Part 3: Strangelets and vacuum bubbles
As with black holes, strange matter - the stuff of which strangelets are made - is thought to normally form only under extreme conditions. At the heart of the most massive neutron stars, the pressure is so great that the force holding the star together against gravity - neutron degeneracy pressure - is overcome. This pressure arises from a simple quantum mechanical effect: the exclusion principle (often called the Pauli exclusion principle). It essentially states that no two particles can occupy the same quantum state at the same time. 'Quantum state' is most easily read as 'position,' but is in fact a sort of mathematical model designed to completely represent a quantum-mechanical system. A well-known example is the way electrons in an atom form into discrete 'shells.' Each shell can be said to allow for a limited number of different quantum states, which explains why each shell can hold only a certain number of electrons.
In a neutron star, the neutrons are packed very tightly together. There are a limited number of quantum states they can occupy, and hence a limited number of low-energy quantum states available. While every neutron 'wants' to occupy the lowest energy state possible, there simply aren't enough to go around, so many are forced into higher energy states. These high-energy state neutrons are almost entirely responsible for the pressure supporting the entire star, which helpfully arises from a quantum-mechanical effect and so does not vanish as the star cools down.1 It is interesting to note that the same process supports white dwarf stars, except in this case electron degeneracy pressure is the driving force. Electrons, being less massive than neutrons, cannot support the same amount of pressure. Hence why white dwarfs are less massive than neutron stars.
Degenerate quark matter, of which strange matter is a special type, is a hypothetical form of matter that forms, as said above, under force great enough to overcome the neutron degeneracy pressure but not great enough to trigger the collapse to a black hole. Just as the atomic structure of matter collapses into neutronium under huge pressure, so a pressure many times greater still breaks up the neutron into its component parts, quarks, which come in a pleasing variety of colours and flavours. In protons and neutrons, quarks are rigidly held in place (so to speak) by the strongest force of nature - the appropriately named 'strong force.' Under extreme conditions, however, nucleons (protons and neutrons) can break down into a 'plasma' of quarks and gluons (gluons are to the strong force what photons are to electromagnetism (photons 'carry' the electromagnetic force between appropriate particles), although they come with a few other perks that photons lack). This process could be thought of as analogous to how a solid, when heated, breaks up into a liquid.
Quark-gluon plasma can be briefly formed in supercolliders2, but strange matter - which contains the highly unstable strange quark, possibly with up and down quarks as well - would require the truly extreme conditions of astronomical bodies such as massive neutron stars to be formed, if it can form at all. Surely, then, particle accelerators pose very little threat.
Once again, there is a loophole that might just allow strangelet - a strangelet is a small nugget of strange matter - production at low-ish energies. The requirement is that strange matter, far from being an unstable substance when removed from extremely high-pressure environments, is in fact more stable than normal matter, even at zero ambient pressure. In this case, ordinary matter is in fact "metastable" - I'd say pseudo-stable myself, because metastability means 'acting stable, but actually not stable at all.' The best analogy is supercooled water. Absolutely pure water can be cooled below 0°C without turning into ice, because of a lack of particulate matter for ice crystals to form on. When even a tiny speck of dust is introduced, the water instantly freezes. Similarly, it could be that ordinary matter is only stable so long as there is no 'example' around onto which matter can freeze - to whit, a strangelet. Therefore, a strangelet in contact with ordinary matter converts that matter into more strange matter, and so on until no more matter is available to be absorbed.
Theories that propose such stranglets are not uncommon, but nor are they mainstream. A lot of criteria have to be met for particle collisions to produce dangerous strangelets (see the writeup on strangelets, for instance). The single strongest argument against strange matter as a more stable state of matter is the "it would already have happened" argument. Somewhere in the solar system, a cosmic ray would have produced a slow-moving dangerous strangelet that ice-nine'd its parent mass - an asteroid, a moon, a planet, the sun - and we would have noticed this by now.
The production of a dangerous strangelet is probably less likely than circumstances conspiring to allow the LHC to produce dangerous mico black holes. There is a possibility it is more likely: the relevant areas of physics are not very well understood. The Opposition like to say that
"1. From what I can gather, there is quite a bit of controversy as to whether or not neutron stars might be strange stars or not. Would it not be prudent to wait until this is resolved?"3
This is of course rather annoying. The idea of experiments such as the LHC is to resolve unanswered questions in physics such as these. "Waiting until this is resolved" might well amount to cancellation - one cannot open a box using the
crowbar inside the box, and one cannot
resolve such questions using the physics that you are only permitted to try to understand
after the questions are resolved.
Vacuum bubbles
This is really the first idea to which the answer is unambiguously "no, that will not happen." The claim is3 that the LHC could cause spacetime to collapse from its current state - which might be only a metastable state - into a more stable state that would be a 'true' vacuum; it would have completely different physical constants from the universe we know, and life as we know it could not exist. Also, as with the rogue strangelet and the supercooled water, it would expand - at nearly the speed of light - and eventually destroy everything. In this case, nothing more is needed than a "it would have happened already." Why? Simple. A true vacuum bubble, initiated by a cosmic ray collision, would, even if it were hurtling forwards at nearly light speed (which seems unlikely for a state of spacetime) expand to engulf everything. This evidently has not happened. If cosmic ray collisions haven't already created a true vacuum, collisions in a particle accelerator will not either.
⇐ Back to part two Forward to part four ⇒
Bibliography
1 - http://hyperphysics.phy-astr.gsu.edu/Hbase/astro/pulsar.html
2 - http://physicsworld.com/cws/article/news/22043
3 - http://www.lhcconcerns.com/LHCConcerns/Forums/phpBB3/viewtopic.php?f=13&t=131&p=938#p938
Note: this section is in need of references. Suggestions are welcomed.