Category: History

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.

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.

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.

  1. 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.
    ↩︎
  2. 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.

A quantum survery – 3 thoughts

One of the joys of studying quantum mechanics, at any stage of a career, is to be aware of the fact that there is more scope for interpretations and understanding. This notion has not changed for several decades. A recent survey reinforces this thought.

There are at least 3 interesting points that I infer from the situation:

1) The interpretation of reality at the quantum scale is probabilistic. This has served us well in experiments and has led to the founding of quantum technologies. We are in a situation in the history of science where the philosophical foundations are uncertain, but the technological implications are profound.

2) Having more data is always good, but for a new leap of thought, we may have to pay attention to new connections among the data. Can AI play a role in this?

3) There is more room for exploration in the foundations of quantum physics. Philosophy of physics has a role to play in this exploration. Physics students and researchers with (analytical) philosophical inclination have an opportunity to contribution. This needs a grounding in understanding mathematics and experiments related to quantum physics. I see this as a great opportunity for someone to enter the field.

Conclusion: Good time to explore the foundations of physics*

*subject to support from society

Philosophy of Science – ideas – cartoon

Ideas in philosophy of science, especially in the 1800s and early 1900s, had their origin in physics. Two philosophers who were deeply influenced by physics were Karl Popper and Thomas Kuhn. Below is a cartoon depiction of the same. Of course, the origins of ideas in philosophy of science have diversified in recent years, and biology and technology (especially AI) dominate the scene nowadays.

A note on experimental physics

Experimental physics is one of the crucial ingredients of physics. There are at least two major tasks within its realm. The first is to examine nature through observation. These observations can then be extrapolated into systematic measurements that can be quantified. The second aspect is that experimental physics serves as a platform to test hypotheses that are already formulated by theory. In this way, it acts as a conduit connecting theory to real-world situations. Additionally, it reveals the limitations of any theory, thereby serving as a valuable test bed.

These two tasks are essentially intertwined: an observation can lead to new hypotheses, and, conversely, a well-formulated hypothesis can lead to systematic measurements.

For example, while hunting for astronomical radio sources, an important discovery was made: the observation of the cosmic microwave background. This finding turned out to be one of the crucial ones in physics, providing vital insights into the Big Bang theory and becoming a foundational aspect of observational cosmology. Another example is the special theory of relativity, where the Michelson-Morley experiment ruled out ether, which enabled Einstein to formulate his theory with greater confidence.

These two examples offer a snapshot of the possibilities within experimental physics and highlight its essential role in the duality between theory and experiment in physics. In a way, experiments and theory complement each other, and are like two sides of a coin.

Tony Tyson and a giant CCD camera

Recently, I came across an interview with Tony Tyson, one of the main scientists related to the Rubin telescope. He says:

“We can do better than this. We can build a larger telescope by making larger mosaics of larger CCDs.”
— Tony Tyson

On a day when India lost a test match, the first sentence rings loud…anyway, the topic of this post is a fascinating development happening in observational cosmology.

Tony’s suggestion above is a great, ambitious way to explore the Universe….by building effective observational tools that can image and comprehend the observable…and perhaps unobservable too…

For students: Observational cosmology is a great place to explore cutting-edge science: physics (experiments + theory), maths, engineering & computation…all come together..

Check out the interview of Tony Tyson…one of the brains behind the cameras of Rubin Observatory…plenty to learn…

Just like test cricket, observational cosmology needs patience…perhaps a good lesson for life too…