?

Light will bend if in a gravitational field, in which case the space itself is not Euclidean, so the photon is traveling what seems to be a straight line for that coordinate system (a geodesic). In changing from one medium to another, a photon will change direction so that might be a curve, but in that case there is an interaction with the material.

 

If you have light go around a circle while there is rotation, e.g. in a laser gyroscope or ring laser, you'll find that the speed isn't constant, but you aren't in an inertial frame. (Sagnac effect)

Light will bend if in a gravitational field, in which case the space itself is not Euclidean, so the photon is traveling what seems to be a straight line for that coordinate system (a geodesic).

 

Right, that kind of makes sense, unfortunately I won't be covering the maths for another couple of years, so I can't really appreciate precisely what's going on.

 

In changing from one medium to another, a photon will change direction so that might be a curve, but in that case there is an interaction with the material.

 

So a change in speed would be down to the refractive index in that case ?

 

If you have light go around a circle while there is rotation, e.g. in a laser gyroscope or ring laser, you'll find that the speed isn't constant, but you aren't in an inertial frame. (Sagnac effect)

 

Due to the frame rotating, and therefore accelerating...I could just look up the Sagnac effect, thanks for the response.

So a change in speed would be down to the refractive index in that case ?

 

Yes.