As the universe expands, it pulls on all atoms harder and harder. Meaning that when the universe keeps expanding, reality is ripped apart. If humans could harness the amount of force to rip apart reality and create their own, time travel would be entirely possible. Now, think about this, if humans invented time travel, why did we not have a visitor from the future yet to help us out?
I don't think you understand how entropy works. The theory of the Big Bang states that the explosion harnessed enough energy to create every and all things we have now. As the momentum pushes the energy further out obviously it becomes more spaced out. There's no pull on atoms, that's gravitational pull and that's between large masses of matter. Nothing is ripped apart. Entropy is when the energy runs out, basically, or expands fully and cannot go any further, then it begins to retract. I have no clue where any "ripping part comes from." The most common theory of time travel is a Tipler Cylinder.
The premise is that rather than going in one direction as was thought with a wormhole, you would travel faster than the speed of light raised to the 1000 power, wehre it theorized you can literally "break the fourth wall," or go fast enough to hit the fourth dimension, time. It came from the idea of teleportation, getting from point a to point b with no journey in between, the same idea is applied here. You move fast enough you simply arrive, no travel, no journey. Think of it as a 10 foot wall soldiers have to climb. Rather than going over it through a serious of events like a wormhole would be, you simpler walk around the wall. Very interesting theory.