Nathan Whelan, of Dunedin, asks :-
Is it true that if you travel upwards in space for long enough you will eventually end up coming from a downwards direction?
Jenni Adams, a theoretical physicist at the University of Canterbury, responded.
We don't actually know the answer to your question! Whether or not we would return to the same point after travelling upwards in space depends on the shape or topology of the Universe. If the Universe had the topology of a donut, then the answer would be yes.
Our current observations do not tell us what sort of shape the Universe has but we do know that if the Universe does have the shape of a donut then the distance around the donut is further than we can see. To understand what I mean by this consider the light coming to us from a star in a donut shaped Universe. The light we see from this star may have travelled directly to us, or it may have gone once (or twice or many times) around the donut Universe before our telescopes intercepted it. So to investigate whether the Universe is donut shaped we can look for multiple images of the same star. The images formed by the light that has travelled many times around the Universe will appear further away. We must also remember that the light which has travelled around the donut Universe has taken longer than the light which comes directly to us and so will be showing us what the star looked like when it was younger. As we have not seen any images like this we can deduce that if the Universe is donut shaped then the donut is so large that light from stars has not yet travelled all the way around it.
With improved telescopes and further observations we hope that one day we will be able to answer your question Nathan.