What is the Higgs?
nytimes.com
nytimes.com
I really hate this molasses explanation of the Higgs field. The problem is, it is wrong, suggests a wrong intuition and obstructs actually interesting physics. It is wrong, because the mass is something very different from friction. It suggests a wrong intuition, because the snow field, or the molasses, generates a force when something is moving through the medium. But there is no medium to move through. ( And mass acts, when there is a change of velocity, friction if there is velocity.) And the last point, the Higgs mechanism is a mathematical manipulation, which gets a term into the equations, that looks exactly like a mass term would. ( But without breaking electro weak symmetry.) There is really a lot of interesting physics going on here. The most fundamental question is probably, what is the relation between reality and physical models. If in one model the Z boson is massive, and in a equivalent model the Z boson is massless, but both models agree on every quantitative prediction. In which sense can we say that the Z boson is massive?
I think that the “added mass” can be a better analogy (A ball moving inside water drags part of the water, so to accelerate the ball you must accelerate part of the surrounding water, so the apparent mass is greater then the mass of the sphere. This is unrelated to viscosity. More information: http://en.wikipedia.org/wiki/Added_mass). But most people don’t have a good intuition about this effect, and I’m not sure that the analogies can be extrapolated to the correct equations.
The main problem is that Higgs bosons are extremely difficult to explain. I tried a few times to explain the Higgs bosons to “normal” people (like someone with only a Math mayor and no advanced Physics knowledge). I tried to explain it without equations, in a 10 minutes coffee talk. By the time I could explain the “Higgs field vacuum expectation value” and how it produces something that looks like a mass the people usually are totally bored and lost the thread of the explanation :(. I never could reach the part of the explanation about how the “Higgs bosons” appear in the Higgs field :( :(.
It's super that there's a lot of interesting physics going on here, but you haven't explained any of it in a way I can understand, and I'm half-decent for a layman. (I don't quite understand basic quantum mechanics yet, for instance.)
I sympathize with the problem of bad analogies providing incorrect intuitions. That's a problem in popularizing science, especially cutting-edge science. But you're not going to make any headway against these inaccuracies unless you push against the door from the other side with correct intuitions.
The way physicists currently construct theories is based on mathematical symmetries. And in particular the theory of the electro weak interaction is build on a symmetry between the electro magnetic force and the weak force. So this gives the prediction that the weak force should be similar to the electro magnetic force, especially that it should have infinite range. But the experimental observation is, that the weak force acts only on very small distances, usually less than a femto meter.
The solve this problem, Peter Higgs noted that the symmetry between electromagnetism and the weak force should exist in the lofty world of mathematics, while in the messy real world the symmetry is broken somehow. So he invented a additional field, which breaks the symmetry. This is somewhat similar to the claim, that a car can go in any direction (the symmetry), but in realistic situations all cars follow the same road. So the road breaks the symmetry, without taking anything away from the ability of the car to go in any direction.
In quantum field theories forces correspond to particles. And the particles associated with the weak force, W and Z bosons, should therefore be similar to photons, the particles associated with electro magnetism. But a force that acts only on small distances means that the field quanta are massive, unlike photons which are massless. So in this view, the Higgs mechanism adds mass to the W and Z bosons, but does not add mass to the photons. But a better explanation would probably be, that the Higgs field limits the range of the electro weak force to the experimentally observed short distances.
Part 1: http://www.youtube.com/watch?v=9Uh5mTxRQcg
Part 2: http://www.youtube.com/watch?v=ASRpIym_jFM
Part 3: http://www.youtube.com/watch?v=6guXMfg88Z8
(If you only watch one part, watch part 2, it's only 170 seconds long.)
2) Not really. In quantum field theory, the fundamental spacetime entity is a field, and quantized excitations of the field are interpreted as particles. So the "Higgs field" is just a postulated field in spacetime, which is associated with the observable particle called the Higgs Boson.
3) No. Roughly speaking, the mathematical mechanism by which the Higgs "gives particles mass" is like this: You write down the theory with the Higgs particle doing its own thing; it turns out this theory can be "viewed" from different perspectives (physicists refer to this as a gauge). If you view the theory from a certain perspective (see: spontaneous symmetry breaking), the algebra of the equation gets all jumbled up. When you untangle the equation by factoring etc, you get back to something that looks like a physics theory, but now the Higgs got mixed into various places in the equation. In some places, it looks just like a "mass charge". This mechanism was originally proposed to get around a nasty problem in physics; our super-awesome theory of electroweak interactions was very clear that the weak bosons (W and Z) must be massless. But when we discovered these particles they were really heavy. The Higgs mechanism is a loophole that allows these bosons to be formally massless in the theory, but which get mixed with the Higgs to give an observable mass as described.
The whole idea of a field having "imaginary mass", and that our universe could be in a spontaneously broken vacuum state (i.e. that we're viewing the theory from a weird perspective) are pretty hard to swallow. This is while the discovery of the Higgs boson is a huge vindication for theoretical physics; it puts all these crazy-sounding ideas on empirical footing.
If you'd like a quick read, here's an "elevator pitch" explaining the Higgs mechanism/boson -- http://dickfeynman.ruhoh.com/physics/higgs-for-laypeople/