Many physicists now believe the universe will end by tearing itself apart — and now it appears that this could happen sooner than anyone expected. Originally, scientists hypothesized that the Big Rip would happen in 20 to 22 billion years based on a reasonable set of parameters — but now it sounds as though we may not have that much time left. And the end of the universe could be much stranger than the graceful "heat death" we've all been looking forward to.
The discovery of a gravitationally repulsive force called dark energy, back in the 1990s, provided cosmologists with a neat and tidy explanation of why galaxies are moving away from each other at an accelerating rate. A surprising implication of this theory, however, was the realization that this same force could eventually cause the Universe to rip apart into nothingness. And the more we learn about this mysterious force, the sooner it looks like this will happen.
Crunching numbers to predict the rip
Dark energy is a kind of cosmological placeholder that helps scientists explain why the universe behaves the way it does. They aren't exactly sure how or why it exists, nor can they come to a consensus on its exact nature. But one thing they do know is that, without it, the universe doesn't make much sense. In fact, scientists believe dark energy makes up about 70% of the current content of the universe, so it's a major player in the cosmological game — a force that will in all likelihood determine the final end-state of the universe's developmental cycle.
To help cosmologists with their chalkboard equations, they have assigned the letter ‘w' when working with dark energy — a way to mathematically depict the ratio of pressure and density of dark energy. The only problem, however, is they're not exactly sure what value to give it. But what they do know is that if they give w a value less than -1, their calculations reveal that dark energy will eventually grow to infinity — a regrettable turn of events that will cause everything in the universe to fly apart from each other — including tiny particles and any other building block of the Universe.
And lamentably, cosmologists are pretty sure dark energy has a value less than -1.
Now, a recent study published in Science China's Physics, Mechanics and Astronomy is reaffirming this assessment — but their calculations show that, when applying a likely value of -1.5, the Universe's potential expiry date has to be pulled closer by as much as 6 billion years.
Previous estimates using a similar value had suggested that the Big Rip wouldn't happen until about 20-22 billion years from now, but after developing and applying a new technique, a Chinese team led by Zhang Xin and Li Miao are suggesting it could happen as early as 16.7 billion years from now — an indication that the Universe is about 2 billion years away from hitting the halfway point in its life. On a more positive note, the researchers have assigned the best fit result at 103.5 billion years into the future.
To reach this conclusion, the researchers devised a new method for coming up with the parameters required for their calculations. Previous estimates had used the Chevallier-Polarski-Linder (CPL) parameterization, but Zhang and Li felt it was insufficient on account of its inability to handle divergences, namely the redshift parameter. In its place, they developed the divergence-free Ma-Zhang (MZ) parameterization — what the scientists say is a method that offers "a more well behaved, bounded behavior."
All this being said, cosmologists are not at all in agreement about the value of w, a cosmological force that may not be tightly constrained. Clearly, any change to its value will have a significant impact on any prediction made about the big rip. Moreover, Zhang and Li are not making any special claims about the value of w, merely that they've devised a potentially more useful parameterization method for making such calculations.
The ultimate fate of the universe
It's worth noting that, given this timescale, and assuming that the big rip will hold as theory, the Universe will never go through the much-considered heat death phase, which was scheduled to start 10100 years from now. And what's particularly disturbing about all of this is, stars and planets will very much be still in existence at the time of the big rip. It's going to be a universe-wide catastrophe, that words cannot even begin to describe.
When considering their data, the cosmologists are fairly convinced that w will continue to exhibit a value less than -1 well into the future — which, in the words of the study's authors, "will lead to a strange future for the Universe."
And the picture they paint is very strange indeed. The cosmologists suggest that dark energy's gravitational repulsion will continually increase until it overcomes all forces holding objects together, causing every structure in the Universe to be torn apart. Nothing will be immune to this cataclysmic event — including those atomic-scale objects that are more tightly bound (they'll be the last to go).
Now, it's very unlikely that our solar system will exist in its current form at that time, but it's worth considering what would happen if it did.
Zhang and Li write that the the Milky Way will be torn apart 32.9 million years before the big rip. The Earth will be ripped away from the Sun two months before the end, and we'll lose our moon with five days left. The Sun itself will be destroyed 28 minutes before the end of time, and the Earth will explode a mere 12 minutes later.
Read the entire paper.