What Made the Bang so Big?

        Earlier in 2014, cosmologists
        thought they were finally
        closing in on an answer
        to that age-old question, “How
        did it all begin?” In March,
        Harvard astrophysicist John Kovac
        announced that a small telescope
        at the South Pole called BICEP2
        (short for Background Imaging of
        Cosmic Extragalactic Polarization)
        had captured signals that apparently
        come from “the first trillionth of a
        trillionth of a trillionth of a second
        in the history of the universe.”
        Independent confirmation was
        still needed, said Kovac, who heads
        the BICEP2 team, but if the result
        held up, it would mean scientists were on the verge of
        witnessing and understanding the moment of creation
        for our cosmos. Then data from the European Space
        Agency’s Planck space telescope rolled in six months later,
        casting doubt over the earlier result. (See “Clouded by
        a Veil of Dust,” opposite page.) The world won’t know
        the final verdict until the BICEP2 and Planck scientists
        release their joint report.
        Assuming its findings
        are validated, BICEP2
        will have amassed the
        strongest support yet
        for cosmic inflation, a
        theory that attempts
        to explain exactly what
        happened during the
        Big Bang, the universe’s
        explosive birth event.
        Inflationary theory
        holds that our newborn
        universe started as a tiny fleck of matter, less than onebillionth
        the size of a proton, and grew exponentially fast
        — expanding faster than the speed of light, in fact, while
        doubling in size at least 100 times.
        Inflation is the brainchild of MIT physicist Alan Guth,
        who came up with the idea in 1979. “I didn’t think it
        would be tested in my lifetime,” says Guth, because when
        he dreamed up the theory, no one could conceive of a
        practical way to verify it.
        The runaway expansion lasted from about 10-36 of
        a second to 10-32 of a second after the Big Bang, but it
        would have deformed space violently enough to produce
        gravitational waves, just as a vibrating drumhead emits
        sound waves. These gravitational waves generated
        during inflation would be so weak by now, 13.8 billion
        years after the Big Bang, that they’d be undetectable.
        But in 1997, five physicists hit upon a possible strategy:
        Inflationary gravity waves could distort the light left over
        from the Big Bang in a discernible way.
        Eons after the primordial blast, this remnant light
        fills all space, constituting
        a faint glow everywhere in
        the sky known as the cosmic
        microwave background,
        or CMB. The key lies in
        determining how that vestigial
        light is polarized — basically,
        how the light waves are
        oriented. Inflation-era gravity
        waves, which alternately
        stretch and compress space
        as they pass through, would
        leave a permanent mark in the
        cosmic radiation background, adding a twist to the CMB
        polarization. This distinctive, swirling pattern is called a
        B-mode. If astronomers could detect that, they would, in
        effect, see the fingerprint of inflation.
        BICEP2 was specifically designed to look for this
        pattern. From 2010 to 2012, the telescope observed a
        small patch of sky visible from Antarctica. Kovac and
        his co-investigators — Jamie Bock of Caltech, Chao-Lin
        Kuo of Stanford and Clem Pryke of the University of
        Minnesota — then spent over a year scrutinizing the
        data. “We checked it 14 different ways to make sure it
        was consistent,” Kovac says, before announcing they had
        identified the telltale vortex-like pattern expected from 
        gravitational waves generated during inflation.
        The researchers believe the signal they detected
        was cosmic in origin and did not come from our own
        galaxy, although that point has come under question.
        The big issue is whether the BICEP2 investigators
        properly accounted for the effects of dust within our
        own galaxy, as it could also have given rise to the
        swirling B-mode pattern.
        While that’s being straightened out, the BICEP2
        team is moving ahead, poring over new data from the
        South Pole’s Keck Array, which is part of the series
        of experiments co-led by Kovac and his colleagues.
        BICEP3, BICEP2’s more sensitive successor, is set
        to begin a three-year observational run in early
        2015. And several competing groups are going after
        the B-mode signal as well.
        If the original claims are substantiated and the
        emerging picture of the universe’s beginning is upheld,
        what would that mean? First, it would tell us that
        gravitational waves, predicted by Einstein’s century-old
        theory of general relativity, really do exist. Second,
        it would greatly clarify our understanding of the
        Big Bang, telling us, as Guth puts it, “what banged
        and why it banged.” Third, it would build an almost
        ironclad case for inflation.
        Some uncertainty would still persist because
        cosmologists don’t fully grasp the underlying physics
        behind inflation. But the story of our universe’s first
        moments would, nevertheless, come into sharper focus
        than ever before — far beyond what many observers
        had deemed possible.

        2018-02-23 3:08 AM Comentarii 0 Vizitator What Made the Bang so Big?, 2015

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