The phenomenon of time dilation, as observed in experiments and calculations, aligns with the predictions of a curved spacetime due to a spherical Earth because of the effects of gravity. According to Einstein's theory of general relativity, gravity is not just a force but rather a curvature of spacetime caused by massive objects.
In the vicinity of a massive object like the Earth, spacetime is curved. This curvature affects the motion of objects and the passage of time. Clocks closer to a massive object, where the gravitational field is stronger, tick more slowly relative to clocks in regions with weaker gravitational fields.
In the case of the Earth, the gravitational field is stronger near its surface and weaker farther away. Therefore, clocks closer to the Earth's surface experience a stronger gravitational field and thus tick more slowly compared to clocks at higher altitudes.
To illustrate this, consider an experiment where two synchronized clocks are placed at different altitudes—one at sea level and another at a higher altitude. Due to the curvature of spacetime caused by the Earth's mass, the clock at sea level, which experiences a stronger gravitational field, will tick slower relative to the clock at the higher altitude.
This observed time dilation aligns with the predictions of general relativity and a curved spacetime due to a spherical Earth because the curvature of spacetime caused by the Earth's mass affects both the motion of objects and the flow of time. The predictions of general relativity have been confirmed through numerous experiments and observations, providing strong evidence for the curvature of spacetime and the resulting time dilation effects.