My theory on time in LOST?

The hydrogen bomb did not cause the flash-sideways. EVERYTHING that Jack and co. did in the past was already accounted for in their timeline, including the bomb core, which didn't go off (if it had gone off, how come it didn't destroy any of the metal in the tunnel that the bomb lay at the bottom of?) Even before the cast had experience the flashes into the past, the things in which they do/did in the past were already accounted for (ex: Pierre Chang hurting his hand, and John Locke giving Ricardo the comp). In LOST, there is no such thing as multiple universes. There is only the one, and everything in the flash-sideways is the same timeline, only after it has been changed by something, which will likely happen later in the season. Therefore the flash-sideways actual happen after the things we see in the present on the island (after for the characters, 'before' in time).