Gravitational Waves Researcher: Prayush Kumar

The Scholars’ Avenue was privileged to have a skype-interview with one of the researchers involved in LIGO Project, Prayush Kumar. He gave very intuitive insights and made us enjoy the conversation with his great sense of analogy and humor.
TSA:  LIGO was being used for other purposes, right? When did this quest for Gravitational Waves start?

Prayush: The idea of gravitation having wave-like characteristics is a century old. While doing a linear approximation of Einstein’s General Relativity it was discovered that the approximation would have a wave-like solution. During the years 1910-1940, people refused to believe that it was an actual physical phenomenon. In their view it could be something which came up because of the ambiguities in General Relativity. Einstein’s General Relativity has a lot of ambiguity. In fact, Einstein wrote a paper disproving the existence of Gravitational Waves to Physical Review Letters (PRL) which was rejected but was published in some other European journal.  In the 1980s, LIGO came into existence and the idea of building an interferometer to detect gravitational waves from astrophysical sources was thought of. After formally getting the funding, the interferometer was made and observations were made from 2001-2010 but nothing was observed. An upgradation was made to increase the number of detectable sources to thirty times the previous value. Then finally, we started seeing things.​

TSA:  What was your role in particular in this project?

Prayush: I’m gonna answer it as briefly as possible. The signals which were to be detected were extremely weak. There was a lot of noise and the signal was buried deep in that noise. The precision required to measure the signal was comparable to that when you are measuring the distance between two stars with the allowable error being equal to the width of human hair. My role was in the same domain.

TSA: How do we know for sure that the detection made was a proof of gravitational waves coming out of the collision of two black holes and not a result of some other astronomical phenomenon?


Prayush: We can know this only by excluding all other possibilities. We excluded everything that could have been a reason.  We excluded that it was any environmental noise source by monitoring the environment. The climate monitors gave a negative for any environmental noise near any of the two interferometers. If it was an extraterrestrial phenomenon, the signal would have reached both the interferometers at the same time. That was the whole point of building two interferometers and not one. Eliminating these two factors confirmed that it was a gravitational wave as nothing else could have moved the interferometers’ arms that much. Now, how do we know that it was a result of a collision of two black holes? The signal was thankfully so loud that it sufficed the General Relativity’s prediction of black hole collision to a great extent.

TSA:  Is this also how we know that it released a humongous amount of energy?

Prayush: This was confirmed by determining the mass of two black holes before collision while they were spinning and the final mass of the combined body. We observed that a lot of mass was lost. It was three times the mass of our sun being converted completely into energy! The amount of energy released was three times mass of sun times c squared. But this much energy produced waves of minuscule wavelength. What does it tell us? It tells us that the fabric of space-time is extremely rigid. It takes up a lot of energy to create ripples in space-time.

TSA: How did you end up working in LIGO after being at BITS and what advice would you give to the students who wish to pursue a career in Physics?

Prayush: Before answering this question I’d like to talk about what Engineering and Science really are. Engineering is creative in nature; it takes information and creates more information out of it. Simplest of scientific theories can be used in engineering to create very useful information. Science, on the other hand is destructive in nature – it destroys the underlying phenomenon to its simplest possible form and then explains it. The explanation is what we call a theory. By destructive I mean that in a single A4 sheet you can enlist all the laws of physics that govern nature and the entirety of physics can be derived from it.

Now, the choice of where you want to end up working should be based on the fundamental nature of these two domains, in other words, which of the two are you? So, that is basically my advice. I’d like to say that there is no age for switching from Science to Engineering and vice-versa. For instance jab mai PhD kar rha tha (when I was pursuing my PhD) then my office mate used to be an army officer and at the age of 40 he said f*** this and decided to pursue a PhD. So, at your (IITians’) age you should think that you can do anything. I was doing Electrical Engineering and all I did was that I took one course in Gravitation and it interested me. And then what I did was that I found people who were doing research in the field and I emailed them, as simple as that. I emailed 20-30 people and one of them got back to me.

TSA: How did you start learning about Physics and Gravity?

Prayush: Mostly, I read books. In Pilani we didn’t have any attendance criterion so my attendance used to be 5-10%. I like learning from books more than learning from professors.

TSA: It is hard to know where to begin, whom to approach, what is your advice on this?

Prayush: No, no it’s not. There is a very simple recipe. Firstly, find something which is relevant to your field of expertise right now. For instance, if a person is doing computer science, hypothetically if he wanted to enter the field of physics, I would suggest him to start working on Black Entropy and Black Hole Information theory. That is closest to computer science that you would find in Physics. Read books by good teachers on the subject and once you start reading, you gain some basic understanding. Spend some time on learning, say 2-3 months. Then find out who all in the world are doing research on the topic. You are going to find a lot of people across the globe. And you just write them e-mails being frank, saying ‘Hey! I’m doing this. These are my skill sets, this is what I can provide you. If you have a project, I can do coding, I can do the grunt work and you can teach me.’ And they’d be like ‘Oh Sure! I have a project which you can do.’ And they’ll contact you. Once you do a summer internship with some professor, it is much easier to find a PhD version of it. So, step-1 is to find what to do and step-2 is to find where to do.

TSA:  What made you different from the other students?


Prayush: This is more of a personal advice, I wouldn’t say it would work for everyone. I tried to separate my interest from the world around me. We get influenced by what our surrounding is, what people around us are doing, saying and thinking, and that affects us in good and bad ways. The problem arises when this effect starts leaking into what you really want to be. That should not happen. One way to accomplish this is being brutally honest with yourself. You have to be honest about your strengths and weaknesses and make sure that your future plans include your strengths, and not your weaknesses. Being brutally honest is not as easy as it sounds, it hurts your ego.

The second advice would be to associate with older and more learned people, like your faculty. By doing this you would realize that out of the 5 things that you are doing right now, only 1 thing matters in the long run. Somethings which you are doing might help you in placements but by the time you reach the age of 35-40, you won’t even remember what you did to get placed.​

TSA: Apart from proving the general theory of relativity, what other implications does the discovery of Gravitational Waves have?

Prayush: While selling the LIGO project to U.S. government, it was told that LIGO would find Neutron Star Collisions. The black holes observed in this experiment are already 3 times more than most of the black holes. This single observation has given astrophysics a lot to think about. A lot of the formation theories about stars are now invalid. Now, with the discovery of Gravitational Waves people can study the chemical nature of Universe and how mass is distributed around in the universe. It will also tell a lot about complex systems and about the evolution of universe.

TSA: Do you think that the findings of the experiment could have a practical application for humans in the near future?

Prayush: It will have many benefits especially when it comes to control systems. I cannot come up with concrete examples but to push a system back to its normal state when an external factor disturbs the system could be one of them. This is a feat for both science and engineering.

TSA: We have information that there are plans to have similar experimental setups all over the world. We’d like you to shed some light on the same.


Prayush: Yes, in fact, there is going to be one in India too, if the Prime Minister agrees to it. There would be a total of five experimental setups for better detections. Construction of such setups has already been started in Italy and Japan. Very creative technology is also being used for the same. Construction of a detector completely inside a mountain is being carried out which would help in curbing a major proportion of noise. The reason for having multiple setups is triangulation, if we see some object with respect to two points, it can be anywhere in the loci of a ring. To have a point location, we must have another detector as we live in a 3D world.

TSA: What are your plans from now on?

Prayush: I want to learn numerically solving General Theory of Relativity problems and understand complex systems like the early universe.  I’d like to numerically simulate the beginning of the universe. This is more of a future plan but it’s something which I’d like to work on.

TSA: Have you seen the movie Interstellar? Does it make sense to you?


Prayush: The fact that he regains his human form after getting into a black hole is absurd. The black hole rotates at a very high speed. If a human happens to go near the surface, he/she would turn into a spaghetti and would wound the black hole like woolen yarn ball. Even if we hypothetically assume that he regains his human form, the fact that he would end up in a time where his daughter is alive is highly unlikely. It is much more likely that he would be thrown into a distant corner of the universe. So, the last part where all the emotional drama happens is unlikely, apart from the fact that he doesn’t turn into spaghetti.

Links for more information:

1. A well compiled and not-too-long article discussing the human quest for these waves:

2. An article regarding LIGO India Project:

3. What these waves look like as they travel from those black holes towards us? (video; 43 secs):

4. How would the same black holes would look to human “eyes”, if one was standing next to them? (video; 35 secs):

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