Inflationary cosmology and exponential growth

Ciao, folks. Welcome to another post in the chronology of the universe series. In the previous post fundamental forces of nature, we discussed all the forces and fundamental particles and their interactions with each other. We also had a post about the early stages of the universe in after the bang of the big bang. In this post of Inflationary cosmology and exponential growth, we will talk about the inflation theory. Inflation theory simply suggests a rapid expansion of the early universe. This theory was proposed by Allan Guth of MIT. Guth had suggested that the universe increased by million million million million( 1 with 30 zeroes) times in just a tiny fraction of second. Let’s hop into the ride to understand the wild science of inflation.

Back history

To understand why we needed inflation, let us go back to the probably first theory about the growth of the universe.

The predecessor of inflation

The activation of fundamental forces

Those particles who were managed to escape from annihilation would have started feeling a strong force that will bind nuclear together. Quarks that ran away from antiquarks would have started combining to form protons and neutrons. Within a few fractions of seconds, the universe had photons, neutrinos electrons, and few protons and neutrons. About one hundred seconds after the big bang the neutrons and protons came together to form a nucleus that in return had attracted electrons. However, it took millions of years for the electromagnetic force to kick in. Once electrons started combining with nucleus atoms started appearing. Our universe keeps on expending and on slightly denser regions, gravity showed its magic. These regions came together to form galactic clouds of hydrogen and helium.

Galaxies, stars, and supernovae

Why we need inflation?

The horizon problem

There are several reasons to think that inflation might have happened. Firstly our universe (observable) is very large and flat. Secondly, CMBR is very smooth almost identical so it tells us that in the past our comparably very tiny universe was close enough that every part was in contact with another one. However, the size of the observable universe is so big that it would have not possible for parts to come in contact with each other. The speed of light would be the same so how did the universe manage to come in contact and be so similar. For different far away parts to get mixed up will take time. For instance, if we put 2 drops of two food colors into a plate separately it will take time for them to get in contact and mix. This similarity of CMBR is also called the horizon problem.

The flatness problem

Inflation explains that when the universe was very small( yes we are not talking about the singularity, nobody talks about singularity these days), inflation kicked off and it had blown up the universe into a very large size. It was large and different parts were unapproachable now but this smoothness was retained. According to the inflation theory, our observable universe is part of a larger wider universe. You can very well say it multiverse. Our universe is flat because it may be a tiny portion of the larger universe/multiverse. And this multiverse might be curved. Now the question arises that what force can expend the universe so fast. There are many terms for this force like dark energy or say a stronger version of dark energy that caused the inflation in the first place and still working in the weaker form for the normal expansion of the universe.

The math of inflation

The simple maths behind the expansion of the universe starts as after 10–37 seconds universe started to grew. With every passing 10–37 it grew double in size. Alan Guth had proposed at least 100 doubling periods for everything in the universe to get uniform. I used to think because of expansion, the universe must have gotten bigger. Which is correct but the bigger in my thinking was very large more than the size of a galaxy. But with research, I came to realize that inflation was one of the earliest activities in the universe. The most important aspect of it explains that it grew very large within a few fractions of second i.e. A very small amount of time.

Alan Guth’s model

The intact symmetry and antigravitational push

To understand Guth’s model we have to go the same way as the hot big bang model. In the early universe, everything was very chaotic and because of extremely high energy, the universe was full of radiation. At that time all the four fundamental forces were combined in one single force. Their symmetry was still intact. With the ongoing expansion, symmetry had to break and all force would become separate. Guth suggested that in the inflationary universe the temperature dropped down to a critical point but symmetry remain intact and hadn’t broken. It was an unstable stage and this has produced more energy which otherwise would have not been there. This energy had created an antigravitational push. The universe was also expanding in the first place but this push had increased the speed of expansion very fast.

Drawbacks of the old inflationary model

The model explained by Alan Guth has some minus points According to also Guth the phase transition(the symmetry breakage) happened very fast, almost immediately. The universe was already very large after inflation. Symmetry breakage happened in local small regions at different times and slowly these regions met with each other and the whole universe went into a normal expansion stage. There were some problems. Even if inflation stopped but the universe was still growing with the speed of light. The local regions of symmetry breakage couldn’t mix with others before they were drifted apart because of the growing size of the universe. In this situation, with passing time different regions would only be kept on moving away. Then, they would have developed into different patches of the universe with different characters. But we see whooping uniformity on large scale.

Revisions of inflationary theory and new models

The emergence of a multiverse

The new insight on inflationary cosmology

To complement the chaotic inflationary theory, scientists believe that the quantum field was responsible for inflation. It is unlike any force we have seen before. Quantum field called inflaton in this case can create space and it has inert energy that acts as repulsive gravity/cosmological constant. So this energy of inflation had started the exponential expansion. When the inflation ended then started the particle pair production of matter. BICEP -1 and 2 was created for the study of the early universe and gravitational field. These two telescopes were used to detect the gravitational filed waves(traveling at light speed) produced at the time of inflation. These gravitational waves could remain forever and they could change the properties of CMBR. Scientists working on that claimed to have detected the gravitational waves from the inflation. It was one of the first trials for inflation detection.


  1. MIT lecture on Inflationary cosmology: Is our universe part of a multiverse? Part 2
  2. Read The origin of the universe: inflation by Centre of Theoretical Cosmology
  3. Inflationary universe theory by

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