The universe may be eating itself up on the inside, but don't worry: physicists studying this phenomenon, called "spacetime decay," think it's unlikely.
The idea that in some development scenarios the universe would be completely destroyed by an expanding bubble of nothing has not been recalled since 1982, when theoretical physicist Witten presented the possibility of self-criticism of the universe in the journal Nuclear Physics. He wrote: "A hole spontaneously forms in space and rapidly expands to infinity, absorbing everything that may occur on the way."
Considering that a bubble of nothing destroyed the universe either 13 billion years before the publication of the article, or 38 years later, it would be reasonable not to pay attention to such theories. But three physicists from the University of Oviedo in Spain and Uppsala University in Sweden argue that we can benefit from the idea of an all-consuming, universe-destroying bubble.
The fact that our universe is mostly vacuum is one of the reasons it exists in a relatively stable state. In quantum field theory, which links quantum physics and the dynamics of spacetime, vacuum is understood as the minimum possible energy state.
"Excited" quantum states with energies above the vacuum state do not last long and have a tendency to quickly calm down to lower energy states by emitting photons. The vacuum, on the other hand, has no lower energy states to which one can continue to decay, and therefore exists in a stable state.
Since most of our universe is in a vacuum, in a state of minimal energy, we don't need to worry about the decay of spacetime. However, in theoretical physics, such assumptions have no place.
In the early 1970s, several Russian physicists separately explored the idea that there is something in between a stable vacuum and an unstable non-vacuum: a vacuum-like state that appears to be stable due to its very long pre-decay period. This "false vacuum" helps eliminate inconsistencies in theories about early conditions in the universe.
Although the concept of a false vacuum has been proposed to describe only the pre-Big Bang transition, recent research in the Higgs field (the quantum force field detected by CERN's particle accelerator) suggests that we can still live in a false vacuum: what was previously considered stable (the lowest energy) Higgs state may not be the lowest energy state.
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The possibility that the stability of our universe is a very long-term illusion has raised the question of how and for what reason a thin false vacuum could disappear. One answer is because of the "nothing bubble".
A bubble from nothing is one example of a “space-time bubble,” where space-time has different properties inside and outside the bubble. If a bubble of nothing spontaneously forms in the space of a false vacuum, then it will grow, and ultimately absorb the entire Universe.
But why has nothing bubble formed yet? The answer lies in string theory, a popular and successful candidate for the title of “theory of everything,” which describes tiny strings with properties that other fundamental particles lack. In particular, strings have an oscillatory state that explains quantum gravity. In other words, the theory combines phenomena in quantum physics with the effects of gravitational fields. This is why string theory is so popular.
The mathematics of string theory only works if there are more than four dimensions: three spatial dimensions, a temporal dimension, and then many other dimensions that are so small they cannot be detected - they are tightly compressed and hidden and deduced purely mathematically.
According to this math, nothing bubbles will form in 4D spacetime. Their place is only in the "uneven" multidimensional space-time.
In other words, as Czech string theorist Lubos Motl notes, a bubble of nothing is dangerous, because if it were to happen, it must have already happened.
That way, we don't have to worry about the bubble swallowing up all of spacetime. But if you are wondering what the universe looked like before the Big Bang, then it is definitely worth studying the theory of bubbles nothing more closely.
Kirill Panov