Heroes of Science: Max Planck

The father of quantum physics, Max Planck was one of the foremost theoretical physicists of the 20th century whose work ushered in a new era of science

If you had to choose two scientists of the 20th century whose work most affected its course and discoveries, the first would no doubt be Albert Einstein, but the second could be Max Planck. Einstein’s theory of relativity revolutionised how humans perceived and understood space and time, while theoretical physicist Planck’s development of quantum theory, with his  probing work into atomic and subatomic processes, radically transformed how physics was understood and directly led to many other discoveries and inventions that still have a widespread impact today. Easily Max Planck’s most important discovery was his realisation that the energy of electromagnetic waves is contained within indivisible ‘quanta’ packets that have to be radiated or absorbed as a whole. This is commonly referred to as Planck’s black-body radiation law and, as can be seen in detail within ‘The big idea’ explanation below, it is both simple and incredibly enlightening. However, when Planck delivered his research for the first time in 1900, it was anything but, with its suggestions seemingly conflicting directly with all of classical physics. Indeed, even Planck himself did not fully believe his
law was correct, only reluctantly deducing it through a cold sense of logic. His remarkable discovery was not recognised either by the existing scientific establishment, with recognition only coming after Einstein himself adopted the idea of quanta and later introduced the follow-on theory of wave- particle duality in 1909. Following this, Planck was suddenly seen as the genius he had always been and became one of the most prominent scientists of the early-20th century, attending among numerous others, the celebrated Solvay Conference in Brussels in 1911. Indeed, famously it was due to Planck’s input at the conference that Henri Poincaré – the most famous mathematical physicist of the 19th century – could provide mathematical proof that Planck’s radiation law required the existence of quanta and, as a knock-on effect, converted many of Europe’s top scientists to this new quantum theory. And so quantum theory was born, and over the following decades it was built upon and expanded by some of the most well-known scientists of all time. From Einstein to Niels Bohr, Erwin Schrödinger to Paul Dirac, Planck – as the father of quantum theory – had given them an entirely new way to look at and understand the processes of the physical world – one which they would go on to explore in much more detail through the nuclear age.

 

The big idea

Planck’s law is a mathematical relationship formula created in 1900 by Max Planck to explain the spectral-energy distribution of radiation emitted by an idealised black-body phenomenon. Key was Planck’s assumption that sources of radiation are atoms in a state of oscillation and that the vibrational energy of each atomic oscillator may have a series of discrete values but never any fixed value between. This discovery, along with the ground-breaking work of Albert Einstein, led directly to the end of the age of classical physics and ushered in the era of quantum theory.

In their footsteps…

Max von Laue

Max Theodor Felix von Laue was a student under Max Planck and later Nobel prize winner, receiving the prestigious award for his discovery of the diffraction of X-rays by crystals. For four decades he was one of the foremost scientists in Germany and spent much of his later years re-organising Germany’s broken scientific institutions post-WWII.

Gustav Ludwig Hertz

A German experimental physicist and another Nobel prize winner, Gustav Ludwig Hertz was one of Max Planck’s earliest students, later going on to win the prestigious physics accolade for his experiments into inelastic electron collisions in gases. Indeed, Hertz had one of the longest careers of any of Planck’s students, dying aged 88 in 1975.

Top 5 Facts

  • Max Planck was born Karl Ernst Ludwig Marx Planck, but by the age of ten he began signing his name as simply ‘Max’. He would continue to use this for the rest of his life, largely abandoning his other forenames.
  • He was one of the first physicists to understand the importance of Albert Einstein’s theory of relativity, using his influence to promote the young Einstein’s seminal work and expand upon it.
  • Max Planck was one of the German scientists who signed the Manifesto of the Ninety-Three, a 1914 proclamation that supported the German military actions in the early period of World War I. He later regretted
    signing the declaration.
  • After World War I Planck was considered the highest scientific authority in the whole of Germany and consequently held positions at Berlin University, the Prussian Academy of Sciences and the German Physical Society.
  • During WWII Planck was one of very few scientists to remain in Nazi-led Germany, advocating a ‘persevere and continue working’ motto.

 This article was originally published in How It Works issue 53, written by Rob Jones

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