“Excited” quantum states with energy above a vacuum state don’t stay excited for very long, and tend to quickly decay down to lower energy states by emitting photons and other packets of energy. In quantum field theory, which connects quantum physics and the dynamics of spacetime, a vacuum is better understood as the lowest possible energy state. But the fact that our universe is mostly vacuum is part of the reason it exists in a relatively stable state. It's commonly understood that a vacuum is a region of total emptiness, so it’s confusing to think that our entire universe which contains planet earth, distant galaxies and everything in between is almost entirely a vacuum. In particular, understanding the conditions for spacetime decay through a bubble of nothing is a step towards connecting the best theories about the tiniest building blocks of the universe-strings-with theories about space and time itself. But three physicists at the University of Oviedo in Spain and the University of Uppsala in Sweden argue that we can learn important lessons from an all-consuming, universe-destroying bubble in a wonderfully titled paper, “Nothing Really Matters”, submitted to the Journal of High-Energy Physics this month. Given that a bubble of nothing has not in fact destroyed the universe, neither in the 13 billion years before Witten published his paper nor in the 38 years since, it would be reasonable for physicists to push it down the research priority list. He wrote: “A hole spontaneously forms in space and rapidly expands to infinity, pushing to infinity anything it may meet.” The idea that in specific scenarios the universe would be entirely destroyed by an expanding bubble of nothing has been around since 1982, when theoretical physicist Edward Witten introduced the possibility of the universe eating itself in a paper in Nuclear Physics B journal.
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