Category: physics

Engineering Civilizations

1.    Introduction:

Welcome to essays in the global history of physics, where we discuss people, ideas and technology connected to physics in the historical context. Let me explain why the global history of physics is important. Physics, as you know, is one of the central disciplines of natural sciences from which various branches of science and technology have emanated.

Understanding the evolution of such an important output of human thought is imperative. It not only gives us a glimpse of how people over the ages have thought about ideas but also reveals how those ideas are connected to philosophical and technological questions that were of interest to people in the past. In fact, it is that dual connection of physics to philosophy and technology that makes it interesting, important and intellectually rich.

This series of essays aims to capture the historical evolution of physics by paying attention to the global evolution of the subject. In doing so, we will visit the people from the past and learn about their ideas and technologies that eventually led to the topics within physics. 

Here, I need to emphasize the global aspect of history. Conventionally, the history of science as a discipline has been criticized for being Eurocentric in nature. In recent years, as highlighted by James Poskett’s excellent book Horizons (1), there has been an emerging scholarship in the history of science to reveal a decentralized evolution of science and that includes some developments in physics itself. In these essays, I will give credit to people, ideas and technology irrespective of their origin and emphasize curiosity as a basic human instinct prevalent across space and time.

This thought reinforces science, specifically physics, as a global intellectual pursuit over many ages and times. The way I will do this is to take on a particular branch of physics and discuss its evolution in chronological order. Of course, my aim is not to cover everything that is known but to highlight some interesting developments in that field with attention to some interesting people, ideas, tools and technologies at the relevant place and time.

Such an exercise cannot be done in one single essay. So, I intend to cover the chronological evolution with a series of essays spanning all the branches of physics. Yes, it will be a long journey, and I hope you will accompany me in this one endeavor.

2.    How a physical phenomenon is explained.

 One starts with a concrete situation of a particular problem. Associated with this situation is a general law. One applies the general law to the situation in a logical manner and utilizes mathematical descriptions where precision is needed. This logical and mathematical description leads to an explanation witha concrete prediction. Observations must test this prediction. The ability to predict a future observation is one of the remarkable traits of science in general and physics in particular (2). It is through this ability to predict that one can envisage the utility of a physical concept. That utility forms the seed of development towards technology.

As you may observe, there is a nice connection between scientific inquiry and the eventual realization of technology. This connection is what makes science and technology go hand in hand. Importantly, this is one of the outstanding features of physics and historical explanation, as we intend to do in these essays, which will justify the claim.

This connection between science and technology is not a one-way coupling. In fact, many interesting questions in physics have emerged out of technological development across various eras of human history. This recognition of jugalbandhi between science and technology is at the heart of the essay series.

Physics has played a critical role in engineering civilization over the centuries. This role has been explicit in recent times, say around the last 300 years or so. But what is interesting is that inquiries in physical sciences have implicitly influenced the growth of a civilization.

This growth is not only materialistic but also intellectual in nature. Therefore, understanding the evolution of physics gives us a glimpse of the evolution of humankind. Of course, it may not be the complete picture, but at least we learn about people, ideas and technology that gave rise to the world that we identify as a physical, real entity.

3.    Engineering Civilizations

Let us start with some ancient civilizations. The oldest tools used by humans were stones. In fact, the ‘Stone Age’ gets its name from this. According to archeological explorations, the earliest stone tools found in Lomekwi, Kenya, date back to 3.3 million years ago (3). This is the Paleolithic age, in which hunting and gathering were the main occupations of human beings. The stone tools found within India at Attirampakkam, a village close to Chennai in Tamil Nadu, date back to around 300 thousand years ago (4). From such archeological evidence, humans were acquainted with toolmaking long ago. Towards the Neolithic age, we also have evidence of pottery in civilizations, indicating a gradual change to farming and agricultural occupations that were assisted by toolmaking based on clay and fire.  I need to emphasize that knowledge of these tools was handed over from one generation to another without a formal writing process. The oldest written record dates to around 3500 BCE in the form of a cuneiform script from Mesopotamian civilization, which is somewhere around present-day Iraq (2). Such writing itself needs small tools, such as a stylus and a platform, such as clay, to imprint the written text. Well before any form of writing became part of any civilization, tools and structures had to be invented.

An interesting element of the Indus Valley Civilization was that they used measurement scales (5). In the Harappan museum, one can find a linear scale made of a shell that has nine divisions with a small circle engraved on it. A periodically divided scale indicates a quantitative measure of length and indicates the sophistication of thought, both from device and utility viewpoints.

A remarkable aspect of this scale is the utility of the shell as the material. Given that shells are robust and can sustain large temperature fluctuations, they make for an excellent choice as a material for scale. One must really marvel at how humans came to the point where such a design was implemented without modern tools, scientific knowledge or a written script.

To emphasize this fact, one of the earliest texts from the Indus Valley civilization dates to around 3000 BCE. Of course, in this case, the script is yet to be deciphered completely. What is interesting is that ancient civilizations achieved remarkable engineering feats even before any formalization of scientific disciplines, including physics, came into the picture.

This is because for civilization to survive, grow and sustain, they had to manage their natural resources and construct structures. These tasks would not have been feasible without an intricate understanding of how things work and how they can be used to construct physical structures. This can be achieved only through certain tools and techniques.

The civilizations would not have evolved without this engineering and, therefore, deserve credit as a human achievement. These tools and techniques have implicit physics in them. Of course, there was no formal discipline called physics until around 300 BCE, but the empirical knowledge about tools and techniques for construction was already present long before physics became a formal discipline of science.

4.   The role of philosophy

As human beings cultivated crops, their mobility was confined to a smaller region compared to the hunter-gatherer era. This settlement at a place gave humans leisure to think and wonder about nature. As a consequence of this thinking, philosophical thoughts emerged (6).

Questions pertaining to philosophy, such as what life is and how humans live and interact with nature, occupied human minds. This exploratory era also gave rise to the need to understand the world, explore nature and harness it. Inquiries pertaining to the motion of celestial objects and that of common living and non-living things captured the attention.

To understand the intellectual foundations of physics, one needs to understand its connection to philosophy in general and philosophy of science in particular. The connection between reality and physical law is through an abstract formulation (2). Reality has its own complications, and a physical law retains only a small set of the complications that are evident in reality.

Although this connection between reality and a physical law looks to be straightforward, historically, there has been a large intellectual struggle to come to this point. It has not been an obvious task to connect reality to physical laws. And by studying the history of physics, it is evident that the route has been anything but smooth.

Another important aspect I need to emphasize is how reality becomes a raw material for scientific investigation. In essence, reality provides a kind of formless raw material on which physical laws can be formulated. These physical laws are drawn from a simplified structure of reality, and there is a process of encoding reality in a language that is amenable to scientific investigation.

This process of going from a multi-faceted reality to a slightly more precise physical law is done through assumptions, and these assumptions play a critical role. The pathway from reality to general laws has been through inductive methods, at least in the historical context. In the inductive method, there is an extrapolation from the finite to the general principles.

Based on certain observations in a concrete situation, one derives a general law. Now, the question is, how does one derive such a general law? This generalization is based on a logical process, and one of the best tools to implement logical analysis is mathematics. This is where the role of mathematics becomes so important in physics. If one needs to go from a concrete, realistic situation to an abstract principle, one will have to utilize mathematical tools such as geometry to convert the reality into an abstract formulation. An important aspect of physics and science, in general, is that once this abstract formulation has been postulated, the physical law can be tested going forward. The results can be checked by performing observations, and these observations can confirm or reject the induced hypothesis.

When it comes to the observation, there are two elements. The first is the observed object, and the second is the observer themselves. The demarcation between the observer and the observed object seems trivial; historically, it has not been the case. Because the observed object can interact with the observer, the physical laws that are derived from such observations must ensure that the observers themselves are not perturbing the physical reality. 

Also, the judgment of objectivity itself is a complex process because the criteria of truth have a social connection. This means what we call a factor of truth is closely connected to the social realities in which the observation is performed. This social connection brings in another layer of complication, and one must understand the philosophy behind these processes. 

As you can see, formulating science and, in our case, physics has not been a trivial task, given that these philosophical questions must be addressed to get a satisfactory answer. Understanding and discriminating science from other forms of human activity has not been a trivial exercise either, but it is with the help of philosophy that progress has been made.

This also highlights the intricate connection between philosophy, physics, experimental observation and technological developments as a network of events that interact with each other. Each part of this network plays a critical role and, many times, feeds back important information in the process. Therefore, to understand physics, we need to not only appreciate the philosophical questions but also be aware of technological developments.

Because many of the developments in the realm of scientific philosophy were motivated by technology and vice versa, this is also the reason why the history of physics is so interesting. It brings together all these epistemological components into one single platform and creates an intellectual magic that has played a critical role in understanding nature and the universe, that which can be observed and, in some cases, that which cannot be observed.

So, how did ancient people think about a subject called physics? What were the initiating thoughts of philosophers that led to physics? If we want to address these questions, we need to pay attention to some of the philosophers who thought and wrote about science. Among them, one of the earliest to do so was Aristotle. In the next essay, we will discuss his physics. 

References:

[1]       J. Poskett, Horizons: A Global History of Science. Penguin UK, 2022.

[2]       K. Simonyi, A Cultural History of Physics, 1st edition. Boca Raton, Fla: A K Peters/CRC Press, 2012.

[3]       “Lomekwi Stone Tools: the oldest artifact in the world.” Accessed: Mar. 24, 2025. [Online]. Available: https://www.thearchaeologist.org/blog/lomekwi-stone-tools-the-oldest-artifact-in-the-world

[4]       S. Pappu, Y. Gunnell, M. Taieb, J. Brugal, and Y. Touchard, “Excavations at the Palaeolithic Site of Attirampakkam, South India: Preliminary Findings,” Curr. Anthropol., vol. 44, no. 4, pp. 591–598, 2003, doi: 10.1086/377652.

[5]       S. Guha, A History of India through 75 Objects. Hachette UK, 2022.

[6]       P. Adamson, Classical Philosophy: A history of philosophy without any gaps, Volume 1. in A History of Philosophy. Oxford, New York: Oxford University Press, 2014.

Hints Before a Discovery: The Case of Neutrons

In the late 1920s, the quantum theory of matter was still under construction. Questions such as what are the constituents of a nucleus of an atom were pertinent. The then understanding was that a nucleus was made of protons and electrons. Yes, you read it right. People thought that electrons were part of an atomic nucleus. But those were the times when quantum theory was evolving, and many ‘uncertainties’ persisted. For example, if one considered a nitrogen nuclei, it was postulated that it had 14 protons and 7 electrons.

The other important aspect during that time was the question of spin statistics, including that of nuclei, which was under exploration. The classification of nuclear spin in terms of Fermi-Dirac statistics or Bose-Einstein statistics was under study, and researchers were trying to sort it from theoretical and experimental viewpoints. Going back to the example of nitrogen nuclei, it was categorized to obey Fermi-Dirac statistics.

Enter Rasetti and his Raman Spectra

With this backdrop, let me introduce you to Franco Rasetti. Franco was an Italian physicist who was visiting Caltech in the US on a research fellowship. This was 1929, and many exciting quantum thoughts were in the air. C. V. Raman had just discovered an inelastic scattering process in the visible frequency spectra of molecules, and there was interest in understanding the quantum nature of the interaction between light and matter. Motivated by this, Rasetti set up an experiment at Caltech to probe Raman spectral features of molecular gases. Rasetti was an elegant experimentalist and, later, went on to become a close associate of Enrico Fermi and played a crucial role in the nuclear fission experiment[I].

Coming back to the work of Rasetti’s experiment, he took up the problem of understanding the Raman effect in diatomic gases (nitrogen and oxygen) and wrote a series of papers[ii]. Among them, he published his observations on rotational Raman spectra of diatomic gases (nitrogen and oxygen). Specifically, he performed a series of experiments and recorded beautiful spectral features of rotational lines of diatomic nitrogen. In that work, Rasetti discussed the specific selection rules from an experimentalist viewpoint and identified that the even lines in the spectral features were much more intense compared to the odd lines.

Guys from Gottingen

During the same year, working in Göttingen as postdocs of Max Born were Walter Heitler and Gerhard Herzberg. These two gentlemen studied the paper of Rasetti with great interest and went on to write an interesting paper in Naturwissenschaften (in German)[iii]. The translated title of the paper was “Do Nitrogen Nuclei Obey Bose Statistics”.

In that paper, Heitler and Herzberg studied rotational Raman features of nitrogen molecules and compared them to hydrogen molecules. They considered arguments based on the symmetry of the eigenfunctions and associated them with statistics (Fermi or Bose). Hydrogen nuclei obeyed Fermi-Dirac statistics, whereas Nitrogen counterpart did not. From the analysis of symmetry, they found that Rasetti’s observation contradicted the convention that Nitrogen nuclei obey Fermi-Dirac statistics. So, with this contrast, they clearly indicated that the nuclei of nitrogen should obey Bose-Einstein statistics, provided Rasetti’s experiments were correct.

How was the discrepancy resolved?

In 1932, James Chadwick[iv] went on to discover the neutron, and this discovery laid the foundation for understanding the constituent of a nucleus. With the new observation, one had to account for the presence of neutrons inside the nucleus. In the context of Nitrogen nuclei, it was found that it contained 7 protons and 7 neutrons, and the total spin was 1 (in contrast to spin ½ of hydrogen). This ascertained that Nitrogen nuclei obeyed Bose-Einstein statistics and removed the discrepancy from the observed rotational Raman spectra of Rasetti.

3 takeaways

What can we learn from this story? The first aspect is that experiments and theory go hand in hand in physics. They positively add value to each other and connect the real to the abstract thought. Second, it emphasizes the importance of careful observations and their interpretation. The third lesson is that Rasetti, Heitler and Herzberg were all young people and learned from each other’s work. They were essentially post-docs when they did this work, and we are still discussing it today.

Sometimes, good work has a long life.

[i] https://en.wikipedia.org/wiki/Franco_Rasetti

[ii] https://www.nature.com/articles/123205a0

https://www.pnas.org/doi/epdf/10.1073/pnas.15.3.234

https://www.pnas.org/doi/epdf/10.1073/pnas.15.6.515

[iii] https://link.springer.com/article/10.1007/BF01506505

[iv] https://en.wikipedia.org/wiki/James_Chadwick

Stern-Gerlach experiment – the first picture

The above picture is from Friedrich, Bretislav, and Dudley Herschbach. “Stern and Gerlach: How a Bad Cigar Helped Reorient Atomic Physics.” Physics Today 56, no. 12 (December 1, 2003): 53–59. https://doi.org/10.1063/1.1650229.

During the formative years of quantum mechanics (early 1900s), the spin and orbital angular momentum of atoms were found to be quantized by theoretical arguments. Experimental proof was lacking.

Stern-Gerlach experiment provided the first experimental proof in 1922. They took a beam of neutral silver atoms and deflected them through an inhomogeneous magnetic field.

Silver atoms have an unpaired electron in their outermost orbit. If they were to obey quantum mechanics, they should exhibit a spin of +1/2 or -1/2. When subjected to an external magnetic field, the electrons with +1/2 or -1/2 should spatially split into two. That is exactly what Stern and Gerlach observed, and below is the first picture of the same.

To quote the authors:

Gerlach’s postcard, dated 8 February 1922, to Niels Bohr. It shows a photograph of the beam splitting, with the message, in translation: “Attached [is] the experimental proof of directional quantization. We congratulate [you] on the confirmation of your theory.” (Courtesy AIP Emilio Segrè Visual Archives.)

This experiment was one of the most important observations in quantum mechanics and further confirmed the quantization of spins, which is now common knowledge in physics.

Superstitions – Kepler, Galileo & Newton

Superstition is a belief system or behavior of an individual that cannot be justified with evidence and logic. It is usually associated with people who do not (or do not want to) think critically. From the history and philosophy of science, we learn that a few famous thinkers of the past had some form of belief that can be termed superstitious. Of course, they were products of their times and environments, but it is always interesting to learn about the contradictions.

Take, for example, Kepler, Galileo and Newton. They were 3 important figures who laid the foundation of classical mechanics (along with many other things). But they also had their pet beliefs that were neither logical nor scientific.

In the preface of his book, Karl Popper has to say about the superstition of the 3 individuals mentioned:

Each of the three intellectual giants was, in his own way, caught up in a superstition. (‘Superstition’ is a word we should use only with the greatest caution, knowing how little we know and how certain it is that we too, without realizing it, are caught up in various forms of superstition.) Galileo most deeply believed in a natural circular motion – the very belief that Kepler, after lengthy struggles, conquered both in himself and in astronomy. Newton wrote a long book on the traditional (mainly biblical) history of mankind, whose dates he adjusted in accordance with principles quite clearly derived from superstition. And Kepler was not only an astronomer but also an astrologer; he was for this reason dismissed by Galileo and many others.

Of course, I am bringing this up not to justify any superstition. But to highlight the fact that people whom we call ‘heroes’ are humans and have their beliefs and flaws. We may derive inspiration from their work, but not all aspects of their character may be suitable for emulation.

We will have to adapt what is good and discard what is not. You may ask: what is the definition of ‘good’? Well, that is a topic for a different debate, but in this context, I would say ‘good’ are the ideas and methods developed by the abovementioned that are testable and falsifiable. Karl Popper may be happy with that definition.

Article on Gerhard Herzberg

The October 2024 issue of Resonance, Journal of Science Education

highlights the life and science of Gerhard Herzberg.

He was one of the greatest molecular spectroscopists who laid the foundation of atomic and molecular quantum mechanics and deeply impacted molecular astrophysics and astrochemistry.

He lived an extraordinary life, first in Europe learning quantum mechanics and then escaping 1930s Germany as his wife was of Jewish origin. Then, he settled in Canada to build and lead his lab, which was considered the ‘mecca of spectroscopy’ at NRC, Ottowa.

I wrote a sci-biography article about him in this issue

Link to full edition: https://www.ias.ac.in/listing/articles/reso/029/10

If you don’t know – Resonance is a pedagogical journal published by the Indian Academy of Sciences. It is a true open-access journal. Free to read and does not charge the authors to publish.

Do explore the past editions. There are some absolute gems. https://www.ias.ac.in/listing/issues/reso

Physics is a point of view about the world

picture from : Hopfield, John J. “Whatever Happened to Solid State Physics?” Annual Review of Condensed Matter Physics 5, no. Volume 5, 2014 (March 10, 2014): 1–13. https://doi.org/10.1146/annurev-conmatphys-031113-133924.

The title of this blog is the closing line of an autobiographical essay written by John Hopfield (pictured above), one of the physics Nobel laureates today: “for foundational discoveries and inventions that enable machine learning with artificial neural networks.”

In this essay, he retraces his trajectory across various sub-disciplines of physics and how he eventually used his knowledge of physics to work on a problem in neurobiology that further connects to machine learning.

The title of the essay is provocative(see below) but worth reading to understand how physics has evolved over the years and its profound impact on various disciplines.

Reference: Hopfield, John J. “Whatever Happened to Solid State Physics?” Annual Review of Condensed Matter Physics 5, no. Volume 5, 2014 (March 10, 2014): 1–13. https://doi.org/10.1146/annurev-conmatphys-031113-133924.

Thanks to Gautam Menon for bringing the essay to my notice.

By the way, Hopfield and Deepak Dhar shared the 2022 Boltzmann medal, and after the award, he gave a wonderful online talk at IMSc, Chennai. Thanks to Arnab Pal of IMSc for bringing this to my notice on X.

Let me end this post quoting Hopfield from the mentioned essay:

What is physics? To me—growing up with a father and mother who were both physicists—physics was not subject matter. The atom, the troposphere, the nucleus, a piece of glass, the washing machine, my bicycle, the phonograph, a magnet—these were all incidentally the subject matter. The central idea was that the world is understandable, that you should be able to take anything apart, understand the relationships between its constituents, do experiments, and on that basis be able to develop a quantitative understanding of its behavior. Physics was a point of view that the world around us is, with effort, ingenuity, and adequate resources, understandable in a predictive and reasonably quantitative fashion. Being a physicist is a dedication to the quest for this kind of understanding.

Let that quest never die!

Optothermal revolution – preprint

We have an Arxiv preprint on how a mixture of colloids (thermally active + passive particles in water) can lead to the emergence of revolution dynamics in an optical ring trap (dotted line). Super effort by our lab members Rahul Chand and Ashutosh Shukla.

Interestingly, the revolution emerges only when an active and a passive colloid are combined (not as individuals) in a ring potential (dotted line)

the direction (clock or anti-clockwise) of the revolution depends on the relative placement of the colloids in the trap

This revolution can be further used to propel a third active colloid

There are many more details in the paper. Check it out: https://arxiv.org/abs/2409.16792

Questions as a class assignment

Over the years, I have been giving student assignments to write about their questions (rather than answers to my Qs).

Snapshot of email to my class below.

I have found some gems in the process and importantly reduces the ‘burden’ of single right answers. Student feedback on this process has been positive.

Even in the ChatGPT era, it is the quality of Qs that determines the answer, and in this assignment, students are free to choose their Qs as per their interest and experience connected to what I teach…something harder for ChatGPT to grasp (as of now).

Interesting times ahead.