Cosmology - A Beacon from the Big Bang in Scientific American of October 2014

This document contains comments about the article A Beacon from the Big Bang by Lawrence M.Kraus In Scientific American of October 2014.
If the recent discovery of gravitational waves emanating from the early universe holds up under scrutiny, it will illuminate a connection between gravity and quantum mechanics.

"Introduction"

The putative signal came embedded in radiation left over from the action of gravitational waves that originated in the very early universe etc.

Gravitational waves are also caused by something. For example two rotating black holes cause gravitational waves (ondulations in a gravity field). It is important to identify what is the cause of the gravitational waves in the early universe.

It would help us connect our best theories of the subatomic (quantum) world with our best theories of the massive cosmos - those based on Einstein's general theory of relativity.

It is a question to which extend there exists a physical link between the behaviour of individual subatomic particles (during the early universe) and the behaviour of the total mass and energy described by GR at present.

And it might even provide compelling (though indirect) evidence of the existence of other universes.

compelling evidence can never be indirect.

The road to inflation

The first paradox has to do with the large scale geometry of the universe.

Geometry is a mathematical concept.

Even after such a long period (13.8 billion years) it has remained almost perfectly flat.

This implies that the universe was always mathematical flat.

A flat, three dimensional universe is the universe most of us might have imagined we live in - in it, light travels, on average in straight lines.

A geometric flat universe is an universe in which two parallel (virtual) lines never cross.
IMO on average light in our Universe does not follow straight lines. Light is bended when it comes close to mass.
The problem is that the physical interpretation (related to the cosmological parameters) of the CMB radiation require that radiation travels in a straight line.
Next we read:

The trouble is, GR implies that a flat universe is far from guaranteed - in fact it is a special perhaps unlikely, outcome.

I do not think that GR specifies the processes that took place immediate after the Big Bang.

When matter or radiation is the dominant form of energy in the universe, etc, then a slightly nonflat universe will quickly deviate from the characteristics of a flat universe as it expands.

Using the above definition that in a flat universe light travels in a straight line I assume that in a nonflat universe light does not travel in a straight line.
The question is what does this has to do in the way space expands.

If it were off by just a bit the universe today would look open - where space is curved like a saddle - or closed - where space is curved like the surface of a sphere.

The problem is that we start mixing here mathematical concepts with physical concepts, specific with the size of the universe as space expands.
When you consider the shape of the entire at present it should be an tremendous sphere which started, as explained below (See * ) with the size of an atom. The issue is how will this size evolve. That is not a geometric issue but a physical issue.
The way light rays behave, has to do what is happening in side this sphere. To a high extend at present they will move in straight lines. However these light rays will be bended when they meet mass like a galaxy or a star.
Next we read.

For the universe to still appear flat today, its early characteristics would have had to have been absurdly fine-tuned.

Why ?
That light generally speaking follows a straight line is not very special.
That light is bended by mass the same
The cosmological parameters are calculated based on observations. It is not the other way around

The second paradox has to do with the fact that the universe appears to be the same in all directions - it is isotropic.

The question is how can we, based on what is observed (which is an image of the past), conclude that the entire universe at present is homogeneous and isotropic.
Most probably the entire universe is not homogeneous. Exploded stars are also not homogeneous.

Light from one side of the vast observable universe has only recently been able to reach the other side. This distance means that far-off regions of the universe could not have previously communicated with one another. How then could they have evolved to be so similar.

Light has nothing to do with this issue.
The main reason is because we assume that our entire universe has a common origin. That means the sequence of processes that happened throughout the evolution of the universe are the same. How slower this evolution how easier that they are more or less synchronised.

Guth arrived at the idea, which is called inflation, by thinking about a central part of the standard Model of particle physics called spontaneous symmetry breaking, which describes what happens when forces that were once unified become separate.

In a sense Guth's are idea is that forces that were inactive at a certain moment became active and a split instant later became inactive.

There is good evidence that spontaneous symmetry breaking has already occured at least once in the universe. Accordingly etc two of the universe fundamental forces the electromagnetic force and the weak force appear dissimilar today etc. At one time they were a single unified force.

The issue is that symmetry breaking in this case is a chemical reaction from one set of "old" particles into a set of "new" particles because of a change in environmental conditions (drop in temperature). Inflation is something completely different. It requires two changes with no trail.

But as the universe cooled, it went a phase transition that changed the nature of empty space.

This concept of empty space is in conflict with the text of the Box at page 50/51. See below.

Instead of being empty it was filled with a background field. This background field known as the Higgs field developed throughoout the universe.

How is this scalar field measured? IMO this it not possible because you do not know where the Higgs particles are. That means you do not know it shape nor how it can influence the expansion speed of the universe.

The Higgs field affects the way particles propagate through space.

That may be possible but you do not know how.

Those particles that interact with this field - the ones that convey the weak force, for example - experience a resistance that causes them to behave as massive particles. Those that do not interact with the field - for example the photon carrier of the electromagnetic force - remain massless.

That is easy to write but difficult to prove that the cause is the Higgs Field. Anyway the Higgs Field should be everywhere as stong in order to give each identical particle the same mass.

This fantastic picture was validated in 2012 with the discovery of the Higgs boson.

The detection of the Higgs boson was a fantastic result.

Perhaps, Guth reasoned, a similar symmetry-breaking event occured even earlier in the unverse's past. ect. We call them GUTs because they unify the three non gravitational forces of the universe into a single force

symmetry-breaking in respect to GUTs is well established concept.
The most important is not so much that symmetry-breaking is involved, but the creation of new particles.

In a similar fashion, the field that caused the GUT phase transition might have briefly stored tremendous latent energy throughout space.
During the short period of inflation this energy would have produced a gravitational repulsion that could have caused the universe to expand exponential fast.

The text shows twice that the author is not very convinced.
The most important issue is which chemical reactions (processes) caused this to happen. Symmetry-breaking is not enough.

What is now the observable universe could have increased in size by more than 25 orders of magtitude in less than 10^-36 second.

Again the author expresses doubt.
The term observable universe is a very bad choice because this is a human based concept. What you should use is the size of the entire universe "created" by the Big Bang. The important issue to consider is that if the entire universe increased with a factor 25 in a 10^-36 second that this has almost no influence what happened there after.

As compelling as the idea of inflation may be, however as of yet we do not have a fundamental theory of exactly how inflation would have played out, largely because we do not know the details associated with grand unification, such as the precise energy level at which the forces would have been unified.

The issue is not so much "Grand unification of the different forces" backward in time but the diversification of forces forward in time. More specific the details of the processes involved to create new particles as the universe expands.
As the above sentence implies we have a lack of bassic knowledge. This is a really big problem because it emplifies that inflation could be wrong.

While the simplest inflation theories explain much of what we observe in the cosmos today, different versions of inflation could have produced radically different universes.

Which to a certain extend demonstrates that we do not know how inflation functionates.

What we really need is evidence that the universe actually underwent inflation and if so to explore the detailed physics associated with it. Gravitational waves it turns out provide just such an opportunity.

First of all you must know the physical processes (chemical reactions) that caused inflation.
Gravitational waves also have a cause.

Gravitational-Wave Signatures

A time-varying source of energy - forexample, the motion of a planet around the sun or of one star around another - would propagate away from the source at the speed of light.

Newton's Theory assumes that gravity acts instantaneous. When you use Newton's Law and when you try to simulate the movement of the planet Mercury around the Sun you will not succeed. When you assume that gravity does not act instantaneous it is possible using Newton's law to simulate the movement of the planet Mercury. The problem is that the speed of gravity (gravitons) should be faster than the speed of light.

As gravitational waves pass by the distance between nearby objects changes very slightly.

What happens is slightly different. The movement of massive objects around each other are the cause of gravitational waves and they cause smaller objects to wiggle.

Because gravity is so weak compared with electromagnetism, gravitational waves are extremely difficult to detect. Einstein doubted wheteher they would ever be found.

IMO the explanation of the movement of the planet Mercury is the best evidence that gravity does not act instantaneous.

Fortunately, however, the universe can provide us with a much more powerful source of gravitational waves: the fluctuating quantum fields in the moments after the big bang.

What is measured is polarization of the CMB radiation. What we want to know is what caused this.
If gravitational waves and or quantum fields fluctuations are involved is of less importance.
Anyway the most important is the cause of each i.e. the processes involved.
*

When the universe was very young, it was compressed into a volume much smaller than the size of an atom.
At such tiny scales the rules of quantum mechanics reign.

It is much more important which type of chemical processes took place during that period.
Next we read:

And yet because the amount of energy packed into each bit of that tiny space was extremely high this large energy requires us to use the theory of relativity to describe it.

The use of SR or GR is not the panacea (universal remedia) for all cosmological issues. Each theory requires observations and they are generally speaking not available
anyway: It is much more important which type of chemical processes took place during that period.
Next we read:

Quantum field theory tells us that at very small scales all quantum mechanical fields are wildly fluctuation.

The asumption is that just after the Big Bang the temperature was very high. This is equivalent with high fluctuations of the atomic particles involved.

If all other quantum fields behave similarly during the period when the inflationary energy density dominated the expansion of the universe then the gravitational fields may have fluctuated as well

First you have to explain what gravitational waves immediate after the Big Bang are.
Gravitational waves have nothing to do with temperatures which reflect the energy (quantum fluctuations) of sub atomic particles. See also Reflection 2 - Inflation field

During the exponential expansion of inflation any initial quantum fluctuation with a small wavelength will be stretched along with the expansion.

The issue is if the underlying atomic movements also will "be stretched" i.e damped. What happens is that the temeperature will drop. At the end of the paragraph:

During inflation the frozen oscillation will grow, a process that amplifies these initial quantum oscillations into clasical gravitational waves.

The last part should be interpreted as: "into classical variable gravitational fields". Because that is what gravitational waves are. The issue is how. strong are these variable fields. IMO very weak and random.
At the end of the next paragraph:

In other words, if we can find gravitational waves from inflation we get not only a smoking gun confirmation that inflation once took place but also a direct view in the quantum process that drove inflation.

IMO this sentence is much too simple and optimistic.

Smoke from the gun

The CMB radiation might help. etc
In this sense it is the oldest visible light in the universe.

I doubt if you can "see" the CMB radiation. Observe Yes.
Lets continue to read:

If gravitational waves existed on large scales at the time the CMB radiation was created when the universe was 380000 years old then we might be able to see sign of it in the CMB.

The issue is suppose we can detect is that also a reason to assume that during the first second after the BB there was a hige but very quick period of rapid expansion.

Back then, free electrons would have been immersed in a radiation bath that was slightly more intense in one direction than another because large scale gravitational waves would have been compressing space in one direction and stretching in another.

The real explanation comes when you can explain how inflation causes these gravitational waves.
At the end of the paragraph.

The spatial distortion produced by gravitational waves could cause the electron scattered CMB radiation to have a greater amplitude along one axis than along the perpendicular one. In other words the CMB can be polarized.

Even if this is true it is not clear how you can use this to explain "inflation".
Gravitational waves (disturbances) in the universe travel in all directions through the universe in 3D. At any point in space you can these disturbances and influences in all sizes (frequencies and amplitudes) coming from each possible direction. To assume that the (IMO random) movements of the gravitons and synchronize the photons in some way or another requires a more detailed explanation.
At the end of the paragraph:

researchers present their results in terms of a ratio: the ratio of a possible gravitational-wave polarization signal to the magnitude of the measured temperature fluctuation signal.

Even if polarization is measured (which is) it is extremely unlikely that the cause comes from a period of rapid expansion.
IMO if CMB radiation already became polarized 380000 years after the Big Bang it is very difficult to explain that the culprit is inflation

The new Results

Polarization observations are very difficult, and although statiscally, the signal is clear, other possible astrophysical processes could produce effects that might mimic a gravitational-wave signal from inflation.

When polarization of the CMB radiation is measured you should try to identify the (original) cause. Maybe they are completely gravitational-waves unrelated.

Several groups etc have concluded that dust could reproduce all (or most of) the claimed BICEP2 polarization signal.

I expect that the dust is electrical charged.

The scientists point out however that the shape of the observed spectrum fits the inflationary prediction remarkably well - somewhat better than dust predictions do.

I expect that the relation between the polarization pattern and the CMB radiation is zero (or close). See also: Pinwheels

What Gravitational Waves Reveal

Gravitational waves interact so weakly with matter that they can travel basically unimpeded from the beginning of time.

Gravitational waves are caused by the the relatif movement of matter. If matter does not move the strength of gravitational field is inverse squared function of distance.
However if the supposed gravitational waves are the cause that the CMB radiation is polarized than this issue is of no importance.

Not only would the BICEP2 findings represent the first detection of gravitational waves themselves - a fundamental prediction of general relativity -

If the BICEP2 detects polarization of the CMB radiation than this is no reason

Next we read:

If the BICEP2 signal is indeed the smoking gun from inflation we will have much more to learn about the universe.

Implications for the Multiverse

Recall that inflation is driven by a field that stores and releases tremendous amounts of energy during a phase transition.

Inflation (if it happened) is caused by something within it self. Inflation (Fast expanding of Space) is not caused by a field.
The problem is when you claim that something is caused by a field than you have to explain what caused this field.

It turns out that the necessary characteristics of this field imply that once the process starts the field driving inflation will tend to continue to inflate the universe ad infinitum.

Such a scenario is easy to propose. But: How do you know ?
Which are the underlying processes involved ?
When you study Figure 10.6 The Inflationary Universe - by Alan H Guth page 185, you will see that the original idea of Alan Guth was that the inflationary period was very short.
Ses also: Reflection 3 - The Big Bang: One or Many

Andrei lLinde showed that as long as some small region of space completed its phase transition after sufficient expansion this region could encompass our entire observe universe today.

What "you" should explain is the entire universe. The discription of the entire universe should match what is observed.

In such a picture of "eternal inflation" our universe is then part of a much bigger structure that could be infinitely big and might ultimately contain an arbitrarily large number of disconnected universes that may have formed may be forming or will form.

and all those universes are created by an inflation field that existed already before the Big Bang
Unfortunately the article does not answer the question if at this moment there are many universes. When you believe in the Multiverse concept I think there are many.
When that is the case how can they be physical at present be totally disconnected from each other ?

Reflection 1 - Speed of light

In a flat universe light travels in a straight line at 300000 km/sec. The issue is was this always.
It is easy possible that in the first 100000 years after the Big Bang (Before the CMB radiation was decoupled) light on average did not travel in straight lines nor that it speed was 300000 km/sec.
This sounds a strange assumption but if you compare it what happened inside a black hole and in between its horizon this is not so strange because light cannot escape from a black hole.

Reflection 2 - Inflation field

How is it possible that something "new" can be caused (explained) by something that by itself is also "new". Why should it be possible that a period of rapid expansion (inflation) should be caused or explained by a field and to be more explicit by a "particle" called inflaton which for that reason only exists for a small period of time.
The whole concept of a field is to some extend a mathematical concept except if you can quantify it. For example a gravitation field becomes quantized by introducing the concept of gravitons. Gravitons are the building blocks of a mathematical field between existant particles with mass. This field fluctuates in concordance with the position of the moving masses involved. The movement of this field are called gravitational waves. Those waves are in fact waves (changing densities) of the gravitons.
In the same manner the expanding universe also causes fluctuations in the entire gravitaional field of the entire universe. However this field can not be used in order to explain inflation.

To call gravitons the building blocks of a mathematical field is a misnomer. Gravitons are much more a package of energy. Photons are to a large extend the same. Photons are also much more a package of energy. You can count them. They have a frequency. And we humans are lucky that we can observe them however only those photons within a very narrow defined range of frequencies.

As said above the expanding universe causes changes in the gravitational field of the entire universe. This are 3D changes. How faster the the universe expands and how larger the inhomogeneities how larger the fluctuations in the gravitational field during the period of inflation (in theory). The problem is what we observe is the CMB radiation which reflects (supposedly) the state of the universe at moment of decoupling. This is the period 380000 years after the Big Bang. See also Wikipedia Cosmic Microwave Background. To assume that that the rapid expansion of the universe leaves (happening in the first second after the Big Bang) a specic finger print in some way or an other in the CMB radiation (created much later) seems to me difficult to accept cause and effect relation.

Reflection 3 - The Big Bang: One or Many

At the end of Scientific American article we read:

In such a picture of "eternal inflation" our universe is then a part of a much bigger structure that could be infinitely big and might ultimately contain an arbitrarily large number of disconected universes that may have formed, may be forming or will form.

IMO all of this is speculation. The opinion of Andrei Linde is that the inflation field will inflate the universe ad infinitum.
The problem of such a proposal is how did such a field start. When was it created. In fact such a field, which almost by definition explains nothing, creates more problem than it solves.

The problem of the idea of Multiverses is that there exists no clear definition of what it incorporates. When you have no clear definition you can also not claim that it is wrong. The same problem exists also of the concept of inflation.

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