Universe: Creation
Universe: Creation
| Topics: |  Cosmology The Universe |
Creating Matter from Empty Space
Erwin Schroedinger (Schrödinger), by 1939, believed that quantum mechanics itself required that the universe had to be closed because only then would wave functions act discontinuously. Recall that in the Bohr-Heisenberg atom, the orbit that each electron takes around the nucleus is the path for which exactly an integer number of wavelengths of the electron wave function can be accommodated around the orbit's circumference. This leads to discrete states within the atom. Schroedinger believed that the same must be true of the universe. Its closed geometry acted to provide a finite spatial extent within which discrete quantum states would be possible. By studying what happens to the wave function of an electron in an expanding, closed universe, Schroedinger uncovered what he described as an exciting result. The vibrations can be decomposed into two waves traveling the universe in opposite directions, but
..."if in a certain moment only one of them is present, the other one can turn up in the course of time. This is a phenomenon of outstanding importance. With particles it would mean production or annihilation of matter, merely by the expansion [of the universe]. Alarmed by these prospects, I have investigated the question in more detail..."
His resulting calculations contained in some 45 equations, showed that the creation of matter could not occur in this way if the universe were expanding at constant velocity...as it is today...but is only likely when there is rapid acceleration as was likely during the first few moments after the Big Bang.
In 1953, Bryce DeWitt presented a paper at the American Physical Society meeting in Cambridge Massachusetts entitled "Pair Production by a Curved Metric." He described how in a universe that has a perfectly flat spacetime geometry, small-scale curvature changes can cause pair production in a scalar field. Even if the only field existing in such a universe is the single scalar field, the quantum fluctuations that always occur in any field will interact with the local curvature changes in the spacetime and stimulate the creation of particle-antiparticle pairs.
The production of matter out of rapidly changing spacetime fluctuations was also explored some years later by Andrei Sakharov and by Leonard Parker in 1968-9. Beginning with a small number of fundamental particles in an expanding spacetime, new particles are stimulated into existence out of the quantum fluctuations in the seed particle fields. The number of particles increases as the expansion continues, however, the reaction of the created particles back upon the expansion causes the expansion to slow. This then reduces the production rate of new particles. This process produces equal amounts of matter and antimatter. The current rate of production is about one Pi Meson in a volume as large as the entire observable universe but "...conceivably it was much higher near the start of the Friedman expansion."
By 1972, the scant literature on the physical conditions in the early history of the universe focussed on the problem of the initial Singularity, whether it was avoidable, and what implications it held for the emergence of structure in the universe. No one seriously considered it possible to speak intelligently about what might have preceded the Big Bang.
The Universe as a Vacuum Fluctuation
Edward Tryon, in a short but influential 1973 paper, was the first to propose that since, as a whole, the total rest mass energy of the stars and galaxies in our universe, E = mc2, was just balanced by its gravitational energy, that the total energy of the universe was zero. Heisenberg's Principle would then predict that Delta E * Delta t = h, so that Delta t = infinity. In other words, our universe had a characteristic analogous to those ghost-like quantum particles that flash in and out of existence within the atom and disturb the electron's energy levels thereby producing the Lamb Shift. As Edward Tryon once remarked, "The universe is just one of those things that happens from time to time."
In the present universe, all of the quantum numbers that characterize matter have total values of zero. This means that for every + charge there is a - charge, for every matter particle there is somewhere an anti-matter particle, and the total energy of the universe measured as the sum of kinetic, gravitational potential and rest mass energies, is exactly zero. The only other physical system which shares these nulled quantum numbers is the vacuum state. Therefore, the universe arose from a chance primordial fluctuation in the vacuum whose total energy and lifetime are constrained by Heisenberg's Uncertainty Principle. Vacuum fluctuations that lead to universes as big as ours are rare, but they are always appear impressively large and old to the sentient life they support.
The Decay of the False Vacuum
In 1977, a number of theoreticians including Peter Frampton, Sidney Coleman and K. Sato, began to investigate the energy of the vacuum state as predicted by various unification theories. The vacuum state is defined in all field theories as the lowest achievable energy state of the quantum system. A particular field theory may predict more than one minimum energy vacuum state so that a system described by such a field theory might eventually find itself tunneling from a higher vacuum state to a lower-energy one. The physical expression of such a process in the cosmological arena would have bubbles of the lower-energy 'true vacuum' spontaneously form within a 'false vacuum' like bubbles forming in a freshly opened bottle of soda pop.
An infinitely old universe must be in a true vacuum state no matter how slowly the transition from false to true vacuum may be. At the time of the Big Bang, however, the state of the universe could have been far from any vacuum, true or false, and as the universe expanded it got caught in a false vacuum state instead of a lowest-energy true vacuum.
Simple quantum corrections to Einstein's classical equation for gravity lead A. Starobinsky in 1980 to cosmological solutions in which the universe is initially in the eternally-expanding De Sitter stage. This phase has no singularity at time zero so there is no Big Bang event. The quantum corrections arise from allowing the matter fields to be represented quantum mechanically. The model avoids the Friedman Singularity only if the gravitational fields are not so strong that their quantum gravity corrections have to be included near the Planck scale.
According to Sato and Kodama, and Gott, open universes may be continually created, perhaps in infinite number, from a prior deSitter false vacuum as the phase transition spontaneously converts part of the false vacuum into true vacuum bubbles. The vacuum bubbles in the true phase are complete, but disjoint, universes that are filled by particles and radiation produced out of vacuum fluctuations in the local spacetime.
Weak Curvature Fluctuations
Following the developments in Grand Unification Theory, as the Planck scale is approached, F. Stecker proposed that the energy density and curvature of spacetime do not continue to rise, but actually decrease sharply because of a presumed analog to the weakening of the strong force seen at high energies. The strength of the unified forces diminish as the scales grow smaller and the energies become larger. This also might apply to gravity so that at the Planck scale, the universe enters an indefinite-duration state of weak-to-vanishing gravity where spacetime curvature fluctuations become smaller in amplitude and energy. The universe is born when, eventually, a low-energy quantum fluctuation in spacetime curvature sets-off the expansion.
Inflationary Cosmology
Alan Guth and Andre Linde proposed in 1981-2 that the Big Bang begins in a hot dense state, but as it cools through the GUT transition energy at 1015 GeV and 10-35 seconds, it gets caught in a false vacuum state. This causes the universe to exponentially grow in size in a quasi-deSitter state. The expansion ceases once the universe enters its true vacuum phase, with a concomitant release of energy that appears as a fireball phase of particle and radiation creation by 10-33 seconds. The expansion then resumes the Friedman phase. The transition occurs by the nucleation of true vacuum bubbles within the expanding matrix of the deSitter false vacuum phase. These bubbles either merge together to form the present day uniformity of the universe (Old Inflation), or remain as separate domains that grow to sizes billions of times larger than our observable universe (New Inflation).
The supermassive, scalar Higgs field is identified as the culprit whose phase transition initiates Inflation. When asked by Alan Lightman how he pictures the Big Bang and what came before it, Alan Guth answers that,
"In the hypothetical theory of quantum gravity, there will be a Hilbert space of all possible states of the universe. The different states...will clearly have different possible geometries for the universe, and among all of those states...one possibility is a universe with zero points...a universe with its radius equal to zero...and that's what I take as the starting point for the universe [but the idea that the universe came into being] probably has no precise meaning [since as Steven Hawking notes] you really should not talk about the universe beginning at a [particular] time.."
Inflation was eventually superceded by various other incarnations that presumed to improve on the defects of previous versions of Inflation. One of these is Supersymmetric Inflation in which Supersymmetric Grand Unification Theory is used as the starting point for the underlying physics. The culprit now switches from the Higgs field to another scalar field called the Inflaton field. The reason for this switch is that the quantum fluctuations in the Higgs field would be so strongly tied to matter fields that the matter in the universe would collapse into supermassive black holes. The Inflaton scalar field, on the other hand, is designed by hand to be weakly tied to matter, yet still has the mathematical properties necessary to cause inflation nonetheless.
Vacuum Fluctuations in a Pre-existing Flat Spacetime
R. Brout, Francois Englert and Gunzig carried Tryon's idea further by adding more detail to this basic model, proposing that the universe was created by a local quantum fluctuation within a pre-existing 4 dimensional spacetime. Matter fields were created out of the rapidly varying geometry which then acted back on the spacetime geometry to create still more matter. In a cooperative process, the universe expanded in an Inflationary state which ended once the spacetime irregularities had smoothed-out sufficiently. However, BEG did not provide much insight into whence the first quantum fluctuation arose, only that the initial starting state was a flat, eternally expanding, and completely empty of matter, 'deSitter'-like spacetime.
The universe is considered as a region filled with matter embedded in an underlying Minkowski (flat) spacetime. The Parker-Sakharov-Wald mechanism is used to create particles out of the gravitational curvature fluctuations in spacetime. The first 'matter' nucleates around some point in spacetime. This stimulation of matter production occurs over a region in which the matter field has quantum coherence (About the compton wavelength of the matter particles).
As the stimulated production of new matter proceeds, this matter flows outward in space and forward in time. This process tends towards a constant matter density in space, but eventually the particles become accelerated as they scatter off of the rapidly changing gravitational fields. This causes the quantum coherence effect to break down, and the "fireball stage" of particle production comes to an end. The expansion of the matter and radiation then proceed as in the standard Friedman cosmology with no further particle creation taking place. The spacetime structure of the universe during the fireball stage is that of the De Sitter model. The origin of the universe is interpreted as a phase transition from a higher symmetry state at energies near the Planck limit of 1019 GeV.
Gunzig begins, once again, with the notion of a pre-existing flat, empty 4-dimensional spacetime, but embedded in this spacetime is a physical field that is normally constant at every point in spacetime. This field, like all quantum fields, is subject to fluctuations that locally produce a distortion in the otherwise flat geometry. In a self-sustaining process, gravitational energy is transferred from local curvature fluctuations into a rich sea of quantum black holes which then decay into matter and anti-matter touching off the Big Bang. A dramatic feature of this model is that the more uniform and flat the initial spacetime is, the more likely it will be unstable to such spontaneous curvature fluctuations, and to give birth to a 'child' expanding universe. GGP speculate that as our universe grows more uniform and flat in the far future, it too may become the 'Mother spacetime' for an instability leading to the creation of a new universe. Once born, this Child universe becomes totally disconnected from the parent universe. No direct spatial or physical link remains to the original universe that created it. By this remarkable process, a universe may, therefore, be self-creating and eternal. This quantum production of a universe out of a pre-existing spacetime need not have happened once. If one may bring forth a single universe by this mechanism, it is just as easy to spontaneously create an infinite number, indeed, the quantum character of spacetime seems to demand this possibility.
Vacuum Fluctuation in a Prior, Curved Spacetime
Although Edward Tryon's 1973 proposal was intriguing, Atkatz and Pagels pointed out that the concept of total energy is not rigorously definable in highly curved spacetimes. The only spacetime with zero total energy is exactly flat and empty everywhere. As a result, Tryon's idea was probably not correct, at least in the way that it was originally envisioned, since at its earliest moments, spacetime was in a highly curved state and not 'flat' at all. Atkatz and Pagels were able to carry Tryon's proposal and BEGs subsequent elaboration upon it, a step further, proposing that just as radioactive nuclei spontaneously decay by emitting particles, spacetime itself was initially in a quasi-static and empty state. Through a process called quantum tunneling, this primordial state spontaneously decayed into an expanding universe wherein particle creation and inflation occurred in a 'Fireball' phase. They discovered, however, that only closed, finite universes could arise from such a tunneling event. Rather than the universe starting from a flat, empty spacetime as BEG had proposed, the pre-existing state may already have had some topological structure to it and may also have had a non- zero total energy by virtue of its state of curvature.
Although there are two possibilities for the initial spacetime prior to tunneling, closed (finite) or open (infinite); the latter possibility is ruled out because it has infinite volume and vanishing tunneling probability. The only remaining possibility, it seems, is that the universe tunneled out of a pre-existing spacetime that was not flat as in the BEG proposal, but one which was already highly curved and finite. This means that, if you accept the Atkatz and Pagels theory, the initial spacetime was not "empty spacetime in its lowest energy state" but an already curved spacetime that was not in its lowest energy state of curvature.
An intriguing connection between this scenario and higher-dimensional unification theories has also been proposed. Since Superstring, grand unification theories require that spacetime be constructed from 10 or possibly 26 dimensions of which 6 (or 22 ) space-like dimensions had a compact topology, Atkatz and Pagels suggested that the pre-creation phase may have possessed a 10-dimensional, closed geometry in which 4 spontaneously grew to become our familiar 4-dimensional world at large. The birth of our universe, like the formation of ice from cold water, was a phase transition involving not just a change in particle attributes or forces, but may have included a spontaneous change in the very dimensionality and geometric structure of spacetime. An initial spacetime configuration quantum mechanically tunnels into a Fireball State in which particle creation occurs. Only spatially closed universes result. The prior spacetime configuration is in the form of a classically-stable, static spacetime. Unlike Tryon's model which is based on the strict conservation of energy throughout cosmogenesis, this model accepts the fact that in strongly curved gravitational fields, total energy is not defined because there no longer exists a reference, asymptotically flat space time against which it can be defined.
Dimensional Compactification
Chodos and Detweiler investigated a simple 5-dimensional cosmological model and discovered that prior to the Big Bang, the universe may have started out as a multidimensional object possessing more than 4 spacetime dimensions, but its expansion drove some of these dimensions to become small relative to the others. Our present universe is one in which 4 of the dimensions grew to large scales, however, there may exist compact dimensions to the physical manifold that have shrunk to sub-atomic size.
In 1917, Herman Weyl developed a theory of 'scale invariance' that later became the corner stone of modern gauge field theory: the basis for QED, QCD and electro-weak theory. Terry Bradfield investigated whether the universe may have gone through an early, scale-invariant, Weyl phase just before the Big Bang. In this stage, each of the many dimensions to spacetime were initially in a symmetric state. This means that in each of the dimensions, the universe appeared completely homogeneous and isotropic. Then, some of the dimensions to spacetime entered an inflationary phase and expanded to become the present set of anisotropic dimensions with 4 large ones and up to 6 internal ones.
When the Friedman cosmological models are formulated in D-dimensional general relativity, a variety of higher-dimensional cosmologies emerge. For D=4, the regular 4-dimensional spacetime, you recover the problems with the Initial Singularity. For the dimensionalities favored by String Theory of D=10 and D=26, M. Demianski and other co-workers discovered in 1991 that near the Planck Era, 4 of the dimensions expand while the remaining dimensions contract much as Chodos and Detweiler had shown in 1980 for 5-dimensional spacetimes. The bottom line is that by using spacetimes favored by string theory, you still wind up with initial states for the universe that are multi-dimensional, but evolve into the current 4 large dimensions, plus a collection of internal, compact dimensions suitable for particle physics.
Something from Nothing
Rather than the pre-existing state being a flat spacetime, or even a closed multidimensional one, this earliest conceivable state may have been quite literally nothing. As Frank Wilczyk notes,
"The reason that there is Something instead of Nothing is that Nothing is unstable."
More than a clever play on words, the physicists usage of the word Nothing carries with it an even more barren landscape than one normally imagines. Andre Vilenkin imagined a nothingness that was the complete negation of all conceivable attributes that we might attach to the particular fields within spacetime, or even to spacetime itself. It represented a state containing no fields, time, or space. The concept of dimensionality was also irrelevant, and without time it was the ultimate state of non-existence. Heinz Pagels vividly describes this condition in his book "Perfect Symmetry" as,
" The nothingness 'before' the creation of the universe is the most complete void that we can imagine – no space, time or matter existed. It is a world without place, without duration or eternity, without number...yet this unthinkable void converts itself into the plenum of existence – a necessary consequence of physical laws. Where are these laws written into the void? It would seem that even the void is subject to law, a logic that existed prior to time and space."
The advantage of this state was that since everything of physical significance was negated, one may not logically inquire where that negated state arose since to do so would imply that either a place or time exist prior to the universe's coming into being, and neither of these concepts has any meaning. All further talk of 'prior states' is halted once and for all. But, this interpretation is not the final word.
Quantum Metric Transformations
According to Jim Hartle and Stephen Hawkings, the Big Bang singularity did not occur because when the universe was small, its quantum state near the Planck Scale was dominated by metrics that had a signature of (1,1,1,1) and therefore, time became an imaginary coordinate with a space-like character. The origin of the universe cannot be assigned to a particular moment, so there is no singularity. The universe, in essence, emerged from a no-time state of pure space. Quantum fluctuations in the spacetime metric changed the signature from being purely Euclidean ( 1,1,1,1) to the familiar relativistic one (-1,1,1,1). The Euclidean spacetime tunneled into an inflationary DeSitter spacetime which started the Big Bang.
Pre-Geometric Vacuum State
According to Akama and Terazawa, the origin of the Big Bang represents a local and spontaneous phase change of spacetime from a pre-geometric phase to a geometric one. The gravitational field, and therefore the metric of spacetime, is a composite of more fundamental mathematical objects. At high-energy, spacetime dissociates into its constituent sub-fields just as ordinary atoms dissolve into their component sub-atomic particles. Under these conditions,m spacetime disappears entirely although the fundamental fields out of which it is composed, remain. These fields exist in another kind of manifold than physical spacetime. The dependency of how these fields interact as you change their energy, can be expressed mathematically, and it turns out that their potential energy reaches a minimum at the origin of the Big Bang. Prior to the Big Bang, pre-geometric fields interacted at energies above the Planck energy, and as they cooled, they underwent a phase transition at the Planck energy where the dynamical phase changed to favor the integration of these primordial fields into the synthesis of spacetime.
Eternal Inflation
There is a single spacetime that transcends not only the particular universe we live in that arose from a single miniscule patch, but also includes an infinite number of other mini-universes that developed from all the other patches as well. Rather than search for a specific unification theory that uniquely leads to the particles and forces in our universe, Andre Linde proposed that all possible GUTs are realized. As a consequence, in some of these patches, Inflation may have occurred leading to many other 'big' universes of which we are just one possibility. Some of the 'failed' universes may have lived only a microsecond or a few million years before dissappearing back into the quantum foam of spacetime. Each of the inflated domains is vastly larger than the region within them that any one observer may perceive and will appear very uniform within these locally observable regions. However, on the largest scales, these domains are part of a complex foam in spacetime and may be interconnected by tunnels or 'wormholes' For some domains, these tunnels may have evaporated, rendering these universes utterly disconnected in spacetime from one another. It may also be possible that the creation of new universes is a process occurring even now. According to Linde,
"We find ourselves inside a four-dimensional domain with our kind of low-energy physics, not because other kinds of mini-universes are impossible, but simply because our kind of life cannot exist in other domains...It is extremely complicated, if not impossible, to construct a theory in which only one kind of compactification can occur, leading precisely to a four-dimensional, inflationary universe, with the low-energy particle physics of our own experience....Now it seems more likely that the universe is an eternally existing, self-producing entity, that is divided into many mini-universes much larger than our observable portion, and that the laws of physics, and even the dimensionality of spacetime, may be different in each [of them].."
Soviet physicists Gurevich and Mostepanenko also considered the existence of an ensemble of universes, each manifesting spacetimes of all possible dimensionalities. In the cosmology formulated by Blau, Guendelman and Guth in 1987, the quantum gravity foam may be constantly creating bubble universes that pinch-off from our spacetime, some of which may even expand into universes like our own. Since their expansion occurs in a region of spacetime completely disconnected from our own, they are forever beyond observation.
The artificial manufacture of such universes may be possible under laboratory conditions, unfortunately, calculations seem to indicate that these conditions may not be easily achievable. A similar idea was later formulated by Ghoroku and Coleman in 1994. Universes can interact with each other at the quantum level via wormholes. A great many universes could be created from nothing, each disconnected at the classical scale, but in contact at the Planck-level via quantum wormhole interference.
These universes are considered to be defined by fields in superspace, and can be coherently coupled to each other via universal wavefunctions. As a result of quantum interference, and the spawning of baby universes by our own spacetime, the cosmological constant has a vanishing magnitude in all universes similar to our own as Sidney Coleman pointed out.
Stringy Cosmology
Gasperini and Veneziano applied String Theory to understanding the physics of the Big Bang near the Planck Era. The initial singularity is avoided. The curvature grows to a maximum, then starts decreasing as we pass through the Planck Time into the present expansion era. String Theory suggests that the pre-Big bang era may have been a state in which oscillations in the expansion of spacetime occurred in the current mixture of internal and external dimensionality. After some time, these oscillations settled down to the present 6+4 or 22+4 split with 4 large dimensions and up to 22 compact dimensions.
Mark Bowick and L. Wijewordhana also discovered that if you use string theory to describe the dynamics of gravity and matter fields near the Planck Era, that above a critical energy, the vibration modes of the string get excited to higher and higher energies until the entire physical system —the universe— experiences a phase transition in which the strings evaporate.
David Meyer, in 1993, also combined string theory with work in quantum gravity to show that the appearance of time and ticking clocks may have occurred as a phase transition between disordered a-causal states and one in which causal connections between states can be defined. While a theory based upon causality may appear to have in it an inherent notion of time, this may have arisen by way of a phase transition in the theory perhaps similar to the kind that occur in superconductors.
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Preview Image
"Five Year Microwave Sky" - The detailed, all-sky picture of the infant universe from three years of WMAP data. The image reveals 13.7 billion year old temperature fluctuations (shown as color differences) that correspond to the seeds that grew to become the galaxies. The signal from our Galaxy was subtracted using the multi-frequency data. This image shows a temperature range of ± 200 microKelvin. View full-size image. Internal Linear Combination Map, Galactic coordinates, Mollweide projection. Linear scale from -200 to 200 uK. Wilkinson Microwave Anisotropy Probe (WMAP) Science Team, NASA.
Citation
Odenwald, Sten, Ph.D. (Contributing Author); Bernard Haisch (Topic Editor). 2009. "Universe: Creation." In: Encyclopedia of the Cosmos. Eds. Bernard Haisch and Joakim F. Lindblom (Redwood City, CA: Digital Universe Foundation). [First published May 2, 2008].
<http://www.cosmosportal.org/articles/view/138895/>
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