Analogies are a powerful way to explain complicated scientific concepts. I use them as much as I can whenever I describe particle physics in this blog or when I give a outreach talk in a school. However, good ones are not always easy to find. One usually needs examples from everyday life, which are simple to describe and which do not possess distracting features.
Today I wish to try my luck with you, to see if you come up with an analogy which is better than the one I could find to explain a feature of weak interactions. I must say I am not dissatisfied with my own find, but it is always good to subject oneselves to external judgement.
You probably know, if you read this blog, that photons are mass-less particles carrying the electromagnetic interaction, while W and Z bosons are very massive particles carrying the weak interaction. A stark disfference in the phenomenology of electromagnetic and weak interactions at low energy is that the former have a infinite range, while the latter have a very short range of action. Another is the very reason why W and Z bosons carry the interaction we call "weak": at low energy, the strength of the weak force is much smaller than that of the electromagnetic force.
The fact that a massive particle has a short range of action may probably be easy to explain; harder is to let our listeners grasp the property that a force brought about by a massive body must be less intense. This in the subatomic world is due to the much smaller probability of emission of these massive bodies; and it is not easy to find a real-life analogue of such a feature.
Below is the analogy I came up with. If you have a better one, please share it in the comments thread!
Today I wish to try my luck with you, to see if you come up with an analogy which is better than the one I could find to explain a feature of weak interactions. I must say I am not dissatisfied with my own find, but it is always good to subject oneselves to external judgement.
You probably know, if you read this blog, that photons are mass-less particles carrying the electromagnetic interaction, while W and Z bosons are very massive particles carrying the weak interaction. A stark disfference in the phenomenology of electromagnetic and weak interactions at low energy is that the former have a infinite range, while the latter have a very short range of action. Another is the very reason why W and Z bosons carry the interaction we call "weak": at low energy, the strength of the weak force is much smaller than that of the electromagnetic force.
The fact that a massive particle has a short range of action may probably be easy to explain; harder is to let our listeners grasp the property that a force brought about by a massive body must be less intense. This in the subatomic world is due to the much smaller probability of emission of these massive bodies; and it is not easy to find a real-life analogue of such a feature.
Below is the analogy I came up with. If you have a better one, please share it in the comments thread!
The large mass of W and Z particles is the reason why weak forces are called that way: the mass of these vector bosons is a hindrance to their ability to mediate long-range interactions, and a parameter which determines the interaction strength. To understand how a massive mediator may be less effective than a mass-less one, take a cup of hot chocolate and a raw chocolate bar: the former disperses around with its vapour very small, light-weight particles, which you can easily smell from a distance; the latter can only release a small speck of solid chocolate if you get very close and inhale powerfully.
The speck is much more massive than the corpuscles evaporating from the cup, and is thus incapable of carrying the chocolate interaction far away; furthermore, even at small distance the experienced chocolate smell from the bar is way less intense, because of the small rate at which the bar releases a speck of chocolate when you sniff it!
The behaviour of the smell of the cup and the bar when sniffed may be likened to the behaviour of electromagnetic and weak interactions at low energy: the former interaction will appear much more intense. Now, however, let us imagine for the sake of arguing that we construct a computerized sniffer that analyzes the odour of solid as well as liquid materials. It works by taking the material under test, vaporizing it, and analyzing the absorption lines of the produced vapour. Such a device will find that cup and bar of chocolate have the same intensity of chocolate smell. Likewise, electromagnetic and weak interactions become equally strong at very high energy, once the different mass of chocolate particles and solid specks -pardon, of photons and W/Z bosons- becomes irrelevant.
By the way, I usually don't like analogies at all, because they always break up and when one tries to fix them one is always creating even more problems than one solvel. In the case of weak interactions I think it's plenty clear to explain the effects as they are. The qualitative rules of QFT and their basic consequences are just so simple that it's needless to create analogies that take as much time to explain and moreover are just incorrect. Which is also what Feynman says in his Strange theory of light and matter -- he tells us that usually simplicity of theories as explained to layman audience is only achieved by lots of misinformation and mystification. And he goes on to explain QED as it really is (albeit he gives just a qualitative picture) and the book is well accesible even at high school level.