**Photon’s
delay in the gravitational field**

In
the post “The gem (1)”, the equation for photon’s velocity was derived, which tells
us that the photon’s velocity is not constant in the gravitational field:

Before the equation for photon’s velocity, the equation for gravitational time was derived:

From these two equations, followed the equation for the photon’s path-element:

The Earth’s gravitational influence on the speed of light is practically neglectable. Namely, if we take that the speed of light is , then, according to the equation

on the Earth’s surface it would be

Even If we encounter the influence of Sun, the velocity of a photon would be

But,
very near the Sun’s surface, it would be ,
which is less than .

Let’s assume that a photon travels from Earth to Mars and back, along some path which passes very near the Sun surface.

If the speed of light would be constant, the photon would travel from Earth to Mars and back for some time . But, according to the equationit should travel longer, for some time

So, let’s calculate the

The path-element of a photon is

Along the path , we’d have

for Sun is approximately 3 km.

The minimal value for is , so we have that even the maximal value of exponent is very, very small

Hence, for our calculation, it is sufficient to take just the first two terms of the Taylor series for the function

that is,

Let us divide the photon’s route in four sub-routes:

, , ,

Let us first consider the last sub-route

If we take the point to be the coordinate origin, and the direction of -axis *from ** to * , we’d have

The additional short distance which our photon has to travel is in the Earth’s vicinity. That is very far from Sun, so along the distance we can consider that the velocity of our photon is practically .

So, we get that the time dilation of our photon after it traveled from to isThe sum-time-delay along the last sub-route and the along first sub-route would be

The sum-time-delay along the second sub-route and the third sub-route would be

The total time delay would be

Pic2

If we use these data (the data from Shapiro experiment, shown in the Pic2), we would get the time delay which Shapiro got in his measurement:<!--EndFragment-->

(Google: “Earth Mars Shapiro time delay”)