Thursday 31 March 2022

Yet Another Time Travel Argument

Recently I had yet another argument about time travel which could be relevant to Poul Anderson's Time Patrol series.

Imagine:

(i) Twenty years minus five minutes ago, I appeared/arrived on a Time Patrol timecycle.

(ii) I then performed some action - it does not matter what - which had consequences at the time.

(iii) Possibly, although not necessarily for this example, that past action not only had immediate consequences but also initiated a sequence of consequences that have continued until now.

(iv) Recently I acquired a timecycle.

(v) Five minutes from now, I will mount the timecycle and travel exactly twenty years pastward. 

It should be clear that:

(a) the immediate consequences of my past action occurred twenty years minus five minutes ago;

(b) the sequence of consequences, if any, has already occurred between that past action and the present moment;

(c) none of these consequences is waiting to be activated five minutes hence;

(d) if there was any sequence of consequences, then that sequence has not prevented me either from existing now or from recently acquiring a timecycle.

Needless to say, in a confused argument, it sounds as if the other party is denying some of (a)-(d). But the confusion is so great that nothing is clear.

31 comments:

Sean M. Brooks said...

Kaor, Paul!

The only "solution" I can think of is that alternate time lines split off from each other. But then how could you arrive in Timeline A to begin the sequence of actions affecting history? You should have left a Timeline B which resulted from your actions in Timeline A.

Ugh, these complexities hurts my head! (Smiles)

Ad astra! Sean

paulshackley2017@gmail.com said...

Sean,

In this example, there is only a single timeline.

When more than one timeline is involved, timeline B might not split from timeline A but succeed it in a second temporal dimension just as a later state of the three dimensional universe succeeds an earlier state of that same universe in the first temporal dimension.

Paul.

Sean M. Brooks said...

Kaor, Paul!

That clarifies what I had been trying to think out and say.

Ad astra! Sean

S.M. Stirling said...

I think in the TIME PATROL universe, the thing is that there is no "extra-dimensional" space in which linear causation continues to function.

So you can get genuinely uncaused effects.

Eg., if you go back and prevent your parents meeting, you continue to exist, because you're prior to the alteration. But the entire life you remember -never did- exist.

Saying this can't happen reveals that you're trying to preserve linear causality; but the sequence is completely nonlinear... "infinite discontinuities" again.

paulshackley2017@gmail.com said...

But the problem is that a Time Patrolman says of himself here and now, "I might turn out never to have existed." I think that that is contradictory.

I googled "infinite discontinuities" but, of course, could not understand the mathematics.

S.M. Stirling said...

It's only contradictory if one makes certain assumptions -- notably, that existence is irrevocable; you have existed, therefore in at least some sense you will. But that's not necessarily so in this imaginarium.

Existence in the Time Patrol universe is always -conditional-.

One of the underlying weirdnesses of the Time Patrol universe is that nobody, from moment to moment, is -guaranteed- to have ever existed at all.

The Time Patrol itself is carefully designed to overcome this.

For example, the temporal location of the Academy, prior to human history, ensures that every single Patrol operative is in a situation where some chunk of their world-line -cannot- be nullified by some -historical- change.

Eg., say that Stane, the 'tragic villain' in the first story, killed Manse and his friend and succeeded in his plan to make Britain the seed of a scientific universal state.

That would mean that nothing -subsequent- to that date would be the same. No Danellians.

But because the Patrol exists -prior- to the 5th century locus of change, it cannot be eliminated that way.

Every single Patrol member is still "there", millions upon millions of them.

paulshackley2017@gmail.com said...

I once calculated how many members the Patrol has from information given in "Delenda Est" but would have to look it up.

The assumption that I make does not involve propositions in the past or future tense. My only assumption so far is the logical premise, "if p, then p," e.g. "If I exist now, then I exist now." "I who exist now do not exist now" is surely contradictory?

(Computer slow downs might delay future replies.)

paulshackley2017@gmail.com said...

Therefore, "It might somehow turn out to be the case that I who exist here and now at this set of spatiotemporal coordinates in this timeline do not exist here and now at this set of spatiotemporal coordinates in this timeline" is contradictory?

Sean M. Brooks said...

Kaor, Mr. Stirling!

One objection to the argument you made is that if someone wants to change history, in the Time Patrol imaginarium, he could go back to before the Patrol Academy existed, to prevent it from existing at all, or destroying it. Efforts to prevent that destruction might lead to an endless regression!

Ad astra! Sean

S.M. Stirling said...

Paul: this is precisely the objection that the recruit Elizabeth Gray makes in an early scene in the first story:

"I think you're describing a logically impossible situation. I'll grant the possibility of time travel, seeing that we're here, but an event cannot both -have- happened and -not- happened. That's self-contradictory"

The instructor answers:

"Only if you insist on a logic which is not Aleph-sub-Aleph-valued," aid Kelm.

He uses an example of her going back and preventing her own conception, and she objects:

"But then I'd exist without -- without an origin!" she protested. "I'd have life and memories, and... everything... though -nothing- had produced them.

Kelm shrugged. "What of it? You insist that the causal law, or strictly speaking the conservation-energy-law, involve only continuous functions. Actually, discontinuity is entirely possible."

S.M. Stirling said...

Sean: yes, you could cause a change before the Academy.

But not that that would also destroy any history you wanted to -preserve-, which is the usual motivation of time-criminals.

The time criminals want to change history; but a change before the Academy is a change before the existence of human beings. There would -be- no human history.

So even the Exaltationists would have no human planet to rule if they did something before then.

S.M. Stirling said...

There are ways around the Academy; but I think you'd have to do something -ecological- if you were intervening before the existence of humans.

What comes to mind is "bio-bombing" -- say go back to the Cretaceous, and introduce modern grasses, scattering the seen very widely. They'd spread explosively because that was a vacant ecological niche; the ancestors of grass were not significant at that time, so there was a lot of bare ground.

Whatever happened with evolution after that (the emergence of modern grasses caused upheaval planet-wide) it wouldn't produce the same result.

But you'd be the only humans every to have existed. If you did it with remote-controlled time-jumping machines, you could wipe out -yourself- at the same time -- abort the whole of human history, though there would be scattered individuals (researchers, etc.) before that too.

If it was some villains wanting power, the way to do it would be to go back to the Oligocene -with people-. Say, a couple of hundred peasants from some period with equipment, seeds, tools, and animals.

(Like that story THE NEST.)

Then you could hop ahead a generation at a time, maintaining an air of supernatural power, until there was something worth ruling, rather like Stane intended to do.

That way the human race would emerge without an evolutionary history, and you'd 'always' have ruled it.

paulshackley2017@gmail.com said...

Mr Stirling,

I don't know what "Aleph-sub-Aleph-valued" means.

I accept that there are several different logically possible scenarios and that they include a single discontinuous timeline. In such a timeline, it is possible that a time traveler appears and prevents her parents from meeting. In this case, the time traveler has prevented her birth and her own remembered earlier life up to a moment of departure into the past. However (in this scenario), that earlier life has not first existed, then not existed. It has simply not existed. Nowhere in this scenario does it make sense for anyone to say, "I exist now but it might turn out that I do not exist now."

Paul.

paulshackley2017@gmail.com said...

In this example, I should have said that the time traveler prevents a meeting between the man and woman who would otherwise have been her parents. Physically, she has no parents although a genetic check, if this could be done, would identify her as a child of that man and that woman.

(Something about King Roger of Sicily is on TV right now.)

I hope that clarity in the exposition of examples prevents some conceptual confusions. Have you ever got into a discussion with someone who thought that, if a time traveler from now changed the course of events 200 years ago, the consequences of his changes would come into effect now, not 200 years ago?

S.M. Stirling said...

Paul: let's say that instead of going back and killing your father, you send an automatic time-machine with explosives, and set the explosive to go off microseconds after the time-jump mechanism is activated.

(I think that's mentioned as happening with the bomb the Exaltationists used against the temple in Tyre, which is why the Time Patrol couldn't remove the machine before it went off).

The explosion arrives, your father is killed, there's -nothing- left, not even the time machine, which is atomized in the same explosion.

So history is changed -- you aren't born.

But you are the reason you weren't born.

Your -action- is now part of history, but -you- aren't.

You never existed, you don't exist now, and you caused that state of affairs.

In essence, the reason you never existed is that you existed.

S.M. Stirling said...

Or, to use the scenario I outlined above, say you send automatic time-machines with grass seeds back to the Cretaceous.

Your existence is the reason that humanity (including you) never existed.

S.M. Stirling said...

So the consequences of a change in history exist -simultaneously- throughout all time after the change.

paulshackley2017@gmail.com said...

That can work. But, if my father is killed by a bomb that would have been set by me, then I never exist.

paulshackley2017@gmail.com said...

Other confusing arguments:

someone thinks that, if a time criminal flees from the 20th century to the 19th and, half an hour later, a Time Patrolman departs in pursuit, then the Patrolman must arrive in the 19th half an hour after the criminal instead of arriving 5 minutes earlier to apprehend him on arrival;

someone thinks that, if I depart the 20th century and spend a month in the 21st, then I must return to the 20th exactly a month after I left it.

paulshackley2017@gmail.com said...

Any consequence that affects many times is not "simultaneous," of course, but Temporal would have appropriate temporal adjectives.

S.M. Stirling said...

Paul: right. And you are the reason you never exist.

paulshackley2017@gmail.com said...

Because of the kind of person that you would have been and the decisions that you would have made if you had existed.

Sean M. Brooks said...

Kaor, Mr. Stirling!

And I think the Exaltationists would be willing to do precisely that, if they had thought of it, go back to before the Academy existed, and bio-bombed the Cretaceous Earthy. And first have colonists reading for settling that Earth, a las "The Nest."


Ad astra! Sean

S.M. Stirling said...

Sean: though that would leave the Patrol -- or whatever individuals survived -- in a very desperate position.

Hmmm. Maybe Manse and Wanda were on a vacation to see the dinosaurs...8-).

S.M. Stirling said...

The truly awkward thing about rectifying a biobomb attack on the remote past would be that you couldn't go forward to just before it was launched, because it was launched from the remote future that no longer exists.

(This rules out the sort of intervention outlined in DELENDA EST, where they could use the Academy or the winter sports resort as an HQ and then go forward to just before the crucial moment.)

Essentially, the attack comes from nowhere. You could only thwart it by doing something to remove it as it occurred or shortly after.

Sean M. Brooks said...

Kaor, Mr. Stirling!

The Exaltationists were pure nihilists, and they certainly would not mind putting the Patrol in a desperate position!

All the complications you and Paul have discussed here makes the idea of a mutable time line a la that of the Time Patrol VERY alarming! And I really hope that is not the kind of universe WE are living in.

Ad astra! Sean

S.M. Stirling said...

Sean: yes, in the Time Patrol universe you might just go out of existence -- never have been -- at any instant, due to time travel shenanigans or just to a quantum fluctuation.

So the Time Patrol is the agency that preserves existence from chaotic modification.

paulshackley2017@gmail.com said...

Well, that is what the Patrol says.

I try to argue that:

three-dimensional states of the universe succeed each other along the familiar temporal dimension;

four dimensional continua/different timelines succeed each other along a second temporal dimension;

to an inhabitant of a "later" timeline, a "deleted" timeline has never existed;

to a time traveler who has passed from a "deleted" timeline to a "later" timeline," the "deleted" timeline has ceased to exist:

to an inhabitant of a "deleted" timeline, there is no moment in his timeline when he ceases to exist.

Sean M. Brooks said...

Kaor, to both Mr. Stirling and Paul!

Both: And I far, far prefer the alternative Paul argued for, that "deleted" timelines simply became inaccessible to people from the Time Patrol's timeline. Much more comforting than the alarming scenario Stirling outlined.

Ad astra! Sean

paulshackley2017@gmail.com said...

Sean,

I think that a scenario can be not only alarming but also inconsistent/incoherent. Suppose that, in Timeline A, a man lives from 1900 to 1990. I think that it makes no sense to suggest that, within Timeline A, in 1940, it suddenly comes about that the man was not born in 1900 and therefore has not lived from 1900 until 1940 and also of course will not live until 1990.

Paul.

Sean M. Brooks said...

Kaor, Paul!

And, if I understand this correctly, such a scenario would only work if there was a Timeline B, splitting off from A at a point where such a man had not yet begun to exist.

Ad astra! Sean


Postscript: Dr. Shackley's daughter asked me to inform blog readers that, due to problems with his computer, he will be "absent" until Good Friday.