More vacuum is always possible, to an extent. Human-made vacuums are so far from empty that I must either disregard them as vacuums or define vacuum in relative terms. To be clear, a vacuum is a void containing no matter; it’s literally just space-time. So humans can make low-density regions, or quasi-vacuums, with no comparison to the near vacuum of space (who knows but there is surely a couple hydrogen atoms per cubic centimeter). Anyway, I want to talk about vacuums where the fabric of the universe is the limiting factor and not how much a human can suck out of a can.
A total vacuum would be impossible for two reasons, both follow the same fundamental logic I believe. The first reasoning is from basic physics and the second is one from conceptual physics. First, nothing except space-time by itself is the ultimate vacuum but the external pressure would be nearly infinite so it would be impossible to form or contain for any amount of time. At the smallest volume of vacuum matter will occupy it as repelling charges or kinetic motion moves matter to the place of least resistance (think law of entropy). Albeit, by random chance a pure vacuum could exist for an instant but for the second reason even a spontaneous-flash-vacuum may be impossible. This second reason clinches it because the void would instantly contain something as particles flux into and out of existence in the fields that exist inherently in space-time. This comes from the Casimir Effect where a subatomic void will have outward pressure apparently manifesting something where there is nothing (a space less than an atom acting like it has an atom squeezing in). Really. a pure vacuum is an ideal impetus for virtual particles to form. The instant a pure vacuum occurs a particle is formed. So, a vacuum is self-defeating.
Further Details and Bonus Material:
This all may sound like hooey, but at least the impossibility of a vacuum of pure nothing does obey the laws of thermodynamic conservation. The energy required to void a given volume could (all or in part) reallocate to make these particles erupt from the fields in the void. The amount of energy used to make pure vacuum would equate to the energy of particles manifesting in pure vacuum. Simply, vacuum creation equals particle creation.
And it can reverse, vacuum reduction equals particle reduction as some particles compress to composite particles and energy is conserved through radiation and kinetics. That’s about what it’s like when atoms are formed. That’s another story, of course.
But a potential example to support this vacuum claim is readily available in the theory of quarks. If quarks are pulled apart (they always come in pairs or threes) sufficiently their binding energy is reallocated and a new set of quarks appear. Following E=mc^2, the energy used to pull them apart against their binding energy eventually converts to make new quarks, rather than remaining potential energy of separated quarks. The only way to separate a quark set is to give each quark a new partner. Perhaps it’s applicable towards pure vacuum.
A final note (and a happy ending) must address dark energy and/or vacuum energy. Dark energy is the unknown force that we observe as a cosmological constant of expansion. An apparent force is steadily expanding space-time itself causing an expanding universe. Perhaps anti-vacuum particle formation incessantly fills in voids forcing space to expand. Some energy forced things apart, equal energy fills the voids, and it’s all tumbling outward toward equilibrium. An entropic, heat-death destiny…. then, naturally, it collapses back down toward singularity. Ad infinitum it’s endless universes in series! This allows for the probability of a universe with sufficient conditions for life to eventually appear to be 100% given infinite tries. We’re guaranteed to exist, as are tons of other wonky realities.
The Broad Spectrum Life 