“In all chaos there is cosmos, in all disorder a secret order.”
Carl Gustav Jung couldn’t have done more justice to his description. If I had one word for our universe, it’s got to be alluring. For centuries, humans have gazed at the night skies, wondering, dreaming, and reaching. I still do. What once seemed infinite and formidable, now poses as the next frontier of innovation. From setting those tiny footprints on the Moon to exploring billion-dollar space startups, conquering space no longer seems like fiction. Or is it?
Our universe is a culmination of everything. It is colossal yet untrammeled. The primal source of energy, everything we know and do not know of, somehow finds a place to exist within. Such grandeur, such abundance, and yet so fragile. And while it may look appealing to our naked eyes, the space is extremely hostile and unforgiving. And sadly, as transient beings, we can simply stand and observe, but not participate in this grand scheme of things. Such is the plight of an inquiring mind.
Despite these inherent uncertainties, some of the greatest minds in history have constructed remarkably precise theories about the origin of everything we see today. The Big Bang Theory, built upon observational evidence and mathematical rigor, provides the most compelling explanation for our universe to date. Yet, as with all scientific models, it remains subject to refinement.
While we cannot be certain about how it all began, all the cosmic signals we’ve captured so far tell a story that sounds convincing enough, and also undeniably accurate.
Our Universe in Huge
Before moving on, it’s very important to grasp the sheer vastness of space. After a point, using kilometers as a unit of measurement becomes impractical; distances become so large that even light, that has left point A, has not reached point B. We use a unit called a light-year, which is the distance light travels in one year, standing approximately 9.5 trillion kilometers.
To put this in perspective, the nearest star after the Sun- Proxima Centauri, is 4.24 light-years away — meaning its light takes over 4 years to reach us. The core of our Milky Way Galaxy (which houses a Black Hole) is about 26,000 light-years away. So technically, what we see on a telescope is how the Milky Way looked 26,000 years ago. Wait for another 26000 years, and we’ll see how the Milky Way would look today. Distant galaxies are billions of light-years away, so the light we see from them left those galaxies billions of years ago. And since space itself is expanding, those galaxies might have shifted farther away. A bit of a tongue twister, but yes!
Now What Exactly is this Big Bang Theory?
Not the TV show guys, come on!
So back in the 1920s, an American astronomer — Edwin Hubble, made one of the most groundbreaking discoveries in cosmology. Indeed a true ingenious, he somehow observed that the farther away a galaxy is from Earth, the faster it is moving away from us. He did so by observing a phenomenon called Redshift, which is based on how a light wave stretches and becomes red as its wavelength increases (which I talk about later). This observation gave birth to the concept of an expanding universe, and eventually, the Big Bang Theory.
The Big Bang theory proposes that the universe began as a single, infinitely hot, and dense point roughly 13.8 billion years ago. In physics, we call this a singularity. This is what lies at the core of black holes- a location in spacetime where the gravitational field and density of a celestial body become infinite. Since the gravity (a pulling force) is infinite, nothing can escape. One way we can make density infinite is to fit an infinite amount of mass in a volume as small as possible (like a dot). Known physical laws no longer apply, which makes studying black holes incredibly complex.
One might ask then, why aren’t Black Holes also expanding the same way as our Universe did?
Well, the singularity at the beginning of the universe wasn’t just a point in space; it was space itself compressed into a single point. The Big Bang wasn’t an explosion into space but space itself expanding. On the other hand, a black hole singularity exists within space. It is not space itself but rather a highly dense point within space where gravity is so strong that nothing (not even light) can escape. Energy is not radiating outward but rather drawing everything inward, reinforcing the singularity (making it stronger).
For an expansion like the Big Bang, you need space itself to be inflating. A black hole’s singularity does not have the mechanism of inflating space; instead, it acts as a dense gravitational well pulling space inward rather than pushing it outward.
For nerds: The universe’s singularity had incredibly low entropy (a highly ordered state), causing expansion to generate complexity. A black hole has maximum entropy, meaning no order is left — only a gravitational point with no push to expand. Remember that entropy is not a cause but an effect. And that’s why you don’t skip your thermodynamics class.
Coming back to the Big Bang — in a fraction of a second, rapid expansion took place, setting off the formation of matter, energy, and time itself. But then again, where’s the proof?
Human Cognition Takes Us 13.8 Billion Years Back
Thanks to the groundbreaking works of 3 amazing scientists, we now know that the universe is 13.8 billion years old, give or take a few million. The idea originates from Friedmann’s equations, derived from Einstein’s General Theory of Relativity.
Nerds, gather ‘round: Einstein’s General Theory of Relativity, published in 1915, revolutionized our understanding of gravity. It challenged the idea of gravity that Newton introduced in classical physics. Instead of treating gravity as a force, Einstein described it as the curvature of spacetime caused by mass and energy. He also came up with very complex equations, which is a topic for another day. For now, picture spacetime as an infinite cloth that can stretch itself based on the gravity and energy radiated by a celestial body (see graphic).
In 1922, a Soviet physicist by the name of Alexander Friedmann discovered solutions that suggested the universe wasn’t static, as Einstein originally assumed, but could expand or contract. Friedmann’s equations, derived from general relativity, describe how the universe evolves based on parameters like the density of matter, radiation, and dark energy. These equations laid the bricks for modern cosmology by predicting that the universe could either expand or contract depending on its initial conditions.
A few years down, in 1927, a Belgian priest by the name of Georges Lemaître proposed the concept of a primeval atom, proposing that the universe originated from a single, extremely dense and unstable state. Building on this, it was finally in 1929 that Sir Edwin Hubble provided empirical proof. By analyzing the spectral lines of galaxies, he discovered a linear relationship between the distance of galaxies and their recession velocity. In layman’s terms, Sir Edwin expressed that if galaxies were moving away from each other as we speak, they must have been closer in the past. Extrapolating backward leads us to a point of infinite density and temperature — a singularity, where all the galaxies were condensed into one tiny point — marking the beginning of time, space, and matter a.k.a. the Big Bang.
What Drove this Expansion?
I n physics, at the moment of the Big Bang, time was effectively zero. Call it the starting point of everything we know. A question then arises, what was there before the Big Bang? Let me explain with an analogy.
Think of a weighing scale. The smallest measurement you can take is zero, right? There’s no such thing as a negative weight on a standard scale. Similarly, in the context of time, t = 0 marks the very birth of time itself. There’s no t = -1, at least not in the way we currently understand time.
Now, some scientists hypothesize that something could have existed “before” the Big Bang, but as of now, we just don’t have the acuity or evidence to explore that possibility with certainty. So, for the sake of simplicity, the best answer is that time began at the Big Bang — and before that, “before” might not even make sense. Let me explain how a tiny point came to be the Space as we know it today.
In the earliest moments of the universe, at t = 0, the initial singularity began expanding at an unfathomable rate. And sadly, we do not know why. While the exact cause remains uncertain, theories such as quantum fluctuations, phase transitions, or higher-dimensional brane interactions attempt to explain it — though none are yet proven. What we do know is that this expansion triggered extreme heating, pushing the temperature to around 1⁰³² Kelvin. At such extreme temperatures, stable particles couldn’t exist. Any attempt to form matter was immediately disrupted by the overwhelming energy. Particles constantly collided, annihilated, and reformed in a chaotic loop, preventing the existence of atoms or protons.
Almost instantly, a phase called inflation took place, where the universe expanded exponentially within a fraction of a second. This inflation expanded the scale of the universe by a factor of 1⁰²⁶. This is equivalent to stretching a 1-nanometer object in length up to 10.6 light years. This rapid expansion smoothed out irregularities and set the stage for the large-scale structure of the cosmos.
Following inflation, the universe entered the radiation-dominated era, where high-energy photons and neutrinos (another elementary particle) drove the expansion, exerting intense pressure. Eventually, as the universe cooled further and the radiations became less intense, free electrons combined with nuclei (protons + neutrons) to form atoms. Matter came into existence taking over as the dominant force as more and more complex elements started to form. This transition marked the beginning of the matter-dominated era, where gravitational attraction played a larger role, pulling gas into clumps that would later form galaxies and clusters.
For billions of years, matter governed the universe’s expansion, but about 5 billion years ago, expansion somehow started accelerating instead of slowing down. Scientists attribute this to dark energy, an unknown force that repels gravity and pushes galaxies apart at an increasing rate. Dark energy is a topic very little known about because we lack the means to directly observe it. This phase, known as the dark energy-dominated era, continues today, shaping the fate of the universe for the next few billion years.
CMB: The Rainbow after Big Bang
When you switch off a light bulb and place your hand near it, you can feel its warmth, right? The same goes for our universe. Given the Big Bang’s scale, the residual heat persists in the form of a faint radiation known as the Cosmic Microwave Background (CMB). This radiation originated about 380,000 years after the Big Bang, during an epoch known as recombination when the universe had cooled enough for neutral atoms to form.
As discussed previously, before this era, the universe was filled with a hot, dense plasma (plasma is an electrically charged gas) of free electrons, protons, and photons, which scattered photons in every direction. This scattering prevented photons from traveling freely, rendering the universe opaque. Once the temperature dropped to about 3,000 K, electrons and protons combined to form neutral hydrogen atoms, allowing photons to decouple from matter and travel freely through space. These decoupled photons have been propagating ever since, and we now detect them as the Cosmic Microwave Background or CMB.
The CMB is essentially a snapshot of the universe in its infancy, capturing the moment when it first became transparent to light — about 380,000 years after the Big Bang. Powerful telescopes, namely Planck and WMAP are used to map these radiations. At that time, the universe had cooled to roughly 3,000 K, allowing electrons and nuclei to combine into neutral atoms. Today, we observe the CMB at a much cooler temperature of about 2.725 K, stretched by billions of years of cosmic expansion. Though remarkably uniform, it contains tiny temperature fluctuations (called anisotropies) that hold vital clues about early density variations. These subtle temperature differences reveal how matter was distributed in the early universe and ultimately led to the formation of galaxies, clusters, and cosmic structures.
Beyond just temperature, the CMB offers a detailed map of the universe’s composition. By studying the patterns in its anisotropies, scientists can infer the relative amounts of normal matter, dark matter, and dark energy. These insights help refine models of cosmic evolution and structure formation. Furthermore, the CMB has been instrumental in pinning down the universe’s age with accuracy. By analyzing the spectrum and distribution of its fluctuations, cosmologists have traced back the timeline of cosmic expansion with impressive precision.
Measuring the Silence Between Stars
Alright, let’s talk about one of the coolest concepts in physics — Redshift!
Ever noticed how an ambulance siren sounds different as it moves toward you versus when it speeds away? That’s the Doppler Effect in action. The same thing happens with light! When an object moves away from us, the waves it emits stretch out, lowering their frequency because the same wave would need to cover a longer distance at the same time, thereby reducing the effective number of waves every period that reaches us. And when it comes to light, this means shifting toward the red end of the spectrum — hence, redshift. Oh, come on now! Yes, red light has the lowest frequency. You skipped your Physics class also, didn’t you?
This was the discovery that Sir Edwin Hubble made. The light that telescopes captured from distant galaxies demonstrated a redshift, meaning they were moving away from us. That was solid proof that the universe was expanding. Not only that, but the farther a galaxy is, the faster it’s moving away and that space itself isn’t just a passive backdrop — it’s stretching, as we speak.
The Space Continues to Expand
After centuries of work in the field of cosmology, the current observable universe sits at a diameter of approximately 98 billion light years. Crazy right? Mind you, we’ve only set our eyes on approximately 5% of the observable universe. But if the universe is only 13.8 billion years old, how can it stretch up to 98 billion light-years? That’s like saying I was born 10 years ago but I’m 40.
If you couldn’t guess, it’s because the universe itself is expanding. (dude, get off your phone and pay attention!) Even though light from the farthest galaxies has only traveled for 13.8 billion years, the fabric of space has also been stretching continuously. This expansion means the distance between us and those galaxies has also increased.
Assume there is a galaxy G some y light years away from us. So even though the light from G arrived in our eyes after y years, the distance y might have become z (and in most cases, z >>> y). This is also one challenge two-way interstellar communications face.
This also implies that space can expand faster than the speed of light. This is because Space itself is not matter which is why it isn’t bound by all the laws of physics that govern matter.
Summing Things Up
From gazing at the stars in wonder to unraveling the very beginnings of our universe — what a journey we’ve been on as a species! Truly, it is mind-blowing to reflect on how our curious minds have propelled us to these discoveries.
If you made it this far, I hope you’ve picked up something fascinating today. I truly think I’d make a great teacher (XD) but for now, you’ve got something new to drop in your next conversation! Now, you’re going to be that “cool” kid in your circle.
Every breakthrough we make is a testament to a certain, should I say, congenital drive we humans have to understand everything around us. Yet space has this beautiful way of keeping us humble, doesn’t it? When you truly grasp the vastness of what’s out there, you can’t help but feel incredibly small. And somehow that’s not depressing, but awe-inspiring. Like being part of something so much bigger than ourselves.
Intimidating? Absolutely. But beautiful? Beyond words. And we’re just getting started.