TIME LOOP

Another fan theory that was quite popular back in the day. This theory began near the end of the third season, and modified through to the end.

Fan Theory: Time Loop Theory 
It suggests the island itself is in a perpetual time loop, disconnected from the time of the rest of the world, and pushing the button was resetting the time loop to keep it there. It's why people don't age, why women can't give birth and much, much more.

It's a very intriguing concept, but the time-travel exploration of the past two seasons suggests other ways these characters are zipping through time. It is like Groundhog Day but with a twist, as the day's events don't repeat themselves,  just the characters biological state stays constant.

But there is a question why some people time shift and others did not. There is another question why some people like Desmond mentally time shifted and others did not. Some fans believe in the end time travel was not an explanation but red herring filler to keep the series on the air.

But for the sake of argument, if the island was in its own "time bubble," what could that mean? Clearly, one could consider this the "fountain of youth," a mythical place that explorers have tried to find since landing in the New World. Perhaps that is why Widmore was keen to return; after leaving the island, he began to age normally. Likewise, when Alpert was on the plane leaving the island, his hair began to gray.

But how time worked on the island would still be subject to debate. Women on the island did get pregnant and go through the first two trimesters. It was near the end that things would go wrong and the expectant mothers would die. So time does not fit a linear pattern, or even a daily skip. It was once described as a rapid river, and as such it meanders and at times circles back around events (rocks or obstacles).

If the island was out of time, then it would not have been difficult to find because an island is a stationary object. However, it was difficult to find so there is an element of spacial flux at work. Daniel's rocket experiment confirmed that the island itself was a moving object. This result defies normal Earth physics.

This brings into the realm of possibilities that this island is in a different dimension, where are thoughts and truths about physics and nature are different - - - altered but close to our experiences of reality.

If the characters are in a place that has shifted from both normal time and space, how could anyone leave to go back to their old life? The logical answer is that they cannot. They are trapped in this time-space sphere. But we were shown powerful people like Jacob leaving the island to recruit "candidates" to come to the island to joust with the Man in Black. We don't know if the island universe is a parallel one where everyone on Earth has a time-space shifted twin, but that fits into the mold of consistent sci-fi logic. The island then would be a sub-universe in a twin parallel universe, which would then mean that the "real" characters in our world were not harmed, aware or lost on the island. And the last statement is the problem with a time loop theory: to explain the concepts of the time bubble leads one to discount the connection to our own world.

For if the island time-space bubble was floating about on Earth, then those captured inside its time-space matrix would never be able to leave. Six days on the island could equate to six decades in the world outside the bubble. If one thinks that an element of quantum mechanics like time is embedded in each living organism's DNA, then removing that living thing from its normal environment would most likely cause death.

Time travel, mental time skipping and the like was a real problem in the LOST story lines. It was not well explained and mostly shown in contrary context to normal science fiction standards.