Multiverse Cosmological Models

[Vast]

Authors: P.C.W. Davies
Comments: 15 pages, no figures, review paper

Recent advances in string theory and inflationary cosmology have led to a surge of interest in the possible existence of an ensemble of cosmic regions, or universes, among the members of which key physical parameters, such as the masses of elementary particles and the coupling constants, might assume different values. The observed values in our cosmic region are then attributed to an observer selection effect (the so-called anthropic principle). The assemblage of universes has been dubbed the multiverse. In this paper I review the multiverse concept and the criticisms that have been advanced against it on both scientific and philosophical grounds.

There is much confusion and mystery surrounding the Multiverse Theory. At present there is a wide range of different Multiverse Theories, which this paper does a good job in giving the basic concept behind the different variations

Multiverse cosmological models

 

[meteor]

It has been an entertaining reading (written in a popular level). Various of the multiverse models discussed are Smolin's "natural selection of universes", Everett's relative formulation of QM, the ekpyrotic scenario and the most recent of all, Tegmark multiverse

 

[Vast]

So many to consider and contemplate, however going by what’s popular or otherwise consistently theorized, that being Smolin’s “baby universes”, Everett’s “many-worlds” theory, pre big bang or eternal inflation, hopefully one scenario will show more promise than other’s which seem to be more counterfactual in nature.

 

[Dlanorrenrag]

Anthropic Principle

Suppose Being is directed in a way that is made subject to gross laws and decisions that we can measure and make, but that it is also directed by causes and decisions that can only be weighed at a level of mathematically infinite calculations? Chaos theory demonstrates that any number of extremely minor changes at a small scale can effect extremely profound changes at the great scale of many complex systems.

Might an Intelligent Architect who receives infinite artistic feedback be able to pull the strings of Being much as desired, simply by applying chaos theory combined with quantum indeterminacy? If so, perhaps such an infinite Architect could not communicate such infinite capacity to the comprehension of a sub-component. But, could such an Architect communicate involvement to our intuition and faith, simply by occasionally demonstrating fantastically extraordinary or fortuitous coincidences that defy all reasonable expectations under our understandings of the gross laws which nourish our survival?

Given our ability to imagine infinite multiverses and other non-limits on our infinite imaginations, non-faith appears to be non-falsifiable. So, is non-faith more a matter of attitude and disposition, or one of logic or experience?

 

[Vast]

To those that study the universe, will come across certain aspects which will seem to suggest the universe had been fine-tuned. Many multiverse theories use natural selection to determine the laws of physics and so forth. Other’s like the many-worlds theory seem to be more like a schizophrenic interpretation of reality.
Another is to suppose that God selected this universe, or that an intelligent architect is behind the scenes.

But faith doesn’t constitute science, it is a part of ones religion.

 

[Dlanorrenrag]

Faith In Science

I agree. But, I also think faith in values or spirituality often drives intuition, which often leads to useful scientific notions. At its limits, I am not sure that science is completely separate from faith or art. At some limits, thinking something so sometimes seems to help make it become so. Someday, might scientific pharoahs be able to say, "So let it be written, so let it be done"? Or, as Shakespeare said, "For there is nothing either good or bad, but thinking makes it so."

I think religious faith should try not to be blind to, or jealous of, science. Generally, my intuition is that humanity should endeavor towards a more mature understanding of a sort of actively involved artistically scientific Creator. Might not an appreciation of limits of science and religion further that endavor? Obviously, my line of thinking is not meant to further science per se, but only to point to room for a faith in values that can accompany our faith in science.

 

[Vast]

I understand you line of thinking, and how you apply that to the universe, but I do not share your vision of humanity endeavoring to reach a more mature understanding of God.

I don’t mean to say faith doesn’t have its place, but in regards to scientific discoveries it is a bit off topic.

 

[Dlanorrenrag]

Aesthetic Preferences

Unless buried beneath the lines, scientists must recoil from respect for spirituality to such a point that they are amenable of positing “mathematical proofs” for somethingness arising from nothingness and/or for the potentialities of non-existence and existence to be equivalent. Next will be death as being equivalent to life---but only, of course, in a “mathematical, non-spiritual sort of way.” Given our propensities for religious chauvinism, we have learned from hard history that it must be thus. Yet, it also seems intuitive that our age is fast approaching an overlap between science’s arrival to the point of proof by aesthetics and religion’s need to mature us towards some kind of civilized respect for common values. In the meantime, any overlap just leads to a big clash. Is there basis for recognizing far out or aesthetic positions in science that cannot be rationally defended?

 

[Vast]

Your evaluation of religions background and it’s relation to such fundamental concepts, (if that’s what it is) has its rightful place in history, and by all means it still plays a large role in the world today.

So what if our age is fast approaching some new understanding, who are you to say its an intelligent architect, and who am I to say the universe is another way? Discoveries will be made regardless, and if a clash of ideas concerns you, perhaps it’s because some things are not yet well understood by either side?

 

[Dlanorrenrag]

Are Values An Example Of *No-Thing* To Science?

I am no one in particular---just a searcher, like everyone else. What I would like to get a scientific, logical, or objective grip on is this: how, if at all, might we begin to find objective guidance for agreeing on any values? Is any search for a basis for sharing values so chaotic, random, nonsensical, and lacking in meaning as to be unworthy of any scientific analysis at all, except to deem it unworthy? How is it that science can find something of order in chaos, and something in nothing, but can find *nothing* of science in values?

Is it scientific to posit that science has no role in forming value beliefs? Are values *“something”* to science, or *“no-thing”* to science? Practicing medicine would seem to be both a science and an art. What about clarifying or practicing ethics?

***If we preach that science, logic, and objectivity should have a *nothing* role in shaping ethics, then to what kind of humanity do we leave the role of shaping ethics?

Even if “nothing” else, cannot science and/or physics gradually lead us past kinds of religious chauvenism, towards new metaphors for appreciating or considering old mythical explanations of existence, perhaps towards ways carrying more survival or other value than convincing ourselves that an Ultimate Source of values must be limited to a String Violin, a White Elephant, a Slavemaster, or Whatever?

 

[Nereid]

These are indeed good questions, and worthy of discussion in PF. However, I feel they are better discussed in another sub-forum, perhaps Metaphysics and Epistimology? Maybe a Mentor would be so kind as to move this thread there.

Alternatively, we could get back on track by discussing multiverse models.

 

[VikingF]

What is really the main difference between the infinite inflation cosmology by Linde and the baby universe cosmology by Smolin?

Is it correct to say that in the "baby-universe" multiverse, a universe is generated by a "mother universe", while in the inflation multiverse, a universe is generated independently of the other universes?


(Sorry about the bumping, but I thought it was better to add my question to this already-existing thread, than to create a new thread about the same topic)

 

[Vast]

What is really the main difference between the infinite inflation cosmology by Linde and the baby universe cosmology by Smolin?

Is it correct to say that in the "baby-universe" multiverse, a universe is generated by a "mother universe", while in the inflation multiverse, a universe is generated independently of the other universes?

Hi Viking. I think you can say that in both scenarios, a universe is created from an older one. The differece between the models however, is that in the inflationary model, space expands so much so that new universes are created out of quantum fluctuations in the vacuum of space. (think of a soap bubble tearing itself apart into two) While Smolins model has universes created from black holes.

 

[marcus]

What is really the main difference between the infinite inflation cosmology by Linde and the baby universe cosmology by Smolin?

Is it correct to say that in the "baby-universe" multiverse, a universe is generated by a "mother universe", while in the inflation multiverse, a universe is generated independently of the other universes?
...

Smolin's CNS hypothesis PREDICTS SOMETHING CONCRETE rendering it FALSIFIABLE.

Actually it predicts several things TESTABLE BY ASTRONOMICAL OBSERVATION. He presented the idea in 1994 and the predictions have not yet been empirically shot down. So it is a standing challenge.

So CNS is in the standard realm of traditional Empirical Science and not in the realm of speculative philosophy and the unknowable. This sharply distinguishes it from a bunch of untestable Multiverse notions.

the various predictions of CNS can be rolled into one "master prediction" which Smolin gives in this paper
http://arxiv.org/abs/hep-th/0407213
It is statement S at the bottom of page 29.

 

[VikingF]

Hi Viking. I think you can say that in both scenarios, a universe is created from an older one. The differece between the models however, is that in the inflationary model, space expands so much so that new universes are created out of quantum fluctuations in the vacuum of space. (think of a soap bubble tearing itself apart into two) While Smolins model has universes created from black holes.

Ok, so it is the creation process that is the main difference then? I saw a picture describing the inflationary model once (the one in the link below), but I think it looks more like Smolin's "baby model", the way it is described in this paper, than Linde's inflationary model.
Here it is:
http://www.stanford.edu/~alinde/BubbleUniverse3.jpg

Smolin's CNS hypothesis PREDICTS SOMETHING CONCRETE rendering it FALSIFIABLE.

Actually it predicts several things TESTABLE BY ASTRONOMICAL OBSERVATION. He presented the idea in 1994 and the predictions have not yet been empirically shot down. So it is a standing challenge.

Is it fair to say that this theory is more likely to be true than e.g. the inflationary theory or the ekpyrotic, you think? In the papers I have read, it seems like Linde's theory is the most known/popular...

 

[marcus]

Here is a way to paraphrase statement S

Think about the 30-odd dimensionless parameters of the Standard Models of cosmology and matter. They define a 30 dimensional space. Our universe is characterized by a point in that space----the values of those numbers determine everything, the size and age of the universe, the periodic table of elements, chemistry, star physics, the properties of water, etc.

We always are asking WHY ARE THE PARAMETERS THOSE PARTICULAR NUMBERS? why is it that point in parameter space instead of some other?

SMOLIN STATEMENT S SAYS YOU CANNOT FIND A DIRECTION TO MOVE FROM THAT POINT IN SUCH WISE THAT WILL INCREASE THE ABUNDANCE OF STELLARMASS BLACK HOLES.

it is a very simple challenge. It challenges you to find some modification of the fundamental constants ( like increasing the mass of a certain quark, or the strength of a certain force) that would, if it could be implemented, result in stars being more likely to condense and to eventually collapse into black holes. Something, for instance, that would make more stars end up as BH and fewer end up in gradually cooling white dwarfs or gradually cooling neutron star-----more holes and fewer cinders.

Surely if you understand star physics you can find some constant, in some physical law, which if you change it will make stars more likely to end up as black holes! (Unless by some strange coincidence we are at a local optimum!)

but since 1994 nobody has---apparently.

Surely if you understood cosmological structure formation---the condensation of gas clouds----the coagulation of galaxies and stars----the catalytic role of supernovae---then you could suggest a little "improvement" in one or two of the parameters that would make astrogenesis more prolific and lead eventually to more black holes.

No one CLAIMS to have have done this. I would say Abraham Loeb may have come closest. He has cleverly found a flaw in Anthropic reasoning about the Cosmological Constant, but this is not the same.

==================

Anyway that is the empirical core of Smolin's CNS idea. Is or is not our universe at a local max for black hole abundance?

If you can show it is NOT then that is FINE! then we can look for some other ideas. But if it IS at a local max (which challenge has stood for over ten years) then we have some explaining to do.

A possible explanation would be that we are in a branch of the universe that is optimized for branching------that BH formation is part of a reproductive mechanism and the more BHs you have the more offspring you make. The 30-odd parameters serve as "genes" and have some ability to mutate.

But I would minimize the importance of conjecturing explanations like that until someone has really tried hard to disprove STATEMENT S, really taken up the challenge to falsify it.

Smolin says finding a neutron star about a certain mass would, as far as he is concerned, falsify the idea----you can read the argument about that in the paper I linked to, or in the original 1994 paper.

 

[Vast]

Is it fair to say that this theory is more likely to be true than e.g. the inflationary theory or the ekpyrotic, you think? In the papers I have read, it seems like Linde's theory is the most known/popular...

I might just add, that observations would equally give support to the inflationary model. That is, the accellerating expansion of the universe seems to indicate the expansion will continue to expand faster and faster, until the universe rips itself apart. Not to favour one model over another, as Marcus pointed out in order to be science and not metaphysics, one needs to test and make predictions. We should be able to make some progress within the next couple of decades.