Hubble, Arrow of Time, and Entropy
Country: United Kingdom
Date: Fall 2012
If the arrow of time theory is correct and entropy must continually increase, does this mean that Hubble's idea of a big crunch is impossible as entropy would effectively have to work in reverse? If so can entropy ever reach a maximum?
It is important here to remember that the second law of thermodynamics (that entropy of the universe must increase with each spontaneous process) is a law - for the present set of conditions. There is nothing in science that says that these laws may not be adjusted or even repealed if conditions change drastically. If a Big Crunch becomes possible - if the universe's gravity is sufficient to stop the expansion and begin a compression, then a spontaneous process would result in a decrease in entropy and we can imagine that some science laws will have to be adjusted. This is fine - science always adjusts to new data. Current data however indicates that there is too much missing mass to create a reversal of the expansion of the universe, there is even some evidence that there is something that is causing an acceleration of the expansion, as such, data seems to indicate that the Big Crunch may never happen.
Greg (Roberto Gregorius)
The ultimate correct answers to your questions must be left for time to resolve, but here is what we know:
The arrow of time theory is correct because it contradicts itself. That is, if one could go back in time and change events, then the period of time in which one originally went back in time would not exist.
Current observations show that the universe is expanding; and, that the rate of acceleration is increasing. But like as I said before, the ultimate answer is not known, but the evidence shows that entropy will continue and instead of a big crunch, our ultimate fate will be a the quiet of a vacant void.
The idea of an edge (frontier) to our universe is a semantical question to me because if the universe is the single (uni) sum total all that there is, then what would be on the other side of it? So entropy will continue without end (forever) unless it runs into a fixed edge to the universe which, if there is an edge, appears to be expanding.
Your questions are valid. A Big Crunch or a Big Bounce would seemingly defy all known entropy theory. However, a Big Crunch or a Big Bounce does answer other cosmological questions. Branes helps with the entropy effects and so does the Multi-verse, but those also have troublesome behaviors.
We do not have an adequate answer for all of the questions involving something as huge as the Universe... yet. People are looking at pieces trying to find a unified model.
Questions such as yours are why and how other forms of hypotheses are developed. A scientist(s) concentrates on one such question and solves it. Then another scientist may work on another question(s) and solve it. As the questions lead to more questions and solving begins to form more hypotheses; eventually we will find a working model that seems to answer most of the questions most of the time.
For the present, we have models that work for relatively large facets of cosmological behaviors. Unification is the paramount endeavor.
Your last question is by far the most intriguing from my standpoint... are we entirely correct about cosmological entropy?
Thanks for your question! Peter E. Hughes, Ph.D. Milford, NH
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Update: December 2011