The possibility that light could have wave like properties was first observed by James Maxwell in Scotland and Hendrik Lorentz in the Netherlands in the late 1800s during diffraction experiments, however they did not fully understand the physics behind this phenomenon. Heinrich Hertz of Germany was the first person to see the photoelectric effect in 1887 when he discovered that if he shone ultraviolet light onto a metal plate it would shoot sparks. This in itself was not surprising as metals were good conductors of electricity but what was surprising was that the electrons were so easily removed from only a sudden burst of incoming energy (American Physical Society, 2005). Subsequently, in 1899, J.J. Thompson in England demonstrated that ultraviolet light hitting a metal surface caused the ejection of electrons. The recognition that these ‘sparks’, witnessed by Hertz, were in fact electrons, came from Thompson’s earlier discovery of electrons in 1897 and his use of specialist equipment. Further investigations into the photoelectric effect eventually disproved the classical theory of electromagnetic radiation; when it interacted with electrons, light just did not obey the laws it was supposed to (Elert, 1998). Einstein, although clearly not the first scientist to observe the photoelectric effect, was the first physicist to explain why the phenomenon occurs, repairing the tear in Hertz’s theory and hence officially forming the wave particle duality theory.
For the photoelectric effect to occur, the light waves must be above a certain frequency. However, according to the theory of physics, the light’s intensity should be critical. Einstein explained that light consists of quanta, “packets” with fixed energies corresponding to certain frequencies. One such light quantum, a photon, must have a certain minimum frequency before it can liberate an electron. This minimum frequency came to be known as the wave function and is readily used in photon energy calculations today.
The discovery of the photoelectric effect led Einstein to work and develop an equation with leading quantum physicist Max Planck, essentially proving that photon energy is proportional to its frequency. Einstein and Planck’s equation, , was written in 1905 is still used today as a fundamental equation in quantum physics.
The discovery of the photoelectric effect won a Nobel Prize because of the impact it had on the field of physics. It wasn’t simply an experiment: it was the accurate explanation of a new phenomenon, wave-particle duality, allowing theoretical physics to expand infinitely into what we know now to be quantum mechanics. Before Einstein and his theories, physics was largely centred around Newtonian laws and mechanics, which was, at that time, very well respected in the scientific community. Without his work on quantum physics, the field may have stayed unchanged for decades, preventing endless amounts of technological advancements which are indebted to the discovery of photoelectric effect.
An example of these technologies are phototubes which are photo emissive detectors based on a small glass tube containing electrodes where the external photoelectric effect is utilised, usually filled with low pressure gas or vacuums. Photodiodes use the same principle as phototubes: they both can detect light, measure its intensity and, most importantly, turn light into electrical energy. These are used within industrial process control, pollution monitoring and light detection within fibre optics telecommunications. It is also used in solar cells, imaging, and many other applications (Britannica, 2020). The ability of the photodiodes to transform light energy into electrical power is an essential part of the production of solar energy, an important source of renewable energy and a crucial component in the journey towards a sustainable future.
The photoelectric effect is especially prominent in medical physics: the photomultiplier tube, a highly sensitive extension of the phototube, is used in spectroscopy research and scintillation counters because of their ability to virtually detect single photons. Additionally, they can also support applications which detect nuclear isotopes and X-rays to create cross section scans of the body, vital for the development of medical physics, as it plays a crucial role in assisting medical professionals to get a more accurate representation of the part of the body which is failing. These are just a couple of examples illustrating how Einstein’s century-old work on the photoelectric effect continues to serve the field of physics, highlighting both its importance for subsequent research and impact on the future in a wealth of different disciplines; and consequently, proving its worthiness of a Nobel Prize.
When considering why the photoelectric effect won a Nobel Prize, it is also worth asking why the photoelectric effect was commended for a Nobel prize rather than Einstein’s other theories and discoveries. Was this one Nobel prize representative of all his work?
Einstein is best known for his derivation of the equation the mathematical outcome of his research, work, and formation of the special theory of relativity. This theory, as opposed to his general theory of relativity 1915, is related to space and time and how they link, in objects travelling at constant velocity. In his theory, Einstein states that the closer an object is to travelling at the speed of light, the closer its mass comes to infinity, as it is unable to go any faster than the cosmic speed limit (Howell, 2017). The equation, mentioned in special relativity, is fundamental in combining the conservation of mass and energy by the same principles, and simplified a large portion of theoretical physics, which at the time was ground-breaking. Special relativity forms the basis for modern physics, from predicting the existence of black holes and light bending due to gravity, to the behaviour of Mercury in its orbit (Emspak, 2017).
Following his success with special relativity, Einstein went on to try and include acceleration in his theories, and in doing so, formulated the general theory of relativity which introduces gravity. This theory states that massive objects have an influence and can cause distortions within the space-time material that makes up the universe. Mercury was used as experimental evidence as its orbit was observed to be shifting very gradually due to the curvature of space-time around the sun (Redd, 2017). Another piece of evidence used to prove general relativity was gravitational waves, predicted by Einstein in the 1920s but only proven in 2016. Gravitational waves occur when two significantly massive objects, such as two black holes, violently collide and create ripples in the space-time material. General relativity is still used today as an essential tool in modern astrophysics, where it provides the foundation to understanding black holes and gravitational waves. Although the photoelectric effect has contributed massively to the field of quantum physics, both general and special relativity have helped to rewrite physics as we know today, as well as develop a deeper understanding to the universe, arguably more deserving of a Nobel prize.
Furthermore, when discussing why the photoelectric effect won the Nobel Prize in 1921, the context of the time must also be considered. The circumstances leading up to Einstein’s win can be divided into two elements: within the scientific community and outside of it. Outside of the Scientific community, Einstein was a pacifist and a Jew, which, in the context of a post-war, early 1920s Germany experiencing the growing rise of anti-Semitism, made him less popular to the government of the time; in 1933 he renounced his German citizenship for political reasons and emigrated to America (Nobel Media , 2018). Whilst the Nobel Committee has no political affiliations and is an independent organization, there is no doubt that the increasing tension for German Jews at the time, may have played a role in both the delay of Einstein’s commendation for the photoelectric effect, and the lack of any further recognition for his work on relativity.
Within the scientific community there was mounting pressure on the Nobel committee to reward Einstein, not only for the photoelectric effect but for all his work for the theoretical physics field, including general and special relativity. Einstein was recommended 62 times by highly respected scientists from 1909 until his eventual award in 1921 (Nobel Media , 2018). In his letter of recommendation (1919), Neil Bohr cited the photoelectric effect, Brownian motion, the theory of specific heats and “first and foremost… relativity advances of significance for the development of research in physics”, hence showing that even a prominent physicist in the quantum field who would win the successive award, believed relativity was key the future of physics. Furthermore, in 1921, Léon Brillouin, well known for being a founder of solid-state physics who worked with quantum mechanics, wrote “Imagine for a moment what the general opinion will be in fifty years from now if Einstein’s name does not appear on the list of Nobel Laureates” (Pais, 1982).
A century later, Einstein is a household name who made multiple breakthroughs in theoretical physics; not being named on the list of Laureates, would discredit the Nobel Organization, regardless of the political situation at the time. The Nobel Committee defended their decision by stating “further experimental verification was needed”, despite there being ongoing experiments into the orbit of Mercury in relation to relativity. Max Planck won the Nobel Prize for physics in 1918, “in recognition of the services he rendered to the advancement of Physics by his discovery of energy quanta”, despite the fact that although he produced what was an incredibly important formula, it lacked crucial solid derivation. In this context Einstein’s well-rounded concept of relativity, although it lacked sufficient evidence, should have been awarded a Nobel prize.
The Nobel Committee postponed rewarding Einstein’s relativity for possibly political reasons and lack of sufficient experimental evidence. However, ultimately it was due to the immense pressure from leading physicists that he was awarded the Nobel Prize in 1921, albeit for a less ground-breaking discovery: the photoelectric effect. Another possible explanation for this is that Einstein’s other work was too ahead of its time, and the Nobel Committee simply lacked the intellectual capability to comprehend such ground-breaking concepts questioning the nature of the universe, to award him a Nobel Prize. This is easily criticized with the benefit of hindsight and either way, Einstein’s work on relativity was underappreciated by the Nobel Committee.
To discredit Einstein’s Noble Prize for the photoelectric effect would be remiss as it shaped the principals for Quantum physics, a field which is still expanding a century later for which we still use Einstein’s field equations. However, to not give any credit to general and special relativity would also be remiss, given how much these two theories have changed our understanding of the nature of the universe as a whole.
Without a doubt, the photoelectric effect was deserving of a Nobel Prize: it won because it forms a fundamental basis for quantum physics. But regardless of insufficient evidence or understanding at the time, relativity, which Einstein himself described as being “the only one that was revolutionary” should have been awarded a Nobel Prize, as he truly was writing the physics of the future.
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