A few years ago, the particle accelerator at CERN commenced its first run at 7 TeV in an attempt to find the elusive Higgs Particle. At the time, some physicists expressed their concern that this run might lead to the end of the world.
This story was immediately picked up by the media, and was published almost everywhere. But the story in the media missed the point entirely!
The media insisted that the main problem would be the accelerator creating a "black hole" which would suck up the earth. But this was never the point the physicists were worried about!
In this article I present the actual theory which had physicists worrying about the end of the world coming about in the particle accelerator. It is a sound and logical theory, which we will explain using barely any complicated mathematics. Its name is the Theory of the False Vacuum (catchy, huh?)
The Theory is based off of this article by Sidney Coleman, a very famous physicist. The idea behind it is that the universe might be in an unstable vacuum state, and not in its true vacuum. Assuming this is true, Coleman asked himself what would we expect to happen to the universe as we know it.
Coleman's answer is very grim indeed, but let's take a look anyway!
This is a very loaded question, but we'll stick to a simple definition - a vacuum is the state with the lowest potential energy. To visualize this, imagine a ball on a roller coaster:
Let's say we put the ball at any point on the roller coaster and push it in a certain direction, and then leave it for a while until the ball rolls to a stop. Where would we expect to find the ball?
We would of course expect to find it at the lowest point on the track (A). We call the lowest point on the track the "vacuum" of the theory. Putting a ball there means it will most likely stay there.
But this theory has another "vacuum", the second lowest point (B). If we put a ball there with only a small push, it would most likely stay there. We call this an "unstable" of a "false" vacuum - It resembles a vacuum, but is definitely not the lowest vacuum. A big enough push would make the ball roll into the correct vacuum.
In his paper, Coleman considered the consequences of being in a universe which is in an unstable vacuum (like point (B) in the roller coaster). Since the vacuum is unstable, eventually a big enough push will lead our universe to "roll" into the true vacuum. This would lead to the entire structure of the universe changing - the values of the constants of nature (the speed of light, Plank's Constant, the masses of particles...) would change, leading to extremely dramatic consequences. This "roll" into the true vacuum will most certainly mean the destruction of earth, and would make the rest of the universe unrecognizable to us.
This "roll" would come about in the form of a "true vacuum bubble" - at first only a small bubble-like segment of space would be in a true vacuum space, and this bubble would expand in all directions at the speed of light.
Coleman shows that if a bubble was to expand and reach earth, the change would be so quick that we would never notice it was happening. Quite unfortunate....
The short answer is that we don't know. Currently we don't even know how to check whether or not the universe is at its stable vacuum.
And yet, many physicists believe we are indeed in an unstable vacuum. Some argue that since there is only one true vacuum but many false ones, there is a higher probability of our universe residing in a false vacuum. Others argue that the symmetry breaking properties of the Standard Model indicate that we are at a false vacuum. But these are just theoretical arguments, and at the moment no one can say for sure whether or not the universe is at its true vacuum.
Even though we cannot say for sure whether or not the universe is at a false vacuum or not, it shouldn't worry us too much. Even of we are at a false vacuum, there is nothing to indicate that the roll into the true vacuum should happen anytime soon (and even if it does, the change would happen too fast for us to notice). Meanwhile, this question has aroused the interest of science fiction writers, and a few books discussing how humanity might try to deal with a roll into the true vacuum have been published (e.g. Greg Egan's "Schild's Ladder).
To learn more one can try looking into theories on the false vacuum online, or try one of the science fiction books on the subject.
As for the experiments at CERN, physicists were worried (and some still are) that running the accelerator at high enough energies will create energy densities so big that they might initiate our roll into the true vaccum. But since we have no idea whether we are at the true vacuum or not, or even what kind og energy densities are needed in order to initiate the roll, there's really no use worrying about it yet!