By Leo Li
Before sci-fi writers and Marvel’s founding fathers began exploiting the (meta-)physics of the multiverse, physicists and cosmologists — atavistically resembling their Greek philosophising counterparts — had already conceived of this dangerous notion. The fictional pens gave the multiverse its name and fame, but the empirical minds imbued reality and possibility into what otherwise would be considered lunacy and sorcery.
Multiverse (n.): a group of universes which contains our Observable Universe. Cosmologists taxonomise universes in subgroups — like Max Tegmark’s four levels and Brian Greene’s nine types — according to different multiverse theories. Notable theories are the Big Bubble, the many-worlds and M-theory. Before examining some of these theories, let us first revisit the history of our Cosmos. In the beginning the Cosmos created space and time. It had existed as a Big Bang singularity before, one in which the laws of physics break down. Then, from unity sprang out one after another the four fundamental forces: gravity, the strong nuclear force, the weak nuclear force, and electromagnetism.
Gravity is the only one out of these four horsemen which disobeys the principles of quantum mechanics, the darkness that governs the microscopic, and instead allies with general relativity, the light that governs the macroscopic. The darkness and the light disagree with each other. The darkness dominated before the light came about. In the first 10-43 seconds after the Big Bang known as the Planck era, the cosmos was a fathomless sea of quantum fluctuations. Afterwards, along with the Light came the Inflationary Era, which occurred 10-36 seconds after the Big Bang. In the span of 10-32 seconds, our observable universe expanded exponentially in spacetime and became the flat universe we are familiar with today, only devoid of galaxies, stars and our little blue planet. Inflation ceased at the 10-32-second mark, but our observable universe’s spherical causal boundary — the cosmological horizon — continues expanding even now, constantly being pioneered by photons emitted 14 billion years ago.
How does the multiverse fit into this narrative then? Well, it doesn’t fit in, but out! Our bubble of universe is named the observable universe precisely because we cannot see what lies beyond its cosmological horizon. Light signals beyond the horizon, travelling at max speed c, are undetectable. We are cursed by the second postulate of relativity, blinded to what lurks in the unobservable cosmos. It can be infinitely many bubble universes similar to ours. Every one of them is like a snow globe which contains a cosmological habitat governed by a different set of physical laws. They are a product of eternal inflation, a proposal that inflation never ceased at the 10-32-second mark, but has only been shredding off anomalous and self-contained fractal-volumes of bubble universes, none of which participate in the exponential expansion ever again.
Another more quantum mechanical theory imagines universes in the multiverse landscape as forking rivulets instead of dissociated bubbles: the many-worlds theory. Near-perfectly encapsulated by the Marvel TV series Loki, the Multiverse River encounters a branch point at an event which has multiple outcomes.
Instead of classical determinism, quantum mechanics’ principle of superposition — the ‘lunacy’ Schrödinger introduced in the infamous 1952 Dublin lecture — dictates that all outcomes occur all at once. Exempted from the manipulation of Marvel’s Time Variance Authority, parallel rivulet universes are constantly created. Some physicists view the Big Bubble theory as a redundancy or a self-explanatory component to the many-worlds interpretation. Bubble universes, rather than being paper cut-out copies, are organic, fluid variants of each other, like living cells undergoing reproductions and mutations.
Superseding general relativity and quantum mechanics is (super-) string theory, which gives birth to the notoriously abstract M-theory. In this theory, constituent elementary particles up to entire composite universes are contained in branes, a hyper-dimensional abstraction which ushers in extra dimensions.
The cosmos, at the end of the day, would have 9 spatial + 1 temporal = 10 dimensions. It has more than enough spacetime to encapsulate our 4D (3 spatial + 1 temporal) observable universe, and thus could accommodate many other universes existing in different dimensions.
Notwithstanding the plethora of possibilities, the multiverse theory is embroiled in much controversy for our inability to either empirically validate or falsify it. Its metaphysical edge, though of great novelistic value, provokes many scientific purists who predicate their theories solely on empirical inductions and logical deductions.
However exciting it is to see beyond our universe’s horizons, it is crucial we look within them for evidence to the multiverse. Studying what exactly occurred during and before Inflation could be the critical spell to transmute mysticism into robust scientific enquiries.
After all, any sufficiently confounding cosmic mystery is indistinguishable from magic; what demystifies sorcery, or elevates it through understanding, is a venturing and enquiring passion for the unknown.
Illustration: Adeline Zhao