Are they, though? I thought the Novikov conjecture postulated that time-travel would change nothing at all: if you travelled back to the past, you had "always" travelled back to the past, and anything you did there was already part of history before you started on your journey (aargh, time-travel tenses are hard). Michael Moorcock's Behold the Man[0] would be a good fictional example.

This, on the other hand, suggests you can change the fine detail of history (e.g. the identity of patient zero) but not its broad strokes (the occurrence of a global pandemic).

At least, that's what I gather from the article: I haven't read the paper, and suspect it would be a waste of time as my maths and physics are both rudimentary.

[0] https://en.wikipedia.org/wiki/Behold_the_Man_(novel)

If there are such physical laws to allow details to change while broad strokes must happen, I'd be curious what exactly differentiates a detail from a broad stroke. But all the same, this idea imagines a more timey-wimey view of history that doesn't have just one state. This is an idea explored heavily in Neal Stephenson's "The Rise and Fall of D.O.D.O"

The difference is entropy/uncertainty. You can change anything whose effects are too small to measure or distinguish from equivalent energy states.

> I thought the Novikov conjecture postulated that time-travel would change nothing at all

Not exactly, from the wiki article:

> The simplest way to impose the principle of self-consistency in quantum mechanics (in a classical space-time) is by a sum-over-histories formulation in which one includes all those, and only those, histories that are self-consistent.

So it is possible to change the past, but only in ways that are self-consistent and don't give rise to paradoxes.

Regarding the ramifications for free will:

> Novikov supports this point of view with another argument: physics already restricts your free will every day. You may will yourself to fly or to walk through a concrete wall, but gravity and condensed-matter physics dictate that you cannot. Why, Novikov asks, is the consistency restriction placed on a time traveler any different?

Im reading "The Time Patrol" by Paul Anderson. It describes that even if an individual is killed, it's unlikely to matter much because a species is more like a collective DNA wise. They even go hunting in the past, have possible children there, etc. It's only in very specific cases that the time patrol has to step in to make sure that "X" specific significant event happens the way it's "Supposed to"

I haven't finished the book yet though :)