Tuesday, August 07, 2018

Dear Dr B: Is it possible that there is a universe in every particle?

“Is it possible that our ‘elementary’ particles are actually large scale aggregations of a different set of something much smaller? Then, from a mathematical point of view, there could be an infinite sequence of smaller (and larger) building blocks and universes.”

                                                                      ~Peter Letts
Dear Peter,

I love the idea that there is a universe in every elementary particle! Unfortunately, it is really hard to make this hypothesis compatible with what we already know about particle physics.

Simply conjecturing that the known particles are made up of smaller particles doesn’t work well. The reason is that the masses of the constituent particles must be smaller than the mass of the composite particle, and the lighter a particle, the easier it is to produce in particle accelerators. So why then haven’t we seen these constituents already?

One way to get around this problem is to make the new particles strongly bound, so that it takes a lot of energy to break the bond even though the particles themselves are light. This is how it works for the strong nuclear force which holds quarks together inside protons. The quarks are light but still difficult to produce because you need a high energy to tear them apart from each other.

There isn’t presently any evidence that any of the known elementary particles are made up of new strongly-bound smaller particles (usually referred to as preons), and many of the models which have been proposed for this have run into conflict with data. Some are still viable, but with such strongly bound particles you cannot create something remotely resembling our universe. To get structures similar to what we observe you need an interplay of both long-distance forces (like gravity) and short-distance forces (like the strong nuclear force).

The other thing you could try is to make the constituent particles really weakly interacting with the particles we know already, so that producing them in particle colliders would be unlikely. This, however, causes several other problems, one of which is that even the very weakly interacting particles carry energy and hence have a gravitational pull. If they are produced at any substantial rates at any time in the history of the universe, we should see evidence for their presence but we don’t. Another problem is that by Heisenberg’s uncertainty principle, particles with small masses are difficult to keep inside small regions of space, like inside another elementary particle.

You can circumvent the latter problem by conjecturing that the inside of a particle actually has a large volume, kinda like Mary Poppins’ magical bag, if anyone recalls this.


Sounds crazy, I know, but you can make this work in general relativity because space can be strongly curved. Such cases are known as “baby universes”: They look small from the outside but can be huge on the inside. You then need to sprinkle a little quantum gravity magic over them for stability. You also need to add some kind of strange fluid, not unlike dark energy, to make sure that even though there are lots of massive particles inside, from the outside the mass is small.

I hope you notice that this was already a lot of hand-waving, but the problems don’t stop there. If you want every elementary particle to each have a universe inside, you need to explain why we only know 25 different elementary particles. Why aren’t there billions of them? An even bigger problem is that elementary particles are quantum objects: They get constantly created and destroyed and they can be in several places at once. How would structure formation ever work in such a universe? It is also a generally the case in quantum theories that the more variants there are of a particle, the more of them you produce. So why don’t we produce humongous amounts of elementary particles if they’re all different inside?

The problems that I listed do not of course rule out the idea. You can try to come up with explanations for all of this so that the model does what you want and is compatible with all observations. But what you then end up with is a complicated theory that has no evidence speaking for it, designed merely because someone likes the idea. It’s not necessarily wrong. I would even say it’s interesting to speculate about (as you can tell, I have done my share of speculation). But it’s not science.

Thanks for an interesting question!


  1. When I was around 13 years old I wrote my first science fiction story titled The Dwarf Dimension about just this idea.

    In one sense this does happen. This is seen with a correspondence between the high energy and low energy limits of the universe, called UV-IR correspondence. The Maldecena AdS~CFT correspondence shares this feature. With AdS_n you have that the bulk gravity with Z = ∫D[g]e^{-iS[g]} is equal to the (ψ|ψ) = ∫D[ψ]e^{-iI[ψ]} on the conformal boundary for a CFT_{n-1}. On the bulk of the AdS_n there is gravitation that is dual to quantum field theory on the boundary. Quantum field theory is constructed with local operators according to the Wightman commutator condition on spacelike surfaces. This removes nonlocal quantum physics in order to define causally ordered (time ordered products of) fields on a path integral. Since the nonlocal physics is not significant from an experimental perspective this is not a problem. However, with black holes and holography this convenience is not so affordable. In effect gravitation and quantum gravity are nonlocal.

    This dualism is a sort of equation that correlates the nonlocal quantum gravitation on a tiny scale, or equivalently high energy or UV, with local quantum fields that are lower energy or IR. This equation

    nonlocal UV gravity = local IR quantum field sources

    is really a way of stating Einstein's field equation. So we have with gravitation the prospect that structures on a large scale have a recursion with structures on a tiny scale, say at the Planck or string scale.

    This means though structures on a tiny scale are simply those within the observable universe. Of course there is the multiverse, but I will defer going there for now. The idea of there being some sort of universe within an elementary particle, or on a very small scale, is a sort of projective blow up of a point. This may also have something to do with the above correspondence. The geometry of entanglements of states, look at the book Bengtsson-Zyczkowski Geometry of Quantum States: An Introduction to Quantum Entanglement, have Grassmannian realizations. The AdS geometry is then a lower energy decomposition from such geometries. Spacetime is built from entanglement, and this stems in part from the Page-Wooters demonstration on the emergence of time and Raamsdonk hypothesis. So in a funny way if you try to find a universe within the smallest of particles, say an electron, you end up finding the universe we are in.


  2. 'The problems that I listed do not of course rule out the idea. You can try to come up with explanations for all of this so that the model does what you want and is compatible with all observations. But what you then end up with is a complicated theory that has no evidence speaking for it, designed merely because someone likes the idea. It’s not necessarily wrong. I would even say it’s interesting to speculate about (as you can tell, I have done my share of speculation). But it’s not science.'

    All this seems eerily similar to String Theory, doesn't it?

    In fact, isn't String Theory precisely one such example of a theory in which elementary particles are not elementary (or rather are not particles but vibrations of a string)? And doesn't String Theory run into all sorts of problems similar to what you described in the article, and try to circumvent those problems by introducing ever more complicated constructions (D-branes, supersymmetry, 11 dimensions, compactification, moduli stabilization, etc...) just to keep itself compatible with observations? And does String Theory have any experimental evidence to support it? And isn't it being researched merely because some people like the idea that particles are made of strings?

    It appears that you could have equally well given String Theory as an example in your article, instead of the Baby Universes Theory. And concluded that it's not science.

  3. It seems like this Russian nesting doll arrangement of universes would play havoc with the notion of conserved quantities. Is that the case?

  4. We know (or strongly suspect) from the Fermi exclusion principle, that all electrons are identical, and that furthermore they are also identical at different times. So if there's a universe inside each electron, it must be a very boring, static, one.

  5. Dear Sabine, and what if our universe is a particle? Hope not to irritate you too much drifting in No-science arguments, but it is just for today.
    Many thank.
    PS Your book is fantastic!

  6. Hi Sabine,

    What if the components of a granular space-time were made of many constituents? Lets say 10^60 that were tightly bound, unbreakable from the outside?

  7. Possible to let us turn off the animated GIFs while reading? Aaaaagh....my eyes...

  8. A recent paper by George Ellis and other (which I learned about from the Twitter feed here a few weeks ago) points out that if your theory allows infinite quantities or infinitesimal quantities (no limit in either direction), you run into paradoxes, of which energy conservation is one. That made me happier since I have long felt that a finite, discrete universe made more sense. Unfortunately one is taught to equate physics with Calculus, usually without the information that Calculus provides an excellent approximation to (finely) discrete systems, so the fact that Calculus works, e.g. for designing a bridge, does not prove that the bridge is actually composed of an infinitesimally-continuously material.

    Therefore the current movie "Ant-Man and the Wasp" made me less happy. It makes negative sense in either its physics or biology. I don't mind a bit of fantasy, but it should involve wizards and wands, not "scientists" in lab coats, writing on blackboards.

  9. It's bigger on the inside! It's a Tardis!

  10. The World of the Electron (by Valery Bryusov, 1922 - translated from Russian)

    What if these things we call electrons
    Are worlds with continents and seas,
    And art and craft, and war and peace,
    And scrolls and scrolls of memories?

    And Universe in every atom,
    With fivescore planets circling round -
    With all the things that here abound,
    But also things we've yet to fathom?

    Быть может, эти электроны
    Миры, где пять материков,
    Искусства, знанья, войны, троны
    И память сорока веков!

    Ещё, быть может, каждый атом -
    Вселенная, где сто планет;
    Там - всё, что здесь, в объеме сжатом,
    Но также то, чего здесь нет.

  11. Roger Penrose's cosmology is somewhat similar to your idea of a universe inside a particle. Eventually in the very long run, all particles will decay into photons and black holes will evaporate into photons. Everything will be photons and the expansion of spacetime will make their wavelengths very long, lightyears long.

    There is no constraint on wavelength. It can be very long or very short. Since photon energy depends on wavelength, there's no constraint in energy. It can have any energy because it can have any wavelength. Frequency is a measure of time. The inverse of frequency is the period or the time equivalent of wavelength. So time also depends on wavelength and also unconstrained. The photon does not have a sense of size and time. It doesn't know whether its wavelength is long or short, whether its period is long or short. To a photon, one nanosecond and one billion years are indistinguishable.

    This peculiarity has amazing consequences in cosmology. In a universe with only photons, you can change your measurement scale. Change a lightyear into a nanometer and assume the photon is small like a gamma ray. It doesn't know it's big. You can restart the universe by creating matter via pair production by gamma rays. No observers will be around to protest, hey your subatomic particle is bigger than a galaxy! Nobody will object, it will just happen.

    You have successive generations of big bangs and universes. Each universe is exponentially bigger than the previous one. Like the Mandelbrot set, you can zoom in forever and universes just keep coming out. It never ends. It's infinite. Watch the zoom in of the Mandelbrot set on Youtube. It's like a psychedelic hippie art. If you believe infinity is God's handiwork, she must be a hippie artist.

  12. Meh - turn the question upside down. Is all the matter in our universe really just quasiparticles in the condensed matter of a larger universe?

  13. What is being suggested is essentially multiverses each consisting of a limited matrix of shared stable properties … ones that interact with mathematical precision in predictable ways. It would imply that our Universe is constantly interacting with other Universes in the multiverse at every level and perhaps at point in time. According to Tegmark and Aguirre et al this is impossible. Personally I believe the Universe is at least self-dual … meaning that it is not the homogenous bubble that we are being force fed on a daily basis. So although I think this particular idea is a long shot … in a larger sense I empathize with your thought process. Don't stop thinking … ever.

  14. Whatever arguments one may raise against this conjecture, I am not sure one can use arguments of Quantum Mechanics.

    Surely what the conjecture implies is that many of those bizarre and counter-intuitive quantum behaviours we observe at the limits of our measurement scale are simply a manifestation of much more regular stuff going on at a much smaller scale.

    I have always been intrigued that a particle as simple in structure as a neutron can give us no clue as to whether it will decay in the next second, or a million years from now. We simply have to accept that its future is purely probabilistic. It is interesting to conjecture that there is a universe of internal structure in there where some cataclysmic event is required to finally rip it apart.

    It is interesting to think about, but whether useful in the advancement of Physics is another matter.

  15. The suggestion sounds very much like Leibniz' monadology. And the comment that string theory sounds very much like this rings true. Your objection seems to me a sound one, against Leibniz, and against string theory as well. But then I'm rather scientistic according to philosophy. And worse, it seems at this point that any purely QM/superstring style theory has a covert form of predetermined harmony in generating spacetime. Well, to be precise, nobody who adheres to antirealism seems to have even a sketch of an explanation of where the reality we see comes from. Or maybe it's just not an interest?

  16. Isn't this whole thing a joke about The children of Atom in fallout 3? And yes, I took the time to listen to Confessor Cromwell.

  17. Peter Shor,

    You can always keep amending theories. Simply change Pauli's exclusion principle for another suitable and more complex rule that has the same end effect for 'externally identical fermions', but allows different internal structure.

    Of course this reinforces Sabine's main point of the post... With each amendment the theory should lose confidence from it's proponents, which do not seem to be happening (maybe is but taking a very long time) mostly for sociological reasons.

  18. Interesting piece, but the animations make it very difficult to focus on the content - at least for me.

  19. Folks,

    Sorry about the ani-gif eye-pain, lol. I got somewhat carried away there. I swear I'll not make a habit of it.

  20. jim_h,

    I have a trick I have used for several years: open WordPad, say, resize it to fit the animated gif, and then place it on top of it. Although you will have to move it while reading/scrolling the article, it certainly helps on concentrating.

  21. Well, I loved the Mary Poppins one, although I don't think it's the one you meant.

    Waaaayyy back when I was little girl, she was the first female I read about who had any agency at all.

    Too bad Walt Disney messed it up (go figure). It doesn't change my opinion of her importance in a world (at that time) void of strong female characters. Narnia's Susan and Meg's Wrinkle in Time who grow up to be non-entities, bleh. Lord of the Rings worst of all, with its iconic females on pedestals, without flaws.

    I know you meant to mock her with the carpet bag thing (as well as perfectly apt for your blog post - it fits well, so no criticism there!), but the Mary Poppins that P.L. Travers (not the Walt Disney version) wrote about would be a good choice for bed time story reading with your little girls. Perhaps not as necessary these days with stronger female role models than when I was a child (yourself included), but the P. L Travers Mary Poppins is still a good read for them.

    It's hard for working parents to spend the time with their children that they should, but bed time book reading are second to dinner time daily recaps to provide a structured way to convey your interest in them and teach them your values.

    And no, that’s not Mom’s job, but better carried out by Dad, and in my household these days, Grandpa.


  22. Sabine said ... Thanks for an interesting question!

    I didn't know when it came to science you could be such a softy.

    I love science fiction more than most and that kind of speculation from non-scientifically minded people is expected. However we also see it in professional researchers because they "want/believe" their pet peeve ideas "have to be right". To quote a researcher who I have much respect for, "nature doesn't have to be anything".

    I don't think too many researchers realize that the studying of empirical evidence and evaluating it in a logical, rational, well reasoned manner has not been thorough enough to give in to forming rampant speculations in pursuit of answers.

  23. The idea of worlds within worlds etc., was entertained by soviet physicists in the sixties. They called such particle-worlds 'friedmons'in honour of Friedmann. A quick search sent me to the Sao/Nasa database, where the abstract of paper by Blokhintsev states " According to the hypothesis, a friedmon universe may be merely part of a vaster universe of friedmons freely moving in a metaspace of a large number of dimensions greater than 4. They constitute a friedmon gas, the molecules of which are entire universes of the same type as our Universe, but perhaps larger and perhaps much smaller. "

  24. To see a World in a Grain of Sand
    And a Heaven in a Wild Flower
    Hold Infinity in the palm of your hand
    And Eternity in an hour

    ---William Blake (whose poor-person's grave was recently marked with an expensive tombstone)

  25. In his book Infinity and the Mind, Rudy Rucker (who is part of the chain giving me an Einstein number of at most 4) discusses his crazy idea of "circular scale", which is similar in some respects. For what it's worth, he says that Kurt Gödel found it interesting.

  26. "The idea of worlds within worlds etc., was entertained by soviet physicists in the sixties."

    When studying physics, I had a textbook from East Germany. Probably for the same reason, it called "elementary particles" "microparticles" (or, rather, the corresponding terms in German).

  27. @ Louis Tagliaferro

    What you said is pretty much what I meant when I said "That's the thing..."

    Empirical evidence is under attack these days, and Dr. Hossenfelder is the most staunch defender against that attack that I've been able to find.

    As such, she must address arguments that empirical arguments are so last century, seriously, logically and without emotion.

    There are too many people these days arguing that empirical evidence is not necessary.

    However, I do believe that researchers have studied it thoroughly. They just don't like what they have found.


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