In the context of Einstein's special theory of relativity (SR), there are no experiments that directly observe or investigate the precise moment of turnaround in an inertial frame. This is because SR deals with inertial frames of reference, which are frames that are not subject to acceleration or forces. Turnaround points, where an object changes its direction or undergoes acceleration, introduce non-inertial effects that fall outside the scope of SR.
Special relativity is primarily concerned with the behavior of objects moving at constant velocities in the absence of external forces. It provides a framework to understand the effects of time dilation, length contraction, and the relativity of simultaneity for observers in relative motion. However, the theory does not specifically address acceleration, turning points, or non-inertial frames.
Experiments in SR typically involve observations made from inertial frames and involve objects or observers that move at constant velocities relative to each other. These experiments have provided substantial empirical evidence supporting the predictions of SR, such as time dilation in particle accelerators and muon decay experiments.
To study the effects of acceleration and non-inertial frames, one needs to consider general relativity (GR), which is Einstein's theory of gravity. GR accounts for gravitational effects and allows for the description of accelerated frames and the behavior of objects under the influence of gravity. Within the framework of GR, there have been experiments and observations that provide evidence for the effects of acceleration and non-inertial frames, such as the Pound-Rebka experiment and the Hafele-Keating experiment, which both demonstrated gravitational and kinematic time dilation.
In summary, experiments within the realm of special relativity typically focus on the behavior of objects in inertial frames and do not directly address the specific moment of turnaround or non-inertial effects. For studies involving acceleration and non-inertial frames, Einstein's general theory of relativity is the appropriate framework.