Science's ongoing quest to find the smallest possible things remains tantalisingly incomplete, as physicist Prof Andy Parker explains.
Physics has a problem with small things. Or, to be more precise, with infinitely small things.
We imagine that we can move any distance we like, no matter how small.
This perception was exploited by Zeno in one of his famous paradoxes. Achilles could never actually get anywhere since the distance he would have to cover could be halved an infinite number of times - halfway there, halfway again, and so on. He would have to take an infinite number of ever-smaller steps to reach his goal.
Mathematicians have explained this apparent paradox, and are completely comfortable with infinite numbers, as well as infinitely small distances and objects. Their answers are used in physics to describe the world inside the atom.