The top quark is the most massive elementary particle that we have so far discovered at particle accelerators. One usually describes this by saying that the top mass is about 185 times larger than the mass of a whole proton; but since the proton is a composite object, it is not the best comparison stone; I would prefer to compare the top mass to the mass of the lightest quark, which we only roughly know to be in the range of a 2 to 5 MeV. Then one gets a more dramatic picture: the up quark and the top quark are both elementary particles, but the latter is 50,000 times larger than the former. Can that be true ?

"This time we're shooting through a brick!"

Larry Nodulman (during a discussion on the reconstruction of electrons in the CDF II detector, just refurbished with a new set of silicon microstrip layers (SVX'), more powerful and capable of identifying the impact parameter of charged tracks with a dozen micron accuracy, but also heavier and bulkier than its predecessor, and thus providing more material for multiple scattering of particles.)

A 1.1 metric Ton satellite will re-enter the earth's atmosphere in the next 48 hours, fragmenting into smaller pieces as it falls. The exact location of the fall is unknown, so you better watch out... Or not.

I was discussing this event with my daughter this morning, and it ended up being an instructive discussion on random events of very low probability. If we are totally oblivious of the satellite orbit, and forget different likelihood of earth surface points for the re-entry (the very north and south latitude are much less likely), we can try and compute how likely it is that one of, say, 50 large fragments of the satellite will end up falling within a 100 m^2 area around us -which would be frightening enough.