Because bound states in the Universe are not the same as completely free particles, it may be conceivable that the proton is less stable than we observe it to be by measuring the decay properties of atoms and molecules, where protons are bound to electrons and other composite structures. With all the protons we’ve ever observed in all our experimental apparatuses, however, we’ve never once seen an event consistent with proton decay. (GETTY IMAGES)

You Are Not Mostly Empty Space

They say that atoms are mostly 99.99999% empty space. But quantum physics says otherwise.

If you were to look at what your body is made of, at smaller and more fundamental levels, you’d find a whole miniature Universe of structure inside you. Your body is made of organs, which are in turn made of cells, which contain organelles, which are composed of molecules, which themselves are linked-up chains of individual atoms. Atoms exist on extremely tiny scales, just 1 ångström across, but they’re made of even smaller constituents: protons, neutrons, and electrons.

The tiny sizes of the protons and neutrons making up each atom’s nucleus are known: just one femtometer apiece, 100,000 times smaller than an ångström. But the electron itself is indistinguishable from point-like, no more than 1/10,000th the size of a proton or neutron. Does this mean that atoms — and by extension, everything made of atoms — are mostly empty space? Not at all. Here’s the science of why.

From macroscopic scales down to subatomic ones, the sizes of the fundamental particles play only a small role in determining the sizes of composite structures. Whether the building blocks are truly fundamental and/or point-like particles is still not known, but we do understand the Universe from large, cosmic scales down to tiny, subatomic ones. (MAGDALENA KOWALSKA / CERN / ISOLDE TEAM)

In our normal experience, if you want to know how big something is, you just go ahead and measure it. For non-quantum objects, this isn’t a problem, as…