“Where did we come from?” and “where are we going?” are two of my favourite questions as a human being.
But taking the very longest view, the answer to both turns out to be shockingly similar, according to University of Michigan physicist Fred Adams.
Adams and a colleague, Gregory Laughlin, who’s now at the University of California, Santa Cruz, decided to predict the incredibly distant future of the universe in the mid 1990s.
It was neither easy, nor a hot topic at the time. “It had been almost 20 years since anyone had looked at the problem and we knew a lot more about physics and astrophysics,” Adams told Tech Insider.
So Adams and Laughlin asked what might happen in the next googol years — or 1 with 100 zeroes after it.
We first heard about their predictions for the universe when we talked to Rachel Sussman, who used their ideas as the skeleton for her current art installation, “A Selected History of the Spacetime Continuum” at the Massachusetts Museum of Contemporary Art.
The result is a mind-twisting dive into a scale of thinking we don’t usually get to wrestle with. Here’s what it looks like.
The five eras
For the first million years after the Big Bang, the universe was in the primordial era. “The basic idea is that when you first make a universe there’s no stars, there’s no stellar-like bodies, it’s just particles,” said Adams.
Then helium production begins, the first step on the road to building stars.
“To be fair, we don’t know exactly when the very first star was made,” said Adams. But star creation is the hallmark of the second era, the stelliferous era. That’s where we are now, and where we’ll be for tens of trillions more years, Adams said.
One of the key advances Adams and Laughlin made in sketching out their five eras was realising that stars would continue for much longer than physicists had previously realised.
By running a new stellar evolution model, Adams and Laughlin realised that small stars can access and burn much more of their hydrogen fuel than had been believed. They also calculated that having heavy metallic elements in their cores makes stars live longer than usual.
They figured out that the stelliferous era would get a boost, too, thanks to brown dwarfs — small, dense, old stars that can collide to form new stars.
But nothing lasts forever. It will take a very long time, longer than anyone can truly grasp, but eventually all of these stars “basically grind to a halt,” Adams said.
That will mark the beginning of the degenerate era.
Adams is quick to point out there’s no moral judgment in the name: It borrows a term from quantum mechanics to mark the time when “we go from a universe filled with stars to a universe filled with stellar remnants,” Adams said. (Stellar remnants are brown dwarfs, white dwarfs, and neutron stars — the small dense stars that are typically the last stop in a star’s evolution.)
But the degenerate era gets much bleaker than a bunch of bits of dead stars.
Eventually, the atoms that we — and everything else in the universe — are made of will literally disintegrate, thanks to a phenomenon called proton decay. That’s the big idea that wasn’t incorporated into any of the universe predictions that were around before Adams and Laughlin got to work.
Protons are the positively charged particles in atoms, which physicists in the 1970s proposed might be able to break down into smaller subatomic particles. But proton decay happens very, very slowly — so slowly we’ve never seen it happen.
During the degenerate period, though, proton decay will finally catch up with us, leaving nothing but black holes to survive into the aptly named black hole era.
Black holes get their name from how dark they are; astronomers can only see them by studying how their gravity impacts their surroundings.
After all the stars and protons decay away, Adams says, “black holes will be the brightest things in the sky.”
How can that be? Assuming that the idea that made Stephen Hawking famous is true (a notion few physicists doubt), they will glow very faintly in Hawking radiation — when individual particles manage to escape the pull of the black hole thanks to the sacrifice of another, perfectly positioned particle.
While black holes are providing gentle mood lighting to the universe, they’re also slowly evaporating, said Adams. It doesn’t matter now, but by the time the universe is 10 to the 60th power (that’s a 1 with 60 zeros after it) years old, it will.
“If black holes are shining, if they’re evaporating, if they’re providing energy, eventually they will go away,” Adams said, and then “we’re back to particles again.”
That’s the last era of the universe, the dark era, which will look eerily like the early days of the universe.
“Instead of ashes to ashes or dust to dust, it’s really particles to particles,” Adams said.
But will it happen?
Since Adams and Laughlin came up with the five eras in the 1990s, the biggest physics discovery has been confirming the universe’s expansion is accelerating and it won’t then collapse in on itself.
That actually makes it easier to predict what will happen to the universe. “I basically just have to account for the death and destruction of everything we have now,” Adams said, since with no collapse there won’t be new structures to account for.
Each cluster of galaxies will drift farther and farther away from its neighbours faster and faster, but within each cluster, his and Laughlin’s predictions from 1997 are still valid. “Our job as futurists is easier, we just have to kill everything we have now.”
Of course, this whole timeline could be wrong.
“You always have to admit that you don’t know that that’s what’s going to happen,” Adams said, adding that the further into the past or future you go, the more uncertainty you face. He and Laughlin actually decided not to publicly calculate anything past a googol, or 10 to the 100th power, years in the future. “We decided we didn’t believe [those predictions], or we didn’t believe them enough to put them in the book.”
Not only do numbers become absurdly large, but the further into the future you get, the more likely it is that something you didn’t think of will show up and throw a wrench in your prediction.
Adams supplied a cautionary tale of calculating too far into the future. In a paper published in 1979, theoretician Freeman Dyson calculated the incredibly slow speed at which nuclear fusion and fission would turn all matter in the universe into iron — the most stable element on the whole periodic table.
It’s an incredible, incomprehensible number: a 1 followed by 1,500 zeroes. The only problem is Dyson didn’t take proton decay into account. It turns out proton decay means “the whole rock will be gone before it turns into iron,” Adams said.
And there’s a big assumption underlying the entire timeline. “This projection assumes that we actually know what the laws of physics are and they don’t change much,” Adams said.
“We think we understand it at least well enough to do the projections,” he added, “But we would like experimental verification so we really know what we’re talking about.”
That validation may be around the corner. Experiments are already up and running to pin down the speed of proton decay, what dark matter and dark energy are (and how they may shape the universe’s fate), and to confirm the existence of Hawking radiation.
Adams stands by the five eras theory, even as he wants to iron out its wrinkles and patch its holes.
“Everything that I said is probably going to be true, but if we knew all the details we could fill in a richer story,” he said.
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