Mathematically which function is most suitable to describe the path of the light in cosmic space ?

Question

It has nothing to do with A. Einstein.

...because that's a theory, not a mathematical function...

Answer 1

Einstein's tensor equation. Here it is;

http://en.wikipedia.org/wiki/Einstein_tensor

Added : Sorry but it has everything to do with Einstein. As the light travels through space, it will come across masses which warp the space around them. Einstein's tensor describes these paths called geodesics that the light will follow.

Answer 2

Depends on how you look at it. Technically light always moves in a perfectly straight line [so in 3-D space its best described as a direction vector and a point the light passes through], however if the space is distorted by gravity, this straight line may effectively curve.

This is why black holes pull in even light. The light doesn't actually bend, the space it is travelling in does.

Its quite an abstract concept that space itself can be stretched and distorted, and the rubber sheet analogies provide a good method of imagining the process.

Unfortunately, Einstein has everything to do with this. So the above answerer is correct.