Originally posted by Chrawnus
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This article (from a series of 6 articles) by Alan Guth from counterbalance.org has been posted before on these forums, but I think it's still relevant. The article deals with the issue of eternal inflation and what it has to say about the question of the ultimate beginning, i.e not only the beginning of our universe, but even further back than that. Here's what Guth has to say about this issue:
http://www.counterbalance.org/cq-guth/didth-frame.html
Some clarifications here. The universe Guth is speaking about here is the greater universe, not our universe, as can be shown by what Guth writes in the previous 5 articles (they can be accessed by clicking on the links on the right hand side of the page titled "Introduction", "How Does Inflation Work", "Evidence for Inflation", "Eternal Inflation: Mechanisms" and "Eternal Inflation: Implications") especially in the fourth article and the article titled Introduction where he writes:
http://www.counterbalance.org/cq-guth/index-frame.html
Here Guth is, it seems to me speaking of our own universe. Which means that the question of whether our universe had a beginning or not is not really up for question. In other words, the question that remains to be answered is not whether our universe had beginning, but whether or not the greater universe that produced our universe (supposing the eternal inflation theory is correct) had a beginning.
In the fourth article Guth tries to explain the mechanisms behind eternal inflation, and has this to say, after describing how the repulsive-gravity material's (Guth's name for the false vacuum) expansion rate, which is faster than the repulsive-gravity material's decay rate leads to a scenario where an infinite number of pocket universes (of which ours is one) are created in a exponentially growing sea of repulsive-gravity material:
http://www.counterbalance.org/cq-guth/etern-frame.html
In other words, when Guth is speaking of the universe from this point on in the series of articles on counterbalance.org, it can be safely assumed that he is talking about the fractally structured greater universe and not our own pocket universe unless Guth clarifies otherwise.
Going back to the last article in the series, we can conclude the following:
1. The BGV theorem applies to every model of eternal inflation that has been found so far, which means that the greater universe that produced our pocket universe had to start out as a singularity, and thus must have had a beginning.
2. Guth's opinion on the matter is that it " it looks like eternally inflating models necessarily have a beginning.", despite the fact that quantum fluctuations would violate one of the assumptions upon which the theorem rests.
Guth concludes with the following:
In conclusion, Alan Guth believes that the BGV theorem when applied to the eternal inflation models that have been found viable so far, makes it probable that the universe (understood here as the greater universe that has a fractal structure, and which produced our pocket universe) had a beginning. In other words, he thinks that the BGV theorem can be applied to the greater universe, and that the BGV theorem makes it probable that the greater universe necessarily had a beginning.
Here's links to the entire series of articles for those interested, or those who want to check that I have understood Guth correctly on this matter:
http://www.counterbalance.org/cq-guth/index-frame.html
http://www.counterbalance.org/cq-guth/howdo-frame.html
http://www.counterbalance.org/cq-guth/evide-frame.html
http://www.counterbalance.org/cq-guth/etern-frame.html
http://www.counterbalance.org/cq-guth/etern1-frame.html
http://www.counterbalance.org/cq-guth/didth-frame.html
http://www.counterbalance.org/cq-guth/didth-frame.html
Some clarifications here. The universe Guth is speaking about here is the greater universe, not our universe, as can be shown by what Guth writes in the previous 5 articles (they can be accessed by clicking on the links on the right hand side of the page titled "Introduction", "How Does Inflation Work", "Evidence for Inflation", "Eternal Inflation: Mechanisms" and "Eternal Inflation: Implications") especially in the fourth article and the article titled Introduction where he writes:
http://www.counterbalance.org/cq-guth/index-frame.html
Here Guth is, it seems to me speaking of our own universe. Which means that the question of whether our universe had a beginning or not is not really up for question. In other words, the question that remains to be answered is not whether our universe had beginning, but whether or not the greater universe that produced our universe (supposing the eternal inflation theory is correct) had a beginning.
In the fourth article Guth tries to explain the mechanisms behind eternal inflation, and has this to say, after describing how the repulsive-gravity material's (Guth's name for the false vacuum) expansion rate, which is faster than the repulsive-gravity material's decay rate leads to a scenario where an infinite number of pocket universes (of which ours is one) are created in a exponentially growing sea of repulsive-gravity material:
http://www.counterbalance.org/cq-guth/etern-frame.html
In other words, when Guth is speaking of the universe from this point on in the series of articles on counterbalance.org, it can be safely assumed that he is talking about the fractally structured greater universe and not our own pocket universe unless Guth clarifies otherwise.
Going back to the last article in the series, we can conclude the following:
1. The BGV theorem applies to every model of eternal inflation that has been found so far, which means that the greater universe that produced our pocket universe had to start out as a singularity, and thus must have had a beginning.
2. Guth's opinion on the matter is that it " it looks like eternally inflating models necessarily have a beginning.", despite the fact that quantum fluctuations would violate one of the assumptions upon which the theorem rests.
Guth concludes with the following:
In conclusion, Alan Guth believes that the BGV theorem when applied to the eternal inflation models that have been found viable so far, makes it probable that the universe (understood here as the greater universe that has a fractal structure, and which produced our pocket universe) had a beginning. In other words, he thinks that the BGV theorem can be applied to the greater universe, and that the BGV theorem makes it probable that the greater universe necessarily had a beginning.
Here's links to the entire series of articles for those interested, or those who want to check that I have understood Guth correctly on this matter:
http://www.counterbalance.org/cq-guth/index-frame.html
http://www.counterbalance.org/cq-guth/howdo-frame.html
http://www.counterbalance.org/cq-guth/evide-frame.html
http://www.counterbalance.org/cq-guth/etern-frame.html
http://www.counterbalance.org/cq-guth/etern1-frame.html
http://www.counterbalance.org/cq-guth/didth-frame.html
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