Question

before einstein, everyone pretty much thought of space as a sort of blank nothingness that separated objects like planets, solar systems, stars, and galaxies. this nothingness of space was a humongous, rigid background, with all of the matter in the universe arranged on it like pieces on a game board. newtons force of gravity ruled this game, pulling things closer together and making them move against the spacey backdrop of nothingness.. which detail should be included in the summary of this excerpt? people thought that space was ruled by the planets. people thought that space was unchanging. space included planets, solar systems, and galaxies. space had matter arranged at a great distance.

Explanation:

The text states that before Einstein, space was seen as a rigid, unchanging backdrop with matter arranged on it. The idea of an unchanging space is a key - concept in the excerpt. The other options are misinterpretations. Space was not thought to be ruled by planets, the text focuses on the nature of space rather than what it includes in terms of celestial bodies, and the great - distance arrangement of matter is not the main point.

Answer:

People thought that space was unchanging.