In the past weeks I have been writing a piece about the Large Hadron Collider for a science popularization magazine, and I found myself squeezing my brain for a good analogy to the work of particle hunters. The idea I had was to convey the importance of energy and intensity, two parameters which must both be maximized by a particle accelerator in order to reach deeper in the structure of matter.

Anybody who knows a thing about particle physics is familiar with the fact that the higher is the energy of a particle collider, the more massive particles it can produce. If there is a particle X whose mass is Y, there is no chance to produce it at an accelerator whose maximum energy is 0.1 times Y: you need to reach or exceed collision energy Y if you want to see X. So this looks like a concept which is not too hard to get a grip of.

Much harder is to explain why more intense beams are required to probe deeper. In December 2009, when news of the first particle collisions at the LHC made headlines, it was not infrequent to find people asking what had been the result of the experiment. It was not easy to explain that the experiment will last two decades! Intensity is needed, and time. The product of illumination and observation time is what eventually provides a better chance to make out the subtler features of low frequency phenomena.

In the end, I have put together the following analogy. I am changing the wording a bit (and thus worsening my perfect prose) because the magazine comes first, and am also summarizing it since I am taking it out of context, but the meaning is there:

"Like speleologists who in their explorations of the underground find themselves leaning on the edge of a huge unknown chasm, physicists explore all the territory they have a chance to light up with their lamps. To see further, they need more powerful lamps, capable of illuminating deeper, puncturing the darkness of the cavern. But their light also needs to be as intense as possible, and to shine for longer time, to allow them to make up more clearly what they are illuminating."

Of course, the analogy is imperfect because for light, intensity and energy are rather interchageable concepts. Maybe by thinking along the lines I have provided above, some of you may suggest a smarter analogy ?