In his classic “Feynman lectures on physics”, Richard Feynman starts by saying:
If, in some cataclysm, all of scientific knowledge were to be destroyed, and only one sentence passed on to the next generation of creatures, what statement would contain the most information in the fewest words? I believe it is the atomic hypothesis that all things are made of atoms — little particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into one another.
Of course atoms are not the basic unit, they are composed of nuclei surrounded by electrons. The nuclei are then composed of protons and neutrons (and short-lived virtual particles such as pions), and the protons and neutrons are themselves composed of quarks and gluons.
But what is the ultimate level? What, when one goes down to the most fundamental level, are things made of? While there are lots of opinions there is no accepted answer, and mulling it over for myself I realised that none of the options are attractive in the sense of aligning with intuition about what “physical stuff” would be made of. Here are some of the possibilities: Continue reading