The 4-Percent Universe

by Richard Panek

  But all his friends could do was shrug and say that yeah, they would love him to be on their team, but he was part of the other team.

  In early 1996, Filippenko defected. A few months later he was able to exact a revenge of sorts. As Riess was finishing his PhD work at Harvard, Perlmutter approached him with the offer of a position at LBL and, by extension, on the SCP team. Down the hill at UC Berkeley, Filippenko countered with a Miller Fellowship—the same honor that Filippenko himself had once held as a young postdoc.

  Riess didn't have to think too hard. He'd be doing astronomy with a friend. He'd be doing astronomy on a team to which he already belonged. He'd be doing astronomy.

  Exactly. For Filippenko, Riess's MLCS method was precisely the kind of tool that an astronomer would know was necessary—would feel a need to invent—before proceeding to the next step. And now Riess apparently wanted to show him where that next step had led.

  Riess pointed to the notebook on his desk. He walked Filippenko through the calculations he'd made, he described the back-and-forth that he and Schmidt had been having, and he said that the result didn't seem to be going away. Filippenko studied the notebook for a few moments, then straightened up. He was shaking his head.

  "Man," Filippenko said, "be sure the measurements are done right."

  Well, yes. By January 4, Riess had taken the paper as far as he could. He sent Schmidt the material for the final round of cross-checking. Then he waited.

  "Well Hello Lambda!" Schmidt e-mailed him on January 8, the day of the AAS press conference. Schmidt had finished his spot checks and found nothing wrong. His statistical level of confidence was the same as Riess's: 99.7 percent. It was time to let the rest of the team know.

  When Pete Garnavich got to the AAS meeting, he had already studied the SCP's paper in Nature, and as the lead author on the High-z team's HST paper—due to appear in the Astrophysical Journal on February 1—he certainly would have sought out the SCP's even more recent data on his own. But he knew, too, that his team was getting a bizarre result; Riess and Filippenko had confided it to him before the press conference. They had also instructed him to keep the result quiet. On January 9, Garnavich visited the AAS poster session meeting to see for himself how close the SCP was to getting that same bizarre result.

  Close.

  Clearly the SCP supernovae were falling in the low-omega range. The fate of the universe was to expand forever. Ho hum.

  But what about a cosmological constant? Could the SCP claim evidence for a non-zero lambda? Could they say with some conviction that the universe would have negative mass—essentially, that it wouldn't exist—without the addition of a positive lambda to the equations?

  Not quite, as far as Garnavich could see. The error bars above and below the points on the graph representing the supernovae could certainly accommodate such an argument. Some of the upper limits, and some of the supernovae themselves, fell within the range of the upward curve designating a universe with non-zero lambda. But some didn't. Garnavich concluded that the SCP wasn't ready to claim anything explicit, anything definitive. He reported back to his colleagues that High-z was still in the lambda game.

  Riess flew east for his wedding on January 10. He returned to Berkeley two days later, for a one-night stopover on his way to his honeymoon. That evening he checked his e-mail. The string of boldface unread messages stretched down the screen. Riess scrolled. Still it stretched. When he got to the bottom of the list, he checked the time stamp to see how long the conversation had been going on without him. Forty-eight hours—"an eternity."

  He started at the bottom—a question from Schmidt: "how confident are we in this result?"

  "In your heart," Kirshner wrote back, "you know this is wrong, though your head tells you that you don't care and you're just reporting the observations."

  "I don't know about anyone else," another team member responded later that day, "but MY heart tells me nothing about the cosmological constant." They had a result; they had a confidence level. Which led to the second question: Did they need to believe it in order to publish it?

  Kirshner didn't want to risk reporting evidence of a cosmological constant that they would have to retract later. "That would be like saying 'Omega must be 1' based on 4 supernovae and then saying 'Omega must be Zero' when you get one more. Perlmutter has already done that. He's a year ahead of us, but I don't think we want to duplicate that path!"

  Bruno Leibundgut, writing back from Germany that same day, agreed. "There is no point in writing an article if we are not very sure we are getting the right answer."

  Mark Phillips, in Chile, concurred. "Press releases and a barrage of ApJ Letter/Nature articles may impress the public or scientists who have only a casual interest in the subject, but the hard-core cosmology community is not going to accept these results unless, as Bruno says, we can truly defend them."

  Schmidt, however, disagreed. "As uncomfortable as I am with a Cosmological constant," he wrote, "I do not believe we should sit on our results until we can find a reason for them being wrong (that too is not a correct way to do science)."

  Correct way or not, there was a further concern: priority.

  "Of course we want to remain true to our scientific ideals," wrote another member of the collaboration. "But this has to be balanced with realpolitik."

  "Who knows?" Filippenko wrote. "This might be the right answer. And I would hate to see the other group publish it first." And if it's the wrong answer? Another team member argued that there was no downside: "If it turns out in the fullness of time that a cosmological constant exists they"—the SCP—"can claim to have found it. If it does not, their claim will be forgotten and no one will attach much blame to them for being wrong." Reporting that same conclusion before SCP did was was a no-lose proposition. If the High-z team was right, they would get priority; if they were wrong, they'd get a free pass. High-z had a reasonable argument, so why not make it?

  Why not? Riess saw no reason. He leaned into his keyboard and started to compose a response that he could send to the whole group. When he looked up from the screen, he found his bride staring back at him.

  "I cannot believe," she said, "you are working on an e-mail when we are on our way from our wedding to our honeymoon."

  "Well, this is a really important one."

  "Oh, I think I'm going to be hearing this all the time."

  "No, no," he said. "This—you're not. This really is—this is the one."

  She shook her head and left the room. Riess bent back to the keyboard, composing an e-mail that would answer all the questions.

  Heart or head?

  "The data require a nonzero cosmological constant!" he typed. "Approach these results not with your heart or head but with your eyes. We are observers after all!"

  Publicity? Priority? Realpolitik?

  "You see, I feel like the tortoise racing the hare. Everyday I see the LBL guys running around but I think if I keep quiet I can sneak up....shhhh..."

  Finally, quick letter or War and Peace?

  "I think I can answer the group's dilemma about a quick kill paper vs a detailed explanation .... you all said you wanted a detailed exposition of the data so that's is what I have been working on. Brian said that adding the data stuff to the paper should only take a week, well I did it already before the wedding."

  He hit send, and the next morning he left for his honeymoon in Hawaii. (Also, an observing run at Keck.)

  For Perlmutter, the extra effort he'd put into the preparations for the AAS meeting had paid off. The media coverage focused primarily, and rightly, on the consensus that the participants in the press conference had reached—the fate of the universe. The New York Times ran it on the front page, under the headline "New Data Suggest Universe Will Expand Forever." The San Francisco Chronicle, the hometown paper for the SCP team, had also put the news on [>]. The local paper for the AAS meeting, the Washington Post, ran its story on page A3: "Universe Will Keep Expanding Forever, Research Teams Say." But it w
as the SCP that the Post singled out for a rave. "Perlmutter bowled over the audience with an unexpectedly large sample," the article said. "Garnavich's team presented three." And then, of even greater significance to the astronomy community, came a news article in the journal Science three weeks later.

  The author of the article, James Glanz, a PhD in astrophysical sciences, covered his beat as if it were City Hall. He had written about the supernova searches over the past several years, but his most recent reporting mentioned a possibly imminent discovery. In the October 31 issue he wrote that both teams had submitted papers supporting the conclusion that the universe would expand forever—a scenario that held whether the universe was open or flat, whether omega was less than 1 or exactly 1. But then he added that such a never-ending expansion would be "perhaps boosted by large-scale repulsive forces."

  "The results," he continued, a few paragraphs into the article, "still leave an opening for some theories in which matter plus its equivalent in energy, supplied by the cosmological constant, add up to a flat universe."

  The article in late January also included a reference to "a quantum-mechanical shimmer in empty space, called the cosmological constant," but this time Glanz focused on the SCP's contribution to the AAS meeting:

  Not only did the results support the earlier evidence that the expansion rate has slowed too little for gravity ever to bring it to a stop; they also hinted that something is nudging the expansion along. If they hold up, says Perlmutter, "that would introduce important evidence that there is a cosmological constant."

  "It would be a magical discovery," adds Michael Turner....

  Since the frantic exchange of e-mails early in the month, the High-z collaboration had been trading drafts, exploring the math, debugging the code (Schmidt and Riess had missed a few glitches, but nothing important), examining the photometry and the spectroscopy and the charts and graphs and tables—all in the cause of making their case scientifically responsible. Now they had a further concern. Glanz's article, complete with a reproduction of a contour graph showing SCP's preliminary analysis of forty supernovae, seemed to be suggesting that the SCP was beating them at beating the SCP at beating them at their own game.

  Alex Filippenko would be speaking at the upcoming UCLA Third International Symposium on Sources and Detection of Dark Matter in the Universe, in Marina del Rey. The High-z team would be submitting their paper only a couple of weeks after that. Why wait? he asked. Filippenko suggested he could announce the team's findings at the UCLA meeting. "This is our chance to make a big splash," he said.

  But why not wait? argued other members of the team. The paper will be out soon enough. Let the science speak for itself.

  Filippenko, however, argued back that if the SCP was as close to claiming a discovery as their AAS presentations suggested, then those two weeks might make a crucial difference in terms of establishing priority. "You can check and recheck your results forever," he said, "but at some point you've got to have the balls, basically, you've got to have the courage, to announce your result and to say, 'Okay, here is an accounting of our uncertainties. This is where we stand.'"

  The discussion stalled there. But then, just days before the UCLA meeting, Jim Glanz called Filippenko. He didn't know whether Glanz was using the old reporter's trick of pretending to know more than he did, but for Filippenko the conversation was all he needed to convince a majority of the High-z team. "Glanz is going to be breaking this story whether we're in it or not," Filippenko said. "So why not be in it?" Give him the evidence. Give him the quotes. And give him the news peg.

  Make the announcement, and tell him about it first.

  On February 22, Filippenko took his seat at the UCLA conference and listened as Gerson Goldhaber gave a presentation on the SCP team's latest results. Then he listened as Saul Perlmutter gave a presentation on the SCP team's latest results. As far as Filippenko could tell, nobody was claiming a discovery; all he heard was that the SCP had "evidence" for lambda.

  He took a deep breath. It was now his turn to present. Filippenko stood up, paused, and then said either you had a result or you didn't. And the High-z team did.

  The ghost was real, and it was most of the universe.

  9. The Tooth Fairy Twice

  MIKE TURNER WAS following in David Schramm's footsteps. He was walking along the hallways and footpaths, among the blackboards and picnic benches, of the Aspen Center for Physics, a summer retreat for theorists under head-clearing blue skies. One look at the mountains, one deep breath, and you could see why a big-as-all-outdoors guy like Schramm had fallen in love with the place at first sight in 1976, enough to make Aspen his second home. Eventually he'd served as the chairman of the board for the Aspen Center, from 1992 until shortly before his death. But Schramm was gone now, and Turner had agreed to take his place opposite Jim Peebles in the "Nature of the Universe Debate" at the Smithsonian, so when Turner ran into Peebles at the Aspen Center, he had a question for him. For obvious logistical reasons, the organizers had bumped the event from April 1998 to October—and just as well. Turner and Peebles needed a new topic.

  "Are you still willing to debate non-flat?" Turner asked.

  Peebles shrugged.

  "Jim, debates have a yes-or-no question. Correct me if I'm wrong, but you and Dave were supposed to debate whether or not the universe is flat. He got flat and you got non-flat." Turner asked his question again. Did Peebles really want to argue publicly that the universe wasn't flat?

  "No."

  The answer didn't surprise Turner. Both theorists knew that defending a non-flat universe in late 1998 would feel like defending the Steady State cosmology in late 1965. Within months of the January AAS press conference where Perlmutter unveiled the SCP's forty-two supernovae, and within weeks of the February UCLA meeting where Filippenko made his announcement, a consensus had emerged in the Big Bang community of astronomers, astrophysicists, cosmologists, and theorists: The universe wasn't what it used to be.

  Since Hubble's discovery of evidence for the distance-velocity relation, astronomers had been following a syllogism: One, the universe is expanding; two, the universe is full of matter attracting other matter through gravity; therefore, the density of matter will affect the rate of expansion. So: How much was the expansion slowing? This question was what the two supernova teams had dutifully set out to answer, and they had succeeded: It wasn't.

  The expansion wasn't slowing. The universe the two teams observed wasn't one where distant Type Ia supernovae were brighter than they should be at this particular redshift or that particular redshift, and therefore nearer. It was one where they were dimmer, and therefore farther. It wasn't a universe that was doing what an expanding universe full of matter acting under the influence of mutual gravitational attraction should be doing. It was doing the opposite.

  The expansion of the universe was speeding up.

  James Glanz broke the story in the February 27 issue of Science. Even though he had hinted at the possibility of a positive lambda in two previous articles, in October and January, such a result would be so difficult to accept that the community, rightly, was treating the possibility with what he considered "a preponderance of skepticism." An agreement between the two teams, however, might change that dynamic. Even before Filippenko's announcement at the UCLA meeting, Glanz had begun rounding up quotes from the High-z team. "To be honest," Bob Kirshner said, "I'm very excited about this result." Adam Riess said he was "stunned." Most quotable of all, from Brian Schmidt: "My own reaction is somewhere between amazement and horror." He elaborated: "Amazement, because I just did not expect this result, and horror in knowing that it will likely be disbelieved by a majority of astronomers—who, like myself, are extremely skeptical of the unexpected."

  By the end of the day that Science published Glanz's article, February 27, Riess had appeared on CNN and PBS. (NewsHour interviewer: "Why did some scientists react with what one called amazement and horror to these conclusions?") Articles in magazines and newspapers ap
peared around the world in the following week, culminating in a 1,600-word feature in the New York Times ("'My own reaction is somewhere between amazement and horror,' said Dr. Schmidt, the team leader").

  At Berkeley Lab, the SCP team also responded with amazement and horror. Amazement because they had succeeded in finding nothing less than the fate of the universe, and horror because acceleration itself was what everyone suddenly wanted to talk about—and the High-z team was getting the credit for it. As Perlmutter said in a lab press release, the two teams were in "remarkably violent agreement."

  "Basically, they confirmed our results," Gerson Goldhaber told the New York Times. "But they won the first point in the publicity game."

  "Hey, what's the strongest force in the universe?" Kirshner said in the same article. "It's not gravity, it's jealousy."*

  In early March, the High-z team submitted "Observational Evidence from Supernovae for an Accelerating Universe and a Cosmological Constant" to the Astronomical JournaL.† The first week of May—a few days before the paper was even officially accepted—Fermilab convened a conference on the two supernova teams' results. A straw poll of the sixty or so attendees showed that forty were willing to accept the evidence.