From the Dark Sea to the Dark Space

Author: Rabia Asghar 

PhD (Biomedical Engineering), MSc (Zoology)

---

There are places above us where the light reaching our eyes began its journey billions of years ago. There are also places beneath us where sunlight has never reached. One journey takes us into the deepest oceans, the other into the depths of space.
These two frontiers, one beneath our oceans and the other beyond our atmosphere, are separated by direction but united by mystery. For centuries they have captivated, fascinated, and inspired humanity. The ancient phrase "As above, so below" offers a compelling lens through which to view them, suggesting that the patterns of the universe, the mysteries it contains, and the truths it reveals are echoed across different realms of existence. This perspective becomes even more powerful when we compare the dark sea with the dark expanse of space.

​The concept of the "Twin Abysses," inspired by recent discoveries of candidate supermassive black hole pairs, evokes a striking sense of connection between the unknown depths of space and the unexplored oceans of Earth. Imagine standing on a quiet beach at night. Before you lies the seemingly endless darkness of the ocean; above you stretches the vast blackness of space, illuminated by distant stars and galaxies. Although remarkable technological progress has been made, humanity has explored only a small fraction of the deep ocean. In many respects, we have mapped the surface of Mars in greater detail than the deepest regions of Earth's oceans.
Both environments remain inhospitable to human life. Whether facing the crushing pressures of the ocean or the vacuum of space, survival depends upon technology, preparation, and courage.

The astronaut is more similar to the deep-sea diver than many people realise. Both leave familiar surroundings and venture into environments where every breath depends upon carefully engineered life-support systems.
Most people associate darkness with emptiness. Yet neither the deep ocean nor deep space is empty. In the ocean's greatest depths, countless organisms generate their own light through bioluminescence, using it to communicate, hunt, and survive. Likewise, the darkness of space is filled with stars, nebulae, and galaxies that create an extraordinary cosmic tapestry. In both realms, darkness is not the absence of life or activity. Instead, it provides the backdrop against which wonder becomes visible.
​

Figure 1. From cosmic voids to ocean depths, darkness is never empty. It speaks in light. (Image credit: AI-generated artwork)

Echoes of the Universe
Nature often repeats familiar patterns across vastly different scales. Similarities can be found between the structure of the Universe and the organisation of living systems. Galaxy clusters form web-like networks that resemble neural connections. Ocean circulation shares characteristics with atmospheric circulation and planetary dynamics. Branching river systems resemble blood vessels and even the branching paths of lightning.
These recurring patterns suggest that universal physical principles operate across many different scales of nature. Gravity shapes both the motion of galaxies throughout the universe and the tides of Earth's oceans. Even more remarkably, the elements that make up every living organism on Earth were forged within ancient stars.

The sea and the sky are not separate stories. They are chapters from the same book.
Deep ocean and deep space evoke remarkably similar emotions. For many people, the thought of endless water beneath them or infinite darkness above them inspires unease. Both environments test our instincts, challenge our limits, and remind us how little we truly know. Yet curiosity often grows where uncertainty begins.

Every great exploration and every significant discovery begins with a simple question:
​
"What lies beyond?"

Humanity has always been driven to explore. Both the deep ocean and deep space invite us to venture further, even when we do not yet know all the answers.
​

Our World Extends Outwards and Inwards
Exploration is often described as the search for new worlds. In reality, it is equally a search for ourselves. When we look towards the stars, we seek answers about our origins, our future, and our place in the universe. When we descend into the oceans, we uncover hidden dimensions of our own planet and the remarkable life it sustains.
The path outward is also a path inward. The sea reminds us to be humble before nature's mysteries, while the immense distances of space provide perspective. Together, they reveal that knowledge is effectively limitless and that discovery is among humanity's defining characteristics.

​For researchers in space medicine and extreme-environment physiology, the parallels between the deep ocean and deep space extend well beyond symbolism. Both environments demand advanced life-support systems, autonomous decision-making, psychological resilience, and innovative approaches to human survival. Technologies developed for underwater exploration continue to influence human spaceflight, while advances created for astronauts increasingly benefit marine research and other challenging environments on Earth. These shared lessons demonstrate how exploration in one frontier can help unlock progress in another.
​

Figure 2. The farther we explore outward, the deeper we understand what lies within. (AI-generated artwork)

As Above, So Below
The dark sea and the dark reaches of space reflect one another. One lies beneath our feet, the other beyond our reach. Both challenge our understanding, ignite our curiosity, and remind us that the universe is far bigger, stranger, and more beautiful than we often imagine.
"As above, so below" is more than a philosophical phrase. It is an invitation to recognise the deep connections that unite seemingly different worlds. Whether in the darkness of the ocean depths or beneath a star-filled sky, we discover the same enduring truth: the greatest mysteries are not only above us or below us. They remain within our reach to explore.
Humanity's journey into the unknown has no final destination. Whether descending into the deepest trench or reaching towards the most distant stars, exploration continues to expand both our knowledge and our imagination.
​

Figure 3. Patterns of gravity, motion, and light connect the macrocosm of space with the microcosm of Earth's oceans. (AI-generated infographic)