Time

The goal of this Tag is to assemble films with a fantasy or sci-fi bent in which the element of "time" plays a significant role. Particular attention will be given to the classic theme of time travel. Given the high level of interest this topic generally elicits, we thought it would be fitting to go into some depth here.

Time is something we all refer to every day, and it plays a fundamental role in all our lives, but comprehending its elusive nature has proven a formidable challenge for the human intellect. The great thinkers of antiquity wrestled with its mysterious workings, endeavoring to formulate a definition of time based on their own personal sensibilities and perspectives. Attempts ranged from the purely metaphysical viewpoint of the Pythagoreans ("Time is the all-encompassing sphere") to the physical-mathematical theory offered by Aristotle ("Time is the calculable measure of motion with respect to before and afterness"), all the way to the Augustinian conception, a sort of proto-existentialism ("Time is a distension of the soul that on one side turns to the past and on the other side to the future"). But when St. Augustine lamented his dissatisfaction with his own theories - "My soul yearns to know this most entangled enigma. I confess to Thee, O Lord, that I am as yet ignorant of what time is" - he could just as well have been expressing mankind's general frustration in attempting to fully understand this enigmatic concept.

The Heraclitean heritage which saw "temporality" as a linear progression of past, present, and future events was embraced by Newtonian physics which considered time as an absolute and independent parameter. Then came Albert Einstein who turned everything on its head in 1905. Working from two "simple" postulates - the special theory of relativity and the invariant speed of light - he concluded that time is relative. This was a revolutionary assertion not only because it made us realize that time is far more complex than had previously been assumed, but because the idea that time depends on motion suggests the intriguing possibility that it could somehow be manipulated. In fact, the temporal dilation predicted by special relativity has been experimentally demonstrated on more than one occasion. It's believed that at velocities approaching the speed of light, time dilation would actually send a hypothetical "chrononaut" into the future. Although theoretically sound, the countless practical obstacles are - for now at least - insurmountable. Einstein published his theory of general relativity in 1916, thus broadening the physical laws of special relativity to include non-inertial reference frames (i.e., a frame of reference that undergoes acceleration with respect to an inertial frame) (+). That brings us to the counterintuitive phenomenon of gravitational dilation of time which would permit travel into the future following prolonged proximity to an extraordinarily massive object (does the black hole in "Interstellar" ring any bells?). In fact, from the general relativity point of view, gravity isn't a force exerted by masses over a distance, but rather an effect of the warping of space and time caused by the matter and energy present in the cosmos (+).

Spacetime warping (or curvature) opens the door to the motherlode of time travel speculation - potentially traveling into the past. This possibility is closely linked to the theoretical existence of "closed timelike curves" (CTCs), curious trajectories in which a material particle eventually returns to the exact coordinates in time and space where it started, without violating the laws of special relativity (i.e., something traveling along a CTC could journey into the future but arrive in its past). That's why curvature is key: for CTCs to comply with the laws of relativity and not exceed the speed of light, spacetime cannot be flat. As the 1940s drew to a close, mathematician Kurt Gödel was among the first to find a solution (i.e., the "Gödel metric") to Einstein's field equations that was compatible with the presence of closed timelike curves. Working from his own calculations, he developed a "rotating universes" model which would theoretically allow travel into the past. Among various potential "time machines" proposed by eminent scientists based on this line of reasoning, we would cite the "Tipler cylinder" and Ronald Mallett's "Space-time Twisting by Light" (STL) project. So far, we've offered examples of theoretical devices designed to exploit closed timelike curves. But instead of attempting to identify spacetime configurations that would allow time travel within the constraints of general relativity, some conjectures take an entirely different tack, examining ways to circumvent those constraints altogether. Enter the famous "hyperspace", the perfect gimmick for making an end run around that frustrating limit prohibiting information from exceeding the speed of light.

Hyperspace as a sort of "cosmic shortcut" first appeared in science fiction in the early 20th century (+) and quickly became popular because the concept allowed for faster-than-light (FTL) travel, a core sci-fi trope. The ultimate cosmic shortcut, however, is represented by a hyperspace pathway called a "wormhole" (aka "Einstein-Rosen bridge"). As a spacetime singularity produced by two black holes, a wormhole would be consistent with Einstein's general theory of relativity, but its existence remains speculative. Even more speculative is the theory that a wormhole might be a sort of tunnel connecting separate, potentially distant points in time and/or space, or even different (parallel) universes. One of the many problems inherent in such intrinsically unstable tunnels (they would tend to collapse gravitationally) concerns how they could be kept "open" for potential travelers. In the case of the navigable wormholes described in Carl Sagan's "Contact" - the basis of the 1997 Robert Zemeckis movie of the same name - they were stabilized with the help of exotic matter with unknown antigravitational properties.

In science fiction (and other genres as well), time travel can take on even more bizarre forms than those mentioned so far: We've got Victorian steampunk-style contraptions ("The Time Machine" - 1960), magical portals ("Army of Darkness" - 1993), tachyon transmissions sent via dreams ("Prince of Darkness" - 1987), and even strange designer drugs ("Synchronic" - 2019). Then there's the time inversion concept - a clear violation of the second law of thermodynamics - which we find in both literature ("Counter-Clock World" - 1967; "Hyperion" - 1989) as well as film ("Tenet" - 2020). Speaking of "Tenet", writer/director Christopher Nolan explained that his story is based on the idea "that if you could invert the flow of entropy for an object, you could reverse the flow of time for that object". Finally, our list wouldn't be complete without mentioning the "time viewer" (sometimes called a "chronoscope"), a hypothetical device which allows the viewer to witness historical or even future events. Such devices frequently appear in both literature and film, ranging from Isaac Asimov's 1956 short story "The Dead Past" to John Woo's 2003 feature film "Paycheck" (based on Philip K. Dick's short story of the same name) (+). One particularly intriguing time viewer is the "functional chronovisor" supposedly built in 1952 by Pellegrino Ernetti (1925–1994), an Italian priest and scientist (allegedly with the help of Enrico Fermi and Wernher von Braun, among others). At least, that's the claim laid out in Father François Brune's 2002 book "Le Nouveau Mystère du Vatican" ("The Vatican's New Mystery"). It sounds like science fiction, but Brune swears the chronovisor exists, tucked away somewhere within the walls of the Vatican where it remains a closely guarded secret to this day.

Further complicating matters, the possibility of time travel - especially to the past - introduces antinomic (paradoxical) situations that touch on key elements of how we interpret reality, such as cause and effect and free will. Wrinkles such as the "grandfather paradox" and the possibility of meeting a younger or older version of yourself raise questions about whether the universe is capable of protecting the timeline, and if so, how. World-renowned minds have reflected on the matter: Stephen Hawking's 1992 "Chronology Protection Conjecture", the Novikov self-consistency principle, and Hugh Everett III's many-worlds interpretation (MWI) of quantum physics are all attempts to avoid time travel paradoxes.

The truth is that a deep, authentic understanding of the nature and workings of time is dependent upon discovering the secrets of quantum gravity. Until modern science manages to overcome the apparent contradiction between the laws of subatomic particles - where the temporal dimension seems to lose its continuity - and the dictates of general relativity (the basis of current models of the structure and evolution of the universe), our curiosity about the mysteries of time will have to settle for ingenuous notions and answers that are anything but satisfying.