time travel

[Zevon]

does anyone know more about closed time curvatures and historical imperative?

[Zevon]

Time travel is possible, first a few principals. Space-time is a graph for this discussion and to travel in time you need a CTC - a closed time curvature, this is basically a loop in a space-time graph where you can go behind yourself or in front of yourself in this loop.To create the loop you need to distort space-time into a loop. How to distort space-time? Easy, mass distorts space time, this is how wormholes achieve such strange characteristics and how wormhole time travel is possible, but only by moving the wormholes around at near light speed, an obvious energy problem.An easier way is to look at what mass is. E=mc2 says mass is just energy, so energy could distort space-time and does. Light is a handy form of energy, bending light light into a ring could create a CTC, by travelling around the ring you would create a helical (helix like) line in space-time. The more times around the ring, the more times around the helix and the further you travel in time and space. The hard parts are that you can't travel back to before the time machine was first built and the paradoxes inherent o all time machines (stay tuned for this). But also bending light at it's full speed requires huge amounts of energy. However if you slow the light down by passing it through a more dense medium it is easier to bend and doesn't lose any of it's energy. Dense enough mediums exist at near absolute zero so a plausible method for space-time travel exists for the future, with a laser and a freezer. (Admittedly one hell of a laser and the mother of all freezers.) This manipulation of physical laws is similar to possibilities of faster-than-light displacement. you'll never beat .light in a straight race, but you could get somewhere before light does if you both start in the same place. Enter warp drives and wormholes, but they require too much explaining for such a sunny day. See ya'll in the garden.

[Zevon]

Now back to those inherent problems. Most of the paradoxes have been covered so I will focus on the one theory postularted that bo one here has recognised. When a time machine is nearly constructed it suddenly won't work, opinions are divided as to why but theories are the laws of physics will change, rendering the machine uselss. Part or all of the machine will stop working or be destroyed, and for each part you repair or replace another will break. Finally the entire universe wqill end, this theory has also been advanced for a possible outcome of humanity. Stephen Hawking says that a possibility is once we undertsnad the universe it will be instantly destroyed and remade but more complex.
Of course this may have happened dozens or even near infinite times already with each successive universe getting more complex but being eventually solved and destroyed.
Another attitude towards paradoxes is the 'other worlds' approachg where whenever you travel in time you enter a parallel universe and by returning to the present you return to your original universe where yopu haven't made any changes, only the parallel universes have changed. The only way to get to your own universe is to return to exactly the same point that you left in space and time.
A final approch is that the only way to solve a pardox is to do it. The universe might not care if you kill your grandfather and the llogic of it, as long as the space-time laws aren't violated. You could kill yopur grandfather and you might stop existing or not, wither way the universe won't really care. Odds on you will still exist due to the space-time graph being essentially the same as before you killed him. For more on this see 'historical imperative'.