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And now for the science bit. Concentrate.
rho meson
rho
As I'm sure you're all aware, the earth has not been destroyed. Fancy that. However, in the middle of all the scaremongering, the pseudoscience and the hardon gags, there's some cool physics going on here, and I'll take any flimsy excuse to geek out about physics.

The cool thing about the LHC (Large Hadron Collider) is that it's colliding hadrons. Which I'm sure has many of you asking, "what's a hadron?" Let's take a brief excursion into what's known as "the standard model". In the standard model, there are three types of particles.

First, there are the particles that are involved in the transmission of forces. These are called "gauge bosons"1. These sit off to one side, and aren't really relevant for what I'm about to discuss.

The second and third types2 are quarks and leptons. These are split up into 3 families, with the first one comprising all everyday matter. In this family we have up quarks and down quarks (both quarks, obviously) and then we have electrons and electron neutrinos (both leptons). These make up all regular matter. Two up quarks and a down quark make a proton. Two down quarks and an up quark make a neutron. Protons, neutrons and electrons make up all the chemical elements. Neutrinos are weird little things that are important for things like radioactive decay3 and keeping the sun burning, but otherwise don't do a whole lot.

The second and third families are pretty much identical to the first family except that they're a lot more massive, and a lot more unstable4. This is why they don't exist in everyday matter. Whenever they do happen to form, they very quickly break down into ordinary matter.

The particles of the standard model, in tabulated form.

OK, so what's a hadron, and why is this significant? A hadron is a composite particle made up of multiple quarks. See the rho meson in my icon up there? That's a hadron. It's made up of two quarks (an up quark and an antidown antiquark), which are joined together by a gluon (one of the force-carrying gauge bosons). Protons and neutrons are both hadrons as well.

Before LHC came LEP, the Large Electron-Positron collider. This was shut down and dismantled in 2000 to allow for the construction of the LHC. The big difference between the two is apparent in the names: LEP collided electrons with positrons, whereas LHC will be colliding hadrons (specifically, protons).

Protons have a lot more mass than electrons do. Over a thousand times as much. This also means they have over a thousand times as much energy. Remember E = mc2? The E stands for energy and the m for mass; so the more mass something has, the more energy it has too5. This means that when we collide them and turn their masses into energy (in addition to the kinetic energy they have from whizzing around at very close to the speed of light) we liberate much more energy. This is exciting.

The amount of energy that we get all in one place is something that hasn't been extant in the universe at large since fractions of a second after the big bang! When you hear people talk about how the LHC will allow us to get closer to the big bang, this is why. We're not going to be recreating the big bang or anything like that. The total energy involved is very small, but it's all concentrated in one place.

So we're seeing very high energy conditions that haven't existed naturally since the beginning of the universe. What can we expect to see? Well, part of the fun of all this is that we just don't know6. If we were certain about what was going to happen, we wouldn't be doing it. By making observations, we'll be able to test current hypotheses to see which ones fit with reality, and we'll hopefully also see completely new things that we hadn't expected, that will lead us to make new predictions.

However, just because we don't know what's going to happen, doesn't mean that we don't have some idea. One of the big hopes is that we'll be able to detect a currently theoretical particle called a Higgs boson.

The Higgs boson is connected to mass. Mass is really interesting, because it does two things which on the face of things shouldn't be connected at all. First there is gravitational mass: the greater an object's mass, the greater the force applied to it by gravity (a rock is heavier than a feather). Then there's inertial mass, which applies to how difficult it is to start or stop something from moving. The greater an object's mass, the harder it is to affect it's motion. It's a lot easier to push a feather aside than it is to push a rock.

Galileo knew about how the two were the same. It's the reasoning behind his apocryphal experiment with the leaning tower of Pisa, and the realisation that all objects fall at the same rate. Einstein knew this as well. The basic underlying principle of his theory of general relativity is that because the masses are the same, there's effectively no difference at all between gravity and acceleration.

What we don't know is why they're the same thing. In fact, we also don't know why mass exists at all. We certainly don't know why the different particles of the standard model happen to have the masses that they do. There's a lot about mass that we don't understand.

This is where the Higgs boson comes in. This is part of an untested and unproven hypothesis about the origin of mass. Essentially, the Higgs boson is part of the mechanism that's responsible for mass even existing in the first place. However, according to the best current models, it's only going to be possible to actual observe one of these at very high energies. The sort of very high energies that existed shortly after the big bang. The very sort of energies we'll be approaching with LHC.

The best case scenario here is that we'll see a Higgs boson, and by observing its behaviour, we'll be able to come up with new models and new theories that explain all this stuff that we don't understand. Then, things like the different masses of different elementary particles might be a natural consequence of the theory, that would just happily fall out of the equations, rather than just the empirical data that we have at the moment. It might help us come up with the much-vaunted "theory of everything" that unites general relativity and quantum mechanics.




[1] "Gauge" is because they follow a set of rules called gauge symmetries; bosons because they're described by mathematics pioneered by a chap called Bose.

[2] Collectively called Fermions after a guy called Fermi.

[3] Beta decay, to be specific.

[4] If memory serves, the most stable of these particles is the muon (the second generation equivalent of the electron) which has a man lifetime of about two millionths of a second under normal conditions.

[5] The c is the speed of light.

[6] Note that just because we don't know what will happen, this doesn't mean we can't say that some things definitely won't happen. We know that it won't turn the LHC into a large green blancmange. We also know that it won't destroy the earth.

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I haven't finished this, but I'm going to take it to work with me tomorrow for some proper education.

I always wanted to be good at smart things. THANK YOU!!

♥ It's just all so damn fascinating!

Having left school (not of my own accord) before physics was taught, this is all very new and cool for me. Thank you.

Also, I am a sad, sad person because in between being all intellectually intrigued-like, I parsed this:

OK, so what's a hadron, and why is this significant?

as:

OK, so what's a hardon, and why is this significant?

*headdesk*

Hmm... methinks someone's mind was elsewhere. ;)

I'm rather proud to say that I understood most some of that.

For me, physics is that pesky 'thing' that means though you are roughtly 14 hours away, it would still take me 2 days to get there. To break that down to protons and electrons without the benefit of a cup of coffee is beyond me, however.

Yay science! I really enjoyed this explanation, and it's just at the right level for biologist me, thanks for writing it.

Well said.

Y'know, whenever anyone said something to me about the world ending - seriously - I told them how you'd told and showed me these things were safe, years ago. You should be proud.

You do for physics what Dan Dennett does for philosophy, and do it well. :)

Thanks for taking the time to write that - it's a really good explanation!

Er- Sorry to bother you, but I really really liked this. Mind you, I kept hearing Ponder Stibbon's voice (Terry Pratchett's Science of Discworld) through the whole thing. :) I'm a string theory fan (yeah, I know, "is that a theory of physics or of philosophy?"), so I'm hoping like crazy for the Higgs Boson. Though the universe doesn't always behave as one hopes...

Noticed you're a Feynman fan-don't suppose you'd be interested in explaining the sum-over-paths aspect of his quantum electro-dynamics in a similar fashion? There's a scifi plot that depends upon particles that affect each other backwards and forwards thru time, and a friend of mine said that Feynman's mathematics actually supported that...

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