Tomorrow much will be written and said about the Apollo 11 mission, which brought humans to the surface of the Moon for the first time. On July 20, 1969, Neil Armstrong and Buzz Aldrin climbed down a short ladder and set foot on the dusty surface of our natural satellite - "one small step for a man, one giant leap for mankind," in Armstrong's famous words. For many, this feat showcased technological mastery and a rare sense of national purpose during a divisive era. For others, it was a bold stroke in the Cold War against communism.
I can't say I attributed any special meaning to the event at the time (I was only seven years old, after all!). But now, forty years later, I'm most struck by its implications for the unity of physical law. After all, getting humans to the lunar surface (and back!), alive and unharmed, required us to assume that physical processes - most of all gravity, but also the propagation of radiation, the flow of electric current, and much else besides - would operate under the same rules that they followed here on Earth.
Evidence for this already abounded in the mere fact that our solar system's other planets were (mostly) spherical; that the spectra of distant stars and galaxies showed the same chemical fingerprints that we see in gas-filled "neon bulbs"; that unmanned spacecraft already had successfully reached, probed, and photographed our Moon. But the tangible feat of sending Men to this airless, dusty worldlet and bringing them back, along with samples of its rocks and soil - this, in my view, made it all the more certain that nature's laws were indeed universal.
We now have solid evidence that the atoms in quasars billions of light-years away are constructed just like those in our own bodies - evidence that the laws of physics rule not only far from home, but back in the dawn of time. The evidence comes courtesy giant telescopes that gather the light of these blazing galaxy cores and devices that break that light apart into a rainbow of finely gradated colors. (Perhaps unknowingly, you've done something similar if you've put on a pair of "rainbow glasses" and stared at a fluorescent light bulb.) Alas, we won't be sending men (or women) to the quasars, nor back in time. But we may return one day to the Moon. And if we do, it will be in no small part because we have come to grips with the universal laws of physics.