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The Five Eras of the Universe
Cosmology · 25 Oct 2025 · No. 3 · objkey.com/2-3
There are five eras in the universe's lifecycle. Right now, we're in the second era.
The first era was the Primordial Era, lasting only a fraction of a second after the Big Bang—yet within that infinitesimal window, everything was decided. In those initial moments, the universe was impossibly hot and dense, a roiling soup of quarks and energy where the fundamental forces of nature were unified into one. As space expanded and cooled, matter and antimatter annihilated each other in a cosmic flash, leaving behind a tiny surplus of matter that would become everything we see today. Protons and neutrons formed, then the first atomic nuclei. This era set the initial conditions for everything that would follow across billions of years.
We currently inhabit the Stelliferous Era—the age of stars. This is the universe at its most luminous and alive, a cosmos ablaze with light. Galaxies spin in vast cosmic webs, stars ignite and die in spectacular supernovae, planets coalesce from swirling disks of dust, and on at least one of them—perhaps many—life has emerged to contemplate its own existence. This era began roughly 13.8 billion years ago when the first stars ignited in the primordial darkness, fusing hydrogen into heavier elements and seeding the universe with the building blocks of complexity.
The Stelliferous Era will continue for trillions of years to come, though star formation has already peaked and begun its long decline. We are living in the universe's golden age, its most generative and creative epoch, though we're still relatively early in this chapter. Our sun is a middle-aged star in a middle-aged galaxy. Countless generations of stars will be born, live, and die long after our own solar system has vanished. But eventually, the raw materials will run out. Hydrogen will be locked away in stellar remnants or dispersed too thinly to collapse into new stars.
Cosmology · 25 Oct 2025 · No. 3 · objkey.com/2-3
There are five eras in the universe's lifecycle. Right now, we're in the second era.
The first era was the Primordial Era, lasting only a fraction of a second after the Big Bang—yet within that infinitesimal window, everything was decided. In those initial moments, the universe was impossibly hot and dense, a roiling soup of quarks and energy where the fundamental forces of nature were unified into one. As space expanded and cooled, matter and antimatter annihilated each other in a cosmic flash, leaving behind a tiny surplus of matter that would become everything we see today. Protons and neutrons formed, then the first atomic nuclei. This era set the initial conditions for everything that would follow across billions of years.
We currently inhabit the Stelliferous Era—the age of stars. This is the universe at its most luminous and alive, a cosmos ablaze with light. Galaxies spin in vast cosmic webs, stars ignite and die in spectacular supernovae, planets coalesce from swirling disks of dust, and on at least one of them—perhaps many—life has emerged to contemplate its own existence. This era began roughly 13.8 billion years ago when the first stars ignited in the primordial darkness, fusing hydrogen into heavier elements and seeding the universe with the building blocks of complexity.
The Stelliferous Era will continue for trillions of years to come, though star formation has already peaked and begun its long decline. We are living in the universe's golden age, its most generative and creative epoch, though we're still relatively early in this chapter. Our sun is a middle-aged star in a middle-aged galaxy. Countless generations of stars will be born, live, and die long after our own solar system has vanished. But eventually, the raw materials will run out. Hydrogen will be locked away in stellar remnants or dispersed too thinly to collapse into new stars.
The third era will be the Degenerate Era, beginning perhaps 100 trillion years from now, when star formation finally ceases entirely and the cosmos goes dark save for the dim, fading glow of cooling stellar remnants. White dwarfs will slowly radiate away their heat over trillions upon trillions of years, glowing first red, then infrared, then finally going cold and black. Brown dwarfs—failed stars that never quite ignited—will drift through the void. Neutron stars will spin down, their rotation gradually slowing. These stellar corpses will occasionally collide, briefly lighting up the darkness, but such events will become rarer as the universe expands and galaxies drift apart.
The Degenerate Era will also see the slow dissolution of larger structures. Galaxies will evaporate as stars are gravitationally ejected into intergalactic space. Planets will spiral into their dying stars or be cast adrift. Any black holes will slowly consume whatever matter remains nearby. This quiet twilight will last incomprehensibly longer than the entire age of stars—a cold, dark cosmos where time stretches out toward infinity and almost nothing happens anymore.
Following that comes the Black Hole Era, beginning perhaps 10^40 years from now, when even dead stars have decayed through exotic processes we've never observed, and only black holes remain as the last massive structures in the universe. These cosmic singularities will slowly evaporate through Hawking radiation, leaking particles back into the void over timescales that dwarf even the Degenerate Era. A stellar-mass black hole might take 10^67 years to evaporate. A supermassive black hole at a galaxy's center could persist for 10^100 years or longer. The universe will be unimaginably vast by then, cold and empty, with these isolated black holes separated by distances beyond our ability to conceive, each one slowly shrinking in the darkness.
The Degenerate Era will also see the slow dissolution of larger structures. Galaxies will evaporate as stars are gravitationally ejected into intergalactic space. Planets will spiral into their dying stars or be cast adrift. Any black holes will slowly consume whatever matter remains nearby. This quiet twilight will last incomprehensibly longer than the entire age of stars—a cold, dark cosmos where time stretches out toward infinity and almost nothing happens anymore.
Following that comes the Black Hole Era, beginning perhaps 10^40 years from now, when even dead stars have decayed through exotic processes we've never observed, and only black holes remain as the last massive structures in the universe. These cosmic singularities will slowly evaporate through Hawking radiation, leaking particles back into the void over timescales that dwarf even the Degenerate Era. A stellar-mass black hole might take 10^67 years to evaporate. A supermassive black hole at a galaxy's center could persist for 10^100 years or longer. The universe will be unimaginably vast by then, cold and empty, with these isolated black holes separated by distances beyond our ability to conceive, each one slowly shrinking in the darkness.
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