Measurements of the recessional velocity, distance and age of stellar explosions called supernovae provided the first direct evidence that the rate at which the universe is expanding is increasing.
Empires may rise and civilizations and ecosystems may crumble in the billions of years to come, but matter as we know it will endure, according to a new study eyeing the future of the universe.
The universe's ceaseless expansion, accelerated by the still-unseen and mysterious dark energy, will ultimately yield an environment in which matter nonetheless remains while radiation energy dwindles away, researchers said. The finding runs contrary to previous thinking that suggested matter would gradually decay into a radiation-heavy universe.
"Even if matter begins to decay, it will still be the dominant sort stuff in the universe," said physicist Lawrence Krauss of Case Western Reserve University, the lead author of the new study. "That's why I've kind of said that diamonds are forever."
Future unlike the past
Krauss and colleague Robert Scherrer of Vanderbilt University used mathematical models to determine that in the far future, radiation--including heat, light and all other forms--will vanish faster than it can be replenished through the decay of matter into component protons, neutrons and electrons. At the crux of the issue is dark energy, a hypothetical field or energy which permeates space and tends to accelerate the universe's expansion.
"It means that the future isn't like the past, and that the future is once again different than we thought," Krauss told SPACE.com.
The research was detailed April 25 in the online edition of the journal Physical Review D.
Previous theories suggested that radiation, not matter, would win out in the end because matter would decay into additional radiation over trillions of years.
"The universe started out radiation-dominated," Scherrer said in an interview. "Today, the universe is mostly matter and what's left over from the radiation is the famous microwave background, which is very dilute."
Bleak future for life
Matter may win out over radiation in the distant future thanks to dark energy, but the odd force, as-yet unobserved directly, overall paints a bleak and lonely picture for life as we know it.
"This is kind of one little small saving grace that we've stumbled across," Scherrer said of matter's perseverance, adding that current universe forecasts predict a very cold cosmos in which life will have a hard time surviving.
Over the next 100 billion years, dark energy is expected to accelerate the most distant galaxies and stars in the universe beyond the speed of light, meaning that they will be invisible to future observers. Some objects once visible at half the universe's current age of about 13.7 billion years are already invisible from the farthest vantage points, and in about 10 trillion years, only the local cluster of galaxies, including our own Milky Way, will be visible, researchers said.
"The future is bad," Krauss told SPACE.com. "A universe with dark energy is the worst of all possible universes for the long-term future of life."
After just one trillion years, Krauss added, astronomers will no longer be able to observe the universe's expansion, constant microwave background, red shift of galaxies and other cosmic hallmarks.
"Those are really all at the basis of our modern understanding of cosmology," said Krauss, who said he first began theorizing about the future of the universe to discern how it might end. "People of the future won't be able to know what the universe is doing."
That puts astronomers in a unique position today to study the universe, he added.
"I think we should be buoyed by the fact that it's amazing what we're able to understand here in this random time in the middle of nowhere in the universe," Krauss said.