Imagine this scenario: a version of you in a parallel world is leading a life you regretted quitting during your senior high school. “The road not taken,” in fact, has already been taken by you in another alternate reality (Frost, 1995, p.207). Furthermore, multiple copies of you are working in various occupations in different worlds and realizing all your potential. This fascinating picture recapitulates the essence of the multiple universes. Amazing as it is, how plausible is the multiverse? This article aims to investigate the possibility of the multiverse and its consequent influence on human beings.                                                                              

Hugh Everett III first proposed the concept of multiple universes in his Ph.D. thesis “The Theory of the Universal Wave Function” in 1957 and now his Many Worlds Interpretation becomes a mainstream voice of the multiverse. It consists of two cornerstone concepts of quantum mechanics: superposition, the quantum state of the universe, and measurement, a localized quantum state at a given position. Two well-known examples are often cited to illustrate these elusive concepts. First of all, the double-slit experiment divulges the Wave function of particles. If we shoot electrons, photons, or atoms through a single slit in a barrier, we will see one line of particles on the screen on the other side. If we add one more slit and shoot particles through two slits, or double slits, an amazing phenomenon occurs. Contrary to our expectation of two lines, multiple lines appear on the screen, which violate the law of classical physics. One possibility is that particles interact with each other and produce a wavelike interference (O’Dowd, 2016; Muller, 2020). To consolidate this hypothesis, physicists conducted the experiment again: to fire electrons one by one through double slits, still, multiple lines of particles appear on the screen. Particles, therefore, are not isolated entities, but “wavicles”: “pointlike particles are also waves” (Temming, 2019). This Wave function of each particle is superposition, which includes all its possible trajectories. In this case, one particle may simultaneously take both paths, traveling through the double slits, and thus create numerous lines on the screen. To verify the trajectory of electrons, the scientists install a device to observe the process, then a more miraculous phenomenon takes place. The electrons fired through the double slits formulate TWO lines on the screen, and the wavelike interference pattern disappears (“First-Ever Evidence,” 2022). Observation has actually changed the entangled quantum state and produced a different reality. This process is called measurement.

Erwin Schrödinger’s thought experiment is another compelling example. A cat is placed inside a sealed steel chamber, along with a flask of poison and a Geiger counter. The counter has a bit of radiative substance which has an equal probability of decaying and not decaying. If one of the atoms decays, it will trigger the device to shatter the poisonous flask and kill the cat. If not, the cat is alive. Therefore, before opening the box, the atom is in a state of superposition: both decayed and not decayed; likewise, the cat is also in a state of superposition: it could be dead, alive, and even both dead and alive. In this way, “an indeterminacy originally restricted to the atomic domain becomes transformed into macroscopic indeterminacy, which can then be resolved by direct observation” (Schrödinger, 1935, p.328). When an observer opens the box, the quantum state collapses into a localized state: he could only see one state of the cat, either dead or alive. This process is called measurement, or, to be more precise, decoherence, because of its environmental interaction. However, from the perspective of the cat, the observer and his environment are also in a quantum state. In other words, the universal Wave function does not collapse, at least not collapse to one reality. The moment the observer opens the box, he gets quantumly entangled with the cat and “decoheres the branching of the Wave function” into a reality in which he sees the cat dead; but it also produces another alternative reality in which he sees the cat alive (Muller, 2020). These two versions of him inhabit different worlds and do not interact with each other.

Scientists agree on superposition but disagree on measurement. Everett (1957) proposes “relative state functions” to identify stable structures within the Wave function that will be localized into many worlds (p.33). “Spontaneous Collapse Theories,” advocated by Ghirardi Rimini and Weber, contend that particles undergo localization at random times and collapse independently (Bacciagaluppi, 2020). Another compelling school of the multiverse is “Hidden Variables” approaches, among which de Broglie and David Bohm’s “Pilot Wave Theories” are the most developed model. These scientists argue against simultaneous collapse and for the evolution of the multiverse. “The total configuration is ‘trapped’ inside a single component of the Wave function, which will guild [pilot] its further evolution” (Bacciagaluppi, 2020). Different from de Broglie and David Bohm, Niels Bohr construes the multiverse as “a symbolic representation, a shorthand for the quantum phenomena that are constituted by applying the varying complementary classical pictures” (Bacciagaluppi, 2020). For J. von Neumann (1955), the reality is already an interaction of “psycho-physical parallelism,” and if we want to obtain purely physical phenomena, a movable boundary must be drawn between the observer and the observed (p.420). Apart from these mainstream theories of the multiverse, there are other influential interpretations. Our reality, Julius Brown (1990) argues, is merely a simulation program running on a gigantic cosmic computer and there are millions of worlds like ours in the cosmos (pp. 37-39). Besides, J. Garriga et al (2016) explore the multiverse from the perspective of the Big Bang Theory. After inflation ends, vacuum bubbles eventually become black holes. If the bubble’s mass is smaller than a certain value, the bubble “collapses to a singularity” (p.2). Otherwise, the bubble grows exponentially and infinitely. “This leads to the formation of a wormhole which eventually ‘pinches off’ leading to a baby universe” (p.9). The infinite expansion of the bubble, Garriga and his fellow scientists conclude, is “leading to a multiverse structure” (p.9).

Our scientific investigation of superposition and measurement demonstrates the solid theoretical foundation of the multiverse. To be accepted as “true” also calls for empirical evidence. That is, whether we regard the multiverse as true or not, also depends on the “correspondence between the quantum state of the Universe and our experiences” of the world (Vaidman, 2021). On the level of theory, scientists, based on quantum mechanics, have made many astonishing discoveries that have an amazing degree of accuracy with quantum predictions. Brian Greene (2011) draws an impressive diagram to illustrate the matching precision between the theoretical curve of “the cosmic microwave background radiation” and “the observational data” indicated by small circles (p.61).

The multiverse is also built on such a solid theoretical foundation of the universal Wave function. Stephen Ornes compares quantum theory to be a magic “recipe.” “Using quantum theory to build technology is like following a recipe without knowing how food changes as it cooks. Sure, you can put together a good meal” (Ornes, 2017). Likewise, quantum mechanics detects the existence of the multiverse, although scientists at the current time could not figure out where and why many worlds exist.

To be true, by the standard of classical physics, it must be verified by evidence. Despite limited resources, scientists do discover compelling evidences of many worlds. In 1964, Arno Penzias and Robert Wilson discovered cosmic microwave background radiation (CMB) and won the 1978 Nobel Prize in Physics. Continued expansion of the universe over the eons leads to the fluctuation of temperature around 2.7 degrees Kelvin. However, an extremely abnormal “Cold Spot” in the constellation Eridanus violates the law, and becomes known to many scientists as the “Eridanus Supervoid.” “The Cold Spot was caused by a collision between our universe and another bubble universe.” Professor Tom Shanks concludes: “the Cold Spot might be taken as the first evidence for the multiverse – and billions of other universes may exist like our own” (Shanks, 2017). The solid theoretical foundation, together with compelling scientific evidence, reveals to us the hidden reality of the multiverse. 

If we came to know the theory of the multiverse was true, it would revolutionize our life in a profound way. First of all, it challenges the uniqueness of individuals. Each individual, we believe, is a unique entity in terms of his/her biological life (DNA) and intellectual life. The multiverse, however, suggests that numerous copies of “I” who have the same DNA and same mindset inhabit different parallel worlds. This naturally casts a shroud on our cherished value of uniqueness: I am just one of many copies who simultaneously exist in different hidden worlds. The challenging definition of self, as a replicant rather than a unique individual, compels us to painfully reconstruct the position of human beings in the universe.

Furthermore, the multiverse bulldozes free will. People have free will to choose what they like, refuse what they dislike, and take the corresponding consequences. This becomes not only the creed of individualism but also the keystone of modern society. What if, we are told, free will is just an illusion? This is precisely the harsh reality that the multiverse exposes us to. At the moment of measurement or decoherence, the universal Wave function branches out of many worlds, and the observer is thrown into one alternate reality. In other words, our destiny is already chosen, without our knowledge, and cast into one of many worlds. Free will is merely an illusion. “Waves simply evolve from one shape to another in a manner described fully and deterministically by Schrödinger’s equation” (Greene, 2011, p. 228).[1] If “Life, Liberty, and the pursuit of Happiness” are “self-evident truths” to modern citizens (“Declaration of Independence,” 1776), the multiverse denies the unique biological life of individuals, deprives them of their “unalienable right of liberty,” and precipitates them into the perplexity of the world. Despite its perplexing effects, the multiverse furnishes us with a window to catch a glimpse of the hidden truth and compels us to transform our inveterate epistemology.

The multiverse, along with its theoretical foundation of quantum mechanics, is bound to reshuffle our epistemological edifice. In classical physics, scientists do experiments, observe results, and gain knowledge of the world. Our knowledge of the world, we assume, is the way the world unfolds itself. However, quantum mechanics on which the multiverse is built bulldozes this ingrained epistemology. The nature we are observing is not nature itself, but its responding way to our method of observation. Like the Wave function in a constant process of becoming, it collapses into a fixed reality at the moment of our observation. Unfortunately, we hold this fixed reality as the complete gamut of the constantly becoming cosmos. In fact, our reality, quantum mechanics informs us, merely serves as a window to usher us to have a glimpse of infinite universes in the cosmos. These unknown territories, daunting but captivating, await our exploration.  

Despite the controversy, the multiverse becomes a hidden reality for many scientists. Superposition and measurement, two cornerstone concepts of quantum mechanics, become the solid theoretical foundation of the multiverse. Moreover, the discoveries of the cosmic microwave background radiation and the “Eridanus Supervoid” consolidate the empirical existence of many worlds. The multiverse, even if it could not be completely testified, is bound to be a paradigm shift of human epistemology toward life, liberty, and the pursuit of truth.

Notes

[1] Different from the Many Worlds approach, in the Copenhagen approach, “‘dice throwing’ makes an appearance” (Greene, 2011, p. 228). An individual’s life is determined very much like the spinning “roulette wheels” (228).

References 

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