After the recent news of the new ongoing Wonder Woman-Superman romance - now getting its own book - it leaves me with one question. What of the events of the Justice League International Annual where Booster meets Rip for the first time in the new 52 and everything is revealed as being wrong somehow? There are no real answers as of yet, but it did get me thinking as to the difficulties of writing realistic time travel.
Time travel is of course a tricky concept to write because of what is known as the grandfather paradox (basically what would happen if you killed your own grandfather in the past). This is one of the fundamental problems with writing time travel that is grounded in logic and science. I looked up a short article that I read some time ago (it is here if anyone is interested in reading it.) The basic problem with time travel basically is one of entropy and determinism (explained in much greater detail in the article.) Essentially it boils down to, that if you are going to travel through time that it is going to be in a way that is pre-determined just as our present reality is (providing you believe in determinism versus free will.) The simple explanation here to justify time travel is to create time travel which is not scientifically based but rather to create it which is supernaturally based. As those that believe in a higher power have a different perspective on determinism (that it is controlled by a deity) then mankind traveling is not necessarily inconsistent with this. Though it is still inconsistent with hard science, and if that is the approach then it is not going to work.
The only option that I can conceive of to make something somewhat hard in terms of science is the bending of time itself. As described in the article time is another dimension, but it is maybe reasonable to think that time would only be bent locally. This is the base of a black hole. They bend the space continuum in a localized spot (defined by their event horizon) but beyond that things are relatively normal. This is why we can have a supermassive black hole at the center of a universe, but being outside of its event horizon we are not really in danger of being swallowed up. So if space and time can be bent in a localized place, might this mean that an observer can have an effect outside of that localized area? I am not sure of course, but maybe this is a realistic place to start, that if mankind is to time travel that we would not do it on Earth. Or to put that another way if Rip and Booster are going to save the world, they would not be doing it from Earth.