This chapter deals with the search for free, unbound quarks. In the last chapter, and perhaps even more so in this, we have reached the cutting edge of research in particle physics. And as in many similar frontier style activities, things are not always nice, tidy and civilised. One of the main questions we address in this chapter is ‘have free quarks been found?’. There are three main answers: ‘yes’, ‘no’ and ‘maybe’. Of course, many people would prefer their answer to be qualified, such as ‘no, I don't think so’ or ‘maybe, but the evidence is not by any means totally convincing’. But of these three broad categories the answers of most particle physicists today would lie in the final two, ‘no’ or ‘maybe’ and the majority of these, I guess, would be in the ‘no’ class. I, on the other hand, would say ‘yes’. The first four chapters, I believe, are fairly unbiassed. I hope this one also turns out that way. But if there are any biasses you now know which way they are likely to lie.

The failure of the early attempts to find free quarks using accelerators at energies around 30 GeV had several consequences. The first of these was to stimulate searches in other areas, particularly in cosmic radiation, where energies much higher than 30 GeV occur. A related area to search is in condensed matter, where one might expect free quarks to accumulate if they came from the cosmic radiation, or were, perhaps, left over from an earlier stage of the Cosmos. Another consequence was to start people wondering if free quarks are ‘allowed’.