More Time Travel

Use a time machine to go back thirty seconds and stop yourself from using the time machine. Bam! Single-generation Grandfather Paradox!

Story 1: Energy/Mass conservation violation destroys the universe. Boring.

Story 2: Energy/Mass conservation destroys the machine and everything around it. News reports your death in the explosion, and everything goes on unchanged.

Story 3: Both 'you's are destroyed, but the machine's fine. Everything goes on unchanged. (Technicians looking at mangled remains: "John said he was going to see what happens if he went back and prevented himself from going back." "Yeah. Let's be sure not to do that.")

Story 4 (and MY answer to the paradox): Just before you enter the time machine, another you steps out and stops you. "Why'd you stop me?" "I wanted to see what would happen." "But that's what I was going to do!" "Well, here we are. Now what?" (The very act of going back in time creates a new timeline that includes the traveler's appearance. The traveler vanishes from the original timeline, never to return. A similar traveler from another timeline may or may not appear in the original one, but only if he doesn't interfere with the original traveler's plans, or it's another divergent timeline.)

Story 5: The original you vanishes the instant the traveling you arrives. Still a new timeline.
"That's odd. I was going to enter the machine, but now I'm here, coming out of it." (Conservation of mass/energy destroys the original you the instant the traveling you arrives.)

Note: If there is only one reality/timeline/universe, time travel is impossible due to violation of conservation of mass/energy.

Similarly, even with multiple timelines, a traveler must arrive at the same one leaves, to preserve the mass/energy total.

Travel into the past adds matter to the past. How is that affected by Energy/Mass Conservation? Establishing the field that projects the matter into the past requires energy equal to the mass? Once established, the field is stable, and shutting it off returns the traveler? Or is it a one-way trip until an equal amount of energy is expended to remove the matter from the past?

Nature sems to violate Consrvation all the time on the quantum scale, for short periods. Perhaps the time travel field allows temporary violation on a macro scale? Field must be collapsed in a controlled fashion. Uncontrolled collapse releases all the energy at once -- the traveler is yanked back to the present, and is now at ground zero of the release. This is considered a Bad Thing.

The traveler experiences the travel while the field is being established? And again while it's collapsing.