Tennis Ball in Space
What if we place a tennis ball in the Solar System? Will it stay in its place, fall onto the Sun, or fly out of the Solar System and through the Galaxy? It all depends on how it moves and relative to what.
Case 1. The ball is static relative to the Sun and placed equidistantly between Earth and the Sun. It will fall onto the Sun. It happens because to orbit the Sun, it should fly at roughly 30 km/s in a direction tangential to its orbital trajectory. To be more precise, the ball in this case moves at the same speed as the Solar System in the Galaxy and as the Galaxy in the Universe.
Case 2. The ball is static relative to the Galaxy and placed equidistantly between Earth and the Sun. It will quickly fly out of the Solar System at a speed around 200 km/s. The Sun will be unable to keep it. It happens because the Solar System orbits the Galaxy at about 230 km/s. To be more precise, it is the Solar System that will fly out of the ball’s location in the Galaxy, while the ball itself will start to move on a highly complex hyperbolic trajectory pulled by various celestial bodies. The ball in this scenario initially moves at the same speed as the Galaxy.
Case 3. The ball is static relative to a galactic cluster or some other galaxy. It cannot be static relative to emptiness because there is no such thing as an aether. As a result, it will move at a certain speed throughout the Galaxy on a bending trajectory. But the Galaxy's escape velocity is about 550 km/s. Therefore, if the ball's speed is less than that, it will not be able to escape the Galaxy and will start orbiting within it on a very elongated, irregular orbit, unless it hits something in space, the probability of which is extremely low. If the ball's speed exceeds the escape velocity, then it will eventually enter the intergalactic medium.
Page published: March 31, 2026