The Self-Reproducing Inflationary Universe in Scientific American of November 1994

This document contains comments about the article The Self-Reproducing Inflationary Universe by Andrei Linde In Scientific American of November 1994
For in introduction about the Inflation Theory read this: The Inflationary Universe in Scientific American May 1984 by Alan H.Guth and Paul J.Steinhardt
In the last paragraph I explain my own opinion.
The article starts with the following text:
Recent versions of the inflationary scenario describe the universe as a self-generating fractal that sprouts other inflationary universes.
It seems to be seen if this is correct.

page 32

In its standard form, the big bang theory maintains that the universe was born about 15 billion years ago from a cosmological singularity - a state in which the temperature and density are infinitely high.
The concept of temperature is always tricky because it is a human based concept. A concept of density is also tricky. What is for sure that the initial state of the "Universe" was small and extreme masif. The most important question to answer is what came before.
Of course , one cannot really speak in physical terms about these qauntaties as being infinite.
That is correct. The concept of a singularity also does not exist implying something infite.
One usually assumes that the current laws of physics did not apply then.
That is wrong reasonning. One does not know what the physical conditions are.
As the universe expanded it gradually cooled.
As the universe expanded the frequency of the radiation decreased.
Remnants of the primordial cosmic fire still surround us in the form of CMB radiation.
Remnants of the primordial radiation is still surrounding us.
  1. The first problem is the very existance of the Big Bang. What arose first the universe or the laws determing its evolution.
    The real question is how did someting start that had the intrinsic capabilities to develop quarck's, complex molucules and even human live. Physicals laws and mathemathics have nothing to do with this behaviour.
    What arose first: the universe or the laws determining its evolution?
    The laws of physics are descriptions. They do not exist. The whole issue is a physical issue.
    Explaining this initial singularity - where and when it all began - still remains the most intractable problem of modern cosmology.
    The concept of "The Self-Reproducing Inflationary Universe" does not make evrything easier. See also Reflection 1
  2. The second problem is the flatness of space.
    The issue is not so much the flatness problem. The issue is was the universe always flat and if not how would this be established based on observations.
  3. A similar discrapency between theory and observations concerns the size of the universe. Why is the Universe so big.
    The question to answer is how come that the Big Bang created out of a tidy speck so much energy.
    This problem would be much simplerer if all the protons could annihilate with all the anti-protons and all the neutrons with all the anti-neutrons and the result would be zero implying that nothing is left over.

  4. page 33

    The fourth problem deals with the timing of the expansion. The standard big bang theory assumes that all parts of the universe began expanding simultaneously.
    This is only possible when the entire universe (all that what changed after the big bang) was exactly homogenous and this is highly inprobable.
    Who gave the command?
    Nobody.
  5. Fifth, on the very large scale matter has spread out with remarkable uniformity. Across more than 10 billion light-years its distribution departs from perfect homogeneity by less than one part in 10000.
    we do not know what the homogeneity of the present distribution of matter is. We know what the distribution of the radiation is 300000 years after the Big Bang, but we do not know what the present distribution is.
    Hence, we must explain why the universe is so uniform on large scales at the same time suggest some mechanism that produces galaxies.
    Of this only the second part is important.
  6. Finally there is what I call the uniqueness problem. Slight changes in the physical constants of nature could have made the universe unfold in a completely different manner.
    This type of "why" and "if" discussions IMO do not make much sense.
    Moreover the manner in which the other dimensions become rolled up is significant for it determines the values of the constants of nature and the masses of particles.
    How is this done?
All these problems are extremely perplexing. That is why it is encouraging that many of these puzzles can be resolved in the context of the theory of the self-reproducing inflationary universe.
The problem is that such not create more problems than it solves.

page 34

The basic features of the inflationary scenario are rooted in the physics of elementary particles. etc. To unify the weak and electromagnetic interactions despite the obvious differences between photons and W and Z particles, physicists introduced so-called scalar fields.
Scalar fields are just numbers throughout space of a measured quantity.
Now it becomes important what the scalar field in this particular case is and what it does.
These scalar fields fill the universe and mark their presence by affecting properties of elementary particles.
It is dangerous to make such general statements. An electrical field is in general a local concept. It does not fill space.
If a scalar field interacts with the W and Z particles they become heavy.
?
Scalar fields play a crucial role in cosmology as well as in particle physics.
They provide the mechanism that generates the rapid inflation of the universe.
Scalar fields can not be used to explain something.
You have to identify the cause of the scalar field.
An electric field is caused by electrons and causes the movement of electrons.
Indeed, according to general relativity, the universe expands at a rate (approximately) proportional to the square root of its density.
Is this not the other way around? The density decreases as a function of the expansion (rate).
Therefore the expansion of the universe would rapidly slow down as its density decreased.
Density is a calculated parameter of matter in a volume. Immediate next:
The potential energy of the scalar field also contributes to the expansion.
In certain cases this energy decreases much more slowly than does the density of ordinary matter.
All of this may be true, but is it also true? Immediate next:
The persistance of this energy may lead to a stage of extremely rapid expansion or inflation of the universe.
This sentence makes the whole story very conflicting.

page 35

The main difference between inflationary theory and old cosmology becomes clear when one calculates the size of the iniverse at the end of inflation.
It is an almost impossible task to calculate the size of the entire universe based on verifiable observations. It is based on models which require parameters and which are impossible to verify.
Accordingly to some inflationary models this size in centimeters can be 10^10^12. These numbers depend on the models used etc.
Exactly these numbers are pure guess work.
Our universe appears smooth and uniform because all inhomogeneities were stretched 10^10^12 times.
When you increase a volume there is absolutely no garantee that the homogeneities disappear. What is more important that when size increases drastically the physical characteristic of matter involved also changes dratically.
The universe has become so large that we can now see just a tiny fraction of it.
In physical sense that is totally unimportant.
That is why just like a small area on a surface of a huge inflatted balloon our parts look flat.
How is that flatness observed ? What is the definition ?
That is why we do not need to demand that all parts of the universe began expanding simultaneously
The result of an universe where all the parts did not start to expand simultaneous will be an inhomgeneous universe.
In 1982 I introduced the so-called new inflationary universe scenario. [see "The infaltionary Universe" by Alan H.Guth amd Paul J Steinhardt; Scientific American May 1984
For a review see The Inflationary Universe in Scientific American May 1984
This scenario shrugged off the main problems of Guth's model. But is was still rather complicated and not very realistic.
IMO all what is written about eternal inflation smells the same.
Immediate next:
Only a year later did I realize that inflation is a naturally emerging feature in many theories of elementary particles, including the simplest model of thew scalar field discussed above.
See also Reflection 1 .
One just considers all possible kinds and values of scalar fields in the early universe and then checks to see if any of them leads to inflation.
This requires a model or a set of equations. How does one check that this model is correct? The fact that certain parameter values lead to inflation does not mean that the model is correct.

page 36

Because the scalar fields can take arbitrary values in the early universe, I called this scenario chaotic inflation
A scalar field always represents a physical value. The value at each instant represent the physical state as of that moment.
In many ways, chaotic inflation is so simple that it is hard to understand why the idea was not discovered.
Maybe we thought that there no need.
We assumed that the entire universe was created at the same moment, We ssumed that the entire unverse was created from a singularity i.e. had a huge mass that initially it was hot, that initially it was a fluid, highly energetic primordial soup. and that the scalar field from the beginning resided close to the minimum of its potential energy.
The whole issue of a scalar field explains "nothing". You can introduce potential energy but you should explain potential energy of what and how it is calculated
Indeed if all inhomogeneities were streched away how did galaxies form.
By assuming that inflation did not happen.
The answer is that while removing previously existing inhomogeneities inflation at the same time made new ones.
Inflation (rapid space expansion) does not do anything. It are the (new) physical processes involved which do something.
These inhomogeneities arise from quantum effects.
Quantum effects have to do with the behaviour of quarcks.
This all happened before the Radiation Era, Leptonic Era and Hadronic Era as discussed in the book "The Big Bang" by Josph Silk at page 72.

page 37

  1. First inflation predicts that the universe should be extremely flat.
    Flatness of the universe can be experimentally verified because the density of a flat universe is related in a simple way to the speed of its expansion.
    The expansion is accelerated. How does this be in accordance with a flat universe?
  2. Another testable prediction is related to the density perturbations produced during inflation. These density perturbations affect the distribution of matter in the universe.
    Inhomogeneities in the distribution of matter and density perturbations are physical one and the same. There exists no cause and effect.
    Immediate next:
    Futhermore, they may be accompanied by gravitational waves.
    Gravitational waves are the consequences of moving matter. Gravitational waves are an image of the forces which happen throughout the universe when matter moves.
    Both density perturbations and gravitational waves make their imprint on the microwave background radiation.
    Gravitational waves are gravitons.
    I think the link between gravitons and photons is difficult to establish.
    What is even more difficult is the link between inflation and gravitational waves because inflation and the CMB radiation happened at complete different era.
    Immediate next:
    They render the temperature of this radiation slightly different in various places in the sky.
    That may be true. The problem is to establish that these differences really exist and that they are trully caused by what we call inflation. IMO this is impossible to verify.
    This nonuniformity is exactly what was found two years ago by the COBE satellite.
    The COBE satellite found nonuniformaties in the CMB radiation but not that they were clearly caused by inflation.
Nevertheless we should keep an open mind.
For example if observations tell us that the density of the universe is considerably different from the critical density which corresponds to a flat universe, inflationary cosmology will face a real challenge.
Both the density and the critical density are very difficult to measure. The density and the critical density are equal when space expansion is zero, but that is currently not the case.

page 38

The inflationary theory itself changes as particle physics theory rapidly evolves
What inflation theory has to do with particle physics is not clear. Of course the Big Bang and inflation are physical processes. If these processes are not clear then the details of what specific happened during the Big Bang can only be guessed. The same with inflation.
The list of new models includes extended inflation, natural inflation, hybrid inflation and many others. Each model has unique features that can be tested through observation or experiment.
Each model should have at least one specific feature that distinquish them from the rest.
By means of observation it should be decided which of all these theories is correct. I doubt if that is possible.
I doubt also through experiment.
Most however are based on the idea of chaotic inflation.
When some uses the term chaos or chaotic to describe inflation (extreme rappid change) than that implies that the details are not known. 
.                                   .
 .                                X.
  .                               .
   .                             .
     .                        X.
        .                   .
            .     X     .
                  .
<----------------------------------->
             Scalar Field
SCALAR FIELD in an inflationary universe can be modeled as a ball rolling down the side of a bowl.
The whole question is what has this model to do with the reality.
To be more specific how do we know that this model is correct?
Inflation ends once the ball nears the energy minimum (purple) where it wobbles around and heats the universe.

Reflection

When you place a ball near the rim of a bowl and you let the ball go then the ball will move towards the opposite side again and again and finally come to rest at the bottom.
I do not think that the author has this in mind.
Anyway what this bowl and ball has to do with the evolution of the universe, specific to explain inflation, is not clear.
Here we come to the most interseting part of our story to the theory of eternally existing, self-reproducing inflationary universe. The theory is rather general but it looks especially promising and leads to the most dramatic consequences in the context of scenario.
Don't sell the bear's skin before you have killed the beast.
Those rare domains of the universe where the field jumps high enough begin exponentially expanding with ever increaing speed.
That may be true, but how specific do you know that it is true?
From this theory it follows that if the universe contains at least one inflationary domain of a sufficiently large size it begins unceasingly producing new inflationary domains.
That may be true, but how specific do you know that it is true?
In essence one inflationary universe sprouts other inflationary bubbles which in turn produce other inflationary bubbles. See illustration on opposite page.
The illustration is clear but what it meant is not clear.
This process which I have called eternal inflation keeps going as a chain reaction producing a fractallike pattern of universes.
Which are the physical observations which demonstrate that this whole process is true?
Each particular part of the universe may stem from a singularity somewhere in the past and it may end up in a singularity somewhere in the future.
A singularity is typical a mathematical concept. A singularity using Newton's Law is the condition when the distance between the center of two objects is zero. Mathematical that is possible but physical not. This implies that Newton's law is not true for very small distances.
For the evolution of the universe this means that you cannot use the concept of a singularity to describe the start, because its meaning is not clear.
To assume that the universe will end as a singularity is physical very unrealistic.

page 39

From this perspective inflation is not part of the big bang theory as we thought 15 years ago. On the contrary the big bang is a part of the inflationary model.
What the eternal model assumes that there are many Big Bangs i.e. one for each bubble. 
         I I           J J      K  
          I             J       ...H
time      .           F..         H H
 ^     D...      E   F F           H
 |    D D       E E   F      G     .
 |     D         E    .     G G    .
 |      .        .    .      G     .  
         .        ..B..      .     . 
          ...A     B B      C ......
            A A     B      C C
             A      .       C 
              ....  .  ......
                  XXXXX
                 X     X
SELF-REPRODUCING COSMOS appears as an extended branching of inflationary bubbles.
The biggest problem is how the first bubble was created.
Changes in color represent "mutations" in the laws of physics from parent universes.
In the above sketch different colors are identified with different letters.
What the physical differences are between each bubble is not clear.
In this sense the universe as a whole may be stationary, even though the interior of each bubble is described by the big bang theory.

Reflection

What the text at page 39 indicates is that each bubble starts as a singularity with a Big Bang and ends as a singularity.
What the above sketch indicates is that at this moment there are three universe active. Indicated with the letters I, J and K.
In some inflationary models quantum fluctuations are so strong that even the number of dimensions of space and time can change.
In our universe the concept of three dimensions of space and time are already so difficult. To assume more is IMO a nightmare.
Does this mean that understanding all the properties of our region of the universe will require besides a knowledge of physics a deep investigation of our nature perhaps even including the nature of our consciousness.
To discuss other civilizations in our galaxy makes sense. To assume that those civilizations in general resemble us makes sense. To assume that humans have everywhere the same consiousness makes sense
To assume different does not make sense specific in other bubble universes.
The evolution of inflation theory has given rise to a completely new cosmological paradigm which differs considerably from the old big bang theory and even from the first versions of the inflationary scenario.
Sorry, but until know all what has been written in this article does not seem very convincing. See also Reflection 1

Reflection part 1

When you study all what is written about inflation: it is very complicated. The overall impression is that nobody knows.
For further reading select this: The inflation debate April 2011 by Paul Steinhardt: Is the theory at the heart of modern cosmology deeply flawed.

If you want to give a comment you can use the following form Comment form

Created: 22 September 2014

Back to calling page Comments About Scientific American
Back to my home page Contents of This Document