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I have recently discussed time travel a lot on the Poul Anderson Appreciation blog. See here.

And here.

Temporal Vehicles

(i) A "time machine" (antiquated terminology from HG Wells) moves fictitious characters pastwards or futurewards along a single timeline. A variation is a space-time machine, like Poul Anderson's Time Patrol timecycles or Doctor Who's Tardis, which can also move the characters to a different place.

(ii) A different kind of vehicle, with no agreed terminology, would move characters sideways into a different timeline, assuming that other timelines exist.

So how can a character with a mere time machine get into a different timeline? He might travel pastwards and (a) initiate a divergent timeline or (b) return futurewards, passing through the moment at which another time traveler had initiated a divergent timeline.

It follows that a time traveler cannot enter another timeline merely by traveling pastwards.

Stepsons Of Terra by Robert Silverberg

I had two bad experiences with time travel fiction recently, a film and a novel.

While on holiday, I borrowed, but did not finish reading, Stepsons Of Terra by Robert Silverberg.

(i) The characters refer to the "Absolute Past." Every moment is past to some moments but present to itself and future to others so there is no Absolute Past. The relativity of simultaneity means that event A can be simultaneous with event B to one observer but before or after B to another.

(ii) We are told that a building is safely invisible and undetectable because it is three microseconds in the past. It does not make sense to say that anything is now in the past. Even if it were somehow valid to say at 1.00 pm, "The building is now at 1.00 pm minus three microseconds," then, at 1.00 pm plus three microseconds, it would be necessary to say, "The building is now at 1.00 pm," so the building should be detectable at 1.00 pm.

(iii) Ewing is being tortured and is going to be killed but is rescued by an armed, masked man who returns him to his hotel room where he sleeps and recovers. On waking, he meets a group who have time travel. With their help, he travels a few days into the past to become his own armed, masked rescuer. After leaving his younger self asleep in the hotel room, Ewing continues to exist so he should still be in existence when his younger self has traveled into the past. This entails, on the simplest hypothesis, that there is a single timeline containing a single Ewing whose single world-line has a single loop.

However, Ewing concocts a much more elaborate scenario. He thinks that the Ewing whom he rescued is not only younger but also other and that this other Ewing will rescue yet another Ewing. The implications, not spelled out at least in the part of the novel that I read, are:

there is a succession of timelines;
pastward time travel is to the past not of the current timeline but of a succeeding timeline;
each Ewing is born, grows up and is eventually tortured in one timeline but is rescued by the Ewing from the preceding timeline and rescues the Ewing of the succeeding timeline.

Ewing feels obliged to end this regression. To do this, he leaves a written message beside his sleeping self advising that self not to travel into the past, then kills himself! This will ensure that the current timeline will continue to be inhabited by the Ewing who was born in it. It also ensures that, if there is a succeeding timeline, then it will be one in which Ewing is tortured and killed. Why the Ewing who kills himself regards this as a desirable outcome is beyond me.

Before dying, the Ewing who commits suicide reflects that the single factor for which he has made no provision is his own rescuer. That rescuer should have lived out the rest of his life in the preceding timeline. Either there has been an infinity of previous timelines or there has not. If not, then the Ewing of the first timeline could not have been rescued by a Ewing from any previous timeline so the progression could not have got started.

Dimensions

I am going back to basics with dimensions. Many page viewers will not need to read this post.

On the flat surface of a blank sheet of paper, there are two dimensions: horizontal and vertical. Each dimension has two directions. Horizontal: left and right. Vertical: up and down. Each dimension is at right angles to the other. Thus, it is possible to move up or down without moving left or right and vice versa.

We can let the horizontal dimension represent the temporal dimension. In that case, the vertical can represent either one of the three spatial dimensions or a second temporal dimension. In this post, it will represent the latter. A temporal dimension has a direction or "arrow" defined by causality, memory and entropy whereas a spatial dimension does not.

If the horizontal represents our familiar temporal dimension, then a horizontal straight line represents a history or "timeline" from beginning to end. Each point on the line represents a moment of time. To an observer located in one of these points, every point to the left is earlier or past and every point to the right is later or future whereas, to an external observer looking down on the sheet, the points coexist with each other simultaneously.

A second straight line drawn above and parallel to the first line can represent a second timeline existing later then the first timeline in the second temporal dimension which extends up the page. If a time traveler, reversing his arrow of time, "travels" leftwards, then he moves pastward in the first temporal dimension (T1). If he travels upwards, then he moves futureward in the second temporal dimension (T2).

The hero of Ward Moore's Bring The Jubilee leaves a timeline in which the South won the American Civil War and enters a timeline in which the North won. He moves left/pastward in T1 to a decisive battle but also up/futureward in T2 to the second timeline. Thus, he can say, from the point that he has reached in T2, that the first timeline no longer exists. However, it is still visible to an external observer of the sheet of paper. Further, it is of no concern to the inhabitants of the first timeline that they will no longer exist according to an observer in the second timeline.

Contradictions only occur when we try to cram all of these diverse events into a single temporal dimension.

Revisiting Successive Timelines

Rereading Poul Anderson's Time Patrol series reopens the issues of the two "Logic of Time Travel" articles at the beginning of this blog.

In the standard science fiction causality violation scenario, a time traveler originates in timeline 1 and travels to the past of that timeline but then "changes the past," thus generating timeline 2. One way to picture this is to represent timeline 1 by a horizontal line and timeline 2 by a second line emerging at an angle from the point representing the moment of the causality violation but this entails that, at that moment, the time traveler disappears from timeline 1 and creates around himself an entire new universe for timeline 2! I do not think that either the functioning of a time machine or the actions of a time traveler would be able to create all that organized matter and energy.

I think that it makes more sense to model temporal change on experienced change. Thus, in experienced change, a single temporal dimension connects states changed from to states changed to. Each of these states is a configuration of the entire three dimensional universe. Similarly, in temporal change, a second temporal dimension connects changing states. Each of these states is an entire four dimensional continuum with its own internal temporal dimension. It is these temporal dimensions that we call timelines 1, 2 etc. 

A time traveler originates in timeline 1 but either transforms timeline 1 into timeline 2 or causes timeline 2 to succeed timeline 1 along the second temporal dimension - these are alternative descriptions of a single process. In The Shield Of Time, Poul Anderson presents another scenario: a quantum change in space-time-energy transforms timeline 1 into timeline 2.

If a story were set in the timeline 2 of the quantum change scenario but without time travelers, then readers would recognize an alternative history or parallel universe story. However, "parallel" implies simultaneity or co-existence whereas I argue that timeline 1 does not coexist with timeline 2 but preexists and causes it along the second temporal dimension. In that dimension, timeline 1 is not contemporary with but earlier than timeline 2 and therefore is inaccessible to a time traveler who can either remain in timeline 2 or advance to timeline 3 but not return to timeline 1. That is how Anderson describes the relationship between the current and deleted timelines in the Time Patrol series.

The Little Monster III

Copied from Poul Anderson Appreciation:

Poul Anderson, "The Little Monster" IN Anderson, Past Times (New York, 1984).

The title of this story is ironic. A time traveling Boy Scout thinks of Pithecanthropus as "'...those little monsters...'" (p. 161) and they think of him as "...little monster..." (p. 152). And both opinions have to be reconsidered.

The previous post introduced the twelve year old (American) Jerry Parker and the (Spanish) physicist and engineer, Antonio Viana. Now it can be revealed that Jerry is Antonio's nephew, visiting his uncle's time projection lab while on holiday. But how is Jerry accidentally projected into the Pliocene Period, about one and a half million years ago?

The technicians working on the projector had closed the main circuits but disconnected the fail-safe devices and had not told Antonio this. Meanwhile, Antonio let Jerry enter the projector and Jerry, neglecting to ask permission before touching anything, closed the door...

Jerry must endure thirty hours in the Pliocene. However, although "...horrified..." (p. 146) to see the door close, Antonio and the technicians are not obliged to wait thirty hours for Jerry's return because every return is to almost the moment of departure. Looking in through the window of the cylindrical steel projector, immediately after the door has closed, they might have seen a dead body or even bare bones but they in fact see Jerry still alive. Meanwhile, we have read about his thirty hours.

He is in "...1,500,000 B.C., give or take enough millennia that there was no possibility of sending him help." (p. 149)

Uncle Antonio had explained that arrival dates are so uncertain that "'...no two expeditions have landed even within thousands of years of each other.'" (p. 145)

So Jerry is right to think that no help can be sent but seems to forget that there would in any case be no time even to think of sending help. His body, alive or dead, will return immediately after its departure.

That figure of thousands of years between arrivals in the past is an estimate. The expeditions take astronomical instruments but the night sky changes considerably over time. The hero of Anderson's time travel novel, There Will Be Time, carries a small but elaborate instrument that scans star positions, even through an overcast, then tells him his exact date and time of arrival, thus sparing him wasted life-span casting about for his intended destination. But Jack Havig has complete freedom of movement in time, unlike Antonio's anthropologists.

The Little Monster

Copied from Poul Anderson Appreciation:

Poul Anderson, "The Little Monster" IN Anderson, Past Times (New York, 1984), pp. 142-163.

This one-off story, originally published in Way Out, edited by Roger Elwood, 1974, describes a time traveling Boy Scout's encounter with Pithecanthropus. This puts it in the same category as the two Technic History stories in which teenage colonists of an extrasolar planet encounter winged Ythrians.

Jerry Parker is twelve in 1995. The future world of 1995 has:

aircars;
telecasts from Mars;
Mitsuhito's theory of temporal relativistics;
Antomio Viana's engineering application of Mitsuhito's theory;
thus, the new science of Temporalistics.

Every time travel story must clarify its premises, including any limitations on time travel, which help to avoid paradoxes. In this story:

"time projection" involves n-dimensional forces and the warping of world lines;
Viana's lab is a small part of an international project;
it is not yet possible "'...to enter the past at a later date than about one million B.C.'" (p. 144);
the temporal inertia effect prevents travel either to the recent past or to the future and "'...causes great uncertainty about arrival dates'" (p. 145);
time travelers are projected from, not in, a steel cylinder (whereas, in Anderson's "Flight to Forever", the cylindrical time projector carries the travelers in it while HG Wells' Time Machine carries his Time Traveler on it);
anything sent into the past automatically returns "'...after thirty hours [in the past], because of built-up stresses in the continuum'" (ibid.);
it returns to almost the moment of departure and also to the same place even if it moved elsewhere in the past (again unlike the vehicles in "Flight to Forever" and The Time Machine);
time travelers cannot bring anything back with them, except the matter that they have breathed, eaten or drunk because this is held by intermolecular forces.

There is far more in any Poul Anderson novel or collection than can be realized by anyone who merely reads it through once from cover to cover. This single story presents a time travel scenario to rival that of the Time Patrol series and will require more than one post to discuss it fully.

1956

Copied from Comics Appreciation:

In Eclipse Comics and again in Marvel Comics, a 1956 Mick Anglo Marvelman Family story is adapted as a Prologue to Miracleman. As I understand it, the writer of Miracleman changed some of the words but none of the art. For example, the opening words:

"PROLOGUE 1956 An age of lingering innocence, an age of golden dreams for the.. MIRACLEMAN FAMILY" (Miracleman, no 1 (New York, 2014), p. 1..."

- read like a rewrite.

The Marvelman Family story is a hopelessly inconsistent time travel story which, nevertheless, makes perfect sense in this context. (It will emerge that inconsistencies were deliberately built into the Family's early adventures to test their credulity and controllability.)

In the Prologue, the Science Gestapo attacks from 1981 whereas I am sure that, in the original, they came from many millennia in the future. However, this change makes sense because, in the 1980's, Miracleman will recall his adventures of the 1960's.

The story:

in 1981, the United Earth Government prevents Kommandant Garrer's Science Gestapo from enslaving the world;
the Gestapo travels in Chrono Cruisers to conquer instead the world of 1956;
a local compares the Chrono Cruisers to "...space rockets, just like in Dan Dare!" (p. 3), which strikes me as another rewrite;
Johnny Bates, happening along, transforms to Kid Miracleman and fights the invaders but more arrive so he goes at "...atomic speed..." (p. 4) for help;
Kid and Young batter the invaders who, however, recover unexpectedly quickly;
one trooper explains that the atomic storm troopers are arriving in other countries and we see them in Paris and Saigon;
Micky Moran reads stop-press news of the invasion and transforms to Miracleman;
the Miracleman Family and the Army subdue the first landing in Cornwall;
the Family split up to liberate Rome, Washington and Moscow, respectively;
the invaders in Cornwall recover and bombard the Army with "...rare magnetic gases from our secret video rings!" (p. 6) (words are sometimes used with no apparent knowledge of their meanings);
the Family returns to find fighting again in Cornwall;
Garrer orders his men to destroy the Chrono Cruisers, of which more are still arriving, so that he and his men cannot be returned to 1981;
leaving KM to fight in 1956, MM and YM travel "...at atomic speed..." (p. 8) to 1981 when they destroy the Chrono Cruisers before their departure, capture Garrer and hand him over to "...the Commander, Twelfth Area, World Police" (p. 10), who expresses no surprise and says that 1981 can now become a utopia;
ironically, MM hopes that he lives to see it;
in 1956, the atomic troopers fighting KM suddenly vanish!;
then, hearing MM's account, KM accepts instead that they were never there! - while MM jokes that "...that's the way it was...or was it?" (p. 10)

Hopeless:

if the Chrono Cruisers had already arrived in 1956, then destroying them before their departure in 1981 could not possibly prevent them from having already arrived in 1956;
if the Cruisers had not arrived in 1956, then MM and YM would not have traveled to 1981;
and, if the Cruisers had arrived in 1956, then there is no reason why the troopers fighting KM should suddenly disappear at some later time;
please do not tell me that they disappeared in 1956 at the exact same time as MM and YM destroyed the Chrono Cruisers in 1981! (Please don't!)

However, thanks to the ingenuity of the writer of Miracleman, we now know exactly what is really happening here. Gargunza is thinking, "They can even swallow that!"