Question

Q.by what is the universe is expanding?

Answer 1

All the galaxies are moving apart from each other
it's like blowing g of a balloon with some spots on it

Answer 2

The universe was born with the Big Bang as an unimaginably hot, dense point. When the universe was just 10-34of a second or so old — that is, a hundredth of a billionth of a trillionth of a trillionth of a second in age — it experienced an incredible burst of expansion known as inflation, in which space itself expanded faster than the speed of light. During this period, the universe doubled in size at least 90 times, going from subatomic-sized to golf-ball-sized almost instantaneously.