Comments about the article in Nature: Big Bang blunder bursts the multiverse bubble

Following is a discussion about this article in Nature News Vol 510 3 June 2014, by Paul Steinhardt
To read the article select: http://www.nature.com/news/big-bang-blunder-bursts-the-multiverse-bubble-1.15346

• The text in italics is copied from the article
  
• Immediate followed by some comments
  

In the last paragraph I explain my own opinion.

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Introduction

The article starts with the sentence:

When a team of cosmologists announced at a press conference in March that they had detected gravitational waves generated in the first instants after the Big Bang, the origins of the Universe were once again major news.

Next

The results were hailed as proof of the Big Bang inflationary theory and its progeny, the multiverse.

Alan H.Guth in his book "The Inflationary Universe" in chapter 15 calls this "Pocket Universe".
Next the article reads:

The problem is that other effects, including light scattering from dust and the synchrotron radiation generated by electrons moving around galactic magnetic fields within our own Galaxy, can also produce these twists.

What this means is that the idea that the CMB radiation is a clear image as what happens 300000 years after the BB is not as simple as it sounds.
Next:

Now a careful reanalysis by scientists at Princeton University and the Institute for Advanced Study, also in Princeton, has concluded that the BICEP2 B-mode pattern could be the result mostly or entirely of foreground effects without any contribution from gravitational waves.
http://arxiv.org/abs/1405.7351Toward an Understanding of Foreground Emission in the BICEP2 Region by Raphael Flauger, J. Colin Hill, David N. Spergel

That means the physical processes involved the CMB are much more complex.
Next:

The BICEP2 incident has also revealed a truth about inflationary theory. The common view is that it is a highly predictive theory. If that was the case and the detection of gravitational waves was the ‘smoking gun’ proof of inflation, one would think that non-detection means that the theory fails. Such is the nature of normal science. Yet some proponents of inflation who celebrated the BICEP2 announcement already insist that the theory is equally valid whether or not gravitational waves are detected. How is this possible?

The mention of "some proponents" means that not all have the same opinion.
The book by Alan H.Guth at page 219 discusses density perturbations.

The answer given by proponents is alarming: the inflationary paradigm is so flexible that it is immune to experimental and observational tests. First, etc. Second, etc. No experiment can rule out a theory that allows for all possible outcomes. Hence, the paradigm of inflation is unfalsifiable.

In short the proponents mean that inflation theory can not be falsified i.e. there is no way to demonstrate that inflation theory is correct (or wrong).
This is of course strange.
Next:

This may seem confusing given the hundreds of theoretical papers on the predictions of this or that inflationary model. What these papers typically fail to acknowledge is that they ignore the multiverse and that, even with this unjustified choice, there exists a spectrum of other models which produce all manner of diverse cosmological outcomes. Taking this into account, it is clear that the inflationary paradigm is fundamentally untestable, and hence scientifically meaningless.

What this last sentence means is that Paul Steinhardt is of the same opinion i.e. inflation can not be tested.
However his argumentation is confusing. Why using a concept like multiverse which is also untestable ?
The book by Alan H. Guth at page 217 reads:

The first time I heard about this extraordinary possiblity (the intricate pattern of galaxies and clusters of galaxies may be the product of quantum processes) was in the middle of May, when I had a phone conversation with Paul Steinhardt, coinventor of the new inflationary universe

This is remarkable because it suggests that Paul changed his opinion almost 180 degrees.
The last sentence of the article reads:

Advances, including the search for gravitational waves, will continue to be made and it will be exciting to see what is discovered in the coming years. With these future results in hand, the challenge for theorists will be to identify a truly explanatory and predictive scientific paradigm describing the origin, evolution and future of the Universe.

All of that is on our wish list, but has nothing to do with the subject of this article.

For a critical evaluation of the book The Inflationary Universe by Alan H. Guth, read this:

Book review: "The Inflationary Universe"

Reflection part 1 - Inflation theory

The article in Nature raises a conflicting picture.

• First of all the author himself is a coinventor of the inflation theory. Besides that his current work is on the "Cyclic Universe" concept. The first is described by a Lambda value greater than zero (Space expansion). The second by a Lambda value less than zero. In fact basically speaking the two are in conflict which each other.
• The article claims that inflation theory is untestable and scientifically meaningless, because the inflation theory is so flexible and comes in many flavours.
  This is remarkable because many concepts discusssed in the article like gravitational waves, multiverses and bubbles are also untestable.
• What is also remarkable that the article claims:
  The part of the multiverse that we observe corresponds to a piece of just one such bubble.
  Because what has "we observe" to do with the Universe. Why not write:
  Our own "local" Universe (Starting with the BB) is one of the many bubbles in the Universe.
  The problem is such an idea that many BB happened, creating all their own "local" Unverses, is also untestable.
  Part of the problem is to answer the question: to what extend should all "local" Universes (bubble) interfer which each other?
  If they don't than that raises an other question.

  For more about the author read this:

  • Paul Steinhardt * Academic work Wikipedia
  • A Cyclic Model of the Universe by Paul J. Steinhardt and Neil Turok. October 2002.

Also See the video: THE CYCLIC UNIVERSE: PAUL STEINHARDT
One concept he discusses is that because space expands the part of the Universe we can observe observe within our horizon decreases. As such the Universe looses information.
The problem is that our existance has nothing to do with the evolution of the Universe, as such the idea that the Universe looses information, from the human point of view, does not make sense.
The inflation theory is invented to explain the inhomogeneity of the Universe as seeds for the creation of the galaxies.

Reflection part 2

Cosmology is generally speaking based on two concepts: Physics and mathematics.
When you study the evolution of the universe than what you are studing is the evolution of different physical processes (i.e. chemical reactions) which happened and which finally created or builded the present day universe consisting of galaxies, stars and planets.
The chalenge of course is to unravel and to describe those physical processes (these change of events) at most accurate and detailed as possible during the periods applicable. This is not easy.

Newton's Law is a very powerfull tool to describe the movement of objects in the Universe. However only to a certain extend. Newton's Law assumes that the objects are point masses. Those point masses are static. Newton's Law does not describe the evolution of the point masses. The law does describe the inner behaviour of stars, the chemical reactions involved, how they age and can collapse or explode. Neither describes Newton's Law the behaviour of the gas clouds throughout space.

Friedmann's equation to a certain extend has the same limitation. The equation describes the size of the Universe but not the chemical details. The equation gives information about the density and mass of the Universe but not the details. The mass factor used is a combination of baryonic and non-baryonic matter. The equation does not describe each individual. To find this relation the results of the CMB radiation Power Spectrum has to be used.

For a critical evaluation of the Power Spectrum described in the book by Alan H. Guth, read this:

Critical evaluation of Power Spectrum calculation in the book "The Inflationary Universe"

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