Thermodynamics: Understanding Entropy

“Beauty, like order, occurs in many places in this world, but only as a local and temporary fight against the Niagara of increasing entropy.”
— Robert Wiener, The Human Use of Human Beings

When I was a teenager, I came across a YouTube video titled Thermodynamics and the End of the Universe: Energy, Entropy, and the Fundamental Laws of Physics by Eugene Khutoryansky. With a title that was existentially bleak yet scientifically intriguing, I clicked on it immediately.

By then, I already knew—at least abstractly—about heat death. A science book I’d read as a child had introduced it alongside black holes, evolution, and cosmology: the universe expanding, cooling, running out of usable energy. What I didn’t understand were the mechanisms behind it—the equations that wrote this ending into fate.

The video opens with somber music and a line that has stayed with me for over a decade:

“Thermodynamics governs how the entire universe operates—and thermodynamics governs how the entire universe will end.”

Low-polygon, PlayStation-2-era 3D animations unfold on screen, illustrating entropy, energy flow, and time’s arrow. That aesthetic lodged itself deep in my imagination. For years afterward, I would dream in that same visual language: sparse geometric worlds dissolving into uniformity, accompanied by a droning, mournful soundtrack. Dreams of the last humans alive—jumping from galaxy to galaxy, chasing the final remaining stars—until even those burned out. The slow, inevitable death of all life. The end of the universe.

This was not just a physics video. It felt like a portent.

I didn’t know it then, but treating the second law of thermodynamics as something closer to a belief was not uncommon among physicists. When Robert Oppenheimer was once asked whether he believed in God, he replied:

“I believe in the second law of thermodynamics, in Hamilton’s Principle, in Bertrand Russell, and—would you believe it—in Sigmund Freud.”

It is a striking confession—not because it dismisses spirituality, but because it elevates entropy to something like a cosmic truth. I understood that impulse long before I understood the mathematics. As a teenager, the second law felt less like physics and more like prophecy: the universe running down, order dissolving, all structure temporary.

Only years later was I formally reintroduced to entropy—this time stripped of its cosmic dread.

In electrical engineering, thermodynamics appears not as what spells the death of stars and galaxies, but as what enables infrastructure. Of most relevance is power. Coal, natural gas, nuclear—most large-scale energy generation ultimately reduces to the same cycle: produce heat, convert water to steam, drive a turbine. Thermodynamics enters as a tool for calculating efficiencies, losses, and state changes.

Specific entropy.
Specific heat.
State functions.
Isentropic processes.

The stakes were enormous in the sense of money, efficiency, and national infrastructure—but cosmically inconsequential. Entropy was no longer the harbinger of universal death; it was a variable buried in engineering documentation. The same property that once haunted me had been reduced to numbers in tables and charts.

Neither version felt complete.

The engineering definition explained how entropy was calculated, but not why it carried such ontological weight. The teenage vision of heat death captured its existential gravity, but not its mechanism.

What lingered was not the question of what entropy does, but why a statistical quantity—born from atoms and probabilities—should govern time itself.

Entropy is invisible. It cannot be observed directly, only inferred from its consequences. To make it intuitive, science communicators lean heavily on analogy: a clean room versus a messy one, oil dispersing in water, ice melting on a countertop. Entropy becomes synonymous with “disorder”—a word that gestures in the right direction but ultimately obscures more than it reveals.

As I’ve grown older—and, I hope, more careful in how I think about physics—my understanding of entropy has shifted. It has become less about messiness and more about probability. Less about decay and more about statistics.

That shift did not come from engineering coursework. It came from reading Ludwig Boltzmann.

Boltzmann bridged the microscopic world of atoms and the macroscopic world of experience; the reversible laws of mechanics and the irreversible arrow of time. For his era, he possessed possibly most intimate views of entropy conceived up to that point.

He was born in 1844 in Vienna, on the night between Carnival Tuesday and Ash Wednesday—between excess and austerity, rapture and restraint. Whether coincidence or projection, such dualities would follow him throughout his life.

From early on, Boltzmann suffered severe mood swings. While it is neither proper nor possible to diagnose him retroactively, his cycles of manic productivity followed by crushing depression resemble what we now call bipolar disorder. In his elevated states, he produced work that reshaped physics. In his depressive episodes, he withdrew, convinced of the worthlessness of his ideas—and of himself.

At the center of his intellectual life was a belief that placed him at odds with many contemporaries: atoms were real. Influential figures like Ernst Mach rejected them as metaphysical fiction. Boltzmann staked everything on their existence. He believed thermodynamics could only be understood by descending beneath it, into the invisible chaos of molecules in motion.

Before Boltzmann, entropy existed as a law without explanation. It increased, as dictated by the second law, but no one could say why. The equations of mechanics ran equally well forward and backward in time. The universe did not.

Boltzmann’s insight was simple and unsettling: entropy increases not because it must, but because it is overwhelmingly likely. Ordered macrostates correspond to very few microscopic arrangements. Disordered ones correspond to vastly many. Given enough particles and time, the universe drifts not toward decay, but toward statistical inevitability.

Entropy became a measure of multiplicity:

$S = k \ln W$

A single equation—now engraved on his tombstone—linking time’s arrow to the arithmetic of possibility.

But the insight came at a cost. Boltzmann endured ridicule and dismissal. His probabilistic explanation was accused of weakening physics itself. Privately, the resistance cut deep.

His wife, Henriette, remained by his side through illness and conflict. She could love him, but she could not undo his belief that his work—and therefore he himself, as a mind—was inconsequential. He could endure criticism. What he could not endure was insignificance.

The irony was cruel. Boltzmann explained that permanence is an illusion, that individual states are fleeting. Yet he could not bear the thought that his own existence might dissolve without trace.

In 1906, while on holiday in Duino, Boltzmann took his own life.

Within years, the atoms he defended were experimentally confirmed. Statistical mechanics became foundational. History proved him wrong in one narrow sense: his work was not inconsequential.

Yet entropy’s gravity remained.

The universe does drift toward equilibrium. Stars burn out. Structures decay. None of that was ever in doubt. What remained unresolved—and what Boltzmann himself could never reconcile—was whether this inevitability stripped existence of meaning.

Entropy does not deny meaning.

Meaning does not require permanence. Order does not need to win forever to matter. A local, temporary, statistically improbable configuration—the mandalas of Buddhist monks deliberately erased, a living cell maintaining structure for a moment longer, a human mind capable of wonder, a melody remembered after the orchestra has fallen silent, a scientific idea passed between generations—can be consequential precisely because it exists against overwhelming odds.

Entropy may make such configurations rare, but not worthless.

My first encounter with entropy felt like prophecy: everything I loved fated toward erasure. Later, as an engineer, it felt trivialized—reduced to bookkeeping. Boltzmann offered a third way of seeing it.

Entropy is not merely decay. Nor merely accounting. It is the statistical backdrop against which order briefly, improbably appears.

Heat death may be the universe’s long-term fate. But along the way exist pockets of meaning—temporary rebellions against inevitability. Moments not refuted by entropy but permitted by it.