The Day We Found the Universe (27 page)

From there Curtis went on to focus on the spiral nebulae, the subject that Shapley conveniently avoided. Curtis showcased his best evidence, echoing many of the points he had made to the Washington Academy of Sciences just the year before: He stressed that the spiral nebulae displayed the spectra typical for collections
of stars
—not gas; that not one spiral had ever been found within the Milky Way itself; that the spirals are primarily seen away from the Milky Way, because obscuring matter blocks the view through the plane of our galaxy. He paid special attention to the many novae being sighted within some spirals. He showed that if the flare-ups in Andromeda were half a million lightyears distant, their luminosity would roughly match those seen in our own galaxy. Any closer and they would be far too bright. And then there was the movement of the spirals detected by Slipher; the spirals traveled speedily through space unlike any other celestial object in the Milky Way, which suggested that they had to be located outside our galaxy's borders.

All in all, the two men were simply talking at cross purposes. Shapley primarily defended his new vision of the Milky Way—its unexpected bigness—while Curtis hammered away on his contention that the spiral nebulae were far-off galaxies. In hindsight, each turned out to be partly right and partly wrong. Shapley argued for his larger Milky Way (true) but insisted that the spirals were local (wrong). Curtis still believed in a smaller home galaxy (wrong) but persevered in his belief that the spiral nebulae were situated far outside the Milky Way and rivaling it in size (true). At the end of the day, it was a wash.

Everyone in essence went home maintaining the beliefs they held at the start of the lecture. The data were so muddled that Curtis and Shapley could take the same facts and arrive at completely contradictory conclusions. At the time of the debate, there was no overwhelming evidence to settle the inconsistencies either way. Both men were traveling along a precarious road, each viewing his destination through an obscuring fog and interpreting the hazy view in different ways.

There was a winner, however, for best presentation. Curtis headed off that night feeling pretty good about his performance. He received assurances afterward that he “came out considerably in front.” Shapley, on the other hand, was judged more poorly. Russell wrote Hale afterward that his former student sorely needed to enhance the “gift of the gab.” Agassiz, the Harvard evaluator, was not impressed by Shapley's performance at all. “He has … a some what peculiar and nervous personality…lacks maturity and force, and does not give the impression of being a big enough personality for the position,” he reported back to Harvard's president two days after the event. More attractive to Agassiz was Russell, who spoke quite eloquently that night in support of Shapley's arguments during the audience response period. He said that Russell had “more balance more force and a broader mental range.”

The two opponents came to acknowledge what others sensed all along over the course of that April evening. “Yes, I guess mine was too technical,” admitted Curtis to Shapley a couple of months after the debate. “I thought yours would be along the same line, but you surprised me by making it far more general in character than I had expected.” As captivating scientific theater, the so-called Great Debate was ultimately a letdown.

A full year after the debate, however, the two astronomers battled it out once again within the
Bulletin of the National Research Council
. The original intent was to simply print the lectures they had given before the National Academy. But as the articles were being prepared, each man deepened and extended his arguments. It was not during that misty spring night in Washington that Shapley and Curtis had their great debate but rather within the pages of the
Bulletin
. It was the written version, vastly altered and amended, that ultimately established the legend handed down by succeeding generations of astronomers, many coming to believe it was the bona fide transcript of the April scrap.

At first Curtis wasn't keen on publishing his comments, but he indicated he would be willing if both he and Shapley delved more deeply on the technical issues. Shapley agreed. They were originally asked to keep to ten pages, which Curtis joked would force him to follow the laws of writing “generally observed in composing telegrams.” Perhaps, he wrote Shapley, they could “shoot our arrows into the air, to let them fall we know not where.” With his customary down-home wit, Shapley suggested that he would provide “ten pages of buncombe and flapdoodle,” while Curtis could supply “ten more pages of wisdom.”

Shapley also wondered if they should exchange their papers, providing the opportunity to rebut each other's arguments. “Should I go ahead, shoot my shot (or wad), then you use your shillelah (or hammer), then I sneak up behind you and apply my ole horn-handle.” Curtis was game, and over the ensuing months a lively train of drafts and comments went back and forth between them. In the process Curtis pushed Shapley to devote more space to the spiral nebulae, “at least a brief statement of how you explain them if not island universes.” Upon completion, their published remarks each expanded from ten pages to twenty-four, and though it wasn't mentioned until his penultimate paragraphs, Shapley's strongest and freshest ammunition against Curtis involved the spirals. It was there at the end that he played his definitive trump card: The spiral nebulae could not possibly be island universes, because the rotations measured by Adriaan van Maanen at Mount Wilson “appear fatal to such an interpretation.” Shapley now seemed more at ease in dismissing the spirals as simply minor objects. “I see no reason for thinking them stellar
or
universes,” he told Russell during the course of his writing the
Bulletin
article. “What monstrous assumptions that requires before you get done with it.” From that point on, Shapley's strongest weapon against supporters of distant galaxies was van Maanen's twirling spirals.

Although in his heart of hearts he never believed it would happen, even Curtis had to grudgingly concede in his published response that if van Maanen's findings held up “the island universe theory must be definitely abandoned.” Over the succeeding years, van Maanen and his observations stood like a giant wall before island-universe advocates. If the spiral nebulae were truly remote and massive galaxies, how could you possibly explain seeing them rotate over just a few years from so far away? The island-universe theory would not gain general acceptance until its supporters figured out how to breach this formidable rampart.

Van Maanen had begun his measurements of the spiral nebulae in 1915 and continued into the early 1920s. Astronomers took his results seriously because his reputation was exemplary. He was known to be a careful observer who followed intricate astronomical procedures to the letter. And it was easy to accept his conclusions, as they supported an idea of the universe that many readily believed at the time: The Milky Way defined the universe, and the spirals were mere appendages that from their swirling appearance had to be turning. Stars, planets, and moons rotated; planets revolved around the Sun; rotation was a natural feature of the universe. Given that, it was not surprising to hear that the spirals were rotating. In 1914 Slipher had already reported on a spiral rotation from his spectroscopic data, but simply viewing the curving lines of a spiral's misty arms, captured so vividly in photographs, made it impossible to think otherwise.

Adriaan van Maanen (left) with Bertil Lindblad
(Photograph by Dorothy
Davis Locanthi, courtesy of AIP Emilio Segrè Visual Archives)

Van Maanen was the descendant of an aristocratic family in the Netherlands, whose ancestors were ministers, teachers, and noted jurists. Those who knew him attested to his meticulous integrity and high sense of personal honor, instilled by his family's esteemed heritage. After earning his doctorate in 1911, van Maanen had traveled to the United States to work as a volunteer assistant at the Yerkes Observatory. But after his mentor, the noted Dutch astronomer Jacobus Kapteyn, brought him to the attention of Hale, he was soon offered a permanent position at Mount Wilson. The observatory wanted him for his superb and proven skills in gauging the motions and distances of stars. In 1917, in carrying out such observations, he discovered the second known white-dwarf star, a rare find at the time.

Van Maanen was drawn as a student toward this line of work, an endeavor that other astronomers tried to avoid because of the tedium and difficulty in discerning the change in a star's position over time. The procedure involved comparing, with intense concentration, photographic plates taken over intervals of months or years. But to van Maanen the routine was heaven; he even went back to the pursuit two years before his death. “One always returns to one's first love,” he scribbled on a copy of his 1944 paper on stellar parallaxes. To carry out the task, he superimposed the pictures of the stars taken at different times in his special stereocomparator (more often called the “Blink”). This machine allowed the viewer to quickly alternate between two photographic plates taken of the same field at different times. The blinking proceeded so rapidly that an object that had moved between pictures would immediately stand out, while those that remained fixed appeared still. Van Maanen could then slowly turn a micrometer screw to measure the star's exact advancement across the sky. The number of turns measured off the change in the star's position—the amount the star had moved over the years. It was his most cherished instrument at the observatory's Pasadena headquarters, and everyone knew it: The warning “Do not use this stereocomparator without consulting A. van Maanen” was blatantly posted on its front. The sign remained there for decades, long after he had left.

Sociable and well-liked, “Van,” as everyone called him, played a good game of tennis and made sure newcomers to the mountain felt right at home. He was a lively storyteller and also a bit of a playboy. Once Shapley arrived, he and van Maanen became fast friends, as they were nearly the same age. “He could go to a dinner and soon have the whole table laughing,” recalled Shapley. An accomplished chef, van Maanen relished throwing parties where he could put his culinary skills into practice and prepare fine dishes for his cohorts. Shapley and van Maanen further bonded when they discovered they were both disliked by Adams, who was suspicious of them for their liberal outlooks and ambivalence toward the ongoing war in Europe, as well as their ambitions. “Van Maanen and I are in ill-favor because we do or try to do too much,” confided Shapley to a friend.

One of van Maanen's first jobs at Mount Wilson was to measure photographs of spectra taken over the face of the Sun, an endeavor that helped Hale map the Sun's magnetic field. Early reports suggested that the strength of the magnetic field varied with solar latitude, and van Maanen always seemed to see this effect, even though it was later found to be a mistake. Van Maanen's persistence in finding the change was a harbinger of trials to come in succeeding years—not concerning the Sun but rather the spiral nebulae.

Van Maanen first got involved with the spirals in late 1915, when George Ritchey asked him a favor. Ritchey was then using Mount Wilson's 60-inch telescope to produce superb photographs of spiral nebulae. Everyone agreed the images were breathtakingly beautiful. Part of this success was due to Ritchey's inventiveness. He had developed a fast camera shutter, which allowed him to build up an image from a series of short exposures, each taken when the atmosphere was calm. The total exposure time could last anywhere from two hours to more than eight hours, sometimes stretched over two or three nights. This resulted in rich nebular details never before captured.

When he approached van Maanen, Ritchey had recently taken a picture of the spiral nebula M101, the Pinwheel, which he had also photographed in 1910. With both images in hand, he asked van Maanen to put the plates into his trusty stereocomparator and see if any changes could be detected in the nebula over those intervening years. Van Maanen at first measured no variation but got permission from Ritchey to keep the plates to study them further. Adapting methods he had used previously in other work, he chose thirty-two stars, equally bright and positioned uniformly around the nebula on each plate, and measured how dozens of points within the spiral nebula may have shifted in comparison to those stars. Extending his study, he borrowed additional plates of M101 from the Lick Observatory, photographs taken in 1899, 1908, and 1914. He didn't rush. Van Maanen was so meticulous that he even made sure the temperature in the room where he was making his measurements was tightly controlled. He wanted to take care that any thermal expansion, in either the glass photographic plate or the measuring machine, would be negligible.

In the end, he decided that the nebular material within M101 was moving after all, although exactly how was not immediately obvious. “If the results…could be taken at their face value, they would certainly seem to indicate a motion of rotation or possibly motion along the arms of the spiral,” he reported. If turning at his measured rate, M101 was completing one full rotation every eighty-five thousand years. As noted earlier, that meant if the Pinwheel were truly the size of the Milky Way and located way off in distant space, the nebula's edge had to be traveling faster than the speed of light, an impossibility given Einstein's special theory of relativity, which said that no bit of matter can move fast enough to overtake a beam of light.