VISMAYA: History & Philosophy of Physics

Tag: physics

  • Art and Chu – in Bell labs

    Steven Chu and Arthur Ashkin in 1986, in front of the apparatus shortly after the first optical trapping experiment was completed. Image from Chu’s Nobel lecture.

    Steven Chu’s Nobel lecture has some gems. Below, he shares his experience of working with Arthur Ashkin.

    “In 1986, the world was excited about atom trapping. During this time, Art Ashkin began to use optical tweezers to trap micron sized particles. While experimenting with colloidal tobacco mosaic viruses, he noticed tiny, translucent objects in his sample. Rushing into my lab, he excitedly proclaimed that he had ‘discovered Life’. I went into his lab, half thinking that the excitement of the last few years had finally gotten the better of him. In his lab was a microscope objective focusing an argon laser beam into a petri dish of water. Off to the side was an old Edmund Scientific microscope. Squinting into the microscope, I saw my eye lashes. Squinting harder, I occasionally saw some translucent objects. Many of these objects were ‘floaters’, debris in my vitreous humor that could be moved by blinking my eyes. Art assured me that there were other objects there that would not move when I blinked my eyes. Sure enough, there were objects in the water that could be trapped and would swim away if the light were turned off. Art had discovered bugs in his apparatus, but these were real bugs, bacteria that had eventually grown in his sample beads and water.”

    Chu won the physics Nobel in 1997, and Ashkin won the same in 2018. Ashkin was the pioneer of optical trapping and tweezers, and applied it to a variety of problems, including the manipulation of biological matter. Chu harnessed the momentum of light to trap and cool atoms. Both started their work and collaborated at Bell Labs. Chu moved to Stanford, whereas Ashkin stayed back. Bell Labs was a remarkable place in the 1980s, as Chu describes in his lecture :

    “Bell Labs was a researcher’s paradise. Our management supplied us with funding, shielded us from bureaucracy, and urged us to do the best science possible. The cramped labs and office cubicles forced us to rub shoulders with each other. Animated discussions frequently interrupted seminars and casual conversations in the cafeteria would sometimes mark the beginning of a new collaboration.”

    Can the world afford to have another Bell Labs in 2025? Can it recreate the magic?

  • Real is imaginary and vice versa

    This week in my optics class, I have been teaching Kramers-Kronig (KK) relations of electric susceptibility. It is fascinating to see the causality argument emerge from the relationship between the real and imaginary parts of the complex susceptibility. Whereas the time domain explanation is relatively easier to appreciate (that dissipation follows perturbation in time), for me, the frequency domain implication in KK relation is fascinating: the fact that information about the real part of the function at all frequencies can give you insight into the imaginary part at any given frequency (and vice versa) makes it such a powerful mathematical and physical tool. For example, by knowing the absorption spectrum of a medium, you can find out the refractive index of a medium at a particular frequency that is not easily accessible in experiments.

    Two inferences I draw:

    1) Complex analysis combined with differential calculus is one of the most beautiful and powerful mathematical tools invented, and exploring its application in experimental scenarios has made physics intriguing, useful, and profound.

    2) The KK relationship shows how causality and the structure of matter are connected to each other, and by studying them, one will be able to extrapolate the idea beyond the problem at hand and apply it to a different context in physics. It just shows how ideas hop from one domain to another and how mathematics plays a critical role in intellectual arbitrage.

    Real is imaginary and vice versa. Complex numbers zindabad!

  • Chandra with Lalitha – 1940 – photo

    Source: University of Chicago – archives

  • 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.

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    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.

  • 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.
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    2. https://www.ifi.unicamp.br/~assis/Weber-Kohlrausch(2003).pdf ↩︎

  • 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

  • Conversation with Shivprasad Patil

    Welcome to the podcast Pratidhavani – Humanizing Science

    Shivprasad Patil is a Professor in the Department of Physics at the Indian Institute of Science Education and Research (IISER) Pune.

    His main academic interests include nanotechnology, atomic force microscopy, and single-molecular interactions. His research centers on experimental nanomechanics and force spectroscopy, especially for probing phenomena at the single-molecule level.

    In this conversation, we explore his intellectual journey from a small village in Maharashtra to a professor at IISER Pune

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    References:

    Force Spectroscopy Conference. n.d. “Conference on Force Spectroscopy and Microscopy, India.” Accessed July 25, 2025. https://forcespectroscopy.in/.

    My Site. n.d. “Home.” Accessed July 25, 2025. https://nmlab220.wixsite.com/my-site-1.

    “‪Shivprasad Patil‬ – ‪Google Scholar‬.” n.d. Accessed July 25, 2025. https://scholar.google.com/citations?user=rtuNcawAAAAJ&hl=en.

    “Shivprasad Patil – IISER Pune.” n.d. Accessed July 25, 2025. https://www.iiserpune.ac.in/research/department/physics/people/faculty/regular-faculty/shivprasad-patil/313.