One Step Out of Time

Since the work of Maxwell and Einstein fundamentally changed our perception of time, identifying it as a fourth dimension akin to the three of space, movement in this new direction has been a staple of science fiction. Such time travel usually involves great distances of time and journeys of discovery. However a subset of fiction explores a different possibility - the idea that people more or objects may be displaced not years but just minutes or seconds into the future.

A story which goes part of the way towards this situation is The Man Who Saw Too Late by Eando Binder, which appeared in the September 1939 issue of Fantastic Adventures. This describes Pat Riker, a radio ham who is caught by an electrical discharge from his experimental radio setup when he is trying to listen in on an Antarctic exploration mission. He finds that suddenly he is no longer able to see the world around him. Instead, he is only able to see events after a significant delay.

Rather than experiencing a displacement in time, delaying the light reaching him, Riker is experiencing a delay in his perception and the ability of his brain to process the information coming from his eyes. However it has a similar effect, allowing him only to see the past, and leading to nausea due to the mismatched information between eyes and inner ear. While the story tries to explain the delay as resulting from a widening of gaps between synapses in his optic nerve, the eventual solution - using polarised glasses resolves the problem - makes no sense in this context. Either way, he hears and experiences events, but must wait a full three minutes before the sight that explains those experiences reaches him.

A more developed example of displacement in time can be found in the short story Lost in the Future by John Victor Peterson. Published in Fantastic Universe in January 1954, it follows the first two-person crew to travel faster than the speed of light. Reaching Alpha Centauri, they land on a habitable planet and find an advanced, interstellar civilisation. However, to their bewilderment, none of the “extrasolarians” respond to their attempted contact or even appear to notice when they land at a spaceport.

When the people do seem to react, after a lengthy delay, it leads to an inevitable conclusion:

“As we suspected, they probably do have speech and radio—but we can’t pick up either. We’re seconds ahead of them in time and we can’t pick up from the past sounds of nearby origin or nearby signals radiated at light-speed. They’ll see and hear us soon, but we’ll never receive an answer from them! Our questions will come to them in their future but we can never pick answers from their past!”

The two crew members are left with a dilemma regarding how to resolve this problem - and whether they can get back into sync with their surroundings. It seems likely that, unless this proves possible, humanity will forever be cut off from our neighbours.

A similar scenario confronted Jack Westermark, the central character in Man In His Time by Brian Aldiss (appearing in Science Fantasy, April 1965). Westermark travels on the first mission to Mars and is the only survivor of his crew when it crash lands on its return to Earth. When he is recovered, it becomes clear that he is unable to communicate normally, answering questions several minutes before they are asked and reacting to events which are yet to occur. As his wife Janet is told:

“It may be that each planet is encased in its own time field, just as it is in its own gravitational field. From the evidence, it seems that Mars’s time field is 3.3077 minutes ahead of ours on Earth. We deduce this from the fact that your husband and the eight other men with him on Mars experienced no sensation of temporal difference among themselves, and were unaware that anything was untoward until they were away from Mars and attempted to get into communication again with Earth, when the temporal discrepancy at once showed up.”

The result is that Jack and Janet Westermark become increasingly isolated from one another, unable to have a spontaneous conversation. Matters come to a head when Janet rushes into a room, having seen Jack apparently injured, and passes through the place he stood 3.3077 minutes before, causing the injury. Setting aside some incredibly sexist insults, the story raises the possibility that an upcoming mission to Venus will encounter a different time shift, and that ultimately, Earth could be populated by space travellers all living in different and contradictory time zones.

As Aldiss has a character point out, the fact that returning to Earth does not reset the clock acquired on Mars is somewhat illogical, and his explanation that this “pointed to the fact that ‘local times’ were not purely mechanistic but to some extent at least a psycho-biological function” does nothing to explain matters.

The shifts in relative time perception above were accidental or intrinsic to the journey undertaken. The idea that such time displacement could be deliberately caused appeared in the television series Voyage to the Bottom of the Sea (TV, 1964-1968), in its penultimate episode “The Death Clock” (TV, 1968).

In this episode, a junior member of the crew, Corpsman Mallory, has somehow invented a Fourth Dimension machine. He uses it to displace Captain Crane a day into the future. The displaced Crane is invisible and inaudible to his crew (at first), as Peterson’s pioneers had been. However, bizarrely, as a result of the same process, he also acquires a non-displaced duplicate who becomes insanely homicidal and the story veers more into science fantasy than plausible science fiction as it proceeds.

While the series engages with a number of science fictional themes during its run, this episode is shaky at best in its internal logic. The motivation and background of Mallory are never adequately discussed. Eventually, however, the situation is resolved by the destruction of the machine.

Also deliberate is the control of time in Collision with Chronos (a.k.a. Collision Course), a 1973 novel by Barrington J Bayley. This story, set in Earth’s distant future imagined time as an existing four dimensional structure, through which the “absolute present” or “now” sweeps like a wave at a rate of 1 second per second. However in this world, time is not a universal absolute but rather a local phenomenon, so that different worlds and different regions of space can have different "nows" [1]. Unusually, on Earth, there are two waves in existence and they’re sweeping in opposite directions. With the discovery of time travel, humans become aware that they can travel to a different point in history and then proceed at 1 second per second, but for the people and things they encounter at this new point in the structure, the "now" has already passed by, leaving them frozen.

“You can’t talk to the people there because they don’t hear you. They don’t see you either. What’s more you can knock them down and they don’t react in any way at all, just lie there squirming and eventually get up again. It’s as if they were robots going through motions which time has already ordained.”

Travelling to the future is worse: since the “now” in which all life is created is yet to reach this point in the structure, the world is empty and dead. As a result of these experiments, the totalitarian Titan regime of humans on Earth, with its deeply embedded creed of racial supremacy, becomes aware of an “alien” species (and indeed entire biosphere and evolutionary sequence). These are in fact just as native to Earth, but perceive a "now" travelling backwards through time towards the human present, with a catastrophic collision between the two waves just a couple of centuries away. The only prospect of assistance comes from a space station crewed by humans who left Earth millennia before and who have mastered the control of time. Indeed, the people of this settlement, Retort City, use time shifts to speed up delivery of ordered products from their factory zone, and have a time barrier between the two halves of their station. Displacement by a few seconds in time is used as a form of total solitary confinement to punish serious criminals, or even just for a ping-pong like game played on a circular table:

“The table was divided into time-zones each of whose present moment was marginally out of phase with the others. More than quick reflexes were required - one needed to be almost psychic to anticipate where the ball would be returned from or when.”

However these people are of asian descent and thus anathema to the white (or “True Man”) Titans who rule the planet Earth in this period. Their offer of assistance is violently rejected. Eventually the story ends with something of a deus ex machina, but not one that can or will prevent the catastrophic collision entirely.

Another interesting and more recent example can be be found in Kristine Kathryn Rusch’s short story The Room of Lost Souls (Asimov’s, April 2008). This describes an abandoned space station with a room at its heart into which many enter, but few return. One woman who survived the room as a child now works as a ‘diver’, retrieving technology and information from derelict spacecraft. She is hired to determine the fate of a man who entered the room, but her crew is surprised to find the station is gradually growing, as if new segments are being added. Eventually she realises that all the observed phenomena result from a failing ancient and forgotten stealth technology:

“The station isn’t growing. The stealth shield is degrading. The exterior parts of the station move in a slower time frame. The interior part, nearest the stealth tech itself, is moving at an accelerated pace.”

The decay of this stealth technology has lethal implications for anyone caught in the time flux, but its military and commercial potential leads others to place the protagonist and her team in danger.

The idea, as seen here and in others of the examples above, that regions moving in a region with accelerated time may be invisible and undetectable to those moving in the regular time-stream is relatively common in science fiction, even appearing in children’s science fiction such as the puppet series Space Patrol (TV, 1963). Also common are stories of travel substantial distances forward or backward through time (as in Quantum Leap, The Time Tunnel and many others).

Where smaller time shifts are concerned, in many cases explanations are remarkably unclear, as for example in the Star Trek: The Next Generation (TV, 1987-1994) episode “The Next Phase” (1992) in which Enterprise’s Chief Engineer Geordi LaForge and Ensign Ro Laren are presumed lost in a transporter accident. Instead they have had their molecules set “out of phase” so they can move through bulkheads, and other people, with ease but cannot be seen or heard (despite being perfectly visible and audible to one another and being fully aware of the rest of the crew’s actions). Their movements are accompanied by “chroniton fields”, implying that their invisibility and intangibility is associated in some way with a temporal shift relative to the rest of the crew, but the episode falls short of saying so explicitly.

A couple of episodes later, the same series goes further. The two part story “Time’s Arrow” parts 1 and 2 (TV episodes, 1992) involves a complex plot for aliens to infiltrate the past of Earth and harvest human life energy. Led by clues to Devidia II, the Enterprise encounters a cave where the empathic Counsellor Troi is convinced there are humans trapped, but no one is visible. As Geordi explains to Worf:

“Well, whatever or whoever is there, we’re out of phase with it. We’re only talking by a fraction of a second.”

“A fraction of a second would make them invisible?”

“A millisecond, a year, it wouldn’t make any difference. If what we’re reading is true then we’re occupying the same space but in a different time.”

Unfortunately an attempt to rescue the trapped people results in the Enterprise’s android second officer Data being sent five centuries into the past - apparently to his death. The rest of the crew must also travel back in time, where (unlike Geordi and Ro in "The Next Phase") they are able to fully interact with and influence people or events.

Despite the examples above, it’s relatively rare for cause and effect to become out of sync in fiction or for one or more individuals to maintain a fixed time offset relative to others.

An exception, perhaps unsurprisingly given sixty years of broadcast time travel stories, is in the universe of television series Doctor Who.

Perhaps the earliest and strangest example appeared in the 1965 serial “The Space Museum”. Here William Hartnell’s First Doctor and his crew of Ian, Barbara and Vicki land their space-time craft, the TARDIS, on a museum planet called Xeros and experience a range of peculiar events. A glass unsmashes itself and then the crew find first that they are not leaving footprints, then that they are unable to hear others or be seen by them, that they can pass through objects without touching them, and finally that another version of the crew themselves are imprisoned in front of them in a set of exhibition cases. These events lead the Doctor to realise that “the TARDIS jumped a time track and ended up here, in this fourth dimension!”.

In other words the TARDIS landed and let them out several minutes before their actual arrival in time-space. After a short while they return to being ‘in sync’ and their footprints appear, they hear the relevant conversations and their future selves disappear from the cases… giving them foresight of a fate from which they must work to escape. The reasons for all this happening (other than to fill out an under-running script) are not entirely clear, and are attributed to the general unreliability of the TARDIS at this era. 

While this displacement was of order perhaps half an hour and appeared to be shrinking with elapsed time, a more recent Doctor Who storyline has used a time displacement of just one second as a concealment device. The 2008 series of Doctor Who had a recurring theme of planets going missing. When David Tennant’s Tenth Doctor lands on Earth, only to find it vanishing from beneath him, he sets out to find the 27 missing worlds. In the two-part season finale “The Stolen Earth”/”Journey’s End”, he follows a very faint trail of signals to the Medusa Cascade but is unable to find the planets until he discovers that they have been shifted one second into the future by the Daleks. Since the Dalek plan involves destroying the rest of the Universe, he is left with a substantial problem to resolve before eventually guiding the planets back into their correct times with the TARDIS.

The ability of the TARDIS to ‘jump time tracks’ (albeit with difficulty) also appears elsewhere in the series, deployed more differently. One of the lesser used features of the time machine is the HADS or Hostile Action Displacement System. This device, appearing first in the TV serial “The Krotons” (1968) is capable of shifting the TARDIS either in time or space, in response to an immediate threat. It is sometimes described as moving the TARDIS a few seconds into either the future or the past. Indeed, both the Doctor (as, for example, in “The End of Time”, 2009) and the Master (for example in “The Keeper of Traken”, 1981) were known to deliberately set craft to such a displacement in order to conceal them from one another, or remove them from the grasp of other threatening aliens.

Nor are Time Lords and Daleks the only species to use time displacement in the series. The Sontarans also use a time displacement of one second to conceal alien technology in the ATMOS devices they use to attempt xenoforming of Earth in the two part story “The Sontaran Stratagem”/“The Poison Sky” (2008).

So, if displacement in time can be an accident, a consequence of travel, a punishment, a strategy or a concealment in science fiction, does it have any plausibility from a scientific perspective?

To the best of our current understanding, time’s arrow works in one direction only. The second law of thermodynamics requires that every process loses a little of its energy to heat. This can only be reversed locally (for example in living tissue or during crystal formation), and never globally. As time passes, the Universe as a whole becomes a little more disordered. As a result, time has a defined direction - that in which entropy increases - unlike any spatial dimension, in which movement backwards and forwards is simply a matter of perspective. The defined direction of time gives rise to causality - the idea that something cannot occur before the event which causes it to happen. What’s more, under the theory of relativity the most rapid effect is separated from its cause by the minimum rate of information transfer - the speed of light [2]. The arrow of time defines the only direction in which cause and effect can proceed.

This means that we can define a “light cone” - the growing region that light emitted by an object (or bouncing off of it) can reach as time progresses. Slowing light (or indeed sound) down could cause the signal to arrive at a later time than expected, causing a delay in someone’s perceptions, as can slowing down the mental processes that respond to the signal arrival (as in The Man Who Saw too Late). Nothing but reversing the arrow of time could allow an event to be perceived before it occurs.

This is difficult for most people to visualise, but physicists use something called a space-time diagram to conceptualise it. Each individual forms a line moving vertically from the bottom of the page (the past) to the top (the future). They might move from left to right or vice versa (travelling in space). On the other hand, information, in the form of photons, can only travel simultaneously in space and time, being slightly further away from its initial location at each subsequent moment, and so travel through space-time diagrams on diagonal arrows.

Assuming that by some form of applied technology indistinguishable from magic, it was possible to shift someone (lets say Ace) one second into the relative future compared to a static neighbour (who we’ll call Bob), would they remain invisible, as suggested by Doctor Who, Star Trek: The Next Generation and others? Well, this is a hard one to figure out [3] - and explain.

Feel free to skip to the next box if you get lost from this point onwards...

Certainly it may be impossible for Bob to see where Ace is in the time shifter’s personal present, since by the time Bob could be aware of Ace location, time-traveller Ace could well have moved elsewhere. In fact it's possible that by the time Bob can experience them, any photons which bounced off Ace have already travelled out into the Universe beyond him - if Bob is less than 1 light-second (300,000 km) away, then he'll never catch up with those photons. Any photons coming from Ace's position will pass through Bob's space-time location before he can experience them. If none of the photons that bounce of Ace reach Bob's retinas, he can never be aware of Ace's presence and Ace is effectively invisible.

But would Ace be aware of Bob? Again, we need to think in terms of photons of light (from the Sun or some other source) bouncing off Bob and into Ace's retinas. For Ace, this bounce has to have occurred long enough ago for photons to reach him travelling at lightspeed, but if it's too long ago the photons would have gone past. If the two are within 300,000km, the light travel time is less than one second. So an Ace displaced by one second will only see photons that hit Bob after Bob's personal 'now'. Assuming Bob's now coincides with the space-time in which he is embedded, Ace is seeing events (even if they're as small as one photon being scattered) that, according to the Universe as a whole, have not happened yet. And now we're in philosophical territory - does Ace's presence one second in the future require the Universe to be entirely deterministic? In other words, by observing Bob, does Ace force the path of the photon to follow a specific route in Bob's (and the Universe's) future? We could replace Bob or Ace with a building, a star or any other object embedded within space-time.

These arguments break down if the two are moving apart faster than lightspeed, or if the photons coming into contact with Ace are shifting forward by one second per second as well as their elapsed travel time, giving a faster apparent speed, such that Bob never catches up with them.

Both those explanations would be inconsistent with the principles of relativity which gave us the concept of space-time in the first place.

But what about the reverse? What if Ace instead travels into the past relative to Bob? Well, now Ace will theoretically experience some short interval in which they are free to move and act which is never observable by Bob - the photons reporting those events would have gone past Bob before the observer experiences time passing. After a short interval though, Bob's personal clock starts ticking and he will pick up the photons bouncing off Ace a short time before. Again, Ace's actions of a short time before may become visible to Bob (depending on their separation). But any reaction Bob has will occur essentially in Ace's past - the photons carrying news of that reaction will never catch up.

So Ace, or any other person or object shifted backwards in time, may initially be invisible to Bob, giving them a window of action “before time starts” for Bob, but their presence and actions would soon become apparent. Any Ace shifted forward in time would always be visible to Bob, albeit some time later in his personal elapsed experience.

Assuming we can get our head around that confusing maze of light and time-space, is such a timeshift possible in the first place?

Unsurprisingly, the simple answer at the current time is no. We know of no technology or natural event that can cause this to happen. Physicists have nonetheless come up with some theoretical models in which time travel (necessary for the initial displacement) is possible. “Traversable Achronal Retrograde Domains In Spacetime”, for example, is a study of what might be possible if material with exotic properties were available to construct and maintain a spacetime bubble. It is no coincidence that the model was given its memorable acronym. A range of other plausible solutions to relativistic physics do in fact permit time travel - but only under conditions we believe to be untrue or unobtainable in our universe. In the majority of cases, this work is carried out as serious exercises in relativistic thought experiment, and designed to find test cases which might define the limits of theory. And just as writers and readers of science fiction have engaged with relativity in a range of ways, it’s surely no surprise that relativists (as the above example demonstrates) have also engaged with SF.

However the topic also acts as a cautionary tale. The idea that individuals can be shifted in time, perceiving their surroundings without (sooner or later) being perceived in turn, represents a fundamental misunderstanding of relativity as it is currently formulated. In certain cases, such as that of Bayley, where an author is influenced by provably-incorrect pseudoscience, stories risk lending falsehoods credibility and a wider audience.

Of course, for most readers of science fiction, this isn’t a problem: these stories are accepted as fiction, driven more by narrative requirements than by scientific precision. But the cumulative effect of such texts is to create a convention. This can reshape popular expectations and so make it harder for future students (or other users of relevant technology) to accept the mathematical realities of relativistic physics and its limitations). Strange though it may seem, such technologies are far from theoretical - the GPS system that controls everything from parcel deliveries to pick-up services, air traffic control to geofenced central heating is reliant on understanding and compensating for the relativistic time dilation caused by its satellites orbit around the Earth.

As readers, it is easy to find ourselves as confused and disoriented by time displacement stories as are the time-shifted people they describe. It's tempting to see the workings of time and space, relativity and space-time, as arcane mysteries as deep as the origin of many of these time shifts. Perhaps it's because I'm a physicist, that I find it deeply comforting to reflect that time-space is a book we now have the tools to read and interpret. Or perhaps its because I find it comforting, that I'm a physicist.