Cosmology - "POP goes the universe" in Scientific American of February 2017

This document contains comments about the article "POP goes the universe" by Annn Ijjas Paul J. Steinhardt and Abrahom Loeb In Scientific American of February 2017.
The latest astrophysical measurements combined with theoretical problems cast doubt on the long-cherished inflationary theory of the early cosmos and suggest we need new ideas.

Introduction

The new map confirms a theory: that the universe began with a big bang followed by a brief period of hyperaccelerated expansion known as inflation.

The question is how can you deduce from studying the CMB radiation that that the expansion rate is not constant but variable. Specific that direct after the Big Bang this rate increased and decreased?

This expansion smoothed the universe to such an extent that, billions of years later, it remains nearly uniform all over space and in ever direction and flat as opposed to curved like a sphere except for tiny variations in the concentration of matter that accounts for the finaly detailed hierarchy of stars galaxies and galaxy clusters around us.

IMO the Big Bang started as a sphere with a small radius. This radius expanded. The universe at present (now) is still a sphere and the radius is very large.

Following the Oracle

One thing it would tell us is that at some time shortly after the Big Bang there had been a tiny patch of space filled with an exotic form of energy that triggered a period of rapidly accelerated expansion ("inflation") of the patch.

THis sense requires a more detailed explanation. It is a biased sentence.

Most familiar forms of energy, such as that contained in matter and radiation, resist and slow expansion of the universe because of gravitational self-attraction.

The whole concept of the Big Bang has the same problem. Also some form of energy is required to explain the BB.
How do you build and atom bomb from scratch? In fact you need the same amount of energy to build it as what is released when the bomp explodes.

Inflation requires that the universe be filled with a high density of energy that gravitationally selfrepels, thereby enhancincing the expansion and causing it to speed up.

What is the physical explanation of dark energy? versus inflation energy?

It is important to note however that this critical ingredient, referred to as inflationary energy, is purely hypothetical; we have no direct evidence that it exists.

IMO the same with dark energy (and even with the concept of dark matter).

Thus it is clear that inflation is not a precise theory but a highly flexible frame work that encompasses many possibilties.

That is logical because the concept of homogeneity is not well defined. This concept is based on what we observe, but makes a big guess about how the actual universe looks.

For one thing, we could be sure from our basic knowledge of quantum physics that the temperature and density of matter throughout the universe after inflation ends must vary somewhat from place to place.

I don't think that from a principle point of view inflation has nothing to do with this, any way with or without inflation it is extremely difficult to explain what the difference would be.

According to the theory the accelerated expansion ends when the inflationary energy decays into ordinary matter and radiation .

Standard knowledge is that energy describes the physical behavior of objects. Matter can decay into other forms of matter. Energy can also change from one form into one other, Conversion of energy into matter is not possible.

A skier on a hill

Inflationary energy is thought to arise from a hypothetical field, called the inflation, analogous to an electric field, that permeates space and has a strength (or value) at every point in space.

Inflation field requires inflation particle, which is a too outlandish concept.

The "Multimess"

For example, we should consider whether it is reasonable for the universe to have had the initial conditions necessary for any kind of inflationary energy whatsoever.

Issues related to initial conditions started already at the Big Bang. What caused these initial conditions.

not only does inflation require starting conditions that are difficult to obtain, it also impossible to stop inflation once it gets started.

This whole process has "nothing" to do with with starting conditions. It has to do with the physical processes them self. The book "The Big Bang " by Joseph Silk defines different Era's after the Big Bang. Each Era starts when the previous one is finished. The reason why the next one process starts, lies within the final state of the previous process.

This snag traces back to the quantum fluctuations in spacetime.

This has nothing to do with spacetime. It is all controlled by the inner workings of the processes themself.

They cause the strength of the inflation field to vary from place to place, resulting in some spots in space ending inflation earlier than in others.

The fact that total space is not everywhere the same seems logical.

We tend to think of quantum fluctuations as tiny, but as early as 1983, theorists, including Steinhardt, came to realize that large quantum jumps in the inflation field, though rare, could totally change the inflationary story.

What is the physical cause of these so called "quantum jumps"? Anyway quantum fluctuations have nothing to do with the physical processes in the first 1 million years after the Big Bang.

Large jumps can increase the strength of the inflation field to values much higher than average, causing inflation to last much longer.

It is plausible to assume that the inflation period not everywhere was the same, but the explanation cannot be the inflation field but must be something physical. Anyway this is a difficult issue.
The same is mentioned previous.

Within instants, an area that stops inflating becomes surrounded and dwarfed by regions still inflating.

Such a process is physical extremely complex.

And so the process continues ad infinitum.

And who believes such an impossible scenario?
The reader is advised to read the article.

The result is what cosmologists call the multiverse.

In short cosmologists believe that at present there exist an infinite number of universes completely unobservable by us.

We would like to suggest "multimess" as a more apt term to describe the unresolved outcome of eternal inflation, whether it consists of an infinite multitude of patches with randomly distributed properties or a quantum mess.

This whole sentence is both physical and logical not very clear.

Paradigm shift

Either the universe had a beginning which we commonly dub the "big bang" or there was no beginning and what has been called the big bang was actually a "big bounce" a transition from some preceding cosmological phase to the present expanding phase.

Or we do n't know . For some cosmologists this describes a cyclic universe in which the universe goes from expanding to contraction to expanding to contraction. The problem is how do you physical explain this?

Yet a bounce, as opposed to a bang, does not require a subsequent period of inflation to create a universe like the one we find, so bounce theories represent a dramatic shift away from the infaltion paradigm.

The whole question to answer is why do we need a period of rapid expansion in the first place.

Nonemperical science

Still there is a hitch: inflationary cosmology, as we currently understand it, cannot be evaluted using the scientific method.

Why? This is a serious comment.

As we have discussed, the expected outcome of infaltion can easily change if we vary the initial conditions, change the shape of the inflationary energy density curve, or simply note that it leads to eternal infaltion so flexible that no experiment can ever disprove it.

In some sense the same problem also exists with the bounce model and or models without inflation.
What are the observations based on which we decide if the universe is either open, flat or closed?

Some scientists etc. They have proposed that, instead, science must change by discarding one of its defining properties: empirical testability.

A common misconception is that experiments can be used to falsify a theory.

Experiments are the only way to test a theory. When the test fails, that means the outcome is not what is expected, the theory is wrong.
The problem with the Big Bang, the horizon problem, the inflation theory and the cyclic universe model is that generally speaking no experiments can be performed to test each of these theories.

In practice, a failling theory gets increasingly immunized against experiment by attempts to patch it.

Ofcourse when a test fails you can try to modify the theory behind the test. Generally speaking there is nothing wrong with this.

The explanation power of a theory is measured by the set of possibilities it excludes.

I think that that is very difficult to measure. In medical the importance of a medicine if it can cure a desease.
Anyway IMO the importance of a theory is the range of observations it can accurately describe and predict. The power of the evolution theory is that is relevant for all forms of live on this planet. Its explaination power lies in the fact that the differences between the different species follows the same logic i.e the survival of the fittest.

A theory like the multimess does not exclude anything and hence has zero power.

A theory like the multimess has no relevance for all the forms on life here on earth and all what we observe.

Today we are fortunate to have sharp, fundamental questions imposed on us by observations.

I expect the CMB is one of these observations.
The question is what exactly teaches this observation us related to the evolution of the universe. That is an easy question but difficult to answer

.

• The picture at page 31 shows a certain amount of randomness in the temperature distribution. How sure are we that this randomness was also available when the radiation was emitted 13.7 billion years ago? That means the picture at page 31 is an exact undisturbed image of the past.
  
• A different proposition is that 13.7 billion years the temperature at the points of emission were exactly every where the same. That means all the randomness we observe now happened during the 13.7 years that the radiation travelled from the point of emission towards us. Is such an assumption wrong?
  

Which of the two assumptions is correct. How do you test the answer? IMO it is tricky.

Reflection 1 - Alan H. Guth

When you study the book "The Inflationary Universe" by Alan H. Guth you get the idea that he proposed the inflation theory as a solution that the universe is homogenuous and isotropic.
The problem is that this solution in fact is no solution because how do you explain this solution? For a review see: "The Inflationary Universe". Book review
Part of the problem of the inflation theory is that it tries to solve the horizon problem.

Reflection 2 - Testability

The critique in the paragraph Nonemperical science depents very much about the concept of Testability.
For an impression what testability means read this: Science works with testable ideas
Testability depents very much in which sense related to the issue you can actually perform tests i.e. experiments. In the above mentioned documents they study birds and with birds you can perform actual experiments.
To test Newton's Law is more difficult. The actual issue that when you observe many objects their trajectories follow Newton's Law, which indicate a confirmation. Their are also cases where the results don't agree with Newton's Law. This is for example the case when you study the movement of the planet Mercury. The next step is to modify Newton's Law such that the law agrees with all observations or to come up with a complete different law like GR.

When you want to study the evolution of the whole universe the first step is to describe the physical processes involved during the different era's until the present. This you can call a model. To perform experiments is out of the picture. The main thing that you can do is to make observations and to compare them with your model. When you study the above text three models are discussed: Models without inflation, models with inflation, models which a bounce (cyclic models).

This already raises a serious issue because because the first two models are either open or flat and the cyclic model is closed.
The mainstream opinion is that the expansion of the universe is expanded which implies we live in an open universe.

Reflection 3 - Multimess

The theory of the Multi Universe, which reflects the idea that there are many parallel Universes at present in this article is called Multimess, IMO because it is a mess.
The authors of the article, IMO do not agree with the concept of Multi Universe, as such the article maybe biased and may not reflect the idea of the astronomers who support the Multi Universe.

The problem with the Inflation Theory is, that it is very difficult to test. This same problem also exists with the Multi Universe concept.

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