The 20th century witnessed incredible inventions and discoveries as physicists delved ever deeper inside the atom. From the apparatus used to identify the first subatomic particle to the photograph that confirmed the existence of antimatter, Collider showcases some of the most significant objects from the history of physics.
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JJ Thomson and the first particle
In a darkened Cambridge lab in the summer of 1897, JJ Thomson sat watching ghostly flashes of green haze in a glass cathode-ray tube. He was about to open an avenue to a new world of sub-atomic matter.
JJ Thomson in his Cambridge lab, c. 1897. © Cavendish Laboratory
Thomson was investigating cathode rays, a phenomenon produced by passing an electric current through a delicate glass vacuum tube, pumped free of air. Cathode rays were a hot topic in 1897 as they were thought to produce the recently discovered x-rays.
Wilhelm Rontgen’s discovery of x-rays two years earlier had rocked the scientific world and captured the public’s imagination. While using a cathode-ray tube he had found a new type of radiation that could penetrate human tissue and famously used these x-rays to take a photograph of the bones in his wife’s hand.
The first x-ray photograph taken by Wilhelm Röntgen, 1895. © Science Museum / SSPL
Soon, adverts were appearing in newspapers for x-ray-proof underwear, presumably for women scandalised by the thought of peeping-toms wielding cathode ray tubes.
The nature of cathode rays was a mystery. Some physicists believed they were made from waves in the ether, like light. However, Thomson’s experiments in the 1890s provided convincing evidence that the glowing beams consisted of negatively charged particles. But what were these particles?
Thomson’s 'startling' idea
'Are they or are they not,' Thomson rhetorically asked his gentlemanly audience at the Royal Institution in April 1897, 'the dimensions of ordinary matter?'
At the time, many physicists believed matter could not be broken down beyond atoms – 'atom', after all, comes from the Greek word for indivisible.
Thomson argued that the cathode-ray particles, which he dubbed 'corpuscles', were actually far smaller than the smallest atom known. He then made a bold conjecture that corpuscles are more than just the carriers of electricity: perhaps they are the basic building blocks of everything – all atoms, elements and matter.
JJ Thomson’s Royal Institution lecture bill, 1897. © Science Museum / SSPL
It is fair to say that some of Thomson’s colleagues found his idea hard to swallow. One distinguished physicist present at the lecture thought Thomson was 'pulling their legs', and another deemed he was on 'the track of the alchemists'.
The rise of the electron
But by 1900 it was widely accepted that Thomson’s particle did exist, though it quickly merged with the identity of an alternative entity of electricity called the 'electron'.
The electron was first proposed in 1874 (though the word was coined in 1891) by the Irish physicist George Johnstone Stoney, and taken up by a bunch of European theorists in the following decades. Electrons were initially thought to be completely separate from atoms, but Thomson’s cathode-ray experiments convinced the physics world that the electron is a fundamental constituent of all atomic elements.
The identification of the first subatomic particle transformed our picture of matter, initiating a new dawn in science and industry – eventually leading the way to nuclear physics and electronics.
JJ Thomson with electronics pioneer Frank Jewett at Western Electric, 1923. © AT&T Archives and History Center