The big bang could be a normal event in the evolution of the universe and it will happen again and again over a vast time frame
By Ariel Eisenhandler
According to two physicists from the University of Chicago, the Big Bang could be a normal event in the evolution of the universe and it will occur repeatedly over a vast time frame during the expansion, emptying and cooling of the universe. "We would be happy to say that the Big Bang is not an important event in the history of our universe," says Sean Carroll, assistant professor of physics at the University of Chicago. Carol and graduate student Jennifer Chen will publish an electronic paper about their ideas on Arxic.
Carroll and Chen's research came to answer two ambitious questions: why does time only move in one direction and could the big bang have appeared due to energy fluctuations in empty space obeying the known laws of physics?
The question of the arrow of time has bothered scientists for a century because: "Most of the basic laws of physics do not differentiate between past and future." They are symmetrical in terms of time," says Carroll. Closely related to the theme of time is the concept of entropy, a measure of disorder in the universe. As the physicist Ludwig Boltzmann showed about a century ago, entropy naturally increases with time. "You can turn an egg into an omelet, but not an omelet into an egg," says Carroll.
The mystery remains as to why entropy was low in the universe in the first place. The difficulty in the question has troubled scientists for a long time, and most of them have dismissed it and left it as a puzzle to be solved in the future. Carol and Chen made an attempt to answer her now. Previous researchers have approached problems related to the Big Bang with the assumption that entropy in the universe is finite. Carroll and Chen took the opposite approach. "We assume that the entropy in the universe is infinite. She will always be able to grow," says Chen.
To successfully explain why the universe looks the way it does today, both approaches need to include a process called inflation, which is an extension of the big bang theory. Astrophysicists came up with the inflation theory so they could explain the universe, as it appears today. According to the inflation theory, the universe experienced a period of massive expansion in a fraction of a second after the big bang. But there is a problem with this scenario, "a skeleton in the closet," says Carroll. To begin swelling, the universe must contain a tiny microscopic patch of a highly improbable configuration - not something scientists would expect from a randomly chosen initial state. Carroll and Chen claim that a general initial state will be similar to a cold, empty space - specifically not the preferred starting point for the initiation of swelling.
A number of scientists propose, based on the assumption that the entropy in the universe is finite, that a random fluctuation could trigger inflation, but this requires the molecules of the universe to oscillate from a high entropy state to a low entropy state - a statistically slim chance. "The conditions needed to start swelling are not easy to achieve," says Carroll. "There is an argument that it is easier to accept the appearance of the universe from a random fluctuation than the beginning of inflation from a random fluctuation."
Carroll and Chen's scenario of infinite entropy was inspired by the 1998 findings: the universe will expand forever due to a mysterious force called "dark energy". Under these conditions the natural configuration of the universe is one that is almost empty. "In the current universe, entropy is increasing and the universe is expanding and becoming emptier," says Carroll.
But even empty space has faint traces of energy oscillating at the subatomic level. As already suggested previously, by Jaume Garriga of the Autonomous University of Barcelona (Universitat Autonoma de Barcelona) and Alexander Vilenkin (Alexander Vilenkin) of Tufts University, these fluctuations can produce their own large compensations in tiny regions of the universe, separated by large distances in terms of time and space. Carroll and Chen extend the idea dramatically, suggesting that inflation could start "backwards" in the distant past of our universe, so that time would appear to be moving backwards (from our perspective) to observers in our distant past.
Regardless of the direction of their trajectory, the new universes created in those great compensators will continue the process of increasing entropy. In this endless cycle, the universe never reaches equilibrium. If it did reach equilibrium, nothing would happen. There was no arrow of time.
"There is no state that you will reach in which there will be maximum entropy. You can always increase entropy by creating a new universe and allowing that universe to expand and cool," explains Carroll. A new mathematical model allows scientists to describe the time before the universe was formed
Was there a collapsed universe before the big bang?
By Ofri Ilani, Haaretz, 3/7/2007
What was there before the universe was created? When the fathers of the Catholic Church were asked what God did before he created the world, they replied: "He prepared hell for those who would ask this question." But even in the modern era, philosophers and scientists tried to answer this question, and in most cases they did not receive an answer.
But now, astrophysicists from the Department of Physics at the University of Pennsylvania claim to have succeeded in developing a new mathematical model, which describes the beginning of the universe as a "big pulse", instead of the "big bang" model accepted today to describe the beginning of the universe. This means that the current universe was born after the collapse of a previous universe. The theory, developed by a team led by physicist Martin Boiwald from the University of Pennsylvania, was published yesterday in the journal Nature Physics.
The Big Bang theory, based on Einstein's theory of general relativity, is the dominant theory regarding the origin and expansion of the universe. According to this model, the universe expanded from a point that has zero area, but is of infinite density. This point is described by physicists as a "singularity" - an unusual situation in which all the laws of nature collapse, including the theory of relativity itself. For this reason, most researchers believe that no scientific determination can be made regarding the time before the beginning of the universe.
This position is held, among other things, by the physicist Prof. Stephen Hawking, who states in his book "A Brief History of Time" that "as far as we are concerned, the events before the Big Bang have no consequences, so they have no place in any scientific model of the universe."
But in recent years, some physicists claim that looking beyond the big bang barrier is possible. Bojwald is one of the leading researchers who hold this position. His research is based on a relatively new theory called "loop gravity", which has been developed in recent years by mathematicians from the University of Pennsylvania. This theory, which combines the theory of relativity with innovative developments of quantum mechanics, is able, according to the researchers, to "open a window" in the singularity of the beginning of the universe, which will allow a glimpse of the universe that preceded it.
Unlike the big bang theory, the new theory claims that the mass that was concentrated at the beginning of the universe was very large but not infinite, and also that the point from which the universe began to expand was very small, but not zero in size. Due to this, the laws of nature do not collapse at the beginning of the universe, and determinations can also be made regarding the period before the big bang.
According to Boivald, the theory of relativity is partial, and today physicists have mathematical tools that were unknown to Einstein. "Einstein's teachings do not include the fields of quantum physics that are required to describe the high energies that were in our universe in the earliest stages of its development," he says. "But through loop gravity we are able to do it." Bojwald also claims that his new model is simpler and more elegant than the currently accepted model of the beginning of the universe.
What can be said about the previous universe? According to Boywald, it can be established that the structure of the "universe before the universe" was based on the same fundamental geometry as our universe. However, certain properties of that universe may be different from our own, but unknowable due to the unusual physical conditions that prevailed at the beginning of the current universe. Bojwald rules out the possibility of "eternal recurrence", that is, of a series of completely identical universes, which grew and collapsed over infinite time. According to him, "at least some of the features of each universe fail to 'survive the trip' through the great pulse, and are stored in the feminine abyss of cosmic oblivion."
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Everything can be true in this wonderful universe