The Big Bang started it all - but the 'Big Crunch' is what could wipe us out

While the 'Big Bang' is widely accepted as the cosmic event that started our entire universe, scientists warn there might just be a 'Big Crunch' that destroys it all.

As theorized, the 'Big Crunch' would be a horrific scenario whereby the universe's current process of expansion snaps into reverse — ending with galaxies, stars and planets all crashing into one another, as every last shred of matter collapses inward. 

But in the past year, scientists have discovered that 'dark energy,' a force proposed to explain what 'pushes' the cosmos to expand, may be becoming less 'pushy.'

'That means,' as one physics professor put it, 'revising our understanding of basic physics, our understanding of the Big Bang itself, and our understanding of the long-range forecast for the Universe.'

For most people on Earth, the first signs of the Big Crunch would be in the sky, with galaxy clusters and galaxies merging, or stars beginning to collide with each other.

Telescopes would show that the cosmic microwave background (a fossil echo of the Big Bang) was warming up — and would soon reach thousands of degrees Celsius.

For comparison, the current temperature of this background microwave radiation is just under 3 degrees above 'absolute zero' or 'negative 273.15 degrees Celsius,' according to the European Space Agency (ESA), NASA and other experts.

Roughly 300,000 years after the Big Bang, this cosmic microwave background is estimated to have been 3,000 degrees Celsius; and farther back in time, closer to the Big Bang itself, NASA estimates that its heat was as high as 273 million degrees.

'At these high temperatures,' according to NASA's Wilkinson Microwave Anisotropy Probe team. 'hydrogen was completely ionized into free protons and electrons.'

In short, the forces which currently make the universe expand would fizzle out and the universe would fall in on itself, in an obscene reversal of the Big Bang.

All intergalactic matter would condense together with stars and planets sucked into a burning core where the surface of stars would ignite other celestial bodies.

Eventually, the universe itself would become a single, vast fireball, at least according to some astronomers and astrophysicists, with all living things incinerated, and time and space itself wiped out of existence.

The new data suggesting that the Big Crunch may, in fact, be the ultimate fate of our universe emerged from an incredible telescopic system on a modest mountain in Kitt Peak, Arizona — automated with the help of 5,000 tiny robots that reposition its fiber optic cables.

The Dark Energy Spectroscopic Instrument (DESI) is a telescope which has spent three years building a 3D map of the universe, including millions of galaxies, at a speed previously unheard of in astronomy thanks to its robotic systems.

Over the course of one recent record-setting night this year, February 12, 2024, DESI managed to document the locations of nearly 200,000 distant 'redshift' galaxies.

It was data like this, collected by DESI, that appears to suggest that the dark energy 'fuel' responsible for the steady expansion of our universe appears to be weakening.

'The entire cosmological community was really shocked,' according to ex-DESI team member Luz Ángela García Peñaloza, a cosmologist at Columbia's Universidad ECCI.

Physicsts current 'standard model' of how the cosmos works, its history, and how it has evolved is called the Lambda Cold Dark Matter (LCDM) model — and it rests on the assumption that dark energy remains constant throughout all time.

The 'Lambda' in the theory's name, in fact, comes from a constant value, one pairing both Einstein's 'cosmological constant' and the once-presumed-constant of dark energy, a presumption DESI data collected from the past 11 billion years seem upend.

'DESI saw that the "equation of state" of the universe isn't consistent with the usual LCDM model,' García Peñaloza told Space.com, 'but instead, it is showing a hint that dark energy is varying with time.'

'This was pretty surprising because most cosmological observations thus far have favored the LCDM model,' she explained. 

The shocking discovery, she added, 'open a window for variable dark energy models' meaning not just the possibility of a Big Crunch but for other odd outcomes as well.

First theorized in 1998, dark energy is a theoretical force which explains why the universe is expanding, and why that expansion is accelerating.

The idea of dark energy is that the vacuum of space possesses a tiny amount of energy of its own, so faint and difficult to measure that it was dubbed 'dark energy.'

But the hints coming from DESI suggest that not only is dark energy weakening, but there has been a process whereby it first got stronger, only then to slowly weaken.

'If dark energy isn't a strict constant, who knows how it evolves,' as astronomer Joan Najita with the National Science Foundation's NOIRLab said this year. 

'That uncertainty, and the potential unshackling from a cosmological constant,' she noted, 'opens a richer set of potential futures for us.'

If the expansion of the universe continues, fueled by dark energy, another possible end will be almost as nightmarish - a scenario described as the 'Big Freeze', where as the universe expands relentlessly, eventually stars will stop forming.

Existing stars will run out of fuel, and stars travel further and further apart, leading to a lonely, dark universe as one by one the stars blink out.

From our Milky Way galaxy, no other galaxies will be visible.

Once the stars burn out, the dominant features of the universe will be black holes - until they too evaporate, leaving a universe barely above absolute zero, in a new 'dark era' which will last far longer than any which came before it.

But DESI scientists are actually optimistic that the new data (which is still being analyzed) will lead to a new understanding of physics.

The new results will likely mean a new understanding of dark energy — and, thus, even of the 'standard model' scientists have relied on to understand the physics that undergirds our universe.

'Essentially we have to start from scratch,' Physics professor Carlos Frenk of Durham University told The Guardian earlier this year. 

And other researchers believe this reckoning for dark energy is well over due.

'The idea that dark energy is varying is very natural,' according to Princeton University cosmologist Paul Steinhardt.

If it were not, as Steinhardt told Quanta: 'It would be the only form of energy we know which is absolutely constant in space and time.'