Much of the Universe appears to be a vacuum and is something that we think of as the lowest energy state that anything could ever reach but is that really true? Is there another even lower state below that?
We know that even if we could remove all of the matter and all of those pesky blackbody photons the vacuum would still be a complex phenomenon. In this thought experiment there would be no photons in this vacuum and even though the average of the electric and magnetic fields would be zero, their variations would not be zero (see non-html Reference 1).
It is said that the vacuum is filled with virtual particles that briefly pop in and out of existence so that even a void such as this still has an energy associated with it called the vacuum energy and it is thought to be a natural consequence of Heisenberg's Uncertainty Principle.
Okay, now think of a ball on a hill as shown in the figure below. It rolls down that hill until it reaches the bottom and comes to a rest (let's suppose that there is a lot of friction).
Also imagine that the hill is not a just simple hill, it is part of a hilly landscape like the kind you would find in Colorado or Switzerland. The ball in this case has only reached what STEM types would call a 'local minimum'.
The deeper valley to the left of that ball would be called the global minimum and represents the absolute lowest that the ball can go in this scenario.
In the case presented here the ball could in theory get to an even lower energy state but there is another hill preventing it from doing that so it doesn't.
In classical mechanics that would be the end of the story, the ball would just sit there forever and not reach that lower energy state unless something came along and gave it a kick.
However in quantum mechanics particles sometimes manage to break through such barriers exhibiting a mechanism referred to as quantum tunneling (as represented by the green dashed line in the figure above).
(I personally like to think of it not as an actual 'tunneling' per se but more that the barrier itself is 'fuzzy' and the virtual particles providing the force for the barrier are chaotic and probabilistic. In this mental image sometimes the virtual particles are briefly quiescent and do not do an effective job of putting up that barrier. In these very brief moments a particle is simply able to walk on through to the other side.)
Released to public domain. It's a black square, who in their right mind would try to copyright that?
The True Vacuum
So we have the vacuum of our Universe which we know has some kind of energy associated with it. It is at a low energy but an energy that is still there nonetheless. We also now know of the existence local minima and global minima.
What would happen then if the vacuum in our Universe was actually only at a local minima? Is it possible that an even lower energy state exists? Could a small spot in the vacuum of the Universe out there ever accidentally 'tunnel' down to a lower energy state?
Such things have been though about and it is considered that this state would have no waves, it would have no particles. There would be truly nothing at all.
So if the Universe could ever get over that hump that separates the false vacuum state from the true vacuum state by quantum tunneling or some other mechanism it would spell the end of the Universe as we know it.
If a spot in the Universe ever did reach this true vacuum state it would spread outwards at the speed of light (I presume) expanding and consuming everything in its path.
Since it would be expanding at the speed of light, astronomers would have no way of detecting the event. Our telescopes would see no weird dark empty sphere slowly getting bigger and bigger.
The true vacuum front would simply reach us, without warning, and we and the Earth would blink right out of existence. Not even hiding under your covers at night would save you.
I warned you that this would be a scary concept. The fact that there might be a sphere of non-existence expanding outwards at the speed of light consuming our Universe is enough to keep you up and night.
That is until you realize, if true, there is nothing you can do about it and things you can't fix are things you don't need to worry about at all. Also if this true vacuum swept through our galaxy and then our solar system it would all be over faster than you could realize. Sleep tight.
Thank you for reading my post.
Non-HTML Reference 1. Craig, D. P. & Thirunamachandran, T. (1998). Molecular Quantum Electrodynamics (Reprint of Academic Press 1984 ed.). Courier Dover Publications. p. 40. ISBN 0-486-40214-2.
About me: My formal education was in Physics (B.Sc.) and my M.Sc. was also in physics in the area of experimental quantum mechanics. My career, going on 25 years now, is in engineering physics.
I like to blog about STEM topics because:
• it helps me to crystallize my knowledge about things that I already know (the Feynman technique),
• it helps me to learn new topics that I want to know and
• I hope that it teaches and inspires people to be more interested in STEM.
My blogging style is to try to translate scientific concepts and jargon into something that a layperson or STEM enthusiast would enjoy reading.
I also wrote a style guide (link here) for STEM posts that you might find interesting (or not, up to you).