# Physical Analogies: Making the Inconceivable Conceivable

In which we explore some of the more unusual attempts to make huge numbers more understandable.

In the modern world, there’s always a problem when explaining the realm of the very large or the very small to a general audience. When you’re faced with the fact that the sun is 333,000 times more massive than the Earth, which itself is billions of times more massive than the largest of objects that a person would come across in a typical day, you need to find creative ways to bridge the cognitive gap.

Often, this ends up producing some silly results. I’ve been collecting examples for several months now, and now it’s time to share! I will go in order from least silly to most silly.

1. The Astronomical Unit. In Mark Anderson’s book, The Day The World Discovered The Sun, the author recounts an analogy used by John Lathrop in his 1814 work “Lectures on Natural Philosophy” to put the Earth-Sun distance into context. According to Lathrop, the distance from the Earth to the Sun is “…so prodigious that a cannon ball going at the rate of 8 miles in a minute would be more than 22 years in traveling from our globe to the central and solar luminary of its orbit.” This analogy seems mildly silly, but only because a cannon ball is an archaic reference to most modern readers.

2. Precision of Atomic Clocks. This one is a case where the very large is used to explain something very small. Back in January, NPR aired a story “Tickety-Tock! An Even More Accurate Atomic Clock.” The reporter, Nell Greenfieldboyce, described a new atomic clock “…that would neither gain nor lose a second in 5 billion years.” This is just a way of contextualizing the fact that the clock is accurate to 0.2 nanoseconds over the course of a year. However, the report ends by musing that, one day, atomic clocks could be so accurate that they’d lose only 1 second every 50 billion years—a time interval more than 3 times the age of the universe. A true analogy, yes, but a little silly, too.

3. Randall Munroe’s What If? Blog. Munroe has become his own cottage industry of quirky physics speculation, and there’s no better example that his blog, What If?, in which he answers physics questions from readers. In one post, to explain exactly how fast the International Space Station moves as it orbits the Earth, he determines that while listening to the Proclaimers’ song I’m Gonna Be (500 miles), you’d travel about 1000 miles. In another post, he describes the precise flight path of the Rosetta spacecraft as being “…like throwing an object from New York and having it hit a particular key on a keyboard in San Francisco.”

4. The BP Oil Spill. Of course, I’ve saved the best ones for last. If you’re familiar with The Bugle podcast, you might know what you’re in for. In episode 116, John Oliver quotes a news article as saying that the 19 million gallons of oil spilled in the first 5 weeks of the BP oil spill is enough fill a line of 1 gallon milk jugs stretching from New York to Chicago, and back. In episode 117, an adventurous listener wrote in with another analogy—undoubtedly the most silly of the bunch. Specifically: If all the oil spilled in one day were frozen and molded into cricket bats, then laid end to end, it would stretch from London to Paris and back. Also, if you took all the oil spilled by May 1, the cricket bats would stretch from Caracas to Pyongyang and back. Silliness, we have a winner!

At some point, though, all of these examples—whatever their intention—are wrestling with the fundamental fact that daily human life occurs on a very specific scale in time and space, while the universe as a whole covers a much wider range. On some level, this means every physical analogy will seem at least somewhat absurd. I don’t see the silliness ending any time soon! In fact, if you take all the words from all physical analogies published since 1800, represent each one with a pack of gum, and line them up end to end, … okay, you get the idea.