The universe will most likely “die” in roughly 10^100 years, a number called a googol, though the exact timeline and mechanism depend on which cosmological scenario plays out. That number is so large it defies comprehension: it’s a 1 followed by 100 zeros, making the current age of the universe (13.8 billion years) look like a rounding error. But the death of the universe isn’t a single event. It’s a long, slow series of endings, each one snuffing out another source of light, energy, or structure.
The Most Likely Scenario: Heat Death
The leading prediction among physicists is called heat death, sometimes referred to as the Big Freeze. It’s not a dramatic explosion or collapse. It’s the opposite: the universe gradually runs out of usable energy until nothing interesting can ever happen again.
The process unfolds in stages. Stars burn through their fuel and die. New stars form from leftover gas and dust. But that raw material is finite. Around 100 trillion years from now, the last stars will flicker out, ending what astronomers call the Stelliferous Era, the age of stars that began shortly after the Big Bang. At that point, the universe goes dark. The only objects left will be stellar remnants: white dwarfs cooling toward black, neutron stars, and black holes.
Even those remnants won’t last forever. Matter itself may be temporary. Grand unification theories in physics predict that protons, one of the building blocks of every atom, will eventually decay. Current estimates place the proton’s half-life at around 10^33 years or longer. If proton decay happens, every solid object, every planet, every dead star, will slowly dissolve into a thin soup of subatomic particles and radiation over timescales that make a trillion years look instantaneous.
The last survivors will be black holes, particularly the supermassive ones at the centers of galaxies. But even black holes aren’t eternal. They lose mass over time through a process called Hawking radiation, a slow leak of energy predicted by Stephen Hawking in the 1970s. The most massive black holes will take roughly a googol years (10^100) to fully evaporate. Once the last one vanishes in a faint burst of particles, the universe reaches its final state: a near-uniform bath of low-energy photons and scattered particles, hovering just above absolute zero, the coldest temperature possible. Nothing can form, nothing can change, and no energy can be extracted from anything. That’s heat death.
The Big Rip: A Faster, Violent Alternative
Heat death assumes that dark energy, the mysterious force accelerating the expansion of the universe, stays constant over time. But if dark energy gets stronger, the universe could tear itself apart in a scenario called the Big Rip.
The math hinges on a value physicists call the “w-parameter,” which describes the behavior of dark energy. If w equals exactly -1, dark energy stays constant and we get the slow heat death. If w drops below -1, dark energy becomes what’s known as phantom energy, and expansion accelerates without limit. In that case, the fabric of space would eventually stretch faster than any force could hold matter together. Galaxies would be pulled apart first, then solar systems, then planets, then atoms themselves. The timeline depends on exactly how far below -1 the value falls, but some models place it as little as tens of billions of years from now.
Current observations haven’t confirmed or ruled out the Big Rip. Most measurements of dark energy are consistent with w sitting very close to -1, which keeps this scenario on the table as a possibility rather than a probability.
The Big Crunch: Could the Universe Collapse?
There’s a third possibility that has recently gotten fresh attention. If the cosmological constant, the value that represents the energy density of empty space, turns out to be negative rather than positive, the universe would eventually stop expanding, reverse course, and collapse back on itself. This is the Big Crunch: essentially the Big Bang in reverse, with all matter and energy compressing to a single point.
For decades, most physicists dismissed this scenario because observations showed the universe’s expansion accelerating, which pointed toward a positive cosmological constant. But new data from the Dark Energy Survey in Chile and the Dark Energy Spectroscopic Instrument in Arizona has complicated the picture. These projects found that dark energy, which makes up about 68% of the universe’s total mass and energy, may not behave like a pure cosmological constant after all. Something else appears to be going on.
Cornell physicist Henry Tye and collaborators proposed a model in which a hypothetical low-mass particle mimicked a cosmological constant early in the universe’s history but no longer does. This model fits the new data well and tips the effective cosmological constant into negative territory. If that’s correct, the universe would reach a maximum size and then contract, ending in a Big Crunch roughly 33 billion years from now. That’s a startlingly short timeline compared to the trillions-of-years scenarios, though it remains a single theoretical model rather than settled science.
Why the Expansion Rate Matters
How fast the universe is expanding right now is directly tied to predictions about its fate, and physicists can’t quite agree on the number. The expansion rate is measured by the Hubble constant, and there’s a persistent gap between two ways of calculating it. Models based on the early universe (using the cosmic microwave background) give a value of about 67 to 68 kilometers per second per megaparsec. Direct telescope observations of nearby galaxies consistently give a higher value, around 72 to 73.
The James Webb Space Telescope’s largest study of universe expansion, published in late 2024, confirmed this tension. Webb measured a Hubble constant of 72.6, nearly identical to the 72.8 found by the Hubble Space Telescope for the same galaxies. The discrepancy isn’t a measurement error. It points to something physicists don’t yet understand about how the universe works, and resolving it could shift predictions about whether the universe ends in ice, fire, or collapse.
A Timeline of Endings
If heat death is the correct path, the universe doesn’t die all at once. It dies in chapters:
- ~5 billion years: The Sun exhausts its hydrogen fuel and expands into a red giant, consuming the inner planets.
- ~100 trillion years: The last stars burn out. The universe goes permanently dark.
- ~10^33 to 10^40 years: Proton decay (if it occurs) dissolves all remaining solid matter into subatomic particles.
- ~10^100 years: The last supermassive black holes evaporate through Hawking radiation. The universe reaches maximum entropy.
After that final black hole evaporates, the universe still exists, technically. It’s just an endlessly expanding void of near-zero temperature with no structure, no complexity, and no possibility of change. Time continues, but nothing marks its passage. Physicists sometimes call this the Dark Era, and it lasts forever.
The honest answer is that we don’t know with certainty which ending awaits. The heat death scenario is the most widely accepted, but fresh observations of dark energy’s behavior are actively challenging assumptions that seemed settled just a few years ago. What we do know is that every scenario agrees on one point: the universe as we know it, full of stars, galaxies, and the possibility of life, is a temporary phase in a much longer story.