My belief is that the island is actually just a island in the south pacific that was used by the D.I. as a research station. and the hatches on the island are research stations and i think they are also cold fusion power generators. This would explain the magnetic field in the hatches and if you remember the map on the door of the hatch that showed up when Lock got trapped under the door. It looks like a power grid layout and the line are the power flow line that travel between the hatches and the unknown area at the center of the island. This would explain several things like the 108 min. timer and why no one can leave island that easy. First the timer, the 108 min. may be a power compasiter that all the island's exes power goes, so every 108 min. the compasiter of the island has to be purged so the reactor doesn't destabilizes and explode. So when Lock decides not to put the numbers in, the power has no place to go and the reactor starts to destabilizes then Desmond goes down and uses that key i assume to stop the fusion reaction. The unknown area in the middle of the island is some sort of cloaking device that takes the island out of normal space time and the incident they refer to is a rip in the space time continuum and that why there are all sorts older and none related things from different times appear around the island. It could also explain why thees people seem to effect each other in such a way, they effect each other because they changed time in some manner and so their lives are connected. The others can be the original inhabited different points in time that are trapped in the cloaking field but due to their intelligence this is unlikely. The two guys at the south pole who picket up the signal where there because the only way to find the island is to try to detect an E.M. spike and the best place to do this is at the poles.

thats my theory