Length. Width. Height. Duration.
Cue Sesame Street soundtrack and sing along:
One of these things is not like the others,
One of these things just doesn’t belong...
You pluck out “duration” prior to finishing the popular jingle, but there’s far more to the comparison than merely space (length, width, height) versus time (duration). That fourth dimension is laden with implications about our very existence.
Humans experience time differently from space. We can retrace our steps and return to any location in space but time moves relentlessly forward. What happens “before” affects what happens “after” but never the reverse. The Bible, in contrast to the prevailing ancient Near Eastern way of thinking about time,1 accurately described (at the time it was written) this property of the universe, known as causality. Recent advances by scientists seeking to understand how space and time form and interact provide additional support for the biblical notion that causality arises from the Creator.
Earlier Research Leads to Dead-End Street
The Bible clearly states that the universe—and time in particular—had a beginning.2 And three seminal scientific advances during the twentieth century affirmed that statement: (1) Einstein’s theory of general relativity; (2) Hubble’s detection of the universe’s expansion; and (3) Hawking and Penrose’s space-time theorems. However, despite these advances, a vexing puzzle remained.
In relativity, gravity allowed scientists to understand how space-time can adopt many different shapes (think large scale). However, behavior of particles at atomic and subatomic scales (quantum mechanics) ignores gravity and has necessitated quantum theory. Attempts to unify both seemingly discordant physical observations have led scientists to pursue a theory of quantum gravity. String theory represents the most popular attempt to provide a quantum theory of gravity. According to this theory, a multitude of space-time configurations exist with different dimensionality and different laws of physics, but testing remains elusive.
A Road to Main Street
Another recent approach reveals some remarkable properties of the fabric of space-time.3 Instead of trying to develop an overarching theory that incorporates both gravity and quantum mechanics, this alternative approach seeks to build from scratch––using basic quantum mechanical principles––a space-time structure resembling this universe. Such a process ensures the outcome obeys quantum mechanics, while allowing the number and shape of the dimensions to unfold rather than be specified.
Initially, researchers simply started with some representative four-dimensional building blocks of space-time, then allowed them to interact under simple gravitational and quantum mechanical rules, and finally observed the outcome. With no additional input, the results ended at one of two different outcomes—neither of which resembled the stable four-dimensional universe in which we live.
Scientists derived two important conclusions from this work. First, the dimensionality of space is not a fixed quantity. Instead, dimensionality can fluctuate and change depending on how the fundamental constituents of space-time assemble. Second, large, smooth, four-dimensional universes like this one are not stable under these rules.
Realizing that something was lacking in their modeling studies, scientists searched for that missing component. They discovered that adding one simple building block––causality––to the structure resulted in stable, four-dimensional universes. In other words, if the interactions were required to operate such that time always progressed in a single direction, the quantum fluctuations of curvature did cancel out on large scales to produce “normal”-looking universes. Furthermore, the overall results remained unchanged even as a variety of small details changed.
The implications of this research are far-reaching. The arrow of time that allows us to distinguish the past from the future derives from something outside of space and time. Stated another way, something beyond this universe encoded cause and effect into the very fabric of space-time.
While past and future seem like obvious concepts to the average person, they don’t make as much sense from a naturalistic viewpoint. For example, the basic laws of physics work the same regardless of any direction to time. Given the conditions of a system (for example, an interacting group of subatomic particles), the laws of physics predict the state of the system at any other arbitrary time (past, present, or future). Yet people remember the past but must wait for the future to happen.
Ironically, the same publication that describes this research into causality and dimensionality published an article in the previous month’s issue utilizing a multiverse to explain the arrow of time exhibited by this universe.4 The appeal to a multiverse implicitly acknowledges the “beyond natural” (or supernatural) origin of causality in this universe.
Humans on Easy Street
The twentieth-century discovery of a cosmic beginning points to a “beyond natural” cause that brought the universe into existence. The arrow of time (that is second nature to us) also provides evidence that something supernatural affected the space-time fabric of this universe. Otherwise, this creation would not have the three spatial and one temporal dimension required for life.
Given the laws of physics, life requires a universe with three large spatial dimensions and only one time dimension. A universe with fewer spatial dimensions would not permit the spatial complexity life requires. On the other hand, a universe with more spatial dimensions would not allow stable atoms or stable planetary orbits—both of which play a critical role for life. Anything other than one time dimension means that the future or past state of a system would not relate to the present. In other words, a hypothetical living organism in such a universe would not be able to find food or elude danger because the past is unknowable and the future is unpredictable. By imposing causality on the fabric of space-time, a universe with three large spatial dimensions and one temporal dimension results. Causality allows this universe to be habitable.
Causality’s significance for humanity is staggering. Without causality, life becomes a mechanical existence devoid of any hope, joy, or intrigue (or even Sesame Street). Furthermore, although our past influences our future, it does not dictate future events. We can choose among a number of different paths for our future. Though sometimes taken for granted, a universe with such features rouses wonder and gratitude.
This article was originally published in RTB’s ezine, New Reasons to Believe (Summer 2009).