The universe could soon grind to a halt after nearly 13 billion years of expansion, according to new research.
Three scientists attempt to model the nature of dark energy, a mysterious force that seems to be causing the universe to expand ever faster. Dark energy is not a constant force of nature, but an entity called quintessence, which can decay over time.
Even though the expansion of the universe has been going on for billions of years, the force of dark energy may be waning. The model suggests that within the next 65 million years, the universe could stop expanding, and within 100 million years, it could end with the death of the universe.
The study co-author, Paul Steinhardt, Director of the Princeton Center for Theoretical Science, said it could all happen quickly.
65 million years ago, the asteroid that killed the dinosaurs hit the Earth.
The theory is not controversial or implausible, according to a professor at the University of British Columbia who was not involved in the study. The model hinges on past observations of expansion alone, and the present nature of dark energy is a mystery, so predictions in this paper are currently impossible to test. They can only be theories for now.
The expansion of the universe is speeding up and the space between the galaxies is getting bigger. Scientists named the mysterious source of this acceleration dark energy, an invisible entity that seems to work contrary to gravity, and pushes the universe's most massive objects farther apart rather than drawing them together.
Dark energy makes up 70% of the total mass-energy of the universe. Albert Einstein introduced a theory that says dark energy is a constant in space-time. If that is the case, then the universe should continue expanding because dark energy can never change.
A competing theory suggests that dark energy does not need to be constant in order to fit with observations of the past. Dark energy may be a field that changes over time. The idea was introduced in a 1998 paper by three scientists.
quintessence can be either repulsive or attractive depending on the ratio of its potential energy at a given time. Over the last 14 billion years, quintessence was repulsive, but it contributed to the expansion of the universe.
Steinhardt said that the question they were asking was, "Do this acceleration have to last forever?"
Steinhardt and his colleauges predicted the properties of quintessence over the next several billion years. The team created a physical model of quintessence to fit with the observations of the universe's expansion. The team extended their predictions into the future once their model could reproduce the universe's expansion history.
Dark energy in their model can decay with time. If it does that in a certain way, then the anti-gravity property of dark energy goes away and it transitions back into something more normal.
The team believes that the force of dark energy could be in the midst of a rapid decline.
The expansion of the universe is slowing down. Within as few as 100 million years from now, dark energy could become attractive and cause the universe to contract. After 14 billion years of growth, space could start to shrink.
Steinhardt said that this kind of contraction is called slow contraction.
Steinhardt said that the contraction of the universe would be so slow that any hypothetical humans still alive on Earth wouldn't even notice a change. It would take a few billion years of slow contraction for the universe to reach half its current size.
Steinhardt said one of two things could happen from there. Either the universe contracts until it collapses in on itself in a big crunch, or it contracts just enough to return to a state similar to its original conditions.
Steinhardt and another colleague describe in a paper in the journal Physics Letters B a second scenario in which the universe follows a pattern of expansion and contraction, with collapses and remakes. Steinhardt said that our current universe may not be the first or only universe, but the latest in an infinite series of universes that have expanded and contracted before ours. The nature of dark energy is what determines it all.
How plausible is this? The new paper's interpretation of quintessence is a perfectly reasonable supposition for what the dark energy is. We would have no way of knowing until after the contraction phase began.
I think it's just a question of how compelling the theory is and how testable it is.
Steinhardt admitted that there is no good way to test whether quintessence is real or whether the expansion of the universe has started to slow. The authors did a good job fitting the theory with past observations in their new paper. Time will tell if a future of endless growth or rapid decay awaits our universe.
It was originally published on Live Science.
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