When you shine a flashlight at the sky, the light emitted by the flashlight will continue to travel through space until it encounters an object that absorbs, scatters, or reflects the light. In the absence of any such objects, the light will propagate indefinitely.
However, it's important to note that light gradually becomes more dispersed and attenuated as it travels through space. This is due to the inverse square law, which states that the intensity of light decreases with the square of the distance from the source. As a result, the light from a flashlight becomes progressively weaker the farther it travels.
In practical terms, the light from a flashlight is not powerful enough to reach significant distances in the vastness of space. It will eventually become too faint to be detectable by the human eye or most instruments. The exact distance at which the light becomes undetectable depends on various factors, including the intensity of the flashlight, atmospheric conditions, and the sensitivity of the detectors used.
In summary, while the light from a flashlight will continue traveling through space until it encounters an object, it will gradually become weaker and less visible over distance. In the context of the vastness of space, the light from a typical flashlight would not reach far enough to be observable or have any significant impact.