First off all, that was a great finale.
I realize it is only a show, so I could take it that the flash sideways is actually purgatory and that they are ready to "move on" to the afterlife.
However, with all the occasions on the show dealing with science to help explain the incredible things we have seen during this journey(time/space travel, invisibility of island, Desmond's powers....) would it be to outlandish that Lost's version of afterlife has anything to do with concepts such as electromagnetism?
It has been theorized the "Heart of the Island" is related to electromagnetism since we know Desmond was necessary for uncorking the light, because he is the only person who has survived electromagnetic radiation (turning the failsafe, Widmore's test). I believe that the light is the afterlife and that is why someone is needed to protect it from people entering it without properly dying (MIB becoming Smoke Monster). The light was very similar to the Church scene, therefore I believe The Light= Afterlife= Electromagnetic Energy. Further proof is that the Countdown timer from the Swan Station were hieroglyphics mean "underworld" (http://images4.wikia.nocookie.net/__cb20061030060849/lostpedia/images/6/60/Hieroglyphs.JPG) however Carlton Cuse noted that they are "subject to interpretation".
Interestingly, based on research (few minutes on google) I found many articles that related the idea of afterlife with electromagnetism.I skimmed through them, but many things provided insight to what the producers of "Lost" may have had in mind.
http://www.west.net/~simon/brain-soul-consciousness.html
http://www.mathpages.com/home/kmath322/kmath322.htm
http://www.indiadaily.com/editorial/1666.asp