The concept you're referring to is known as "time dilation" in the theory of relativity, and it can indeed seem paradoxical at first glance. However, it is a fundamental aspect of our understanding of the universe. Let me explain.
In the theory of relativity, it is postulated that space and time are intertwined in a four-dimensional fabric known as spacetime. Spacetime is not fixed or absolute but rather is influenced by the presence of mass and energy. This influence is described by the theory of general relativity.
According to general relativity, massive objects like planets, stars, or even black holes create distortions in the fabric of spacetime. These distortions, in turn, affect the motion of objects within their vicinity. One consequence of this is that time itself can be affected by gravity.
In the presence of a gravitational field, time dilation occurs. It means that time passes at a different rate for objects in different gravitational potentials. This effect has been observed and confirmed through experiments and measurements, such as the famous Pound-Rebka experiment and satellite-based atomic clocks.
So, when you say something can be at rest in space but still moving through time, what you're referring to is the fact that even in the absence of any apparent motion through space, time can still elapse differently for different objects due to the influence of gravity. This is not paradoxical but rather a consequence of the nature of spacetime and the way it is affected by mass and energy.
To summarize, time dilation allows for objects to experience different rates of time passage based on their gravitational environment, even if they are not in motion through space. This effect is a direct consequence of the theory of general relativity and has been experimentally confirmed.