J.J. Thompson Discovered the Electron — And Unknowingly Electrified Science Forever

When JJ Thomson appeared before the Royal Institution in 1897 to share his latest discoveries, few in the audience probably realized how much physics was about to change. The particles he described – tiny negatively charged “corpuscles” – would soon be known as electrons, according to a study published in Nature.

And although their discovery marked a turning point in modern science, the journey to this moment hasn’t quite been the eureka breakthrough sometimes described in textbooks.

The discovery of the electron was not a lightning bolt from above. It was a slow slog built on decades of experiments, theoretical conjectures, and even clumsy hands in a finely tuned laboratory. Although JJ Thomson receives much of the credit, his success was largely a product of his environment at a time of intense curiosity about the nature of electricity and matter.

JJ Thompson and subatomic corpuscles

In the late 1800s, the scientific world was buzzing with questions about electricity and light. Several researchers were looking for phenomena that would eventually converge on the idea of ​​the electron. And although Thomson is often considered the ultimate discoverer of the electron, even that title remains open to debate.

“Historians of science disagree on who really ‘discovered’ the electron,” says Jaume Navarro, Ikerbasque research professor at the University of the Basque Country and author of A history of the electron: JJ and GP Thomson. “[M]Everyone working in fields related to electricity has reached conclusions that could be considered the first experimental or theoretical example of the modern electron: Zeeman, Lorentz, Lenard and Larmor are the main players in this story. JJ would therefore only be one piece of this puzzle of building the electron.

Thomson’s key insight came in 1897, when a series of innovative and highly precise experiments helped him determine that tiny subatomic “corpuscles” could themselves carry electricity.

“In 1897, he announced that the best explanation of the interaction between matter and electricity would be the ‘far from impossible hypothesis’ according to which the ‘electrified corpuscles’ of matter were the unitary carriers of electricity,” Navarro explains. And it was only “when he tried to measure the charge/mass ratio of such corpuscles that he came to the conclusion that these corpuscles were probably smaller than the smallest atom.”

Learn more: X-rays supposed to prove what constitutes dark matter do not, in fact, prove the link

Bending particle beams

Thomson’s famous cathodic experiments that revealed the electron seem deceptively simple today. He projected a beam of particles through a vacuum tube and used electric and magnetic fields to bend the particle beams. By varying the intensity of these fields and following the evolution of the angle of deflection of the beam, he was able to determine the charge/mass ratio of the particle. And he discovered that it was an order of magnitude smaller than any known atom.

“The experimental setup seems simple, but it wasn’t,” says Navarro. “[T]The skills needed to create perfect tubes in which a stable vacuum were not available to everyone at the time.

In fact, Thomson’s success was largely attributable to his laboratory’s world-class infrastructure and his own knowledge. The Cavendish Laboratory at Cambridge, of which he became director in 1888, was already becoming a world-class center of experimentation. Thomson was known for being “very clumsy,” Navarro said. But his laboratory assistant, Ebenezer Everett, was highly skilled in glassblowing, capable of producing the high-quality vacuum tubes that were crucial to Thomson’s experiments, according to the UK’s Science Museum.

The discovery of electrons

Popular science often presents great discoveries as “eureka” moments. But that doesn’t quite fit here.

“We tend to dislike ‘eureka’ moments because they tend to be an oversimplification of complex processes,” says Navarro. In Thomson’s case, the real spark came from an entirely different discovery: X-rays.

“The real disruptive element did not depend [Thomson]“It was the discovery of Röntgen rays (X-rays) that really got him and many other physicists interested in them,” says Navarro. “JJ was working with gas-filled discharge tubes, and X-rays occur in a vacuum. So it was X-rays that led him to modify his experimental setup.

Even the scientific community took years to come around to the reality of the electron.

“In fact, even the existence of atoms was still controversial among some physicists and, in particular, among chemists in the late 1800s,” says Navarro. “So a subatomic ‘corpuscle’ was a challenge.”

It was not until decades later that Thomson was widely considered the discoverer of the electron.

“His 1906 Nobel Prize was awarded to him ‘in recognition of the great merits of his theoretical and experimental research on the conduction of electricity by gases,'” says Navarro, “not for any specific discovery, much less for the electron (which he kept calling the corpuscle).”

Prepare yourself for success

As director of the Cavendish Laboratory, Thomson’s influence extended far beyond his own research.

“His leadership of the Cavendish laboratory allowed him to follow and direct many researchers of the time,” Navarro explains. “Moreover, his training at Cambridge helped, but also hindered him in his work”, due to a prevailing belief in the continuity of matter and ether.

In fact, Thomson’s faith in the continuous nature of matter endured for decades, even as quantum theory began to reshape physics. “At the time he published [his 1907 book The Corpuscular Theory of Matter]“His dream of having the electron as the only elementary particle, that is to say as the ‘primary material’ of all material substances, was over,” says Navarro. “But he said that such corpuscular theory was “a policy, not a creed.” »

Fittingly, it was Thomson’s own son, GP Thomson, who would later prove that electrons could also behave like waves, helping to usher in the quantum revolution.

After the spark

However, Thomson did not understand everything about the internal structure of the atom. For example, he pursued the “plum-pudding” model of the atom, a term Navarro notes Thomson never used.

After “discovering” the electron and realizing that it could not account for the majority of an atom’s mass, Thomson “tried (unsuccessfully) to find positive ‘corpuscles’ with a similar experimental setup,” Navarro explains.

Finding no relevant results, “he continued to think that positive electrification was distributed throughout the atom’s ether, with corpuscles located in stable arrangements within this sea of ​​positively electrified aether,” says Navarro.

Nevertheless, Thomson’s original “corpuscle” would ignite entire areas of science and industry. And more than a century later, the electron remains one of the most studied and best understood particles in the universe. Yet its origin story sheds light on the true, messy, collaborative, and often contradictory history of scientific discovery.

Learn more: Advanced quantum material bends the fabric of space

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