Discussion

From the Editors “Hemingway in Love” underscored the great American novelist’s popularity, albeit this time online. A.E. Hotchner’s story was named a top five long read of the week by both Longreads and Esquire, and was shared by the L.A. Times and Longform. Numerous readers on Twitter announced they would be adding Hotchner’s new book, also called Hemingway in Love, to their “to-read” lists. Also on Twitter, at least one reader identified the mysterious library in the image accompanying Jerry Adler’s “Enough Said.” It’s a photograph of the Long Room in the Old Library at Trinity College in Dublin.

It’s Relative

In Brian Greene’s article “Gravity’s Muse,” we find the same time-tried explanation for the curvature of space due to gravity: A moving marble will follow a curved trajectory on a warped wooden floor just as light will do in the presence of a massive object, because of gravity. But the reason that the imaginary marble follows a curved trajectory toward the depression in the floor is that gravity pulls it down. So we explain one effect of gravity by showing another effect of gravity. This is a nicely disguised example of circular reasoning.

Erwin Wechsler, Glendale, California

If the Big Bang is based on Einstein’s theory of relativity, and his theory is based on the tenet that nothing can travel faster than the speed of light, and at the Big Bang all matter moved from a single point to enormous distances in the tiniest fraction of a second, does this not imply that the stars and galaxies moved faster than light, which is impossible according to the overall theory? How do physicists resolve this apparent paradox?

Mike Mellos, Rio Rancho, New Mexico

Brian Greene responds: As for the warped floor, in longer treatments of general relativity (such as my book The Elegant Universe) I myself am fond of emphasizing the limits of this comparison. Analogies in science writing simply provide mental imagery for complex topics, and on that score the warped floor example does a nice job. Most every analogy, if examined thoroughly, fails to fully align with the science, but if it brings the typical reader a step closer to an intuition regarding an otherwise opaque idea, then on balance this outweighs the inaccuracy. The question about the speed of light during the Big Bang is a great and subtle one. Here’s a rough way of thinking about it. In special relativity, Einstein established that no object can travel through space at greater than light speed. However, this does not constrain the speed at which space itself can stretch. Indeed, when we talk about the speed at which distant galaxies separate, we envision those galaxies moving apart because of the swelling of space itself—and there is no limit on that speed.

Learning Curve

I have visited the Gateway Arch in St. Louis (“Curve Ahead”) three times, and was awestruck each time. Suggesting that the construction of this visionary, towering human achievement is to blame for the decline of the city was simple-minded and fatuous. If you really want to explore what happened to the dreams that St. Louis had about becoming the “New York of the Midwest,” you need a much longer, serious investigation.

Brenda Petruzzella, Columbus, Ohio

Problematic Pyramid

On page 37 [“The Power and the Glory"], the photo caption states that the pyramid in the background belongs to Khafre. It actually belongs to Khafre’s son, Menkaure. Khafre’s pyramid is easily distinguished by the intact casing stones near the top.

Sean Berry, Portland, Oregon

Clarification

“Gravity’s Muse” mischaracterized GPS technology. In fact, the signals do not bounce between orbiting satellites and a device like the one in a smartphone; rather, the device determines its location solely from signals it receives from multiple satellites simultaneously.