How small is an atom? Well, a scientist would probably answer that the radius of a typical atom is one tenth of a bilionth of a meter, and that the biggest atom (cesium) is approximately nine times the smallest atom (helium). As far as I know (not much, to be honest…), the answer is right; but it will hardly satisfy the curious child inside each of us.
Something more imaginative can be found in Fritjof Capra’s The Tao of Physics, where he suggests the following analogy. Let’s say that you have an orange, and imagine that such an orange has grown up so much that now it is as big as the earth. Now your orange’s atoms would be as big as normal cherries. Notwithstanding, the nucleus of such a cherry-like atom would be still invisible to our eyes. In order to see it, the atom should be as big as the dome of Saint Peter’s Basilica in Rome, but even thus the nucleus would not be bigger than a grain of salt!
Switching to protons, things become way more difficult! Maybe, as Bill Bryson suggests in his A Short History of Nearly Everything,
No matter how hard you try you will never be able to grasp just how tiny, how spatially unassuming, is a proton. It is just way too small.
But then, fortunately, he depicts the first of a long list of vivid representations, which go through the whole book:
Protons are so small that a little dib of ink like the dot on this ‘i’ can hold something in the region of 5,000,000,000,000 of them, or rather more than the number of seconds it takes to make half a million years.
These verbal representations are great, of course. They stimulate our curiosity, strike our imagination and communicate a childlike sense of stupor which is probably one of the main sources of our knowledge. However, they cannot compete with this last, wonderful, pictorial representation of the scale of the universe. It’s simply amazing, you have to see it!
Enjoy the viewing!