A Multitude of Multiverses
Visions of the Multiverse:
Is our Universe One of Many?
By Steven Manly
Outside of Hollywood and Hogwarts, the idea of a multiple universe reality seems
rather ludicrous if you think about it. After all, the universe includes the
totality of space and time and energy and physical constants and dogs and, yes,
even teenagers. It's such an all?inclusive definition that it's hard to imagine
that there's more to things. How, then, can there be multiple universes?
Let's forget the idea of multiple universes for a moment and ponder the
concept of a single, simple, solitary, stand‐alone
universe. To me,
is a term used to denote everything that exists physically. But, what does it
mean to say something exists physically? The implication is that we can
experience it somehow
we can smell it or taste it or ferret out a signal implying its existence using
a sensitive scientific experiment. Is it possible to imagine realms that might
exist without a physical or causal connection to our known universe? You bet. It
is possible to imagine such realms and that's where the multiverse comes
It's not just the multiverse, however, for there isn't a single
such concept. Rather there are many different multiverse concepts, some inferred
from modern science while others are more a matter of faith. The exact number of
multiverse schemes floating around is difficult to pin down since it depends a
bit on who you ask and how they define a multiverse. In a recent survey of
subject I ran across eleven distinct multiverse concepts.
Though the thought of being part of more than one multiverse is delightfully
perverse, the plurality of multiple universe concepts makes the situation very
confusing. It is helpful to classify the multiverse schemes in terms of how the
universes are separated: by space and/or time, along dimensions other than space
and time, or by faith.
multiverse concepts are nothing new. They are, as you might expect from the
name, a matter of faith and not inferred from current scientific theories. For
example, many people believe deeply in separate planes of existence. Consider
the Christian concept of Heaven. A common theme is that Heaven is a separate
plane of existence where a soul enjoys eternal life and pleasure in God's
presence and in the presence of other elect souls. There's nothing in this that
a physicist would consider as
a scientific, causal connection between Heaven and our universe. Consquently,
idea is a form of a multiverse
multiverses are advocated by the adherents of most other religions.
Though these visions may be different in detail, I categorize them all as a
single multiverse concept.
Multiverse concepts inferred from mainstream scientific theories are quite new,
having been driven by ideas in quantum mechanics and cosmology in the last
hundred years. Perhaps the most recognized multiverse concept of this was
developed in the mid-1950s by young physicist named Hugh Everett. It lies at the core of quantum
mechanics and involves parallel universes separated by dimensions other than
space and time. Quantum mechanics is quite unlike other areas of physics.
Generally, physical theories lead to a particular outcome for a particular
situation. If you throw a rock at this angle and that speed, a physicist can
calculate exactly where it will land. In quantum mechanics, however, the outcome
of physical processes cannot be predicted exactly. Instead, what is calculated
is a probability distribution of what can happen. In Everett's interpretation of
quantum mechanics, known as the many worlds interpretation, in each quantum
mechanical process all possibilities that could happen actually do
happen and evolve as separate emergent realities in the overall description of
the universe. The mathematical space used in the quantum mechanics calculations
includes not only the three dimensions of space and the dimension of time, but
also other quantities relevant for the calculation -- the momentum or the
orientation of a particle that is part of the calculation, for example. Those
other quantities are treated in the calculation as if they are additional
dimensions in the problem. The different threads of reality emerging from a
quantum process occupy different places in the overall mathematical space used
in the quantum mechanical calculation -- in much the same way things can be
separated by distance along spatial dimensions in normal space. These emergent
threads of reality are causally disconnected once separated and effectively
become parallel universes in a multiverse which I call the many worlds
Most of the newer multiverse concepts arise from cosmology. Generally, these
multiverses tend to have universes separated in space and/or time.
The leading scientific theory of the evolution of our universe is called the
inflationary, hot big bang model. In this theory, what became our universe
started out very tiny -- perhaps as a quantum fluctuation. Then, in the briefest
of instants, it became vastly larger than the observable universe at that time
through a process called inflation. After this moment of inflationary
expansion, the expansion of the space slowed dramatically and the energy driving
the expansion was dumped into the radiation and subatomic soup of particles of
the early universe. As the universe continued to expand and cool,
the particles and forces evolved into what is observed today and gravitation
caused the material in the higher density regions to collapse into the stars and
galaxies that surround us.
Two distinct multiverse concepts are spawned naturally in the inflationary, hot
big bang picture. During the period of inflation in the early universe, the tiny
region including what became our universe was blown up to be vastly larger than
our observable universe. This means there are regions of the greater reality
which are similar to what we see in our universe in terms of basic physical laws
and yet are so far removed from us (and each other) that they are now, and will
always be, out of causal contact with us. These regions collectively constitute
a multiverse, which I call the beyond‐the‐horizon
Within this multiverse, causally disconnected regions share the same
physical laws but differ in terms of their initial matter density distributions.
The initial matter distribution in the universe ultimately determines the
structure in that universe like stars and galaxies and dogs. Physicists have
calculated the number of such causally‐disconnect
regions in the beyond‐the‐horizon
multiverse to be larger than the number of possible variations in the initial
conditions -- meaning that all possibilities for the initial conditions must be
present in the multiverse. Anything that could happen does happen
within the greater multiverse.
The second multiverse springing from the hot big bang model arises because
inflation, once started, may not stop except at random points where quantum
fluctuations in the characteristics of the space cause inflation to stop. This
effectively leads to a greater reality consisting of an eternally inflating
matrix of space in which bubble or pocket universes are formed in the random and
causally disconnected spots where inflation stops. This is known as the
bubble multiverse. Each bubble universe within this multiverse might have a
different dimensionality and a different set of physical constants. In other
words, our universe is part of just one bubble in the great bubble multiverse
and the physical laws and forces and particles present in the other bubbles are
different from what we see, with all possibilities being represented in the
The examples above illustrate one of the most intriguing aspects of this
business. The bubble multiverse, if it exists, contains regions within it that
are, potentially, beyond‐
multiverses. In addition, the many worlds picture of quantum mechanics might
underlie the physical processes taking place throughout the bubble multiverse.
Three multiverses in one! Yikes!
The great reality in which we live may consist of multiple multiverses.
The question is not "do we live in a multiverse?" Rather it is "do we
live in multiple types of multiverses and, if so, which ones?"