If travelling backwards in time <i>is</i> possible, Novikov's Self Consistency Principle is a neat explanation of how the Grandfather Paradox may be avoided: <a href="http://en.wikipedia.org/wiki/Grandfather_paradox#Novikov_self-consistency_principle" rel="nofollow">http://en.wikipedia.org/wiki/Grandfather_paradox#Novikov_sel...</a>.<p>Basically, the idea is that if you are alive and capable of travelling backwards in time to attempt (directly or indirectly) your own murder, then your attempt has to fail by virtue of the fact that you're alive in the present. There's a nice thought experiment with a billiard ball here: <a href="http://en.wikipedia.org/wiki/Novikov_self-consistency_principle#History_of_the_principle" rel="nofollow">http://en.wikipedia.org/wiki/Novikov_self-consistency_princi...</a>
Why is the grandfather paradox the grandfather paradox and not the father/mother paradox? Why go back a generation more than is necessary? I've always seen it staged in this way and have never understood why.
If your going to think about time travel and how it really works I think you will also have to simultaneously tackle the "double slit experiment" the phenomenon where a single electron exists in an infinite number of superpositions, all modifying its own existence, while coming to rest as a collapsed wave form as a single particle.<p>The double slit experiment proves to us that a one-universe linear view of time doesn't work. For a particle to seemingly interact with ITSELF, then go back, pick one route, and hit the wall as a particle means that quantum events seem to thumb its nose at our notion of time.<p><a href="http://www.youtube.com/watch?v=DfPeprQ7oGc" rel="nofollow">http://www.youtube.com/watch?v=DfPeprQ7oGc</a><p>If you want do some time traveling yourself, use a laser pointer and three mechanical pencil leads:<p><a href="http://www.youtube.com/watch?v=UANVMIajqlA&feature=related" rel="nofollow">http://www.youtube.com/watch?v=UANVMIajqlA&feature=relat...</a>
We all travel through time at varying speeds all the time:<p>There are two twin brothers. One brother goes on a space journey traveling at 99% of the speed of light. The space traveler stays on his journey for one year, whereupon he returns to Earth. On Earth, however, seven years have elapsed, so his twin brother is 7 years older at the time of his arrival. This is due to the fact that time is stretched by factor 7 at approx. 99% of the speed of light, which means that in the space traveler’s reference frame, one year is equivalent to seven years on earth. Yet, time appears to have passed normally to both brothers.<p>Question: Did the traveler go forward in time or did the Earthbound brother go backward in time when they meet up later?<p>Question: How is it possible that one of the brothers shifted 7 years and yet they can meet in the same universe?