Last week, in the context of a discussion about Physics Today's potential global reach, a question was posed: How many physicists are there on Earth?
One of the discussants had heard that the total number of researchers was 10 million. He hypothesized that of that total, 40% did research in biomedicine, 30% in chemistry, and 30% in physical sciences. The total number of physicists, he concluded, was at most 3 million.
My delayed reaction to the question was to wonder how one might estimate the global number of physicists. Not wanting to spend too much time on finding an answer, I sought a convenient and plausible method.
This photo of our planet was taken in April 1972 by an astronaut aboard Apollo 16 as the spacecraft cruised to the Moon. CREDIT: NASA
As a starting point, I looked at Wikipedia's list of countries and territories by population. The list contains 247 entries, but you can get 80% of the world's population by including just the 34 most populous countries (from China to Poland).
Deriving the number of physicists in a country based on its population depends on a number of assumptions, not least the definition of a physicist. Although there are several ways to define a physicist, the original question was about Physics Today's potential readership. Given that the magazine's print subscribers all belong to one or more of the 10 societies that make up the American Institute of Physics, I chose to define a physicist as someone who belongs to a national physics society.
Most countries have a national physics society, but not all of those websites have English-language versions and not all of them list the total number of members. Still, it was conceivable, I thought, that the proportion of physicists who belong to their national physics society would be more or less constant across countries with the same level of economic development.
What might those constants of proportionality be? The German Physical Society has about 60 000 members (0.07% of the population). The Physical Society of Japan has 18 000 members (0.01%). The Chinese Physical Society has 40 000 members (0.003%). The Ukranian Physical Society has 600 members (0.001%).
Because those proportions vary significantly among rich countries (Germany and Japan) and among poorer countries (China and Ukraine), I opted to calculate two estimates for the total number of global physicists, a high estimate (based on Germany and China) and a low estimate (based on Japan and Ukraine).
For the 34 countries that make up 80% of the world's population, I derived a high estimate of 772 000 and a low estimate of 297 000. Renormalizing for 100% of the population yields 964 000 and 372 000. The world might not have a million physicists, but that's the right order of magnitude.
In totting up the physicists country by country, my biggest realization was that the potential for growth in the number of physicists is huge. Of the 10 most populous countries, only two—Japan and the US—are rich, advanced democracies. The rest—China, India, Brazil, Pakistan, Nigeria, Bangladesh and Russia—have a combined population of 3.78 billion. If those countries became as rich as the Western democracies, the number of physicists would double.
What would result from a doubling of physicists? Journals would have to expand to accommodate the extra scholarly output. The March meeting of the American Physical Society would be even bigger. But the biggest impact might be at the frontiers of science. Giant leaps forward in physics are rare. The more physicists there are, the more likely such leaps are. The person who one day unifies the forces of nature could come from, say, Bangladesh.