Year of
Quantum Science & Technology
Pioneers of Quantum Theoretical
Physics
Part 1
“IYQ25
coincides with the 100th anniversary of the birth of modern quantum mechanics —
the theory that describes the behaviour of matter and energy at atomic and
subatomic scales and has made possible many of the world’s most important
technologies. Over the past century, quantum theory has become foundational to
physics, chemistry, engineering, and biology and has revolutionized modern
electronics and global telecommunications. Inventions like the transistor,
lasers, rare-earth magnets, and LEDs — technologies that brought the internet,
computers, solar cells, MRI, and global navigation into fruition — all exist
because of quantum mechanics.”
Two of the greatest pioneers of quantum science
UNESCO
has proclaimed 2025 as the International Year of Quantum Science
and Technology (IYQ).
This year-long, worldwide initiative will celebrate the contributions of
quantum science to technological progress over the past century, raise global
awareness of its importance to sustainable development in the 21st century, and
ensure that all nations have access to quantum education and opportunities. In
celebration of IYQ25, this series of articles focuses on the key personalities
of quantum theoretical physics and their work – ten of the greatest, from
Planck to Feynman.
Prelude
Dedicated to the promotion of both science and scientific culture, the UNESCO has, over the years, focused on some key themes/events and designated the corresponding year for special attention and international observance. Here is a representative list:
- 2005 – International Year of Physics, celebrating the centennial of Einstein’s ‘Miracle Year’ 1905 marking his groundbreaking publications.
- 2009 – International Year of Astronomy, marking the 400th anniversary of Galileo’s first telescopic observations.
- 2011 – International Year of Chemistry, celebrating the achievements of chemistry and its contributions to humankind.
- 2022 – International Year of Basic Sciences for Sustainable Development.
This year, 2025 has also received similar
attention – as the International Year of Quantum Science and Technology.
IYQ25
The International Year of Quantum
Science and Technology (IYQ) 2025 has been proclaimed by the United Nations to
commemorate the centennial of quantum mechanics and to emphasize its significance
in modern science and technology. The primary objectives of IYQ 2025 include:
1. Increase
Public Awareness: Highlight the importance of quantum science and its
applications in everyday life, aiming to educate the public about its
foundational role in various technologies.
2. Promote
Education and Diversity: Encourage educational initiatives to inspire young
individuals, especially women and those from developing countries, to pursue
studies and careers in quantum science, fostering inclusivity and diversity in
the field.
3. Support
Sustainable Development: Demonstrate how quantum technologies can
contribute to achieving the United Nations' Sustainable Development Goals,
particularly in areas like energy, environment, climate change, agriculture,
healthcare, and industrial development.
4. Encourage
Global Collaboration: Foster international partnerships among academia,
industry, and governments to ensure that the benefits of quantum technologies
are shared globally, with a focus on reducing inequalities in education and
research.
5. Highlight
Scientific and Cultural Significance: Celebrate the history of quantum
science as part of our shared cultural heritage and showcase its impact on art,
culture, and philosophical perspectives.
6. Model
Scientific Conduct: Promote the ideals of scientific inquiry, including
open science practices, international collaboration, and the free sharing of
information, to inspire future generations of scientists.
7. Engage
with the Public: Organize events, workshops, and interactive exhibitions to
make quantum science accessible and engaging to diverse audiences, bridging the
gap between complex scientific concepts and public understanding.
Through these objectives, IYQ 2025
aims to celebrate the achievements of quantum science over the past century and
to inspire a future where quantum technologies play a pivotal role in
addressing global challenges and enhancing the quality
of life worldwide.
Some Applications of Quantum Science
in Everyday Life
Quantum science finds wide
applications in practically all aspects of everyday life. Here are some of the
more distinctive ones:
- Micro- and nano- electronic devices which operate based on quantum mechanics principles like electron tunneling.
- Lasers and a wide range of related optical technologies.
- Nuclear Magnetic Resonance (NMR), which is the foundation for medical imaging.
- Light-emitting diodes (LEDs) and organic LEDs (OLEDs) in televisions, smartphones, and other displays operating on quantum principles.
- GPS and Atomic Clocks which use quantum mechanics to keep extremely precise time for navigation and other applications.
- Superconductors, which rely on quantum physics, are used in Maglev trains, powerful electromagnets, and particle accelerators.
- While still developing, quantum computers promise breakthroughs in materials science, medicine, and complex simulations by leveraging principles of superposition and entanglement.
- Solar Cells - Quantum mechanics explains how light is converted into electricity in solar panels, improving efficiency in renewable energy.
These applications show how deeply
quantum science is embedded in daily life and technology, even if we don’t
always notice it.
Quantum Theoretical Physics
Now, back to the main theme of quantum
theoretical physics and its pioneers. Both as a student and later as a teacher
of collegiate physics, I feel justified in venturing to write about this topic
in a series of articles spread over a few months this year. The subject matter is such that the use of some
mathematical expressions and equations becomes inevitable to convey the gist of
it, and they should not be an impediment to grasp the essence of the article as
a whole, especially from a historical perspective.
First, let us examine the circumstances
that led to a drastic change in our understanding of how nature operates, in
the early twentieth century.
Physics in Crisis
At the turn of the twentieth century,
the world of physics was in turmoil under the dark clouds of conflict between
experiments and theory, facing a series of crises, one of which was the
inability to account for the distribution of energy observed in the spectrum of
blackbody radiation. A blackbody is one that ideally absorbs all the energy
incident on it in the form of electromagnetic radiation such as light, x-rays,
microwaves, etc., and exhibits distinctive characteristics in the energy
radiated by it when heated. The prevailing theory led to an anomalous situation
called the ultraviolet catastrophe! The German physicist Max Planck
overcame this with his energy quantization hypothesis as elaborated later. This, and Einstein’s theory of the
photoelectric effect, together marked the birth of the Quantum Theory.
[Another crisis of the time, the inability
to detect any difference in the speed of light due to the Earth’s motion
through the hypothetical aether permeating all space, was also resolved
by Einstein, with his Theory of Relativity that led to equally revolutionary
developments.]
Annus
Mirabilis
Science historians often refer to
1905 as Annus Mirabilis (the ‘Miraculous Year’), marking the birth of
the greatest revolution in modern physics, with the publication of four seminal
scientific papers by Albert Einstein in the German science journal, Annalen
der Physik. They brought about a radical transformation in our
understanding of the most fundamental physical concepts such as matter, energy,
space, time, charge, spin, etc. One of these papers, on the interpretation of
the photoelectric effect, based partly on the earlier concept of the emission
or absorption of energy in discrete steps (called quanta) first
introduced by Max Planck in 1900, was to lay the foundation for the quantum
revolution that is now in focus in IYQ2025.
While Planck’s photon theory assumed quantization only in the processes
of emission and absorption of energy, Einstein’s explanation of the
photoelectric effect had gone further by postulating even the very existence of
energy in quantized form. This was a huge step forward, placing the quantum
mechanics that followed on a sure footing.
Dramatis Personae
Quantum theory, and the new quantum mechanics that followed it circa 1925, were the result of key contributions from a large number of outstanding personalities*, most notably the following, roughly in chronological order:
- Max Planck (1858 – 1947)
- Albert Einstein (1879–1955)
- Niels Bohr (1885–1962)
- Louis de Broglie (1892 – 1987)
- Werner Heisenberg (1901–1976)
- Erwin Schrödinger (1887–1961)
- Wolfgang Pauli (1900 – 1958)
- Paul Dirac (1902–1984)
- Max Born (1882–1970)
- Richard Feynman (1918–1988)
[*Some notable omissions: Satyendra Nath Bose, Arnold Sommerfeld, Enrico
Fermi, John von Neumann, John Bell, Murray Gell-Mann, Steven Weinberg… and
more.]
With some aid from AI apps DeepSeek
and ChatGPT, their lives and contributions are probed, narrated and discussed below
in an effort to weave a story of quantum theoretical physics in the twentieth century.
The story begins with the failure of classical theory
to account for the observed properties of blackbody radiation and the
resolution of the problem by Max Planck, ushering in the quantum revolution
that finds an echo this year.
Max Planck (1858 – 1947)
and the birth of Quantum
Physics
Max Planck, a name synonymous with the birth of quantum theory, stands as one of the pioneering physicists of the 20th century. His groundbreaking work not only revolutionized our understanding of the physical world but also laid the foundation for modern physics.
Blackbody Radiation
The study of black body radiation and the development
of Planck's formula for the distribution of energy in its spectrum represent a
cornerstone in the history of physics. This work not only resolved a major
theoretical problem at the turn of the 20th century but also laid the
foundation for quantum mechanics that followed. The interplay between
experimental observations and theoretical insights was critical in deriving
Planck's formula, which describes the energy distribution of black body
radiation as a function of wavelength and temperature (see illustration below). It represents years of
hard work by experimenters in different countries, mainly in Europe.
Ultraviolet Catastrophe
A black body is an idealized object that absorbs all
incident electromagnetic radiation and emits energy in a characteristic
spectrum that depends solely on its temperature. By the late 19th century,
experimenters had meticulously measured the spectral distribution of black body
radiation, revealing that the intensity of emitted radiation increased with
temperature and peaked at a wavelength inversely proportional to the
temperature (Wien's displacement law). However, classical physics
struggled and failed to explain the full spectrum of black body radiation.
The Rayleigh-Jeans law, derived from classical thermodynamics and electromagnetism, successfully described the intensity of radiation at long wavelengths but failed catastrophically at short wavelengths. According to this law, the energy density of radiation would increase rapidly and without limit as the wavelength decreased, leading to an anomalous situation dubbed as the "ultraviolet catastrophe." (see illustration below). This discrepancy between theory and experiment highlighted the limitations of classical physics and demanded a new theoretical framework.
In 1900, Max Planck proposed a revolutionary solution
to this problem. By introducing the concept of quantized energy, Planck derived
a formula that accurately matched the experimental data across all wavelengths.
Planck's formula for the spectral
energy density E (λ, T) is given by:
Planck's key insight was to assume that the energy of the oscillators in the black body walls could only take on discrete values, proportional to an integer multiple of a fundamental unit hν, where ν is the frequency of the oscillator.
This is nearly as
famous as Einstein’s E = mc2
This quantization of energy was a radical departure
from classical physics, which assumed energy could vary continuously.
Experimental Validation
Planck's formula was immediately successful in
explaining the observed black body spectrum. Experimentalists had already
gathered precise data on the intensity of radiation at different wavelengths
and temperatures, and Planck's theoretical predictions matched these
observations with remarkable accuracy. For example, the formula correctly
predicted the peak wavelength of emission and the fall-off at both shorter and
longer wavelengths, resolving the ultraviolet catastrophe triumphantly.
The experimental work of physicists like Wilhelm Wien,
Otto Lummer, and Ernst Pringsheim played a crucial role in validating Planck's
theory. Their meticulous measurements of black body radiation provided the
empirical foundation that guided Planck's theoretical efforts.
Theoretical Implications
Planck's work had profound implications for physics.
The introduction of quantized energy levels challenged the classical view of
continuous energy exchange and paved the way for the development of quantum
mechanics. Albert Einstein later extended Planck's ideas to explain the
photoelectric effect, further solidifying the concept of quantization.
Planck's constant h, a fundamental parameter in
his formula, became a cornerstone of quantum theory. Its small value 6.626 x 10-34
Js explains why quantum effects are not observed in everyday macroscopic
phenomena but are critical at atomic and subatomic scales.
The derivation of Planck's formula for black body
radiation exemplifies the synergy between experimental and theoretical physics.
Experimental observations revealed the limitations of classical theories, while
Planck's bold theoretical hypothesis provided a new framework that resolved
these discrepancies. This work not only explained black body radiation but also
revolutionized our understanding of energy and matter, marking the birth of a
new branch of physics. Planck's formula remains a testament to the power of
combining empirical evidence with innovative theoretical thinking.
Planck - Early Life and Education
Max Karl Ernst Ludwig Planck was born on April 23,
1858, in Kiel, Germany, into an intellectual and culturally rich family. His
father, Johann Julius Wilhelm Planck, was a law professor. From an early age,
Planck exhibited a keen interest in mathematics and science, excelling in his
studies. He attended the Maximilians Gymnasium in Munich, where he developed a
strong foundation in classical education.
In 1874,
Planck enrolled at the University of Munich to study physics. Despite being
advised against pursuing theoretical physics—a field considered to have limited
prospects at the time—Planck was undeterred. He later transferred to the
University of Berlin, where he studied under renowned physicists Hermann von
Helmholtz and Gustav Kirchhoff. Planck completed his doctoral dissertation in
1879 on the second law of thermodynamics, a topic that would remain central to
his scientific career.
Academic Career and Early Work
After earning his doctorate, Planck began his academic
career, teaching at the University of Munich and later at the University of
Kiel. In 1889, he succeeded Kirchhoff as a professor at the prestigious University
of Berlin, where he spent the majority of his career. Planck’s early work
focused on thermodynamics, particularly the study of entropy and the behavior
of heat in physical systems. His research during this period laid the
groundwork for his later revolutionary discoveries.
This hypothesis marked the birth of quantum theory, a
radical departure from classical physics. Although Planck himself was initially
hesitant about the implications of his discovery, it paved the way for a new
understanding of atomic and subatomic processes. His work inspired a generation
of physicists, including Albert Einstein, Niels Bohr, and Werner Heisenberg,
who further developed quantum mechanics.
The Reluctant Revolutionary
Although Max Planck is considered the father of quantum theory, he was initially reluctant to accept its deeper implications. His reservations about quantum theory included the following:
- Introduction of the Quantum Hypothesis as a Mathematical Trick: Planck introduced the idea of quantized energy (E = nhν, where n is an integer) to solve the black-body radiation problem, but he saw it as a mathematical convenience rather than a fundamental shift in physics. He hoped that a more classical explanation would eventually emerge.
- Discomfort with Discontinuity in Energy: Classical physics assumed that energy was continuous, but quantum theory introduced discrete energy levels. Planck struggled with the idea that nature could fundamentally be discrete rather than continuous.
- Skepticism Toward the Broader Implications of Quantum Theory: While Planck accepted his quantum hypothesis for black-body radiation, he was skeptical of how it was extended by Einstein (in the photoelectric effect) and later by Bohr (in atomic structure). He initially resisted the idea that quantization applied universally.
- Hope for a Classical Explanation: Planck believed that quantum theory was temporary and that future developments in classical physics might restore continuity. This was also Einstein’s stand as we shall see later. He spent years searching for a derivation of his radiation law that did not require quantization.
- Discomfort with Probabilistic Interpretations: Later developments in quantum mechanics, especially Heisenberg’s uncertainty principle and the probabilistic interpretation by Born and Bohr, were far from Planck’s original vision. He was uneasy about abandoning strict determinism.
Despite these reservations, Planck’s work laid the
foundation for quantum mechanics, even though he, like his contemporary
Einstein, never fully embraced its later developments.
Recognition and Later Career
Planck’s contributions to physics earned him
widespread recognition. In 1918, he was awarded the Nobel Prize in Physics for
his discovery of energy quanta. Despite the acclaim, Planck remained a humble
and dedicated scientist, continuing his research and teaching throughout his
life. He served as the president of the Kaiser Wilhelm Society (now the Max
Planck Society) from 1930 to 1937, promoting scientific research in Germany.
Planck’s later years were marked by personal tragedy and the challenges of living through two World Wars. His first wife, Marie Merck, died in 1909, and his eldest son, Karl, was killed in action during World War I. During World War II, Planck’s home in Berlin was destroyed by Allied bombing, and his second son, Erwin, was executed by the Nazis for his involvement in the failed plot to assassinate Adolf Hitler in 1944. Despite these hardships, Planck remained committed to his scientific work and the pursuit of knowledge.
Later years - a picture of solitude
Planck’s Legacy
Max Planck’s legacy is immense. His introduction of
the quantum hypothesis revolutionized physics and led to the development of
quantum mechanics, which underpins much of modern technology, from
semiconductors to lasers. The Max Planck Society, established in his honor,
continues to be one of the world’s leading research organizations, fostering
innovation and discovery across a wide range of scientific disciplines.
Planck’s life and work exemplify the power of curiosity, perseverance, and intellectual courage. This profound humility and recognition of the limits of human understanding underscore Planck’s enduring influence on science and philosophy.
Point to ponder
Students of science and philosophy may like to debate
a statement attributed to Planck:
"Science cannot solve the ultimate mystery of
nature. And that is because, in the last analysis, we ourselves are a part of
the mystery that we are trying to solve."
Acknowledgement
This article (as also the ones to follow on this
theme) has been inspired by Dr A G Kulkarni of Bangalore who is himself
actively involved in the promotion and advocacy of IYQ25 and other initiatives.
