The Day We Found the Universe

by Marcia Bartusiak

  When the Milky Way was thought to span only 10,000 or 30,000 light-years, it was easier to think of the spiral nebulae as separate galaxies. But everything changed when Shapley claimed the Milky Way was far larger. If the Andromeda nebula was also a galaxy and with similar dimensions to the Milky Way, its distance would have to be farther out than anyone anticipated to appear as it did on the sky. And that meant that the novae that lighted up within Andromeda's disk were even more luminous than any known physical law could possibly explain. Within a matter of months, Shapley made a complete about-face regarding the spiral nebulae. Once a believer in island universes, Shapley now considered it more reasonable to assume that Andromeda and the other spirals were simply closer: either nestled cozily inside our galactic borders or situated just outside, as smaller outlying colonies. They were no longer the Milky Way's equal in grandeur and power but mere appendages. He even speculated at one point that they might be blobs of nebular material somehow being repelled by the Milky Way at high velocities, perhaps due to radiation pressure or electrostatic forces. As our galaxy travels through space, surmised Shapley, it might be driving “the nearby spirals to either side much as the prow of a moving boat cuts through the waves.”

  Formerly suspicious of van Maanen's findings, Shapley now came to like that his friend was detecting the spirals rotate, for it strongly backed his own, newly constructed model of the universe. It meant that the spirals had to be close by, merely secondary members of the Milky Way. Our galaxy reigned supreme. “I believe the evidence is quite against the island universe theory of spirals. I should guess the Andromeda nebula to be not further away than 20,000 light-years,” Shapley told Hector MacPherson, a popular British writer on astronomy.

  With all his advance notices and public declarations, the thirty-two-year-old Shapley was crowing and, like a little boy, wanted his elders to notice his cleverness at completely renovating the image of the universe. “The observational problems opened up are unlimited; the amount of stupid measuring ahead of me is almost discouraging,” he told Hale. “But I am enjoying it all except for a considerable nervous strain at the last.”

  • • •

  Shapley released his findings around the same time that the Mount Wilson Solar Observatory dropped the word solar from its name. Shapley most of all was broadening observations from the mountaintop post to questions far beyond the Sun and into the depths of space and time. What Shapley had done was to hugely extend the Copernican rule. Just as Copernicus in the sixteenth century had removed Earth from the center of the solar system, Shapley relocated the solar system from the heart of the Milky Way. “The solar system is off center and consequently man is too, which is a rather nice idea because it means that man is not such a big chicken. He is incidental—my favorite term is ‘peripheral,’” Shapley bluntly wrote in a 1969 memoir. “If man had been found in the center, it would look sort of natural. We could say, ‘Naturally we are in the center because we are God's children.’ But here was an indication that we were perhaps incidental. We did not amount to so much.”

  Shapley had carried out a tour de force, and his findings hit the astronomical community like a lightning bolt. Praise for the work, from the most eminent corners of astronomy, was immediate. After reading Shapley's completed papers, Eddington wrote Shapley that “this marks an epoch in the history of astronomy, when the boundary of our knowledge of the universe is rolled back to a hundred times its former limit.” In a Scientific American article, Russell described the results as “simply amazing.” And British theorist James Jeans told Shapley that his newly published papers were “certainly changing our ideas of the universe at a great rate.”

  Mount Wilson astronomer Walter Baade later remarked that he “always admired the way in which Shapley finished this whole problem in a very short time, ending up with a picture of the Galaxy that just about smashed up all the old school's ideas about galactic dimensions. It was a very exciting time, for these distances seemed to be fantastically large, and the ‘old boys’ did not take them sitting down.”

  While the news spread quickly within the astronomical community, it took longer to reach the general public, likely due to the shadow of the war and its aftermath. Not until May 31, 1921, did the New York Times report on its front page that Shapley had multiplied the universe's size immensely. Our galaxy, noted the Times reporter, was now 300,000 light-years from end to end, a “super–Milky Way… The young astronomer has proved to his satisfaction by various calculations that the sun, the little speck of light around which a tiny shadow called the earth revolves, is 60,000 light years from the centre of the universe.”

  “Personally I am glad to see man sink into such physical nothingness, and it is wholesome for human beings to realize of what small importance they are in comparison with the universe,” says Shapley in the article. (If any readers were made queasy by Shapley's news, the story was conveniently set just above a tiny advertisement for Bell-Ans pills, a popular 1920s indigestion remedy.) The Chicago Daily Tribune published the same announcement on page 1 as if it were entertainment news: Earth, proclaimed the headline, was now a “Rube…Miles Off Sky Broadway.”

  Not everyone was convinced of this new cosmic scheme. Critics pointed to several weak points in Shapley's arguments, including Hale, who wondered whether the spirals were something other than Shapley imagined. But the Mount Wilson director still supported Shapley's bravado: “You have struck a trail of great promise…. I think you are right in making daring hypotheses, and in pushing the work ahead as you have done, as long as you…are prepared to substitute new hypotheses for old ones as rapidly as the evidence may demand,” Hale responded to Shapley from his wartime post in Washington. Hale preferred his astronomers to take chances. He didn't want them turning solely into unimaginative data gatherers, as Pickering, at Harvard, was wont to do.

  But since Shapley had based his results using such novel methods as the Cepheid beacons and rashly ignored many uncertainties, acceptance was hardly unanimous. Other astronomers had been slowly and methodically measuring the galaxy's dimensions over many years by essentially counting stars, tracing out their distributions and movements over the sky and deep into space. The leader in this endeavor was the highly respected astronomer Jacobus C. Kapteyn, at the University of Groningen in the Netherlands. Though not possessing a good telescope, he organized a massive effort to measure the positions of hundreds of thousands of stars on plates taken at other observatories, partially with the help of state prisoners placed at his disposal. He reached the pinnacle of his life's work when he introduced what became known as the “Kapteyn Universe.” In this model, the largest portion of stars in our galaxy (there was a smaller fraction farther out) were gathered in a space roughly 30,000 light-years wide and 4,000 light-years thick, a sort of squashed football. Moreover, the Sun retained its plum position near the center. But Shapley was declaring that the Milky Way was ten times larger and the Sun pushed far off to the sidelines. It was extremely difficult for Kapteyn and his colleagues to imagine that their time-honored methods for tracking stellar distributions could be so flawed. Others thought so, too. Shapley had constructed a formidable distance ladder outward, but its calibration rested on a measly eleven Cepheids, whose motions were still highly uncertain. If those were wrong, the entire construct toward his fundamental verdict—what he called his “Big Galaxy”—would fall apart like a celestial house of cards. Kapteyn told Shapley that he was “building from above, while we are up from below… When will the time come that we thoroughly mesh?”

  Conservative astronomers were most disturbed by the many analytical leaps of faith made by Shapley, who tended to speak, it was said, with a “carnival barker's certainty of truth.” Though brilliant and original, he was often quick to jump to conclusions based on meager observations. Accuracy seemed to be less important to him than developing a broad, grand picture. Walter Adams, for one, was sure that the fast and slow variable stars that Shapley lumped together in his computations were actuall
y “two different breeds of cats.” (He was right; they were later found to be RR Lyrae stars, variables that are less massive and fainter than Cepheids.) And then there was the issue of Shapley's borrowing ideas and techniques from other astronomers without proper acknowledgment. Adams complained to Hale that Shapley “has never given the credit where it belongs.” In one paper published in the Proceedings of the National Academy, Shapley made no mention of either Hertzsprung or Leavitt, who had both certainly paved the way. This infuriated Adams. As one Harvard astronomer later put it, “I have never seen a quicker mind, a more agile sense of humor, or a more complete absence of what usually passes for humility.”

  Shapley's critics were right to be cautious. In hindsight, he did get certain things wrong. Astronomers, for example, would later reduce the Milky Way's girth from 300,000 to 100,000 light-years, once they better understood the difference between the fast and slow variable stars and affirmed the presence of interstellar dust, which made celestial objects appear dimmer and hence more distant than they actually were. This made Shapley mistakenly believe that the Milky Way was more extensive than it actually was. Yet even when the galaxy's width was reduced to 100,000 light-years, it was still bigger than Kapteyn and his supporters had been hawking. Shapley's discovery held up over time on the essentials: first of all, that the Milky Way was a far larger metropolis of stars than previously suspected and, second, that the Sun was situated in its suburbs.

  Shapley's shift of the Sun's position was fully confirmed in the mid-1920s when Bertil Lindblad, a Swedish expert on stellar dynamics, and Jan Oort, at the Leiden Observatory, in the Netherlands, demonstrated that stars were circulating within the Milky Way around a point situated in Sagittarius, exactly where Shapley had pegged the galactic center. Once Lindblad worked out the theory, Oort rounded up the evidence to prove it. If anyone was still questioning Shapley's pushing the Sun off into the galactic boondocks, Lindblad and Oort swept away all doubts. Like the horse on a carousel, the solar system travels in a continual loop, completing one full circuit around the galactic disk roughly every 250 million years. The last time we were in this neck of the celestial woods, the Appalachian and Ural mountains were just being formed and the dinosaurs were getting ready to rule the Earth.

  Shapley's new model of the Milky Way had broad repercussions, especially regarding the spiral nebulae. The idea of island universes, then on the verge of acceptance, was back on shaky ground. “With the plan of the sidereal system here outlined,” reported Shapley, “it appears unlikely that the spiral nebulae can be considered separate galaxies of stars.” There was still the problem of the exceptionally bright novae seen earlier in the spiral nebulae. How do you explain that? asked Shapley. And then there were van Maanen's rotations to take into account. Not everyone was swayed by Shapley's worries; the most ardent believers in external galaxies still held fast to their convictions—not only Curtis but also such major players as Arthur Eddington, W. W. Campbell, and V. M. Slipher. It was the undecideds who were most affected by Shapley's arguments and so remained huddled on the fence. What resulted were two completely different views of the universe, which were difficult to reconcile. The writer MacPherson poetically put it this way: “We may compare our galactic system to a continent surrounded on all sides by the ocean of space, and the globular clusters to small islands lying at varying distances from its shores; while the spiral nebulae would appear to be either smaller islands, or else independent ‘continents’ shining dimly out of Immensity.” As the Roaring Twenties was about to make its appearance, Shapley voted for the “smaller islands,” Curtis for the “continents.”

  He Surely Looks Like the Fourth Dimension!

  Astronomy was not the only field in a tumult as the nineteenth century turned into the twentieth. Physics, too, was in upheaval.

  Doctors across the globe were still reeling over their newfound ability to use X rays, discovered in 1895 by the German physicist Wilhelm Röntgen, to peer inside the human body. Soon after, in Paris, Henri Becquerel accidentally stumbled upon a phenomenon, what came to be called radioactivity, when he was investigating the properties of uranium salt crystals. And in England J. J. Thomson identified the first particle smaller than an atom—the electron. In the new, topsyturvy world of quantum physics, light itself was soon imagined as either a wave or a particle, and physicists were realizing that their trusted laws of motion, dating back more than two hundred years to Isaac Newton, could not reliably gauge how light, whatever its form, whizzed through space. Using Newton's laws of gravity and motion, scientists arrived at one answer, but upon applying James Clerk Maxwell's laws of electromagnetism, they obtained a differing result. It took a rebel—a cocky kid who spurned rote learning throughout his schooling, always questioned conventional wisdom, and had an unshakable faith in his own abilities—to blaze a trail through this baffling territory, one that involved an entirely new take on space, time, gravity, and the behavior of the universe at large. Before anyone else, Albert Einstein discerned that a drastic change was needed, “the discovery of a universal formal principle,” as he put it.

  This was not the iconic Einstein—the sockless, rumpled character with baggy sweater and fright-wig coiffure—but a younger, more romantic figure with alluring brown eyes and wavy dark hair. While in his twenties and thirties, he was at the height of his prowess. Among his gifts was a powerful physical instinct, almost a sixth sense for knowing how nature should work. This often involved his thinking in images, such as one that began haunting him as a teenager: If a man could keep pace with a beam of light, what would he see? Would he see the electromagnetic wave frozen in place like some glacial swell, as Newton's laws were suggesting? “It does not seem that something like that can exist!” Einstein later recalled thinking.

  After pondering this issue long and hard, Einstein came to realize in 1905 that since all the laws of physics remain the same—whether you're at rest or in steady motion, sitting quietly on a beach or reading on a train—then the speed of light has to stay constant as well in both situations. He had found the answer to his question. No one can catch up with a light beam, no matter how fast they are traveling. Whether your feet are firmly planted on Earth or aboard a spacecraft speeding toward a far planet, you'd measure the exact same pace to light's motion, 299,792 kilometers (186,282 miles) per second.

  How is that possible? It seems to go against common sense. But Einstein ingeniously deduced that if the speed of light is identical for all observers, no matter what their state of motion, then something else has to give. And that something else was absolute time and space. With his special theory of relativity, Einstein completely altered the traditional perspective of classical physics that had been firmly established by his illustrious predecessor. “Newton, forgive me,” said Einstein in his autobiographical notes. “You found the only way which, in your age, was just about possible for a man of highest thought—and creative power.” In Newton's world, there was one universal clock and common reference frame, which made time and space the same for one and all throughout the cosmos. But that scheme no longer held. Instead, space and time were now “relative,” flowing differently for each one of us depending on our motion. Einstein intuited that length and time are adjustable. If two observers are uniformly speeding either toward or away from each other, each will measure space shrinking and time proceeding slower for the other. Their clocks and yardsticks will not match up, as they did under Newton's laws. The only thing that they will agree on is the speed of light, a universal constant that remains unchanged for both travelers. The reason this seems counterintuitive is that we can't readily discern these differences in length and time in our rather humdrum surroundings. The changes are only apparent when the speeds between two objects are enormous, a sizable fraction of the velocity of light.

  Soon Einstein was not satisfied with that adjustment alone. Special relativity was just that—special. It could only explain the properties of objects moving at an unvarying velocity. But that restricted its use t
o a great extent. Most events in nature don't behave so methodically. What if something were speeding up, slowing down, or changing direction? What if an object were accelerating under the force of gravity? Einstein knew that he had to develop a more general theory to deal with these situations, and he struggled with the problem for nearly a decade. It was a formidable job, as he had to do nothing less than recast Newton's venerable laws of gravity in the light of relativity.

  For years success eluded him as he struggled to figure out how to make his equations truly universal and still reproduce Newton's law of gravity for the simplest cases, when gravity was weak and velocities were low. After all, Einstein couldn't just throw out a law that had been time-tested for more than two centuries. His new theory had to agree very closely with Newton's in the everyday realm where physicists had long been conducting experiments, a place where space-time distortions were too small to be overt. But then the theory would have to merge smoothly into either the intense gravity or high-velocity regimes in which the strange effects of relativity at last become obvious. “In all my life I have labored not nearly as hard,” he wrote a colleague in the midst of his deliberations. “… Compared with this problem, the original relativity is child's play.”

  The breakthrough for the thirty-six-year-old physicist finally came in November 1915. Over that month Einstein reported weekly to the Prussian Academy of Sciences on his final progress toward a new theory of gravitation. A key moment arrived in mid month, when he was able to successfully explain a small displacement in the orbit of Mercury, a nagging mystery to astronomers for decades. Einstein later remarked that he had palpitations of the heart upon seeing this result: “I was beside myself with ecstasy for days.”