Will the universe end, and if so, how?

What will happen to the Sun and to Earth?

This part is the most solid. NASA explains that the Sun, like all stars, will eventually run out of energy. Scientists predict it is a little less than halfway through its lifetime and will last another 5 billion years or so. As it starts to die, it will expand into a red giant large enough to engulf Mercury and Venus, and possibly Earth. After that, it will become a white dwarf and slowly cool.

Whether Earth itself is swallowed is not settled. In a 1997 review, the astrophysicists Fred Adams and Gregory Laughlin noted that the Sun will lose a lot of mass as a red giant. Its weaker pull lets the planets drift outward, which could help Earth escape. How much mass the Sun will lose is still uncertain.

Why does dark energy decide the ending?

Dark energy is the name for whatever is making the expansion of space speed up. It makes up about 70% of the universe, according to Berkeley Lab, which manages the DESI survey. For the basics, see What Is Dark Energy?

The simplest idea is that dark energy is a cosmological constant: a steady push built into space that never changes. If dark energy matters as much as it seems to, NASA’s WMAP mission site explains, the universe will in all likelihood expand forever. The same page calls endless expansion the Big Chill or Big Freeze, because the universe will slowly cool as it expands until it can no longer support life.

The strongest objection to that forecast is simple: it assumes dark energy stays constant, and that assumption is now being tested. DESI, the Dark Energy Spectroscopic Instrument, works from a telescope at Kitt Peak in Arizona. In March 2025, using three years of data on nearly 15 million galaxies and quasars, the team reported that, combined with other measurements, its data lean toward dark energy that is weakening over time. That preference ranged from 2.8 to 4.2 sigma. Sigma measures how unlikely a result is to be a fluke, and physicists usually want 5 sigma before they claim a discovery. As Berkeley Lab noted, many 3-sigma results have faded away with more data. DESI’s first-year results in 2024 had shown a similar hint.

Since then, the picture has become more mixed. A 2026 recalibrated analysis of Dark Energy Survey supernovae lowered the strongest combined result from 4.2 to 3.2 sigma, which its authors call only a weak preference for evolving dark energy. In July 2026, a new DESI measurement using hydrogen gas in the distant universe agreed with the standard model. DESI says this could mean the hint will fade, or that a more complex model is needed. DESI finished its planned five-year map in April 2026, with more than 47 million galaxies and quasars, and its first dark energy results from all five years are expected in 2027.

What would the big freeze look like?

If dark energy stays constant, here is a rough timeline pieced together from two well-known studies. These are forecasts built on today’s physics for a universe that keeps expanding, not observations.

• About 100 billion years: Galaxies beyond our Local Group are pushed past our cosmic horizon, as the physicists Lawrence Krauss and Robert Scherrer noted in 2007. By then, the afterglow of the Big Bang would be about a trillion times fainter than today.
• About 10 trillion years: The smallest stars, which burn their fuel very slowly, finish their hydrogen and fade, according to Adams and Laughlin.
• About 100 trillion years: Galaxies run out of the gas needed to make new stars, and the era of ordinary shining stars comes to an end.
• Far beyond that: What is left is mostly the cold remains of stars, and black holes. Even black holes slowly lose mass by giving off Hawking radiation. In Adams and Laughlin’s timeline, the black hole era runs to about 10 to the power of 100 years, a 1 followed by 100 zeros. After that comes a dark era of stray particles and very weak light, the stage they link to heat death.

So what would the universe look like in a trillion years, if dark energy keeps winning? Putting these studies together, other galaxies would have been pushed past our horizon long before, and the afterglow of the Big Bang would be fading toward insignificance. Our home galaxy, likely merged by then with Andromeda and other neighbors, would still hold shining stars, because star formation goes on until about 100 trillion years. Krauss and Scherrer argue that observers in such a galaxy would see a single galaxy, an “island universe,” and would have no way to detect the expansion of the universe or the afterglow of the Big Bang.

As an analogy, picture a party that never ends: the guests drift away one by one, the lights go out, and the room slowly cools. The analogy breaks in one way. Galaxies do not walk out a door; the space between them stretches.

Could the universe rip, crunch or suddenly change instead?

The Big Rip: Not supported

In 2003, Robert Caldwell, Marc Kamionkowski and Nevin Weinberg asked what would happen if dark energy grew stronger over time, a kind they called phantom energy. The expansion would speed up without limit and tear apart galaxies, solar systems, planets and finally atoms, in a Big Rip. In one example they worked out, the end would come 22 billion years from now. The Milky Way would be torn apart about 60 million years before the end, and Earth would explode about 30 minutes before. But a Big Rip needs dark energy that grows stronger. The recent hints point the other way, so the data do not support it for now.

The Big Crunch: Open question

Cosmologists long wondered whether gravity might one day stop the expansion and pull everything back together in a Big Crunch. NASA’s WMAP site explains that this would happen if the universe held enough matter. Dark energy made that look unlikely. But if dark energy is weakening, a crunch comes back into play. In a 2025 paper in the Journal of Cosmology and Astroparticle Physics, Hoang Nhan Luu, Yu-Cheng Qiu and S.-H. Henry Tye fit one model of changing dark energy to recent survey data. In their best fit, the expansion stops about 11 billion years from now, and the universe crunches at a total age of about 33 billion years. The authors note a large uncertainty in their model, and it is one model among many.

Vacuum decay: Open question

A stranger possibility involves empty space itself. As an analogy, picture a ball resting in a small dip partway down a hill, with a deeper valley below. Calculations with the Standard Model, the well-tested theory of particles, suggest that empty space may be in a similar state, called metastable. Through a quantum process called tunneling, a bubble of a lower-energy state could appear somewhere and spread at the speed of light. The analogy breaks because nothing has to push the ball: tunneling lets the change happen on its own, extremely rarely.

How rarely? In 2018, Anders Andreassen, William Frost and Matthew Schwartz published a full calculation. With 95% confidence, they found, our universe should last more than 10 to the power of 58 years, vastly longer than its current age of 13.8 billion years. Their calculation leaves out gravity and any physics beyond the Standard Model, and they note that unknown physics at very high energies could make space less stable or fully stable.

What do people often get wrong?

• “The end is coming soon.” None of these endings is expected for billions of years; the nearest big change here, the end of the Sun’s life, is about 5 billion years away.
• “DESI proved dark energy is changing.” It found hints, not proof, and newer results are mixed.
• “Heat death means the universe gets hot.” It means the reverse: a universe so cold, spread out and dull that almost nothing happens anymore.
• “Expanding space stretches everything.” Caldwell and his colleagues note that systems held together by gravity, such as the Milky Way, stay bound unless dark energy grows stronger, as in a Big Rip.

How can you check this yourself?

• Look for the sigma. A result below 5 sigma is a hint, not a discovery.
• Ask which assumption is doing the work. Every timeline on this page assumes something about dark energy. If a headline gives a date for the end of the universe, check which model it used.
• Watch for 2027. That is when DESI expects its first dark energy results from all five years of data.
• Read the teams’ own words. Berkeley Lab and DESI post plain-language summaries of new results. For a general method, see How to Check a Viral Science Claim in Five Minutes.

The answer stays the same. Nobody knows yet how the universe will end. The slow big freeze leads for now, and the next few years of data will test it.