Listening to the Big Bang- page 1 | Science | Smithsonian
Less than a mile from the South Pole, the Dark Sector Lab’s Bicep2 telescope (at left) searches for signs of inflation. (Steffen Richter / Harvard University)

Listening to the Big Bang

Just-reported ripples in space may open a window on the very beginning of the universe

Smithsonian Magazine | Subscribe

For six months each year, the perennially dark and wind-swept plains of the southern polar ice cap have an average temperature of about 58 degrees Fahrenheit below zero. In summer, when the sun returns for its six-month-long day, the glacial terrain hardly becomes more inviting, with temperatures climbing to minus 20 degrees. Not the kind of place most of us would choose to visit.

But if you’re an astronomer seeking a collection of photons that have been streaming toward us since just after the Big Bang, then the South Pole’s Dark Sector Laboratory is what the Met is to opera or Yankee Stadium to baseball. It’s the premier place to practice your trade. With the coldest and driest air on earth, the atmosphere lets photons travel virtually unimpeded, providing the sharpest terrestrial-based space images ever taken.

For three years, a team of astronomers led by Harvard-Smithsonian researcher John Kovac braved the elements to point a brawny telescope known as Bicep2 (an acronym for the less euphonious Background Imaging of Cosmic Extragalactic Polarization) at a patch of the southern sky. In March, the team released its results. Should the conclusions stand, they will open a spectacular new window on the earliest moments of the universe, and will deservedly rank among the most important cosmological findings of the past century.

It’s a story whose roots can be traced back to early creation stories intended to satisfy the primal urge to grasp our origins. But I’ll pick up the narrative later—with Albert Einstein’s discovery of the general theory of relativity, the mathematical basis of space, time and all modern cosmological thought.

The focal plane of the Bicep2 telescope, shown under a microscope, was developed by NASA’s Jet Propulsion Laboratory. (Anthony Turner / JPL)
Gravitational waves stretched by inflation generate a faint but distinctive pattern, called the B-mode signal, captured by the Bicep2. (BICEP2)
During inflation (shown at left), a gravitational force pushed outward, stretching the universe in a tiny fraction of a second. (WMAP)
The Bicep2 telescope, shown at twilight, achieved the first detection of a predicted gravitational wave pattern, its team has announced. (Steffen Richter / Harvard University)

Warped Space to the Big Bang
In the early years of the 20th century, Einstein rewrote the rules of space and time with his special theory of relativity. Until then, most everyone adhered to the Newtonian perspective—the intuitive perspective—in which space and time provide an unchanging arena wherein events take place. But as Einstein described it, in the spring of 1905 a storm broke loose in his mind, a torrential downpour of mathematical insight that swept away Newton’s universal arena. Einstein argued convincingly that there is no universal time—clocks in motion tick more slowly—and there is no universal space—rulers in motion are shorter. The absolute and unchanging arena gave way to a space and time that were malleable and flexible.

Fresh off this success, Einstein then turned to an even steeper challenge. For well over two centuries, Newton’s universal law of gravity had done an impressive job at predicting the motion of everything from planets to comets. Even so, there was a puzzle that Newton himself articulated: How does gravity exert its influence? How does the Sun influence the Earth across some 93 million miles of essentially empty space? Newton had provided an owner’s manual allowing the mathematically adept to calculate the effect of gravity, but he was unable to throw open the hood and reveal how gravity does what it does.

In search of the answer, Einstein engaged in a decade-long obsessive, grueling odyssey through arcane mathematics and creative flights of physical fancy. By 1915, his genius blazed through the final equations of the general theory of relativity, finally revealing the mechanism underlying the force of gravity.

The answer? Space and time. Already unshackled from their Newtonian underpinnings by special relativity, space and time sprung fully to life in general relativity. Einstein showed that much as a warped wooden floor can nudge a rolling marble, space and time can themselves warp, and nudge terrestrial and heavenly bodies to follow the trajectories long ascribed to the influence of gravity.

However abstract the formulation, general relativity made definitive predictions, some of which were quickly confirmed through astronomical observations. This inspired mathematically oriented thinkers the world over to explore the theory’s detailed implications. It was the work of a Belgian priest, Georges Lemaître, who also held a doctorate in physics, that advanced the story we’re following. In 1927, Lemaître applied Einstein’s equations of general relativity not to objects within the universe, like stars and black holes, but to the entire universe itself. The result knocked Lemaître back on his heels. The math showed that the universe could not be static: The fabric of space was either stretching or contracting, which meant that the universe was either growing in size or shrinking.

When Lemaître alerted Einstein to what he’d found, Einstein scoffed. He thought Lemaître was pushing the math too far. So certain was Einstein that the universe, as a whole, was eternal and unchanging, that he not only dismissed mathematical analyses that attested to the contrary, he inserted a modest amendment into his equations to ensure that the math would accommodate his prejudice.

And prejudice it was. In 1929, the astronomical observations of Edwin Hubble, using the powerful telescope at Mount Wilson Observatory, revealed that distant galaxies are all rushing away. The universe is expanding. Einstein gave himself a euphemistic slap in the forehead, a reprimand for not trusting results coming out of his own equations, and brought his thinking—and his equations—into line with the data.

Great progress, of course. But new insights yield new puzzles.

As Lemaître had pointed out, if space is now expanding, then by winding the cosmic film in reverse we conclude that the observable universe was ever smaller, denser and hotter ever further back in time. The seemingly unavoidable conclusion is that the universe we see emerged from a phenomenally tiny speck that erupted, sending space swelling outward—what we now call the Big Bang.

But if true, what sent space swelling? And how could such an outlandish proposal be tested?

The Inflationary Theory
If the universe emerged from a sweltering hot and intensely dense primeval atom, as Lemaître called it, then as space swelled the universe should have cooled off. Calculations undertaken at George Washington University in the 1940s, and later at Princeton in the 1960s, showed that the Big Bang’s residual heat would manifest as a bath of photons (particles of light) uniformly filling space. The temperature of the photons would now have dropped to a mere 2.7 degrees above absolute zero, placing their wavelength in the microwave part of the spectrum—explaining why this possible relic of the Big Bang is called the cosmic microwave background radiation.

In 1964, two Bell Labs scientists, Arno Penzias and Robert Wilson, were at wits’ end, frustrated by a large ground-based antenna designed for satellite communications. Regardless of where they pointed the antenna, they encountered the audiophile’s nightmare: an incessant background hiss. For months they sought but failed to find the source. Then, Penzias and Wilson caught wind of the cosmological calculations being done at Princeton suggesting there should be a low-level radiation filling space. The incessant hiss, the researchers realized, was arising from the Big Bang’s photons tickling the antenna’s receiver. The discovery earned Penzias and Wilson the 1978 Nobel Prize.

The prominence of the Big Bang theory skyrocketed, impelling scientists to pry the theory apart, seeking unexpected implications and possible weaknesses. A number of important issues were brought to light, but the most essential was also the most
basic.

The Big Bang is often described as the modern scientific theory of creation, the mathematical answer to Genesis. But this notion obscures an essential fallacy: The Big Bang theory does not tell us how the universe began. It tells us how the universe evolved, beginning a tiny fraction of a second after it all started. As the rewound cosmic film approaches the first frame, the mathematics breaks down, closing the lens just as the creation event is about to fill the screen. And so, when it comes to explaining the bang itself—the primordial push that must have set the universe headlong on its expansionary course—the Big Bang theory is silent.

It would fall to a young postdoctoral fellow in the physics department of Stanford University, Alan Guth, to take the vital step toward filling that gap. Guth and his collaborator Henry Tye of Cornell University were trying to understand how certain hypothetical particles called monopoles might be produced in the universe’s earliest moments. But calculating deep into the night of December 6, 1979, Guth took the work in a different direction. He realized that not only did the equations show that general relativity plugged an essential gap in Newtonian gravity—providing gravity’s mechanism—they also revealed that gravity could behave in unexpected ways. According to Newton (and everyday experience) gravity is an attractive force that pulls one object toward another. The equations were showing that in Einstein’s formulation, gravity could also be repulsive.

Tags

Comment on this Story

comments powered by Disqus