I don't know if time is the 4th dimension.. I remember having a drunken "discussion" with a mathematician about this. He said time was something like the 17th dimension, while I was blabbering about something I don't care to remember.
But anyway, the most obvious paradox of time travel, The Grandfather Paradox...
There are two ways to eliminate the paradox. First, the parallel worlds. In this world, the one you're currently living in, you go back in time to do something that will at the end of the day prevent your own birth, so logically in that world you will not be born, but by choosing to do such an action, you have created a new branch of reality. When you go back to the future (in the
new reality) you'll find out you haven't been born, but in the previous ("original") reality you were born and used the time machine -> no paradox.
The other theory I read in a science magazine, but I can't remember it accurately.. some scientists used billiard balls to represent people, did a vast number of "collision tests" on a table and came to a conclusion that the Nature works so that in the long run the "collision" which causes the most minimal effect on the other balls is the most likely to happen. So if you tried to go back in time and push your grandma off the cliff, certain events would take place, rendering you unable to push her off the cliff and thus causing only minimal effects on the future (ie. time is a wide river, you are a pepple, and someone who throws the pepple into the river is the time machine. Does the flow of the river change when you're cast into the stream? Yes, but very little.)
I'll find the magazine and write the article here, unless someone else figured out what I was talking about and beats me to it.
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