SPACE-TIME FOAM

[spectre]

GAMMA GAMMA HEY
http://blogs.discovery.com/cosmic_ray/2009/08/could-death-spiral-spell-doomsday.html
"A gamma-ray burst from a star a few thousand light-years away would
have a threefold impact on Earth. First it would tear up nitrogen and
oxygen molecules in the atmosphere and they would combine to form
nitrous oxides. These would eat up the ozone layer causing a flood of
ultraviolet radiation to reach Earth. The smoggy oxides would darken
the atmosphere, and cool the Earth. The nitrous oxides would rain as
nitric acid, devastating vegetation. Did I say nitrous oxide? Does
that mean we would die laughing?"

WHY LIGHT RUNS LATE
http://brightcove.newscientist.com/services/player/bcpid2227271001?bctid=33527827001
http://www.newscientist.com/gallery/mg20327210-gamma-ray-telescopes
http://www.newscientist.com/article/mg20327210.900-late-light-reveals-what-space-is-made-of.html
Late light reveals what space is made of
BY Anil Ananthaswamy / 12 August 2009

ON THE night of 30 June 2005, the sky high above La Palma in Spain's
Canary Islands crackled with streaks of blue light too faint for
humans to see. Atop the Roque de los Muchachos, the highest point of
the island, though, a powerful magic eye was waiting and watching.
MAGIC - the Major Atmospheric Gamma-ray Imaging Cherenkov Telescope -
scans the sky each night for high-energy photons from the distant
cosmos. Most nights, nothing remarkable comes. But every now and
again, a brief flash of energetic light bears witness to the violent
convulsions of a faraway galaxy. What MAGIC saw on that balmy June
night came like a bolt from the blue. That is because something truly
astounding may have been encoded in that fleeting Atlantic glow:
evidence that the fabric of space-time is not silky smooth as Einstein
and many others have presumed, but rough, turbulent and fundamentally
grainy stuff.

It is an audacious claim that, if verified, would put us squarely on
the road to a quantum theory of gravity and on towards the long-
elusive "theory of everything". If it were based on a single chunk of
MAGIC data, it might easily be dismissed as a midsummer night's dream.
But it is not. Since that first sighting, other telescopes have
started to see similar patterns. Is this a physics revolution through
the barrel of a telescope? Such incendiary thoughts were far away from
Robert Wagner's mind when the MAGIC data filtered through to the Max
Planck Institute of Physics in Munich, Germany, the morning after. He
and his fellow collaborators were enjoying a barbecue. Not for long.
"We put our beers aside and started downloading the full data set,"
says Wagner.

It was easy to pinpoint the source of the data blip - a 20-minute
burst of hugely energetic gamma rays from a galaxy some 500 million
light years away known as Markarian 501. Its occasional tempestuous
outbursts had already made it familiar to gamma-ray telescopes
worldwide. This burst was different. As Wagner and his colleagues
analysed the data in the weeks and months that followed, an odd
pattern emerged. Lower-energy photons from Markarian 501 had outpaced
their higher-energy counterparts, arriving up to 4 minutes earlier
(Physics Letters B, vol 668, p 253).
http://arxiv.org/abs/0708.2889

This should not happen. If an object is 500 million light years away,
light from it always takes 500 million years to get to us, no more, no
less. Whatever their energy, photons always travel at the same speed,
the implacable cosmic speed limit: the speed of light. Perhaps the
anomaly has a mundane explanation. We do not really understand the
processes within objects such as Markarian 501 that accelerate
particles to phenomenal energies and catapult them towards us. They
are thought ultimately to have something to do with the convulsions of
supermassive black holes at the objects' hearts. It could be that
these mechanisms naturally spew out low-energy particles before high-
energy ones. Or they might not. "The more fascinating explanation
would be that this delay is not intrinsic to the source, but that it
happens along the way from the source to us," says Wagner.

Quantum signature
What piqued the interest of Wagner and his colleagues was that the
MAGIC observations were showing just the sort of effect that quite a
few models of quantum gravity predict. Physicists have been on the
lookout for experimental signposts to the right theory for the best
part of a century. "All approaches to quantum gravity, in their own
very different ways, agree that empty space is not so empty after
all," says theorist Giovanni Amelino-Camelia of Sapienza University of
Rome in Italy. Many models based on string theory suggest that space-
time is a foamy froth of particles, and even microscopic black holes,
that spark up out of nothing and disappear again with equal abandon.
The alternative approach favoured by Amelino-Camelia, loop quantum
gravity, posits that space-time comes in indivisible chunks of about
10-35 metres, a size known as the Planck length.

Last year, it was suggested that the signature of just such a quantum
space-time had popped up in unexplained noise plaguing a gravitational-
wave detector in northern Germany (New Scientist, 17 January 2009, p
24). But that interpretation is far from a done deal, and most experts
agree that a more substantive sighting could only come from observing
the possible interactions of space-time with particles passing through
it. According to many string theory models, particles of different
energies should speed up or slow down by different amounts as they
interact with a foamy space-time. A minimum size for space-time
grains, as predicted by loop quantum gravity, could violate the
cherished principle of special relativity known as Lorentz invariance,
which states that the maximum speed of all particles, regardless of
their energy, is the speed of light in a vacuum.

The trouble is that these effects would be observable only with
particles far more energetic than even the beefiest terrestrial
particle accelerators can produce. Even if we could make these
particles, the tiny interactions between them and the fabric of space-
time would not add up to a hill of beans, even over many laps of the
Large Hadron Collider's 27-kilometre-long loop at CERN, near Geneva,
Switzerland. Summed over hundreds of millions or billions of light
years, such interactions could account for the MAGIC travel-time
anomaly. It looks like nature might have provided us with particle
accelerators - distant galaxies - whose products could, for the first
time, allow us to test predictions of quantum gravity against hard
experimental evidence.

As yet, we have only seen a handful of gamma-ray bursts of the energy
and intensity needed to see whether the delay effect is a consistent
feature. In July 2006, the High Energy Stereoscopic System (HESS), an
array of gamma-ray telescopes in the desert of Namibia, saw a high-
energy flare erupt from an active galaxy nearly four times as far away
as Markarian 501. The burst contained marginal evidence for a time-lag
of around half a minute for the most energetic photons, which were
considerably less energetic than those in the flare spotted by MAGIC.
The uncertainties in the data resulting from the detection process,
however, made a definitive statement impossible (Physical Review
Letters, vol 101, p 170402).
http://arxiv.org/abs/0810.3475

It is recent results from NASA's Fermi Gamma-ray Space Telescope,
launched last year, that provide the most tantalising glimpse yet of
something extraordinary going on out there. Last September, it spied a
burst of gamma rays from a source nearly 12 billion light years away.
According to an analysis by Amelino-Camelia and Lee Smolin of the
Perimeter Institute for Theoretical Physics in Waterloo, Canada, the
zippiest low-energy photons beat some of the high-energy stragglers to
Earth by anything up to 20 minutes. Two much closer bursts seem to
contain much smaller delays.
www.arxiv.org/abs/0906.3731v2

The individual observations are pretty consistent with each other,
too, says theorist John Ellis at CERN. He and colleagues have taken
data from the MAGIC and HESS bursts to calibrate a theoretical model
inspired by string theory that assumes the delay effect increases
linearly with distance and photon energy. Using it to estimate the
delay that the highest-energy photon in the Fermi space telescope's
September burst should have experienced, they came up with a figure of
25 seconds, plus or minus 11 seconds. What Fermi had measured for that
particular photon was 16.5 seconds - within the model prediction's
admittedly large margin of error.

The only way to find out conclusively whether the delays are a
consistent signature of a quantised or foam-like space-time, says
Ellis, is to get more data - ideally from sources at many different
distances. "Then we'll be able to see whether we can distinguish
between effects at the source and effects in the propagation," he
says.

Worldwide cover
We also need to observe the same burst with more than one instrument.
Each telescope is sensitive to a different energy range, owing to its
altitude and detector set-up. Combining different data sets will
provide a wider spread of energies from which to tease out any energy-
dependent effect, and also help us get round a persistent irritant to
consistent astronomical observations: Earth's rotation. Not only does
our planet's spin mean that multitudes of photons from the sun
overwhelm any cosmic source for a large proportion of the day, but it
also makes observing a highly directed beam of gamma rays from one
specific direction tricky, even at night: as you train your telescope
on your target, the Earth moves beneath your feet and eventually the
source slips out of sight.

That means MAGIC can observe any burst for a maximum of only 6 hours
on any given night, assuming it is pointing in the right direction
when a new burst arrives. That period could be doubled by using it in
conjunction with a similar instrument - the Very Energetic Radiation
Imaging Telescope Array System (VERITAS) - that sits atop Mount
Hopkins in southern Arizona.

A further gamma-ray telescope, the Major Atmospheric Cherenkov
Telescope Experiment (MACE), 4500 metres up on the Tibetan plateau in
the remote region of Ladakh, India, will open that observational
window still further. When completed in 2011, MACE will be the highest-
altitude gamma-ray telescope in the world, capable of observing gamma
rays with a wide range of energies. "Then we will have another
observatory 5 to 6 hours in front of MAGIC," says Wagner. "That could
lead the way to a continuous, 24-hour observation of certain objects."

What with that and the new high-accuracy data from the Fermi space
telescope, gamma ray telescopes could well uncover quantum space-time
within the next few years. Even so, they still might be beaten to the
line. The definitive answer might come from a very different source,
and a very different quarter of Earth's surface - the South Pole.

That is because a cubic kilometre of ice under the South Pole will
soon be home to the IceCube Neutrino Observatory, whose strings of
detectors will watch for faint flashes of blue light emitted when
neutrinos from cosmic sources smash into the Antarctic ice. Neutrinos
are ghostly particles thought to be produced in the same violent
events that produce high-energy gamma rays. As yet, we have not seen
any neutrinos from outside our galaxy, barring some that burst on us
from a supernova in a neighbouring galaxy, the Large Magellanic Cloud,
in 1987. The neutrinos we do see are lower-energy ones that come from
nuclear reactions in the sun and particle interactions in Earth's
atmosphere. IceCube aims to change that.

And it could see something big. Because the quantum-mechanical
wavelengths associated with neutrinos of the very highest energies are
even smaller than those of high-energy photons, they could be more
susceptible to disruption through interactions with a space-time that
is grainy on very small scales. Francis Halzen of the University of
Wisconsin, Madison, who leads the IceCube experiment, has calculated
together with his colleagues that in one favoured model of quantum
space-time such interactions could dramatically speed up higher-energy
neutrinos (Physical Review D, vol 72, p 065019). "It's a beautiful
signal that could not be explained by conventional astrophysics," he
says.

Humble constructions
That's not the only attractive property of neutrinos when it comes to
testing the idea of a frothy space-time, says Dan Hooper of Fermilab
in Batavia, Illinois. Neutrinos come in three distinct "flavours",
named after the chunkier particles they are associated with - the
electron, the muon and the tau. They tend to morph back and forth
between these different states as they travel, a phenomenon known as
neutrino oscillation. If a distant source is emitting only electron
neutrinos, theory tells us how many should have changed flavours by
the time they reach us.

If neutrinos were interacting with the quantum foam, though, they
would forget their original flavour along the way, leading to equal
numbers of all flavours by the time they arrive here. "That effect
would be hard to explain with normal astrophysics," says Hooper. He
suggests a possible, albeit disputed, source of electron neutrinos in
the Cygnus region of the Milky Way that could be ripe for
investigation (Physics Letters B, vol 609, p 206).

Uncertainties in models of neutrino oscillations make exact
calculations of the expected extent of the flavour-equalising effect
difficult, as Hooper himself points out. And even if we do strike it
lucky and find indisputable signs that either neutrinos or gamma rays
are being affected by the structure of space-time, it will be a long,
hard slog to convert that evidence into a viable theory of quantum
gravity. Amelino-Camelia likens the situation now to that of a century
ago, when anomalous observations - such as the spectrum of black-body
radiation, or the photoelectric effect - that could not be explained
by classical means set physics on the decades-long path towards a
fully fledged quantum theory. It did not come easy.

And so it will be for quantum gravity. "We have to build, humbly, very
humbly, from what we know," says Amelino-Camelia. "Construct simple
theories, which are very far from being a theory of everything, but
intelligible enough that they can guide us to the next spark." Whether
on Atlantic islands, in the Himalayas, deep in the Antarctic ice or
high above Earth's atmosphere, watchful eyes are waiting for signs
from the universe's quantum fabric.

Quantum gravity: why we care
On the scale of profound things in physics, quantum gravity scores an
easy 10 out of 10. Currently, three of the four fundamental forces of
nature can be explained by the exchange of force-carrying particles
that follow the rules of quantum theory. Gravity cannot. According to
Einstein's general theory of relativity, the force arises from the
smooth warping of space-time by massive objects. As such, it remains
resolutely outside the purview of quantum physics.

That must change, physicists agree. Without a quantum theory of
gravity, we not only lack an overarching theory of the workings of the
world, but we are also never going to be able to probe back to the
first tiny fractions of a second after the big bang - a crucial and
eventful period in the evolution of the universe.

The trouble is, there is no agreement on how to get to that theory.
String theory, the avenue preferred by most physicists, melds gravity
and quantum mechanics by arguing that everything in nature arises from
the vibration of tiny strings in 10-dimensional space-time. It has
been roundly criticised, though, for failing to come up with any
prediction that experiments might verify. A rival approach, called
loop quantum gravity, shows mathematically that space-time is woven
out of loops of gravitational field lines. In the evidence stakes, it
has fared no better.

"For many decades, research on quantum gravity was being monopolised
by the idea that we needed to get a perfect theory, with geniuses
producing perfect mathematics, and with no guidance from experiments,"
says Giovanni Amelino-Camelia of Sapienza University of Rome in Italy.
The geniuses desperately need something to tether their models to
reality. For that, they could do with a touch of MAGIC.

QUANTUM GRAVITY
http://arstechnica.com/science/news/2007/08/probing-quantum-gravity-with-gamma-ray-bursters.ars
Probing quantum gravity with gamma ray bursters : Researchers use
gamma ray bursters to show the influence of quantum gravity on the
refractive index of the vacuum
BY Chris Lee / August 23, 2007

With quantum mechanics the undisputed king of the small, and general
relativity governing the very large, physics has developed fantastic
descriptive power. With one exception: where quantum mechanics meets
general relativity, neither theory is very good. This meeting point
occurs when there is a lot of energy in a very small space. Now, even
though the distance suggests that quantum mechanics should rule, the
energy tells us that gravity is just as influential. However, our
understanding of gravity is based on a smooth space-time, while
quantum mechanics tells us that, at some scale, everything is
discrete. Applying general relativity to a discrete space-time yields
results that are absurd. So, for the last 40 odd years, physicists
have been searching for a way to unify general relativity and quantum
mechanics.

Despite the fact that there is no unified theory, we know a lot about
what features it must possess. This gives experimental physicists and
astronomers something to do while the theorists sit around waiting for
their muse to turn up. One of the common features of most quantum
gravity theories is the prediction that the vacuum will be dispersive
for very high-energy photons (e.g., 150GeV or more). What that implies
is that higher energy photons experience a slightly higher refractive
index than lower energy photons, which means that the high energy
photons travel slower through the vacuum and arrive later than the low
energy photons.

In research submitted to Physical Review Letters, a large
collaboration of astronomers are hoping to publish the first
observational evidence for quantum gravity. By observing the burst
characteristics of two gamma ray bursters, the team was able to
conclude that the vacuum was indeed dispersive. This is not quite as
simple as it sounds. Getting the data was simply the first part. To
show that the high-energy photons did indeed travel slower, they also
had to reconstruct the emission profile of the source. That is, using
only the data they collected, they had to figure out when the photons
were emitted relative to each other.

Various methodologies of source reconstruction were used. For
instance, we know that the apparent duration of the gamma ray burster
is only going to be increased by dispersion, so the dispersion can be
figured out by "undoing" the dispersion such that as much energy as
possible is emitted during the most active part of the flare. In a
related method, the total duration of the flare can be minimized,
giving another value for the dispersion. They found that both methods
give overlapping values for the time delay and a related quantum
gravity mass (a scaling parameter used to obtain the dispersion). As
befits a ground breaking observation, the error bars are rather large,
coming in at around +70 percent and -25 percent—they really needed
that tighter lower bound.

Their results—a time difference of 3–4 seconds after traversing huge
distances—rely heavily on the reconstruction of the source's emission
profile so they also checked that using computer models. Essentially,
they made up a bunch of sources that gave photons arbitrary emission
times and tested their ability to calculate the vacuum dispersion on
those. More specifically, they used computer generated profiles that
were then dispersed by a vacuum that was either dispersive or non-
dispersive. In all cases they recovered the original source profile to
within the uncertainty of they experimental observations. This tells
us that the source profile is probably the leading cause of
uncertainty in these observations.

Has quantum gravity made a sudden leap forward? Probably not, but this
is the first real data against which such a theory can be tested,
which means that theorists will suddenly have to start paying
attention to experimental results again and modify their theories
appropriately.

MAGIC
http://magic.mppmu.mpg.de/
HESS
http://www.mpi-hd.mpg.de/hfm/HESS/
FERMI
http://fermi.gsfc.nasa.gov/
VERITAS
http://veritas.sao.arizona.edu/
ICE CUBE
http://www.icecube.wisc.edu/info/explained.php
BOONE
http://www-boone.fnal.gov/index.html

CONTACT
Robert Marcus Wagner
http://www.rwagner.de/
http://www.mpp.mpg.de/~rwagner/
email : rwagner [at] mppmu.mpg [dot] de / rw [at] rwagner [dot] de

Giovanni Amelino-Camelia
http://www.roma1.infn.it/~amelino/
email : amelino [at] roma1.infn [dot] it

Francis Halzen
http://icecube.wisc.edu/~halzen/
email : halzen [at] icecube.wisc [dot] edu

Dan Hooper
http://home.fnal.gov/~dhooper/
email : dhooper [at] fnal [dot] gov

John Ellis
http://library.web.cern.ch/library/Archives/isad/isath.html
http://en.wikipedia.org/wiki/John_Ellis_(physicist)
email : john.ellis [at] cern [dot] ch

Lee Smolin
http://www.leesmolin.com/
http://www.edge.org/3rd_culture/bios/smolin.html
email : lsmolin [at] perimeterinstitute [dot] ca

QUANTUM FOAM
http://www.astronomycafe.net/qadir/ask/a11792.html

This is an idea that was originally proposed by Nobel physicist John
Wheeler back in the early 1960's to describe what space-time 'looks
like' at scales of 10^-33 centimeters. The basic idea is that gravity
is a field with many of the same fundamental properties as the other
fundamental 'force' fields in Nature. This means that the state of
this field is, at some level, uncertain and described by quantum
mechanics. Since Einstein's general theory of relativity requires that
gravitational fields and space-time be one and the same mathematical
objects, this means that space-time itself is also subject to the
kinds of uncertainty required by quantum systems. This indeterminacy
means that you cannot know with infinite precision BOTH the geometry
of space-time, and the rate of change of the space-time geometry, in
direct analogy with Heisenberg's Uncertainty Principle for quantum
systems.

Wheeler imagined that this indeterminacy for space-time required that
at the so-called Planck Scale of 10^-33 centimeters and 10^-43
seconds, space-time has a foaminess to it with sudden changes in its
geometry into a wealth of complex shapes and textures. You would have
quantum black holes appear at 10^-33 centimeters, then evaporate in
10^-43 seconds. Wormholes would form and dissolve, and later theorists
even postulated 'baby universe' production could happen under these
conditions. The problem is that we have no evidence that 1) gravity is
a quantum field and 2) that space-time has this type of structure at
these scales.

CONTACT
John Hagelin
http://hagelin.org/about.html
email : JHagelin [at] malawpc [dot] com

SPACE-TIME BOILS
http://www.youtube.com/watch?v=84_kXpsDJEk
http://ldolphin.org/qfoam.html
Is the fabric of the Universe a seething mass of black holes and
wormholes?
BY Michael Brooks Lewes / New Scientist / 19 June 1999

On your kitchen table are the following implements: a chainsaw, a
wooden mallet and a pair of boxing gloves. Your mission, should you
choose to accept it, is to use one of these tools to split an atom. It
is, of course, a ridiculous assignment, but it would sound like
child's play to researchers studying quantum gravity. They believe
that the very fabric of space-time is a seething foam of wormholes and
tiny black holes a hundred billion billion times smaller than a
proton. But the experimental tools available to test this idea are
absurdly clumsy: the best particle accelerators can barely examine
scales a million billion times larger.

"Many people have said it's going to be impossible to test quantum
gravity, so there's no use even thinking about it," says John Ellis, a
theorist at CERN, the Geneva-based European centre for particle
physics. But, he says, it's too important to ignore. Quantum gravity
is needed to describe the first instants of creation, when quantum
fluctuations ruled the Universe, and it could even lead us to a full
understanding of how our Universe works-the elusive Theory of
Everything that will tie all the forces of nature together. "This is
the grand theoretical challenge the 20th century has left physics to
solve in the 21st century," says Ellis. "Even if it looks hopeless you
should nevertheless think about it."

Astonishingly, it doesn't look hopeless any more. Since the beginning
of this year, physicists have proposed a handful of foam-probing
experiments that could shed light on quantum gravity. Against all the
odds, they can now embark on a journey down to the lowest level of
reality, where quantum mechanics and gravity meet. Quantum mechanics
describes how particles interact with each other to generate all but
one of the forces in nature. So most physicists believe it must work
for gravity, too. But how? The best description of gravity we have is
Einstein's theory of general relativity, which says that what we feel
as gravity is actually the effect of curved space-time. General
relativity works beautifully for gravitational forces in the Universe,
successfully predicting the existence of such outlandish objects as
black holes.

But problems are looming, Ellis says. "We know there are
inconsistencies in these theories. It's just a question of when the
inconsistencies are going to show up in the data." The best solution
would be to find the underlying theory from which relativity and
quantum mechanics can be inferred. There's no telling what insights
such a theory would yield. Physicists struggling to marry Einstein
with quantum mechanics have already made one startling discovery. In
1971, Russian physicist Yakov Zel'dovich guessed that black holes
aren't truly black, but instead combine with quantum-mechanical
fluctuations to emit photons and other particles. Stephen Hawking
proved the idea three years later, and these emissions are now called
Hawking radiation.

All fledgling theories of quantum gravity also make a more general and
even weirder prediction: the structure of space and time is very
different from the gentle curves predicted by general relativity. The
American physicist John Wheeler realised in the 1950s that if you look
at things on a scale of about 10-35 metres, quantum fluctuations
become powerful enough to play tricks with the geometry of the
Universe. Space and time break down into "fuzziness" or "foaminess". A
spaceship that size could find itself negotiating virtual black holes,
or getting sucked into one wormhole after another and tossed back and
forth in time and space.

If you think this idea of a space-time foam sounds horribly vague,
you're in good company. So do the researchers. "It's a very vague
thing," says Chris Isham, a theoretician at Imperial College, London.
"General relativity is about space-time, and quantum theory tends to
involve quantum fluctuations in things. Therefore, if you talk about
quantum gravity, there might be some sort of fluctuation in something
to do with space-time. It's that sort of level of argument."

In the race to create a more substantial theory of quantum gravity,
there are two main contenders. Abhay Ashtekar of Pennsylvania State
University contends that space and time aren't fundamental properties
of the Universe. Instead, they are supposed to emerge from a purely
mathematical theory ("Beyond space and time", New Scientist, 17 May
1997, p 38). But impressive as the mathematical framework is, no one
is sure how to pull physical realities, like space, time and gravity,
from it.

Cat's cradle
The other idea is based on superstrings: minuscule loops or strings
about 10-35 metres long, floating through space-time. Matter arises
from specific kinds of vibration in these strings, just as notes are
the result of certain vibrations of a violin string. There are a huge
number of variants of the strings idea, but researchers believe that
they are merely different versions of a single, all-encompassing
structure called M-theory ("Into the eleventh dimension", New
Scientist, 18 January 1997, p 32). This is physicists' favourite
Theory of Everything, with the potential to unite all the forces of
nature and explain the properties of every subatomic particle. But it
is still in its infancy, and so far has little to say about how
quantum gravity manifests itself in the Universe.

Giovanni Amelino-Camelia of the University of Neuchâtel in Switzerland
decided not to wait around for the theorists to agree on what exactly
is going on. Earlier this year, he published some calculations in
Nature which imply that quantum gravity is accessible to experiments
after all. If space-time is a frothing mess, he reasoned, the distance
between two objects should always have some random fluctuations as the
bubbles constantly form and burst. And by measuring the amounts of
fluctuation, we might be able to rule out some of the theories-or even
discover some real quantum foam.

So rather than the usual tool of fundamental physics-a superpowerful
particle accelerator-what he needed was a good tape measure. The
California Institute of Technology has just such a device. Their
interferometer splits a laser beam in two, and bounces the resulting
beams off two mirrors, each 40 metres away but in different directions
(see Diagram). The reflected beams are then recombined, producing an
interference pattern that reveals tiny changes in the paths they took
to reach the mirrors. If the path lengths fluctuate, the interference
pattern will fluctuate too-it will be "noisy".

Amelino-Camelia compared the [Detecting quantum foam] noise levels in
the Caltech Detecting quantum foam interferometer with the noise that
quantum gravity theories predict. So far, he reckons this experiment
has seen off at least one approach to quantum gravity. Theories based
on "deformed Poincaré symmetry" say that quantum mechanics distorts
certain symmetries of space-time-its immunity to rotation, inversion
and other similar changes. But it turns out that that would produce
bigger random fluctuations than the Caltech system's noise limit, so
Amelino-Camelia politely suggests that this approach is almost
certainly wrong. This is no mean feat, as the fluctuations he's
talking about are equivalent to a change of 1 metre in the diameter of
the Universe.

That still leaves superstrings and the Ashtekar approach undamaged.
But finally, quantum gravity theories are tethered on an experimental
leash, and there are other plans in the making to help pin down this
fuzzy foaminess. Last year, working with Amelino-Camelia and
researchers from the University of Athens, Houston Advanced Research
Center and Texas A&M University, Ellis suggested using gamma-ray
bursts. These flashes of high-energy photons arrive at Earth from the
other side of the cosmos, and if they have travelled through a space-
time that is fuzzy, says Ellis, they should have become distorted.
Roughly speaking, the shorter wavelength photons in the burst should
arrive at Earth later than their long wavelength companions, because
they fall down the microscopic holes in space-time more easily. Using
today's gamma-ray detectors, it should be possible to see this effect.
Unfortunately, the researchers are still working out exactly what a
quantum gravity signature would look like.

Decay and transformation
Ellis has helped to develop yet another plan for unveiling quantum
gravity, one first suggested in 1995. The delicate physics of neutral
kaons, subatomic particles that exist for less than a millionth of a
second, could be affected by quantum fluctuations in space-time. Kaons
and their antiparticles (antikaons) decay and transform into each
other, but they do it at very slightly different rates. Ellis believes
that quantum gravity may affect-in a very small way-these decay and
transformation rates. As with the gamma-ray bursts, predicting the
effect precisely is still beyond the theorists, but it might be
possible to isolate it in future particle accelerator experiments

While we wait for these experiments to mature, a new generation of
interferometers could eliminate a few more theories. These
interferometers are designed to search for another peculiar
gravitational phenomenon: gravity waves. Although gravity waves have
nothing to do with quantum gravity directly, they could still have a
big impact on its theory-makers. When massive objects such as stars
move very suddenly, general relativity says that they should send
space-time ripples out across the Universe. Astrophysicists hope to
see these gravity waves emitted by supernova explosions, or by black
holes orbiting one another or even colliding.

The biggest new gravity-wave detector, the Laser Interferometer
Gravitational-Wave Observatory (LIGO), is being built at Hanford in
Washington State, and Livingston, Louisiana (two versions are needed
to rule out the effects of seismic waves). As in the Caltech
interferometer, laser light from a single source is split and sent
down two perpendicular arms, and reflected by mirrors suspended at the
end of each. But LIGO's arms are 4 kilometres long, and two more
mirrors at the junction of the arms send the light back along the same
path so the beams can bounce back and forth many times before
recombining. A gravitational wave passing though this apparatus would
change the lengths of the two arms by different amounts, and so change
the interference pattern caused when the two light beams recombine.

When it is fully operational by 2002, LIGO will be the world's largest
precision optical instrument. The device is so sensitive that, despite
its massive scale, it should detect movements in the mirrors as small
as 10-18 metres, or a thousandth of the diameter of a proton. VIRGO, a
slightly smaller European interferometer, will have about the same
sensitivity.

Amelino-Camelia says LIGO's noise levels will set new limits on
quantum gravity. Mark Coles, head of the LIGO Livingston observatory,
is unsure. "We don't have any operational experience as yet, so all
the predictions of noise performance are simply extrapolations from
the Caltech interferometer." But even if that is true, there is a
grander scheme to look forward to. LISA, the Laser Interferometer
Space Antenna project, will consist of six spacecraft arranged in
pairs at the corners of an equilateral triangle orbiting the Sun-an
interferometer stretching over millions of kilometres. LISA is due for
completion in 2015.

In the meantime, atom interferometry could provide yet another avenue
for quantum gravity research. Ian Percival, a theoretical physicist at
London University's Queen Mary and Westfield College, believes that
atom interferometers, which replace laser light with a beam of atoms,
should be able to detect fluctuations in the time element of the foam.

It's not just space that is beaten to a froth: time is also stretched
and squashed, fluctuating by around 10 -44 seconds as the bubbles
appear and disappear. Small, but possibly detectable, Percival says.
According to quantum mechanics, atoms have a wave-like nature, so a
single atom can be split into two separate waves and sent along two
different paths. When the two atomic waves recombine, any difference
in their "internal clocks" due to the effects of quantum gravity
should destroy the atomic wave interference pattern.

Steven Chu of Stanford University and Mark Kasevich of Yale University
have managed to separate atomic wave packets by 1 centimetre before
recombining them. They saw an interference pattern. According to
Percival, that could be interpreted in two ways. Either space-time
fluctuations don't exist-in which case quantum gravity theories are in
real trouble-or both paths experienced the same fluctuations. He
favours the latter: the fluctuations could be "correlated" over these
distances, he says. They might even spread from one place to another.
As yet, however, no one really knows.

Few people believe that a satisfactory theory of quantum gravity is
just around the corner. "It may be that the actual theory is so
different from anything we know about that we are hundreds of years
away from it," Ellis says. But now experiments are now becoming
possible, things are looking up. Eventually we should narrow in on one
true description of the fabric of the Universe. The apple, one might
say, has fallen from the tree.

LOOP QUANTUM GRAVITY
http://www.newscientist.com/article/mg19125645.800-you-are-made-of-spacetime.html
You are made of space-time
BY Davide Castelvecchi & Valerie Jamieson / 12 August 2006

Lee Smolin is no magician. Yet he and his colleagues have pulled off
one of the greatest tricks imaginable. Starting from nothing more than
Einstein's general theory of relativity, they have conjured up the
universe. Everything from the fabric of space to the matter that makes
up wands and rabbits emerges as if out of an empty hat. It is an
impressive feat. Not only does it tell us about the origins of space
and matter, it might help us understand where the laws of the universe
come from. Not surprisingly, Smolin, who is a theoretical physicist at
the Perimeter Institute in Waterloo, Ontario, is very excited. "I've
been jumping up and down about these ideas," he says. This promising
approach to understanding the cosmos is based on a collection of
theories called loop quantum gravity, an attempt to merge general
relativity and quantum mechanics into a single consistent theory.

The origins of loop quantum gravity can be traced back to the 1980s,
when Abhay Ashtekar, now at Pennsylvania State University in
University Park, rewrote Einstein's equations of general relativity in
a quantum framework. Smolin and Carlo Rovelli of the University of the
Mediterranean in Marseille, France, later developed Ashtekar's ideas
and discovered that in the new framework, space is not smooth and
continuous but instead comprises indivisible chunks just 10-35 metres
in diameter. Loop quantum gravity then defines space-time as a network
of abstract links that connect these volumes of space, rather like
nodes linked on an airline route map. From the start, physicists
noticed that these links could wrap around one another to form braid-
like structures. Curious as these braids were, however, no one
understood their meaning. "We knew about braiding in 1987," says
Smolin, "but we didn't know if it corresponded to anything physical."

Enter Sundance Bilson-Thompson, a theoretical particle physicist at
the University of Adelaide in South Australia. He knew little about
quantum gravity when, in 2004, he began studying an old problem from
particle physics. Bilson-Thompson was trying to understand the true
nature of what physicists think of as the elementary particles - those
with no known sub-components. He was perplexed by the plethora of
these particles in the standard model, and began wondering just how
elementary they really were. As a first step towards answering this
question, he dusted off some models developed in the 1970s that
postulated the existence of more fundamental entities called preons.

Just as the nuclei of different elements are built from protons and
neutrons, these preon models suggest that electrons, quarks, neutrinos
and the like are built from smaller, hypothetical particles that carry
electric charge and interact with each other. The models eventually
ran into trouble, however, because they predicted that preons would
have vastly more energy than the particles they were supposed to be
part of. This fatal flaw saw the models abandoned, although not
entirely forgotten. Bilson-Thompson took a different tack. Instead of
thinking of preons as particles that join together like Lego bricks,
he concentrated on how they interact. After all, what we call a
particle's properties are really nothing more than shorthand for the
way it interacts with everything around it. Perhaps, he thought, he
could work out how preons interact, and from that work out what they
are.

To do this, Bilson-Thompson abandoned the idea that preons are point-
like particles and theorised that they in fact possess length and
width, like ribbons that could somehow interact by wrapping around
each other. He supposed that these ribbons could cross over and under
each other to form a braid when three preons come together to make a
particle. Individual ribbons can also twist clockwise or anticlockwise
along their length. Each twist, he imagined, would endow the preon
with a charge equivalent to one-third of the charge on an electron,
and the sign of the charge depends on the direction of the twist.

The simplest braid possible in Bilson-Thompson's model looks like a
deformed pretzel and corresponds to an electron neutrino (see
Graphic). Flip it over in a mirror and you have its antimatter
counterpart, the electron anti-neutrino. Add three clockwise twists
and you have something that behaves just like an electron; three
anticlockwise twists and you have a positron. Bilson-Thompson's model
also produces photons and the W and Z bosons, the particles that carry
the electromagnetic and weak forces. In fact, these braided ribbons
seem to map out the entire zoo of particles in the standard model.
Bilson-Thompson published his work online last year (www.arxiv.org/abs/
hep-ph/0503213). Despite its achievements, however, he still didn't
know what the preons were. Or what his braids were really made from.
"I toyed with the idea of them being micro-wormholes, which wrapped
round each other. Or some other extreme distortions in the structure
of space-time," he recalls.

It was at this point that Smolin stumbled across Bilson-Thompson's
paper. "When we saw this, we got very excited because we had been
looking for anything that might explain braiding," says Smolin. Were
the two types of braids one and the same? Are particles nothing more
than tangled plaits in space-time?

Smolin invited Bilson-Thompson to Waterloo to help him find out. He
also enlisted the help of Fotini Markopoulou at the institute, who had
long suspected that the braids in space might be the source of matter
and energy. Yet she was also aware that this idea sits uneasily with
loop quantum gravity. At every instant, quantum fluctuations rumple
the network of space-time links, crinkling it into a jumble of humps
and bumps. These structures are so ephemeral that they last for around
10-44 seconds before morphing into a new configuration. "If the
network changes everywhere all the time, how come anything survives?"
asks Markopoulou. "Even at the quantum level, I know that a photon or
an electron lives for much longer that 10-44 seconds."

Markopoulou had already found an answer in a radical variant of loop
quantum gravity she had been developing together with David Kribs, an
expert in quantum computing at the University of Guelph in Ontario.
While traditional computers store information in bits that can take
the values 0 or 1, quantum computers use "qubits" that, in principle
at least, can be 0 and 1 at the same time, which is what makes quantum
computing such a powerful idea. Individual qubits' delicate duality is
always at risk of being lost as a result of interactions with the
outside world, but calculations have shown that collections of qubits
are far more robust than one might expect, and that the data stored on
them can survive all kinds of disturbance.

In Markopoulou and Kribs's version of loop quantum gravity, they
considered the universe as a giant quantum computer, where each
quantum of space is replaced by a bit of quantum information. Their
calculations showed that the qubits' resilience would preserve the
quantum braids in space-time, explaining how particles could be so
long-lived amid the quantum turbulence. Smolin, Markopoulou and Bilson-
Thompson have now confirmed that the braiding of this quantum space-
time can produce the lightest particles in the standard model - the
electron, the "up" and "down" quarks, the electron neutrino and their
antimatter partners (www.arxiv.org/abs/hep-th/0603022).

All from nothing at all
So far the new theory reproduces only a few of the features of the
standard model, such as the charge of the particles and their
"handedness", a quantity that describes how a particle's quantum-
mechanical spin relates to its direction of travel in space. Even so,
Smolin is thrilled with the progress. "After 20 years, it is wonderful
to finally make some connection to particle physics that isn't put in
by hand," he says. The correspondence between braids and particles
suggests that more properties may be waiting to be derived from the
theory. The most substantial achievement, Smolin says, would be to
calculate the masses of the elementary particles from first
principles. It is a hugely ambitious goal: predicting the masses and
other fundamental constants of nature was something string theorists
set out to do more than 20 years ago - and have now all but given up
on. As with string theory, devising experiments to test for the new
theory will also be difficult. This is a problem that plagues loop
quantum gravity in all its guises, because no conceivable experiment
can probe space down to 10-35 metres.

Ironically, the best arena in which to look for experimental proof
might be the largest scales in the universe, not the smallest. "The
closest anyone is getting to making predictions is in the area of
cosmology," says John Baez, a mathematician and expert on quantum
gravity at the University of California, Irvine. Markopoulou is now
trying to think of ways of testing the braid model using the fossil
radiation left over from the big bang, the so-called cosmic microwave
background that permeates the universe. Physicists believe that the
patterns we see today in that radiation may have originated from
quantum fluctuations during the earliest moments of the big bang, when
all of the matter in the universe was crammed into a space small
enough for quantum effects to be significant.

Meanwhile, Markopoulou's vision of the universe as a giant quantum
computer might be more than a useful analogy: it might be true,
according to some theorists. If so, there is one startling
consequence: space itself might not exist. By replacing loop quantum
gravity's chunks of space with qubits, what used to be a frame of
reference - space itself - becomes just a web of information. If the
notion of space ceases to have meaning at the smallest scale,
Markopoulou says, some of the consequences of that could have been
magnified by the expansion that followed the big bang. "My guess is
that the non-existence of space has effects that are measurable, if
you can only see it right." Because it's pretty hard to wrap your mind
around what it means for there to be no space, she adds. Hard indeed,
but worth the effort. If this version of loop quantum gravity can
reproduce all of the features of the standard model of particle
physics and be borne out in experimental tests, we could be onto the
best idea since Einstein. "It's a beautiful idea. It's a brave,
strange idea," says Rovelli. "And it might just work."

Of course, most physicists are reserving judgement. Joe Polchinski, a
string theorist at Stanford University in California, believes that
Smolin and his colleagues still have a lot of work to do to show that
their braids capture all of the details of the full standard model.
"This is in a very preliminary stage. One has to play with it and see
where it goes," Polchinski says. If the new loop quantum gravity does
go the distance, though, it could give us a new sense of our place in
the universe. If electrons and quarks - and thus atoms and people -
are a consequence of the way space-time tangles up on itself, we could
be nothing more than a bundle of stubborn dreadlocks in space. Tangled
up as we are, we could at least take comfort in knowing at last that
we truly are at one with the universe.

Supersizing quantum gravity
For loop quantum gravity to succeed as a fundamental theory of
gravity, it should at the very least predict that apples fall to
Earth. In other words, Newton's law of gravity should naturally arise
from it. It is a tall order for a theory that generates space and time
from scratch to describe what happens in the everyday world, but Carlo
Rovelli at the University of the Mediterranean in Marseille, France,
and his team have succeeded in doing just that. "Essentially we have
calculated Newton's law starting from a world with no space and no
time," he says (www.arxiv.org/abs/gr-qc/0604044).

Newton's law of gravity describes the attractive force between two
masses separated by a given distance. However, it is not so simple to
measure this separation when space has a complex quantum architecture
of the sort in loop quantum gravity, where it is not even clear what
is meant by distance. This has been the biggest obstacle to showing
how Newton's law can emerge from quantised space.

The naive way to measure length in quantised space is to hop from one
quantum to another, counting how many steps it takes to reach the
final destination. According to loop quantum gravity, however, the
fabric of space seethes with quantum fluctuations, so the distance
between two points is forever changing, and can even take several
values at the same time.

Working with Eugenio Bianchi of the University of Pisa, Leonardo
Modesto of the University of Bologna and Simone Speziale of the
Perimeter Institute in Waterloo, Ontario, Rovelli circumvented the
problem. The team found a mathematical way of isolating regions of
space for long enough to measure the separation between two points.
When they zoomed out and used this mathematics to look at space-time
on much larger scales, they found that Newton's law popped out of
their theory.

The calculation by Rovelli's team does not yet reproduce the full
complexity of Einstein's general relativity, which also describes
masses large enough to curve space appreciably. Their result does
point in the right direction, however. Lee Smolin of the Perimeter
Institute calls it a major step forward. "Their work shows that loop
quantum gravity definitely has gravity in it," he says. "It's no
longer just pie in the sky."

BLACK HOLES AS REPRODUCTIVE ORGANS
http://www.nytimes.com/1997/07/13/magazine/the-cosmos-according-to-darwin.html
http://www.metanexus.net/magazine/tabid/68/id/5115/Default.aspx
http://thankgodforevolution.com/node/1679

Darwin could not have anticipated, for example, the work of physicist
Lee Smolin of the Perimeter Institute for Theoretical Physics in
Waterloo, Ontario. Smolin has utilized Darwinian concepts to shape a
theory of the universe that he calls “cosmological natural selection.”
He developed a theory that posits the existence of a vast number of
unseen universes, each generated by the collapse of a black hole. The
conditions of those collapses bestow each universe with its own set of
fundamental parameters, such as the masses of its various subatomic
particles. Just as life diversified on Earth, the “multiverse” in
Smolin’s theory evolved from simple beginnings into a complex and
varied assemblage of universes, each exhibiting a distinctive set of
traits.

Cosmological natural selection could help to solve one of the main
conundrums in physics: the seemingly arbitrary values of the
fundamental constants in our universe. Why is a neutron, for example,
more massive than a proton rather than the other way around? If a
wealth of universes with unique parameters exists, Smolin says, then
our own case does not seem so special or so unlikely. In fact,
cosmological natural selection specifically favors universes—like ours—
in which massive stars can form and give rise to new black holes. “By
using Darwinian methodology, I was able to get an explanation for the
improbable complexity of our universe,” Smolin says.

UNIVERSAL ECOLOGY
http://www.edge.org/documents/ThirdCulture/z-Ch.17.html
BY Lee Smolin / 1995

What is space and what is time? This is what the problem of quantum
gravity is about. In general relativity, Einstein gave us not only a
theory of gravity but a theory of what space and time are — a theory
that overthrew the previous Newtonian conception of space and time.
The problem of quantum gravity is how to combine the understanding of
space and time we have from relativity theory with the quantum theory,
which also tells us something essential and deep about nature. If we
can do this, we'll discover a single unified theory of physics that
will apply to all phenomena, from the very smallest scales to the
universe itself. This theory will, we're quite sure, require us to
conceive of space and time in new ways that take us beyond even what
relativity theory has taught us.

But, beyond even this, a quantum theory of gravity must be a theory of
cosmology. As such, it must also tell us how to describe the whole
universe from the point of view of observers who live in it — for by
definition there are no observers outside the universe. This leads
directly to the main issues we're now struggling with, because it
seems very difficult to understand how quantum theory could be
extended from a description of atoms and molecules to a theory of the
whole universe. As Bohr and Heisenberg taught us, quantum theory seems
to make sense only when it's understood to be the description of
something small and isolated from its observer — the observer is
outside of it. For this reason, the merging of quantum theory and
relativity into a single theory must also affect our understanding of
the quantum theory. More generally, to solve the problem of quantum
gravity we'll have to invent a good answer to the question: How can
we, as observers who live inside the universe, construct a complete
and objective description of it?

Most of my work as a scientist has been directed to the problem of
quantum gravity. I like working on this problem a great deal,
especially as it's the only area of physics I know of where one is
daily confronted by deep philosophical problems while engaged in the
usual craft of a theoretical physicist, which is to make calculations
to try to extract predictions about nature from our theoretical
pictures. Also, I like the fact that one needs to know a lot of
different things to think about this problem. For example, it's likely
that quantum gravity may be relevant for understanding the
observational data from astronomy, and it's also likely that the new
theory we're trying to construct will make use of new mathematical
ideas and structures that are only now being discovered. So although
I've worked almost solely on this problem for almost twenty years,
I've never been bored.

I have days in which I spend the morning working on a calculation, to
check an idea I had the night before, and then I'll go to a lunch
seminar, where I hear astronomers discuss the latest evidence for some
crucial question, like how much dark matter there is. Then I spend the
afternoon studying the paper of a friend who's a pure mathematician,
after which I meet a philosopher for dinner and continue an argument
we're having on the nature of time. And what's wonderful is the way
that these different subjects, which until recently were disconnected
from one another, often seem to illuminate one another. Of course,
sometimes it's not so ideal; teaching and bureaucracy take up a lot of
time — although in reasonable doses, I must say. I love teaching also.
But there are really many days when I feel very fortunate and can't
imagine that I'm being paid to live like this.

For the last eight years or so — really, it doesn't seem so long! —
I've been working with several friends on a new approach to combining
relativity and quantum theory. We call this approach "nonperturbative
quantum gravity." It's enabling us to investigate the implications of
combining general relativity and quantum theory more deeply and
thoroughly than was possible before. We aren't yet finished, but we're
making progress steadily, and recently we've got the theory well
enough in hand that we've been able to extract some experimental
predictions from it. Unfortunately, the predictions we've been able to
make so far can't be tested, because they're about the geometry of
space at scales twenty orders of magnitude smaller than an atomic
nucleus. But this is further toward a solution to the problem than
anyone has gotten before — and, I must say, further than I sometimes
expected we'd be able to go in my lifetime.

In this work, we've been combining a very beautiful formulation of
Einstein's general theory of relativity discovered by my friend Abhay
Ashtekar with some ideas about how to construct a quantum theory of
the geometry of space and time in which everything is described in
terms of loops. That is, rather than describing the world by saying
where each particle is, we describe it in terms of how loops are
knotted and linked with one another. This approach to quantum theory
was invented by another friend — Carlo Rovelli — and myself, and also
by the very interesting Uruguayan physicist Rodolfo Gambini.

The main result of this work is that at the Planck scale, which is
twenty powers of ten smaller than an atomic nucleus, space looks like
a network or weave of discrete loops. In fact, these loops are
something like the atoms out of which space is built. We're able to
predict that — just as the possible energies an atom can have come in
discrete units — when one probes the structure of space at this Planck
scale, one finds that the possible values the area of a surface or the
volume of some region can have also come in discrete units. What seems
to be the smooth geometry of space at our scale is just the result of
an enormous number of these elementary loops joined and woven
together, as an apparently smooth piece of cloth is really made out of
many individual threads.

Furthermore, what's wonderful about the loop picture is that it's
entirely a picture in terms of relations. There's no preexisting
geometry for space, no fixed reference points; everything is dynamic
and relational. This is the way Einstein taught us we have to
understand the geometry of space and time — as something relational
and dynamic, not fixed or given a priori. Using this loop picture,
we've been able to translate this idea into the quantum theory.

Indeed, for me the most important idea behind the developments of
twentieth-century physics and cosmology is that things don't have
intrinsic properties at the fundamental level; all properties are
about relations between things. This idea is the basic idea behind
Einstein's general theory of relativity, but it has a longer history;
it goes back at least to the seventeenth-century philosopher Leibniz,
who opposed Newton's ideas of space and time because Newton took space
and time to exist absolutely, while Leibniz wanted to understand them
as arising only as aspects of the relations among things. For me, this
fight between those who want the world to be made out of absolute
entities and those who want it to be made only out of relations is a
key theme in the story of the development of modern physics. Moreover,
I'm partial. I think Leibniz and the relationalists were right, and
that what's happening now in science can be understood as their
triumph.

Indeed, in the last few years, I've also realized that the relational
point of view can inspire ideas about other problems in physics and
astronomy. These include the basic problem in elementary particle
physics, which is accounting for all the masses and charges of the
fundamental particles. I've come to believe that this problem is
connected as well to two other basic questions that people have been
wondering about for many years. The first of these is: Why are the
laws of physics and the conditions of the universe special in ways
that make the universe hospitable for the existence of living things?
Closely related to this is the second question: Why, so long after it
was formed, is the universe so full of structures? Beyond even the
question of life, it's a remarkable fact that our universe seems,
rather than having come to a uniform and boring state of thermal
equilibrium, to have evolved to a state in which it's full of
structure and complexity on virtually every scale, from the subnuclear
to the cosmological.

The picture that emerges from both relativity and quantum theory is of
a world conceived as a network of relations. Newton's hierarchical
picture, in which atoms with fixed and absolute properties move
against a fixed background of absolute space and time, is quite dead.
This doesn't mean that atomism or reductionism are wrong, but it means
that they must be understood in a more subtle and beautiful way than
before. Quantum gravity, as far as we can tell, goes even further in
this direction, as our description of the geometry of spacetime as
woven together from loops and knots is a beautiful mathematical
expression of the idea that the properties of any one part of the
world are determined by its relationships and entanglement with the
rest of the world.

As we began to develop this picture, I also began to wonder whether
the basic philosophy behind it might extend to other aspects of
nature, beyond just the description of space and time. More precisely,
I began to wonder whether the world as a whole might be understood in
a way that was more interrelated and relational than in the usual
picture, in which everything is determined by fixed laws of nature. We
usually imagine that the laws of nature are fixed, once and for all,
by some absolute mathematical principle, and that they govern what
goes on by acting at the level of the smallest and most fundamental
particles. There are good reasons why we believe that the fundamental
forces should act only on the elementary particles. But in particle
physics we have been making another assumption as well: that there are
mechanisms or principles that pick out which laws are actually
expressed in nature, and that these mechanisms or principles also work
only at enormously tiny scales, much smaller than the atomic nucleus;
an example of such a mechanism is something called "spontaneous
symmetry breaking." Given that the choice of laws makes a great
difference for the universe as a whole, it began to seem strange to me
that the mechanisms that choose the laws should not somehow be
influenced by the overall history or structure of the universe at very
large scales. But, for me, the real blow to the idea that the choice
of which laws govern nature is determined only by mechanisms acting at
the smallest scales came from the dramatic failure of string theory.

Like many of the young people trained in elementary-particle physics
in the 1970s and '80s, I had great hopes for string theory, since it
seemed to have the best possible chance of providing a fundamental
unified theory. Indeed, I still think there are ideas in string theory
that may be right, and its exploration has led to the uncovering of
some beautiful and deep mathematics. But as a theory of the elementary
particles, it has certainly so far failed, for while it initially
seemed that there was only one possible consistent string theory, we
now know there are a great many such theories, each apparently as
consistent as the others and all leading to different universes. Thus,
string theory hasn't solved the problem of how the world chooses to
have the particular collection of particles and forces it does. And
whatever the theory's future, I've come to doubt that it ever will.

This crisis led me to wonder whether the search for the principles
that determine which laws of nature govern our world could succeed, if
we continue to look only at mechanisms that act on very small scales.
Instead, I began to ask myself whether there might be mechanisms that
could in some way couple the properties of the elementary particles to
the properties of the universe created by their interactions — perhaps
even on astronomical and cosmological scales. By this I mean nothing
mystical. Since the universe has a history, and did apparently pass
through a stage when it was very small, there might be some mechanism
that coupled the properties of things on the largest scales to the
properties of things on the smallest scales. Thus, about five years
ago I began to wonder whether there might be some way in which the
properties of the elementary particles are chosen by the universe
itself, during its evolution. Wondering about this made me notice and
take seriously what many people had pointed out previously — that the
properties of the elementary particles and the conditions of the
universe seem very well chosen for the universe to develop structure
and life. It does seem that this is true — that if almost any other
set of forces and particles had been chosen, the universe would not
only not contain life, it would be much less rich in structure and
variety of phenomena than our world is.

Many of the people who've noticed this have become advocates of the
anthropic principle. This is the idea that the properties of the world
have somehow been chosen because of — or at least are explained by —
the fact that with this choice intelligent life like us can exist. I'd
always resisted this idea, and I still do. The anthropic principle is
said to come in two forms, a weak form and a strong form. In its weak
form, I think it's just the observation that the world in which we
find ourselves is very special. This doesn't explain anything, it only
points out the need for an explanation of how the world got to be
special — an explanation that must be made in terms of some mechanism
acting in its past. The strong form — that the laws of physics are
somehow chosen in order that life can exist — is, to me, really more
religion than science. Indeed, I'm not surprised to find that several
advocates of the strong form of the anthropic principle are writing
books and papers connecting their belief in the anthropic principle
with Christian theology. This is fine, for religion, but it isn't
science. Instead, when I realized that people like Martin Rees and
Bernard Carr were right — that the world is very special in ways that
seem a priori extremely unlikely — I began to wonder whether there
might be some real mechanism, something taking place earlier in the
history of the universe, that might explain how the properties of the
elementary particles have been selected so that the world has the
enormous amount of structure and variety it does.

At this time, I was reading a lot of biology: Richard Dawkins on
evolution, Harold Morowitz on self-organization, and James Lovelock
and Lynn Margulis on the Gaia idea. And I remember wondering whether,
if the earth can be understood as a self- organized system, maybe the
same thing was true for larger systems, such as a galaxy or the
universe as a whole. This was also summertime, and I was sailing a
lot, and I spent a lot of time letting the boat drift and wondering
what kind of mechanisms of self-organization might have acted early in
the history of the universe to select the properties of the elementary
particles and forces in nature. It seemed to me that the only
principle powerful enough to explain the high degree of organization
of our universe — compared to a universe with the particles and forces
chosen randomly — was natural selection itself. The question then
became: Could there be any mechanism by which natural selection could
work on the scale of the whole universe?

Once I asked the question, an answer appeared very quickly: the
properties of the particles and the forces are selected to maximize
the number of black holes the universe produces. This idea came right
away, because of two ideas I was familiar with from my work on quantum
gravity. The first is that inside a black hole, quantum effects remove
the singularity that general relativity says is there — and that we
know is there from the theorems of Penrose and Hawking — and a new
region of the universe begins to expand as if from a big bang, there
inside the black hole. I remember Bryce DeWitt, who is one of the
great pioneers of quantum gravity, telling me about this idea shortly
after I began to work for him, on my first postdoc. The second idea —
which comes from John A. Wheeler, another great pioneer of the field —
is that at such events the properties of the elementary particles and
forces might change randomly. All I then needed to make a mechanism
for natural selection was to assume that these changes are small,
because reading Dawkins had taught me the importance for natural
selection of incremental change by the accumulation of small changes
in the gene. Then, with the universes as animals and the properties of
the elementary particles as genes, I had a mechanism by which natural
selection would act to produce universes with whatever choices of
parameters would lead to the most production of black holes, since a
black hole is the means by which a universe reproduces — that is,
spawns another.

This was in 1989. I still don't know if the idea is right. But what
I'm very proud of is that the idea is testable. Most ideas about why
the elementary particles have the properties they do which have been
proposed in the past few years aren't testable. This is the main
reason the field is in such a crisis. But this idea leads to a
prediction, which is that if I could change any of the properties of
the elementary particles the result should be either to decrease or to
leave alone the number of black holes the universe makes. This is
because the idea implies that almost every universe, and therefore
most likely our own, has parameters that maximize the numbers of black
holes it can make.

When this idea first came to me, I didn't take its prospects very
seriously, and I imagine neither did most of my colleagues. I also
didn't know much astrophysics, and I imagined that it would be an easy
matter to test what would happen to the rate of production of black
holes if you changed, for example, the mass of one or another sort of
elementary particle, or the strength of one of the forces. So to test
the idea, I started to learn some astronomy and astrophysics. So far,
I haven't found a way to change the properties of the particles and
forces to make a universe that makes more black holes, and I have
found several changes that decrease their number. I've also brought
the question to a number of astrophysicists, who know the field much
better than I do. I've been very pleased that these people, some of
whom I admire very much, were interested enough to spend the time to
examine such an unusual idea. They made some interesting suggestions,
and although no one was able to propose a change of parameters that
clearly leads to the production of more black holes, several
interesting possibilities, which I'm studying now, did emerge from
these conversations. Certainly, if the idea's wrong, I'll be grateful
if someone proposes a test that would kill it. I believe more in the
general idea that there must be mechanisms of self-organization
involved in the selection of the parameters of the laws of nature than
I do in this particular mechanism, which is only the first one I was
able to invent. But it seems that the situation at present is that
there's much more testing that needs to be done, and lately I've been
spending more time on this. Perhaps what's most amazing to me is that
after five years this rather improbable idea is still not dead.

Whether it dies or not, I've learned enough astronomy to discover
something that's completely changed my view of cosmology. This is that
the idea that there are principles of self-organization acting on
astronomical scales seems really to be true. During the last ten years
or so, people who study galaxies have discovered evidence that
feedback effects and mechanisms of self-organization are indeed
happening at the level of the galaxies; they are, in fact, essential
for galaxies to form stars. They're also necessary to the existence of
spiral galaxies. The idea that a galaxy is a self organized system —
more an ecology than a nonliving clump of stars and gas — has become
common among astronomers and physicists who study galaxies.

Thus, it seems to me quite likely that the concept of self-
organization and complexity will more and more play a role in
astronomy and cosmology. I suspect that as astronomers become more
familiar with these ideas, and as those who study complexity take time
to think seriously about such cosmological puzzles as galaxy structure
and formation, a new kind of astrophysical theory will develop, in
which the universe will be seen as a network of self-organized systems.