Gravity

Not really gravity, but more along the lines of universal gravitation or if you like simply

Every single point mass attracts every other point mass by a force heading along the line combining the two. The force is proportional to the product of the two masses and inversely proportional to the square of the distance between the point masses.

This is truly the force that binds the stars, moves the earth around the sun, and is the power behind the tides. It is what keeps us constantly trying to fall to the center of the Earth. It is what attracts us, in a fundamental way, to every other thing in the universe. According to Sir Isaac it is a force something that does not think, breathe, or have a sense of fashion. We rarely think about it except when we a) drop and break something or b) when, after too many pints, we find the floor by looking up over our shoulder. It is relentless and ruthless, do not appeal to gravity's sense of justice, do not beg it for mercy. It is not good, it does not need justice; It is not evil, it does not need to be merciful. It simply just IS, and a lot of very bright people have spent a lot of time trying to figure it out. They come up with complex formulas, and whole new theories just to explain why planet A is acting a damn fool and orbiting planet B in such an erratic fashion. It reminds us that hitching our wagon to any particular star may led to quite unexpected, and unintended results.