There is a silence that is not an absence of sound, but a consequence of distance. We gaze at the star-flecked backdrop of the night sky and feel a connection to the universe, yet this is an illusion born of ancient light. The true, deeper reality is one of profound and growing isolation. The universe is not a static arena; it is an expanding fabric, stretching in ways that sever connections faster than they can be formed. This reality presents us with a paradox as unsettling as it is beautiful: the universe may be infinite in its potential, yet our island of causality is finite and shrinking. The relentless expansion of the universe ensures that for humanity, the probability of ever encountering another sentient civilization is not just small, but effectively zero.
We are taught that nothing can travel faster than light. This is true for motion through space—a rocket, a radio wave, a subatomic particle. But Einstein's theory of gravity reveals a grander, more subtle truth: the fabric of spacetime itself has no such speed limit. The space between distant galaxies is not empty stillness; it is a dynamic entity, constantly creating new distance. Hubble’s Law quantifies this: the farther away a galaxy is, the faster it recedes from us. Beyond a critical boundary—approximately 14 billion light-years away—galaxies are fleeing from us at velocities exceeding the speed of light. Their light, emitted long ago, still reaches us, painting a picture of a connected past. But the light they emit today will never find us. The bridge is burned behind the photons that arrive at our telescopes. We are surrounded by a horizon beyond which lies a universe forever lost to us, a cosmos of phantoms receding into a superluminal fade.
Now, consider a secure hash function like SHA-256. Its design demands that it be computationally infeasible to find two different inputs that produce the same output, a collision. The number of possible inputs is astronomically vast, and mathematically, collisions must exist. Yet, the probability of finding one by chance is so infinitesimally small—less than the chance of a single, designated atom in the entire observable universe spontaneously quantum-tunneling into our hand—that for all engineering, financial, and practical purposes, we treat the function as collision-free. We build the global internet, secure trillions of dollars, and safeguard national secrets on the foundation of this effective impossibility. The mathematical abstraction permits a possibility, but the physical constraints of time, energy, and computation power render it meaningless.
Transposing this logic onto the cosmic scale, the input is the set of all possible configurations of matter, energy, life, and sentience across the entirety of the universe. The output is our observable reality—the sphere of space from which light has had time to reach us in the 14 billion years since the Big Bang. The collision we seek is not a matching hash for two entirely different inputs, but a meaningful encounter with another technological civilization.
The accelerating expansion of the universe acts as the ultimate one-way hash function. It ensures that the vast majority of potential inputs—the worlds, stars, and possible civilizations that lie beyond our cosmic horizon—are forever barred from producing a collision, an encounter in our causal sphere. The probability of a civilization arising not only in our galaxy, which is challenging enough, but within our ever-shrinking local group of gravitationally bound galaxies, is vanishingly small. And even if one did, the probability of our timelines overlapping by millions of years to allow for a conversation across the interstellar void is smaller still. The expansion of space adds a final, insurmountable barrier: it systematically and permanently removes an ever-increasing portion of the universe from our pool of potential partners. The number of possible connections is not just finite; it is actively and exponentially decaying.
Therefore, the question “Are we alone?” ceases to be a statistical query about the abundance of life and becomes an epistemological one about the nature of existence. If a tree falls in a forest on a planet 50 billion light-years away, and the space between us is expanding faster than light, does it make a sound? More pointedly, does it exist in any frame of reference that matters for our reality? The answer, in a brutally practical sense, is no. Its existence is a mathematical footnote in the equations of cosmology, but it is causally disconnected. It can have no influence on our past, present, or future. It is a collision that will never be found.
This realization reframes the Fermi Paradox—the famous “Where is everybody?”—not with an answer of scarcity, but one of accessibility. The silence of the cosmos is not necessarily a Great Filter that has eliminated all others; it may be the static hiss of an irreparably disconnected network. The universe is not silent because it is empty, but because it is too vast and growing too fast for any signal to bridge the gaps before the chasm becomes infinite. We are not alone in a barren universe, but we are marooned in a sea of spacetime that is pulling us apart faster than any lifeboat can paddle.
In the end, this cosmic hash function — an expanding universe making contact between sentient civilizations mathematically infeasible — presents us with a humbling and singular responsibility. The effective impossibility of contact with an alien lifeform is not a cause for despair, but a clarion call for maturity. It forces us to confront the fact that our future, for all practical purposes, is entirely in our own hands, starting from planet Earth and organically growing outwards, step by step. The stewardship of our planet, the preservation of our consciousness, and the legacy of our species are projects for which we bear sole responsibility. There will be no deus ex machina from the stars, no galactic community to save us from ourselves. The growing isolation of our cosmic island means that the immense, beautiful, and fragile experiment of life on Earth is the only one we will ever know. We are the universe become self-aware, looking out at an infinite expanse of unreachable neighbors, and in that gaze, we must find the wisdom to care for our precious home.
