There are something like ten million million million million million million million million million million million million million million (1 with eighty [five] zeroes after it) particles in the region of the universe that we can observe. Where did they all come from? The answer is that, in quantum theory, particles can be created out of energy in the form of particle/antiparticle pairs. But that just raises the question of where the energy came from. The answer is that the total energy of the universe is exactly zero. The matter in the universe is made out of positive energy. However, the matter is all attracting itself by gravity. Two pieces of matter that are close to each other have less energy than the same two pieces a long way apart, because you have to expend energy to separate them against the gravitational force that is pulling them together. Thus, in a sense, the gravitational field has negative energy. In the case of a universe that is approximately uniform in space, one can show that this negative gravitational energy exactly cancels the positive energy represented by the matter. So the total energy of the universe is zero. (Hawking, 1988, 129) [thanks to Ross King for this quote]
There is a still more remarkable possibility, which is the creation of matter from a state of zero energy. This possibility arises because energy can be both positive and negative. The energy of motion or the energy of mass is always positive, but the energy of attraction, such as that due to certain types of gravitational or electromagnetic field, is negative. Circumstances can arise in which the positive energy that goes to make up the mass of newly-created particles of matter is exactly offset by the negative energy of gravity of electromagnetism. For example, in the vicinity of an atomic nucleus the electric field is intense. If a nucleus containing 200 protons could be made (possible but difficult), then the system becomes unstable against the spontaneous production of electron-positron pairs, without any energy input at all. The reason is that the negative electric energy can exactly offset the energy of their masses.
In the gravitational case the situation is still more bizarre, for the gravitational field is only a spacewarp - curved space. The energy locked up in a spacewarp can be converted into particles of matter and antimatter. This occurs, for example, near a black hole, and was probably also the most important source of particles in the big bang. Thus, matter appears spontaneously out of empty space. The question then arises, did the primeval bang possess energy, or is the entire universe a state of zero energy, with the energy of all the material offset by negative energy of gravitational attraction?
It is possible to settle the issue by a simple calculation. Astronomers can measure the masses of galaxies, their average separation, and their speeds of recession. Putting these numbers into a formula yields a quantity which some physicists have interpreted as the total energy of the universe. The answer does indeed come out to be zero within the observational accuracy. The reason for this distinctive result has long been a source of puzzlement to cosmologists. Some have suggested that there is a deep cosmic principle at work which requires the universe to have exactly zero energy. If that is so the cosmos can follow the path of least resistance, coming into existence without requiring any input of matter or energy at all. (Davies, 1983, 31-32)
Once our minds accept the mutability of matter and the new idea of the vacuum, we can speculate on the origin of the biggest thing we know - the universe. Maybe the universe itself sprang into existence out of nothingness - a gigantic vacuum fluctuation which we know today as the big bang. Remarkably, the laws of modern physics allow for this possibility. (Pagels, 1982, 247)
In general relativity, spacetime can be empty of matter or radiation and still contain energy stored in its curvature. Uncaused, random quantum fluctuations in a flat, empty, featureless spacetime can produce local regions with positive or negative curvature. This is called the "spacetime foam" and the regions are called "bubbles of false vacuum." Wherever the curvature is positive a bubble of false vacuum will, according to Einstein's equations, exponentially inflate. In 10-42 seconds the bubble will expand to the size of a proton and the energy within will be sufficient to produce all the mass of the universe.
The bubbles start out with no matter, radiation, or force fields and maximum entropy. They contain energy in their curvature, and so are a "false vacuum." As they expand, the energy within increases exponentially. This does not violate energy conservation since the false vacuum has a negative pressure (believe me, this is all follows from the equations that Einstein wrote down in 1916) so the expanding bubble does work on itself.
As the bubble universe expands, a kind of friction occurs in which energy is converted into particles. The temperature then drops and a series of spontaneous symmetry breaking processes occurs, as in a magnet cooled below the Curie point and a essentially random structure of the particles and forces appears. Inflation stops and we move into the more familiar big bang.
The forces and particles that appear are more-or-less random, governed only by symmetry principles (like the conservation principles of energy and momentum) that are also not the product of design but exactly what one has in the absence of design.
The so-called "anthropic coincidences," in which the particles and forces of physics seem to be "fine-tuned" for the production of Carbon-based life are explained by the fact that the spacetime foam has an infinite number of universes popping off, each different. We just happen to be in the one where the forces and particles lent themselves to the generation of carbon and other atoms with the complexity necessary to evolve living and thinking organisms. (Stenger, 1996)
Where did all the matter and radiation in the universe come from in the first place? Recent intriguing theoretical research by physicists such as Steven Weinberg of Harvard and Ya. B. Zel'dovich in Moscow suggest that the universe began as a perfect vacuum and that all the particles of the material world were created from the expansion of space...
Think about the universe immediately after the Big Bang. Space is violently expanding with explosive vigor. Yet, as we have seen, all space is seething with virtual pairs of particles and antiparticles. Normally, a particle and anti-particle have no trouble getting back together in a time interval...short enough so that the conservation of mass is satisfied under the uncertainty principle. During the Big Bang, however, space was expanding so fast that particles were rapidly pulled away from their corresponding antiparticles. Deprived of the opportunity to recombine, these virtual particles had to become real particles in the real world. Where did the energy come from to achieve this materialization?
Recall that the Big Bang was like the center of a black hole. A vast supply of gravitational energy was therefore associated with the intense gravity of this cosmic singularity. This resource provided ample energy to completely fill the universe with all conceivable kinds of particles and antiparticles. Thus, immediately after the Planck time, the universe was flooded with particles and antiparticles created by the violent expansion of space. (Kaufmann, 1985, 529-532)
...the idea of a First Cause sounds somewhat fishy in light of the modern theory of quantum mechanics. According to the most commonly accepted interpretation of quantum mechanics, individual subatomic particles can behave in unpredictable ways and there are numerous random, uncaused events. (Morris, 1997, 19)
Monday, May 25, 2009
Vacuum Fluctuations
Some interesting views on the vacuum fluctuations which began the universe
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