This is a good 10 minute video by Ken Wilber on Emptiness as it relates to the existential level of consciousness. Interestingly, emptiness is NOT a vacuum. It is pure awareness, ONE without another. Here, Ken talks about it as the witness who watches sensations, perceptions, etc. arising and is not identified with any of the contents of consciousness. He also goes into some of the nuances and connotations of the word emptiness in various Buddhist traditions.
Emptiness is empty of inherent existence. In other words, it can be equated with the ground of Being. Everything that exists in the sense of standing out from the ground of Being is an object to awareness which is pure subject. You can compare this state to what was happening before the big bang. There was nothingness in the sense of pure potential and pure awareness. There were no things, therefore, you wouldn’t be able to make dualistic distinctions.