The End Will Come Earlier: Scientists Adjusted the "Death Date" of the Universe

With the universe currently estimated to be about 13.8 billion years old, that leaves just over 19 billion years before it all ends in what scientists call the Big Crunch.

While the universe has been expanding outwards since the Big Bang, the powerful explosion that is believed to have given birth to everything in existence, the Big Crunch will see the opposite happen - with all matter collapsing back into a single point of energy, the Daily Mail reports.

Researchers from New York's Cornell University and China's Shanghai Jiao Tong University have created a new cosmic model that suggests dark energy, the force thought to be driving the expansion of the universe, will weaken over time and give way to gravity.

Scientists are still trying to prove that dark energy actually exists, but they believe it acts as a repulsive force, counteracting gravity’s tendency to pull everything together. If dark energy were to disappear completely in 33.3 billion years, as the new study suggests, the gravity of all the stars, galaxies, and black holes would essentially cause the universe to collapse under its own weight.

This updated model of the Universe now provides a much shorter timescale for our existence, which previous theories suggested could continue without any limitations.

Chelsea Gode of NASA explained in a statement: “What exactly is dark energy? The short answer is we don’t know. But we do know that it exists, it is causing the universe to expand at an accelerating rate, and that somewhere between 68.3 and 70 percent of the universe is dark energy.”

In the new study, the scientists focused on the role of dark energy in this process, using a model called axion Dark Energy (aDE) to interpret recent data suggesting that dark energy behaves differently than previously thought.

Scientists believed that dark energy was a cosmological constant, a fixed, unchanging energy density that was infinitely accelerating the expansion of the universe.

This includes a recent 2020 study in the journal Astronomy & Astrophysics that concluded that the universe's dark energy has a positive cosmological constant, meaning its value never drops and continues to allow the universe to grow.

However, the new aDE model found that dark energy may actually have a negative cosmological constant of about -1.61, suggesting that the Universe may eventually reach a maximum size and then collapse in a Big Crunch.

"The age of our universe is fundamental to cosmology. Since the inception of the Big Bang theory, we have known that it is finite," the researchers wrote on the pre-print server Arxiv.

"Using the best-fit model values as a guide, we conclude that the lifetime of our Universe is 33 billion years," they added in a study submitted for publication in the Journal of Cosmology and Astroparticle Physics.

The researchers analyzed the latest data from the Dark Energy Survey (DES) and the Dark Energy Spectroscopic Instrument (DESI), which studied how fast the universe is expanding, using phenomena such as exploding stars (supernovae) and the distribution of galaxies.

The findings suggest that dark energy may not be as stable as several previous studies have suggested, the Daily Mail notes.

The study's authors used the aDE model, which includes a cosmological constant (a value that affects whether the universe expands or contracts) and an ultra-light particle called an axion.

By fitting this model to the data, they calculated key values such as the cosmological constant and the equation of state (a measure of how dark energy behaves). The scientists then used these values to predict the future of the universe, calculating when it might stop expanding and collapse.

Unlike standard models, which assumed that dark energy was constant, this model allowed dark energy to weaken over time as the axion field evolved.

The axion field is like an invisible superluminal energy wave that spreads throughout the universe like ripples on a pond, but exists everywhere in space. Assuming that dark energy is so flexible, it turns out that this repulsive force may have an "optimal value" that is negative, meaning that it will disappear as more time passes since the Big Bang.

There are still many unknowns about the end of the universe as we know it. For one thing, scientists still don't even know what dark energy actually is.

NASA has put forward four theories about this invisible force that may be holding back the end of time.

One theory is that it is vacuum energy, a constant background energy in space related to Albert Einstein's cosmological constant. This theory causes the universe to expand faster, but it is a puzzle to modern scientists because its predicted strength does not match new observations.

Dark energy may be a shifting energy field or fluid called "quintessence" that fills space and acts in the opposite way to ordinary matter, changing over time and space, causing the expansion of the universe to accelerate.

NASA has also suggested that dark energy could arise from defects in the structure of the universe, such as hypothetical one-dimensional "folds" called cosmic strings that formed when the universe was young, pushing space outward.

However, the researchers suggest that this could be explained by a flaw in Einstein's theory of gravity, meaning that the expansion of the universe does not depend on dark energy at all.