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On St. Patrick’s Day, the BICEP2 collaboration published a stunning discovery —— traces of gravity waves created during “inflation”, our universe’s initial hyper-rapid expansion. This may well be the greatest discovery in physics of the last decade, and merits an immediate newsletter.
The Inflationary Big Bang theory is science’s best model of the evolution of our universe. This new evidence provides further validation of the entire theory and greatly strengthens its weakest link.
The Big Bang theory was first proposed in 1927 by George Lemaitre, a Roman Catholic priest and cosmologist. Lemaitre said our universe began as an infinitesimal “primeval atom” and expanded ever since. But the theory had several glaring problems.
In the late 1970’s, hoping to solve these problems, Alan Guth and Andre Linde independently proposed an addition to the Big Bang model: an initial, extraordinarily brief period of extraordinarily rapid expansion. Guth said the universe doubled in size at least 100 times, expanding trillions of trillions of times faster than the speed of light. (Inflation does not contradict Relativity; Einstein said no thing can travel through space faster than light, but space itself can expand at any speed.) Guth said this period of “inflation” stopped before the universe became 10–34 seconds old; that’s 100 trillionths of a trillionths of a trillionth of a second.
Why did Guth propose inflation — what problems did it solve? The explanation is too long for a newsletter, so I included it on my website: click here.
While inflation’s math successfully swept away the Big Bang’s problems, the idea seemed contrived. Inflation seemed like a rag sewn over a gaping hole in an elegant gown. But now, a key prediction of this ragtag theory has been confirmed, and inflation is becoming a fashionable accessory.
Inflation’s hyper-rapid expansion would produce immense gravity waves. First described by Einstein in 1916 in his theory of General Relativity, gravity waves are oscillations in the fabric of spacetime. Einstein said as energy and mass move they change the curvature of spacetime. These changes propagate outward at the speed of light in the form of a wave, alternately stretching and compressing space. (Think of throwing a rock into a pond and watching waves ripple outward.) The NASA Ames computer simulation below illustrates gravity waves emanating from two orbiting black holes.
Below is a sequence of images showing how a passing gravity wave would affect Earth. It would be stretched vertically and compressed horizontally (at t=1). Later it would be compressed vertically and stretched horizontally (at t=3). The stretching and compressing directions would flip-flop repeated as the wave passed, separated by moments of normalcy (t=0,2, and 4). Here, the effect is greatly exaggerated; in a typical case, Earth’s diameter would change by less than the size of one atom. This “quadrupole” trait is unique to gravity waves.
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In 1974, Hulse and Taylor discovered indirect evidence of gravity waves: two orbiting neutron stars slowly converging precisely as Einstein predicted, as gravity waves deplete their orbital energy. But many attempts to directly detect gravity waves have failed.
After 13.8 billion years, the gravity wave tsunamis of inflation have faded, becoming too faint to directly detect. But they left unique fingerprints in the Cosmic Microwave Background (CMB) radiation, a form of light that is the afterglow of the Big Bang’s primordial fireball. Inflation’s gravity waves imprinted “B-mode“ polarization in the CMB. (All forms of light are composed of photons with electromagnetic fields. In unpolarized light the photons’ fields point in many different directions, while in polarized light all the fields point in the same direction.)
The BICEP2 image below shows a small swatch of sky. Each short line indicates the direction and strength of CMB polarization at that location, while red marks areas of clockwise polarization twist and blue marks counterclockwise twist. The unique quadrupole nature of gravity waves imprints these B-mode twists.
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This is the first convincing direct evidence of gravity waves — gold stars to BICEP2, Guth, Linde, and Einstein!
To see back to the beginning of time, BICEP2 scientists went to the end of the world — the South Pole, where extreme cold provides Earth’s driest and clearest skies. Even the Antarctic is far too warm for their instruments, which were cooled below –450°F. For three years, BICEP2 scanned the sky with superb precision. Their research paper claims a B-mode signal that is 5.2 standard deviations above the background, meaning the chance that this is a statistical fluke is less than 1 in 3 million. Funded by NSF, BICEP2 includes scientists from Harvard, Caltech, Stanford, and the University of Minnesota.
This discovery opens an entire new field of research: ever better B-mode measurements and analyses promise new insights into the beginning of our universe.
Best Regards,
Robert
Mar 22nd, 2014
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South Pole Telescope, with BICEP2 at the left
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