Determining the charge of an electron

 "Take the shortest route, the one that nature planned - to speak and act in the healthiest way.  Do that, and be free of pain and stress, free of all calculation and pretension." - Marcus Aurelius

Spoiler alert:  This isn't really a post about determining the electrical charge of an electron.  It's about something else that I'll get to later on.  But first, a little history about the science and technique involved in trying to determine the fundamental unit of charge - the charge carried by one electron.

In 1913, a physicist named Robert Millikan and his brilliant assistant, Harvey Fletcher, set up an experiment to determine the fundamental unit of electrical charge.  A diagram of their experimental apparatus is below:

A fine mist of oil was sprayed in at the top, and a few droplets would make it through a pin-hole.  X-rays would ionize the oil droplets, causing them to develop an electrical charge.

The droplets would tend to fall due to gravity (a known constant), and would reach terminal velocity due to air friction.  Next, a charge would be placed on the brass plates until the oil drop stopped falling due to the force of the applied electric field.  The amount of voltage required to stop the charged oil droplets from falling against the force of gravity was measured.  And so with a many measurements and a few calculations, it was possible to determine the charge of an individual electron.

With this measuring technique, it became clear that there were discrete values of charge, with no values in between - so it was clear that there were actual discrete units of charge, which was not something that was widely accepted at the time.  The value was determined to be 1.5924 x10^-19 Coulombs.  

That's the explanation of the experiment.  Now we have arrived to the spoiler alert that I mentioned.  

A lot of "science" is not trust-worthy.  Below is a discussion of something called "confirmation bias" regarding this famous oil-drop experiment - a tendency among human beings to interpret or find things that agree with previously held beliefs.  

Physicist Richard Feynman (RIP) points out how the original value was not quite right, and how repeated efforts to correct it gradually changed the value - all in the same direction, until we have the currently accepted value.  

"We have learned a lot from experience about how to handle some of the ways we fool ourselves. One example: Millikan measured the charge on an electron by an experiment with falling oil drops, and got an answer which we now know not to be quite right. It's a little bit off because he had the incorrect value for the viscosity of air. It's interesting to look at the history of measurements of the charge of an electron, after Millikan. If you plot them as a function of time, you find that one is a little bit bigger than Millikan's, and the next one's a little bit bigger than that, and the next one's a little bit bigger than that, until finally they settle down to a number which is higher."

"Why didn't they discover the new number was higher right away? It's a thing that scientists are ashamed of—this history—because it's apparent that people did things like this: When they got a number that was too high above Millikan's, they thought something must be wrong—and they would look for and find a reason why something might be wrong. When they got a number close to Millikan's value they didn't look so hard. And so they eliminated the numbers that were too far off, and did other things like that ..."

There is currently in the scientific community a "replication crisis", or "reproducibility crisis", where claims made in a scientific paper cannot be replicated by another team of scientists.  The replication crisis mostly affects the Social Sciences and Medicine, although all areas of scientific inquiry are suspect at this point.  

Because reproducing results is a fundamental part of the scientific method, this calls into question a great deal of scientific inquiry, particularly in the Social Sciences, but most importantly, in Medicine!!!!   I'll leave it at that for right now.  

There will be a follow-up post shortly, discussing a few more recent aspects of the current Covid-19 pandemic.  You can keep this post in mind while you mull that next one.