August Sennor on Time

August Sennor

"...nothing in a Reality made un-Real can be detected" - August Sennor

In Isaac Asimov's time travel novel, The End of Eternity, things are made un-Real by Reality Changes. However, what happens when something passes from one Reality into another? Where does one Reality start and the other end?

Asimov's basic strategy for dealing with time travel paradoxes is to assume that that there are multiple Realities, or time lines. If you travel back in time and change something, then you create a new Reality...sometimes. Asimov made a distinction between "micro-changes" and Reality Changes.

Even Eternals sometimes forgot the difference between micro-changes (small “c”) and Changes (large “C”) which significantly altered Reality. -the thoughts of Andrew Harlan in The End of Eternity

The Reality Change that is of most concern is the Change that destroys Eternity, the time travel machine itself. When that Reality Change takes place, the time travel kettle that carried Andrew Harlan and Noÿs Lambent back in time disappears. However, the two time travelers are protected by a field-generator, "surrounded by an aura of physiotime (an effluvium, so to speak, of Eternity) and therefore protected from any of the effects of Reality Change", as described by Asimov. They remain to live out their lives in the new Reality.

In The Start of Eternity I show R. Nahan traveling back in time. He repairs the positronic brain of R. Gohrlay, a change which is a "large C" Change. In the Reality where Gohrlay's positronic brain is irreversibly damaged, Nahan goes on to develop the technology for time travel. In the new Reality that is created by the time traveling Nahan, Gohrlay recovers her positronic brain functions and she goes on to lead the way in developing time travel technology. In that new Reality, there is no need for Nahan to travel back in time. Unfortunately for the noble time traveling Nahan, the "physiotime field-generator" has not yet been invented. According to the "logic" previously used by Asimov, I assume that the time traveling Nahan will disappear, just like the kettle did. However, can anything from the old Reality remain in the new reality?

The Foundations of Eternity

Clearly, according to Asimov, the effects induced in a new Reality by time travelers can remain after a Reality Change occurs. This seems like a recipe for miracles. A time traveler goes back in time, makes a change to the course of events, causes a new Reality to come into existence, then disappears. The cause of some events in the new Reality has disappeared.

In the case of Nahan and Gohrlay, Nahan uses nanites to repair Gohrlay's positronic circuits. The nanites themselves must disappear along with Nahan when the Reality Change occurs. However, I suppose that the nanites can leave behind some information from the future for Gohrlay in the form of alterations to her memory circuits. It seems miraculous...I wish that August Sennor were here to check my "logic". Asimov showed Sennor making the argument that time travel paradoxes are impossible because something always changes in Time so as to avoid any potential paradox. Unfortunately, even if that is true, it does not tell us exactly what is allowed for time travelers.

Time Travel

How does the universe "know" if the kettle is part of the old Reality or if it has become part of the new Reality? If Nahan writes his name on the wall, "Nahan from the 57th century was here", that inscription could exist as part of the old Reality, just as Cooper's magazine ad did, as a "micro-change". How does the universe distinguish between micro-changes and a Reality Change? I guess this is where we have to take Asimov's advice. Time travel as a plot device is supposed to be fun. Don't ruin it by asking too many questions.

Related Reading: Time Travel and Aliens

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