The Universe – Big Bang Theory, Red Shift and Blue Shift

As a kid, every one of you must have wondered what lies beyond the thick blanket of sky, the common mysterious roof we all share. The stars, the Sun, the Moon all seemed to be so closely related to us.

And then one day, you must have come across the terms – Universe, Big Bang theory, and many other heavy fascinating words accompanied with millions of myths. Let’s today get to know the cosmic system of matter and energy of which our Earth and hence the whole human race is a part of, the Universe.

What is the Universe?

Universe has fascinated the ancient hunter-gatherers, guiding them for the paths and change in time, middle-age astrologers, helping them predict the future, and lately the physicists and the scientists making them learn its mysteries.

In earlier times, a self-centered human species used to believe that the Earth, the Sun, the Moon are the main objects of creation. But to its surprise, it was discovered that Earth is only a small ball of rock in a space of unimaginable vastness.

Also, the birth of the solar system is just one event among many others that occurred in an already mature universe.

How Universe Came Into Being – THE BIG BANG THEORY

It is believed and has been proven with several pieces of evidence that the universe was once very hot, very small that has ever since been expanding and cooling down. The more generic, early hot, dense phase of the universe is known as ‘The Big Bang’.

First three minutes after the Big Bang saw several changes. With charged electrons and protons, the universe was a superhot fog. No atoms could be created for the next 379,000 years. After the creation of atoms, several structures were formed including galaxies, planets, stars etc.

The expansion of the universe accelerated with time, when dark energy started dominating over gravitational forces.

It is believed that after millions of years, when the universe reaches its maximum size, it will start contracting and thus reach a state similar to Big Bang, known as Big Crunch or the death of the universe.

Assumptions of the Big bang theory

The Big Bang Theory is based on two major assumptions –
1. The universality of physical laws
2. Cosmological principle (that is, on large scale universe is homogeneous and isotropic)
Earlier considered as postulates, these assumptions have gained several pieces of evidence to be considered true.

Timeline of the Big bang theory

1. SINGULARITY

When using the laws of physics, we trace back the path to the origin of the universe; we land ourselves onto a point of high density and high temperature known as a singularity (or sometimes as Big Bang).

From the expansion rate, the age of the universe has been calculated to be around 13.8 billion years ago. What lies earlier to the singularity is not particularly known as laws of physics couldn’t be applied there.

2. INFLATION AND BARYOGENESIS

There are several phases in this stage. All these phases are given here in chronological order.

Phase                                             Features

Plank Epoch                                  Time duration of this phase – 0 to 10^-43 sec 

                                                       Size of Universe – 10^-35 m wide

                                                       The temperature of Universe – 10^32 degree Celsius. All four fundamental forces namely,                                                                             Electromagnetic force, Weak Nuclear force, Strong Nuclear force, Gravitational force are unified at one

Grand Unification Epoch             Time duration of this phase – 10^-43 to 10^-37 sec

                                                       Gravitational forces separated as the temperature fell

                                                       Phase transition caused cosmic inflation and the universe grew exponentially, even faster than the                                                               speed of light.

Electroweak Epoch                      Time of initialization of this phase – 10^-36 sec

                                                       Strong Nuclear forces separated

Inflation stopped at around 10^-33 to 10^-32 sec mark followed by reheating; which resulted in the production of quarks, gleon, plasma, and other elementary particles.

At this point, random motions of particles were at relativistic speeds. Particles – antiparticles pairs were continuously created and destroyed in the collision.

At some point, baryogenesis reaction occurred, leading to a very small excess of quarks and leptons over antiquarks and antileptons, and hence the predominance of matter over antimatter.

3. COOLING

In this stage, the density and temperature of the universe decreased, and hence, the energy of each particle decreased. At 10^-12 sec, Electromagnetic and Weak Nuclear forces separated, and at 10^-6 sec, quarks and gleon led to the creation of baryons i.e. protons and neutrons.

Due to low temperature, no more protons and antiprotons could be created, and hence, mass annihilation followed. Matter and antimatter neutralized each other. The predominance of former led to the creation of matter and hence the formation of other entities.

Now, protons, neutrons and electrons no longer moved relatively. Hydrogen, Helium nuclei and Deuterium were formed, and rest energy density came to gravitationally dominate photon radiations. After about 379,000 years atoms were formed which were able to emit radiations.

4. STRUCTURE FORMATION

Slightly denser region of uniformly distributed matter gravitationally attracted nearby matter and became denser. This is how several structures like planets, stars, etc were formed.

5. COSMIC ACCELERATION

In the present time, the dominant form of energy in the universe is Dark Energy. Earlier when the universe was relatively small, it was countered by gravitational force to a remarkable extent.

Now that the universe has expanded for dark energy to dominate (Dark Energy content is 96% out of which 26% is from those stars and galaxies which are non-luminous), it has accelerated the expansion of the universe.

Hence, the galaxies we are able to see today might not be visible to the coming generations as they may have shifted far apart.

What is Cosmic Microwave Background?

Cosmic Microwave Background is the oldest light in the universe found in all directions. Its nature being the same everywhere makes it clear that it is not produced by any star or any other celestial body. It is considered as the thermal radiation left over after the big bang.

It is very crucial in studying space and the universe and is a crucial support to the correctness of the Big Bang Theory. Unlike a traditional optical telescope that shows the space between stars and galaxies to be completely dark, a sensitive radio telescope shows a faint glow.

The glow is strongest in the microwave region of the radio spectrum, hence its name.

Evidence Supporting Expansion of the Universe

WHAT IS REDSHIFT?

Redshift refers to the phenomenon where the wavelength of the EM Radiations from an object increases. There are several causes of redshift. Major three are named as under-

1. Objects move apart in space (an example of Doppler Effect)
2. Space is expanding (known as Cosmological Redshift)
3. Strong gravitational fields distort space-time and exert force on light (known as Gravitational Redshift)

When an object moves away, light shifts towards the red end of the electromagnetic spectrum i.e. wavelength increases. (Don’t get confused by the word red. This is applicable to any part of the EM Spectrum including X-rays and gamma-rays).

Redshift is measured by examining absorption and emission lines in the spectrum. The lines are unique for each element and have the same spacing. But as the object moves, the lines are found at different wavelengths.

WHAT IS BLUESHIFT?

Blueshift, also referred to as ‘negative redshift’, is the exact opposite of the redshift. In blueshift, wavelength decreases, and energy increases. When an object moves closer, light shifts towards the blue end of the EM spectrum, i.e. wavelength decreases.

HOW DOES REDSHIFT PROVE THAT UNIVERSE IS EXPANDING?

It is proved using Olbers’ Paradox, a paradox relating to the problem of why the sky is dark at night even though the luminosity of the galaxy is overall infinite. He concluded that the universe is expanding and that is a cause of redshift.

Redshift implies energy and hence intensity is decreasing, leading to a dark sky. Therefore, redshift provides evidence that the universe is expanding.

WHAT NEXT? WILL THE UNIVERSE KEEP EXPANDING WITH NO ENDS?

No. It is believed that at some point the universe will enter a stage after which it will begin to collapse. Redshift will then be followed by Blueshift, i.e. the universe will start contracting.

The size of the universe will be maximum at that point. It would end in a state similar to the Big Bang, known to us as a Big Crunch or the death of the universe.

Conclusion

The universe we are living in is full of mysteries. The most accepted theory of its origin and its end, the Big Bang Theory states how the universe expanded from a pinpoint cosmos to the one spread to unimaginable vastness.

It is still expanding, but just like a parabolic curve (though not symmetric), it will end as a pinpoint object.