A Forest Laboratory

On the track of particles

Not all phenomena can be observed with an unaided eye. For instance, an ammeter is used to watch the flow of current, while a measurement of the length of an object requires a device unjustly called a ruler. Let's try to observe

Virtual Particles. Through the trees in forests or coppices, especially in suburban areas, staggering silhouettes thread their way here and there. These are the unsober. Nothing can stop a true researcher, so let's proceed with our observation. (Actually we can easily produce an unsober in household conditions, using half a litre of a 40% C_2 H_5 OH water solution per 50 kg weight of a sober and adding an appropriate amount per every 10 kg of his weight.) Watching carefully an unsober's trajectory we notice two interesting regularities:

  1. The unsober changes his route at every obstacle (a tree in our case).
  2. The unsober also changes his route without any apparent reason as if there were an obstacle invisible to our eyes.

How can this astonishing phenomenon be explained?

In his stride about the forest the unsober most evidently collides with objects that cannot be seen in any way (the scattering of the unsober on air molecules has no significance here due to the very small mass of the molecules). To change noticeably the unsober's direction of motion the objects must have a relatively large mass (of the order of 1 kg or more).The same occurs in the world of elementary particles. All we have to do is to substitute e.g. electrons for the unsober and, correspondingly, replace the trees by heavy atomic nuclei. The invisible obstacles will then turn into the previously mentioned virtual particles.

Let's briefly recall the basic properties of virtual particles. Firstly, by definition they cannot be observed in any direct way. We can only analyse the effects of their presence by observing the changes in the direction of motion of the real particles -- in our case, of the unsober. Secondly, the mass of a virtual particle can assume any value whatsoever and it is related to the interaction time by the well-known indeterminacy priciple:

Let's get going with our measurements. From a group of unsober we choose one mild specimen (in case there is no mild unsober, we make use of our elder brother's help) and we follow his movements for a determined - rather long - time, scrupulously counting the number of collisions with virtual trees (particles!). We perform the measurements again and again for different time intervals, always noting the results in our data-book. Next, for each measurement we compute the number of collisions per time unit and from that we take an arithmetic mean. We thus get an average number of virtual trees (particles) that appear in a time unit. We can perform the measurements in a tree with variable tree density, thereby determining the dependence of the number of virtual trees on the density. This obviously corresponds to different densities of atomic nuclei (protons, for instance) with the maximal density possible corresponding to completely degenerated nuclear gas in which virtual particles are practically inexistent. We can easily model this situation by a forest so dense that no unsober can make his way through the trees.

Finally, we can continue our observations in the open space (in the vacuum!). In this manner we shall be able to evaluate the number of virtual particles in the vacuum, which has not been achieved by any other method to this day.

To complete our work, a proposition for the more advanced experimenters: Using our unsober (and this time he must be mild) you can verify the indeterminacy principle mentioned above. It is sufficient to know the mass of a virtual particle and the time of its collision with the unsober. The product of the two quantities should be greater than the table value of Plack's constant. Substituting in the product the mass of a proton for the computed mass of a virtual particle and the typical nuclear time 10^{-24} seconds for the time of collision you should get a number not very different from .

This result is another argument in favour of the virtuality of objects the unsober collide with.

And how can the mass of these particles and the collision time be determined by observing the unsober's movements? Use your brains. Write to us and tell us how you managed. The most interesting answers will be published. Good luck!

Mme PIPSZTYCKA