[zeugma]

There is something else that is never addressed. Where we were in the past in terms of space is very different to where we are now since the earth /solar system/ galaxy and who knows what else are all in motion.

Exactly!

I've brought this up many times in time-travel discussions. The Earth, she rotates. She also travels around the sun. The solar system travels around the galaxy's rotation. The several galaxies in our local group have relative motion relative to each other. The universe itself appears to be expanding. Taken together the cumulative Delta-V is significant. If you want to go back to see the dinosaurs, you're going to need not only a time machine, but a spaceship with an FTL drive, and damn good records of the relative positions of not only our sun within it's galaxy, but the motions of the Local Group as well.

The computation required just to find your way home would be ... astronomical.

All that said, I still really like time travel stories, as long as the writer remembers causality. Breaking causality pisses me off.

[mlo]

"The computation required just to find your way home would be ... astronomical."

Relativity. There is no base reference. All of that motion is relative.