To understand, let's consider the idea of parallel worlds. By siddhis, or mystic perfections, one can take shortcuts across space. Besides moving from one place to another in ordinary space, the mystic siddhis enable one to travel in the all-pervading ether or to enter another continuum. The classical example of a parallel continuum is Krishna's transcendental realm of Vrindavana, said to be unlimitedly expansive and to exist in parallel to the finite, earthly Vrindavana in India. The Sanskrit literature abounds with stories of parallel worlds.
Mystical travel explains how the worlds of the devas are connected with our world.
In particular, it explains how Jambudvipa, as a celestial realm of devas, is connected with Jambudvipa as the Earth or part of the Earth. Thus the double model of Jambudvipa makes sense in terms of the Puranic understanding of the siddhis. For centuries the cosmology of the Bhagavatam has seemed incomprehensible to most observers, encouraging many people either to summarily reject it or to accept it literally with unquestioning faith. If we take it literally, the cosmology of the Bhagavatam not only differs from modern astronomy, but, more important, it also suffers from internal contradictions and violations of common sense. These very contradictions, however, point the way to a different understanding of Bhagavata cosmology in which it emerges as a deep and scientifically sophisticated system of thought.