[Paleopsych] New Scientist: The world turned inside out

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The world turned inside out
http://www.newscientist.com/article.ns?id=mg18124395.200
4.3.20

    IN EVERY time and in every culture, there have been stories of
    creation - how the universe began. In our time the story is that of
    the big bang, the incredibly hot, dense state from which the universe
    expanded. But this is not the whole story.

    "To believe that the big bang is the first moment of time is more
    religious mysticism than science," says Lee Smolin of the Perimeter
    Institute in Waterloo, Ontario, Canada. Smolin is not suggesting that
    the big bang never happened: astronomical observations and Einstein's
    general theory of relativity leave little doubt that it did. But they
    don't explain why it happened or what may have come before.

    Martin Bojowald of the Max Planck Institute for Gravitational Physics
    in Golm, Germany, has come up with a possible solution to this
    problem. He has taken a theory called loop quantum gravity, first
    proposed by Smolin, which ascribes a complex quantum architecture to
    space, and used it to peer into the core of creation. What he found
    there was not a beginning at all, but rather a portal to a universe
    that came before, a universe that, as it turned out, was completely
    inside out.

    The notion of the big bang arises from Edwin Hubble's discovery in the
    1920s that the universe is expanding right before our eyes.
    Cosmologists naturally followed the story backwards, and they now
    conclude that some 14 billion years ago, all the matter in the
    universe must have been crammed into a single, dimensionless point.

    But Einstein's equations of general relativity can't describe what
    happens at this point, called a singularity - let alone what could
    have come before it. They can only predict that at the singularity,
    space warps beyond repair. So, while relativity can give us a
    comprehensive account of our cosmic beginnings, it cannot tell us what
    caused the big bang to happen.

    Fortunately, general relativity is not the only theory in the cosmos.
    When it comes to the very small - the realm of atoms and electrons and
    quarks - quantum mechanics reigns. Both theories allow physicists to
    understand the world before them with incredible precision, and in
    that sense both theories are "right". But there's a catch: they
    completely contradict one another in their descriptions of the basic
    structure of space itself. Unlike the active, malleable fabric of
    general relativity, the space of quantum theory is a fixed and passive
    backdrop against which elementary particles dance. It can't be both.

    This problem becomes particularly pronounced when dealing with space
    in its most extreme condition - at the singularity that lies in the
    belly of the big bang. There, the intense gravity requires a
    description from general relativity, while the incredibly small volume
    brings quantum mechanics to bear. Physicists need a new theory of
    quantum gravity that can reconcile both these worlds.

    For years string theory, which says that elementary particles have a
    structure that resembles tiny loops of string, was the only contender.
    But in the 1990s Smolin and colleagues developed an alternative - the
    theory of loop quantum gravity. And LQG can cope with the singularity,
    says Bojowald.

    Smolin, working with a small group of physicists including Ted
    Jacobson, Abhay Ashtekar and Carlo Rovelli, developed LQG by rewriting
    the equations of general relativity in a quantum framework. The new
    framework described space as if it were made up of tiny loops a mere
    10-35 metres in diameter. These loops, the team suggested, are the
    very building blocks of space. Understanding the structure of the
    universe became a matter of understanding how the loops link together.
    The web-like networks of the theory, called spin networks, encode on a
    two-dimensional map all the information needed to construct a
    three-dimensional quantum space. So, for example, each vertex on the
    web is taken to represent a volume in space, while each line
    represents an area. According to the theory, both the volumes and
    areas can only increase in discrete steps.

    But how can this web-like pattern tell us anything about the origin of
    the universe? The key is that the passage of time can be represented
    as a function of the volume of the loop universe, something that is
    possible in other theories that attempt to construct space-time from
    individual quanta (New Scientist, 4 October 2003, p 36). Since volume
    is made up of individual loops, time also hops along in discrete
    jumps. As Bojowald followed cosmic evolution backwards, the volume
    grew smaller and smaller until it reached the big bang itself. And
    that was where things got really interesting.

    In the quantum network, areas and volumes are finite and indivisible.
    There cannot be a singularity, because space just cannot get that
    small. And since the theory no longer broke down, Bojowald could
    continue following time back beyond what had previously been viewed as
    the beginning.

    There he found an entire universe on the other side of time zero, a
    looking-glass world where expansion is replaced by contraction - and a
    big crunch reflects our big bang. "When we follow the universe beyond
    the classical singularity, we can do so forever, until we reach
    negative infinity," Bojowald explains. "Therefore, the universe does
    not have a beginning. It has always existed."

    The looking-glass universe would have looked very similar to the one
    we know, with all the same laws of physics. Except, that is, for one
    bizarre thing: it was inside out. Because Bojowald measured time in
    volume, he found that as he ventured into negative time, the
    orientation of space flipped so that its volume and other spatial
    quantities became negative.

Cosmic event

    Bojowald likens the spatial flip to a balloon. If we idealise a
    balloon as a perfect sphere, and then deflate it, it will collapse to
    a single point. If we then imagine it continuing to collapse even
    further, all the points will pass through one another until the
    balloon reinflates, with the inside of the sphere now on the outside.
    Any object in the balloon would be reversed left to right, and that is
    just what happens in the universe before the big bang.

    So would this make a difference? "This would be mostly imperceptible,"
    says Smolin, "as most properties of the universe and most of the
    fundamental laws are symmetric under the exchange of left for right."
    But there are a few exceptions. Some reactions involving neutrinos and
    kaons are asymmetrical, because the reactions' products are
    preferentially spinning in one direction rather than the other. In the
    universe on the other side of the big bang looking glass, those
    directions are reversed. So although in Bojowald's model the big bang
    no longer marks a beginning of time, it remains a vitally significant
    event in cosmic history: the time when space flipped over, and left
    and right reversed. The universe has an eternal past, but all the
    details of the big bang evolution that have been worked out by
    cosmologists on this side of the big bang still apply.

    The theory also provides a way to explain why the early universe
    apparently underwent the brief but extraordinarily fast period of
    expansion known as inflation. As soon as the universe flips from
    inside out to the right way round, it starts expanding. But because
    volume is made up of individual loops, it cannot grow smoothly.
    Instead, it tends to jump stepwise, and this creates a kind of outward
    pressure on the universe. This, it turns out, is just what is needed
    to get the universe inflating, and removes the need to introduce any
    arbitrary fields like the inflaton, without which inflation cannot be
    explained in standard models of the big bang.

    The same scenario could solve another problem in general relativity:
    revealing what happens in the dark depths of black holes. Here, too,
    singularities resist any description in terms of classical general
    relativity. Relativity says at most that time stops at the centre of a
    black hole, and light rays halt in their tracks. In Bojowald's
    picture, the space of the black hole may invert itself and open up
    into an entirely new inside-out universe. Smolin, for one, has long
    believed that black holes in our universe hide umbilical cords to a
    host of baby universes.

    Smolin and Bojowald's ideas remain controversial among the majority of
    physicists. Most, like Sean Carroll of the University of Chicago,
    believe that string theory is closer to the right track than LQG. "The
    best evidence is the incredible fruitfulness of the string theory
    idea," Carroll says. From the idea of strings, physicists have been
    able to derive all the symmetries of space-time and the forces we see.

    String theorists even have their own ideas on what caused the big
    bang: a collision between membranes or "branes" existing in higher
    dimensions (see "Can String theory solve the singularity puzzle?"). In
    their picture, too, the universe has always existed.

    But Smolin points out that string theory cannot explain one important
    feature of nature: space. In LQG, general relativity - and with it,
    the notion of space - is built in from the start. String theory, by
    contrast, takes quantum mechanics as its starting point, and so the
    strings wiggle against a fixed spatial background that is unaccounted
    for by the theory.

    Supporters of Bojowald's approach say this means that applications of
    string theory to the singularity just don't work as well. Too many
    assumptions are involved both in what strings are and in how they
    behave. Smolin finds Bojowald's approach far more elegant. "Martin's
    work is clean," he says. "The only assumptions are the principles of
    general relativity and of quantum mechanics."

    Elegant calculations are one thing, but what about experimental
    evidence for LQG and the looking-glass universe? At the moment there
    is none, but that may change within a few years when NASA's Gamma Ray
    Large Area Space Telescope (GLAST), scheduled for launch in 2006,
    starts getting results.

    Giovanni Amelino-Camelia of Harvard University suggests using its data
    to track gamma-ray photons from billions of light years away. In our
    everyday lives the effects of loopy space are negligible, but if space
    is grainy on the smallest scale, as LQG says it is, then the gamma-ray
    photons will have accumulated a noticeable spread during their
    billions of years travelling through space. An instrument like GLAST
    should be able to observe such an effect, and when its measurements
    are analysed it may turn out that the big bang is just one small piece
    of a much bigger story

Can string theory solve the singularity puzzle?

    String theorists have their own ideas about what came before the big
    bang - and they do not include a looking-glass universe. String
    theorist Gabriele Veneziano, for one, has attempted to use the finite
    size of strings to avoid a singularity, leading him to a universe that
    has existed forever (New Scientist, 3 June 2000, p 24).

    And physicists Paul Steinhardt of Princeton University and Neil Turok
    of the University of Cambridge, UK, proposed a model in which the
    extra dimensions of string theory are put to cosmological use (New
    Scientist, 16 March 2002, p 26). According to their "cyclic model",
    the three dimensions of space we experience actually live on the
    surface of a brane (short for "membrane") that is floating in an
    additional dimension. Another brane hovers a microscopic distance from
    ours, and every few trillion years the two branes collide. What we
    perceive as the big bang, the model says, is just one of these
    collisions.

    "The idea that underlies the cyclic model," explains Steinhardt, "is
    that what appears to be a classical singularity in the usual 3-space
    plus one time dimension corresponds to a collision between branes in
    an extra dimension. There is a singularity in the sense that an extra
    dimension is disappearing, but it's not our three dimensions that are
    disappearing."

    This cycle, in which the branes move toward one another, collide, and
    then move apart again, can repeat over and over again eternally, which
    means the universe may never have had a beginning. The model also
    makes testable predictions. In the standard model of cosmology,
    inflation would have stirred up gravitational waves whose imprints
    should still be discernible in the cosmic microwave background. The
    cyclic model, however, doesn't need inflation, so it predicts no such
    primordial gravity waves. Experiments that look for gravitational
    waves may be able to distinguish between the two.