Source: University of Chicago – archives
Chandra with Lalitha – 1940 – photo
Month: August 2025
When Chandra wrote to Hawking
Learning is a lifelong process, and even the best researchers have to update their knowledge as and when they come across new information. Subrahmanyan Chandrasekhar was undoubtedly one of the most accomplished mathematical astrophysicists in the 20th century, and his range of topics covered almost all aspects of astrophysics. Chandra (as he was known) was a lifelong learner, and took up new topics within astrophysics, researched them deeply, and wrote definitive books on them, which are still of great utility even today. In his research process, Chandra consulted various scholars across the world, irrespective of their age, and learned new things.
In 1967, Chandra, aged 57, wrote a letter to a 25-year-old researcher, Stephan Hawking, to learn more about his work ‘on the occurrence of singularities in cosmology’. In this letter, which is written in a desperate tone, Chandra mentions that he is grappling with some mathematical aspects of Stephen Hawking’s work and is asking him for references that he can consult to understand his papers. Chandra describes reading Hawking’s papers as ‘climbing a staircase moving downwards’. Below, I reproduce the letter (from the University of Chicago archives).
To this letter, Hawking dutifully replies (see below), suggesting specific books on topology and differential geometry. Hawking also suggests some of his published papers. Hawking himself downplays his knowledge of mathematical aspects related to the work, and mentions that it improved after he consulted the mentioned books. Below, I reproduce the handwritten letter (from the University of Chicago archives).
There are two aspects that are interesting to note: one is the fact that even accomplished researchers have to learn and relearn many things as they get exposed to new information, which calls for humility and setting aside egos, and the second aspect is that ideas are built on existing ideas available at that time, and a major part of it is to learn from papers, books and of course communicating with people, as Chandra did in this case.
Science, after all, is a human endeavor.
Conversation with Arka Banerjee
Welcome to the podcast Pratidhavani – Humanizing Science
Arka Banerjee is a cosmologist and an Assistant Professor of Physics at IISER Pune. His research focuses on exploring the connections between fundamental physics at microscopic scales and the formation and evolution of large-scale structures in the Universe, such as galaxies and cosmic voids. To pursue these questions, he develops new simulation methods, constructs summary statistics for cosmological data, and generates forecasts for upcoming observational surveys.
In this episode, we explore his intellectual journey and research.
References:
“Arka Banerjee – Home.” n.d. Accessed August 23, 2025. https://arkabanerjee.github.io/.
“Arka Banerjee – Google Scholar.” n.d. Accessed August 23, 2025. https://scholar.google.com/citations?user=kLde9gcAAAAJ&hl=en.
“Arka Banerjee – IISER Pune.” n.d. Accessed August 23, 2025. https://www.iiserpune.ac.in/research/department/physics/people/faculty/regular-faculty/arka-banerjee/381.
“Arka Banerjee – INSPIRE.” n.d. Accessed August 23, 2025. https://inspirehep.net/authors/1671323.
Some Optical and IR observatories in India
Below are ‘locations of some of the optical and infrared observatories marked on the Indian map’.
from: Narendranath, Shyama, Shashikiran Ganesh, Dipen Sahu, et al. 2025. “Solar System Research Prospects for the Decade and Beyond.” Journal of Astrophysics and Astronomy 46 (2): 34. https://doi.org/10.1007/s12036-025-10060-0.
Happy Independence Day & de Broglie’s birthday
Happy Independence Day to my fellow Indians !
15th Aug also happens to be birthday of Louis de Broglie, the famous French physicist who played a critical role in understanding wave-particle duality in quantum physics, and laid an important foundation through his formula
λ = h / p ;
where, λ is the wavelength of quantum particle with momentum p and h is the Planck constant.
See here for more details.
de Broglie studied and discovered the wave nature of electron, for which he received the Nobel prize in physics in the year 1929. In 1920s, understanding light from a quantum mechanical viewpoint was a challenge. Reconciling light, both as a particle and a wave, was counterintuitive and required a leap of thought that was provided by de Broglie. On 12th Dec 1928, delivered his Nobel lecture and mentions:
“I thus arrived at the following overall concept which guided my studies:
for both matter and radiations, light in particular, it is necessary to introduce
the corpuscle concept and the wave concept at the same time. In other words
the existence of corpuscles accompanied by waves has to be assumed in all
cases. However, since corpuscles and waves cannot be independent because,
according to Bohr’s expression, they constitute two complementary forces
of reality, it must be possible to establish a certain parallelism between the
motion of a corpuscle and the propagation of the associated wave.“
This duality still remains, as we try understand the nature of light and harness it for information processing.
Interestingly, de Broglie was one of persons who nominated CV Raman for the Nobel prize in 1930 ! Below snapshot is from the Nobel prize nomination archives.
A bit of advice…to students
To paraphrase something I tell my students, especially when they are starting a research project –
There are certainly many people in the world who think better than us. But the competition reduces when it comes to the people who take their thoughts and ‘do’ something with them. Novelty of ideas is in the novelty of connections of ideas. There is always more scope for new connections of old ideas.
Generally, the game is won not in out-thinking, but in out-doing. This does not mean that doing excludes thinking. In fact, many times, doing fosters thinking.
Conversation with Kollegala Sharma
Welcome to the podcast Pratidhavani – Humanizing Science
Kollegala Sharma is a renowned science communicator and prolific Kannada writer, celebrated for making science accessible through articles, books, radio dramas, podcasts, and translations. A former chief scientist at CSIR-CFTRI Mysore, he has received prestigious awards for his exceptional contributions, including pioneering India’s first Kannada science podcast and editing the state’s popular science magazine, Kutuhali.
In this conversation (in English), we discuss what motivates him to do what he does so well…communicate science…
References:
Akka TV, dir. 2022. Lecture 107 | Science Journalism : Introduction | Shri. Kollegala Sharma. 44:38. https://www.youtube.com/watch?v=031_4I0W9I8.
“Amazon.In.” n.d. Accessed August 6, 2025. https://www.amazon.in/Books-Kollegala-Sharma%60/s?rh=n%3A976389031%2Cp_27%3AKollegala%2BSharma%2560.
“CFTRI.” n.d. Accessed August 8, 2025. https://cftri.res.in/faculty_detail/2062.
Falling Walls Foundation, dir. 2020. Breaking the Wall to Language, Geography and Social Separation. 05:12. https://www.youtube.com/watch?v=_nscnJFd–8.
Kollegala Sharma | Mysuru Literature Festival. n.d. Accessed August 6, 2025. https://www.mysuruliteraturefestival.com/lit-fest-2024/kollegala-sharma/.
Mandram, dir. 2018. Science and Language – Dr Kollegala Sharma. 27:49. https://www.youtube.com/watch?v=dSqO-AOu9io.
Spotify. n.d. “Learn and Unlearn.” Accessed August 6, 2025. https://open.spotify.com/show/1JYHPAvzx3RuWcO8hL6Cjy.
X (Formerly Twitter). 2025. “(4) Kollegala Sharma (@kollegala) / X.” July 27. https://x.com/kollegala.
YouTube. n.d. “Kollegala Sharma.” Accessed August 6, 2025. https://www.youtube.com/channel/UCCtB6my4ohaYOnQvBRnPEuA.
Light as EM wave – in Maxwell’s words
Every year, I teach an optics course to physics majors (including physics iPhD students and MS Quantum Tech students). In the process of introduction, I discuss how light was discovered to be an electromagnetic wave. One of the thrills of this topic is to quote Maxwell from his legendary 1865 paper1, in which he makes this monumental connection. Every time I teach this, I get an intellectual kick, even after doing this for almost 1.5 decades.
The highlighted text is the famous statement. Before that, Maxwell compares his result with two experimental results and confirms his prediction. I follow this up with Hertz’s experiment.
Note: Electric waves and telegraphy were already known before Maxwell’s paper. There were papers that discussed about velocity of light and its connection to electric waves. See this paper2, for example. However, these interpretations were not as comprehensive as Maxwell’s case, and importantly, the field theory viewpoint needed Faraday’s experiments and Maxwell’s interpretation.
- Maxwell, James Clerk. 1865. “VIII. A Dynamical Theory of the Electromagnetic Field.” Philosophical Transactions of the Royal Society of London 155 (January): 459–512. https://doi.org/10.1098/rstl.1865.0008.
↩︎ - https://www.ifi.unicamp.br/~assis/Weber-Kohlrausch(2003).pdf ↩︎
THE DIARY AND OBSERVATIONS OF THOMAS ALVA EDISON
Thomas Alva Edison was one of the greatest inventors we know about. Sometime ago, I stumbled upon a book titled THE DIARY AND OBSERVATIONS OF THOMAS ALVA EDISON, and it was an interesting read. In there, we obtain an insight into Edison’s view on many different subjects, including education, work, religion, etc. Edison was a person with strong views. His working methods were unconventional. Here are a few interesting facts I learnt from this book:
1) Edison had to recruit many executives to his labs; he always emphasized on a memory test and gave them a questionnaire to answer. He insisted that memory is very important for decision making, and he usually employed those people who had very good memory. Edison wrote “…Certainly the brain should have the facts. If a brain possesses an enormous number of facts, those facts, through action of the subconscious mind, will automatically keep themselves available when needed and will automatically keep themselves out of the way, not interfering when not required.”
2) Edison’s view on education was interesting and bold for his times, and he believed that learning through movies would be vital for future education. As early as the 1890s, he said that the best way to teach geography is either by taking the student on a tour or by showing them a movie. Edison wrote
“…motion pictures can be applied to a scientific, systematic course of memory training in the schools, taking the children at an early age when the mind is plastic enough to adapt itself most readily to new habit of thought.
Most of our text books fail on two big counts. They are not sufficiently human, and their application is not sufficiently practical”
3) In the following lines, Edison gives an insight into how he worked: “When I want to discover something, I begin by reading up everything that has been done along that line in the past-that’s what all these books in the library are for. I see what has been accomplished at great labor and expense in the past. I gather the data of many thousands of experiments as a starting point, and then I make thousands more.”
“ …..The motive that I have for inventing is, I guess, like the motive of the billiard player, who always wants to do a little better-to add to his record. Under present conditions I use the reasonable profit which I derive from one invention to make experiments looking towards another invention…..”
4) Edison rates the phonograph as his greatest discovery. He writes, “Which do I consider my greatest invention ? Well, my reply to that would be that I like the phonograph best. Doubtless this is because I love music. And then it has brought so much joy into millions of homes all over this country, and , indeed, all over the world.”
5) The following quotation by Joshua Reynolds was hung in every room of Edison’s laboratory “ There is no expedient to which a man will not resort to avoid the real labor of thinking”
There are many more fascinating thoughts of Edison, many agreeable and a few disagreeable ones, in the above-mentioned book, and if you happen to find it, read it through…it’s a classic and insightful read.
The above text is from a 2011 post on my old blog.