Scientists reveal 'death date' of the universe is sooner than previously believed
A team from the US and China have discovered that our universe will reach its 'death date' and stop expanding when it turns 33.3 billion years old.
Since the universe is estimated to be roughly 13.8 billion years old right now, that leaves just over 19 billion years to go before everything ends in what scientists call a 'Big Crunch.'
While the universe has been expanding outward since the Big Bang, the massive explosion believed to have kickstarted everything in existence, the big crunch would be the reverse - where all matter collapses back into a single point of energy.
Researchers from New York's Cornell University and China's Shanghai Jiao Tong University created a new cosmic model that suggests dark energy, the force believed to be driving the universe's expansion, will weaken over time and succumb to gravity.
Scientists are still trying to prove that dark energy actually exists, but they believe it acts like a repulsive force, counteracting gravity's desire to pull everything together.
If dark energy finally fades after 33.3 billion years, as proposed in the new study, gravity from all the stars, galaxies, and black holes would essentially force the universe to cave in under its own weight.
This updated model of the universe now provides a much shorter timeline for our existence, which previous theories suggested might keep going without any limitations.
While dark matter is a type of matter which can't be observed or seen, dark energy is a type of energy which doesn't interact in a normal way with matter. Scientists have proposed that these two things might make up the vast majority of the universe
NASA's Chelsea Gohd 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's making the universe expand at an accelerating rate, and approximately 68.3 to 70 percent of the universe is dark energy.'
In the new study, scientists focused on the role of dark energy in this process, using a model called the axion Dark Energy (aDE) model to interpret recent data suggesting that dark energy behaves differently than previously thought.
Scientists believed dark energy was a cosmological constant, a fixed, unchanging energy density driving the universe's accelerated expansion indefinitely.
This includes a recent study from 2020 in Astronomy & Astrophysics which concluded that the universe's dark energy has a positive cosmological constant, meaning its value never drops off and keeps allowing the universe to grow.
However, the new aDE model found dark energy may actually have a negative cosmological constant of around -1.61, which suggests the universe could eventually reach a maximum size and then collapse in a Big Crunch.
'The age of our universe is of foundational importance in cosmology. Since the establishment of the Big Bang Theory, we know it is finite,' the researchers wrote on the pre-print server Arxiv.
'Using the best-fit values of the model as a benchmark, we find the lifespan of our universe to be 33 billion years,' they added in the study submitted for publication in the Journal of Cosmology and Astroparticle Physics.
The researchers analyzed recent data from the Dark Energy Survey (DES) and the Dark Energy Spectroscopic Instrument (DESI). These projects studied how fast the universe is expanding by looking at things like exploding stars (supernovae) and the way galaxies are spread out.
The data revealed that dark energy might not be as steady as several previous studies previously concluded.
Study authors used the aDE model, which includes a cosmological constant (a value that affects how the universe expands or contracts) and an ultra-light particle called an axion.
By fitting this model to the data, they estimated key values, like the cosmological constant and the equation of state (a measure of dark energy's behavior).
They then used these values to predict the universe's future, calculating when it might stop expanding and collapse.
Unlike standard models which assumed that dark energy is fixed, this model allowed dark energy to weaken over time as the axion field evolves.
An axion field is like an invisible, super-light energy wave that spreads throughout the entire universe, kind of like ripples on a pond but existing everywhere in space.
Allowing dark energy to be flexible in this way revealed that this repulsive force could have a 'best-fit value' which is negative, meaning it'll fade away as more time since the Big Bang passes.
There's still a lot of uncertainty concerning the end of the universe as we know it. For one, scientists still don't even know what dark energy really is.
NASA has come up with four theories about this invisible force that could be holding back the end of time.
One possibility is that it's vacuum energy, a constant background energy in space tied to Albert Einstein's cosmological constant.
The theory pushes the universe to expand faster but has created a puzzle for modern scientists because its predicted strength doesn't match newer observations.
Dark energy could be a changing energy field or fluid, nicknamed quintessence, that fills space and acts opposite to normal matter, varying across time and space to drive the universe's accelerated expansion.
NASA has also speculated that dark energy might come from defects in the universe's fabric, like hypothetical one-dimensional 'wrinkles' called cosmic strings, formed when the universe was young, pushing space outward.
However, researchers suggest it could be explained by a flaw in Einstein's theory of gravity, meaning the universe's expansion does not rely on dark energy at all.
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