Relatività

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Einstein: “Light must bend in a gravitational field”, but light also always takes the shortest path, maybe the shortest path under gravity is not a straight line. Gravity thus must bend space. Thanks to Marcel Grossman he then proved the theory with the math needed. Newton thought that space and time were fixed.
John Wheeler: “Space-time tells the matter how to move. Matter tells space-time how to curve.”
This theory proved itself practical by anticipating Mercury’s ellipse, which was a mistery.
Gravity bends space.

Time

Light also moves at the same constant speed, no matter the referencing frame. Speed is

$$\frac{distance}{time}$$

But we already said that light always has the same speed, so the speed of light near gravity and the speed of light in empty space is the same. But the lenght traveled by light near gravity is greater then the one in empty space, this means that the time it takes must pass slower near the gravitational field.
Gravity slows time down.

Ricapitolando

La misura propria è la più lunga:

$$L=\frac{L_0}{\gamma }$$

Dove:

$$\gamma =\frac{1}{\sqrt{1-\frac{v^2}{C^2}}}$$

Il tempo proprio è il più corto:

$$\Delta t^1=\gamma \Delta t_0$$

per comodità si usa anche:

$$\gamma =\frac{1}{\sqrt{1-{\beta }^2}}$$

dove

$$\beta =\frac{v}{c}=\sqrt{\frac{{\gamma }^2-1}{{\gamma }^2}}$$

Questi effetti dilatanti valgono solo sulla direzione della velocità.