Era of Atoms – Epochs of the Universe (Mission 07)

This is your mission 07 of the epochs of the Universe.

The Era of Atoms forms photons that now produce light.

So if you want to travel back in time and experience the Era of Atoms, then this article is for you.

Let’s get started!

Table of Contents

Mission 07 of the Epochs of the Universe – Era of Atoms

You are now moving to the next epoch, Mission 07, Era of Atoms. 

As the Universe continues to expand, we have seen the developments that have occurred until this point. 

In the previous epoch, the Era of Nuclei, the Universe is filled with fully ionized particles, free electrons, and photons. 

Now in this epoch, we see what happens to the particles as they form neutral atoms.

Let’s dive right in and learn more about the Era of Atoms.

Mission Timeline – Era of Atoms

Mission timeline Era of Atoms.

Mission Map – Era of Atoms

Mission map Era of Atoms.

Mission Data – Era of Atoms

  • Current Epoch: Era of Atoms
  • Age of the Universe: Between 300,000 years and 1 billion years.
  • Size of the Universe: It has expanded by a factor of more than 1000.
  • Current Temperature: Between 3000 Kelvins and 60 Kelvins.

Mission Briefing – Era of Atoms

The Era of Atoms happens after the Era of Nuclei. This is when free electrons bind with the nuclei to form neutral atoms between 300,000 and 1 billion years. 

The photons (light particles) were not affected anymore by matter after the atom formation. Therefore, the Universe is comprised of neutral atoms and photons that now produce light.

Is light visible in this epoch?

What caused the atomic nuclei to combine with the free electrons?

 How was the cosmic microwave background formed?

We will answer these questions in more detail below.

What Do You See?

The Universe has evolved through time, and we have seen developments in each epoch. It has expanded from a tiny single point to a massive space filled with particles. However, it has been expanding at a slower rate after the Inflationary Epoch. 

In this era, the size of the Universe has increased by a factor of more than 1000. Compared to its size in the Era of Nuclei, it has grown bigger.

In reference to the mission data, you can see that as the Universe is expanding, it is getting older. The timeline of the Era of Atoms is between 500,000 years to 1 billion years after the Big Bang. 

Within this timeline, the fully ionized particles combined with the free electrons; and the photons with specific line energies were absorbed by matter. 

In this epoch, two events occurred:

  • Recombination: When the fully ionized particles combine with the free electrons to form the first neutral atoms.
  • Photon decoupling refers to photons releasing as newly formed atoms settle into a stable energy state. The photons that were in the same energy line as the first neutral atoms are absorbed into matter.

After recombination, the photons are released, and radiation is no longer trapped. Photons are now free to produce light. 

Matter does not affect the photons anymore; matter now becomes transparent to visible light for the first time. Although, of course, photons have been producing light in the previous epochs. Still, it was impossible to see the light, nor can it be observed by us through telescopes. 

The photons could not travel anywhere since the free electrons were absorbing them.

Finally, we can see that visible light now exists in the Universe. Thus, the first visible light has been produced.

As the Universe cooled, the free electrons combined with the atomic nuclei to form neutral atoms. The first neutral atoms were the hydrogen atom and helium atom. 

What Do You Feel?

Between 500,000 years to 1 billion years, the Universe’s temperature was low enough for free electrons to combine with the nuclei to form neutral atoms. In this epoch, the temperature of the Universe was between 3000 Kelvins and 60 Kelvins. 

The drop in temperature caused the photons and matter to decouple, making the Universe transparent.

The Era of Atoms produced light, neutral atoms. The temperature of the Universe at this time could only allow for the formation of light elements. 

The temperature was a bit high for heavier elements to form. The heavier elements are produced during the formation of stars and galaxies, which is the next epoch.

After recombination and photon decoupling, matter was free to cool below the temperatures of the photon particles. 

The photon field no longer changed its properties, like its temperature, through interactions with free electrons. 

The photon field is what we now see as the residue of the Big Bang. The photon field is the radiation discovered by Arno Penzias and Robert Wilson in 1964 called the cosmic microwave background (CMB). 

The CMB shows the furthest point back in time that we can observe. This means that we understand the Universe at least 500,000 years after the Big Bang, which is when the cosmic microwave background is discovered. 

Since the birth of the Universe, radiation has redshifted by a factor of 1000 from 3000 Kelvins to 3 Kelvins and is the same in all directions. 

The 3000 Kelvins photons from the end of the Era of the Nuclei have cooled since 500,000 years after the Big Bang to 3 Kelvins.

What is Happening? Scientific Explanation

Here’s the scientific explanation of what’s happening in the Era of Atoms.

Appearance

Two events occur in this epoch: photon decoupling and recombination. In recombination, the nuclei combine with the free electrons to form neutral atoms. 

The word recombination is a misnomer because the nuclei and free electrons combined at no point in the previous epochs. In photon decoupling, the photons are released from matter as the neutral atoms settle into a stable energy state.

After photon decoupling, the photons were now free to move around through space and produce light. Thus, for the first time, the Universe became transparent to visible light. 

Light existed in the previous epoch, but it could not be seen or observed through a telescope since free electrons were absorbing them.

The temperature of the Universe is dropping as the Universe continuously expands. In the Era of Atoms, the temperature is between 3000 Kelvins and 60 Kelvins. 

The drop in temperature is what causes the nuclei and free electrons to combine to form neutral atoms. 

As for the size, the Universe has expanded by a factor of more than 1000 compared to the Era of Nucleosynthesis. As a result, the massive Universe is filled with neutral atoms and photons that produce light.

The photon field is what we see now as evidence of the Big Bang. It is the cosmic microwave background radiation that was discovered by Penzias and Wilson in 1964. 

The 3000 Kelvins photons from the end of the Era of Nuclei cooled down from 500,000 years after the Big Bang to 3 Kelvins. Thus, the CMB marks the furthest point of the Universe that we can observe since, before that, the Universe was in total darkness. 

Time

The Era of Atoms occurs after the Era of Nuclei. This epoch happens between 300,000 years and 1 billion years after the Big Bang. During this very long period, neutral atoms have formed, and the photons have decoupled from matter.

Light existed, but we could not see it before now because the photons were trapped. Now, the Universe has become transparent to visible light since the photons are free to move around through the Universe.

The duration of this epoch is about 999,500,000 years.

Mission Summary – Era of Atoms

Overall, in the Era of Atoms, the atomic nuclei and the free electrons combine to form the first neutral atoms. This process is known as recombination. 

Also, photons are released from matter and are free to move around through the Universe. The photons produce light that now makes the Universe transparent to visible light.

The photon field in the Universe is a remnant of the Big Bang, and it is known as the cosmic microwave background (CMB) that Wilson and Penzias discovered in 1964.

The temperature of the Universe during this epoch is between 3000 Kelvins and 60 Kelvins. 

The Universe cooled, and the temperature was low enough to allow the nuclei and electrons to combine. The Universe is still expanding and becoming more extensive. 

All these are happening between a timeline of 300,000 years and 1 billion years after the Big Bang.

Addition Mission Resources–Era of Atoms

Here are a few frequently asked questions.

Did Light Exist in This Epoch?

The photons are released from matter as the neutral atoms settle into a stable state in a process called photon decoupling. They produce light and are free to move around the Universe. 

The Universe is transparent to visible light for the first time since the Big Bang.

What Is Recombination?

Recombination describes the fully ionized nuclei combining with free electrons to form neutral atoms. 

The word recombination is a misnomer because the atomic nuclei and free electrons combined at no point in the previous epochs.

What Is Cosmic Microwave Background (CMB)?

The 3000 Kelvins photons from the end of the Era of Nuclei, which have been cooling down since 500,000 years after the Big Bang, have cooled to 3 Kelvins. 

This is known as cosmic microwave background. It is the radiation that Wilson and Penzias discovered in 1964. 

Epochs of the Universe: Mission Selection