The End of the Universe

For 27 years, cosmologists had a plan for how everything ends: the universe keeps expanding, forever, until every star burns out, every black hole evaporates, and the last photons drift away into nothing. Tidy, if bleak. New data suggests it might not go that way at all.

The universe may be approaching the midpoint of its 33-billion-year lifespan. After expanding to its peak size about 11 billion years from now, it could begin to contract, snapping back like a rubber band to a single point. That endpoint has a name cosmologists have been quietly dusting off: the Big Crunch.

The pivot comes from a recalibration of dark energy, the mysterious force that accounts for roughly 68 percent of all the mass and energy in the universe. The standard model treated it as a cosmological constant, a fixed pressure built into the fabric of space. Cornell physicist Henry Tye updated a long-standing model built around that constant using fresh data, and concluded: "The new data seem to indicate that the cosmological constant is negative, and that the universe will end in a big crunch."

That fresh data comes from two major observatories working independently: the Dark Energy Survey in Chile and the Dark Energy Spectroscopic Instrument in Arizona. One southern hemisphere, one northern, and their findings are in close agreement. Tye and collaborators proposed a hypothetical low-mass particle that behaved like a cosmological constant early in the universe's life but doesn't anymore. The model fits the data while tipping the underlying cosmological constant into negative territory.

Separately, astronomers at South Korea's Yonsei University argue the universe is no longer accelerating. The dimness previously attributed to rapid expansion may instead reflect the age of the stars themselves, a flaw in the "standard candle" measurements astronomers have used to gauge cosmic distances since 1998.

More data is coming. The Vera C. Rubin Observatory in Chile is the next major instrument expected to weigh in, and its observations could either reinforce the new picture or complicate it further.

The universe may be mortal after all. The prognosis hinges on dark matter.

Read the full story at Popular Mechanics, May 2026

Hot Take:You thought murder hornets were bad. Queue end of the universe in three, two, one. In with a bang; out with an, er, crunch.