Michio Kaku is a very intelligent, approchable theoretical physicist, and currently considered the leading authority on string theory. His book, “Hyperspace” is amazing and interesting for anyone interested in physics and/or string-theory. An article in Popular Mechanics gets Dr. Kaku’s thoughts on Desmond’s journey through time:

With new particle physics research recently taking time travel from Doc Brown fantasy to down-the-line possibility, we spoke with Dr. Michio Kaku, whose new book, “Physics of the Impossible,” makes Lost’s flip-flop between past and present look, well, not impossible.
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Maybe. When Desmond warps back to visit Faraday at Oxford University in 1996, he watches Faraday zap a mouse with a dose of radiation, thereby sending her mind into the future. Upon her return a few minutes later, the lab rat can run a complex maze without hesitation; Faraday “unstuck” her in time. And there’s no law of physics preventing this kind of time travel—just a lack of know-how.

The producers of “Lost” have always said that what they do has ‘basis’ in science. It does appear that even their science-fiction appears to be in the realm of possibilities (just not probability).