I've been studying geometric optics and I'm still a little confused with this idea of light ray. In the book I'm studying everything is being done starting from Fermat's principle which states that the ray path is the one which extremizes the optical length.

Now, I thought that because of this, geometric optics viewed light as particles and I thought that a light ray then would be a trajectory of those light particles. But my question here confirmed that geometric optics doesn't care if light is made of particles or waves.

On the other hand, if we think of light ray as "the path taken by light between two points", this is no good, because the idea of trajectory in this sense is not well defined for waves. Indeed, this idea of light ray doesn't even seen clear to me, because as we know if we have some light source, the light doesn't go along one single path, but as a wave it spreads out in all of the directions at once.

So, if geometric optics doesn't care about if light is made of particles or waves, what really is a light ray? How should we understand light rays and ray paths?

I've been studying geometric optics and I'm still a little confused with this idea of light ray. In the book I'm studying everything is being done starting from Fermat's principle which states that the ray path is the one which extremizes the optical length.

Now, I thought that because of this, geometric optics viewed light as particles and I thought that a light ray then would be a trajectory of those light particles. But my question here confirmed that geometric optics doesn't care if light is made of particles or waves.

On the other hand, if we think of light ray as "the path taken by light between two points", this is no good, because the idea of trajectory in this sense is not well defined for waves. Indeed, this idea of light ray doesn't even seen clear to me, because as we know if we have some light source, the light doesn't go along one single path, but as a wave it spreads out in all of the directions at once.

So, if geometric optics doesn't care about if light is made of particles or waves, what really is a light ray? How should we understand light rays and ray paths?

I've been studying geometric optics and I'm still a little confused with this idea of light ray. In the book I'm studying everything is being done starting from Fermat's principle which states that the ray path is the one which extremizes the optical length.

Now, I thought that because of this, geometric optics viewed light as particles and I thought that a light ray then would be a trajectory of those light particles. But my question here confirmed that geometric optics doesn't care if light is made of particles or waves.

On the other hand, if we think of light ray as "the path taken by light between two points", this is no good, because the idea of trajectory in this sense is not well defined for waves. Indeed, this idea of light ray doesn't even seen clear to me, because as we know if we have some light source, the light doesn't go along one single path, but as a wave it spreads out in all of the directions at once.

So, if geometric optics doesn't care about if light is made of particles or waves, what really is a light ray? How should we understand light rays and ray paths?

I've been studying geometric optics and I'm still a little confused with this idea of light ray. In the book I'm studying everything is being done starting from Fermat's principle which states that the ray path is the one which extremizes the optical length.

Now, I thought that because of this, geometric optics viewed light as particles and I thought that a light ray then would be a trajectory of those light particles. But my question here confirmed that geometric optics doesn't care if light is made of particles or waves.

On the other hand, if we think of light ray as "the path taken by light between two points", this is no good, because the idea of trajectory in this sense is not well defined for waves. Indeed, this idea of light ray doesn't even seen clear to me, because as we know if we have some light source, the light doesn't go along one single path, but as a wave it spreads out in all of the directions at once.

So, if geometric optics doesn't care about if light is made of particles or waves, what really is a light ray? How should we understand light rays and ray paths?