Is the expansion of space time a result of a galaxies gravity? If we take the classic trampoline example of space time I can explain what I mean. Each galaxy makes a dent in the trampoline, the more mass a galaxy gains the deeper the dent. Now if we take 2 bowling balls and place them far enough away on our trampoline that they don’t get stuck in each other’s dent then the space between them will stretch. As each galaxy gains more mass or fall into their own black hole then the space will continue to expand. It seems that the expansion of space time is a result of gravity. So why do we require dark energy?