There is nothing about infinity that makes any intuitive sense. Don't even try to imagine that you 'understand' infinity well enough to have an intuitive idea what it represents! For instance, infinity is so big that you can stuff an infinite number of infinite manifolds ( universes) in an infinite 4- dimensional space-time, and still have lots of room left so that they do not 'touch'. A manifold in 4-dimensions can be infinite and expanding because from the local properties you can deduce that it is locally flat, and undergoing dilation. IF this is true for all parts, then by deduction, you conclude that the entire 3-dimensional manifold must also be expanding. How this is possible is an issue of our limitations in reconciling seemingly conflicting evidence in an arena of experience we cannot be intuitively familiar with. Just like in quantum mechanics when we are forced to accept that an 'object' can behave both as a particle and a wave.