Origin of the Universe

 

There are several theories for the origin of the universe. Some of the popular ideas have one significant postulate that the universe originated ex-nihilo. It means that the universe is created 'out of nothing.' We will analyze this concept based on scientific methods to find the truth. The modern Big Bang theory of the universe is the most accepted theory based on scientific concepts. It can explain several phenomena in the universe, such as the galaxies' origin and the planetary systems' formation.

The composition of various universe's constituents can provide pointers for its origination. Also, the constituents' composition reveals the universe's four fundamental interactions. Understanding the relationship of these interactions with the physical entities points to features of the universe that are the operating principles for the various phenomenon happening in the universe. Therefore, we will present the Big Bang theory of the universe's origin based on the constituents' composition and characteristics.

Characteristics of the constituents

We know that matter, energy, dark matter, and dark energy constitute the universe. The composition and fundamental interaction of the constituents provide indicators for the universe's origination. Therefore, we present the fundamental particles and interactions essential for understanding the universe's origin.

Matter and antimatter

The gravitational interaction holds all the planets in orbits around a star. Similarly, the stars are bound to galaxies. The gravitational interaction is responsible for maintaining the galaxies and the planets together. The amount of matter in a planet or anything is measured by the mass of a body. Any two bodies made of matter have a mutual gravitational force of attraction. The gravitational interaction between two bodies is proportional to the masses of the bodies. The constant of proportionality is known as the gravitational constant. It is also one of the universal constants.

All galaxies, stars, and planets are made of matter. Matter is made of atoms that have several elementary particles. A simplified diagram of an atom is shown in Figure 1 21. As shown in Figure 1.21, the nucleus of an atom is made of neutrons and protons. The protons or neutrons are made of quarks. There are many more such elementary particles that make up an atom.

 

Figure 1 21: A simplified diagram illustrates an atom's structure (not to scale, the nucleus is much smaller in an atom).

All the elementary particles are grouped into two categories as fermions and bosons. The fermions are also known as matter particles, while the bosons are interaction carriers. One well-known example of a boson is the photons we see as light. The other types of bosons help in gluing the fermions together. Thus, the gluons pack protons and neutrons in the nucleus of an atom. Furthermore, each of the matter particles has an antimatter particle. Therefore, antimatter exists, although we observe it mainly in laboratories.

The protons and neutrons in the nucleus are held together with a powerful force called strong interaction. It is a fundamental interaction. In addition, one more fundamental interaction in an atom is known as the weak interaction. Radioactive decay and nuclear fission are possible due to weak interaction.

Energy

Various types of energy exist in the universe. For example, we get heat and light radiation energy from the Sun. Also, the radiation energy in the interstellar medium is an example of electromagnetic waves. Electromagnetic waves exert a force known as electromagnetic interaction. It is another fundamental interaction, and photons are the carrier of it. The energy of an electromagnetic wave is proportional to its frequency. Therefore, we can use a constant to convert the frequency into energy for an electromagnetic wave. We call it Planck's constant, and it is also a universal constant.

As mentioned earlier, light is also a form of electromagnetic wave. The velocity of electromagnetic waves is constant and equal to the velocity of light. Moreover, it is constant everywhere in the universe. Thus, the velocity of light is also a universal constant.

Dark matter

Dark matter is not visible as it does not interact with ordinary matter and energy. However, it exerts a considerable gravitational interaction indicating that it is made of something very dense. Therefore, dark matter may have black holes. A black hole is a region in spacetime with intense gravity so that even light cannot escape from it.

Dark energy

Matter, energy, and dark matter exist in the universe's space. Even the existing space is a form of energy. It is known as dark or vacuum energy. Dark energy has a unique property in that it exerts negative pressure. Thus, it causes the expansion of the universe. Dark energy is the most significant constituent of the universe.

From the composition of the four constituents of the universe, we learn about four fundamental interactions. Also, we find three universal constants used to represent the relationships of interactions with the components. We can express the relationship between matter, energy, and interactions by equations involving a few constants. These constants hold their value everywhere in the universe. The universal constants are the gravitational constant G, the velocity of light c, and the Planck constant ℏ.

Mass to energy conversion

It is well known that matter and energy are interconvertible. The conversion of matter of mass 'm' to energy 'E' is governed by the equation

E=mc²

where 'c' is the velocity of light. Thus, matter can be created from energy or vice versa.

It is also possible to create matter from space or vacuum energy. We can explain this from the uncertainty principle. We know that it is impossible to measure the position and momentum of any matter particle with arbitrary accuracy. It is known as the uncertainty principle. For example, to measure the velocity of a quark along with its position, light or anything used to measure it will change the position itself. Such changes are known as quantum fluctuations. Due to quantum fluctuations, elementary particles and antiparticles are generated and annihilated continuously in a vacuum. These elementary particles constitute matter.

It is also possible to generate energy by combining the elementary particle and antiparticle. Thus, matter and antimatter annihilate to create energy. For example, Figure 1 22 depicts the annihilation of two matter particles, an electron and a positron. The annihilation produces two gamma rays as energy.

 

 

 

Figure 1 22: An illustration of matter particles electron and positron annihilating to two gamma rays' energy.

 

Now, we are familiar with the essential attributes of the components and the universe. Therefore, we can postulate a theory of the origin of the universe.

The Big Bang Universe

We will briefly present the Big Bang theory of the universe's origin. After that, we will explain the creation of all the constituents of the universe.

As mentioned earlier, gravitational forces hold the planetary systems and galaxies together. On the other hand, we observe that the galaxies are moving away from each other. Using modern tools and techniques, we can measure the recession velocities of the galaxies. From any observation point, some galaxies will be nearby while others will be relatively far. The velocities of the galaxies are proportional to their distance from the observation point. The galaxies farthest away are moving with the greatest speed. This observation implies that all the galaxies would have been together if we extrapolate backward in time. In the distant past, these started moving away from a single point.

At the beginning of the universe, there was no time and no matter except this single point. It is postulated that the whole mass of the universe was concentrated in the point; it had almost infinite density and temperature, and this starting point is called the gravitational 'singularity.' This point started expanding rapidly in a kind of burst. This proposition about the universe's origin is known as the Big Bang theory. An illustration of a few events in the universe after the Big Bang is shown in Figure 1 23.

 

Figure 1 23: It illustrates the formation of elementary particles and the first hydrogen element in the events after the Big Bang (not to the scale).

 

As shown in Figure 1 23, at the start of the universe time, 10⁻⁴³ second, the temperature was above 10³² degrees Kelvin. The expansion of the universe results in the fall of temperature in space. Within a tiny fraction of a second after starting, the expansion became more rapid. Following the exponential inflation, the conditions became conducive to producing the elementary particles of the atoms within a fraction of the first second. The temperature was favorable for creating elementary matter particles and antiparticles. All the space became occupied by a soup of hot ionized quark-gluon plasma. About one second after the Big Bang, it was still very hot at about 10 billion degrees Kelvin. The universe was a big sea of electrons, protons, neutrons, photons, positrons and neutrinos.

As it continued to cool down to about a billion degrees at about 10 seconds, the protons and the neutrons started to combine to make deuterium. After that, atoms began to form as electrons combined with deuterium to make hydrogen and helium in a process known as Big Bang nucleosynthesis, as shown in Figure 1 23.

Before these combinations, the universe was opaque due to elementary particles all over space. However, the combination process created empty spaces, and the universe became transparent. The combination process happened between 375,000 to 380,000 years after the Big Bang when the universe's temperature dropped to about 4000 degrees Kelvin. This process of recombination continued for nearly 100 years. We know that the photons are emitted during the recombination process. The photons can move freely as the combination also creates voids. As a result, the universe becomes transparent. These radiations are observed as cosmic microwave background radiation (CMBR) presently. It is also referred to as the afterglow of the Big Bang that can be seen today.

As shown in the Figure 1.21, hydrogen and helium are the oldest elements formed from elementary particles. Lithium and beryllium were constituted from hydrogen and helium as the conditions of temperature and pressure were favorable for such formations. However, the conditions were not conducive to creating still heavier elements.

The big blobs of hydrogen and helium gas were the initial stages of the stars. Later, the fusion reaction formed heavier elements in the different layers of these stars. The fusion reactions are exothermic reactions that give out heat as it is happening in the Sun. The formation of heavier elements up to iron happens by fusion. Still heavier elements are formed by proton or neutron capture in the stellar systems.

In the early stages of the universe, with the element formation, the atoms accumulated due to gravity. As a result, we observe most of the material mass is concentrated in the galaxies. However, the galaxies also have enormous giant molecular clouds that are very dynamic due to the stellar winds. The stellar winds are fast-moving flow flows of material such as protons, electrons, and atoms of heavier metals that are ejected from stars.

At some point, the molecules start to collapse into each other due to gravity. It becomes a catastrophic event with a rotator motion, acquiring more mass with each rotation. This process is known as accretion resulting in a star. As the accretion disc rotates, not all the mass is accreted by the star itself. Instead, there are also other accretion points revolving around the disc, and these become the star's planets.

A representation of the timeline of the Big Bang universe is shown in Figure 1 24. As shown in Figure 1.24, the universe originated from a point that started expanding. Then, it created matter particles due to quantum fluctuation. It is followed by rapid inflation resulting in the cooling of the universe. Finally, it created a condition for recombination that gave to afterglow light seen as CMBR. The first star appeared at about 400 million years after Big Bang. After that formation of galaxies happened, giving rise to the present universe.

 

Figure 1 24: An illustration depicting the timeline for the significant events of the universe beginning from the Big Bang.

Source: Credit to NASA/WMAP Science Team [Public domain].

 

In the present universe, we have matter and energy. In addition, there are two other components: dark energy and dark matter. Dark matter is a matter that we cannot see, but it exerts considerable gravitational influence. Dark energy is a type of energy causing the universe's expansion. It is the most significant component of the universe. It is estimated that dark energy is 69% of all the matter-energy composition of the universe. The second major universe component is dark matter (26%). The rest of the universe is constituted by baryonic matter and less than 5% radiations.

The density of matter-energy in the universe plays a role in determining the universe's shape. Computer simulation shows different shapes of the universe depending on the density. A density that makes the universe flat and infinite is known as critical density. At present, it is estimated that the matter-energy density of the universe is equal to the critical density, which implies that we have a flat universe. The flat universe means that it will continue to expand forever. However, suppose the density ever becomes greater than the critical density. In that case, the expansion will reach maximum, and it will start to slow down from there, ultimately leading to a big crunch. The big crunch is one possible scenario in which the universe's expansion eventually reverses, and the universe collapses to size 'zero' again.

The universe's age is estimated based on the galaxies' measured velocities. The estimate predicts the age of the universe to be 13.8 billion years. The age has also been verified based on the parameters of a few other natural phenomena. All the evidence supports the universe's age to be 13.8 billion years with an accuracy of plus or minus 21 million years.

The earliest traces of life on Earth are found in the imprints of microbes preserved in sedimentary rocks estimated to be more than 3.8 billion years old. Carbon, hydrogen, oxygen, and nitrogen are the major constituents of all living bodies. Initially, these individual elements were formed in atomic forms. Then, a specific combination of the atomic elements created a molecular state. Finally, these molecules combined further with a particular arrangement to form a long chain. One of these long chains that we recognize as deoxyribonucleic acid (DNA) was the seed for the emergence of life.

When the conditions were ripe for the emergence of life, the evolution of living beings started. The evolution from single-cell organisms to multi-cell complex animals and plants is well-established. With evolution came intelligent life, especially in the form of human beings. The curiosity of human beings started the search for finding the origins.