The twin paradox, as described in special relativity, involves two twins, one of whom remains on Earth (the stationary twin) while the other travels at a high velocity to a distant star and back (the traveling twin). When the traveling twin returns, they find that they have aged less than the stationary twin.
It's important to note that the twin paradox can be understood purely in terms of special relativity without the need to invoke general relativity or gravity. In special relativity, time dilation occurs due to relative motion between two observers. When the traveling twin accelerates and changes direction to return to Earth, it breaks the symmetry of their motion relative to the stationary twin.
Acceleration and deceleration are indeed involved in the twin paradox, but they are not the cause of time dilation. Instead, the acceleration and deceleration serve to break the symmetry and establish a preferred reference frame (the frame of the stationary twin) to which the time dilation can be attributed.
In the scenario where the traveling twin undergoes acceleration and deceleration, they experience non-inertial motion, which complicates the analysis. Special relativity alone cannot fully describe such non-inertial situations. To accurately account for the twin paradox in this case, general relativity, which encompasses both special relativity and gravity, would need to be considered.
In general relativity, the effects of gravity are described as the curvature of spacetime caused by massive objects. In the presence of a gravitational field, time dilation can occur. This is known as gravitational time dilation. However, in the context of the basic twin paradox without gravity, the time dilation is solely due to relative motion and does not involve gravity.
In summary, the twin paradox can be understood within the framework of special relativity without invoking gravity. The time dilation experienced by the traveling twin is a consequence of relative motion and does not require the presence of gravity.