On Earth As in the Heavens

When it comes to physics, the law is the law.

Until Isaac Newton wrote down the universal law of gravitation, there was little reason to presume that the laws of physics on Earth were the same as elsewhere in the universe. Earth had earthly things going on, and the heavens had heavenly things going on. Indeed, according to many scholars of the day, the heavens were unknowable to our feeble mortal minds. When Newton breached this philosophical barrier by rendering motion comprehensible and predictable, some theologians criticized him for leaving nothing for the Creator to do. Newton had figured out that the force of gravity pulling ripe apples from branches also guides tossed objects along their curved trajectories and directs the Moon in its orbit around Earth.

The universality of physical laws drives scientific discovery like nothing else. Gravity was just the beginning. Imagine the excitement among nineteenth-century astronomers when laboratory prisms, which break light beams into the colors of the spectrum, were first turned to the Sun. Spectra are not only beautiful but contain oodles of information about the light-emitting object, including its temperature and composition. Chemical elements are revealed as unique patterns of light or dark bands that cut across the spectrum. To people's delight and amazement, the chemical signatures in the light emitted by the Sun were identical to those identified in the laboratory. No longer the exclusive tool of chemists, the prism showed that the Sun, as different as it is from Earth in size, mass, temperature, and appearance, contains the same stuff--hydrogen, carbon, oxygen, nitrogen, calcium, iron, and so forth. But more important than our laundry list of shared ingredients was the recognition that the laws of physics prescribing the formation of these spectral signatures on Earth are also operating on the Sun, 93 million miles away.

So fertile was this concept of universality that it was successfully applied in reverse. Further analysis of the Sun's spectrum revealed the signature of an element that had no known counterpart on Earth. The new substance was given a name derived from the Greek word for Sun (helios) and was only later observed in the lab. Thus helium became the first--and only--element in the chemist's periodic table to be discovered someplace other than on Earth.

OK, the laws of physics work in our solar system, but do they work across the galaxy? Across the universe? Across time itself? Step by step, the laws were tested. As with geologists reading Earth's history in stratified sediments, the farther away we look in space, the farther back we see in time. Spectra from the universe's most distant objects, whose light has been travelling for billions of years, show the same chemical signatures we see everywhere else. Indeed, a mathematical quantity known as the fine-structure constant, which controls the basic fingerprinting for every element, must have remained unchanged for billions of years.

Of course, not all objects and phenomena in the cosmos have versions of themselves on Earth. You've probably never walked through a cloud of glowing million-degree plasma, and you've probably never greeted a black hole on the street. What matters is the universality of the laws of physics that describe these phenomena. When spectral analyses were first applied to the light emitted by interstellar nebulae, a signature was discovered that had no counterpart on Earth. At that time, the periodic table of elements had few empty boxes (when helium was discovered, there were two dozen). Astrophysicists invented the name nebulium to serve as a placeholder until they could figure out exactly what was going on. It turned out that in space, gaseous nebulae are so rarefied that atoms go long stretches without colliding with one another. Under these conditions, electrons within atoms behaved in ways that had never before been seen in labs on Earth. The hypothetical nebulium was simply the signature of ordinary oxygen doing extraordinary things.

The universality of physical laws tells us that if we land on another planet with a thriving alien civilization, it will be running on the same laws that we have discovered and tested here on Earth--even if the aliens harbor different social and political beliefs. Furthermore, if you want to talk to the aliens, you can bet they won't speak English or French or even Mandarin. Nor will you know whether shaking their hands--if indeed they have hands to shake--would be considered an act of war or of peace. Your best hope will be to find a way to communicate in the language of science.

Such an attempt was made with the Pioneer 10 and 11 and Voyager 1 and 2 spacecraft, the only ones with enough speed to escape the solar system's gravitational pull. All four spacecraft bore a golden plaque etched with scientific pictograms showing, among other things, the Sun's location in the Milky Way galaxy and the structure of the hydrogen atom. Voyager also carried recorded sounds from Mother Earth, including the sound of a human heartbeat, whale songs, and selections of music ranging from Beethoven to Chuck Berry. While these offerings humanized the message, it's not clear whether they would mean a thing to alien ears--assuming aliens have ears in the first place. My favorite parody of this gesture was a Saturday Night Live skit that appeared shortly after the Voyager launch. The aliens who recovered the spacecraft had only one reply for Earthlings: "Send more Chuck Berry."