Some say the world will end in fire,
Some say in ice.
From what I’ve tasted of desire
I hold with those who favor fire.
But if it had to perish twice,
I think I know enough of hate
To say that for destruction ice
Is also great
And would suffice.

Robert Frost’s 1920 poem “Fire and Ice” is one of his better-known works, and the only one of his poems I have memorized in full.[1] (OK, I don’t have many poems memorized in full that weren’t written by Shel Silverstein.) It’s the kind of poem scientists like to quote because it talks about the end of the world, in sufficiently vague terms that we can use it to illustrate the possible scenarios by which either Earth or the Universe will perish.

So, this recent piece by David Quigg grabbed my attention by connecting Robert Frost and his poem with a real prominent scientist. According to an account he gave many years later, astronomer Harlow Shapley met Frost at a party, where the poet asked him how the world would end. The result a few years later was “Fire and Ice”.

This story comes to us through several removes, both in recollection and years: Shapley told his story in 1960, based on an incident in (probably) 1918, and we receive it from Tom Hansen roughly 40 years after that.[2] In other words, the details aren’t clear, and with human memory being what it is, Shapley may have misremembered aspects of the encounter. Nevertheless, I love the story, all the more since the poem is not really concerned about the scientific end of Earth. Frost is using Earth’s demise as a metaphor, a reflection on human emotion and interaction. Yet, Shapley’s story shows that science was at least in the back of Frost’s mind on that occasion.

In 1918, astronomy was in the midst of a set of new discoveries. Thanks to the work of a number of astronomers, including the Harvard “computer” Henrietta Swan Leavitt, astronomers were learning to measure distances to far-away objects using variable stars. These stars are nearing the end of their lives, during which they swell to immense sizes and pulsate, with their surfaces moving in and out in a periodic fashion. That pulsation leads to a variation in the light output; using a formula, astronomers can use the regular fluctuations to obtain the intrinsic brightness of the star…which can then be used to determine its distance from Earth.

Shapley was one of the pioneers in this technique, using a type known as an RR Lyrae variable stars to measure the size of the Milky Way. That was a profound advance, since it helped determine where the Sun lies in the galaxy (though Shapley’s estimate was off by modern standards), and showed where the galactic center is. For those discoveries, Shapley was one of the most prominent astronomers of the early 20th century. (He was inevitably wrong about other things, most notably his assertion that the “spiral nebulae”, now known as spiral galaxies, were small objects located inside the Milky Way.)

Frost wasn’t asking about Shapley’s research; he was looking for appropriate poetic metaphors. We can think of that as an opportunity missed, but the fate of our planet wasn’t entirely clear back in 1918 or so. Today, we know that when the Sun runs out of hydrogen fuel in its core in about 5 billion years, it will expand into a red giant, likely cooking Earth’s atmosphere away. Fire wins over Earth, whether we associate it with desire or not. Nevertheless, the Universe is on a course to expand forever, emptying out as galaxies grow farther and farther apart. As stars die over trillions of years, they will leave the cosmos dark and cold. Ice, devoid of hate or any emotion, is the cosmic end. Frost recognized a good metaphor, and his own name seems apt in this case.

My favorite Frost poem, “Two Tramps in Mud Time”, also seems apt in this case. The closing stanza reads,

But yield who will to their separation,
My object in living is to unite
My avocation and my vocation

As my two eyes make one in sight. 

Only where love and need are one, 

And the work is play for mortal stakes,

Is the deed ever really done 

For Heaven and the future’s sakes.

Notes

1. If memory serves, Frost’s poems are still under copyright, but the Poetry Foundation lists no such information. I’ll claim fair use, since obviously I’m making no money from this and probably ain’t nobody gonna read this post nohow.
2. Search for Tom Hansen or scroll down on that page to see the full story of Shapley’s 1960 address, and how Hansen disagrees with the astronomer’s interpretation of the poem.