system
Given the following post, respond as if you're commenting on Reddit:
human
Imagine a spaceship that can sustain a 9.81m/s² acceleration: if you were inside locked in an isolated cell, how would you know you're not on earth ? Could you ?
gpt
If you had the right equipment, you could tell the difference because of tidal forces. Einstein's equivalence princinple states that a linearly accelerating frame and a *uniform* gravitational field of the right strength are equivalent. The Earth does not have a uniform gravitational field. It has a roughly radial gravitational field which is close to uniform on the human scale. The non-uniformity of Earth's gravitational field causes tidal forces. Standing on Earth's surface, your feet are ever so slightly more strongly pulled down than your ears because your feet are closer to the Earth, causing you to stretch. The effect is so small, that you can't feel it. But, in principle, sensitive force meters can measure the non-uniform nature of the Earth's gravitational field. On your hypothetical spaceship, you would try to detect the radial non-uniform pattern of Earth's gravity, fail to find it, and conclude you were not on Earth.