If you search for ‘wormhole’ you get a lot of hits on this message board.
I’ll link to a previous thread. [thread=199241]old wormhole thread[/thread]
Anyway, the general idea is you creat a wormhole through space. You move one of the mouths of the wormhole into a strong gravitational field, wait a while, and you now have a wormhole with one end in the present and one end in the past.
Now this possibly leads to some paradoxes. One of which being that you throw a ball into one end of the wormhole at the right speed to have it come out the younger end of the wormhole just in time to knock away the first ball.
In the book, The Future of Spacetime one of the authors postulates that the younger ball couldn’t possibly knock the older ball away, because the older ball must have entered the wormhole. (Maybe it only hit with a glancing blow that wasn’t enough to keep the older ball from entering)
The article writer claims that no situation can exist that doesn’t already take into account any event that happened to the wormhole itself and therefore no paradoxes will exist.
I can imagine a mechanism where a sensor set up outside the younger mouth automatically closes a door set up outside the older mouth. If the younger ball is detected, the door slams down keeping the older ball trapped in the ‘present’. If no younger ball is detected than the door stays open.
Is there a scenario that takes into account all the events that do happen that will negate the paradox? I don’t accept that the universe will just happen to wing a meteor at my older ball at just the right time. Let’s make it a somewhat closed system.
Going further, lets assume no such scenario exists, and you end up with two identical balls: I have just violated conservation of matter in the universe. Is this a possible proof of why such a time machine is impossible? (albeit a highly simplified proof): Or is there a way of perhaps borrowing energy from the wormhole in order to create my second ball. Perhaps the wormhole now shrinks in diameter. Are there any current physical theories that would show such an effect? Did I just make an energy to matter converter?
Whew, that post ended up being longer than I planned…