Cosmological Phase Transition
A cosmological phase transition is a hypothetical scenario that hypothesizes that the universe at any given second could undergo a complete phase transition that would be spawned by a region of space undergoing a process similar to quantum tunneling; however given the expanse of time necessary for such an occurrence to manifest it is theorized that the only time in the universe where this is possible is during the dark era, as the universe progresses infinitely closer to heat death. Now Let me attempt to explain this in detail….
First we must understand the vacuum energy. To put it simply: a vacuum is not necessarily a vacuum. There are miniscule particles flashing in and out of existence, annihilating one another and paying back the energy which they borrowed from the vacuum energy. (This is just a very brief, simple and abbreviated summary of the vacuum energy, for more information read up the nodes on that.) Even empty space has energy in it. This Vacuum Density Energy is only a theory and is one of the many proposed solutions to the Cosmological Constant Problem…
Now continuing onto this Phase Transition Business…. If we assume that the universe has a vacuum energy density then that vacuum energy density has a value that we can represent by some number. For our sake, let’s accept that the value can be represented by 5. (This is arbitrary and has no basis in physical reality) Now, all physical systems have a tendency to evolve towards the lowest energy state available; however, not all systems can readily reach that point. There are such things as energy barriers. Take for example an atom with electrons orbiting the nucleus. The electrons in the third energy level are not in the lowest energy state available but instead are in a local minimum energy level. The electrons have a tendency to evolve towards the lowest energy level possible, but they cannot overcome that energy barrier without an outside contribution of energy. Within a closed system that is impossible; however, that is the great part about the vacuum density energy… (This part of the process is also known as Quantum Tunneling)
If we hypothesize that the universe may be caught in a high vacuum energy state this process of cosmological phase transition becomes possible. The universe could at any moment, have any region of space-time spontaneously convert to a lower energy state (Vacuum Energy state from False to True) via the same principles that govern quantum tunneling on scales closer to the Planck length. Of course as Quantum Tunneling is a relatively uncommon process (I stress relatively uncommon) the time scales necessary for a space in the universe to undergo such a transition are quite great, but not infinite (if the universe is trapped in a higher vacuum energy, then it is inevitable that it will happen at one point, as time approaches infinity). The Energy of the Universe is bound to go from 5 to 4 or 3 (or even lower in our system of arbitrary energy state values). A place in the universe will do it at one point if it is possible, it is the natural progression of energy in a system and at that point nothing can stop it.
This is all purely hypothetical and we cannot be certain that this energy is a definite component of the universe yet (though we’re fairly sure it may be). If this vacuum energy density actually exists than this is more than speculation; it is a real example of what could happen to the universe as it evolves… To truly understand this we must form a complete and coherent theory of the Vacuum Energy and the Cosmological Constant Problem.
Now here is the fun part: What would humans actually experience during a Phrase Transition?
Well firstly, you would experience nothing. It would happen so fast that you wouldn’t even realize it happened. The front would move at the speed of light at least. (Inflation was a period of expansion where the expansion was greater than the speed of light (See Horizon Problem) – this is an event of similar magnitude) and would consume every human an object in the universe before a human brain could process something was happening. The whole universe could consumed in 10^-10 seconds or less.
If you could experience the phase transition here is a brief summary of what would happen. A microscopic location in space would undergo the phase transition. It would bubble (an approximation of the effect) and slowly crystallize surrounding points in space. Nearly instantly, each of those points would crystallize and spread outwards. The universe spanning from the new bubble would be a new universe with completely different laws of physics and forces.
So there it is: Cosmological Phase Transition. Remember that this is all hypothetical; however, also keep in mind, that if it is true; the universe could end at any given moment consuming everything in a horrible, horrible finale, and you would never know it’s coming…
Source for most information: Fred Adams' "The Five Ages of the Universe."