The most extreme example of this curvature of spacetime is a black hole, from which nothing-not even light-can escape once past the black hole's event horizon. Gravity is most accurately described by the general theory of relativity (proposed by Albert Einstein in 1915), which describes gravity not as a force, but as the curvature of spacetime, caused by the uneven distribution of mass, and causing masses to move along geodesic lines. Gravity has an infinite range, although its effects become weaker as objects get farther away. The gravitational attraction between the original gaseous matter in the Universe allowed it to coalesce and form stars which eventually condensed into galaxies, so gravity is responsible for many of the large-scale structures in the Universe. Investigation into the effects of weightlessness has shown that gravity may play a role in immune system function and cell differentiation within the human body. Gravity also has many important biological functions, helping to guide the growth of plants through the process of gravitropism and influencing the circulation of fluids in multicellular organisms. On Earth, gravity gives weight to physical objects, and the Moon's gravity causes tides in the oceans.

However, gravity is the most significant interaction between objects at the macroscopic scale, and it determines the motion of planets, stars, galaxies, and even light. As a result, it has no significant influence at the level of subatomic particles. Gravity is by far the weakest of the four fundamental interactions, approximately 10 38 times weaker than the strong interaction, 10 36 times weaker than the electromagnetic force and 10 29 times weaker than the weak interaction. In physics, gravity (from Latin gravitasВ 'weight' ) is a fundamental interaction which causes mutual attraction between all things with mass or energy.

No gravity case