How can the universe be infinite if it is expanding?
There is no reason the universe can’t be both infinite and expanding. You should not think of the Big Bang as a kind of explosion from a point- rather, it was the beginning of an expansion. The thing that started to expand could have been infinite to start with. Our observable universe started as an object with extremely tiny size, and expanded to the size it is today, but there’s no reason the universe couldn’t be made up of an infinite number of such points, all expanding together.
