Althogh the island group may have began as an utopian ideal, the Dharma experiments, especially those related to "the incident", have created a pocket universe where the laws of reality are somewhat bent or distorted.

This is evidenced by how it is somewhat easy to get into the pocket universe, and difficult to leave. Getting onto the island is either caused by a magnetic incident (such as when the numbers are not entered), or by a sort of "gravitation" where once you get close enough, you are sucked into the pocket.

The universe appears to be somewhat closed. Desmond and also the raft crew wound up back at the island. (This could be similar to a "Land of the Lost" moment when Will, Holly & their father see themselves on a distant cliff, or just like the Asteroids game - if you go far enough, you return to your starting point.)

However, there is a particular heading that permits escape where the attractant or gravitational forces are minimized. Michael & Walt were given a heading which supposedly permits them to leave the island. Ben promised Julia that she could leave the island. There could also be a particular heading that radio communications could escape the island. Perhaps even satellite communications could be established whenever the satellite is in allignment with the line of escape (say perhaps every 108 minutes).

The Numbers
The numbers do not appear to be any known mathematical sequence (in our universe). But in the pocket universe they represent part of the mathematical reality. The numbers 4,8,15,16,23 & 42 fall somewhere between the progression of "triangular" numbers (3, 6, 10, 15, 21, 28) and "square" numbers (4, 9, 16, 25, 36, 49). Using the numbers somehow pulls on the distorted reality of the pocket universe. Perhaps even mathematical constants & natural laws, such as pi or the gravitational constant, are different within the pocket universe.