Unstable State II

Please read An Unstable State first. 

After "'...- blotting them out -...," Yu adds:

"'...the past itself annulled, and we not only cease to be, we never were.'" (p. 290)

But they are - otherwise she could not be saying this - so how can it later become true that they never were? 

It is logically consistent to state that:

(i) from time t0 to time t1, the universe exists but, at time t1, the universe ceases to exist;

- but it is logically inconsistent to state that:

(ii) from time t0 to time t1, the universe exists but, at time t1, the universe not only ceases to exist but also ceases to have existed from t0 to t1.

(ii) implies that, just before t1, it is true to say, "The universe has existed since t0," but that, at t1, it is true to say, "The universe has not existed since t0." That is a contradiction.

This is the kind of contradiction that arises when discussing time travel. Of course it is logically possible that:

there is a Timeline A in which the universe exists from t0 to t1;

there is a Timeline B in which the universe does not exist from t0 to t1 - although that does not pose any threat to inhabitants of Timeline A whose only concern should be the cessation of their universe at their t1;

Timeline B succeeds Timeline A along a second temporal dimension.

All that we need to add is a time traveller disappearing from A and appearing in B and we have now transformed this scenario into a time travel one. To recapitulate this latter kind of scenario:

in Timeline C, I am born and exist until I die;

in Timeline D, my birth is prevented by a time traveller from Timeline C so that I do not exist and therefore do not cease to exist in Timeline D;

that time traveller has experienced me existing, then me not existing, so he might think and claim that I have ceased to exist;

however, I have ceased to exist neither in Timeline C nor in Timeline D;

I have ceased to exist in the second temporal dimension in which D succeeds C;

there is no Timeline E in which I am not born but nevertheless exist, then cease to exist, in adulthood;

we just need to remember that, in the Time Patrol's Temporal language, there is more than one past tense.

Yu talks about a sphere of nothingness expanding outward from a particular point at the speed of light. Therefore, until that sphere reaches any other point, that other point does exist.