About Time

by Adam Frank

  Even before the full network of satellites was put in place, however, events determined that GPS would enter the public domain. In 1983, Korean Air Flight 007 was shot down by Soviet fighters after it got lost over Soviet territory. The attack killed all 263 passengers on board, including a U.S. senator.38 In response, President Reagan declassified GPS, moving it from a purely military effort to a public project. In 1993, President Clinton authorized the military to reduce the amount of “fuzz” it added to the signal made available to the public. This fuzz was called “selective availability” because it meant that the various clients using GPS got different levels of position accuracy. The military, of course, had access to the highest accuracy. In 2000, selective availability was stripped away and GPS began its encroachment into public life and time.39

  The first consumer GPS devices became available in the late 1980s and early 1990s from companies such as Magellan and TomTom. These products made inroads quickly, sprouting applications for everything from the obvious car-mounted units to devices for meter reading and barcode ID positioning.40 As the 1990s progressed, GPS devices rode the wave of increasing power and sophistication that was advancing all forms of electronic material engagement. Once selective availability was dropped, GPS was freed to work its way into culture on new and deeper levels. Of particular importance was the integration of GPS with mobile phone technologies.

  Looking at a film from the 1980s, it is hard to believe that people managed to make their way around modern civilization without mobile phones. The shift from a telephone connected to wire to a telephone in your pocket occurred so quickly and completely, it is as if a Grand Canyon of experience opened between our former lives and the lives we lead now. Watching people staring into their little plastic rectangles as they stand on line in any airport or on a train platform, it is hard not to ask, “What did we do with ourselves before?” Mobile phones, like e-mail and the Internet, formed the substrate of new material engagement and transformed human time in the digital age. But mobile technology was always as much about space as it was about time. When you make a call, the mobile network is tracking your position through electromagnetic signals that travel from the phone to the local network towers. With this emphasis on position determination it was only a matter of time before mobile phones and GPS found common ground.

  It was not a stretch to adapt the clock synchronization so vital to GPS to support mobile position determination. The killer app for this hybrid of GPS and mobile phones was locating emergency callers. In the aftermath of 9/11, the U.S. Federal Communications Commission required that emergency GPS location capacity be included in all U.S. mobile phones.41 From there it was just a short step to including GPS as a feature in the rapidly advancing smart phone market. In 2006, several major American carriers picked up on mobile phone GPS, touting its functionality on their new high-end smart phones. Then Apple released the iPhone and the contours of human-machine interface shifted. The iPhone was wildly successful in redefining what was possible from a handheld device. Because the iPhone was, essentially, a fully Web-connected (and eventually GPS-connected) handheld computer, our interaction with time and space shifted yet again. As competitors took up the iPhone’s challenge, silicon-chip-based material engagement entered the era of “cloud computing”. All human knowledge on all subjects—from the nearest Indian restaurant to the history of Indian cooking—was always instantly available in the wireless aether, “the cloud”. Not having instant access to information, including information about where you were, came to seem like a relic of a different age.

  With the advent of GPS-enabled mobile phones, hyperaccurate space was woven together with hyperaccurate time as the new standard for a cultural life that had accelerated to the speed of the cloud. In this process, we traded the internal arena of personal, inhabited time for a more crowded, more public domain in which we were always available, always locatable and always part of a social network. We were always at work, even on weekends or family trips. We were always visible, even if in a distant country, through our status updates and microblog posts. For good or for ill, acceleration did not just mean going faster; it also meant a seemingly endless expansion of an ever-connected public space that became steadily more difficult to avoid.

  THE DARK UNIVERSE, PART II: ENERGY

  Dark matter did not fit into anyone’s scheme for cosmology but that did not mean it constituted a fundamental problem. In attempting to move beyond their standard model, particle physicists had always expected to discover deeper laws and new forms of matter. The fact that most of the universe’s mass appeared in this dark form was fascinating but could easily fit into the inflationary Big Bang models without angst. Dark energy, the second great discovery of the post–Big Bang era, was another story entirely. While dark matter was hinted at as far back as Zwicky’s work in the 1930s, dark energy appeared suddenly and without warning.

  In 1998, two highly competitive groups of astronomers were each completing a multiyear project with the same goal: they hoped to extend Hubble’s distance-velocity law farther into cosmic space than anyone had before by using a special type of exploding star as a beacon. Recall that Hubble found a straight-line relationship between galaxy recession speeds and galaxy distance. The farther a galaxy was from us, the faster it was moving away—exactly the expectation for an expanding universe. General relativity, however, predicts that Hubble’s straight-line relation should be a local phenomenon only on cosmological scales. Peer far enough out into space and the Hubble law should change due to gravity. Since everything is pulling on everything else, the expansion of the universe should be slowing down. At great distances, cosmologists expected to see Hubble’s straight-line relation bend over—effects of the universe’s gravitational braking.

  The two research groups, one based at Berkeley and the other at Harvard, were racing against each other to find the magnitude of the universe’s deceleration. It was a critical project since the rate of cosmic braking is directly related to the all-important cosmic density parameter, omega. The determination of the cosmic deceleration meant the determination of the total mass-energy content of the universe. It would be a result worthy of a Nobel Prize.

  Each group used the same method. First they looked for special types of supernovae in distant galaxies. Supernovae are the apocalyptic explosions of geriatric stars. Only a few years earlier, a special kind of supernova, called Type Ia, had been found to make an excellent probe for cosmic distance. Type Ia supernovae were standard candles in the same way as Henrietta Leavitt’s Cepheid Variables, which had allowed Edwin Hubble to nab the distance to the Andromeda galaxy. Unlike Cepheid Variable stars, however, supernovae are so bright they can be seen halfway across the known universe. This made the perfect tool for pushing Hubble’s law deeper into cosmic space.

  Finding a distant Type Ia supernova demanded use of giant instruments such as the ten-metre Keck telescope on top of the Mauna Kea volcano in Hawaii (almost four times larger than Hubble’s massive Hooker scope). Each team pushed hard, using these powerful instruments, to find the bend in Hubble’s law and announce a value for cosmic deceleration. But things didn’t go quite as planned.

  “I was just quite frankly denying this was happening”, recalled Brian Schmidt of the Harvard team.42 As data were gathered and analysed, Schmidt’s group was stunned to find no evidence for deceleration. Instead, everything pointed in the opposite direction. According to the supernova observations, the expansion of the universe was actually accelerating. The universe was expanding faster now than it had been billions of years ago. Over in Berkeley, team leader Saul Perlmutter was having the same problem and the same reaction. The Berkeley group’s data (using different supernovae) also showed acceleration. “Is there something wrong with this?” Perlmutter asked his team. After exhaustively checking and rechecking their data, both groups bit the bullet and announced their results. Cosmic acceleration became worldwide news.

  Overnight, cosmology was turned on its head. Rocky Kolb, a
leading cosmologist who literally wrote the book on the early universe, was stunned: “I still have a hard time believing it.”43 In spite of the community’s incredulity, further studies rendered the cosmic acceleration a remarkable fact that would force cosmologists to rethink their business.

  As Newton had showed four hundred years earlier, acceleration needs a force. And, as the physicists of the eighteenth and nineteenth centuries demonstrated, forces need energy. The discovery of cosmic acceleration meant that space was being forced apart and must, therefore, be pervaded by a new form of energy acting like antigravity. While Newtonian gravity only produces attractions, Einstein’s famed cosmological constant had shown physicists that repulsion and gravity could go hand in hand. The supernova data made it clear that some form of antigravitational energy had to exist. Since nothing was known about this newly discovered energy other than its space-stretching ability, it too was given the “dark” moniker.

  Theoretical cosmologists were quick to build models for what was now being called dark energy. The most obvious candidate was Einstein’s long-dismissed cosmological constant. Recall that this constant implied a repulsive force that pushed space-time apart. Einstein had originally introduced it as a way of keeping his preferred static universe from collapsing. Perhaps what the great scientist considered his biggest blunder had in fact been an act of fantastic prescience. For many researchers cosmic accleration implied that the cosmological constant was back with a vengeance. The value for the cosmological constant extracted from the supernova data was, however, puzzling. After Einstein gave up on the idea, physicists assumed the cosmological constant did not exist, or thinking mathematically, its value was exactly zero. But physicists soon recognized that quantum mechanics and its all-important concept of uncertainty implied that even the vacuum of empty space was seething with energy. Because quantum mechanics demands that no system, including the vacuum, can be specified without some uncertainty, “virtual” particles can appear and disappear against the vacuum’s background state of zero energy. When physicists calculated this “vacuum energy”, as it was called, the number they found was huge and would lead to a huge cosmological constant. Such a cosmological constant would have torn space apart billions of years ago which clearly did not happen. Thus physicists had always assumed that some mechanism led to a perfect cancellation of the quantum vacuum energy, resulting in a cosmological constant of zero.

  The observations of cosmic acceleration pointed to a cosmological constant that was far smaller than anyone would have predicted from vacuum fluctuations but still far larger than zero. If dark energy was a cosmological constant, someone needed to explain how it took such an unexpected value. Of course, the link between the newly discovered cosmic acceleration and the brief early period of acceleration that defined cosmic inflation was not lost on scientists. Some researchers proposed that, like the inflation field of the early universe, the cosmos was now pervaded by a similar energy that would also eventually fade away. Drawing on terminology from Aristotle’s 2,500-year-old cosmological texts, the theoretical energy field was given the name quintessence, and a host of new studies explored its potential as a source of dark energy.44

  Alongside the cosmological constant and quintessence, other options for dark energy sprouted like wildflowers in spring. None of them, however, was an obvious or perfect solution. Dark energy had stormed onto the stage and physicists were left to hurriedly pick up the pieces.

  RIPPLES OF CREATION: THE TRIUMPH AND TRAGEDIES OF INFLATIONARY COSMOLOGY

  The cameras were on and the scientists were arranged at a table at the front of the room. It was June 5, 1992, and the new results from the Cosmic Background Explorer (COBE) satellite were set be announced. COBE’s mission was to chart the cosmic microwave background in the sky at a higher resolution than ever before. Scientists were about to get their best, most detailed map of the universe’s all-important fossil radiation. As a first step, the COBE team confirmed, once again, that every corner of the sky glowed with the relic photons. These light particles emerged from the seething cosmic plasma that was 13.7 billion light-years away and 13.7 billion years in the past. Then the COBE scientists had gone further, looking for small variations in the CMB from one point in the sky to the other. These variations translated into telltale lumps and bumps of slightly hotter or slightly cooler primordial gas. For years cosmologists had predicted such tiny variations, small knots in the otherwise smooth cosmic gas emerging from the Big Bang.

  Cosmologists believed the knots had to be there. They were the seeds that had grown into the rest of cosmic history. According to Big Bang theory, all the structures we see in the universe today—galaxy clusters, galaxies, stars, planets and people—must have started as those tiny perturbations. Begin with those tiny lumps, the story goes, and gravity does the rest. Through gravity the dense lumps pull the surrounding gas towards them. The lumps get bigger and denser, pulling even more gas inward from ever-larger distances. In time, the lumps grow into galaxies and galaxy clusters. COBE’s job had been to find those first steps in the ladder of cosmic structure building. The scientists at the press conference were there to affirm that COBE had done its job.

  On the wall behind the scientists was an all-sky map of the inhomogeneities in the CMB. The map was a mottled oval showing amorphous blobs of red for slightly cooler (and slightly denser) gas and blue for slightly warmer (and slightly more rarefied gas)—the earliest seeds of all cosmic structure. The project scientists were beside themselves with joy. George Smoot, the project scientist for COBE, leaned into the microphone and described his reaction on first seeing the completed map: “It was like looking at the face of God.”45 Though he would catch hell from some quarters for his poetic slip of the tongue, Smoot’s characterization was not altogether incorrect. COBE had caught echoes from just after the dawn of time, and in so doing, had retrieved one of the holy grails of Big Bang cosmology and its modern incarnation, inflation.

  Years before COBE, in the early 1970s, two cosmologists, an American named Edward Harrison and a Russian named Yakov Zel’dovich, had used the observed distribution of galaxies in the sky to push backwards and calculate the distribution of perturbations that must have existed in the cosmic plasma after the Big Bang. Their calculations showed how gravity took hold of lumps in the gas after radiation and matter decoupled (when the CMB formed). Working backwards, Harrison and Zel’dovich calculated what the distribution of lumps, or the “spectrum of perturbations”, must have been to produce what we see today.46

  FIGURE 8.7. The ripples of creation. All-sky map of fluctuations in the cosmic microwave background, produced by the Wilson Microwave Anisotropy Probe (WMAP), an orbiting telescope that followed COBE. White represents denser regions, and dark represents under-dense regions of the early universe a mere 380,000 years after the Big Bang.

  A decade later, Alan Guth introduced inflation, and physicists began probing its consequences. In 1982, researchers discovered that inflation theory naturally recovered the Harrison and Zel’dovich spectrum of cosmic perturbation. The inflation field powering hyperexpansion in the very early universe was inherently a quantum mechanical entity—it was a quantum field. Since the very essence of quantum physics is its inherent randomness, the decay of the inflation field must have imposed random perturbations on the rapidly stretching universe. These quantum fluctuations then grew with space-time, transmitting their lumps, bumps and wiggles all the way to the creation of CMB photons three hundred thousand years after the Big Bang. The matter/radiation decoupling of the CMB was the critical turning point in the story. Before the CMB photons were released, matter and radiation were so closely connected that gravity’s attempts to build structure were lost to radiation’s ability to smooth it all away. Once the CMB radiation was decoupled from matter, the cosmic gas was ready to be structured by gravity.47

  It was a significant early triumph for the new inflationary theory. The recovery of the Harrison-Zel’dovich perturbations by quantum fluctuations sh
owed that inflation was good for something. A decade later, the COBE data showed that the same distribution of lumps and bumps in the Harrison-Zel’dovich perturbations was there, clear as day, in the CMB. In 2005, a decade after that, a second satellite, called WMAP probed the CMB at ten times the resolving power of COBE. WMAP’s portrait of the CMB sky allowed scientists to go beyond COBE and make exacting explicit comparisons between different versions of Big Bang theory, including the inflationary Big Bang. Once again inflation was the winner. The inflationary scenario was picking up at least some forms of experimental verification.

  The precision testing of model and data extended beyond inflation’s prediction of the CMB’s minute bumps and wiggles. Mapping the distribution of galaxies across billions of light-years had become a small industry in the 1980s and 1990s. Using dedicated telescopes hooked up to networked computers and huge databases, projects such as the Sloan Digital Sky Survey automated the observation of hundreds of thousands of galaxies. Generating terabytes of data, the 3-D distribution of galaxies was slowly teased out of these observations. Just as structure in the CMB maps could be linked backwards to inflation, structure in the galaxy distribution maps across the entire universe could be linked back to the CMB. Together a consistent story of cosmic evolution emerged all the way from 10–33 of a second out to our current place in time 13.7 billion years later.