gregoire ausgraben lives in a multiverse. his decisions might branch into new universes every time he says yes or no or something else. you might remember Schrödinger cat. he was both alive and dead and was said to be "collapsing" into the dead or the alive state when observed. instead, and this is not pure fantasy, but it is suggested by renowned physicists, he could be alive here and dead there. gregoire would have an infinite number of doppelgängers. maybe he feels it. maybe this is why he can never feel safe and at home. he also feels his life path as ridiculous and ridiculously challenging. or gregoire ausgraben has unconscious access to the so called "wormholes" that would connect universes and his mind is confused. or he is stuck in a wormhole. or he can unconsciously hear the sound of dark matter and his integrity is breaking under the pressure. or he is a bunch of strings half caught in one the 9, 10 or 25 dimensions that curl up invisibly as universes inside our own. or he senses the interactions between our universe and a mirror universe created during the big bang. or and maybe it is all the same, his soul is broken and the path to repair has not shown itself yet. or, he is on it and unable to see it. why, who knows. or.
there is among quantum physicists, astrophysicists, string theorists, cosmologists, black hole theorists, etc, the proposition that our universe is not unique. all these scientists speak of a multiverse, but they do not agree on how this multiverse exists and behaves or on what it is made of or which physical laws it follows. here is a very short overview of some of these ideas. i hope i report correctly what i have read.
“many worlds” and “daughter universes”
the “many worlds” model is one of the interpretation of quantum mechanics. in quantum mechanics, a particle exists in a superposition of all its possible states at once, until, that is, someone tries to make a measurement of it. at that point, [the common belief has been that] possibilities collapse, and one physical state becomes apparent to the observer. in the “many worlds” interpretation of quantum mechanics, all the possible states the measurement might have shown play out in different universes, each with a different version of the observer.
this quantum multiverse is also a possible answer to the question of how human life is connected to the quantum world. this question was addressed in 1957 by a young graduate student, Hugh Everett III. he speculated that for every human situation for which we see different possibilities, then, every possibility occurs by branching into a new universe also called daughter universe. in a simple example where we have to take a binary yes/no decision, if we decide yes, then, the “no” decision is played out in another universe. in fact, we as humans then experience multiple realities but we don’t really know about our doppelgängers.
“bubbles”
the concept of bubble universes arises from the theory of eternal inflation, a variant of the cosmological inflation theory. let’s start with the big bang. the big bang would be a moment where space and time appear ex nihilo, out of a very dense and hot something. it is predicted by Einstein’s general relativity. nobody knows however if it really happened ex nihilo or if, for example, a previous universe existed, contracted and then expanded again.
in the standard big bang theory, the universe expands relatively gradually throughout its history.
with inflation theory, the big bang is followed by a period of extremely rapid expansion. this expansion was so fast that it would be equivalent to a single bacterium expanding to the size of the milky way in a trillionth of a trillionth of a second. expansion is seen as creating a largely homogeneous young something but in there, there were infinitesimal quantum fluctuations, which, when projected into cosmic scales, left some patches with more or less matter/energy. these variations became the scaffolding of the structure of our universe.
in the cosmological variant proposing eternal inflation, some regions of space-time continue to inflate; some spots stop and cool down to conditions that generate a universe. our universe is one of these in the middle of a sea of others and all are called bubbles. an interesting aspect of this model is that the laws of physics might be slightly different in each universe and there could be universes with life created along another path.
universes as primordial black holes
it is also possible that random fluctuations in the hot and dense initial state increased density in some areas and that these came to a gravitational collapse and created black holes. these primordial black holes, unlike the ones created by the collapse of stars would have a wide range of masses, including very small ones. some could be tiny. there is also the possibility that (some of) these primordial black holes are actually universes existing in a state that appears different to an observer on the inside and on the outside. an internal observer would see it as an expanding universe (just like ours). somebody on the outside (like us on earth) would see it as a black hole.
universes made of dark matter and dark energy
because the gravitational forces deployed by our observable matter majorly fail at explaining the particularities of trajectories such as that of stars or galaxies, it is hypothesized that another type of matter exists that is invisible to us (invisible matter, dark matter, matière noire; please note that the choice of “noire” and “dark” was unfortunate, not only scientifically - this matter is not “black”, it is invisible, transparent somehow and it was unfortunate socially also, “black” and “noire” being the skin color of so many oppressed populations). our matter constitutes only 5% of all matter/energy. 26 % would be made of invisible matter and 69% would be made of a mysterious invisible energy (énergie noire), whose nature is even less understood than that of invisible matter. this invisible energy is a theoretical proposition to explain the acceleration of the expansion of the universe. reminder: the expansion of the universe was predicted by Einstein’s theory of general relativity (1920s) and experimentally shown by the1930s, but the acceleration of the expansion was only discovered at the end of the 1990s and it was theoretically unexpected even if some quite simple tweaking of Einstein’s general relativity can account for it.
in a model where universes are made of invisible matter and/or invisible energy (remember E=mc2), worlds exist around us which are made of non identified particles that our physicists predict exist, but whose properties are different from our matter. it is then because these particles are unable to interact with our matter or interact at levels that are under the thresholds of our experimental tools, that the worlds they create are undetectable by us. their universes are invisible.
dark matter
that the universe was expanding was put aside from the 1930s to the 1960s. it is when Professor Vera Rubin at Princeton University noticed something weird in the way stars were moving around the edges of galaxies that it came back to foreground. they were moving faster than it was predicted given the amount of mass we could see. there was more gravity acting on them. dark matter was needed.
since, the nature of dark matter has been up for debate and all sorts of guesses have generated all sorts of names, such as RAMBOs (Robust Associations of Baryonic Objects), MACHOs (Massive Compact Halo Objects), MOND (Modified Newtonian Dynamics), with none of them actually fulfilling all necessary characteristics of dark matter. another possibility is that dark matter is made of some brand new particles we have not discovered yet and some of such theoretically proposed dark matter candidates also have silly names: WIMPs (Weakly Interacting Massive Particles), SIMPs (Strongly Interacting Massive Particles), Sterile Neutrinos, Axions. none of these particles have been proven to exist yet, but we also haven’t been able to rule out the possibility of their existence.
another female scientist, Chandra Prescod-Weinstein studies the theoretical particle called “axion”. something she finds cool about the axion is that if it exists, it would actually solve two physics mysteries at once (the strong CP problem and dark matter).
in hot dark matter models (HDM), dark matter is made of high-energy randomly moving particles created soon after the big bang. in cold dark matter models (CDM), dark matter moves slowly compared to the speed of lighit and is made of a very massive particle that would produce many compact, relatively low-mass clumps of dark matter orbiting every galaxy. in the axion model that Chandra Prescod-Weinstein is looking at, she starts from the idea that dark matter particles should be massive and weakly interacting. then, in an opposite extreme model, an ultra-light dark matter particule (ULDM), commonly called fuzzy dark matter (FDM), is predicted to produce a very blobby, wavy distribution of dark matter in every galazy. some experiments suggests that it is this wavy distribution that is observed.
this fuzzy dark matter would be made of fuzzy axions. they are an extremely light version of axions said to be “fuzzy” because of their wave-like behavior. among neutrinos, there are some of the lowest-mass particles and they have so little mass and electric charge that 100 trillion of them stream through each of us every second and we do not feel a thing. fuzzy axions would even be lighter. “a lot lighter”, Keir Rogers, cosmologist at the University of Toronto said. based on the quantum mechanics duality, these very light particles would have very large wavelengths and fuzzy axions would thus have a wavelength bigger than the size of a galaxy. that could explain another of our problems called the “clumpiness problem”. the “clumpiness problem” is that the universe in reality is not as clumpy as computer simulations of its expansion have predicted. when these simulations however are made including very long dark matter waves, then, they look like what we observe in terms of cosmic microvave background (CMB) and also in terms of clumpiness. it is not sure that dark matter is made of fuzzy axions, but they are very strong candidates.
what else could dark matter be? primordial black holes, modified gravity, a combination of various particles, etc...
mirror universe
another way of thinking dark matter is to consider that dark matter is a something that failed to form atoms during the nucleosynthesis of the big bang. dark matter than would exist as a mirror: every interaction in our universe would have an accompanying interaction inside the dark matter universe—a new kind of universal symmetry. in the physics of normal matter, a neutron and proton have almost exactly the same mass, which enables them to bind together and form stable atoms. If a proton was just a little bit heavier, it would be totally unstable and decay in only a few minutes, making the formation of atoms impossible. in this imaginary scenario, the universe would be left with a sea of free-floating neutrons. perhaps, the researchers suggest, this imaginary, broken cosmos may be a reality and there would be a dark matter mirror version of our universe.
multiverse predicted by the string theory
string theory is a collection of ideas in theoretical physics in which the fundamental building-blocks of nature are not particles (such as the point-like electron) but instead strings. imagine microscopic wiggling rubber bands.
string theory is perhaps the most high-profile candidate for what physicists call a theory of everything – a single mathematical framework capable of describing the entirety of the known universe, i.e. puts together quantum theory and general relativity. this means that gravity is tied up with the three other fundamental forces in one model.
in this model, everything is made of unbelievably tiny strings, whose vibrations produce effects that we interpret as atoms, electrons and quarks.
“In order for that to work, string theory has to make one more radical assumption. that instead of living in a universe with three dimensions of space and one of time, we live in one with either 9, 10 or 25 dimensions of space. These extra dimensions are then curled up so tightly that we don’t notice them – much like a silken thread appears one-dimensional until you get tlose enough to notice its width. this process of curling up, or “compactification”, can be done in countless billions upon billions of different ways. each compactification produces a different spacetime, meaning that string theory can realistically predict a multiverse populated by 10^500 different universes.”
and then, there is brane cosmology ...
the brane multiverse postulates that our universe exists on a membrane which floats with other membranes in a space of higher dimension or "bulk" or "hyperspace". branes are a fundamental object in string theory, just like strings. each brane has its own universe. in some versions of this cosmology, the electromagnetic, the weak and strong nuclear forces are restricted to one brane, but gravity is not, which nices solves the "hierarchy problem", i.e. explains why gravity is so weak compared to the other fundamental forces.
some readings
1960s: Vera Rubin and dark matter: https://www.popularmechanics.com/science/energy/a24501/vera-rubin-the-mother-of-dark-matter-dies-at-88/
2017: multiverse explains dark matter and dark energy: https://ccsenet.org/journal/index.php/apr/article/view/65884
2021: black holes and the multiverse could account for all dark matter, astronomers claim https://www.sciencefocus.com/news/black-holes-and-the-multiverse-could-account-for-all-dark-matter-astronomers-claim
2022: baby universes could present as primordial black holes https://www.innovationnewsnetwork.com/baby-universes-present-primordial-black-holes/8580/
2022: standard model of particle physics: beauties and shortcomings (examples: 1) particle accelerators who that each particle has its own antiparticel but cosmological and astrophysical observations show that most of the matter in our universe is made or particles. there is matter-antimatter asymmetry (Charge conjugation and parity reversal = CP problem; strong CP problem is at the level of the strong nuclear interactions; 2) dark matter is necessary to explain the amount of mass in the universe according to gravitational effects); axion as solution to the strong CP problem: https://www.science.org/doi/10.1126/sciadv.abj3618
2022: dark matter and axions: https://www.wowstem.org/post/chanda-prescod-weinstein https://www.popularmechanics.com/space/deep-space/a44690546/fuzzy-axion-dark-matter-theory/
2023: Dr Chanda Prescod-Weinstein: axion chaser https://www.wowstem.org/post/chanda-prescod-weinstein
2023: the evidence is building that dark matter is made of axions https://www.universetoday.com/162008/the-evidence-is-building-that-dark-matter-is-made-of-axions/
2023: dark matter: time for axion https://news.cnrs.fr/articles/dark-matter-time-for-axion
2023: is dark matter fuzzy https://www.space.com/dark-matter-fuzzy-ultracold-state-of-matter2023: if dark matter is fuzzy, then how fuzzy is it?https://www.mpa-garching.mpg.de/1076681/hl202306
2023 PR: fuzzy dark matter at Newcastle university https://www.ncl.ac.uk/press/articles/latest/2023/06/fuzzydarkmatter/
2023: astronomers discover new link between dark matter and clumpiness of the universe https://phys.org/news/2023-06-astronomers-link-dark-clumpiness-universe.html
2024: axion dark matter https://www.sciencedirect.com/science/article/pii/S055032132400066X#:~:text=As%20a%20result%20the%20axions,dark%20matter%20of%20the%20Universe
2024: primordial black holes contain very little dark matter https://physicsworld.com/a/primordial-black-holes-contain-very-little-dark-matter-say-astronomers/
2024: there could be a mirror universe: https://www.popularmechanics.com/science/a60178516/dark-mirror-universe/ https://www.livescience.com/space/cosmology/there-may-be-a-dark-mirror-universe-within-ours-where-atoms-failed-to-form-new-study-suggests
2024: what is dark matter? https://www.space.com/20930-dark-matter.html
2024: why we might live in a multiverse https://www.scientificamerican.com/article/heres-why-we-might-live-in-a-multiverse/books
Govert Schilling. The Elephant in the Universe: Our Hundred-Year Search for Dark Matter (2022) https://www.hup.harvard.edu/books/9780674248991
Chanda Prescod-Weinstein. The Disordered Cosmos: A Journey into Dark Matter, Spacetime and Dreams Deferred (2022) https://www.akpress.org/the-disordered-cosmos.html
Gianfranco Bertone. A Tale of Two Infinities: Gravitational Waves and the Quantum Origin of the Universe’s Biggest Mysteries (2021) https://global.oup.com/academic/product/a-tale-of-two-infinities-9780192898159?cc=ch&lang=en&
Aurélien Barrau. Au coeur des trous noirs (2017, 2024) https://www.dunod.com/sciences-techniques/au-coeur-trous-noirs-1
Aurélien Barrau. Big Bang et au-delà (2013, 2016, 2023) https://www.dunod.com/sciences-techniques/big-bang-et-au-dela
Aurélien Barrau. Anomalies cosmiques: la science face à l’étrange (2024) https://www.dunod.com/sciences-techniques/anomalies-cosmiques-science-face-etrange-0
Aurélien Barrau. Il faut une révolution politique, poétique et philosophique: entretien par Carole Guilbaud (2022) https://www.zulma.fr/livre/il-faut-une-revolution-politique-poetique-et-philosophique/
Aurélien Barrau. L’hypothèse K: la science face à la catastrophe écologique (2023) https://www.grasset.fr/livre/lhypothese-k-9782246837145/
Michael S. Walker. Quantum Fuzz: The Strange True Makeup of Everything (2017) https://www.prometheusbooks.com/9781633889057/quantum-fuzz/
Brian Greene https://www.briangreene.org/books-and-writings/
