Here’s what you’ll learn when you read this story:

• A new paper adjusts an equation that defines our universe in response to recent new data.
• The cosmological constant, which describes how our universe expands, may not be constant after all.
• Cosmology is already a complicated field of study, so switching up the variables is extra rough.

---

Scientists have recently used an updated understanding of the math of our universe to theorize that the universe will end in a crunch rather than entropy into oblivion. The field of cosmology may be very vocabulary-dense, but the bottom line is that one of our key numbers—the cosmological constant—may have switched teams from positive to negative. (If you switched from gaining one pound a week to losing one pound a week, you, too, might end in a “Big Crunch.”) And using this math, a team of researchers has estimated that our universe has a lifespan of about 33 billion years. That means we have about 19 billion to go before we become crispity crunchity.

Cosmology is, in broad terms, the study of our universe—how it began, how it exists now, and how it will eventually end. Those who publish research on cosmology must work in a different way than many other sciences, because key moments like the Big Bang and an eventual Big Crunch are almost completely outside current human understanding. We can wind time backward by studying stars, black holes, exotic structures, and even the shadows we believe may lead to dark matter or dark energy. But we’re missing huge connecting pieces, like how a tiny amount of matter can explode into a universe.

The cosmological constant is one effort to help answer these huge existential questions. We know that much of the mass and energy in our universe is invisible, or “dark,” but we don’t know the nature of this missing stuff, nor the source of it (though physics indicates that we’re likely swimming amid dark matter at all times). Dark energy, including the cosmological constant, is suggested as a way to balance our observation of how the universe is expanding. The gravity we know is everywhere around us would actually shrink our universe, so if we’re expanding all the time (as we are), that means something is repelling the universe’s parts from each other.

To cosmologists, this meant a positive constant. The universe was “gaining weight,” so to speak, so it would continue to expand at a faster and faster rate because the “weight” grew at a constant rate. But this changed after recent results from both the Dark Energy Survey (DES) and the Dark Energy Spectroscopic Instrument (DESI) earlier this year. Scientists studied the data and found that the cosmological constant may not be constant at all, but rather changing over time and indicating that its influence may be weakening. That would change the most widely believed equation about the beginning of our universe. (Imagine if your math homework changed from “Solve x + 5 = 8” to “Solve x + y = 8”—that’s a whole different skillset!)

Cosmology has been rippling from these DES and DESI revelations for months now, leading to research like this new paper—written by scientists based in the U.S., China, and Spain—which appears now in the peer reviewed journal Journal of Cosmology and Astroparticle Physics. These scientists have built a new, adjusted model for the expected lifespan of the universe by taking a possible negative cosmological constant into account. If the universe will stop expanding at some point and begin to contract, that’s a huge change from the understanding we had of the state of things at this same time a few years ago.

Their conclusions bring with them some newly opened doors. “It is crucial that the DES/DESI observation is confirmed and the aDE model is rigorously tested,” the researchers explain, as science is built on repeated and replicable data that helps researchers refine their conclusions and test new hypotheses. The team also curbs an anticipated question about a so-called Big Bounce, which is a theory in which the universe “crunches” and then re-expands in a predictable cycle:

“Although very unlikely, one cannot rule out that, in the presence of quantum effects, there is a way for the universe to transition to the next cycle. However, this reincarnation will lead to a very different universe from our present one, not to a cyclic universe.”

So, for those hoping to leave a letter for the new universe 18.9 billion years from now, the next paradigm may not have humans, paper, or even stars. Plan accordingly!

Caroline Delbert is a writer, avid reader, and contributing editor at Pop Mech. She’s also an enthusiast of just about everything. Her favorite topics include nuclear energy, cosmology, math of everyday things, and the philosophy of it all.