Question

Why does intergalactic space expand, but not not galaxies and solar systems themselves?

Answer 1

The galaxies and solar system is made of dust and stars which have a certain amount of expansion property with stops after certain period of time. Like the stars present in the universe are made up of only dust which form during the the start of the particular solar system and then when the stars used up all the gases present around them they stop to expand more . This phenomenon happens with galaxies but the intergalactic space present does not consist of this phenomenon of stopping its expansion and so the expansion goes on but after certain period of time the expansion stops and that's the time when the universe all the intergalactic space present ends up and collides.