Our Universe: An Incredible Journey of 13.7 Billion Years

Anupam Das
July 24, 2024

Universe: Stranger Than Fiction

expansion of universe hubble deep field 1 — Image Credit: NASA

“Truth is stranger than fiction”

The above statement aptly applies to our Universe. The more we learn about it, the more we wonder. Scientists are also amazed as they discover new information about our cosmos. This journey started 13.7 billion years ago with the Big Bang and it will continue for trillions and trillions of years. Some of the aspects of our Universe defy our intuition in such a way that not even science fiction would have been able to imagine them.

Let me give some examples. How many stars are in this Universe? With the naked eye, we cannot see more than 4000–5000 stars in a clear night sky. But the actual number of stars in this cosmos is much more than that. There are more stars in it than there are grains of sand on all the beaches of Earth. Scientists have estimated that there may be at least 10²² stars in this Universe. Of course, this number can be much higher. Incidentally, scientists cannot see the entire cosmos even with their most powerful telescopes. We see only a certain part of it. This particular part is called the “Observable Universe”.

So it goes without saying that there are countless stars beyond the observable Universe that we cannot see and may never see. What is the reason for this? This is my second amazing example – the existence of something faster than light. Ever since we started studying physics, we have been told to remember this fact – nothing in space can travel faster than the speed of light (speed of light: 299,792 kilometers per second). The world-famous astronomer Albert Einstein proved this in his “Special Theory of Relativity”.

Faster Than Light

But there really is something that can travel faster than light. Yes! That is the Universe itself as it is expanding faster than light. Then what about the fact that nothing can travel faster than light? Well, the statement is something like this – ‘nothing in this Universe can travel faster than light through space-time. But the Universe is itself the space-time and it is expanding faster than light.

But what does this have to do with not being able to see a large part of the Universe? We see something only in the presence of light. We see objects when light reflects from an object or when an object, such as a star, emits its own light and that light reaches our eyes.

Now, since the cosmos is expanding faster than the speed of light, the light from the stars that are in its invisible part is not reaching us. If the Universe continues to expand faster than light in this way, then most of the Universe will gradually disappear from our view and we will never see that part of the Universe again.

95% of The Universe

Another amazing thing about the Universe is that we can see or observe only 5% of it. This 5% is normal matter. The remaining 95% of the cosmos is invisible and unknown to us. We cannot see or observe this 95% even with telescopes or any other complex and advanced instruments. This 95% is dark energy and dark matter. The cosmos contains 70% dark energy and 25% dark matter. Even today, scientists do not know what exactly this dark energy and dark matter is. Scientists have not yet discovered anything about them. It is not possible to observe or perceive them directly by any scientific instrument.

constituents of Universe — Image Credit: NASA

Scientists are able to deduct the presence of dark matter in that it has gravitational pull and, through gravitation, it affects the light around it. Dark matter also exerts gravitational effects on normal matter in that it dictates the rotational speed of enormous structures like galaxies.

Dark energy is elusive and currently, scientists have no model or theory to explain it. They think that it could be the intrinsic and embedded nature of the space itself. The dark energy is believed to be the factor which is driving the accelerated expansion of the cosmos.

Static Universe

Many scientists, including Albert Einstein, believed that the universe is static. Einstein believed that in the ‘static’ Universe, time stretches out to infinite in that time will continue to expand forever in the future. However, he believed that the space in the cosmos is confined within certain boundaries.

It is important to remember that at this time everyone believed that the Universe consisted only of the “Milky Way” galaxy and that there were no other galaxies outside of it. All the stars, planets, satellites, meteors, comets, and all other matter of the cosmos reside in the Milky Way.

Scientists who believed in this theory believed that the cosmos was eternal and would not be destroyed. It was the same before and it will be the same forever. In this universe, old matter and old stars will be destroyed and new matter and new stars will be formed in their place. Thus this Universe will remain eternally the same.

Einstein’s Equation Against Static Theory

Through his scientific research, Einstein realized, that the Static Universe theory might be wrong. But he was disturbed by the thought that the Universe had a beginning, a fact that would mean that it would have an end. So Einstein believed or wanted to believe that the Universe would always remain in a static and eternal state.

But Einstein’s own equations presented evidence that opposed this static theory. In order to balance his equations and prove the existence of a static cosmos, Einstein introduced “cosmological constant” in his equations. Einstein later called this “cosmological constant” the “biggest blunder” of his life. Amazingly, his “biggest blunder” would later help prove the presence of dark energy in the cosmos. In this context, it is good to say that Einstein’s world-famous discovery of “general relativity” will complement this “Big Bang” theory.

Edwin Hubble’s Discovery

In the 1920s, a ‘part-time’ scientist proved that the Universe is not eternal and that it had a beginning. His name is Edwin Hubble. He is the person after whom the “Hubble Space Telescope” is named. He was a lawyer by profession and an astronomer in his spare time. He had the best telescope of that time.

With this telescope, first, he discovered that there are other galaxies that are independent of our own Milky Way. He discovered that the fuzzy Andromeda nebula is not part of our Milky Way and is actually a galaxy that contains its own stars. This discovery shifted our view of the Universe. Then he discovered that there are more galaxies in the Universe.

He then observed and calculated the red-shift of these galaxies. When light travels from these galaxies, due to enormous distance it stretches and loses its energy and it turns red in color. The greater the redshift of any source of light, the farther away that source is from the observer.

Through these calculations, Hubble discovered that these galaxies are moving away from our Milky Way at an accelerated rate. He observed that distant galaxies are moving faster than nearby galaxies. Galaxies that are twice as far away from us are moving at twice the speed, and galaxies that are three times as far away from us are moving at three times the speed from us.

This law is called ‘Hubble’s Law’ and the rate of expansion is termed as ‘Hubble’s Constant’.

Expanding Universe

This discovery means that, on a larger scale, our Universe is expanding at a rapid rate and due to that, all galaxies are moving away from each other. One thing to note here is that galaxies are not actually moving away from each other. What is actually happening is that the space between these galaxies is expanding and as a result, the galaxies appear to be moving away from each other.

What this phenomenon actually means is that the Universe itself is expanding very rapidly. However, we do not feel the effect of this expansion on a smaller scale. On a smaller scale, the effect of gravity is much more pronounced. So, when we jump high, we come down under the influence of the Earth’s gravity, the Moon revolves around the Earth under the influence of gravity, and the Earth and other planets revolve around the Sun under the influence of gravity. But for the larger structures of the Universe, such as galaxies and galaxy clusters, the effects of this expansion are much more pronounced.

Singularity

An expanding Universe suggests that the Universe was once very small. Scientists proved through mathematics that the Universe, at its birth, was an extremely tiny point, smaller than an atom, smaller than any sub-atomic particle, and smaller than anything in the Universe. In scientific terms, this point is called a “Singularity”.

It is a point that is infinitely small, infinitely dense, and infinitely hot. The existence of this “singularity” has been proved in Einstein’s theory of general relativity. This “Singularity” also exists at the center point of a black hole. When a big and massive star dies in a supernova explosion, its core collapses on itself and the collapse squeezes all its matter – all protons, neutrons, electrons – into a single point, bringing the entire space along with itself down to the Singularity.

Scientists have yet to understand “Singularity”. At this point, all our known scientific theories become meaningless. All the mathematics and formulas of science, even Einstein’s “theory of general relativity”, cannot explain “Singularity” and they all have become useless at this point.

Big Bang

Out of all the existing theories of the beginning of our cosmos, Big Bang is the most established theory. Even though not all aspects of this theory are proof, it has some concrete evidence backing it. The person who first presented this theory was Georges Lemaître. He was born on 17th July 1894 in Belgium. He was both a priest and an astronomer. He was the first one to suggest that the universe could have started from a tiny point.

Although the theory is called “Big Bang” in English, it is not “big” at all and it is not an explosion. Rather, it was a tiny point (Singularity) and it expanded very rapidly (faster than light) in a very short time. In a rough estimation, in 10^{-24 seconds}, the Universe expanded 10²⁴ times.

Now the question may arise where exactly did this cosmic expansion take place? Exactly where in space did this happen? In fact, this expansion happened all over the place. The place where we are standing, where the Earth is, where the sun is, where the Milky Way galaxy is, the part of space we can see and the part of space we can’t see, this explosion took everywhere. The Universe itself was born out of this explosion.

Evidence for Big Bang: Cosmic Microwave Background and The Sacrifices of The Pigeons

One of the strongest evidence for the Big Bang theory is its leftover afterglow which, in 13.7 billion years, has turned into microwave radiation. This afterglow can be seen in the analog T.V. as static noise. Two US scientists, Arno Penzias and Robert Wilson, have accidentally found it.

There is an interesting story behind their discovery and, unfortunately, our bird-lover friends will not find it amusing. Two scientists were working on radio transmission. They had a big radio telescope. However, while working they could detect some anomaly, a background noise. They tried everything possible to remove this background noise but they could not.

In their radio telescope, there were many pigeons, living peacefully. However, two scientists thought that the pigeons’ droppings were the reason behind the background noise. So they have displaced all the ‘poor’ pigeons and cleaned the radio telescope. But even then the anomaly would not go.

Then they realized that the background noise was coming from everywhere and that the source of this anomaly was the Universe itself. So, later they found that it was the afterglow of the Big Bang. It is the remnant light that was released when the first photon was released in the cosmos. The light was traveling for 13.7 billion years and has been stretched into a microwave signal.

The scientists were awarded with Nobel Prize for their discovery. The scientific community has found the first concrete evidence for the Big Bang theory. Everyone was so happy, except for the ‘poor’ pigeons. Let’s spare some thought for their sacrifice for the betterment of science.

cosmic microwave background — Image Credit: NASA

Later, NASA’s WMAP probe made a detailed map of this micro-wave as it radiates through the entire cosmos. This map is called ‘Cosmic Microwave Background (CMB)’ which shows our Universe at its infancy.

Evidence for Big Bang: Accelerated Expansion of The Universe

Another evidence is the expansion of the cosmos. An expanding cosmos does indicate that once it was much smaller everything within it was in much proximity. Edwin Hubble was the first one to provide evidence of an expanding Universe. The expansion rate of the Universe is dubbed as ‘Hubble’s Constant’. However, at that point in time measuring the distance between two points of the Universe was not precise enough. In that, Hubble’s calculation of the Universe’s age made the cosmos younger than the Earth itself.

In the decade of 90S, after the launch of Hubble’s Telescope, the new calculation put the Universe’s age from 9 billion to 20 billion years. Scientists were still in need of more precise measuring techniques. That technique came in the form of a standard candle – Type 1A supernova.

Supernovas are the cataclysmic explosion at the end of a massive star’s life. However, a type 1A supernova is the explosion of the White Dwarf – which is the remnant of a dead mid-weight Sun-like star. If the white dwarf has a companion binary star, then the white dwarf could attract material from its binary companion. When the white dwarf reaches the limit of 1.4 solar mass, then it can stay stable anymore and it explodes. This limit of mass is called the Chandrasekhar limit, named after its discoverer – Nobel laureate Subrahmanyan Chandrasekhar.

The brightness of a type 1A supernova explosion is very precise in that the explosion can be used as a standard candle. Two teams of scientists, one led by Saul Perlmutter of the Berkeley Lab, and the other by Brian Schmidt of the Australian National University, have observed these explosions in different galaxies. Then by measuring the red shift of the light coming from the explosion, they concluded that the Universe is expanding at a much faster rate than we have been anticipating – a discovery that led to the winning of the coveted Nobel Prize.

Unknown Aspects of Big Bang

However, many aspects of the Big Bang theory still remain unknown to scientists. For example, what exactly caused this cosmic expansion is still unknown to us today. Did this event occur spontaneously or did something trigger it? We don’t know precisely. One explanation could be quantum fluctuation. In the quantum realm, a pair of particles spontaneously comes into existence and then annihilates each other instantly.

We don’t know what exactly expanded. We know that space and time were created after this event, but what exactly is space, and how did it come into existence after the Big Bang? We also do not know where the energy, that filled the young Universe, came from.

If this theory is true, then it must be assumed that the Universe was created from nothing. Is this even possible? How can all this be created from nothing? We still don’t know it completely. We also don’t know what preceded this cosmic explosion, or whether there was anything at all. World famous astronomer Stephen Hawking thinks that this question has no relevance. He thinks that just as there is nothing north of the Earth’s North Pole, there was nothing before this cosmic expansion. Everything was created after this cosmic expansion.

Alternate Theories

Many scientists do not agree with the Big Bang theory. Many scientists think there may have been something before the Big Bang. Of course one of the alternate theories, Steady State Theory, has now been rejected. However, many scientists have presented several alternate theories to the Big Bang.

Some of them are – String Theory, Cyclic Universe Theory, Black Hole Origin Theory, and Eternal Inflation Theory etc. These theories are quite interesting in that some of them solve some of the shortcomings of the Big Bang theory. However, these theories are still in conceptual form and proponent of these theories have yet to put forward any concrete evidence to support their point of view.

1. String Theory

The proponents of String Theory are trying to combine quantum field theory and Einstein’s General Relativity. The string theory suggests that the Universe is fundamentally made of very tiny one-dimensional vibrating ‘strings’ which is smaller than any known sub-atomic particles. These ‘strings’ in String theory replace all the known particles and known forces. According to the proponents of this theory, all the particles in the Universe are nothing but ‘strings’ vibrating in unique and different modes.

It also suggests that the Universe is contained in a giant membrane, called “brane”, which floats in the hyperspace alongside other membranes which may contain alternate Universe. Sometimes these membranes come very close to each other and can collide. Due to the collision, a vast amount of energy can come into existence which in turn can create the Universe.

If this theory were to be correct, then it would solve a glaring issue with the Big Bang. If the Big Bang is the starting point of our Universe and there was nothing before it, then it had to be concluded that all the energy and matter in our Universe came from nothing. The String theory explains the existence of all the energy that came after the Big Bang.

2. Cyclic Theory

Cyclic Theory suggests that the Universe goes through an eternal cycle of big bang, inflation, and big crunch. According to this theory, the Universe begins from a ‘Singularity’. Then it expands and creates matter, stars, galaxies, and planets. Then everything in the Universe collapses onto itself and creates another Singularity – an event which is designated as a ‘big crunch’. Then from this Singularity, another Big Bang occurs and in turn, creates another new Universe and this cycle continues.

‘Big Crunch’ is a scientific probability that can occur if our Universe slows down its expansion rate and allows gravity to take over from elusive ‘dark energy’. Right now the data shows that dark energy is dominating the Universe on a larger scale. But if, in the future, gravity becomes dominating and starts to pull all the matter in the Universe closer, then there is a chance that a big crunch might happen and everything collapses back into a ‘Singularity’.

From this Singularity another big bang can happen, creating a new Universe, and the cycle goes on.

3. Black Hole Origin Theory

This theory suggests that our Universe exists inside a black hole. Black Holes are the dead core of massive stars that end their life in a cataclysmic explosion called a supernova when it runs out of hydrogen. During the supernova, while the outer layers of the massive stars explode outwards into the cosmos, its core collapses back onto itself and keeps on collapsing until the core turns into a ‘Singularity’. As our Universe has started from a ‘Singularity’, the Black Hole Origin Theory represents an interesting aspect. It is possible that a whole Universe could exist inside a black hole.

4. Eternal Inflation Theory

Our Universe is almost ‘smooth’ in all directions in that, on a large scale, wherever we look into the cosmos, it more or less has a similar density of matter. It was possible due to the sudden inflation that occurred just after the Big Bang. Due to inflation, the cosmos expanded rapidly (faster than light) in a very short span of time.

According to the Eternal Inflation Theory, this inflation has not stopped at all and in fact, has gained momentum. This causes new baby Universes to expand from one Universe and the process continues which results in a multi-verse.

5. Multi-verse Theory

This theory also posits the possibility of a multi-verse which might exist in a hyper-space. The hyperspace is a 4-dimensional block that could harbor infinite numbers of 3-dimensional Universes. The Universes within the hyper-space could come into existence by its own Big Bang or through some other exotic processes.

Each Universe in the multi-verse could have its own natural and physical laws. Some might harbor intelligent life while others may not. Some may have nothing in it while others can be teeming with stars and galaxies. Some may eternally inflate forever due to dark energy or anti-gravity while some may collapse on themselves due to extreme gravity.

But we must remember that, at this moment, all these alternate theories are only theories. None of this has been scientifically proven yet. Big Bang still remains the most probable explanation of the creation of our cosmos in that it has some concrete pieces of evidence that back this theory.