Dark energy is stretching the universe apart — including the distance between your hand and your shoulder, right now, while you read this. Enter any distance and see how fast space is pulling it apart.
Since the 1920s we have known the universe is not sitting still. Edwin Hubble watched distant galaxies recede — the farther away they were, the faster they fled. The reason, we now believe, is not that galaxies are running away. It is that the space between them is growing. Every cubic centimeter of empty space is, very slowly, becoming more cubic centimeter.
The speed of this stretch is measured by the Hubble constant, roughly 70 kilometers per second per megaparsec. For a distance of one light-year, space itself is inflating at about two centimeters per second. For your arm — 1.8 meters — the stretch is four quintillionths of a meter per second. Your hand and your shoulder are drifting apart by less than the width of an atomic nucleus every second. The universe is pulling you apart, and it is doing a terrible job.
The force behind this stretch is dark energy, the name we gave to something we do not understand that makes up about 68% of the universe. It does not thin out as the universe grows, so it wins in the end. In billions of years, galaxies beyond our local group will be so far away that they vanish over the horizon. Astronomers in the far future will see a static, empty universe and may conclude the cosmos is just a lonely patch of stars.
Here is the strangest part: for distances larger than a few billion light-years, space expands faster than light. That does not break physics — nothing is moving through space faster than light; the space in between is simply growing. It is the universe's one legal way to beat the speed limit. And it means the observable universe is growing heavier by about 3.3 light-years of diameter every single year, whether you like it or not.
It is real. Galaxies recede at speeds proportional to their distance (Hubble's law), and the cosmic microwave background confirms it. In 2026 a new analysis of 1,700+ supernovae questioned whether dark energy is accelerating things — the expansion itself is not in doubt.
Because gravity holds bound systems together. The expansion of space is overwhelmed by local attraction inside galaxies, solar systems, and atoms. The Moon does drift, but for orbital reasons, not cosmic ones — about 3.8 cm a year due to tides.
Technically space inside your arm is expanding, but atoms are bound far more strongly than gravity. The stretch is 4 quintillionths of a meter per second — a billion times smaller than anything your body can feel. You are safe. Your shirt fits.
Dark energy wins. In tens of billions of years, all galaxies beyond our local group will recede beyond our horizon. Future astronomers will see a tiny, quiet, static universe — and may never guess it was born in a bang.