archived as http://www.stealthskater.com/Documents/BigBang_1.doc [pdf]
more of Cosmology at http://www.stealthskater.com/Science.htm
note: because important websites are frequently "here today but gone tomorrow", the following was
archived from http://www.space.com/scienceastronomy/astronomy/bigbang_alternative_0104131.html on May 1, 2002. This is NOT an attempt to divert readers from the aforementioned
website. Indeed, the reader should only read this back-up copy if the updated original cannot be
found at the original author's site.
'Brane-Storm' Challenges Part of Big Bang Theory
By Robert Roy Britt
Senior Science Writer
posted: 02:33 pm ET
18 April 2001
Faster than you can say "Ekpyrotic Universe", a movement has taken hold -- albeit like fingers on
a ledge of eternal skepticism -- that would blow one of the basic tenets of the Big Bang to smithereens.
Think "parallel branes" and "5 dimensions". Science never sounded so cool.
The new idea would not replace the Big Bang, which has for more than 50 years dominated
cosmologists' thinking over how the Universe began and evolved. But instead of a Universe springing
forth in a violent instant from an infinitely small point of infinite density, the new view argues that our
Universe was created when 2 parallel "membranes" collided cataclysmically after evolving slowly in 5dimensional space over an exceedingly long period of time.
These membranes -- or "branes" as theorists call them -- would have floated like sheets of paper
through a 5th dimension that even scientists admit they find hard to picture intuitively. (Our
conventional view of 3-D physical space along with time make up the 4 known dimensions.)
"It's almost crazy enough to be correct."
-- Michael Turner, University of Chicago cosmologist
The idea -- put forth earlier this month at a Space Telescope Science Institute meeting in Baltimore - is based on other theories about possible multiple dimensions that are growing in acceptance. It was
developed by Neil Turok of Cambridge University, Burt Ovrut of the University of Pennsylvania, and
Paul Steinhardt and Justin Khoury of Princeton University.
"The [Ekpyrotic] scenario is that our current Universe is [a] 4-dimensional membrane embedded in
a 5-dimensional 'bulk' space -- something like a sheet of paper in ordinary 3-dimensional space," Turok
told SPACE.com. "The idea then is that another membrane collided with ours, releasing energy and
heat, and leading to the expansion of our Universe."
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Crazy, but viable
"It's almost crazy enough to be correct," says Michael Turner, a longtime University of Chicago
cosmologist who is familiar with the theory. He added that "when you're trying to crack a really hard
problem, you need a crazy idea."
Turner said astronomers have reacted with great excitement to the new theory in part because the
idea of alternate dimensions is largely new to most of them. Cosmologists tend to welcome the idea as a
healthy potential alternative to certain aspects of the Big Bang, but are cautious about the theory's
prospects.
Mario Livio -- who heads up the science division of the Space Telescope Science Institute -- said it's
way too early to predict whether the theory will withstand scrutiny by other researchers. But he called
the concept very important and exciting. "We're talking about a new idea about the origin of our
Universe."
The Ekpyrotic Universe draws its name from the ancient Greek word ekpyrosis, meaning
"conflagration" (disastrous fire or conflict). According to an ancient cosmological model with this
name, the Universe was created in a sudden burst of fire. The modern-day theorists say this ancient idea
is not unlike the collision proposed in the new model.
While the new theory is full of complex math and obscure concepts, it is a somewhat soothing idea
for anyone who has ever wondered what-the-heck lies beyond our Universe. C'mon, admit it! At least
once you thought about the edge of the Universe and mumbled, prayed, dreamed, or asked: "But what is
beyond that."
So, what is beyond the edge of the Universe?
The 5th dimension is what is beyond the edge of the Universe, say the creators of the idea. Though
they argue that there is in fact no "edge".
"There is only one Universe," Ovrut said in a telephone interview. "It does not have a boundary. It's
just one large extended brane that has been hit, heated up, and is expanding."
The mind-bending concept does not involve multiple or parallel universes, as have been suggested
by other researchers.
Instead, Ovrut explains, the 5th dimension is all there, is out there, and embedded in it are multiple
branes. Each end of the 5th dimension is bounded by an infinite brane. Our visible Universe is one of
those. And before the collision it may or may not have contained normal matter. At the other end of the
5th dimension is a brane with physics unlike ours. The branes in between -- while they may contain
matter -- are not universes, and they do not resemble the brane we inhabit.
"There is no reason to assume -- given this conceptual framework -- that there are any other
universes out there," Ovrut said.
Alternative to explain Inflation
A paper on the concept has been submitted to the journal Physical Review D. While the paper has
not yet been accepted for publication, surprised and thrilled physicists who are familiar with it are
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describing the Ekpyrotic Universe as exciting, plausible, and a worthy competitor to a problematic
aspect of the Big Bang known as "inflation".
Inflation attempts to account for the seeming uniformity of the Universe. Look in any direction of
the sky, and there are features in the Universe -- galaxies and clusters of galaxies -- that very much
resemble those in any other direction. The theory of Inflation accounts for this by putting all matter in
one spot at the beginning, then shooting it outward faster than the speed-of-light in a period of inflation
whereby everything developed under similar rules regardless of where it was headed.
Ovrut said that in modeling a collision of branes, his group found that the result would be a Universe
that fits neatly with predictions of the Big Bang. It produces similar temperatures and causes the
resulting universe to expand, for example, and creates matter with the same uniformity predicted by
inflation.
"We are not attacking the Theory of Inflation," Ovrut said. "We're just presenting an alternative."
Turner -- the University of Chicago cosmologist -- said Inflation theory has been so successful that it
has killed all competing theories. But Inflation doesn't address the idea that there might be other
dimensions. Interest in this wild notion has grown among cosmologists in recent years.
In textbooks a century from now, Turner believes there will be one of the following 2 paragraphs:
"A hundred years ago, people were so desperate to try to understand how to put it all together that
they invented additional spatial dimensions. What were they smoking?" Or: "A hundred years ago,
people were so provincial that in spite of much evidence that there should be extra dimensions, they
refused to accept it."
Details of the Ekpyrotic Universe theory
The following technical description was provided to SPACE.com by the authors (Justin Khoury,
Princeton; Burt Ovrut, UPenn; Paul Steinhardt, Princeton and Neil Turok, Cambridge):
Our paper proposes a new theory of the very early universe that resolves the famous puzzles of the
hot Big Bang picture -- the horizon, flatness and monopole problems -- and that generates fluctuations in
energy that seed galaxy formation and produce temperature variations in the cosmic microwave
background. The model is based on the idea that our hot Big Bang universe was created from the
collision of two 3-dimensional worlds moving along a hidden, extra dimension.
The Inflationary model of the Universe -- developed in the 1980's by Alan Guth (MIT), Andre Linde
(Stanford), Andreas Albrecht (UC Davis), and Steinhardt -- was designed to resolve these very same
problems, relying on a period of exponential hyper-expansion or "inflation".
Conceptually, the eEkpyrotic model is very different. There is no inflation or rapid change
happening at all. The approach to collision takes places very slowly over an exceedingly long period of
time. It is quite fascinating that rapid change and very slow change can produce nearly the same effects.
The difference results in one distinctive observational prediction, though. Inflationary cosmology
predicts a spectrum of gravitational waves that may be detectable in the cosmic microwave
background. The Ekpyrotic model predicts no gravitational wave effects should be observable in the
cosmic microwave background.
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In the Ekpyrotic model, when the two 3-dimensional worlds collide and "stick", the kinetic energy in
the collision is converted to the quarks, electrons, photons, etc. that are confined to move along 3
dimensions. The resulting temperature is finite, so the hot Big Bang phase begins without a 'singularity'.
The Universe is homogeneous because the collision and initiation of the Big Bang phase occurs nearly
simultaneously everywhere.
The energetically preferred geometry for the 2 worlds is flat, so their collision produces a flat Big
Bang universe. According to Einstein's equations, this means that the total energy density of the
Universe is equal to the critical density. Massive magnetic monopoles -- which are over-abundantly
produced in the standard Big Bang theory -- are not produced at all in this scenario because the
temperature after collision is far too small to produce any of these massive particles.
Quantum effects cause the incoming 3-dimensional world to ripple along the extra-dimension prior
to collision so that the collision occurs in some places at slightly different times than others. By the time
the collision is complete, the rippling leads to small variations in temperature which seed temperature
fluctuations in the microwave background and the formation of galaxies. We have shown that the
spectrum of energy density fluctuations is scale-invariant (the same amplitude on all scales). The
production of a scale-invariant spectrum from hyper-expansion was one of the great triumphs of
Inflationary theory. And here we have repeated the feat using completely different physics.
The building blocks of the Ekpyrotic theory are derived from superstring theory. Superstring theory
requires extra dimensions for mathematical consistency. In most formulations, 10 dimensions are
required. In the mid 1990s, Petr Horava (Rutgers) and Ed Witten (IAS, Princeton) argued that under
certain conditions, an additional dimension opens up over a finite interval. 6 dimensions are presumed
to be curled up in a microscopic ball called a "Calabi-Yau" manifold.
The ball is too small to be noticed in everyday experience, and so our Universe appears to be a 4dimensional (3 space dimensions and one time dimension) surface embedded in a 5-dimensional spacetime. This 5-dimensional theory -- called heterotic M-theory -- was formulated by Andre Lukas
(Sussex), Ovrut, and Dan Waldram (Queen Mary and Westfield College, London). According to
Horava-Witten and heterotic M-theory, particles are constrained to move on one of the 3-dimensional
boundaries on either side of the extra dimensional interval.
Our visible Universe would be one of these boundaries. The other boundary and the intervening
space would be hidden because particles and light cannot travel across the intervening space. Only
gravity is able to couple matter on one boundary to the other sides. In addition, there can exist other 3dimensional hyper-surfaces in the interval which lie parallel to the outer boundaries and which can carry
energy.
These intervening planes are called "branes" (short for membranes). The collision that ignites the
hot Big Bang phase of the Ekpyrotic model occurs when a 3-dimensional brane is attracted to and
collides into the boundary corresponding to our visible Universe.
The term ekpyrosis means "conflagration" in Greek and refers to an ancient Stoic cosmological
model. According to the model, the Universe is created in a sudden burst of fire -- not unlike the
collision between 3-dimensional worlds in our model. The current Universe evolves from the initial
fire. However in the Stoic notion, the process may repeat itself in the future. This, too, is possible in
our scenario in principle if there is more than one brane and, consequently, more than one collision. We
plan to discuss this possibility in future work, along with further speculations about what preceded the
collision that made our present Universe.
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As a final remark, we feel that it is important to realize that Inflationary theory is based on Quantum
Field theory -- a well-established theoretical framework -- and the model has been carefully studied and
vetted for 20 years. Our proposal is based on unproven ideas in string theory and is brand new. While
we appreciate the enthusiasm and interest with which the paper has been received, we would suggest
some patience before promulgating these ideas in order to leave time for us to produce some follow-up
papers that introduce additional elements and to allow fellow theorists time for criticism and sober
judgment.
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