There's been a lot of talk recently about the Large Hadron Collider. Most of it, unfortunately, has been the press going "there's this big Science thing that could kill us all!" and not having a clue about what is actually going on up there. Unfortunately, journalists are not very good at Science. This hype has been blown so out of proportion that somebody committed suicide. XKCD, our favourite comic, did a comic about it which you should read.
Anyway, I thought I'd clear a few things up. I only did first-year Physics at university, but I've done some reading, and I'm going to try to explain exactly what is going on in Switzerland, in words that even a journalist will be able to understand. I'm leaving out the maths, and oversimplifying some things, but I hope I can at least give some idea of what is going on. (Everything below is as physicists currently see it, but of course might change as we discover new stuff.)
First of all, the bit that everybody pretty much knows: the Large Hadron Collider consists of a very large circular tunnel underneath parts of France and Switzerland, 27km around, and 8.5km across, through which two beams of protons (a specific type of "hadron", explained below) are going to be fired at exceedingly fast speeds. To give you an idea of the geography and dimensions of the LHC, you can look here on OpenStreetMap, where it is clearly marked. The protons are going to be travelling at 99.999999% of the speed of light, which is 299,792,455 m/s (or 1,079,252,840 km/h, or 1,802,617,480,000 furlongs per fortnight). It's fast.
They will be firing two beams through the tube, very close to each other, and then at the right moment, they will shift one slightly so that it collides with the other one. The massive speeds at which they are travelling will mean that when they collide with each other, huge amounts of energy will be released, which will result in lots of bits of matter being created temporarily (you know, e=mc2), and in effect, we will have recreated conditions similar to the universe just after the Big Bang. Don't be alarmed that they are recreating the big bang - they are simply creating a very small area that will contain the sort of particle chaos that would have been around shortly after it, so that they can examine the particles while they're busy rushing around, before they have a chance to settle down and become too well-behaved to observe again.
(An interesting side-note: The proton beams are actually made of lots of clumps of protons, set a small distance apart, so that there will be repeated collisions, each about 2.5 nanoseconds (0.000000025 seconds) apart.)
The idea is that in all this chaos, we will be able to observe a large number of effects that we don't normally get to witness, and that this will shed light on a lot of ideas and theories that we have, and hopefully help us to explain things a bit better than we can now. The data we gather (and we're being quite careful about what we do and do not record) will be recorded and streamed off to datacentres all around the world (including one here in Cape Town), where it will provide physicists with material to study for years to come.
So, that's what the LHC is, and what will happen during the experiments. Now for some background information on the Universe:
The stuff we see every day is all made up of atoms. And atoms are made up of varying numbers of protons, neutrons and electrons. And protons and neutrons are made up of three quarks each.
There are six types of quarks, classified according to strange things like "spin", "charge", "flavour", and "generation", and the most common types are called "up" quarks, and "down" quarks. Two "up" quarks and one "down" quark make a proton; two "down" quarks and one "up" quark make a neutron. ("Down" quarks have 1/3rd negative charge, and "up" quarks have 2/3rds positive charge, so if you add those charges together, you can see why protons have +1 positive charge, and neutrons have a neutral charge.) When a bunch of quarks are bound together to form a particle like this, it is called a hadron - protons and neutrons are the most common types of hadrons. The beams of the LHC are going to consist of a bunch of these protons flying through the tubes, which is why it's called the "hadron collider".
These "up" and "down" quarks are the only ones we really get in the matter we encounter in our day-to-day lives: the others are very unstable, and decay almost instantly after being created.
Apart from the "up" and "down" quarks, the other varieties are called "top" quarks, "bottom" quarks, "strange" quarks, and "charm" quarks. I will now pause for a second while you go and re-read this xkcd comic, especially the final frame.
Get it? Good. I shall continue.
Now that we know what stuff is made of, we can discuss how it interacts with other stuff. There are four (known) forces, or interactions, which can occur between things:
Because physicists like to think that the universe is actually a very simple place, they believe (or hope) that these four forces are actually just different aspects of some Grand Unified force, simply behaving in four different ways. In fact, they have already managed to combine the Electromagnetic force and the Weak nuclear force into one new force, which they call the Electroweak force, which is responsible for both electromagnetic reactions and the weak nuclear interactions. This unification, while it was a great advance, did lead to a problem:
One of the fundamental differences between the W and Z bosons, and the other bosons, is that they are "massive", in the sense that they have a lot of mass. They are much heavier than other particles, and infinitely heavier than photons, which don't weigh anything at all. This was a bit of a problem for the physicists trying to unify the Weak and Electromagnetic forces, because they couldn't work out where the mass came from - why were photons massless, and the W and Z bosons massive, if the two were aspects of the same force? This is where Peter Higgs came in.
Mr Higgs proposed something called the Higgs field, which covers all of space, and sort of "sticks" to some (but not all) of the particles moving through it (or, mathematically - decreases their momentum as they pass through it), giving them mass. This is called the "Higgs Mechanism", and the UCT physics department has a very good explanation of how it works:
Imagine a cocktail party of political party workers who are uniformly distributed across the floor, all talking to their nearest neighbours. The ex-Prime Minister enters and crosses the room. All of the workers in her neighbourhood are strongly attracted to her and cluster round her. As she moves she attracts the people she comes close to, while the ones she has left return to their even spacing. Because of the knot of people always clustered around her she acquires a greater mass than normal, that is she has more momentum for the same speed of movement across the room. Once moving she is hard to stop, and once stopped she is harder to get moving again because the clustering process has to be restarted.
The equations that describe the Higgs mechanism also indicate that there is an extra type of particle, which is also heavy, but had not been detected before. When Higgs originally submitted his paper describing this field, it was rejected, because it "did not predict any new detectable effects". So, he added a sentence at the end, mentioning that the equations seemed to imply the existence of this extra particle, and the paper was accepted. This extra particle is the Higgs boson, which passes its mass on to just about everything else, and would thus be the reason why things have any substance at all (earning it the nickname "God Particle").
To a non-scientist, the above description might set off some warning bells: "He just invented a new boson? Can you just do that?" Higgs didn't just invent the boson, though: he derived some formulae which explained how things interact with the Higgs field, and saw that if the formulae were correct, then it would also mean that the Higgs boson existed. And that's where the LHC comes in.
We've never seen a Higgs boson, and we don't have any actual proof that it exists, but the evidence of the equations, and the way the other particles act and react suggest that it might. This is how Science works: evidence suggests that something might be the case, so we set up some tests to see if the actual practice agrees. If something happens that disagrees with our original idea, we fix it up, or come up with a new one. The results of the experiments at the Large Hadron Collider are going to be examined very carefully, to see whether or not they agree with what Higgs's theories said. This is why we hope to see Higgs bosons flying out of the proton streams: that would positively confirm the theories and equations that he described, which would make our understanding of the universe that much more concrete. Whether or not it happens is debatable, but that's why we're doing the experiments.
Why are people so worried about the Large Hadron Collider? What do they think is going to happen? On the one hand, it's easy to dismiss them as being "Scared Of Big Science" - they heard that the LHC is going to recreate conditions similar to shortly after the Big Bang, and they just don't want that stuff happening anywhere near them. However, there are a few specific worries that people have voiced, which I'll go over quickly now.
Remember a few paragraphs back, I explained that most "everyday" (nuclear) matter is made of protons, neutrons and electrons, which essentially consist of "up" quarks and "down" quarks. Well, if you add "strange" quarks to the mix, you get what is called "strange matter". This can be thought of as a liquid substance totally unlike the nuclear matter that we see around us. The LHC produces a lot of strange matter, but this itself isn't dangerous, because it is very unstable, and decays almost instantly. However, there may also be things called strangelets - tiny, very stable configurations of strange matter. We have never encountered strangelets, but they are theoretically possible. Because they are so stable, they would not decay, and if they came into contact with nuclear matter (which is less stable), they might start converting it into strange mass by adding strange quarks to the up/down mix. The more this happens, the more strangelets there would be, and this would set off a long chain reaction that could turn the whole earth into a huge stable strangelet (known as a "quark star").
The worry, of course, is that the LHC experiments will produce strangelets, but this is highly unlikely: production of strangelets becomes less and less probable at higher energies, and the LHC is very high energy indeed - higher than previous experiments, which failed to create strangelets or destroy the world.
Another popular bugbear that people fear will come out of the LHC is "miniature black holes". A black hole is simply a piece of very, very dense matter. The denser something is (that is, the more stuff that is packed into less space), the more gravity it has, and so the more it pulls other stuff towards itself. A black hole has such high gravity that nothing can break free from it - not even light, hence the black part. Because everything gets sucked into it, its mass increases, and it gets more dense, and the gravity increases even more. You can see why you wouldn't want one of these anywhere near our planet.
Here, the worry is that the LHC experiments will produce enough energy to create micro black holes, which would start sucking the whole planet into them, as depicted on the popular LHC webcams that everybody linked to recently. As a matter of fact, the LHC energies are far too low to create these black holes, and even if they did, they would not be dangerous. Once again, the world is saved by my main man, Stephen Hawking: he predicted a thing called Hawking Radiation, which is a sort of heat that black holes emit. Micro black holes are so small that emitting energy by Hawking Radiation would decrease their mass (remember, energy = mass, e = mc2) fast enough that they would lose their "black hole" status before they had time to suck everything in.
As you may have heard, a helium leak means that the LHC experiments will be delayed two months, but hopefully things will be back on track after that. This is the greatest physics experiment man has yet attempted, and the amazing things we could find out should not take second place to superstitious fears that Science Will Destroy Us All.
I hope that this has been enlightening, and that I haven't been too misleading in my attempts to explain the physics in man-on-the-street language. Let me know if there is anything else I should explain, or any area that is unclear.