Varghese Mathai

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ORAL HISTORIES
Mathai credit University of Massachusetts, Amherst.png

Credit: University of Massachusetts, Amherst

Interviewed by
David Zierler
Interview date
Location
video conference
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Interview of Varghese Mathai by David Zierler on March 10, 2021,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
www.aip.org/history-programs/niels-bohr-library/oral-histories/XXXX

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Varghese Mathai, a faculty member in the Department of Physics at the University of Massachusetts, is interviewed by David Zierler. He discusses his reliance on simulated experiments during the pandemic and the value of this for fluid dynamics generally. Mathai recounts his childhood in Kerala, India, and how his interest in how things flow led to his academic specialty. He describes his undergraduate and master’s work in Mechanical Engineering at the Indian Institute of Science before working at General Electric in the Aircraft Engines Division. Mathai discusses his thesis research at the University of Twente in the Netherlands, where he studied buoyant particles in turbulent flow under Detlef Lohse and Chao Sun. He explains his decision to take a postdoctoral position at Brown University where there was a group focused on soft materials and flows with bio-inspired applications. Mathai describes the opportunities leading to his faculty appointment at UMass-Amherst and his interest in setting up a lab in the middle of a pandemic with clear opportunities to study Covid transmission as a fluid dynamics problem. He explains why the CDC guidance should have taken into greater account the expertise of fluid dynamicists and the protections (and limitations) that masks offer in stopping the spread. Mathai emphasizes the importance of visualization aids so the public can better understand the science of airborne transmission. At the end of the discussion, Mathai explains why, even after the pandemic, he will remain interested in collaborating with biologists to advance human health from the vantage point of fluid dynamics.

 

Transcript

David Zierler:

Okay, this is David Zierler, oral historian for the American Institute of Physics. It is March 10th, 2021. I am so happy to be here with Professor Varghese Mathai. Varghese, good to see you. Thank you for joining me.‎‎

Varghese Mathai:

Thank you. ‎‎

Zierler:

All right, so to start, would you please tell me your title and institutional affiliation?‎‎

Mathai:

Right. I'm a faculty member in the Department of Physics at University of Massachusetts, Amherst.‎‎

Zierler:

When did you join UMass?‎‎

Mathai:

August 2020.‎‎

Zierler:

An exciting time to join faculty. Were you remote from the beginning? Did you start teaching remotely as your first appointment?‎‎ ‎‎

Mathai:

I moved from Rhode Island. I was doing my Postdoc at Brown. So, I could drove from Rhode Island to UMass which is in Western Massachusetts. So, it was kind of convenient move, even in the pandemic times. There were some challenges, but it was all pretty well handled by UMass and the people in the department were quite supportive in making this happen. And since I've moved, it's been mostly remote. But I’ve got an office setup already, as you can see, right now, I'm in my office. But the campus is mostly in remote mode.‎‎ ‎‎

Zierler:

Varghese, a question we're all dealing with right now, particularly for people that work in a laboratory environment, in what ways has the pandemic impacted your research in terms of your collaboration, in terms of access to the instrumentation? For better or worse, how have the last 12 months been for your research?‎‎ ‎‎

Mathai:

Yes, so the pandemic has had a number of impacts on researchers in general, and some of this has been not so good, and some of this has been good, I would say. So, if you say my personal experience, I'm primarily an experimental physicist. And I do experiments inside a laboratory space at tabletop scale. So, when we had the stay-at-home requirements, my experiments were no longer doable in the lab. But this was also a time when I started thinking more seriously about using computer simulations. So, in my personal experience, I've looked more into the computational and theoretical side of research recently, which primarily I could attribute to the pandemic. But at the same time, experimental research in the laboratory has been slowed down. And this, I believe, is not just a personal story, it also applies to a number of researchers, and most of the faculty, students, and other researchers at universities have been trying to adapt. And this is not just limited to research, but also to teaching and instruction, which have all gone into remote mode.‎‎

One of the things I do think has been a good impact in the academic circles is that we are now evermore using remote ways of interacting for scientific exchanges. So, there's a lot more of communication that's happening over Zoom and other kinds of video conferencing. This has certainly brought down air travel as you can imagine. In the initial phase of the pandemic, there was a lot of organizational challenges for holding international conferences fully remote, but they are getting solved now. Now, people are starting to think about conducting many of these conferences virtually. The main strength of this is that it makes the world a smaller place that you do get applicants and visitors and attendees from all over the globe, except for the time difference, which is obviously still a factor.

But now, we are also adapting the conference styles to have more recorded sessions so that attendees from all over the world can attend. So, I do think that from the point of view of disseminating information and education and making research openly accessible, the remote format has certainly helped. Of course, it cannot replace the in-person interaction. So, it comes at a price, but it also comes with several benefits. I think that several of these newly created avenues of communication will continue to be active even after the pandemic.‎‎

Zierler:

Varghese, when did you realize that your area of expertise might be relevant to the all-important question of the physics of COVID transmission? Did this occur to you right from the beginning, or this was an intellectual process for you?‎‎ ‎‎

Mathai:

Right. I'm basically an experimental Fluid Dynamicist and Soft Matter Physicist. The interactions between fluids and soft materials, that definition encompasses everything I do. By soft materials, I mean a wide class of materials which can be air bubbles that are present in an aquarium tank to dust and particles which are present when a volcano erupts to soft-winged flying mammals like bats. You can see, it's a pretty broad definition and I like to look at it in that perspective.

And this also has strong connections to multiphase, in the sense that you have a fluid flow, which is dispersed with elements that are soft and deformable. We can think of a deforming bubble as a soft material, for instance. You can consider a droplet which is deformable and changing its shape due to hydrodynamic effect a soft material.‎‎ So this area of multiphase fluid dynamics, if you look, is all around you. The air that you breathe is not just the constituent gases, but also, there are particles in them. The water that you drink also has a certain level of contaminants. And when you look at the topic of disease transmission, that is very often facilitated by multiphase fluid dynamics.

I worked a little over a year in industry, at General Electric Aircraft Engines Division where I was studying the flows inside the combustor of an aircraft. And during my postdoc I was looking at systems mimicking the wing beats of a flying mammal like a bat. For my Ph.D. thesis research, I was looking at particle-laden turbulent flows, the flows that you can see in the oceans and in the atmosphere. So, you can probably see the breadth of topics that fluid dynamics encompasses, from academia to industry. And I can tell you that all of these different looking topics have very similar fundamental laws from which they branch them out.‎‎ Let me take the example of the study that we did recently about the air flows inside the car, I would think of it as an extension of the knowledge that you gain as a researcher in multiphase fluid dynamics. Essentially, I mean this was not something that required reinventing or re-analyzing the situations. But at every point, we are realizing that when you breathe out, you are breathing out particles, which contain aerosols or larger particles, and there as well, I see a connection to the research I did during my doctoral study.‎‎

Zierler:

Varghese, a question that so many people are dealing with right now, in the world of computer simulations, given that so much of your research agenda relies on real-world experiments, sitting at the tabletop, dealing with physical objects, how can you be sure that the computer simulation is an accurate representation of physical reality? How do you test that against the real deal if you're not using real stuff to make conclusions?‎‎ ‎‎

Mathai:

Yeah, this is a very good question, and it requires a little bit of elaboration. So, by computer simulations or by numerical simulations, you could mean a number of different things, including simulations which are far from the reality you measure, or it could be things which are very close to reality. We do understand the fundamental laws, all the equations that govern fluid flows. They are called the Navier-Stokes Equations, and we do understand in what regimes that they can be considered to be a compressible flow or an incompressible flow. So, these equations are field equations without a solution that has the three dimensions, and also varying in time. The variable that you're trying to solve here is the velocity of the fluid at different points in space and varying in time. Except for a limited number of special cases, these equations are not easy to analytically solve.

So, the general approach to adopt is to numerically solve them, and that is what the computer simulations that I refer to do. So, these computer simulations are basically solving the Navier Stokes Equations, which are derived from Newton's second law, force equals mass times acceleration. Whenever this is a valid, the computer simulations, in principle, when they are solved in the most rigorous way, ought to give realistic results. ‎‎And these computer simulations also come with a process of validating the simulations. And these validations are typically done by comparing with a measurement. So, the idea is that if you compare with enough number of laboratory-based measurements or field tests, and you validate these computer simulations against them. Then the expectation is that you can use them to predict a case which was not done in the laboratory, assuming the prediction lies within the same regimes of fluid flow that were validated.‎‎

So, from this point of view, when we say we are performing a computer simulation solving the full Navier Stokes in three dimensions and time, you can pretty reliably replicate what the air flow or a water flow or a liquid flow. I should point out that such simulations are not just used to confirm experimental observations, but there have been several examples of when fluid dynamics simulations have been used to predict or observe new physical phenomena. Several decades later, it is found in an experiment measurement.

So, the power of computational fluid dynamics, especially when you solve the full Navier-Stokes is tremendous and something that people have to have faith in. When communicating the science though, often, I need to rely on experiments to convince the audience that it really happens the way the simulations predict, because of the public’s acceptance of measurements. So, the two should go hand-in-hand. Then, only the believability aspect is there. But if you ask me, these computer simulations when they are performed in the most rigorous way, they are pretty reliable.‎‎

Zierler:

To what extent is the remarkable, even exponential rise in computational power responsible for the validity of these simulations? In other words, are the things you're working on, would they have been possible even 10, 15 years ago or it's only because of recent advances in computer powers that these experiments are valuable and can be validated?‎‎ ‎‎

Mathai:

I don't know if you're referring to this particular article or it's more generally about fluid dynamics computation?‎‎‎‎

Zierler:

Generally fluid dynamics computation.‎‎ ‎‎

Mathai:

Right. Generally, fluid dynamics computations have the power of doing simulations have increased significantly in the last 20 years. And this is responsible for us being able to simulate things which you could not possibly imagine a few decades back. The approach has slightly shifted towards solving the full Navier Stokes equations in a more rigorous manner as compared to previously, when computational models used to be very popular. And this is ever-changing, and it's also increasing the possibilities using supercomputers. I'm not an expert to talk about supercomputing, but I do have several collaborators who work on this. And based on the conversations I've had with them, what I hear is that problems that you could not imagine studying several years ago have become possible now. And currently, the challenge is to extend it to even further, and parallel computing is very popular in this area of research. ‎‎

Zierler:

If you might use your imagination, I mean, it's an existential question about once we achieve the capacity for true quantum computing, what will we even do with quantum computers? In your field, do you have any guesses, any ideas on what the value of quantum computing might mean for fluid dynamics?‎‎ ‎‎

Mathai:

I wouldn't be a good person to comment on this. I can talk about this like any other person would say that it sounds very promising. And if it's successful, then it will really change the landscape of fluid dynamics simulations as well. The concept that you can explore multiple options at the same time does help with getting results sooner.

In the Netherlands, where I did my Ph.D. study, where supercomputing capabilities are, to my knowledge, very good and accessible to academia. So, there's huge potential if it comes through, but yeah, this is all I can talk about.‎‎ ‎

Zierler:

Well, let's take it all the way back to the beginning. Let's go back to India and we'll start with your parents. Tell me a little bit about them and where they're from.‎‎ ‎‎

Mathai:

Sure, I'm from the south of India from a state called Kerala. My parents, my dad is an Electrical Engineer. My mom was educated in law. I have a sister who's a year older to me, and she's an Electronics Engineer, and she works for a company of Kerala. And I did my undergrad education and my master's education in India. My master's at the Indian Institute of Science, and I did my undergraduate at College of Engineering in Trivandrum. After my master's, I worked for a couple of years for General Electric, in their Aircraft Engines Division in India, in Bangalore. This basically gave me some exposure to computation fluid dynamics.

But my interest, like I said, is mostly in experiments. So, I decided to do a Ph.D. in experimental fluid dynamics, while also having had some experience with computing. And then, I moved to the Netherlands to do my Ph.D. And this was in particle-laden turbulence experiments.‎‎

Zierler:

Did your father involve you at all in his career? In other words, as a kid, did you know what it meant to be an engineer at all?‎‎ ‎‎

Mathai:

Yes, so right from a young age, my father used to show toys or experiments that were done at a tabletop scale, and right from a young age, I had an interest in things that you could observe with the naked eye, and that did instill in me an interest in physics. This is not something that I've prepared to recollect, so I’ll have to think and recollect while I respond. So, in school, until I was probably 13 or 14, the curriculum involved learning a large number of subjects, including the sciences. That was a bit distracting and I couldn't spend a lot of time on my primary interests. So, my interest started to increase and shoot up when I was probably 14 or 15 when I could focus on physics and, specifically mechanics.‎‎

And in India, growing up at 15, if you like mechanics, and if you like physics, one of the popular directions you take is to go into engineering, which is also what I did. And I did talk to my dad about different disciplines of engineering. And because I had shown an interest in mechanics, he suggested that mechanical engineering might be an option. And I read a short paragraph about what mechanical engineering meant, and that seemed to convince me because it had things like Thermodynamics, Newtonian Mechanics, Rigid Body Dynamics, Theory of Machines, and these definitely got me interested, and I enrolled into mechanical engineering. I did study in the same university as my father did. So, he did have contacts with faculty at that university, and that did help me get a better picture of what an undergraduate education at that university was going to be like. This is the oldest college for engineering in the state of Kerala.

Right after I joined there, it was a four-year undergrad, and towards the end of the undergrad, I felt like I should pursue higher education like a masters or a Ph.D. I was not sure at that point whether I should enroll in a Ph.D. program or not. Just like many students in India with an interest to pursue higher education, I applied for a graduate master's program. This required you to compete in an all-India-level examination, which I fortunately did well in, coming 9th at the all-India level. And this basically opened the doors for me to get into the Indian Institute of Science, which is considered my many as India’s premier university for science and technology research.

This is where I actually figured out that I'd like to do my research in Fluid Mechanics, and this is also what made me appreciate the beauty of Fluid Mechanics, which we see and perceive around us. To understand why fluids like air and water flow the way they do, we need to study this subject. For instance, common sense tells us that if you wanted to put out a burning candle flame, you basically blow at it, right? If you blow at it, the candle flame is put out, but if you blow air inwards, it is unusually difficult to put out the candle. This has a lot to do with how fluid flows are in general. So, the Navier-Stokes equations, the same equations can tell you why this is the case. When you blow out, you generate a jet of air, which doesn't expand sideways from your mouth. The air jet comes out directly toward the candle flame and put the flame out. Instead, if you blow in, or when you inhale, the air that comes in is from all around your face. So, the airflow pattern whether you blow out or when you blow in can be very different. And you need to understand Fluid Mechanics to appreciate this. When I encountered these kinds of examples in class — I got inspired to study the subject so as to better appreciate the nature of flows we observe around us.

Flows that you see around you, a hurricane or the tornado, it's got all fluid mechanics and heat transfer phenomena. The fact that weather predictions are very difficult is linked to how nonlinear the governing equations are and how sensitive they are to tiny changes in initial conditions which can change the future a great deal. That's also the reason why beyond a couple of weeks you cannot make accurate weather predictions.

Zierler:

Varghese, a few social and cultural questions. Growing up what language or languages were spoken in your household?‎‎ ‎‎

Mathai:

Right. So, I come from the southern state of Kerala, and in that state, you speak the regional language called Malayalam, and I spoke Malayalam right throughout my childhood days. At my home, my parents and my sister speak Malayalam, so do most of my relatives. In addition to this, growing up in India, you learn a few additional languages. Hindi, which is spoken widely in the north of India, and it can be useful to learn that, particularly while traveling in the northern parts of India. In addition to that, there was English, which was the primary medium of education in my case. But this can vary a lot. depending on the area and community you come from. Essentially, these are the three languages that you learn growing up in my state, Kerala. But let me clarify that in India, you have about 20 recognized regional languages. Because I was born and raised in Kerala, I am somewhat familiar with listening to language of neighboring states, for instance, Tamil.‎‎ ‎‎

Zierler:

What religious or cultural traditions were important in your family growing up?‎‎ ‎‎

Mathai:

Again, this has to do with the state I come from. My family is traditionally from a Christian background and we're from a Syrian Christian tradition. It has its roots that can be traced to Christianity in Antioch, which came to the south of India. I wouldn't be able to tell you the whole history, because I'm not that well read in this. But I can tell you about the origin of my name. Varghese, is the Malayalam language version of George, and Mathai is Malayalam translation of Matthew. I believe the name George has Greek origins - it came from Georgios, and it evolved to the current English version.

Zierler:

So, you celebrated Christmas and Easter and all of the major Christian holidays?‎‎ ‎‎

Mathai:

Yes, that's true, mainly Easter and Christmas.‎‎ ‎‎

Zierler:

What does Christmas look like in Kerala? Is there a Christmas tree?‎‎‎‎

Mathai:

There's a Christmas tree, but it’s a lot less common than it is in the West. The Christmas in Kerala has some elements of what is seen in Europe and the US. There's Santa Claus, with strong links to the church. The church that the community belong to organizes some kind of cultural activities around Christmas. And Christmas is also the time when you have the Christmas holidays. So, if you work or if you have relatives or family who are in different locations in India or abroad, they return to Kerala, and we usually have a get-together with extended family. This can be up to 70 or 80 people who are otherwise chatting in a WhatsApp group. [laugh]. I've not been able to go to those for several years now. But that's usually what goes with Christmas. ‎‎Easter is usually more ritualistic and religious traditions.

I'm not particularly religious, but I do identify with the traditions and cultural aspects of it, and that's usually what I can remember. This has got a lot to do with living in a multi-cultural, multi-religious background. Kerala’s population is about 18% Christians, especially the Syrian Christians, about 50% Hindus, and 20% Muslims, from what I remember. And there's also other communities like Jews, and I might have missed some religions. ‎‎ Growing up, you're always surrounded by people from different religious faiths, the elements of this do pour into Christian traditions as well.

For instance, I studied in a school which did have strong links to Hindu traditions, and that did give me a lot of understanding about the Hindu mythology, for instance. I enjoyed reading about Hindu mythology, I enjoyed knowing about it, and I enjoyed some of the festivals of Hinduism. And there are also festivals like the Onam, which is celebrated by all the people in the state of Kerala, regardless of your religion. Possibly, you can compare that to Thanksgiving here, although Onam does have a mythological origin which is rooted in Hinduism, I think. But today, it is celebrated by almost all communities of Kerala.

Zierler:

Varghese, unfortunately, in India, like so many countries, there's been a rise in nationalism. Has the rise of Hindu nationalism in India been problematic for the Christian community?‎‎‎‎

Mathai:

So, I come from a state which is possibly less affected by this than others. I could be wrong in my interpretation, but in my state, this has so far not been a serious issue. I must apologize if I’m being insensitive to the people who might have been adversely affected by this. What I can say is that, in general, the rise of nationalism, regardless of whether religious or not, is a matter of serious concern. I think education is one thing that can reduce the adverse effects of this. To answer your question, yes in recent years there has been a rise in nationalism that has taken a dimension beyond the simple idea of us loving our country and being proud its culture and traditions. I suppose this is not limited to any one country nowadays, and many societies, including those in the west, are facing this challenge.

Zierler:

Varghese, education in India follows the British model largely where when you enter undergraduate, you already know what you were going to study. Is that correct?‎‎ ‎‎

Mathai:

Yes, that's pretty correct. When you enter undergraduate, you do not have a lot of choice on what courses you do. If I remember correctly, in undergraduate you are required to do 64 courses in four years, and out of the 64, possibly 7 or 8 were electives. Apart from that, you were basically required to do the remaining courses, and it's heavily focused on the theoretical side and giving exams. And in general, we're very good at taking exams, including myself. I think the education approach is probably something that should change. Things might have changed already now; it's been over 10 years since I graduated from undergraduate degree.‎‎ ‎

Firstly, there should be more collaborative learning, and we must recognize the importance of instilling this in the minds of young people. For example, I hadn't heard the word “synergy” until I moved abroad, and I think it's important that this aspect is stressed in the education system. Like I said, things might have already improved a lot by now. I do see many indicators that it has changed.‎‎

Zierler:

The relationship between engineering and physics is really dependent upon the institution. In other words, some places have an engineering physics program where the students get as much physics as the physics students themselves. In other places, engineering is much more relegated to Applied Physics or Electrical Engineering or things like that. How much physics did you have as an undergraduate and a master's student in India?‎‎ ‎‎

Mathai:

Right. So, this is, again, subject to what you call engineering and physics. So, in undergraduate, there's not a lot of physics that you do in India, especially if you are in a Mechanical Engineering program. But at a Master's, you do get to do physics courses, and I studied at Indian Institute of Science which is primarily a research university with a lot of stress on science education. So, we did have the freedom to do a variety of courses.‎ My general impression is that the quality of education at some of these top institutes in India are comparable, if not better than top universities of the world, particularly in terms of the training in the fundamentals of a subject.

Zierler:

What laboratory work did you do in India that was particularly formative to your interests in experimental physics and fluid dynamics?‎‎ ‎‎

Mathai:

Right. So, I did a master's program. In this, you are expected to do a‎‎ master’s thesis or a master report, and this is spread over a period of 9 months. And during the first 3 months of 9, you're supposed to formulate the problem. And in the last 6 months, you're expected to perform this research. So, I worked on a research topic about the “Impact of an Object into a Pool of Water”. So, you might have seen this popular image of when a drop falls on a pool of liquid, you have a crown-shaped splash. So, I worked on a project like this, and it involved performing experiments which yields visually appealing photographs.

Your funding situation is not bad, but it would be great to invest more in research. In my particular case, I was doing the project at a time when my advisor had ordered a high-speed camera. The camera was essential to visualize the events occurring upon water impact and it has still not arrived yet. ‎‎And so, my advisor, Prof. Govardhan was kind enough to talk to the folks at Photron and they lent us a camera for my use. And I got the camera for two weeks, and I worked on this research, completing most of the experiments. In those two weeks, I had to do productive experiments. That was an experience that I still remember, and I enjoy having done this, and this. Also, for the impact experiment, since we did not have the time or resources to build a high-speed launcher device, we decided to climb up on top of a building and drop the projectile, using gravity to achieve the impact speeds that you need. So, this project involved a lot of climbing up and dropping objects into a tank of water.

So, I always felt I learnt a lot being in the labs in India. There were enough resources to do the experiment, but probably not the level you receive at some European or US universities. But this limitation with resources meant that you always think a bit out-of-the-box. And that did have an impact in how I viewed research. And I'm always trying to use opportunities for frugal science without compromising on the quality.

Zierler:

Did you want to take a break from your studies before pursuing the Ph.D. after your master's program?‎‎‎‎

Mathai:

I was unsure what I needed to do after a Masters. I am generally not convinced unless I get a feel of it myself. So, after my master's, I decided to see what industry was like, and I started a job in General Electric, the US company, their Aircraft Engines Division.

Zierler:

Where was this? Where was the division? In India? ‎‎

Mathai:

In India, in Bangalore. My Master's education was from the Indian Institute of Science, Bangalore, and GE was also based in Bangalore. This is one of the Global Research Centers that are based in Bangalore. I think it's one of the larger research centers of GE. This was pretty much a research and development wing of GE except that was mostly focused on computational fluid dynamics to provide insights about aircraft engine combustor development. During this time, I had a lot of opportunities to interact with colleagues in the US. We used to have, if I remember correctly, weekly meetings with folks in the US who did experiments and rig tests.‎‎

That was a point when I realized that field test experiments and computer simulations go hand in hand, and both of these are important to get to a final product or to make technological innovations. I spent a little over a year working there. I did enjoy my job very much, but I felt that I would not enjoy it after maybe 10 years there. So, I made a decision that rather than leave the job at a point where I do not enjoy it, I might as well leave at an earlier stage. I imagined that doctoral research in fluid dynamics can give me a different outlook.‎‎ ‎

Zierler:

Varghese, what advice might you have gotten to pursue a graduate degree outside of India? Was this an opportunity for you to see more of the world? Were you specifically directed toward a particular program? What were your considerations and decisions?‎‎ ‎‎

Mathai:

Right. So, I was open to doing a Ph.D. abroad which could be the US or Europe, and also in India. In India, naturally, the place that I would think of at that point was the Indian Institute of Science in the same department where I did my masters. I was also considering to apply to India. But by then I had already applied to the US, to Europe. I received an offer from, if I remember, University of California, San Diego, and also one an offer from the Netherlands from the University of Twente. This was early in January before other decisions from the US were not out.

And for the application to the Netherlands, this was again initiated by one of my advisors at the Indian Institute of Science who suggested to me there's a professor in the Netherlands, Detlef Lohse, who's very active in fluid dynamics and very well established in the field. You might consider writing to this person. I wrote to Detlef, had a Skype interview which went very well. There were not any technical questions asked in my Skype interview. And after the Skype interview, I received a message from my Ph.D. advisor that they would like me to visit, see the place, give a scientific talk, and then they can tell me if I would be offered or not. ‎‎At that point, I wasn’t sure whether I would have to pay for my flight to the Netherlands, as they had not made the decision yet. Luckily the next day, I received a message that all my travel and accommodation expenses would be taken care of. So, I gladly took the flight to the Netherlands. It was my first flight abroad, I believe, and I had an interview at the University with five professors from the department, my prospective Ph.D. advisors Professor Detlef Lohse and Professor Chao Sun, and Professor Andrea Prosperetti, who was at that time a professor at Johns Hopkins University, and Professor Roberto Verzicco from University of Rome. The interview went very well, I had the chance to see the labs, the research environment there, and I was pretty convinced that this was the place to go.

Zierler:

Was there an expectation that you would need to pick up Dutch or the language was English in the academic environment?‎‎ ‎‎

Mathai:

People in the Netherlands are bilingual. So, I'm a little ashamed to admit that my vocabulary is probably not more than 30 or 40 words of Dutch. [laugh] It's not the country if you want to learn Dutch, because the people there are very open to switching to English the moment they see that someone in the group is not from the Netherlands. So, in the Netherlands if you're doing a master's or a Ph.D., you practically can go around four years without learning any Dutch. I'm not capable of saying a long sentence in Dutch [laugh].‎‎ ‎‎

Zierler:

What were some of the cultural adjustments coming to the Netherlands from India for you?‎‎ ‎‎

Mathai:

I think one of the main difficulties I faced was with how people in the Netherlands worked from 8:00 AM until 4:30 PM and by 5:00 PM, usually all the shopping centers are closed. Even some restaurants close at 8:30 or 9:00 PM. So, it was very different from Indian cities, where 24/7 was the norm.

Another thing I had to get used to was that the Dutch required appointments for almost everything, and this was something I had to get used to. So, in India, you generally don't need appointments. Also, the food was quite different. But I soon realized that I was pretty adaptable with food, although the shift can be a little bit of a challenge for many foreigners. The way things are there, I think it is a great place to have a good work-life balance. In short, I thought I had the most wonderful experiences during my Ph.D.‎‎

Zierler:

In terms of the curriculum, how much coursework did you have to take coming in with a master's? And to what extent were you able to jump right into the dissertation research from the beginning?‎‎ ‎‎

Mathai:

So, my case was a little different that I had done 14 courses during my master's, and many of these were exactly the ones that are required. There's a graduate school, which has a coursework requirement, just like in the US. In addition to that, there were several of courses which are organized by the Dutch Fluid Dynamics Institute named after the Dutch physicist Jan Burgers, and they organized several courses. And I also attended several of these courses.

We had lecturers from the US at many of these courses. I remember professors from University of Maryland, Johns Hopkins, and many universities in the US visit and give these lectures. ‎‎ I think, in the Netherlands you cannot enroll in a Ph.D. program without a master's, although there can be some exceptions.

Zierler:

What was the intellectual process leading ultimately to your thesis?‎‎‎‎

Mathai:

Right. So, the general topic of my Ph.D. research was defined pretty clearly. At the start of my Ph.D., it was about buoyant particles in turbulent flow. In the Applied Physics track, the focus was on the fundamental aspects of these flows. And the first project I was assigned to was to look at how a buoyant sphere would rise in a turbulent liquid. Within 3 months into this research, I figured out that the research was possibly not defined in the best way. I did indicate this to my advisors that it needs a little bit of a re-defining. What I found very impressive was that my advisors were open to this – if you may say – criticism. They were open to discussion as long as the arguments I presented were scientifically justifiable. I felt that there was very little hierarchy in this aspect, which I found very encouraging from the start.

Since then, I found that they were very open to discussions and provided constructive feedback. And the process of learning to write, I had an initial flavor of it from my master's advisors and a lot during my Ph.D. I vividly remember, my advisor Detlef Lohse being critical of a research problem, saying “Varghese, you can pursue this problem, but think carefully whether there's enough mileage in this direction. We all have limited time. So, you can only look at one problem or another, and you have to make a decision whether there is enough mileage in it.” So, every time I was defining a research, or taking a slightly different direction, he made me think and be critical. During writing phase, he makes you realize that every paper should make a point rather than be a compilation of observations and results. He would also generously share his ideas about the different scientific journals and their different scope.

My advisor also shared with me stories about how physics research evolved. I'm not particularly sure if the name I'm quoting is right, but I do remember him telling me about how Heisenberg diverted his interests from quantum mechanics to fluid turbulence, for a brief while. And that also led to a result which we frequently use in our research on turbulent flows. Some of these inspiring and planted in me the idea that one need not be limited to the research area and always look out for good science. So, I do think that my Ph.D. mentors Detlef Lohse and Chao Sun were very role models almost every aspect – from conducting research to guiding students and enabling them to develop as independent scientists.‎‎‎‎

Zierler:

Varghese, to what extent were recent theoretical advances in Fluid Dynamics relevant for your research interests?‎‎‎‎

Mathai:

Right. In principle, this is a 100-year-old field of research.‎‎ ‎‎

Zierler:

Right.‎‎

Mathai:

So, the equations governing most of the phenomena are known for several hundreds of years. We have recently begun to look at the movement of fluids from a Lagrangian perspective. That means you follow the parcels of fluid. This has allowed to gain many new insights. The Navier Stokes Equations governing these flows are inherently nonlinear, and the solutions that they yield can be very different depending on the specific problem that you're trying to solve. Often, this can lead to emergent properties including self-organization and collective dynamics. So even though you could say that it's 100-year-old field, there's still new physics coming up every now and then. And it still continues to fascinate researchers and the general public alike. Now, that’s the story for single-phase flows. Specifically, when you look at multi-phase turbulent fluids, there's an even greater number of unanswered questions. When you look at a particle-laden fluid, many of the phenomena and properties are still not very well understood.‎‎‎‎‎‎‎ I don't know if I should go into the details of those or—?‎‎ ‎‎

Zierler:

Please, absolutely.‎‎

Mathai:

Yeah. So, for instance, you have the energy cascade of a turbulent flow. It is well known that this shows a minus five-thirds scaling in the inertial range of turbulent flow. And this is well known for single-phase turbulence, verified and seen in a number of experiments. This came from Andrey Kolmogorov, who was one of the pioneers in the field. It basically tells you that if you have a cloud of turbulent motion, where is the energy in the cloud of turbulent emotion contained? Is it contained at the largest scale or is it contained at the smallest scale, or what is the distribution of energy at different scales?

Now, what happens to the energy cascade when you have a dispersed phase – say, droplets or gas bubbles or rigid particles? That question is still unresolved, because the distribution changes significantly when you go from a single-phase turbulent flow to a multi-phase cloud, and this is something that we're trying to answer. And it's challenging to answer computationally because you have interfaces of several of these particles which need to be spatially and temporally resolved. So, a lot of precise and intensive computations, if you were to resolve them to the smallest scales of fluid motion.‎‎ Currently, the best methods looking at the most challenging situations are using experiments. And I do experiments on particle tracking, which tells you how these dispersed objects will move around in a cloud of turbulent liquid. The emergence of system properties from collective motion is another area of active research and exploration.

But the kind of questions we ask, have a large number of industrial applications as well, in addition to fundamental physics. Also, the physics is crucial in understanding atmospheric clouds: What triggers rain? And also in the oceans, we need to know more about the dynamics of air bubbles to understand the transport phenomena occurring in the upper ocean mixing layer. Another example, satellite images might show beautiful patterns of plankton blooming in the oceans. This again has links to the plankton responding to the fluid motion and elements of self-organization. Certain patterns emerge in plankton, which can again be understood by modeling the plankton as particles in a turbulent ocean flow. So many of these phenomenological observations, even looking at a swarm of insects or birds, and how their organize themselves, this is a field of active matter, which again is intricately liked to the filed fluid physics. Essentially here the particle, a bird in this case, is treated as an active element following certain physical principles with their own propulsion mechanism. So, all of these are situations where you get emergent properties for the system as a result of interaction between dispersed elements - particles, which can be either passive or active, and the carrier fluid around them. And so, if you ask me the question – are we in a position to predict and model the collective behavior of these systems, I’d say that we are some way from developing fundamental principles for such systems. So, there's a lot of scope for research in these areas‎.‎‎‎‎

Zierler:

Varghese, what did you see as the central contributions of your dissertation research?‎‎ ‎‎

Mathai:

My dissertation research was on passive, buoyant particles in turbulence and one of the contributions that we had was that even if these passive particles have a marginally different density from that of the carrier fluid, they modify the flow and particle dynamics significantly. We also studied how one can change the energy cascade of turbulence using these passive particles, even if they're marginally different in density. And this marginal difference in density is something which you cannot even avoid, practically speaking. The density contrast can also trigger cluster formations in passive particles. Essentially the particles move very differently from how the fluid itself moves, even though they do not have a propulsion mechanism of their own.‎‎

While buoyancy of the particles is the source of all these effects, it manifests in a variety of surprising ways for two-phase flows.‎‎

Zierler:

What opportunities were available to you after you defended the dissertation? Did you want to go back home to India? Did you want to come to the United States? What was most compelling to you?‎‎ ‎‎

Mathai:

I have kind of followed the same logic right from the stage when I was looking to do a Ph.D., I was particular that I worked in an interesting field of research, and with an interesting people. And from my point of view, the university where you do your research in an important factor, but secondary to the above two aspects. So, I was not particular that I wanted to pursue my Postdoc in Europe or in the US. I applied to several places. I did chat with several professors at different universities, and I figured out eventually that the offer at Brown University was a good fit for a Postdoc because I found that the topic of research that was proposed was very appealing to me.‎‎

I visited this time also the university, I planned the visit during one of my conference trips. And I saw the lab and I talked to the PI. I found that the research lab was excellent, and the topics that were on offer and the freedom for pursuing new directions seemed excellent. At that time, I had a postdoc offer from Harvard, from Princeton, and offer possible even at Stanford. I think I went against the advice of some mentors, I chose to go to Brown, primarily because the topic of research in the lab was very appealing.‎‎

Zierler:

And what were they working on at Brown that was so appealing?‎‎ ‎‎

Mathai:

They were working on soft materials and flows. So, the interaction between flows and soft materials, it has a number of bio-inspired applications. I was able to see a link to soft materials with my PhD research on bubbles in turbulent flows. Perhaps that’s not obvious to everyone. One aspect that I found very similar was that when I looked at an air bubble, the shape of a bubble, you could say, is governed by the Young-Laplace equation, which in the simplest terms is a balance between the pressure inside an air bubble and the surface tension force at the interface of the bubble. I saw immediately the soft membranes that were studied in this lab at Brown, were fundamentally similar. So, the only difference, from the viewpoint of the macroscopic physics was that the tension acting on the soft membranes is not a constant, and different from the surface tension of an air bubble. From this viewpoint, an air bubble and a soft deforming material are practically the same, except that you need to know the slightly modified governing equation. But here, you have a nonlinear tension relation. To understand this, we needed to look more closely into these soft materials. So, you have coupled nonlinear differential equations coming from the Navier-Stokes equations governing the fluid flow and the non-linear response of the soft deformable membranes.

Zierler:

What were the funding sources for the laboratory?‎‎ ‎‎

Mathai:

The funding sources, I believe, were from National Science Foundation, Army Research Office, Air Force Office of Scientific Research, and possibly the Office of Naval Research. ‎‎

Zierler:

What are some of the obvious military applications of this research that would make the Air Force and the Army want to support it?‎‎‎‎

Mathai:

Right. So, it's bio-inspired. The research is inspired from bats and soft-winged mammals, the way they fly. One of the interests for Army and Air Force is to look at micro-air vehicles and possibilities for improved maneuverability and stability in flight.

If you can look at the wing of an airplane, traditionally, it looks cambered wing, which leads to a pressure difference compared to the top and the bottom side of the wing. And this pressure difference gives you the lift, and that's what causes airplanes to fly in the simplest sense.‎‎ Now, if you were to replace this rigid wing with a soft wing, then you gain several advantages. One is that depending on the pressure that is experienced on the bottom of the wing, the material could deform or balloon. But when it deforms, you can get a higher lift force compared to a rigid wing. It would also be sensitive to the forces. So, if you get a turbulence in the air, which we know of during air travel as being repeated kicks exerted by the air movement over the wings, this turbulence can be damped out, or absorbed, by the deformation of the soft wings. So, the soft wind can act as a shock absorber. Another benefit is that they have a very high lift-coefficient, even though their drag is slightly higher. So, they can have a lot of applications in micro-air vehicles where the primary objective, as in drones and such, is to get enhanced lift and to be able to navigate air currents which can be turbulent, where gusts of air can perturb the flight path. So, there's a number of benefits to using soft wings instead of rigid wings in these micro-air vehicle applications. So that's one thing.‎‎‎‎

And one of the things that my postdoc research, again, something which I conceived, was to use these bio-inspired, bat flight-inspired wing in an underwater setting. This was again, a place where my training as a physicist came into play. I look at flows of air and water and other liquids in the same way. I had this thought, which I discussed with my Postdoc mentor Kenny Breuer that we can look at these bio-inspired wings, in an underwater setting for extracting more energy out of river flows. That was the motivation, but we essentially look at the fundamental fluid physics. This research, because it's in an underwater setting, could be of interest to the Office of Naval Research.

Zierler:

Another cultural question. Had you ever been to the United States before you got to Brown?‎‎ ‎‎

Mathai:

Oh, yes, I did travel to the United States several time, I believe, 4 times before I even moved here for a job at Brown. These were mostly for conference travel. We have the annual APS Division of Fluid Dynamics meetings. In my first year of graduate school (2014), I applied to American Physical Society DFD meeting. Then, I did not get a US visa on time. So, someone else, a coauthor, presented the work. By 2015, I knew that I should apply early enough to get my visa. So, I applied 4 months before the conference and I could get the visa on time. That was November of 2015. I visited for the DFD meeting in 2016, in 2017, and also in 2018.‎‎

Zierler:

Were there any cultural adjustments that you had to make here? Were you happy that perhaps the stores and restaurants were opened a little later than they were in the Netherlands?‎‎

Mathai:

Yeah, the United States had stores open longer than [laugh] in the Netherlands. That was a good change. Surprisingly, I felt a bigger cultural difference from the Netherlands to the United States, possibly even more than I felt from India to the Netherlands. This could have been because I was younger when I moved to the Netherlands, and it might have been easier to adapt, [laugh]. I do notice a big difference in the way graduate school students approach Graduate School in the United States. The outlook of academia in the US, that's slightly different from the Netherlands, there’s both good and bad. I mean, there's a lot of things I notice every day and still trying to figure out [laugh].‎‎ ‎‎

Zierler:

Varghese, who have been some of your most important collaborators since you arrived in the United States? Were they mostly within Brown, or did you find collaborators beyond Brown?‎‎ ‎‎

Mathai:

Right. I have collaborators all over the world. I do collaborate extensively with computational physicists and engineers. Besides the folks at UMass, I have collaborators at University of Houston and University of Miami. I have collaborations with folks at the Max Planck Institute in Göttingen, at the University of Lille in France, one in ENS Lyon in France. I collaborate with my co-advisor of my Ph.D., Professor Chao Sun who is now at Tsinghua University in China. I recently began interacting with a few researchers in India, and hoping it leads to long-term scientific collaborations. He was a Ph.D. student at UMass, and he moved to India about a year ago.

So, my network of collaborators is pretty spread out. I have collaborators who are in industry in the US and the Netherlands. These are collaborations which initiated very recently. One of them is from a motorsport foundation, and they have interests in the air flows inside the car.

Zierler:

When your postdoc was wrapping up, did you specifically want to stay in the United States? Were you looking for teaching opportunities in the United States?‎‎ ‎‎

Mathai:

I was open to moving to the United States or staying in Europe, both. I applied to several places in the United States and a few places in Europe as well.‎‎ ‎‎

Zierler:

How did the opportunity at UMass come available to you?‎‎‎‎

Mathai:

UMass-Amherst had an opening in Experimental Soft Matter Physics, and I read the advertisement and I knew a bit about the faculty in the department. I talked to my postdoc advisor who said it's a very good place to be at, in the flagship state university of the Massachusetts. I visited, gave an interview. I felt among the on-campus interviews that I gave, this was by far the most appealing one to me after having visited the department. So, it was easy decision for me to accept this position, once the hiring committee was convinced.‎‎ ‎‎

Zierler:

And this was an opportunity for you to set up your own lab?‎‎ ‎‎

Mathai:

Yes. My primary motivations are to set up my lab and to conduct independent and exciting research. And I would also hope to inspire young researchers in the process. I can also see that my department and my colleagues are open to a new faculty member exploring new directions of research, for instance, with COVID-19 airborne transmission research, that came out of the blue. Since the pandemic, I have been taking a slight diversion toward the topic of airborne and droplet transmission. As you can imagine, pandemic-related research was not at all a part of my application package to this faculty position. But my colleagues have been very supportive of these new research directions. I do notice that the importance here is on developing new areas of strength and doing good science with relevance and impact. I can see that this is important for the folks in the department. That is one aspect that I particularly enjoy.

UMass is also a school with a large undergraduate student population. And so far, as I have seen, the undergraduate students that approached me showing interest in laboratory research or computational research, have been very active, smart and motivated. I find that having a large undergraduate student population has helped me build my laboratory. Their contributions to research have also been valuable. I find that the setting at UMass also gives senior graduate students in the lab an opportunity for mentoring. In my view, this is an important part of graduate school, and it may not be possible at smaller-in-size universities.

Zierler:

Of course.‎‎ ‎‎

Mathai:

So, this is something I do feel is an asset.‎‎ ‎‎

Zierler:

And what had been some of the most significant funding sources as you've been building this lab?‎‎ ‎‎

Mathai:

So right now, I'm funded by my startup. I received some funding from the ‎‎Motorsport Foundation, I mentioned that. And I'm also talking to rideshares like Uber and Lyft, and Lyft in particular, I don't know if you need to include that in the write up. ‎‎I'm also submitting proposals to the National Science Foundation, related to airborne and droplet mode of transmission, specifically in certain settings.

Zierler:

We could leave it there.‎‎ ‎‎

Mathai:

Yeah.‎‎

Zierler:

Varghese, the opportunity to build your own lab really invites existential questions about what you want to research. So, with that in mind, to what extent is building this lab a continuation of what you were doing at Brown, and to what extent is it an opportunity to branch into new areas?‎‎ ‎‎

Mathai:

Right. So, as I have somewhat conveyed to you, I'm always open to diversifying and seeing some of the important problems that are around you. And I don't essentially see this as a diversification because the training on multi-phase fluids actually extends to a wide variety of areas. So, from that viewpoint, I do see all of these research directions that I'm taking, including the one about airborne transmission come under the umbrella of multi-phase fluids and turbulence, and some of the training that I received during Ph.D. and Postdoc help me in tackling these projects. But also, the research questions that I ask currently are different from what I did during Ph.D. and Postdoc. But not in the fundamentals required to study these new systems. That's how I would put it. Just as any physicist would try to understand the basic laws to explain the widest number of physical phenomena, I'm also here trying to do that in the area of fluids and soft matter.

Zierler:

Varghese, as you say it, the point is to find the most interesting problems and the most significant problems to work on. And so, on that basis, it makes a lot of sense, of course, why you would become involved in COVID research. My question there is to what extent did you recognize that there was a lack of understanding relating to COVID transmission within the scientific community itself, and to what extent was it a matter of public messaging and that the public really needed to understand these things better than what they were getting from the CDC, from the NIH? What were some of the immediate things that you became aware of as you decided to tackle this issue?‎‎‎‎

Mathai:

Right. So, I can be very honest about this. Sometime in March or April 2020, there was general guidelines laid out by the CDC that transmission occurs through touching surfaces and touching your face or mouth or nose, and that there transmission due to droplets which are released during of a sneeze or a cough. And these were listed as the primary modes by which the kind of transmission of SARS-CoV-2 occurs. There was also a statement that there is not yet enough evidence for airborne mode of transmission. Reading this, as a fluid dynamicist, I always had the feeling this absence of evidence, is not good enough reason to rule it out. We know many diseases which can be transmitted airborne mode.

Zierler:

Absence of evidence does not necessarily imply evidence of absence.‎‎‎‎

Mathai:

Yeah. So, I felt like this was definitely something which could have played a role. And the general guidelines on which the CDC’s 6-feet rule is based on is also something that we understand quite well. I believe that this originated from the research of William Wells in the 1930s and 1950s, which is based on the size of droplets that you sneeze or cough which can be classified into two classes of large droplets and small droplets, and the large droplets fall semi-ballistically, they travel a distance, and then fall, while the smaller droplets might stay in the atmosphere for longer.‎‎ ‎‎And this classification into large and small, we now know is not a good representation of a respiratory expulsion even. Fine sprays of droplets, be it the ones generated by people, or in the fuel nozzle of an engine combustor, almost never come in a clear dichotomy of sizes. As some people have called it recently, it's more like a continuum of droplet sizes in a sneeze or cough. I’m only quoting findings from other people’s research in this topic.

And like I said, a fluid mechanician will generally have a sense of how the airflow is different when you breathe in or when you breathe out, as you blow out a candle. A mask is something that covers your face. And it doesn't take a lot of research to understand that there are gaps for air and tiny droplets to seep through all around a mask, around your nose, or your cheekbone and such. And these are things which are pretty evident to any well-informed person. So, when the initial guidelines from the CDC were out, it did make me think that it was a matter of time before the guidelines would be modified. Recent guidelines from the CDC have included the possibility of airborne transmission for SARS-CoV-2.‎

Zierler:

Varghese, here's the big question though. The Coronavirus is novel. It's SARS-CoV-2, but the science behind respiratory airborne diseases, of course, goes way before 2020. So, the question is begged. What's the big mystery? What would explain this evidentiary gap in the transmission of a respiratory disease given the fact that we've always dealt with respiratory diseases? Why should the guidelines be imperfect just because we're in a pandemic situation? What's the difference between this and the flu or MRSA or SARS or any other?‎‎ ‎‎

Mathai:

Right. With regard to the question of what's the fluid dynamics of multi-phase clouds released during expulsion events, we do have a reasonably good understanding of that, partly, also, there's very recent research from the group of Lydia Bourouiba at MIT, Howard Stone at Princeton, and Deltef Lohse, Daniel Bonn from the Netherlands. I’ve definitely forgotten to mention many contributors, but the experiments with high-speed imagine and the computational fluid dynamics simulations in recent times have allowed us to appreciate the detailed physics of how a turbulent cloud is generated and where the particles end up. So, the physics of these flows is understood to a good degree I would think, but it has not gone across to the public health agencies as much as many of us would have hoped for.‎‎ ‎‎

Zierler:

Is that to suggest that it took a pandemic and everybody to be concerned and wondering what was going on for experts in fluid dynamics, to achieve a large enough platform to say, “Hey, everybody, we know about this stuff. We know how these things work. You should listen to us,” or alternatively, are you aware of Fluid Dynamicists who have studied this in prior generations?‎‎ ‎‎

Mathai:

Oh, yes, there are fluid dynamicists who have studied this in prior generations. Computationally studying this has been very challenging in prior generations. And only in recent years, there have been very good multi-phase simulations showing this cloud. Experimentally, it has been studied. The plumes that you generate around you, for instance, because you're warmer than your surroundings has been studied, and it's obviously a question of how these plumes get transported, and what are the implications of these for the transport of airborne particles and droplets to large distances?‎‎

From a particle-laden flow research point of view, these particles or droplets don't necessarily follow the flow. And from the viewpoint of a physicist, there is a dimensionless number which tells whether a droplet follows the flow or not. So, there's also a very good understanding of where a droplet would go. The general understanding is there among scientists, maybe not to the extent we need to make precise predictions, but definitely to the extent needed to make everyone aware that there are serious risks, and to suggest mitigation strategies.‎‎

For the communication, I believe, it took a pandemic. It took several months of a raging pandemic for the communication to come through and perhaps, even now, not as much as it should. I remember last week I had to take a taxi ride because my car was in auto repair, and I had to convince the taxi driver for about five minutes to lower the car windows. I was concerned for my health, so I had to be very assertive in explaining the risks. And I was surprised even more when the taxi driver mentioned to me that she has an autoimmune condition, but as long as you maintain 6-feet, things are perfectly safe inside the car. Unfortunately, the fact that all windows are closed and the cabin has low ventilation rates, was not coming across as a risk factor. ‎‎So, what's very concerning is that the message is taking a lot of time to get across.

Now, one of the reasons why it might not be getting across is that from a society level, is also the concern that you don't want to create panic. I can certainly understand this. And the other reason could be that if you look at different respiratory infections, the flu, the SARS-Cov-2, the SARS and MERS, the likelihood of getting an infection out of these airborne particles is different for each. And this is also not the realm that fluid dynamics can tackle. We still don't yet know what leads to an infection.‎‎

Zierler:

I mean, all of science doesn't know. This is an open question.‎‎

Mathai:

What finally leads to an infection? That’s an open question, and there are clues to this. Maybe somebody knows but is not willing communicate it. But this is not something that a researcher of fluid dynamics can answer. What we can say is that so there's a lot of biological variability which comes into play. Also, the viral load that's present in the droplets that are released, that depends on the anatomy of the person and a lot of other factors, behavioral and environmental play a role. What we can tell is if you have these violent expulsion events what could be the size distribution of the respiratory droplets? And if you were to say that the viral load is similar in all these droplets, which again we don't know for sure, what is the likelihood of those droplets to penetrate a certain distance?‎‎

And there has been research which shows that a person sneezing without a mask, the distance to which it can propagate can be up to 8 meters, and there's been high-speed photography images which show that this cloud can actually be expelled, and because it's warmer than the surroundings, the cloud has a buoyancy which can cause it to rise instead of settling on surfaces. And if you couple that with the atmospheric flow that's around you, you can have an example where these droplets can remain suspended in the air for much longer distances, farther distances than what the guidelines indicate. Now, it's a question whether you need this to be communicated to the public or not. I think it is important to communicate this. But that’s my personal opinion. I've done it at my level that I can.

Zierler:

Varghese, on that point, you must not have been surprised that this research would have garnered a tremendous amount of media attention. And so, on that question, how have you found the most effective way of communicating to journalists and reporters very complex scientific concepts where you might feel comfortable writing about them in highly specialized journals, but you want to communicate these things because they're not just matters of scientific inquiry, they're matters of quite important public health. So, what have been some of the most effective ways for you to convey this research so that people understand and act upon what you're finding?‎‎‎‎

Mathai:

Right. So, I mean, I do try to publish my research in journals which have a general outreach like the Physical Review Letters or family journals of Nature and Science.‎‎

Zierler:

But your taxi driver with the autoimmune disease is not reading even those journals, of course.‎‎

Mathai:

Yes, so beyond that, in my past, for every research, I do try to communicate it to the university, or the university press usually releases it. And I'm usually open to responding to most people who write to me by emails. I do admire people like Sean Carroll, who are able to get the ideas that they care about, across. We need similar ambassadors, in Fluid Dynamics, which is a highly relevant subdiscipline of physics. We are surrounded by fluids. There’re fluids inside us and around us. I do think it needs to receive as much attention as any other field of physics should. Right now, I'm writing a quick study for Physics Today, tailed for undergraduate level, which I hope will communicate the science to the public. And in the past, roughly four or five of my research works have appeared in general outreach avenues like Physics Today and Science Daily, and such.‎‎ ‎‎

Zierler:

Are you aware if people like Anthony Fauci or the CDC are in touch with Fluid Dynamicists? They're learning from what fluid dynamics has to teach? And that's actually part of the public health messaging for COVID mitigation?‎‎ ‎‎

Mathai:

I have a somewhat strong opinion about this. I feel that this is not necessarily in the realm of medical professionals to answer all of these questions. I think there needs to be steps taken by integrating fluid dynamicists and experts who know more about disease transmission and transport phenomena. It's a vast area of research. It is a 100-year-old field of research. I’ve noticed on TV, that sometimes even medical professionals do certain practices which suggest a lack of awareness. I wouldn't want to name anyone here, but need to make ourselves better aware of how masks/face coverings work and how to conduct ourselves in social settings. ‎‎For instance, it's important to know that when every person walks in a line, there's a trail of potentially contaminated particles behind them. So, if you're maintaining six feet in front of a person wearing a mask or maintaining six feet behind a person who has walked, it's a very different outcome from a fluid dynamics point of view.

At a community level, I don't know how much of this can be easily communicated, but we should make an effort. And I think because disease transmission is too closely linked to how this became a pandemic, that is what is driving it. Even vaccines, variants could emerge, and there is chance that a more transmissible variant becomes dominant. So, transmission is very crucial part of how the pandemic will evolve. People like Anthony Fauci are doing a great job at communicating the risks, and similarly, every expert who has access to the public needs to regularly communicate the risks.

Zierler:

So, let's take this back to January 2020 because it's so interesting to hear your perspective. When an epidemiologist or a virologist sees that there is an epidemic in Wuhan, and then there's some mode of travel to Italy, and then we saw what happened in Italy, right, an epidemiologist, a virologist is going to look at that and go, "We have a problem on our hands here, a significant problem." Would a Fluid Dynamicist come to that same conclusion without the background in biology? Is that something where if you can search back in your memory, you saw what was going on, and you recognize that this was a serious public health issue?‎‎‎‎

Mathai:

Right, so I had to take a flight to Singapore in January of 2020. I was extremely concerned for my health. It was a time when there were 5 or 10 cases.‎‎

Zierler:

And the US government was explicitly stating that this was not a concern.‎‎

Mathai:

Yes, I did wear a mask in the flight. Probably I was among the very few who did. I did take a flu shot before my flight, knowing as little as anybody about infections at that time. I was concerned knowing just about the fluid dynamics of disease transmission. So, you can tell that I was worried without even knowing much about the virus and its infectivity rate. I also considered canceling my trip. In the last moment I decided that I'd take the flight.

Now, there's another aspect of this, which is the ability of this particular virus to infect an individual, and that's not something a Fluid Dynamicist can answer. This can vary from disease to disease. For example, measles which has a very high infectivity rate compared to other. We did not know where the SARS-CoV-2 would fall in this spectrum. We also did not know whether the viral load is high or low in respiratory expulsions, whether the virus is able to latch on to your cells or not and produce an infection. These are things which are open, and I suppose this is the reason why it took a lot of time for everyone to recognize the seriousness. From a Fluid Mechanics point of view, it does not surprise me that when you're standing next to a person who's infected, who's wearing a mask that there is almost always some air leaking through the gaps around the mask, and that you're inhaling a few of percents of the airborne droplets exhaled by your neighbor.

Zierler:

Indoors, you mean? Indoors with poor air circulation.‎‎

Mathai:

Yes, indoors with poor air circulation, possibly even outdoors, but the number will obviously go a lot down. And we should also understand that just because you inhale and exhale air which has a few virions doesn't necessarily mean you get an infection. So that's also an important question. But what's clear is that if you are indoors, even wearing a mask, you certainly inhale a small fraction of virus-laden particles, and whether that can lead to an infection or not is not an easy question. And because there's so much variation in variability in biology that one virus is different from the other, the CDC and the WHO are faced with a difficult problem of having to make critical decisions of whether a certain pathogen is a serious threat or not. Clearly, in the case of COVID-19, the initial assessment could have been better.

Zierler:

So on that point, Varghese, so now let's go back to March, a year ago today, right, let's say, knowing what you know now and bringing all of your expertise in Fluid Dynamics to that meeting, let's say you were at a meeting with Anthony Fauci or the director of the CDC, what are the major points that you would want him to convey from the perspective of Fluid Dynamics that would be easily enough followed by the population so that we would not have had, again, assuming that everybody listens to public health guidance, all of those things, the question is, in a perfect scenario, right, what are the things that you would want Anthony Fauci or the CDC or whoever the authorities are in public health to say, "Everyone, if you do these three or four things, we'll be able to contain this, and it won't become a massive pandemic that will kill half a million people and counting," what would you say?‎‎

Mathai:

Yes, so I think because Fluid Dynamics, like I have—maybe I have convinced you that it's a very visually appealing field. So, there are experimental methods available which actually tell this plume that's around you, the droplets that are emitted every time you talk loudly. Every minute of your talking releases thousands of tiny droplets, especially if you're talking loudly. There are several ways to visualize these droplets and make it look very obvious to even a non-expert in the field. I would have encouraged them to show very simple videos, instead of showing the numbers every day during briefings. Possibly, investing time in showing simple, visualization videos for the general public, revealing to them how many aerosolized particles get transmitted even while standing six feet apart.‎‎ This can be a quick way of making people aware of the risks.

Whenever I have shown these visualizations in front of students or professors at my department or in the smaller avenues, because you're on Zoom, you can immediately see the shock in their faces. You do see raised eyebrows and disturbed faces even from people who are scientists. So, imagine if this were done at an important briefing event aired to the whole country. I would have done this possibly repeatedly once in a while. I think that communicates the message more strongly than a statement that wearing masks is important.‎‎ I can give an example from India, where, in every packet of cigarette, you see a warning which is a bit graphic and possibly disturbing to the viewer. So, I’d say that we really need to air the sneeze that travels up to 8 meters ahead of us, not 6 feet, and we need to show visualizations of the plumes of hot air that each person generates. We need to show laser visualizations of the sparkling droplets that you release every time you speak. Recently, a group of researchers at Princeton have shown that every time you say a P-sound, you're releasing more droplets than when you say, an L-sound. These things need to be communicated, and I think it needs to be done at the level of Anthony Fauci or the President Joe Biden, who are both doing their best. I don't have a good sense of whether showing these expulsions events on TV would create panic or not. I think the message can be presented in a balanced manner. I think being aware of the facts is better than being hidden from the facts. This is my view.‎‎

Zierler:

So, we get the video that shows how we can fill up a room with particles. And this is going to be a big surprise to so many people. But then, that begs the question, okay, now that we see this, what do we do about it? Is the answer simply, if everybody wears an N-95 mask, we don't have to worry about the dispersion of these particles?‎‎ ‎‎

Mathai:

Unfortunately, I think science doesn't work like that. You can say that your risks are reduced, but we should also stop viewing this from the perspective of there's a good or bad. There are no correct answers and the wrong answers here. You make efforts to move towards the optimal situation.

I also think instead of showing infections numbers as bar charts, there should be more communication from anecdotal experiences of infected people. A bar chat is simply a number, it's usually not making the same kind of an impression as you make when you talk to one of the people in emergency healthcare and a patient who survived a serious infection. Again, my personal opinion.

Zierler:

Now that we can talk a year later, here we are in March of 2021. Unfortunately, now the big questions are going to start to be what is the role of transmission in a highly vaccinated population? What public health messaging might fluid dynamicists play as vaccinations become more and more part of the equation?‎‎ ‎‎

Mathai:

Right. I think Anthony Fauci has already communicated clearly that when there's enough infections floating around in the society, you do have every possibility of mutants or variants emerging, and this is just plain evolutionary biology which we should expect. Now, the path of evolution of the pathogen is not easy to predict. All you can say is that variants will emerge, and one could see the possibility of a variant that is more transmissible through the airborne route. And if that were to happen, against out hope, it becomes absolutely imperative that we communicate more clearly the important of mask-wearing, social distancing, and the physics on fluid flows, which are extremely important to limit the spread of the virus.‎‎

So, in this sense, I think it's even more important that we look into the airborne mode which might not have received as much attention. It could very well be this route that leads to the next wave of the pandemic. Almost all of the fluids that we perceive around us, like air and water, are transparent. So, the air motion, the water motion, we general don't see that clearly, but it’s happing all around us. If you think about a person next to you smoking 10 feet away from you, you do smell the smoke, if it's a cigarette smoke. So, the same thing is essentially happening when the person breathes in and breathes out. So, if there are variants which are capable of transmitting an infection through the airborne more effectively than the current strains, I think fluid dynamics research would become even more important to mitigation efforts.

Zierler:

Varghese, now that we have brought the narrative right up to the present, I'd like to ask for my last question, a real theme of your research over your career is you just want to find the interesting stuff to work on. I'm curious if the biological component of fluid dynamics is something that is going to remain central to your research agenda, not just viral transmissions and things like that, but the overall utility of combining a fluid dynamical perspective in biology, do you see that as increasingly central to the research that you want to do in the future, or is it going to be one of many components because as you say, fluid dynamics is all around us, and it's a big world out there?‎‎ ‎‎

Mathai:

Yeah, so I'm very much keen on collaborating with biologists. This is probably something I did not explicitly mention. Growing up as a child, one thing that really interested me was animal behavior, biology, and evolution. Even though I didn't get a formal training in that, it's something that I watch just like I watch Sean Carroll's presentations. Biology is not something I feel I have the training to do research on, but I'm very keen on collaborating with biologists and learning from them and contributing to some of the relevant problems that they are trying to solve. I have researched in the past about the blood flows inside the aortic bifurcations, and there again, you have red blood cells which can behave like particles, and they can accumulate at regions and form clots. My contribution to this study was to help the medical professionals understand the fluid dynamics in the aortic bifurcation. This kind of research is definitely something which needs to be done through collaborations with biologists and medical professionals, if we are to push frontiers forward.‎‎ ‎‎

Zierler:

Well, there's going to be a next pandemic. So, let's hope that fluid dynamicists are part of the conversation from the very beginning.‎‎ ‎‎

Mathai:

Yeah, so that's something that you and I can be certain about! There is going to be a next pandemic, and I think many famous people have warned us about this. I recollect reading somewhere that humans have evolved in such a way that it is hard for us to plan for things that are longer timescale than a few decades. I certainly hope that’s not going to be the case and we are able to be prepared. ‎‎

Zierler:

Varghese, it's been great spending this time with you. Thank you so much for sharing your insights. I really appreciate it.‎‎ ‎‎

Mathai:

Thank you, David.‎‎‎ It has been a pleasure talking to you.

[End]