The Multiverse Theory

[SparkyRailgun]

They say that life is a series of awakenings. It is a process of discovery about yourself and your relationship to the world around you. Some realizations are so profound they change your worldview forever, especially those which challenge the core views of our own nature and the nature of reality which gives rise to the external world.

The process of discovery is not limited to individuals but also occurs in the macrocosm of society as well. When science discovered that our earth is not the center of everything, it came as a surprise. It was also a revelation when we discovered that our sun is just one star in a galaxy with billions of other stars, and that our Milky Way is just one galaxy within the universe, which happens to contain billions of other galaxies as well.

We had become insignificant in the grand scheme of things, a blue speck in an ocean of darkness punctuated only by dim points of light from other suns unimaginably far away.

One of the interesting things about the process of discovery is that it never ends. Perhaps our enlightened view of reality may yet be too limited. Why limit ourselves to just one universe? Perhaps there are more…perhaps infinitely more. It is this thought which is gaining an ever-increasing following among scientists and philosophers because of its great utility in solving difficult conceptual problems in modern physics. It is also an idea which I have come to believe is true and which provides an endless source of inspiration.

The set of all universes is called the ‘multiverse’—it is within this infinite realm of possibility space that we find ourselves to be…welcome…

Reasons to Believe

There are many reasons to believe in the multiverse, some are scientific and others philosophical–I will outline those which are compelling to me personally. These items will no doubt serve as inspiration for future articles on RealityCipher.

1. The Quantum Measurement Problem

Quantum systems behave very differently from the macroscopic objects we interact with in our everyday life, so our common sense and intuition doesn’t help us very much in trying to understand them. One of the counterintuitive features of quantum systems like atoms, electrons, etc is that they can exist in a ‘superposition’ of states simultaneously, i.e. they don’t always have well-defined positions, momenta, etc. and can exist in all of their possible states (aka eigenstates) at once!

When we make some kind of measurement of the quantum system, it seems to be forced to make a choice and so we find that it exists in only one of its eigenstates after we make the measurement—it’s as if the set of all possibilities for the quantum system has suddenly been reduced to a single one by the process of measurement. This process of reduction is sometimes referred to as the ‘collapse of the wavefunction’. The wavefunction is the mathematical description of a quantum system which takes into account all of its possible states.

The Copenhagen Interpretation of Quantum Mechanics asserts that the wavefunction collapse is literally true and that classical, macroscopic systems have the ability to collapse the wavefunction of quantum systems.

There are conceptual problems with this—why must we make the quantum/classical distinction?–or the observer/system distinction? What happens when a mesoscopic system (which is larger than a quantum system but smaller than a macroscopic system) ‘measures’ a quantum system? Or two mesoscopic systems measure each other? When exactly does the wavefunction collapse? The Copenhagen interpretation has no clear answers for these questions as far I know.

These types of problems with the Copenhagen interpretation have caused some people to become disenchanted with the idea. One of these people was Hugh Everett, who published an alternative explanation in his PhD and related work at Princeton in 1957. In his “Relative State Formulation of Quantum Mechanics”, he showed that wavefunction collapse was not necessary. Instead, the quantum system and measuring device become correlated to each other in a special way—they become ‘entangled’ in quantum mechanics terminology.

The Copenhagen interpretation takes too much of an observer-centric view. The wavefunction only appears to collapse because all the eigenstates of the joint (quantum+observer) system are orthogonal, i.e. along separate branches of the complete wavefunction. In other words, it’s not just the quantum system being measured that spans multiple possibilities, but the observer does as well—each possible measurement outcome has a slightly different version of the observer associated with it, each sitting in his or her own private universe.

The idea is elegant and it solves the conceptual problems with quantum measurement in a much cleaner way, and allows us to remove the redundant postulate of wavefunction collapse from quantum theory, thus simplifying it. This interpretation of quantum mechanics was later popularized by Bruce DeWitt who called it the Many Worlds Interpretation (MWI).

All ‘Non-Collapse’ Theories are Variants of the Many-Worlds Interpretation (MWI)

Although it is true that other interpretations of quantum mechanics explain the apparent collapse of the wavefunction differently, all of the ‘no-collapse’ interpretations are really MWI in disguise. For example, the quantum decoherence view and the Transactional Interpretation of Quantum Mechanics both remove problems with deciding when the ‘collapse’ occurs and remove the requirement for a conscious observer, but still involve an exponential number of physical resources.

In the decoherence framework, the coherence of the quantum state ‘leaks’ into the environment (or perhaps the other way around) and this looks like wavefunction collapse even though the combined system (quantum system + environment) remains in superposition.

In the Transactional Interpretation, we end up with a very large number of offer/confirmation waves that are generated when complex systems interact. It seems that a high-dimensional state space is an inherent aspect of quantum theory—one that we can’t really get away from. This means that even if we only have one quantum ‘world’, this will correspond to an exponentially large number of ‘classical’ worlds.

2. Reality Bootstrapping

In Hans Moravec’s fascinating article “Simulation, Consciousness, Existence”, he makes an important and relevant observation: there is no information without selection. In the ‘Everything and Nothing’ section of that article he writes:

“There is no content or meaning without selection. The realm of all possible worlds, infinitely immense in one point of view, is vacuous in another. Imagine a book giving a detailed history of a world similar to ours. The book is written as compactly as possible: rote predictable details are left as homework for the reader. But even with maximal compression, it would be an astronomically immense tome, full of novelty and excitement. This interesting book, however, is found in “the library of all possible books written in the Roman alphabet, arranged alphabetically”—the whole library being adequately defined by this short, boring phrase in quotes. The library as a whole has so little content that getting a book from it takes as much effort as writing the book. The library might have stacks labeled A through Z, plus a few for punctuation, each forking into similarly labeled substacks, those forking into subsubstacks, and so on indefinitely. Each branchpoint holds a book whose content is the sequence of stack letters chosen to reach it. Any book can be found in the library, but to find it the user must choose its first letter, then its second, then its third, just as one types a book by keying each subsequent letter. The book’s content results entirely from the user’s selections; the library has no information of its own to contribute.

Although content-free overall, the library contains individual books with fabulously interesting stories. Characters in some of those books, insulated from the vast gibberish that makes the library worthless from outside, can well appreciate their own existence. They do so by perceiving and interpreting their own story in a consistent way, one that recognizes their own meaningfulness—a prescription that is probably the secret of life and existence, and the reason we find ourselves in a large, orderly universe with consistent physical laws, possessing a sense of time and a long evolutionary history.

The set of all possible interpretations of any process as simulations is exactly analogous to the content of all the books in the library. In total it contains no information, yet every interesting being and story can be found within it.”

So, the library of all possible books contains all information and no information at the same time. If you partially specify a desired book (e.g. the first L letters), you are left with an infinite number of books that match your partial specification and so this requires further disambiguation. Therefore the library is content-free overall since the only way to specify the book you want is to write it!

The Everything-and-Nothing concept may provide the most compelling philosophical reason for believing in the multiverse. The multiverse represents a kind of library of all possible worlds and so we see that our universe necessarily exists because all possible worlds exist. The multiverse is also content-free with no net information, energy, etc. and so has no prerequisites for its own existence.

Any particular reality is able to bootstrap itself into existence because all possible realities exist, and the set of all possibilities is itself a void, requiring no explanation. This idea is beautiful, elegant, and profound with many Taoist concepts interwoven throughout.

The multiverse additionally explains our “cosmic fine-tuning” observations that our universe seems to be so perfectly fit to produce us. The fundamental physical constants have only a very narrow window of values that allow stable matter, chemistry, biology, etc. It appears that the universe must either be designed or there must be an astronomically large number of them for there to be any reasonable chance for ours to occur.

3. Quantum Computing

The novel features of quantum systems—superposition, interference, entanglement—have given rise to a new theoretical class of computer called a quantum computer. Quantum computers have capabilities that far surpass our current computers, especially for certain types of algorithms.

A quantum computer could easily break RSA public-key encryption by efficiently performing integer factorization, and by ‘efficiently’ I mean exponentially faster! How can it do this? Since quantum systems can exist in a superposition of all possible states, they have massive parallelism, i.e. they can ‘explore’ many possible solutions all at once and utilize constructive interference to cause the desired solution to be present at the output with high probability and destructive interference to cancel out the non-solutions.

Quantum logic gates perform phase shifts and entanglement operations on the quantum bits (qubits) and are able to compute any logic operation our digital computers can, it’s just that they can perform some classes of computation much, much more efficiently.

What does this have to do with the multiverse? It’s extremely difficult to understand how a quantum computer can calculate results exponentially faster than our digital computers unless it has access to exponentially more physical resources, i.e. parallel universes. After all, computation requires physical resources.

David Deutsch of Oxford University believes that quantum computers prove the existence of parallel realities–there is just no other explanation for their capabilities.

The realization of practical quantum computers is still probably many years away since they are notoriously difficult to manage due to the requirement of strict isolation from the environment in order to maintain their pure coherent quantum state. Nevertheless, I believe there is general optimism that these problems are not insurmountable and when the first ‘real’ quantum computers are running, it will provide strong empirical evidence for the multiverse.

4. Cosmological Observations

The discipline of quantum mechanics, the physics of very small-scale systems, has led to the idea parallel universes. It is very interesting to me that our study of the cosmology, the study of the largest scale structures and dynamics of the universe, is also suggesting the existence of the multiverse.

Our current cosmological observations suggest that space is infinite and nearly uniformly filled with matter. Since there are only a finite number of quantum states in a given volume (for a given temperature) then we must conclude that structures eventually repeat themselves when we consider a larger volume that exhausts all the these possibilities. In an infinite space filled with matter that can exist in only a finite number of ways, all permutations are played out—this forms the basis for a cosmological version of the multiverse.

In Max Tegmark’s excellent article on Parallel Universes in Scientific American, he describes these ideas in detail and also describes many other categories of parallel universes. By his calculation, you have a twin approximately 10 to the 1028 meters away…

All Roads Lead to the Multiverse

The existence of the multiverse seems to be an inescapable conclusion based on theoretical, philosophical, and empirical reasons. I believe it will someday be common knowledge, just as our knowledge of stars and galaxies is today. The multiverse provides a solution to many puzzles but also introduces a few new ones:

How should we define personal identity if there are an infinite number of near-identical copies of you spread across an uncountable number of parallel realities?
If all possibilities are realized, what does this imply about the nature of our choices and the Free Will vs. Determinism debate?
Do these parallel worlds offer a kind of immortality? If a person’s life story ends in one reality can it be picked back up in a parallel one, providing subjective continuity?
What does it all mean?

I believe that it shows both how truly insignificant and special we are. Against the backdrop of infinite chaos, of an uncountable number of noise universes, we dare to exist, make choices, find love, and live our lives. It means that reality itself is inexhaustible—anything that I can imagine is out there somewhere as well as an infinite number of other things beyond the horizon of my imagination.

It means that I always have a choice and there is always hope…

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