This practice should be begun after attaining at least a fair degree of control over breath, mantra, and meditation. Imagination in its mundane form would be such as sitting around thinking about how great it would be if one got the Lotto numbers correct, or wishing for things that seem out of reach.
All matter expands and contracts.
Everything born or created expands, and then contracts, over and over again. Tantra assigns no negative qualities to this 'emptiness,' but teaches that in order for emptiness to be experienced, consciousness must be put into effect. First, recognize the 'emptiness' in the object of contemplation. Emptiness is the space element, or the 'ether,' and permeates all matter, and is greater than all the other elements. Emptiness also dominates the conscious mind much of the time.