There are several hypothetical ways in which our Universe could end: the Big Freeze (the expansion to a cold and empty Universe), the Big Rip (the tearing of spacetime), and the Big Crunch (the contraction of the Universe into an infinitely dense singularity). My favorite, however, has always been the Big Slurp, also known as vacuum decay. It’s just a quick, clean, and efficient way of completely annihilating the Universe.
To explain how our universe could destroy itself through vacuum decay, we first need to understand two principles:
- Energy Levels: Everything in the Universe has an energy level. The higher the level, the more energy there is in the system and vice-versa.
- Stability: Everything in the Universe tries to move towards its ground state, in which it has as little energy as possible and is completely stable.
If our current understanding of physics is correct, then the Universe acquires its properties from quantum fields. In simple terms, they are the rules of the Universe; they tell particles how to behave and interact with each other. These fields, like everything else, want to be in the lowest energy level possible, which is called a vacuum state. Physicists believe that all quantum fields have already reached their vacuum state, except for maybe one: the Higgs field (which gives particles their mass). It’s entirely possible that the Higgs Field is in a false vacuum state, meaning that it’s metastable (not actively decaying, but not exactly stable either). Essentially, the Higgs field isn’t at its lowest energy level and therefore has absurd amounts of potential energy.
There are two major problems with living in a metastable universe. One is that if you create a high enough energy event, you can, potentially, push a small part of the Universe from the false vacuum into the true vacuum (lowest energy state). The other problem is that through random quantum fluctuations, quantum tunneling (when a particle “tunnels” through a barrier from one region to another, including vacuum states) could also push part of the Universe into the true vacuum.
These two events would create a vacuum decay “bubble” of the new stable Higgs field that will expand in all directions at the speed of light. The sphere is surrounded by a shell of near-infinite energy that eliminates everything it touches from existence. It will continue to grow forever until it has completely consumed the Universe and incorporated it into the true vacuum. However, this isn’t the worst of it. If the energy level of the Higgs field changes, it changes all of physics. For example, how fundamental particles behave, how atoms interact, and how the universe is structured will fundamentally change. Basically, vacuum decay could not only destroy life, it could also destroy chemistry itself, making life as we know it impossible.
Despite all of this, should we worry? Not really. One reason is that during the first tiny fraction of a second of the Big Bang, when the Universe just started to expand, enough energy should have been created to push the Universe into the true vacuum. The fact that we’re still here indicates one of three things: not enough energy was created to tip us over the edge, expansion did not take place at all, or the Universe is more stable than previously thought. The next reason is that the lifetime of a metastable universe is predicted to be much longer than the current age of our Universe. Finally, the vacuum decay bubble may have already been created, but it might never reach us if it’s located on the opposite end of the Universe. After all, the Universe is extremely vast, and the speed of light is relatively slow on the universal scale.