Up until Oct. 7, 2013, my modest blog averaged about 18 hits per day. Then this happened:

A post of mine, the 9 kinds of physics seminar, had gone viral. I was shocked, to the say the least.

I spent some time investigating what happened. The original post went out on a Thursday, Oct. 3. Nothing much happened, other than a few likes from the usual suspects (thank you, John Zande!) I did share the post with Facebook friends, which include not a few physicists. (Note: I don’t normally share my blog posts to Facebook.) Then on Monday, Oct. 7, the roof caved in.

It started in India. Monday morning, I had over 800 hits from India. My initial thought was that I was bugged somehow. But soon, hits started pouring in from around the world, especially the USA.

And then it kept going.

On Tuesday, Oct. 8, the Physics Today Facebook page shared the post, where (as of today) 451 more people have shared it, and 188,000 people have **liked** it. (Interesting question: my blog has only had 130,000 views. Are there really **that** many people who **like** Facebook posts without even clicking on the link?)

The viral spike peaked on Wed., Oct. 9. I had discovered by then that my post had been re-blogged and re-tweeted numerous times, by other physicists around the world. If you Google “The 9 kinds of physics seminar” you can see some of the tweets for yourself.

Why did the post go viral? Who knows. I’m not a sociologist. I think it was a good post, but that’s not the whole story. More importantly, the post was funny, and it resonated with a certain segment of the population. If I knew how to make **another** post go viral, I’d do so, and soon be a millionaire.

What’s fascinating to me, though, as a math nerd, is to examine how the virality played out mathematically. Here’s how it looked for October:

I don’t know anything, really, about viral cyberspace, but this graph totally matches my intuition. Note that for the last few days, the hits have been around 400/day, still **much** greater than the pre-viral era.

After the spike, is the decay exponential? I’m not a statistician (maybe Nate Silver could help me out?) but I do know how to use Excel. Hence:

The decay constant is 0.495, corresponding to a half-life of 1.4 days. So **after the peak, the number of hits/day was reduced by 1/2 every 1.4 days**.

This trend didn’t continue, however. Let’s extend the graph to include most of October:

Over this longer time span, the decay constant of 0.281 corresponds to a half-life of 2.5 days. **The half-life is increasing with time**. You can see this by noticing that **the first week’s data points fall below the exponential fit line**. It’s as if you have a radioactive material with a half-life that increases; the radioactive decay rate goes down with time, but the **rate** at which the number of decays **decreases** is slowing down. (Calculus teachers: cue discussion about first vs. second derivatives.)

Maybe this graph will help:

The long-term decay rate seems to be 0.1937, corresponding to a half-life of 3.6 days. At this rate, you would expect the blog hits to approach pre-viral levels by mid-November. I doubt that will happen, since the whole experience generated quite a few new blog followers; but in any case, the graph should level off quite soon. What the new plateau level will be, I don’t know.

Where’s Nate Silver when you need him?

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If you enjoyed this post, you may also enjoy my book *Why Is There Anything?* which is available for the Kindle on Amazon.com.

I am also currently collaborating on a multi-volume novel of speculative hard science fiction and futuristic deep-space horror called **Sargasso Nova**. Publication of the first installment will be January 2015; further details will be released on Facebook, Twitter, or via email: SargassoNova (at) gmail.com.