So, a true vacuum is a vacuum devoid of space/time and any form of particles, correct? Is it correct that a true vacuum can have an energy state, even if it is devoid of particles? According to the uncertainty principle, a system has unstable energy (and cannot have 0 energy because of this), so given this can a universe form from a true vacuum spontaneously? I've heard Vilenkin say a universe can 'quantum tunnel' into existence. Even though I thought quantum tunneling was restricted to quantum particles tunneling through already existing material. He also said that when a false vacuum forms from this, the change in states causes an explosion of energy, and also commented that "well you might ask why there is a true vacuum state, and I will talk about that later", but he didn't say much else about it. Is there anywhere I can get good information on what we know about true vacuums and quantum tunneling in this context, or anyone that knows much about this explain it here briefly? I can't really find anything on the internet on the subject.