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The standard model has a number of constants whose specific values are under scrutiny. The fine-tuning problem is that these constants must be a very narrow range for the universe to exist in a real sense - ie the creation of stars and galaxies.

One aspect of the multiverse theory is to determine some or all them via a darwinian process. The hope is that this will both reduce the number of constants, and also drive the constants to the range required.

The best it that it can do is to reduce the number of constants to one.

But surely then the fine-tuning problem still exists, in that this one constant carries the probability (tending to certainty) that a universe with our constants (that is our universe) can emerge?

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  • I don't quite get what you mean by the two last paragraphs. As far as I understand, one way the multiverse theory - in some versions - could solve the fine-tuning problem is that if every possible universe eventually exists, then there will exist a universe with such constants as to make possible intelligent life that in turn could ask such questions. We simply happen to be in one of those universes, which is why we see the constants as if they were fine-tuned. – Koeng Sep 20 '13 at 16:45
  • @Koeng: There are various kinds of multiverses, I'm referring to one outlined by Smolin - cosmological natural selection. Intriguinly, the version that you mention seems to have a family resemblence to the one announced by Leibniz - that we live in the best of all possible worlds - that is one which has the right range of constants to support the universe as we know it. – Mozibur Ullah Sep 20 '13 at 17:17
  • Yeah, but that idea depends on a definition of a "best world", and it seems to just change the fine-tuning to somewhere else. Also, maybe different possible worlds could give rise to intelligent life, not necessarily only ours. Regarding the Smolin theory - I didn't know it, just read the wikipedia page -, I think that not necessarily the problem exists when you reduce all constants to one. If enough probability peaks exist, we are just one among others, and in the same way we wouldn't say "that universe is fine-tuned to have ~no~ humans in it". – Koeng Sep 20 '13 at 22:02
  • yes, thats true. I was just using Leibnizs possible worlds to show that the multiverse is not new idea; except of course it is, in the specific form it takes in physical cosmology. You're right I'm tying in two related problems - the number of constants and the specific value they take. – Mozibur Ullah Sep 21 '13 at 18:40
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If there is a premise that the universe only occurred once, then it is highly improbable that all the constants would be finely tuned as they are. If on the other hand you take the premise that our universe is not eternal, that there have been other universe before and others in the future, then it can happen. There have been universes in the past and there will be universes in the future where the constants that allow the phenomena of our universe not to occur. Perhaps the universe right before the present universe was completed disjointed because the constants were not in tune. Perhaps a universe that has the correct balance occurs in 1 out of every 100 trillion universes that have occurred in the past, and won't occur again for the same period of time. It's kind of like throwing a pair of dice. If you get an occurrence of a sequence of 3 rolls with 5,8,2; you know that if you keep on rolling, sooner or later you will get the same sequence to occur. If you think that in the eternity of time universes are coming and going, then any type of universe will sooner or later occur. The same logic stands in a multiverse, most of the universes will probably be non-functional blobs so to speak.

Here's an extension to the best universe musing - what are the chances that we are living at a time where our moon just covers our sun completely during a total solar eclipse? what are the chances that the planet that we are on has at this point in time has 2 stable magnetic poles, not multiple poles, or drifting poles (which thus allows a stable magnetic field around us and thus allows electronic gadgets and telecommunications to exist)? What are the chances that our sun and system are in an eddy of the our galaxy, thus allowing our weak magnetic belt (the Van Allen belt) to protect us from our sun's solar winds (outside our eddy, in the galactic arm the galactic wind is so strong that it would overpower the solar winds and strip our weak magnetic field right off and life would not be possible as we know it). Or that we have evolved our civilization about half way between 2 ice ages? I can keep piling on the coincidences.......

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Their was an truly amazing article in the August 2011 edition of the Scientific American that addresses the issue of the multiverse. In this article the noted and internationally famous cosmologist George Ellis calls into questions the validity of trying to explain away the apparent fine tuning of the universe with a call to Multiverses.

A few quotes.

“Similar claims [about a multiverse] have been made since antiquity by many cultures. What is new is the assertion that the multiverse is a scientific theory, with all that implies about being mathematically rigorous and experimentally testable. I am skeptical about this claim. I do not believe the existence of those other universes has been proved—or ever could be. Proponents of the multiverse, as well as greatly enlarging our conception of physical reality, are implicitly redefining what is meant by ‘science.’”—pg 39

“For a cosmologist, the basic problem with all multiverse proposals is the presence of a cosmic visual horizon. The horizon is the limit to how far away we can see, because signals traveling toward us at the speed of light (which is finite) have not had time since the beginning of the universe to reach us from farther out. All the parallel universes lie outside our horizon and remain beyond our capacity to see, now or ever, no matter how technology evolves. In fact, they are to far away to have had any influence on our universe whatsoever. That is why none of the claims made by multiverse enthusiasts can be directly substantiated.”—pg 40-41

“A remarkable fact about our universe is that physical constants have just the right values needed to allow for complex structures, including living things. Steven Weinberg, Martin Rees, Leonard Susskind and others contend that an exotic multiverse provides a tidy explanation for this apparent coincidence: if all possible values occur in a large enough collection of universes, then viable ones for life will surely be found somewhere. This reasoning has been applied, in particular, to explanation the density of the dark energy that is speeding up the expansion of the universe today. I agree that the multiverse is a possible valid explanation for the value of this density; arguably, it is the only scientifically based option we have right now. But we have no hope of testing it observationally.”—pg 42

“All in all, the case for the multiverse is inconclusive. The basic reason is the extreme flexibility of the proposal: it is more a concept than well-defined theory. Most proposals involve a patchwork of different ideas rather than a coherent whole. The basic mechanism for eternal inflation does not itself cause physics to be different in each domain in a multiverse; for that, it needs to be coupled to another speculative theory. Although they can be fitted together, there is nothing inevitable about it. … Nothing is wrong with scientifically based philosophical speculation, which is what multiverse proposals are. But we should name it for what it is.”—pg 43

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  • Exactly, speculative physics is nothing to be ashamed. – Mozibur Ullah Sep 25 '13 at 10:21

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