What’s in an atom?
Mostly nothing. The vast majority of an atom is empty space.
To get it into perspective, imagine an atom the size of an international sports stadium. The
electrons are right up at the top of the stands, each smaller than a pin-head. The nucleus of the atom is
on the centre spot of the pitch, and is about the size of a pea.
For many centuries, atoms, which were entirely theoretical, were thought to be the smallest
possible units of matter, hence the word, which means ‘not-cut’ in Greek.
Then, in 1897, the electron was discovered, followed in 1911 by the nucleus.
The atom was split and the neutron discovered in 1932. This was by no means the end of the matter. The positively charged protons and uncharged neutrons in the nucleus are made of still smaller elements. These even tinier units called quarks are given names like ‘strangeness’ and ‘charm’ and come not in different shapes and sizes but ‘flavours’. The distant satellites of the nucleus, the negatively charged electrons, are so odd they are no longer even called that but ‘Probability Density Charges’. By the 1950s, so many new subatomic particles (over 100) had been found that it was becoming an embarrassment. Whatever matter might be, no one seemed able to get to the bottom of it. Enrico Fermi, the Italian-born physicist who won the Nobel Physics Prize in 1938 for his work on atomic reactors, was quoted as saying: ‘If I could remember the names of all these particles, I’d be a botanist.’
Since Fermi’s time, scientists have settled on the number of subatomic particles inside an atom at twenty-four. This best guess is known as the Standard Model, giving the impression that we have a pretty good idea what’s what. The universe in general, as far as we can tell, is as underpopulated as the atom itself. Space, on average, contains just a couple of atoms per cubic metre. Occasionally, gravity pulls them together into stars, planets and giraffes, which seems equally extraordinary.
The atom was split and the neutron discovered in 1932. This was by no means the end of the matter. The positively charged protons and uncharged neutrons in the nucleus are made of still smaller elements. These even tinier units called quarks are given names like ‘strangeness’ and ‘charm’ and come not in different shapes and sizes but ‘flavours’. The distant satellites of the nucleus, the negatively charged electrons, are so odd they are no longer even called that but ‘Probability Density Charges’. By the 1950s, so many new subatomic particles (over 100) had been found that it was becoming an embarrassment. Whatever matter might be, no one seemed able to get to the bottom of it. Enrico Fermi, the Italian-born physicist who won the Nobel Physics Prize in 1938 for his work on atomic reactors, was quoted as saying: ‘If I could remember the names of all these particles, I’d be a botanist.’
Since Fermi’s time, scientists have settled on the number of subatomic particles inside an atom at twenty-four. This best guess is known as the Standard Model, giving the impression that we have a pretty good idea what’s what. The universe in general, as far as we can tell, is as underpopulated as the atom itself. Space, on average, contains just a couple of atoms per cubic metre. Occasionally, gravity pulls them together into stars, planets and giraffes, which seems equally extraordinary.
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