Luke Groskin: Begins with the dusting of pollen or perhaps a pinch of pepper. For some, a simple glance at the Sun can trigger a desperate dash for a tissue. This is, of course, a sneeze - an act that was once believed to be the explosive release of our very soul. And when viewed in the right light, a sneeze can take on a whole new dimension.
Dr. Lydia Bourouiba: And if you forget the fact that it is a sneeze, it's actually pretty beautiful process. I think that they all are quite beautiful actually.
Luke Groskin: Dr. Lydia Bourouiba is an Assistant Professor at MIT and researcher of Applied Mathematics.
Dr. Lydia Bourouiba: And actually, it's really the new frontier to try to use more physics and mathematics to try and understand biological problems.
Luke Groskin: Problems such as, "How diseases spread?"
Dr. Lydia Bourouiba: We have a lot of work that is done at the cellular level. So, interactions between cells, viruses, and tissues and then a lot of work that is done at the population level looking at average behaviors or using large statistical model.
Luke Groskin: To predict rates of infection or mortality, but it turns out there is actually very little research into modeling that moment when my germs become your germs.
Dr. Lydia Bourouiba: As there is no history of physical studies that really examined these problems of what is really contact and transmission, and get the physical picture right to describe what's happening when you are actually sneezing. And so thinking about all these things, that's when I realized that actually fluid mechanics could help because when you think about it, a sneeze or a cough is obviously a fluid.
Luke Groskin: With the help of an MIT colleague, Dr. John Bush, Dr. Bourouiba set about quantifying the physics of sneezes and coughs.
Dr. John Bush: If you saw someone sneeze within the naked eye, you'd see drops flying out and they go at whatever their initial speed is and that determines their range. So, [inaudible] that large drops go further than small drops. Basically, there is no consideration whatsoever of the gas phase.
Luke Groskin: They call this the multi-phased cloud.
Dr. Lydia Bourouiba: It is really to try to highlight the fact that it's not just droplets being emitted, but they are really this background, turbulent, hot, and moist air that is swirling around [inaudible] these droplets further away.
Luke Groskin: To define that how important this cloud is to the spread of diseases, Dr. Bourouiba needed to visualize sneezes and coughs in their finest detail.
Dr. Lydia Bourouiba: You need to basically have a camera that is not as light-sensitive, so basically black-and-white camera. And then, we illuminated the droplets so that the scattered light from the droplets would be projected to the camera. So, you have an individual standing there and sneezing, and then you laugh a lot.
Luke Groskin: Sneeze after sneeze, Dr. Bourouiba collected data which she could then use to model the act.
Dr. Lydia Bourouiba: So, the [analysis is realized] on image processing techniques and algorithms that are have to be developed to [inaudible] the cloud and the droplet trajectories.
Luke Groskin: Turns out we grossly underestimated the effect of the multi-phased cloud.
Dr. John Bush: And you think of the cloud as being turbulent because it's a very disordered, vigorous motion. If characteristic speed in that cloud is larger than its settling speed, then it will be dominated more by that internal cloud motion than by its settling speed.
Luke Groskin: Translation?
Dr. John Bush: The smaller drops go much further than the large drops.
Luke Groskin: Because the cloud keeps them afloat.
Dr. Lydia Bourouiba: And right now, the finding shows that these clouds, particularly under usual conditions of temperature and buoyancy, has a tendency to go higher in the room and get sucked into the ventilation system. That could be in [this end] of the building and somebody could be in contact with my pathogens through infiltration in the ventilation system without me actually meeting that person.
Luke Groskin: It's a little disturbing, no?
Dr. Lydia Bourouiba: I'm definitely more aware of sneezers and coughers all around.
Dr. John Bush: But it does definitely impact the sort of design of places where pathogen transport is critical, particularly in hospitals, classrooms, and airplanes.
Luke Groskin: And like all good research should do, a stream of questions flows from this new model of sneezing.
Dr. Lydia Bourouiba: If, for example, we were to change the ambient conditions indoor - temperature and moisture - by how much would we extend the horizontal versus vertical range of the cloud? Once you have an individual that is sick, what happens and how is that different? And then, by adding obstacles-
Luke Groskin: Such as an elbow or a tissue-
Dr. Lydia Bourouiba: Now, we can also assess their effect.
Luke Groskin: However, Dr. Bourouiba and Dr. Bush have proven once and for all that math doesn't need to be a dry subject.
Dr. John Bush: And then, people aren't really aware of what the applications are, but if you actually use it for describing physical systems, you realize what a powerful tool it is.
Luke Groskin: For "Science Friday," I'm Luke Groskin.
There may be small errors in this transcript.