The Cosmos


A Tour of the Multiverse

Once upon a time—roughly 13.7 billion years ago, to be more precise—our universe was created in the Big Bang. From a virulent exploding fireball bursting with elementary particles, the universe evolved into the pitch-black expanse we currently observe, majestically sprinkled with star-studded galaxies. But is this really the full story? Today, cosmologists are learning that the incredible tale of our universe might be just one slim chapter in a much bigger volume: a book of universes that is infinitely large—and that is still being written.

In this video, I’ll explain why scientists think that our universe may be just one of many. I invite you to watch the pencast, then read on!

Our entire observable universe is very large, having a diameter of roughly 40 billion light years, and encompassing hundreds of billions of galaxies, each of which may contain billions of stars. Yet in the version of cosmology that I study, called eternal inflation, this is just a small fraction of an infinitely large universe which itself is only one out of an infinite number of other universes! Each of these “other” universes is the product of its own “local” big bang. Instead of being the ultimate creation event, our Big Bang merely marks the emergence of our local universe into the far grander “multiverse,” like a lone bubble materializing in an infinite flute of fizzing champagne. Each bubble represents an infinite universe, and our cosmic champagne flute is home to an infinite number of bubbles!


Bubbles within bubbles: The multiverse of eternal inflation.

So where do all the bubbles come from? Why couldn’t we just have one universe? Cosmologists believe that our universe experienced a period of very rapid expansion, called inflation, in the moments after the Big Bang, and they have confirmed this with a great deal of observational and theoretical evidence. It turns out that if the universe ever underwent an inflationary stage, then, even if inflation ends in one place, elsewhere inflation will continue. Once inflation starts, it never ends! The result is a mind-boggling proliferation of universes.

But there is more than one way to make a multiverse. The multiverse also emerges from string theory, which suggests that we actually live in 10 or 11 dimensions, not the mundane four (three spatial dimensions plus time) that we’re used to! That’s seems like a stretch, but since string theory is our best candidate for getting gravity and quantum mechanics to agree with each other, we need to take the idea of extra dimensions seriously. Since we only experience four dimensions, we must ask: where did all the extra dimensions go? This is where an idea called “compactification” comes in. Physicists have been able to show that if we start with a higher dimensional world, some of the extra dimensions can be “compactified” so that we don’t “experience” them directly. However, different compactifications describe lower dimensional universes with different physical properties, so we can experience them indirectly!

It turns out that there is a huge number of different ways to compactify these extra dimensions—googols of ways, in fact! All these different options offer a huge menu of different types of possible universes.

Take eternal inflation and add it to string theory, and you have not just an enormous number of possible universes, but a mechanism for creating them. Eternal inflation sees to it that the multiverse actually gets populated by each option on the menu via an ongoing process of nested bubble nucleations.

Tell us what you think on Twitter, Facebook, or email.

Delia Schwartz-Perlov

    Delia Schwartz-Perlov is a Postdoctoral Fellow at the Tufts Institute for Cosmology. She studies cosmology, quantum field theory and general relativity, and has a special interest in the study of inflation, the multiverse and the string theory landscape. When she is not pondering the mysteries of the multiverse, she studies piano, yoga, and art.

    • Noah Perlov

      It’s brilliant!

    • Brandon Bowers

      Nicely Said, easily understandable and enjoyable. Thank you for shedding some light onto the subject.

    • Dynodeke96

      Theoretical physics for idiots, excellent!

    • By definition, we only have access to our universe (if we know about it, we consider it to be in our universe). Since we can never have information about other universes, then, by definition, we can never measure anything regarding other universes. If we never measure the presence of another universe, then how is postulating the presence of other universes anything like science?

      Science is about making hypothesis that, at least in principle, can be tested, right? Putting forth a hypothesis that cannot be tested, even in principle, seems closer to theology. Are we counting the angels dancing on the head of a pin?

      I would really like to hear the answer to this, Delia. I can’t ask Hawking, I can’t ask Suskind, and I can’t ask Randall, so I’m asking you.

      • Dperlov

        There are various ways in which one can create a multiverse. I’ll try to answer your question by only focusing on the theory of eternal inflation.
        Scientists didn’t sit down one day and simply postulate the existence of other universes. We had the Big Bang theory with tons of data to support it. But there were some puzzles, and cosmic inflation was developed to explain those puzzles. Being a scientific theory, inflation also made predictions – many of which have been beautifully confirmed. Soon after inflation was discovered, it was realized that once it stats, it never ends, and the generic eternal nature of inflation was discovered.

        While we can’t go and visit other bubble universes, their existence is one prediction (out of many) of the theory of inflation. If we have good evidence to believe inflation, we have to take seriously even the “philosophically hard to swallow ” predictions.
        In a nutshell, a given theory might make many predictions. For the theory to be scientific, at least one of it’s predictions must be falsifiable. But it is not necessary that ALL of it’s predictions are falsifiable.

        Also, the observational situation with eternal inflation is not so bad. There is some hope that in our past, other bubble universes have collided with the boundary of our bubble. Signatures of such collisions might lie in the CMB radiation. People are looking into the data – so at least it’s an issue that is being explored scientifically.
        Furthermore, there is indirect evidence that we live in a multiverse (related to the apparent fine-tuning of the constants of nature) but I won’t go into that further here, because it’s worthy of it’s own blog.

        You might enjoy reading the following two short articles about the multiverse by Alex Vilenkin and Max Tegmark at

        • 1) Thank you for taking the time to reply.
          2) I looked at the articles. It sounds like the multiverse idea is just another way of getting up to more than 3+1 dimensions, except this time on a grand scale rather than a infinitesimal scale. How so? Well, if two “universes” collide then they must both be embedded in a higher dimensional space they share. This requires more dimensions.

          In other words, it sounds to me like string theory requires more than 3 dimensions and therefore string theorists are creating a reality to fit their theory rather than creating a theory that fits reality.

          Thanks for the link. I was trained in UChicago style GR, so it was good to see Ellis on my side. 😉

    • Yomismo

      I’m more or less of the same opinion as Howard. I know that there is a lot of maths involved that are unknown to me, and also I guess that maybe we could find the way to get information about other universes using some kind of particle or by other method that maybe someone may discover in the future. But right now, this sounds more like sci-fi, doesn’t it? Correct me if I am wrong!

      Anyway, I think this is a great post, thanks for the video!

    • Mott Phys

      this is very important for developing of physicsmthrough others dimensions,beyond

    • Joultimo

      It is only our 3 dimensional + time perception at limits our ability to see or experience other dimensional universes. The fundemtal nature of human perception is what limits the other dimensions from being seen or measured. From this static dimensional perception quantum physics shows realities which cannot be grasped by us. If we can isolate our mind from our human self and change its way of perceiving, we can access the multidimensional universes that exist as mere theory.
      We were mind born into human bodies of a single universe within a single dimension so our perceptions and our laws are of a single dimension. Mind can be changed, perception can be altered. Just as the observer effects things on a quantum level, the mind breaking free of its single dimensional perception will unlock the multidimensional universe.

    • Tieaquilt

      Very interesting!

    • The bubble within the bubble theory sounds much like the infinite nature of a fractal image such as Mandelbrot’s set

      • Mott Phys

        is very interesting your thoughts;but think that the multiuniverse have not patterns of fractals.i think that the multiples universes generated
        by infinities bubbles are holographycs processes of space-time.from two to the case even diensions,2 and 4,is process of renormalizations of the functions to conformal invariance of fields.
        these multiverses are derived of btreakdown of symmetries.
        that will go configuranting the spacetimes to the bubbles

        • Mott Phys

          i think the the multiples universe are derived by the symmetry breakdown of symmetry as cp to several decayment as meson k,meson b,charm mesons…and think that the violation of PT,that wouls linked to conservation cp to the stronger interactions,does apearing the infinities spacetime continuos( extradimensions of spacetime derived of SUPERSTRINGS leading to lorentz’s invariance and pt broken,but cpt is conserved in the global.and,tthere is and the axions;there is the time with two orientations curving the space in ttwo oposite poles ,that is left-right hande spins broken),
          then there are particles that travel with speed faster than the speed of light
          and the BLACK HOLES.does not exist of the form that tthink,but
          are produced by ibteractions of extradimensions and theirs compactifications in complex compactifications structures,where speed of light can to obtain different speeds_constant and limit-
          with each event horizons.

    • Is it excepted by most that each bubble universe is infinite in size? The idea of a bubble implies that is has boundaries.

    • Samleesam

      While it is great fun to consider these ideas, I wonder why scientists can’t admit that they really have no idea what is going on and quite likely never will.

    • Baffled

      If 70% of our universe is dark energy, and the amount of dark energy is 10 to the negative 122, please explain!

    • Christine C

      So I really enjoyed watching the NOVA series on the Multiverse so I went looking for more information. That is where I read this very short synopsis of the same concept. I really do love all of it and I don’t need science to tell me that this is true because I innately know that it is true the same way we all know that with life comes death and with dark there is light. With all this in mind however there is still one set of questions that I’m not sure will ever be able to be explained. They start out with an acceptance of not believing or disbeliving in “God” or whatever deity, and continue with where did all this stuff come from in the first place? Because even for believers you can then also ask when challenged, where did god come from? There is no answer for either question, but there is a concept that supposedly makes sense for everything but our actual existence. The concept being that everything has a beginning and an end in terms of existence. But that could never explain our current predicament of where did it all come from. So I ask has it always been? Will it always be? Is there some way to even begin to figure it out? I think that the only way we may ever know is to never truely “know” anything.
      As soon as we put a finite answer with a question we instantly put an end to ever truely knowing what that answer is. For example if we would have never challenged the fact that the earth was the center of our solar system, then we wouldn’t ever have been able to explain many occurrences that we know today to hold true. But there is always going to be someone who won’t just accept a standard.
      The only problem now is trying to not limit the great minds that help to expand our knowledge as a collective to what is currently acceptable. I think that where we are going wrong with this entire quest of knowledge is in how society has tried to quiet the brilliant minds that can help to answer these seemingly impossible questions.

    • Kenegbert3rd

      While I have every confidence that physicists will eventually come up with a grand unified hypothesis, I wonder sometimes if the current raft of their possible explanations (bubble universes, infinite expansion, the holographic principle, M-theory…) is not analogous to all the medieval Christian theologists’ obsessing upon how many angels can dance on the head of a pin
      or who else occupies the first circle of Hell besides Marcus Aurelius. All endeavors eventually take odd turns. To make that final leap we may just have to come up with a different hypothetical location to leap from. I’m optimistic, though. Keep up the good work, NOVA.

    • PRD

      Cool explanation. Have you or any of your colleagues tried to calculate the mass per cubic centimeter of the eternally inflating universe? I ask because I would like you to consider the following…

      Suppose the eternally inflating universe contains so much mass (and is expanding so rapidly) that the sheer momentum of this mass tears holes in the fabric of space – just like your champagne bubble analogy where bubbles spontaneously appear when the pressure in the bottle is relieved.

      It follows then that perhaps our universe was not formed by the explosive “push” of a ‘Big Bang’ but rather by the stretching “pull” of a ‘Big Tear’. In other words our universe is expanding at an ever increasing rate not because of some mysterious force called Dark Energy which is pushing everything apart but rather because of the gravitational attraction of the surrounding inflationary universe which is pulling and stretching everything apart.

      The ‘Big Tear’ totally eliminates the need for Dark Energy resulting in a simpler, more elegant universe. What do you think?

      • PRD

        For what its worth…

        In a universe created by a ‘Big Tear’ there would be very little stretching near the center because the gravitational force of the inflationary universe pulling from all directions would cancel out. However, as you moved closer to the edge of the universe the stretching would become more pronounced. Until at the very periphery the gravitational gradient would become so great that you would be ‘spaghettified’ as you crossed an Event Horizon into the Eternally Inflating Universe.

        A ‘Torn Universe’ then is kind of like an anti-Black Hole, literally tearing you into oblivion instead of crushing you into a singularity.

    • In the NOVA episode of Fabric of the Cosmos, Universe or Multiverse? Brian Green explains that the accelerating expansion of the universe was thought to be explained by dark energy (vacuum energy?), but the value of dark energy is trillions & trillions of times too small to cause the observed acceleration. He then invokes multiverse theory as an explanation of that small value, because if there are an infinite or even really large number of universes, the value found in our universe for dark energy is not surprising.

      Here’s my question: how does that explain the rate of expansion of the universe that dark energy was supposed to explain? It’s still too small, whether it’s an understandable number in light of multiverse theory or not.

      • Mott Phys

        in all the multiunverses the speed of light is different to all? the speed of light in the vaccum would be measured by other value? if there multiples universe the speed of light could have values differents to each one theirs?the cosmic accelerations could to explain the creationof multiples bubbles.where each one theirs contain several universe in potential to if expamd in differents spacetime,with possibles
        different physics lawas.
        then the multiuniverses place that the speed of light is not fundamental to the cosmos,as weell as the gravity would be variable.each universe will contain extradimensions.

    • PRD

      According to the Big Bang the universe started out as an infinitely dense, infinitely hot, infinitely small point which exploded into the universe we see today. If this is true we should be able to make the following three assumptions. 1. the universe has a center, 2. the universe is roughly spherical in shape and 3. unless we are at the center of the universe (which is highly unlikely) the rate of expansion of the universe should vary depending on which direction we are looking.

      I have also heard it said that the universe is like a loaf of bread which, as it rises, expands equally in all directions. These two theories seem to contradict one another and so my question is…

      From the observations made to date is the universe expanding equally in all directions or is the rate of expansion different depending on which direction you look Thank you.

    • Hakuin Suso

      Just a few of thoughts that arose as Delia did her thing.

      First, she states that in eternal inflation multiple universes “can” arise. Does this mean that universes other than our own do not necessarily have to arise? If so, what are the conditions necessary to make a universe arise? (Or not arise, as the case may be.) I suppose that question could be rephrased as, “What makes inflation stop in any particular place in the eternal inflation?”

      Second, there may be proof that inflation did or is occurring, but such proof only supports the theory, it does not make it undeniable fact. A more encompassing theory may still come along that doesn’t support multiple universes.

      String theory, on the other hand, is from what I’ve heard untestable. And I’ve heard there are four of five different versions each of which could equally explain the universe as science finds it. So is it really “good science” to support the predictions of one theory that has some proof, with another that has no proof, especially when the result is a state of affairs (i.e., multiple universes) that can’t be proven at all? (If indications of two universes bumping into each other is found in the cosmic background radiation it will be interesting, but not definitive proof the multiple universe concept is true.)

      Third, the impression I’m getting from the theory of multiple universes is that every possible situation that ever could exist or will exist is found made manifest in these universes. Isn’t this like saying that physicists can measure both momentum and position precisely at the same time? Something we’re told can’t happen?

      Saying every possibility “happens” may work as a way to remove the observer from physics, but it also means that ultimately absolutely nothing happens. For when you add every possible negative value to every possible positive one, you get zero. Nada. Nothing.

      Finally, and this is just a bit on the side, when Delia was drawing the first universe in inflation did anyone else think of the Taoist Yin Yang Symbol? Specifically, the white dot in the black teardrop?

    • I think she is right.

    • Wtrevenzoli

      My crazy idea? We are not the universe. We are the result of the intersection of two (or more) different universes that are overlapping in some extent. The conflicting Quantum Mechanics vs. Gravitational Mechanics could be proof that different laws are coexisting or being generated because of such collision. The Big Bang happened when the tip (or tips) touched like hot iron on cold water, generating a chain of events and specific laws that will evolve while these two bubbles are crossing their “paths”. Our gravitational rules didn’t exist then: – they just show up as a result of such collision, evolved, or are evolving while following its own path.

    • Rbobar

      To: Delia Schwartz-Perlov

      From: Robert T. Bobar

      You would certainly need extra spatial dimensions to keep the parallel universes from being part of the same universe.

      I hope you took your analytical geometry very seriously.

      Because it depends on what you know, how well you know it, and perhaps if you truly accept mathematical reasoning as a perfect conclusion. A conclusion; mind you, that you desperately want to know. Math is just the kind of thing that will paint you into a corner with no way out but the right way.

      You would be surprised, about the calibra of the people in which questions of reality have remained as elusive as grease lightning. So it is not a test of your intelligence but instead merely the luck of the draw that life throws at you. You just need to be wise enough to know when you are hearing the ring of truth, and when you are not.

      Let us go back to the simple concept of thinking about what a dimension is by examining them in Cartesian Coordinates.

      This Coordinate System has the simple feature that every point of space has a unique identity (x, y, z) in three dimensions.

      Also notice that a one dimensional line in the space requires two extra background dimensions; and so is not the same as a naked single dimension that requires no such extra background dimensions. Usually teachers merely confuse this subtle point by making the fallacious claim that the axes are simply lines. But you must think deeper than that if you want to know.

      Since you have had some dealing with mathematical proofs this should go easy; sometimes they can be very simple. And you happen to be in luck, the proof is so very simple in fact that it virtually can be reasoned out without mathematics. So here it goes:

      Draw a circle with chalk on the ground around yourself then jump over the circle without touching it. By doing this you have proven that space cannot be two dimensional. Since you could easily apply The Pythagoras Theorem (in 3-dimensional form) to show that the height of your jump was in the third dimension. Now just take this thought experiment one dimension higher, instead of a circle we will use its higher dimensional counterpart the sphere.

      Now you’re set in order to prove a 4th dimensional space (using The Pythagoras Theorem in a 4-dimensional form); all you need to do, now, is to jump out of the sphere without touching the surface of the sphere.

      Um, Can’t Do That ??? ——-> BECAUSE SPACE IS ONLY 3-DIMENSIONAL.

      This conclusion is not depended on our senses to perceive small sizes (curled up), since it can be made into any size you would like.

      This means M-Theory is not true, but most people for whatever reason will not accept this; so here are two pieces presented for mass appeal their way:

      Brian Greene has become such an entertainer lately but I prefer mathematics rather than entertainment.

    • Be the first to check out ! It comes to multiverses from bottom up.

      “The scope of the Theory of Something is not narrow – it is almost Everything, including hot topics like the Higgs particle, dark matter, dark energy, black holes and universes. Starting from the smallest, the one and only fundamental charge particle – the negtrino that fills up all space in a cubic Grid and also is the building block of all other particles and matter – the ToS ends with the universes. The ToS even tries to explain how there can be Something out of Nothing – the origin of our universe – and proposes the equation for Everything.”

    • Tesserian

      I remember reading that when Hubble first showed that our Milky Way was but one of a large number of galaxies, the other galaxies that had been discovered were called “pocket universes” or “island universes,” as our galaxy had been previously considered to be the known universe. Perhaps we need new terminology for today- teragals? Tera-galactic clusters…?

    • Masanori S.

      Hi Dr. Schwartz. I am a big physics fan and have watched several videos on the quest of unifying the electroweak /strong forces described by Quantum Mechanics with gravity described by General Theory of Relativity. However, I haven’t heard a sound explanation of why physicists want to unify all the forces into a single Superforce Theory. Is there a valid argument to imply that all forces of the Universe we live are manifestations of one single force? Say, what if there were two fundamental forces of the Big Bang. Wouldn’t that be a whole game changer in physics, even for string theory?

    • Mikael Wåhlberg

      🙂 Truly interesting!

    • Cyd Pais

      delia, a great fan of the multiverse, its amazing, the odds its fascinating, i think multiverse and the string theory is something great…. alan guth is a great guy, would like to hear from you, pl keep me posted on this if you have time..
      cyd Pais

    • Walter Iego

      I have tried to piece together evidence of universes colliding, but I am all over the place. Is there any good article on the subject anywhere?