All Dark Matter in the Universe Could Be Primordial Black Holes – Formed From the Collapse of Baby Universes Soon After the Big Bang

Baby Universes

Baby universes branching off of our universe shortly after the Big Bang appear to us as black holes. Credit: Kavli IPMU

The Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) is home to many interdisciplinary projects which benefit from the synergy of a wide range of expertise available at the institute. One such project is the study of black holes that could have formed in the early universe, before stars and galaxies were born.  

Such primordial black holes (PBHs) could account for all or part of dark matter, be responsible for some of the observed gravitational waves signals, and seed supermassive black holes found in the center of our Galaxy and other galaxies. They could also play a role in the synthesis of heavy elements when they collide with neutron stars and destroy them, releasing neutron-rich material.

In particular, there is an exciting possibility that the mysterious dark matter, which accounts for most of the matter in the universe, is composed of primordial black holes. The 2020 Nobel Prize in physics was awarded to a theorist, Roger Penrose, and two astronomers, Reinhard Genzel and Andrea Ghez, for their discoveries that confirmed the existence of black holes. Since black holes are known to exist in nature, they make a very appealing candidate for dark matter. 

The recent progress in fundamental theory, astrophysics, and astronomical observations in search of PBHs has been made by an international team of particle physicists, cosmologists and astronomers, including Kavli IPMU members Alexander Kusenko, Misao Sasaki, Sunao Sugiyama, Masahiro Takada and Volodymyr Takhistov.

To learn more about primordial black holes, the research team looked at the early universe for clues. The early universe was so dense that any positive density fluctuation of more than 50 percent would create a black hole. However, cosmological perturbations that seeded galaxies are known to be much smaller. Nevertheless, a number of processes in the early universe could have created the right conditions for the black holes to form.

Hyper Suprime-Cam (HSC) is a gigantic digital camera on the Subaru Telescope. Credit: HSC project / NAOJ

One exciting possibility is that primordial black holes could form from the “baby universes” created during inflation, a period of rapid expansion that is believed to be responsible for seeding the structures we observe today, such as galaxies and clusters of galaxies. During inflation, baby universes can branch off of our universe. A small baby (or “daughter”) universe would eventually collapse, but the large amount of energy released in the small volume causes a black hole to form.  

An even more peculiar fate awaits a bigger baby universe. If it is bigger than some critical size, Einstein’s theory of gravity allows the baby universe to exist in a state that appears different to an observer on the inside and the outside. An internal observer sees it as an expanding universe, while an outside observer (such as us) sees it as a black hole. In either case, the big and the small baby universes are seen by us as primordial black holes, which conceal the underlying structure of multiple universes behind their “event horizons.” The event horizon is a boundary below which everything, even light, is trapped and cannot escape the black hole.

A star in the Andromeda galaxy temporarily becomes brighter if a primordial black hole passes in front of the star, focusing its light in accordance with the theory of gravity. Credit: Kavli IPMU/HSC Collaboration

In their paper, the team described a novel scenario for PBH formation and showed that the black holes from the “multiverse” scenario can be found using the Hyper Suprime-Cam (HSC) of the 8.2m Subaru Telescope, a gigantic digital camera — the management of which Kavli IPMU has played a crucial role — near the 4,200 meter summit of Mt. Mauna Kea in Hawaii. Their work is an exciting extension of the HSC search of PBH that Masahiro Takada, a Principal Investigator at the Kavli IPMU, and his team are pursuing. The HSC team has recently reported leading constraints on the existence of PBHs in Niikura, Takada et. al. Nature Astronomy 3, 524–534 (2019)

Why was the HSC indispensable in this research? The HSC has a unique capability to image the entire Andromeda galaxy every few minutes. If a black hole passes through the line of sight to one of the stars, the black hole’s gravity bends the light rays and makes the star appear brighter than before for a short period of time. The duration of the star’s brightening tells the astronomers the mass of the black hole. With HSC observations, one can simultaneously observe one hundred million stars, casting a wide net for primordial black holes that may be crossing one of the lines of sight.  

The first HSC observations have already reported a very intriguing candidate event consistent with a PBH from the “multiverse,” with a black hole mass comparable to the mass of the Moon. Encouraged by this first sign, and guided by the new theoretical understanding, the team is conducting a new round of observations to extend the search and to provide a definitive test of whether PBHs from the multiverse scenario can account for all dark matter.  

Reference: “Exploring Primordial Black Holes from the Multiverse with Optical Telescopes” by Alexander Kusenko, Misao Sasaki, Sunao Sugiyama, Masahiro Takada, Volodymyr Takhistov and Edoardo Vitagliano, 30 October 2020, Physical Review Letters.
DOI: 10.1103/PhysRevLett.125.181304


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  • If there are trillions and trillions of them out there, they could easily contain the dark matter we suspect exists. Using the Andromeda Galaxy and gravitational lensing to spot them is a brilliant idea.

    • I'm not sure that using gravitational lensing to hunt for primordial black holes is new. But the main advance of the paper is to show that they can rapidly test their proposal that way.

  • The writer says that a "bigger" baby universe is seen by an internal observer as an expanding universe, but from the outside as a black hole. So...does that mean that our universe, which we see as expanding, could also be a black hole in another universe?

    • We could have an infinite 'onion' of a black hole inside a baby universe inside a black hole.... This is mind boggling.

    • Good old question!

      The response you get if you study the question is that black holes have an outside, while the universe in its entirety hasn't [ ].

      "People sometimes ask, "Is the universe a black hole?" Or worse, they claim: "The universe is a black hole!" No, it's not, and it's worth getting this one straight."

      "But a black hole is not "a place where a lot of mass has been squeezed inside its own Schwarzschild radius." It is, as Wikipedia is happy to tell you, "a region of space from which nothing, including light, can escape." The implication being that there is a region outside the black hole from which things could at least imagine escaping to. For the universe, there is no such outside region. So at a pretty trivial level, the universe is not a black hole.

      You might say that this is picking nits, and the existence of an outside region is beside the point if the inside of our universe resembles a black hole. That's fine, except: it doesn't. You may have noticed that the universe is actually expanding, rather than contracting as you might expect the interior of a black hole to be."

      The false vacuum bubbles proposed in the paper have a so called domain wall boundary which is different from black holes. "They undergo rapid expansion until the energy density inside the bubble exceeds the energy density in the exterior, which happens at some point before the end of inflation at time t_i . After that, the bubble contracts and collapses to a black hole." So at the time they look like black holes they would no longer look like a universe for inside observers I think - they would be spaghettified and squashed [technical terms].

      The paper do discuss wormhole connections as support for how the dynamics work. Those connections would be impossible in our flat space. But I'm not sure how that changes the "[doesn't] look like a universe" aspect.

  • Interesting, though I'd like to know more detail on the physics of the internal versus external state of a "universe-containing" black hole.

    Also an obvious question: what observable effect does matter falling into such a black hole have which an observer inside could detect, and is it one we could look for to see if we're inside one? (I wouldn't be surprised if it just ends up as part of the Big Bang though.)

    • Good points! See my response to D. Hughs for some of that (which comes out as that they likely are waxing a tad poetic with what they find in their paper).

    • It sounds like You are saying “We are the Centre of the Universe “ , could there have been other Big Bangs and Black Holes ?

    • Also, the Big Bang as a singularity or similar is cosmology 40 years out of date. See :

      "Among most people who study the early Universe, inflation is accepted as the new consensus theory. We might not know everything there is to know about inflation, but either it — or something so similar to it that we don't have an observation to tell them apart — must have happened.

      With all that said, what does that mean for our cosmic origins? From a timeline perspective, what comes first: the Big Bang or inflation?"

      " An inflating Universe doesn't begin in a singularity like a matter-dominated or radiation-dominated Universe does. All we can state with certainty is that the state we call the hot Big Bang only came about after the end of inflation. It says nothing about inflation's origins."

      "There are a lot of people who mean "the initial singularity" when they say "the Big Bang," and to those people, I say it's long past due for you to get with the times. The hot Big Bang cannot be extrapolated back to a singularity, but only to the end of an inflationary state that preceded it. We cannot state with any confidence, because there are no signatures of it even in principle, what preceded the very end-stages of inflation. Was there a singularity? Maybe, but even if so, it doesn't have anything to do with the Big Bang.

      Inflation came first, and its end heralded the arrival of the Big Bang. There are still those who disagree, but they're now nearly a full 40 years out of date."

  • The big picture is this, in a nutshell. We, are in a black hole. Everything that we are looking at, is outside the black hole. That is why there are so many strange things like the expansion of the universe, quantum entanglement, everything is because of our perspective. Looking from the inside out if a black hole.

    • They are different solutions to general relativity.

      Black holes are straightforward (well) results of collapse when a sufficiently massive star runs out of fuel and its fusion core radiation pressure vane. We have images of black hole shadows, and their discovery gave the 2020 Nobel Prize in Physics.

      Wormholes are putative, extradimensional solutions which needs a lot of exotic conditions and, IMO, breaks the simple 3D space that recent cosmology has observed we live in.

  • Spyroe theory claims that all energy in the universe can be understood by measuring it as if it were winding and unwinding based on a common shape, the shape that would define all humans. Organizing vortices on the xyz axis. View the shape you will agree that it can solve paradoxical questions. Spyroe theory suggests we live in one of the six sections which limits how much of the universe we can observe. Half of the universe is winding in and half is winding out. There is a centre. Two of the three axis combine at the centre to change energy direction with no loss.

    • Pseudoscience mumbo jumbo - and what is stated without evidence can be dismissed without evidence.

      • It is true that you do need evidence, math and experimental data but who will perform such a task? The scientific establishment? Not a chance. They work for their sponsors. The problem is the scientific establishment is the only ones who have the credibility and knowledge to verify a radical new idea. So we as humans are stuck waiting for a small group of people to decide what we all should believe is real. Not fair. What about the people who are possibly gifted and have a great way of describing our surroundings. They get ignored or criticized for giving suggestions. Remember particles and forces only exist because we choose to use and believe in them, not because they are there otherwise.

        • Science provides evidence. And scientists are the experts - there is no 'gift' in that but hard work. Facts can be accepted or not, but we can't 'believe' in them - you can have your own opinion ("belief") but not your own facts. And of course facts are robust - the universe has been out there for 14 billion years - claiming else is just more pseudoscience.

          You have as little evidence for your conspiracy theory as you have for your pseudoscience.

          • Careful when you use the word “fact”. What is fact? Remember we are talking about theories. Theories are used to understand something that is a mystery to us. Everything we know and believe in of science can all change with one new idea. Particle and forces are used by humans to describe the universe but are they real? A fact? Of course NOT. We use experiments to ask the universe a question based on our theories. The universe responds, reveals itself with particles, “look it’s an electron”. But you know the electron is as much of a representation of the universe as it is a representation of ourselves. What we observe has a lot to do with what we believe in. You talk about pseudoscience, but you don’t mention that theoretical physics is based on observation proof not just math, but what about string theory. Humans can not see strings yet string theory is the leading approach to quantum gravity. Is that fair? The outsider cannot say a thing without proof but the insides can follow a personal believe without proof? Not fair. The biggest fear of the insiders is an outsider coming along with an idea that proves everything they know to be useless. This is why they ignore all ideas from the outsiders. Actually even if you are an insider you cannot go off and start a new idea on your own. There are rules. The insiders follow direction from their supervisors. Don’t believe me? Go to a lecture and try to talk to a scientist about your new idea. See what happens don’t be surprised if they walk away from you immediately. Not because you are wasting their time, because they need to make advancements completely by their own results. Last thing they want to do is mistakenly prove your idea correct.

          • I laugh at the evolutionist/creationist arguments, as if either side can actually KNOW the truth.

            As a student (once a student, always a student) of cognitive psychology, "religion"/"philosophy", and metaphysics, it is clear to me that we simply can not "know" (are incapable of knowing) "the truth". The Bible says it, the older Vedic texts say it, the Buddhists say it, the Taoists say it, AND the modern scientists say it. One will ALWAYS be a student of these ultimately unknowable subjects...

            The Cognitive Science of the Embodied Mind, though the work of linguistics and other sub-branches, makes it clear that all that we CAN know, comprehend, understand, imagine, is metaphorical, and those metaphors are based on less than a dozen or so basic concepts: in-out, up-down, left-right, front-back, etc. (I forget the rest at the moment). Those basic concepts combine to produce higher and higher (more complex) levels of metaphors that give rise to all other concepts/ideas/words that our awareness/consciousness produces.

            Furthermore, it is =impossible= to =know= if there is more to "reality" than we can imagine or perceive. MAYBE we can account for all of existence using our embodied mind, but MAYBE not.

            Mathematics is a human invention. MAYBE it describes the universe completely (and as such is the "language of 'GOD'" as the Gnostics say), MAYBE not; but ===there is no way for us to know===. However, all "good thinkers" can realize that math is NOT a "perfect" representation of reality. Math is linear, where the reality we "experience" is circular/spiral/curved. Find a strait line in the universe: I challenge you. Not even light travels in a "perfectly" strait line. Now try to describe a curve mathematically: you can't "exactly". Those pesky π (pi), ϕ (phi), ∞ (infinity) numbers (to name but a few) keep getting in the way. Math "works" for us because the level of "precision" is "good enough" for our level of "perception".

            How about a simple photon: is it a wave or particle? Is "electricity" in a wire a wave of energy or a stream of electrons? We rely on our "math" to answer questions about processes we can not ===directly perceive===, trying to fit a round peg into the square holes of perception of the conscious awareness of our embodied mind. Yet the math leaves us with an ambiguous answer to these very simple basic questions about "reality"; and then we "kick the can" down the hall, mathematically, further trying to understand, in terms of our embodied mind's metaphors, what it means to be BOTH a wave and particle. But no thought is given, mathematically, to the concept that we can not actually CONCEIVE the reality of what a photon IS or what electricity IS; because mathematics IS an embodied concept.

            The Tao that can be spoken of is not the Tao.
            Simple as that.

            "Women, Fire, and Dangerous Things: What Categories Reveal About The Mind" - George Lakoff - 1987 - University Of Chicago Press

            "Metaphors We Live By" - George Lakoff & Mark Johnson

            "Where Mathematics Comes From" - George Lakoff & Rafael E. Núñez

          • Forever a student. Talking about spirals? That’s how this conversation started.

            Spyroe theory is a concept that uses organized spirals.
            Look it up. It’s the common shape of nature. It’s the human logo.

          • Pseudoscience is still pseudoscience hwoevre dressed in postrmodern philosophy and religious superstition - or conspiracy theory.

            Science is really simple, it is the only known method to arrive at knowledge. It uses math as a tool - but famously isn't founded on it, c.f. how quantum physics cannot be axiomatized but needs observation to establish useful parameters at every scale [ ] - as well as observed, robust facts and theories predicting facts. Theories builds on observation and predict them, like images they comprise "a thousand facts" and are best seen as superfacts as soon as they are well tested and robust as other facts.

            [After bioinformatics study, I maintain that anyone can go to free genome databases such as NCBI and test evolution by aligning and treeing a protein gene, on their own in 30 minutes after doing the tutorials, and that it is just laziness to demand further tests before looking for yourself that evolution is an observable fact. It is "a killer app".]

            String theory has pretty much been rejected by the Large Hadron Collider failing to see its natural supersymmetric dark matter candidate. "Because supersymmetric extensions of the Standard Model of particle physics readily predict a new particle with these properties, this apparent coincidence is known as the "WIMP miracle", and a stable supersymmetric partner has long been a prime WIMP candidate.[1] However, recent null results from direct-detection experiments along with the failure to produce evidence of supersymmetry in the Large Hadron Collider (LHC) experiment[2][3] has cast doubt on the simplest WIMP hypothesis." ["Weakly interacting massive particles" @ Wikpedia] There is also the related problems that string theory needs anti-de Sitter space or a "lift" to de Sitter space - but space looks flat and string theory in de Sitter space looks unphysical [cd. "Dark Energy May Be Incompatible With String Theory" @ Quanta Magazine], and that ultimately it clashes with observed inflation ["The zoo plot meets the swampland: mutual (in)consistency of single-field inflation, string conjectures, and cosmological data" @ arxiv].

            No, scientists don't walk away from useful ideas, it's because you are wasting their time of course. "The Dunning–Kruger effect is a cognitive bias in which people with low ability at a task overestimate their ability. It is related to the cognitive bias of illusory superiority and comes from people's inability to recognize their lack of ability. Without the self-awareness of metacognition, people cannot objectively evaluate their level of competence." ["Dunning–Kruger effect" @ Wikipedia] That's why the test of the competence of ideas is not to harass scientists, but to peer review publish (which on the other hand is a topic one may well ask for help in).

          • Not true. Physicists walk away from you if you are talking about your ideas because they don not want to one glossy manny years later think they came up with it. No different than film producers do not to take someone’s script and read it without a release. Trust me on that. I used to think like you. I thought the scientific establishment was working for everyone, discovering “what the universe is” but not true at all. They work for their sponsors to make useful technology. What they say is the universe is only one version of the universe. The universe is a mystery! No way we will ever know “what it is”. We can only describe it the way we are able to describe it. Sure particle and forces can describe the mysterious field but it isn’t what it is. Spyroe theory hasn't been fully developed but it is based on Rene Descartes idea of a vortex universe. Here it is. Imagine the whole volume of the universe being winding and unwinding vortices. When you move matter it is unwinding from where it is and winding up the volume of space it enters. It’s that simple. Type spyroe theory up on google you will see the shape that represents one quantum of energy. The concept can explain the paradoxes like entanglement and double slit. The shape has been used for a design of a spherical propeller. The propeller uses hundreds of magnets in a specific order within the propeller blades which are identical to the shape of DNA. When in motion the magnetic field matches the planetary movements- Thus the shape of the magnetic field produced follows the shape of the natural magnetic field of the universe. And FYI I know this concept is just art until it is tested. And FYI I have studied theoretical physics for 30 years and have to say that the only way man can move on into a new paradigm is to discard all we know and start over. Modern physics is useless without a different concept of time.

  • Thank you, D. Hughes for pointing out what was obvious to an amateur like me. If a peer reviewed, published article actually discussed "baby universes," I'd enjoy reading it. I wouldn't necessarily pay to read it.

    I am beginning to imagine, however, that our perception of the origins and composition of the universe, past and present, could very well require the idea of multiple universes.

    That's because our idea of the "universe" is a mythological construct. Space and time are ever changing. Who the heck knows what happens from time to time in various places beyond the typically reliable observations obtained from the perspective of our own little ant hill?

    • Our observations covers 14 billion years of time and a 100 billion lightyear diameter volume, and presumably an observer on Andromeda would say much the same and so on.

      I don't see the need to insert uncertainty after the last few decades have replaced earlier uncertain cosmology (where cosmic and star ages differed with a factor 2) with precision cosmology at 1 % uncertainty and decreasing.

      We know this, There is a lot we don't know, but e.g. that space is 3D flat is unlikely to go away.

  • A beautiful , reasonable teoric view, to probe that we need to visit one of them,(black hole)unfortunate is not back tickets.

Kavli Institute for the Physics and Mathematics of the Universe

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