Bhagawan Krishna spent his childhood in the green pastures of Vrindavan with his foster mother Yashoda to escape his uncle Kamsa, who wanted to persecute him. Young Krishna was playfully naughty, teasing his friends, stealing butter, and swimming in the river Kalindi. One day, while playing in Vrindavan, his friends complained to Yashoda that Krishna had been eating earth. She called Krishna before her. Krishna, innocent and playful, denied it. Yashoda asked the child to open his mouth. She looked inside and saw something no mother could have ever imagined.
She saw mountains, rivers, the sun, the moon, the sky with numerous stars and planets, the vastness of creation and the cosmic order. In a bewildering turn of vision, Yashoda saw herself standing there, looking into the mouth of the child. She saw the universe contained within something infinitely smaller than the universe itself.
It took thousands of years, and instruments far more powerful than the human eye, for man to understand that what we see is only a tiny part of the universe. Earth is only a small planet among trillions of stars and planets in billions of galaxies. What we can see in the observable universe – galaxies, stars, planets, moons, black holes, supernovae – is only 5 percent of it.
And yet, the deeper mystery is not merely how large the universe is. It is, actually, what the universe contains that we cannot see. The remaining 95 percent is occupied by dark matter (27%), which reveals itself only through gravity, and an even more mysterious component, dark energy (68%), which appears to be driving the expansion of the universe to accelerate.
What we can see is only a small part of what exists.
How big is the universe?
In fact, we do not know the size of the entire universe. But we can estimate the size of the observable universe — the region from which light has had time to reach us since the Big Bang. It contains an estimated 200 billion to 2 trillion galaxies, and each galaxy contains billions of stars, planets, and moons. Our home galaxy, the Milky Way, alone contains around 100 billion stars. In addition, the universe has room for an innumerable number of black holes, dwarfs, neutron stars, interstellar material, etc.
How vast is the universe?
The observable universe is around 92 billion light-years across. Light would take 100,000 light-years to cross our Milky Way alone. The 92 billion light-years is not a boundary — the whole universe could be enormously larger and it is expanding.
How old is the universe?
About 13.8 billion years old. If light has travelled for only 13.8 billion years, how can the object it came from now be 46 billion light-years away (the radius of the observable universe)?
Because space itself has been expanding all through those 13.8 billion years.
When we observe light from a galaxy that has been traveling for 10 billion years, we are seeing it as it was 10 billion years ago, not as it is today. And it is no longer 10 billion light-years away — space expanded while its light was travelling.
Cosmologists have found that visible matter constitutes only about 5% of the total energy content of the observable universe. About 27% is dark matter, and about 68% is dark energy.
Dark Matter
Gravity keeps planets in orbit. Outer planets move slowly around the Sun. Scientists expected the same for galaxies — stars far from the centre should move slowly.
But they do not. Outer stars spin fast.
To remain in orbit at that speed without flying apart, there must be much more gravity than visible stars can provide. Scientists also found that light from distant galaxies bends more than visible mass can explain. This too needs extra mass to cause extra gravity. These findings led to the theory of dark matter — different from antimatter.
Dark matter is an invisible form of matter that does not interact with electromagnetic radiation, including light. Hence, it remains hidden. But its presence is implied by its gravitational pull. The leading explanation is that it is made of unknown particles — weakly interacting massive particles (WIMPs) or axions — or possibly primordial black holes. Dark matter serves as gravitational scaffolding for cosmic structures. Every galaxy sits inside its own dark matter halo.
Evidence: the flat rotation curves of spiral galaxies, the velocity dispersion in elliptical galaxies, gravitational lensing around galaxy clusters as predicted by General Relativity, and the detailed pattern of the Cosmic Microwave Background (CMB).
Dark Energy
The universe is expanding in all directions. It was expected that this expansion would slow down due to gravity. To their surprise, cosmologists observed the opposite.
The farther we look, the faster the expansion is.
Galaxies are not flying through space like rockets — the space between galaxies itself is expanding, and that expansion is accelerating. This led to the theory of dark energy, the force behind the accelerated expansion. It dominates, contributing about 68% of the energy in the observable universe.
The first evidence came from measurements of distant supernovae. Their redshift pattern shows acceleration. Earlier, cosmologists believed gravity would slow expansion. The exact nature of dark energy remains a mystery.
Einstein had introduced a cosmological constant in his field equations to allow a static universe. Later, it was realized that his static model was unstable, and Edwin Hubble showed that the universe is expanding.
The term ‘dark energy’ was first coined by cosmologist Michael Turner in 1998. Dark energy is thought to be very homogeneous, not dense, and interacts only through gravity. It uniformly fills the universe. It is the invisible pressure of space itself, pushing space apart — an intrinsic property of space with constant energy density. One candidate is vacuum energy from quantum fluctuations.
A tiny excess of matter over antimatter (Baryon Asymmetry), for reasons still unknown, remained after the early annihilation of matter and antimatter. That tiny excess became all the matter we see today, while the heat from that early hot epoch remains as the CMB glow.
Evidence for dark energy is indirect but convergent: supernova distances and redshift, the large-scale wave patterns of mass density, CMB measurements, gravitational lensing, and large-scale structure — all consistent.
There are two worlds of motion: solar-system scale, where gravity dominates, and orbits are stable and predictable; and cosmological scale, where expansion dominates, and galaxies recede as spacetime itself expands. The discovery of accelerating expansion won the Nobel Prize in 2011.
The phantom dark energy model predicts its force could grow until it dominates all other forces, tearing apart galaxies, solar systems, and eventually atoms themselves — ending the universe in a ‘Big Rip’.
The mischievous universe
Krishna continued to be mischievous. Yashoda catches him and decides to tie him to a large wooden mortar as punishment. She takes a rope and tries to tie him. But strangely, the rope is always two fingers too short. Yashoda adds another piece. Still too short. She keeps adding rope.
Even today, thousands of years later, science faces the same predicament Yashoda faced when trying to comprehend the hidden secrets of the universe.
Author: Jarard Thomas
Date: 26/09/26.
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