Measuring really really small stuff
I'm working w/ the volunteers getting the web page set up with a list of speakers and talks for DataBS Conf. We should probably be ready this week, maybe. But until then here's the registration form again!
A short while ago, someone on our discord shared this with me about how scientists used extremely clever methods to come up with measurements of the weight of a single yeast cell in the 1950s. I promise that it's a good and short read.
Niko McCarty
The gist of the method is that Stokes' Law allows for the calculation of the drag force on a spherical object moving within a dense liquid and the fact that an object falling through a fluid like water is being pulled down by gravity as well as pushed up by buoyancy. Buoyancy is related to the difference in densities between the sphere and the fluid with the greater the difference the greater the force. The trick is that when the sphere hits terminal velocity falling through the liquid, the drag force is exactly equal to the downward force (which is dictated by gravity minus buoyancy). If you set those forces equal to each other, do some formula rearrangement, and have the density of the fluid known, you can solve for the density of the sphere. From the sphere's density, if you visually measure the size of the cell under a microscope, you can figure out its mass. *Phew
All the above math only works out if the cell being measured approximates a sphere. The example cited happened to be measuring yeast cells which are apparently pretty darned spherical. So the scientists involved could put yeast cells on a microscope slide and record video of them falling steadily against a calibrated scale to measure the size and falling rate of the cells. The resulting calculations are supposed to be quite close to modern day measurements using more sophisticated equipment.
Once the critical assumption of spherical shape breaks down, like with a lot of other cells, you can't use Stokes' Law any more and have to find another method. While I'm far from a practitioner in this space, it seems the current hot stuff for doing super micro weight measurements involve tiny devices called microcantilevers (I can't even find a Wikipedia page for these things). They're extremely tiny little devices that are often made using the same photolithography and etching technology used to make microprocessors. Like their name, these microcantilevers are essentially a bar of material attached on one end and hanging out in free space on the other. They can be designed in all sorts of ways to suit the task at hand – for instance layering a material on a surface that has affinity for a molecule being studied. Measurements are (somehow) made using either light-based sensors, or electrically using components (like piezoelectric devices) built into the microcantilever themselves. One day I'll dive more into how these things work, but there's a whole giant field involved that I can't shove into my brain today.
Most of us data folks have it easy
I typically look at the highly specialized measurement methods used in the physical sciences with a bit of awe. First, I wasn't aware that there existed a method to measure the weight of individual living cells, let alone there existing multiple different techniques to choose from. But besides biology, physicists have to come up with measurement methods to detect all sorts of particles, and astronomers have to come up with increasingly clever methods to extract information out of light that has travelled for billions of years to reach us.
Meanwhile, my biggest measurement headache involves whether users are satisfied after using a product feature, or whether users find a form so confusing they gif up. While there's some interesting questions about perception and psychometrics on occasion, we're not exactly pushing the boundaries because the questions we have to answer rarely requires us to.
But I think this is a nice reminder to us that just because there are well-known, convenient methods for doing things doesn't mean there couldn't be the possibility of something different. We should at the least raise our heads up from the daily grind and pause for a moment to consider whether a new technology or question enables a new variation on an existing method. It might not be new to the world (let's face it, very little of what we do will ever be unprecedented), but it might be an evolution that's new to your organization.
Think about your tech stack, think about your questions and the theories/hypotheses behind them. There might be a way to squeeze more information out of the world than you're on the lookout for the opportunity. And sometimes, the idea is compelling enough to try.
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I’m Randy Au, Quantitative UX researcher, former data analyst, and general-purpose data and tech nerd. Counting Stuff is a weekly newsletter about the less-than-sexy aspects of data science, UX research and tech. With some excursions into other fun topics.
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