Particles’ Matter

Salutations,

Upon reading a wonderfully worded and concise piece on this very topic by Professor Jon Butterworth I am going to attempt to provide you with an accurate account of the history of particles  and their investigators.

The realm of sub-atomics was pioneered by John Dalton in Manchester, who concluded after a myriad of experiments that elements react in fixed ratios and so therefore there must be a tiny unit of mass which makes up all things. His ideas were swiftly followed by those of my personal hero (I must say) Dmitri Mendeleev who devised a way in which to order all elements into a small table based on their chemical and physical properties, which we know today as the periodic table. What made this man so special was his realisation that there were some undiscovered elements and so he left gaps for these in his table, and this allowed him to even predict properties and atomic numbers of those missing elements. His work proved to be highly accurate for 1869 and so he can be seen as ‘the father of chemistry.’

Advancing this new-found knowledge of the particle came soon after and in 1897, a man named JJ Thompson found himself discovering a new type of particle- the electron. He did this by noticing that the rays in his cathode ray experiments were made up of the same charge and mass; it did not matter which metal he used, they were all the same. Because these electrons had so little mass, he assumed correctly that something else must make up the majority of the mass of an atom, which led on to the next discovery, the nucleus.

Thompson had predicted the ‘plum pudding model’ for the atom in which the negative electrons were dotted in a ‘pudding’ of positive charge. It wasn’t until Rutherford, Geiger and Marsden (another few of my favourites) performed the amazing scattering experiment that science was changed forever. Synonymous with particle physics, the scattering experiment involved firing a beam of alpha particles at thin gold foil. The men shockingly concluded that because some alpha particles bounced back, the mass of an atom must be concentrated into a tiny pocket of space. The nucleus was born.

The discovery of the neutron in 1932 was much more difficult for James Chadwick as equipment at the time was unprepared for discovering new particles; it was geared towards knocking electrons off of atoms in order to investigate ions in cloud chambers. This would be insufficient for neutrons because they have no charge and therefore would not leave a trail in the cloud chamber. Cleverly, Chadwick realised that the neutron must have around the same mass as a proton and that it will transfer its energy as heat, like everything does. He fired neutrons (beryllium hit by alpha particles) into metals which contain protons and monitored them emerging on the other side, from which he proved the existence of the neutron.

The Eiffel Tower plays an unlikely role in the discovery of particles, as when Theodor Wulf was at the top in 1909, he observed that there were more charged particles there than at ground level. He had discovered all sorts of hadrons such as pions sigmas and omegas. Another pressing dilemma was the seemingly impossible breaking of the ‘law of conservation’ which occurred during beta decay. This was resolved by Pauli, Reines and Cowan as they discovered antineutrinos scattering off of protons and during this process producing positrons and neutrons. Because of Dirac’s breakthroughs of the 1920s unifying quantum mechanics and relativity, scientists were able to reveal the discovery of neutrinos.

From 1967 to 1995 scientists were able to postulate the existence of and then prove the existence of all 6 types of quark.  The theories of quantum electrodynamics relating the quantum theory and electromagnetism, and the theory of quantum chromodynamics were developed, but there was no issue more disturbing than the weak force. The answer came in 1964 when the W and Z bosons were first announced, allowing particles to acquire mass. However, this predicted the existence of another massive particle with no charge which would conclude the standard model of particle physics. As many will remember, this momentous revelation came in 2012, when thanks to CERN and the Large Hadron Collider, the discovery of the Higgs Boson was made.

This is our current understanding of particle physics, and perhaps the particles might one day be ordered in a table like that constructed by Mendeleev for Chemistry. Maybe there might be more to particle physics than we think…

I hope you enjoyed this post, keep your eyes peeled for my next article!

Lara

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