Heaven is eternal and Earth everlasting. They can be eternal and everlasting because they do not exist for themselves, And for this reason can exist forever.
Everything that has name and form must begin in time, exist in time, and end in time. These are settled doctrines of the Vedanta, and as such the heavens are given up.
Without going outside, you may know the whole world, without looking through the window, you may see the ways of heaven. The farther you go, the less you know. Thus the sage knows without traveling; he sees without looking; he works without doing.