How does Dr Who do this?

Have you ever wanted to travel in time?  The idea seems quite attractive in spite of  the obvious potential paradoxes.

On top of the 'usual' risk of accidentally (or purposefully) killing one of your own ancestors and thus forcing yourself not to have existed, or the freak accident of reappearing inside a wall that somebody built while you were not looking, there is another subtlety that most people don't think about.

Not only do you have to find a way to travel in time, you also have to plan to travel in the three spatial dimensions and three complex rotations in order to land in the same place on the same planet.  Think about it.  The earth is speeding through space on its orbit around the sun, rotating as it goes.  The sun is circling the centre of the galaxy, and the galaxy itself is moving.

So imagine yourself getting into a time machine in your house and just going back or forwards 10 seconds to try the new 'toy' out.  Surely no paradoxes can be caused by that.  Other family members probably wouldn't even notice.

However, think how far your house has traveled through space in that 10 seconds.  When you re-materialise you will be in the vacuum of space with no way to return.

It might be OK if you are cocooned in the tardis with a friendly Time Lord, but for us lesser mortals it will be much less comfortable.

Time travel seems too risky.  Making the machine itself almost seems easy compared with the problem of trying to get to the right place, the right way up.


Added 10th September:
See Monty Python's Universe Song and a further link to a nice Facebook page about how fast the earth is moving through space. 


Small note: I seem to remember Asimov using this idea in one of his novels.  Its not new - but just an unusual thought.