What is a false vacuum decay?
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Long story short–our entire existence, nay, the existence of the entire universe as we know it could be drastically changed as a bubble of universe with new laws of physics is formed and these changes propagate outwards at the speed of light. These new laws of physics would not likely be as stable as those in our current state and our universe could become a devastated mess, effectively destroying everything.
The basic concept is that things want to be in the lowest energy state possible and when they are there they are stable. This applies to all of physics from a ball at the top of a hill that wants to roll down to exited and ground electron orbitals in atoms.
The second concept is that our universe is full of fields for the forces and fundamental particles. Electromagnetism has a field but so do the electrons themselves. We think that all the fundamental fields are in the lowest energy state (called the vacuum state which is where the name comes from) except for possibly 1: the Higgs field.
This is possibly not stable but metastable. It is a false vacuum (name). Like being in a ditch but still halfway up the hill. This would be fine if it stayed there but, due to quantum fluctuations it might jump out. It will then of course roll down the hill.
As it rolls it releases energy (like a ball picking up speed) and this energy will kick the balls out of their ditches all around it. Leaving analogy this will create an expanding sphere of new true vacuum with immense energy around it. This will expand at the speed of light and destroy everything it touches. Within this new area the very laws of physics are fundamentally different.
This could have already begun and we would never know until it is too late. Sweet dreams.
A false vacuum decay means there is some quantum field that is stuck in an unstable (or rather “metastable”) state which then converts into its stable state ie. the true vacuum.
Beyond that it’s somewhat difficult to eli5 because a vacuum in quantum physics probably isn’t the vacuum you’re thinking of, which is a region of space with no matter. A quantum vacuum is a state of lowest energy, and if a decay occurred it would release massive amounts of energy and wipe out anything in the vicinity.
All things want to be relaxed; not do anything. They don’t want to move or bounce or spin. They just want to sit still.
So if a ball is on top of a hill, it will roll down to a place where there is nowhere to roll anymore. When the ball rolls down, it’s called a decay. When there’s nowhere to roll anymore, some people call it a “vacuum”.
But imagine a great big hill and below that hill is a meadow. And below the meadow is another hill. Now think back to that ball rolling down the great big hill and imaging it stopped on the meadow. It’s in a state of vacuum decay because it stopped, but it’s a false state because there is still somewhere roll. Now if something happens to give it a push, it will roll down the second hill.
That’s why some people say that’s it’s in a vacuum decay which is false; it still has somewhere else to go, if only it got a push.
Things try to get to their lowest possible energy level. Wood burns, because it contains a lot of chemical energy, and turns into ash, which is very low on it and is very stable. Salt dissolves in water because dissolved molecules have less energy etc.
There is a theory that the actual building blocks of our universe that dictate even the most basic laws of physics like gravity are not in their most energetically stable state. If something somewhere happens and they go to a state of less energy, this could cause a chain reaction engulfing the entire universe and might change the entire way it functions. Humans and earth might or might not be compatible with the new laws of physics or we might just be wiped from existence by the energy released from the changing of state of those building blocks.
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