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.