huh. Time doesn't travel any more than a location in space travels. its static and charted on just an additional axis. We travel through time, in one direction (and not even at an absolute fixed speed) becuase thats just how we roll, dawg.

Anyway in order to not totaly mess everything up(negate free will), if time travel exists than it has to do so with alternate universes, OR if it does not (there are other posibilities), thinking of it in terms of alternate universes simply to clarify individual 'sets' of realized possibilities is still more convinient for us humans to grasp, so it will work for our purposes here as well. Though here we get caught up in definitions. So lets just agree now that for the sake of this post a 'universe' is all the space and locations and things within that physical space that currently consitutes what ever the entierty of that which we inhabit is. An alternate universe could be a copy of this only because one thing was changed somewhere a very very small ammount of time ago that had more than one outcome, it split into how ever many universes are required for each outcome to be realized. This is NOT to be confused with entierly different sets of base variables which can be found at the root of this universe (and its alternate forms). Those would also be alternate universes i suppose, but not related to ours in any way.

To visualize think of a tree. It has a trunk and many branches which themselves branch off, every time anything that has more than one possibility. (and thanks to those peksy electrons which exist in a cloud and not a real location at any given moment you can be assured there are a metric assload of universes)... And further there are many other trees planted next to that tree, possibly. Or perhaps our root variables are the only possible ones for any universes at all. But now im just rambling about pointless things.

So, to time travel you go between the possible instances of possibilities that could have evolved from the base set of sercumstances which are responcible for creating that which is right now that we are inhabiting.

The long story short, and the point im trying to make. Is that if they are time traveling to prevent humans from destroying the future, in order to avoid the paradox that would be created by them doing so (and then preventing any reason for them to come back in time to stop anything becuase nothing ever happened), we must assume they have traveled to an alternate universe, and not went back in time through their own exact chain of possibility that lead to the universe that was destroyed by humans.

And if that is the case there is nothing stopping them from going back, snagging hyperdrive technology, and then going further back, killing the humans in the 15th century, and then going forward, distributing hyperdrive technology, and living in a universe free of humans having ever invented even the steam engine, yet still having hyperdrive.

They would just have needed to go through 4 universes.

1. That was destroyed

2. That they took hyperdrive technology from the humans. This one also ends up getting destroyed.

3. That they destroyed the humans. This one does not get blown up but nobody ever gets hyperdrive. (or some other race invents it)

4. Where there are no humans and hyperdrive, them having given the hyperdrive to the races in a universe made up of a chain of possibilities that started after the human race was eradicated. And they live happily ever after.

The only possible reason they do not do this is they take pitty on universe number 2. But then universe number 4 would never exist with out their intervention, so its a fairly even trade off, and universe number 3, while everyone moves around slowly, gets to live untill the whole thing burns out and is silent.

But no matter what they do, their future that was destroyed, stays destroyed. They cant change that because it happened. Just like they cant change the horrible things that will happen in other universes.

What you should take from this all is that events are absolute and set in stone, but if you are clever you can just avoid the universes that you dont like. In this sense free will is simply a mechanism to switch which road you are all, but all roads are already fully paved and quite real.

Or time travel is not possible. (or everything exists as a sort of cohesive possibility.. mush)