Postulating time travel is an example of theoretical physics running amok. Let's look at some very basic requirements for such a feat to be possible. First, all time would have to exist simultaneously, somewhere in space. For example, out there somewhere the dinosaurs would have to be roaming around in some kind of a time warp. Otherwise it would be impossible to visit them just by traveling at a some hypervelocity in an indeterminate direction. Furthermore, every instant of time would have to be preserved forever. Time travel could not recreate these times, they would have to be there independently.
There seems to be no logical limit to what the scientific mind can imagine, based on mathematical formulations. For this we can be grateful, since these brilliant imaginations have led to marvelous ideas and theories which defy the understanding of most of us. This has led to the notion that if the physicists propose a theory it must be possible. Yet a little logic can readily refute many of them. I can recall attending a Steven Hawkings lecture in which he stated (through his voice synthesizer) that Maxwell's Equations, a kind of Physics Rosetta Stone, are valid for time running backward as well as forward. This would coincide with what was then thought to be the inevitable collapse of our expanding universe, a time when gravitational forces would overcome the initial acceleration of the Big Bang. (The recent discovery of Dark Energy, an anti-gravitational force, has rendered the collapsing universe idea obsolete).
Even without the Dark Energy intervention, this notion is absurd on its surface. For time to run backward, we would have to reverse the law of entropy, which is at least as inviolate as Maxwell, maybe more so. Entropy states that in the physical world all things go from order (segregated) to disorder (integrated), and that this process is irreversible. This is one of those theories that proves itself by observation. Mixing a cake, for instance, takes all of the segregated ingredients; flour, sugar, baking powder, a pinch of salt, milk, etc, and integrates them into a batter. This process cannot be reversed, as would be necessary if time were to run backwards. Try to imagine extracting each ingredient and re-segregating it into its own container. Or take it further after the cake has been baked, eaten and eliminated. Need I go further?
Still the physicists persist. I have read of one model of the universe in which time exists perpetually as incremental wafers through which we move. We just haven't learned how to negotiate them backwards yet. Aside from the notion of total predestination (a most unscientific assertion) this theory seems to have been fabricated out of whole cloth, just to propose a way it might all be possible. Hawkings, I understand, has long since disavowed his assertion of time flowing backwards.
Now I must rest my case, since to persist would seem to be piling on. Still, I need to add a personal opinion that this whole assertion of time travel is tied into the hope for immortality and redemption, a hope to reverse the past or escape the confines of future mortality. Sorry, but as the Bard has said:
"What's done cannot be undone"
Or from Omar Khayyam's Rubiayat:
"The moving finger writes, and having writ moves on,
Nor all your piety nor wit,
Shall lure it back to cancel half a line,
Nor all your tears wash out a word of it."