There are 5 eras in the universe's lifecycle. Right now, we're in the second era.

Astronomers find these five chapters to be a handy way of conceiving the universe's incredibly long lifespan.

Image based on logarithmic maps of the Universe put together by Princeton University researchers, and images produced by NASA based on observations made by their telescopes and roving spacecraft

Image source: Pablo Carlos Budassi
  • We're in the middle, or thereabouts, of the universe's Stelliferous era.
  • If you think there's a lot going on out there now, the first era's drama makes things these days look pretty calm.
  • Scientists attempt to understand the past and present by bringing together the last couple of centuries' major schools of thought.

    If you're fortunate enough to get yourself beneath a clear sky in a dark place on a moonless night, a gorgeous space-scape of stars waits. If you have binoculars and point them upward, you're treated to a mind-bogglingly dense backdrop of countless specks of light absolutely everywhere, stacked atop each other, burrowing outward and backward through space and time. Such is the universe of the cosmological era in which we live. It's called the Stelliferous era, and there are four others.

    The 5 eras of the universe

    There are many ways to consider and discuss the past, present, and future of the universe, but one in particular has caught the fancy of many astronomers. First published in 1999 in their book The Five Ages of the Universe: Inside the Physics of Eternity, Fred Adams and Gregory Laughlin divided the universe's life story into five eras:

    • Primordial era
    • Stellferous era
    • Degenerate era
    • Black Hole Era
    • Dark era

    The book was last updated according to current scientific understandings in 2013.

    It's worth noting that not everyone is a subscriber to the book's structure. Popular astrophysics writer Ethan C. Siegel, for example, published an article on Medium last June called "We Have Already Entered The Sixth And Final Era Of Our Universe." Nonetheless, many astronomers find the quintet a useful way of discuss such an extraordinarily vast amount of time.

    The Primordial era

    Image source: Sagittarius Production/Shutterstock

    This is where the universe begins, though what came before it and where it came from are certainly still up for discussion. It begins at the Big Bang about 13.8 billion years ago.

    For the first little, and we mean very little, bit of time, spacetime and the laws of physics are thought not yet to have existed. That weird, unknowable interval is the Planck Epoch that lasted for 10-44 seconds, or 10 million of a trillion of a trillion of a trillionth of a second. Much of what we currently believe about the Planck Epoch eras is theoretical, based largely on a hybrid of general-relativity and quantum theories called quantum gravity. And it's all subject to revision.

    That having been said, within a second after the Big Bang finished Big Banging, inflation began, a sudden ballooning of the universe into 100 trillion trillion times its original size.

    Within minutes, the plasma began cooling, and subatomic particles began to form and stick together. In the 20 minutes after the Big Bang, atoms started forming in the super-hot, fusion-fired universe. Cooling proceeded apace, leaving us with a universe containing mostly 75% hydrogen and 25% helium, similar to that we see in the Sun today. Electrons gobbled up photons, leaving the universe opaque.

    About 380,000 years after the Big Bang, the universe had cooled enough that the first stable atoms capable of surviving began forming. With electrons thus occupied in atoms, photons were released as the background glow that astronomers detect today as cosmic background radiation.

    Inflation is believed to have happened due to the remarkable overall consistency astronomers measure in cosmic background radiation. Astronomer Phil Plait suggests that inflation was like pulling on a bedsheet, suddenly pulling the universe's energy smooth. The smaller irregularities that survived eventually enlarged, pooling in denser areas of energy that served as seeds for star formation—their gravity pulled in dark matter and matter that eventually coalesced into the first stars.

    The Stelliferous era

    Image source: Casey Horner/unsplash

    The era we know, the age of stars, in which most matter existing in the universe takes the form of stars and galaxies during this active period.

    A star is formed when a gas pocket becomes denser and denser until it, and matter nearby, collapse in on itself, producing enough heat to trigger nuclear fusion in its core, the source of most of the universe's energy now. The first stars were immense, eventually exploding as supernovas, forming many more, smaller stars. These coalesced, thanks to gravity, into galaxies.

    One axiom of the Stelliferous era is that the bigger the star, the more quickly it burns through its energy, and then dies, typically in just a couple of million years. Smaller stars that consume energy more slowly stay active longer. In any event, stars — and galaxies — are coming and going all the time in this era, burning out and colliding.

    Scientists predict that our Milky Way galaxy, for example, will crash into and combine with the neighboring Andromeda galaxy in about 4 billion years to form a new one astronomers are calling the Milkomeda galaxy.

    Our solar system may actually survive that merger, amazingly, but don't get too complacent. About a billion years later, the Sun will start running out of hydrogen and begin enlarging into its red giant phase, eventually subsuming Earth and its companions, before shrining down to a white dwarf star.

    The Degenerate era

    Image source: Diego Barucco/Shutterstock/Big Think

    Next up is the Degenerate era, which will begin about 1 quintillion years after the Big Bang, and last until 1 duodecillion after it. This is the period during which the remains of stars we see today will dominate the universe. Were we to look up — we'll assuredly be outta here long before then — we'd see a much darker sky with just a handful of dim pinpoints of light remaining: white dwarfs, brown dwarfs, and neutron stars. These"degenerate stars" are much cooler and less light-emitting than what we see up there now. Occasionally, star corpses will pair off into orbital death spirals that result in a brief flash of energy as they collide, and their combined mass may become low-wattage stars that will last for a little while in cosmic-timescale terms. But mostly the skies will be be bereft of light in the visible spectrum.

    During this era, small brown dwarfs will wind up holding most of the available hydrogen, and black holes will grow and grow and grow, fed on stellar remains. With so little hydrogen around for the formation of new stars, the universe will grow duller and duller, colder and colder.

    And then the protons, having been around since the beginning of the universe will start dying off, dissolving matter, leaving behind a universe of subatomic particles, unclaimed radiation…and black holes.

    The Black Hole era

    Image source: Vadim Sadovski/Shutterstock/Big Think

    For a considerable length of time, black holes will dominate the universe, pulling in what mass and energy still remain.

    Eventually, though, black holes evaporate, albeit super-slowly, leaking small bits of their contents as they do. Plait estimates that a small black hole 50 times the mass of the sun would take about 1068 years to dissipate. A massive one? A 1 followed by 92 zeros.

    When a black hole finally drips to its last drop, a small pop of light occurs letting out some of the only remaining energy in the universe. At that point, at 1092, the universe will be pretty much history, containing only low-energy, very weak subatomic particles and photons.

    The Dark Era

    Image source: Big Think

    We can sum this up pretty easily. Lights out. Forever.

    Tonight, if it's clear, maybe you want to step outside, take a nice deep breath, and look up, grateful that we are where we are, and when we are, in spite of all the day's hardships. We've got a serious amount of temporal elbow room here, far more than we need, so not to worry, and those stars aren't going anywhere for a long, long time.

    Yug, age 7, and Alia, age 10, both entered Let Grow's "Independence Challenge" essay contest.

    Photos: Courtesy of Let Grow
    Sponsored by Charles Koch Foundation
    • The coronavirus pandemic may have a silver lining: It shows how insanely resourceful kids really are.
    • Let Grow, a non-profit promoting independence as a critical part of childhood, ran an "Independence Challenge" essay contest for kids. Here are a few of the amazing essays that came in.
    • Download Let Grow's free Independence Kit with ideas for kids.
    Keep reading Show less

    Divers discover world's largest underwater cave system filled with Mayan mysteries

    Researchers in Mexico discover the longest underwater cave system in the world that's full of invaluable artifacts. 

    Divers of the GAM project. Credit: Herbert Meyrl.
    Technology & Innovation

    Keep reading Show less

    The surprise reason sleep-deprivation kills lies in the gut

    New research establishes an unexpected connection.

    Reactive oxygen species (ROS) accumulate in the gut of sleep-deprived fruit flies, one (left), seven (center) and ten (right) days without sleep.

    Image source: Vaccaro et al, 2020/Harvard Medical School
    Surprising Science
    • A study provides further confirmation that a prolonged lack of sleep can result in early mortality.
    • Surprisingly, the direct cause seems to be a buildup of Reactive Oxygen Species in the gut produced by sleeplessness.
    • When the buildup is neutralized, a normal lifespan is restored.

    We don't have to tell you what it feels like when you don't get enough sleep. A night or two of that can be miserable; long-term sleeplessness is out-and-out debilitating. Though we know from personal experience that we need sleep — our cognitive, metabolic, cardiovascular, and immune functioning depend on it — a lack of it does more than just make you feel like you want to die. It can actually kill you, according to study of rats published in 1989. But why?

    A new study answers that question, and in an unexpected way. It appears that the sleeplessness/death connection has nothing to do with the brain or nervous system as many have assumed — it happens in your gut. Equally amazing, the study's authors were able to reverse the ill effects with antioxidants.

    The study, from researchers at Harvard Medical School (HMS), is published in the journal Cell.

    An unexpected culprit

    The new research examines the mechanisms at play in sleep-deprived fruit flies and in mice — long-term sleep-deprivation experiments with humans are considered ethically iffy.

    What the scientists found is that death from sleep deprivation is always preceded by a buildup of Reactive Oxygen Species (ROS) in the gut. These are not, as their name implies, living organisms. ROS are reactive molecules that are part of the immune system's response to invading microbes, and recent research suggests they're paradoxically key players in normal cell signal transduction and cell cycling as well. However, having an excess of ROS leads to oxidative stress, which is linked to "macromolecular damage and is implicated in various disease states such as atherosclerosis, diabetes, cancer, neurodegeneration, and aging." To prevent this, cellular defenses typically maintain a balance between ROS production and removal.

    "We took an unbiased approach and searched throughout the body for indicators of damage from sleep deprivation," says senior study author Dragana Rogulja, admitting, "We were surprised to find it was the gut that plays a key role in causing death." The accumulation occurred in both sleep-deprived fruit flies and mice.

    "Even more surprising," Rogulja recalls, "we found that premature death could be prevented. Each morning, we would all gather around to look at the flies, with disbelief to be honest. What we saw is that every time we could neutralize ROS in the gut, we could rescue the flies." Fruit flies given any of 11 antioxidant compounds — including melatonin, lipoic acid and NAD — that neutralize ROS buildups remained active and lived a normal length of time in spite of sleep deprivation. (The researchers note that these antioxidants did not extend the lifespans of non-sleep deprived control subjects.)

    fly with thought bubble that says "What? I'm awake!"

    Image source: Tomasz Klejdysz/Shutterstock/Big Think

    The experiments

    The study's tests were managed by co-first authors Alexandra Vaccaro and Yosef Kaplan Dor, both research fellows at HMS.

    You may wonder how you compel a fruit fly to sleep, or for that matter, how you keep one awake. The researchers ascertained that fruit flies doze off in response to being shaken, and thus were the control subjects induced to snooze in their individual, warmed tubes. Each subject occupied its own 29 °C (84F) tube.

    For their sleepless cohort, fruit flies were genetically manipulated to express a heat-sensitive protein in specific neurons. These neurons are known to suppress sleep, and did so — the fruit flies' activity levels, or lack thereof, were tracked using infrared beams.

    Starting at Day 10 of sleep deprivation, fruit flies began dying, with all of them dead by Day 20. Control flies lived up to 40 days.

    The scientists sought out markers that would indicate cell damage in their sleepless subjects. They saw no difference in brain tissue and elsewhere between the well-rested and sleep-deprived fruit flies, with the exception of one fruit fly.

    However, in the guts of sleep-deprived fruit flies was a massive accumulation of ROS, which peaked around Day 10. Says Vaccaro, "We found that sleep-deprived flies were dying at the same pace, every time, and when we looked at markers of cell damage and death, the one tissue that really stood out was the gut." She adds, "I remember when we did the first experiment, you could immediately tell under the microscope that there was a striking difference. That almost never happens in lab research."

    The experiments were repeated with mice who were gently kept awake for five days. Again, ROS built up over time in their small and large intestines but nowhere else.

    As noted above, the administering of antioxidants alleviated the effect of the ROS buildup. In addition, flies that were modified to overproduce gut antioxidant enzymes were found to be immune to the damaging effects of sleep deprivation.

    The research leaves some important questions unanswered. Says Kaplan Dor, "We still don't know why sleep loss causes ROS accumulation in the gut, and why this is lethal." He hypothesizes, "Sleep deprivation could directly affect the gut, but the trigger may also originate in the brain. Similarly, death could be due to damage in the gut or because high levels of ROS have systemic effects, or some combination of these."

    The HMS researchers are now investigating the chemical pathways by which sleep-deprivation triggers the ROS buildup, and the means by which the ROS wreak cell havoc.

    "We need to understand the biology of how sleep deprivation damages the body so that we can find ways to prevent this harm," says Rogulja.

    Referring to the value of this study to humans, she notes,"So many of us are chronically sleep deprived. Even if we know staying up late every night is bad, we still do it. We believe we've identified a central issue that, when eliminated, allows for survival without sleep, at least in fruit flies."

    Withdrawal symptoms from antidepressants can last over a year, new study finds

    We must rethink the "chemical imbalance" theory of mental health.

    Bottles of antidepressant pills named (L-R) Wellbutrin, Paxil, Fluoxetine and Lexapro are shown March 23, 2004 photographed in Miami, Florida.

    Photo Illustration by Joe Raedle/Getty Images
    Surprising Science
    • A new review found that withdrawal symptoms from antidepressants and antipsychotics can last for over a year.
    • Side effects from SSRIs, SNRIs, and antipsychotics last longer than benzodiazepines like Valium or Prozac.
    • The global antidepressant market is expected to reach $28.6 billion this year.
    Keep reading Show less
    Scroll down to load more…