There may have been a second Big Bang, new research suggests

A Hubble Telescope image of the galaxy cluster Cl0024+1654, showing red pinpricks of stars on a blue field of dark matter
Dark matter, represented as blue light in this Hubble Telescope image of galaxy cluster Cl0024+1654, may have exploded into the universe one month after the Big Bang, new research suggests. (Image credit: European Space Agency, NASA and Jean-Paul Kneib (Observatoire Midi-Pyrénées, France/Caltech, USA))

The Big Bang may have been accompanied by a shadow, "Dark" Big Bang that flooded our cosmos with mysterious dark matter, cosmologists have proposed in a new study. And we may be able to see the evidence for that event by studying ripples in the fabric of space-time.

After the Big Bang, most cosmologists think, the universe underwent a period of rapid, remarkable expansion in its earliest moments, known as inflation. Nobody knows what triggered inflation, but it’s necessary to explain a variety of observations, like the extreme geometrical flatness of the universe at large scales.

Inflation was presumably driven by some exotic quantum field, which is a fundamental entity that soaks all of spacetime. At the end of inflation, that field decayed into a shower of particles and radiation, triggering the "Hot Big Bang" that physicists commonly associate with the beginning of the universe. Those particles would go on to coalesce into the first atoms when the cosmos was around 12 minutes old and — hundreds of millions of years later  — begin clumping into stars and galaxies.

But there's another ingredient to the cosmological mix: dark matter. Once again, cosmologists aren't sure what dark matter is, but they see the evidence for its existence through its gravitational influence on normal matter. 

In the simplest models, the end of inflation and the ensuing Hot Big Bang also flooded the universe with dark matter, which evolved along an independent track. But this assumption is made merely for the sake of simplicity, two cosmologists proposed in a paper appearing in February on the preprint database arXiv. Scientists see no evidence for the existence of dark matter until far later in the evolution of the universe, after the elusive substance had enough time to exert gravitational influence, so there's no need for it to have filled the universe in the Hot Big Bang alongside normal matter. Plus, because dark matter does not interact with normal matter, it might have had its own "Dark" Big Bang, the researchers claim.

The Dark Big Bang

In their paper the researchers explored what a Dark Big Bang would look like. First,  they hypothesized the existence of a new quantum field — a so-called "dark field," that is necessary to allow dark matter to form completely independently.

In this new scenario, the Dark Big Bang only gets underway after inflation fades away and the universe expands and cools enough to force the dark field into its own phase transition, where it transforms itself into dark matter particles.

The researchers found that the Dark Big Bang had to obey certain constraints; if too early, there would be too much dark matter today, and if too late, there would be too little. But if the Dark Big Bang happened when the universe was less than a month old, it could agree with all known observations.

Introducing a Dark Big Bang has several advantages. First, it's consistent with what scientists know about dark matter: if it doesn't interact with normal matter, then there's no reason for them to share a common origin. Second, it allows the researchers to create models of dark matter without having to worry about how they'll affect the behavior of normal matter at very early times, which gives scientists much more flexibility in creating models.

But most importantly, the researchers found that a Dark Big Bang produces a particular signature in gravitational waves, which are ripples in space-time that still slosh around the universe in the present day. That means the theory could one day be testable.

The researchers admit that current gravitational wave experiments do not have the sensitivity to find signatures of the Dark Big Bang. But another probe of gravitational waves using distances to far-flung pulsars, known as Pulsar Timing Arrays like the NANOGrav experiment, might just be able to do the trick.

Paul Sutter

Paul M. Sutter is a research professor in astrophysics at  SUNY Stony Brook University and the Flatiron Institute in New York City. He regularly appears on TV and podcasts, including  "Ask a Spaceman." He is the author of two books, "Your Place in the Universe" and "How to Die in Space," and is a regular contributor to, Live Science, and more. Paul received his PhD in Physics from the University of Illinois at Urbana-Champaign in 2011, and spent three years at the Paris Institute of Astrophysics, followed by a research fellowship in Trieste, Italy. 

  • LaraK
    There's an inconsistency in the beginning: it says that inflation both preceded and came after the big bang. I thought inflation came right after but then it says that there was inflation and then the field decayed and then there was the hot big bang. so which is it.
  • surewhynot
    dark energy filled the universe? isn’t dark energy the universe? Lol
  • HattinGokbori87
    Let's hope the Dark Matter theory will die a shameful death just like the Ether theory ASAP. It is starting to be used as an answer to everything just like how many biologist use the words "a remnant of evolution" whenever they don't know the function of an organ.
  • TallDave
    see Carr 2021, the PBH theory explains both the ratios of dark matter to baryonic and the observed LIGO distribution of black hole mergers via primordial acoustics

    no new particles required

    the potential for stable Planck-mass WIMPy MACHO primordial black hole remnants is particularly intriguing since they have exactly the right cosmic profile (non-interactive but having mass)
  • skynr13
    Possibly it wasn't just a second BB, but that the universe cooled enough for Dark Matter to exist. If other forms of matter and energy couldn't exist during and just after the BB, then Dark Matter will have to wait too!
  • skynr13
    LaraK said:
    There's an inconsistency in the beginning: it says that inflation both preceded and came after the big bang. I thought inflation came right after but then it says that there was inflation and then the field decayed and then there was the hot big bang. so which is it.
    A singularity came before the BB, then inflation, which could be the same as the BB.
  • Hartmann352
    I urge you to read the paper titled "Spectral Sirens: Cosmology from the Full Mass Distribution of Compact Binaries" by Jose Mar ́ıa Ezquiaga and Daniel E. Holz.

    A black hole is usually where information goes to disappear -- but scientists may have found a trick to use its last moments to tell us about the history of the universe. In a new study, two University of Chicago astrophysicists laid out a method for how to use pairs of colliding black holes to measure how fast our universe is expanding -- and thus understand how the universe evolved, what it is made out of, and where it's going. In particular, the scientists think the new technique, which they call a "spectral siren," may be able to tell us about the otherwise elusive "teenage" years of the universe.

    In their new paper, Holz and first author Jose María Ezquiaga suggest that they can use our newfound knowledge about the whole population of black holes as a calibration tool.

    For example, current evidence suggests that most of the detected black holes have between five and 40 times the mass of our sun. "So we measure the masses of the nearby black holes and understand their features, and then we look further away and see how much those further ones appear to have shifted," said Ezquiaga, a NASA Einstein Postdoctoral Fellow and Kavli Institute for Cosmological Physics Fellow working with Holz at UChicago. "And this gives you a measure of the expansion of the universe."

    The authors dub it the "spectral siren" method, a new approach to the 'standard siren' method which Holz and collaborators have been pioneering. (The name is a reference to the 'standard candle' methods also used in astronomy.)

    The scientists are excited because in the future, as LIGO's capabilities expand, the method may provide a unique window into the "teenage" years of the universe -- about 10 billion years ago -- that are hard to study with other methods.

    Researchers can use the cosmic microwave background to look at the very earliest moments of the universe, and they can look around at galaxies near our own galaxy to study the universe's more recent history. But the in-between period is harder to reach, and it's an area of special scientific interest.

    "It's around that time that we switched from dark matter being the predominant force in the universe to dark energy taking over, and we are very interested in studying this critical transition," said Ezquiaga.

    The other advantage of this method, the authors said, is that there are fewer uncertainties created by gaps in our scientific knowledge. "By using the entire population of black holes, the method can calibrate itself, directly identifying and correcting for errors," Holz said. The other methods used to calculate the Hubble constant rely on our current understanding of the physics of stars and galaxies, which involves a lot of complicated physics and astrophysics. This means the measurements might be thrown off quite a bit if there's something we don't yet know.

    By contrast, this new black hole method relies almost purely on Einstein's theory of gravity, which is well-studied and has stood up against every way scientists have tried to test it so far.

    The more readings they have from all black holes, the more accurate this calibration will be. "We need preferably thousands of these signals, which we should have in a few years, and even more in the next decade or two," said Holz. "At that point it would be an incredibly powerful method to learn about the universe."