World War II is having a moment, at least in the minds of people doing Google searches. Google Trends, a tool that measures the popularity of search terms over time, shows that there have been dramatic spikes in searches for topics related to the war, including: Reichstag fire, Pearl Harbor, fascism, Kristallnacht, and Nazi Germany.

Searches for “Reichstag fire,” the event that precipitated Adolf Hitler’s declaration of martial law in 1933, peaked worldwide the month after the Brexit vote in Britain and again in October 2016 before the US election. Those searches eventually reached an exceptional five-year high in the first week of February 2017. In the United States, searches related to the event when Dutch communist Marinus van der Lubbe lit the German parliament building on fire were most popular in Arizona and New Hampshire.







As Berkeley statistician Hyunyoung Choi and Google researcher Hal Varian explain in a paper about Google Trends, there is not much of a secret sauce in computing what’s trending:

The query index is based on query share: the total query volume for the search term in question within a particular geographic region divided by the total number of queries in that region during the time period being examined. The maximum query share in the time period specified is normalized to be 100 and the query share at the initial date being examined is normalized to be zero. The queries are “broad matched” in the sense that queries such as [used automobiles] are counted in the calculation of the query index for [automobile].

Worldwide searches on Kristallnacht saw a five-year high on November 9 and 10, 2016, the anniversary of the night when tens of thousands of German Jews were deported to death camps. There is always a small upswell of interest in this term every year on the anniversary, but in 2016, searches of the term in the US jumped from the 25-30 range to 100. The annual spike of interest in Pearl Harbor was also dramatically higher than usual, jumping from a previous high of 70 to 100.

Searches on "Nazi Germany" jumped from typical levels of 25-50 to 100 in the first week of November, right before the US election. Worldwide searches for “fascism” also jumped from a baseline of 10 to 55 the week before the US election, but the authoritarian ideology saw an unprecedented spike in the first week of February, with searches for "fascism" jumping from 15-20 to 100 around the world.

These searches don't mean millions of people are suddenly abandoning their interest in the usual internet fare: post-Superbowl searches on "Lady Gaga" are far more popular than those on "Reichstag fire." Instead, what Trends reveals are peaks of interest that are far above the typical amount.

It may seem like these correlations between search terms and political events mean something, but it’s not always easy to show a direct connection between Google searches and real-world events. In 2008, researchers at Google published a paper in Science showing that Trends could predict flu season, with people’s searches for terms like “sniffles” and “cold remedy” always coming a few weeks before flu season hit. But then Google Flu Trends failed horribly a few years later, with its predictions off by 140 percent, showing that people don't always search for what ails them.

There are counter-examples, of course. In their article about Google Trends, Choi and Varian remark that it’s an excellent tool for “predicting the present,” noting that upticks on searches for a given country are correlated with jumps in tourism to that place. It can also be a good leading indicator for the financial industry, surfacing consumer trends that affect markets.

But can we track public mood or social changes through Google Trends? Data analyst Seth Stephens-Davidowitz thinks we can. In a now-famous study, he used Trends to predict how different counties would vote in the 2012 US election based on numbers of searches in those areas that contained racist words (the more racist searches, the fewer votes for Obama, even among people who typically voted for Democrats). Stephens-Davidowitz followed up with another study showing that areas with high numbers of racist word searches had higher-than-average rates of mortality among African-Americans. The upshot of this work, he argued, is that areas where people used racist words in searches were also areas where there were measurable signs of racism.

When it comes to the current search spike on World War II subjects, Stephens-Davidowitz admits he's uncertain. "I am not totally sure what to make of it," he told Ars via e-mail. "It may just be people interested in this topic, so they can prevent a future fascist takeover of the United States."

Interestingly, there have been no noticeable spikes in searches for other World War II topics, such as Adolf Hitler, the Holocaust, Weimar Germany, and the US bombing of Hiroshima and Nagasaki. It seems that people are focusing on popular ideologies during the war, as well as pivotal historical events. Perhaps they're turning to history to understand key events that are happening in our own time. Or maybe they're just hearing those terms a lot in the media and are trying to figure out what the heck pundits are talking about.