Tuesday, 6 June 2023

Time Travellers

The term, "time traveller," turns out to have two completely different meanings, epitomized respectively by Jack Havig in Poul Anderson's There Will Be Time and by Manse Everard in Anderson's Time Patrol series.

Jack Havig
Havig exists only in a single timeline. If he time travels from 1960 to 1970, then he is visible and tangible in 1960, exists invisibly and intangibly between 1960 and 1970 and becomes visible and tangible again in 1970. His entire world-line is continuous between his birth and his death although most of it is undetectable.

Manse Everard
Unlike Havig, Everard time travels not by his own volition but in or on a vehicle. If he time travels from 1960 to 1970, then he does not exist between those years. Thus, his world-line is discontinuous. Also, he bears memories, and even physical scars, from events that do not occur in this timeline. He could enter an alternative timeline and not return from it in which case, unlike Havig, he would not be born and die in the same timeline. Some of what Everard can do is so different that, I think, it no longer counts as time travel.

14 comments:

S.M. Stirling said...

I'd say it's still time travel -- but a different -type- of time travel.

I have more trouble suspending disbelief with Havig.

He tries to change what's occurred and finds it impossible. But the way that happens -- something always 'comes up' to prevent him -- smacks too much of some sort of conscious agency for my taste.

Sean M. Brooks said...

Kaor, Mr. Stirling!

Two types of time traveling discussed here.

THERE WILL BE TIME, featuring Jack Havig and Caleb Wallis, in an immutable time line.

The Time Patrol stories, featuring Manse Everard and chaotic, all TOO mutable time lines.

I dunno, things like Jack Havig tripping over something and breaking his leg as he tried to prevent his father's death made sense to me in THERE WILL BE TIME. It seems to me something like accidents of that kind would be necessary in an immutable timeline.

Ad astra! Sean

paulshackley2017@gmail.com said...

Sean,

But, if such accidents became common, then the laws of probability would change. If we want no causality violations but the laws of probability to remain the same, then we have to imagine little or no time travel. Jack Havig's situation seems impossible.

Paul.

S.M. Stirling said...

Paul: agreed.

The thing is, in Havig's universe something will ALWAYS happen 'by accident' to prevent him changing the past.

But that is logically impossible unless something -- specifically, someONE -- is -causing- that to happen.

It's not an accident, it's flipping a coin and getting an -infinite- number of heads or tails in a row.

Or having a quantum fluctuation always go one way.

To my way of thinking, if time travel is possible at all, then time is mutable. Given the chaotic nature of physical reality, that makes sense.

paulshackley2017@gmail.com said...

More interesting in the Havig universe is when time travellers can change the significance of known past events. Thus, on Crucifixion Day in Jerusalem, the Eyrie recruited, among others, Havig and Boris. Later along his timeline, Havig sent his man, Boris, to be recruited by the Eyrie. Also, Phase Three of the Eyrie Plan was controlled by Havig's group. When Wallis visited, they were able to dupe him that it was still his show.

S.M. Stirling said...

Paul: that strikes me as rather arbitrary.

Sean M. Brooks said...

Kaor, to Both!

I feel quite unable to comment adequately in such a discussion. But one conclusion I drew is that the Copenhagen interpretation of quantum mechanics and Everett's work about alternate universes makes me far PREFER there to be parallel universes/timelines than to be believe the universe is chaotically mutable and unstable.

Ad astra! Sean

S.M. Stirling said...

Sean: I'd prefer to believe in alternate universes myself. On the one hand, it's currently an untestable/non-falsifiable mater. On the other, it is 'intuitively' more plausible to me.

Sean M. Brooks said...

Kaor, Mr. Stirling!

I agree, and a lot less SCARY.

Ad astra! Sean

paulshackley2017@gmail.com said...

I don't think that our currently existing world can cease to exist now because of anything that happened in its past.

S.M. Stirling said...

Paul: not cease to exist in the sense of 'be destroyed', but in the sense of 'never existed at all'.

paulshackley2017@gmail.com said...

I agree. But it sometimes sounds as if people are saying that the following could happen: I live from 1949 until 2023, then, in 2023, it suddenly becomes the case that I did exist from 1949 until 2023. That could not happen.

paulshackley2017@gmail.com said...

Of course the word, "not," is missing in there:

...it suddenly becomes the case that I did NOT exist from 1949... etc.

paulshackley2017@gmail.com said...

Surely it is also said not only that there might be a timeline in which the world that we know does not exist but also that the world that we know might cease to exist at any moment?