[Paleopsych] New Scientist: The world turned inside out
checker at panix.com
Sun Jan 30 19:21:27 UTC 2005
The world turned inside out
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
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,
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
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.
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
"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
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.
More information about the paleopsych