They aren't bound by the physics of this particular universe.
http://www.fox.com/fod/play.php?sh=fringe&ep=1259174899500 ,
http://www.fringetelevision.com/2009/12/many-months-of-fringes-observer.html ,
http://iliketowatchtv.blogspot.com/2009/11/fringe-august-observer-going-rogue.html ,
http://www.fringetelevision.com/2009/12/many-months-of-fringes-observer.html ,
http://iliketowatchtv.blogspot.com/2009/11/fringe-august-observer-going-rogue.html ,
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FRINGE & the MIB, etc.
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The Adjustment Bureau is an entertaining movie about benevolent MIB like beings that help to edit & direct humanity onto a better life path.
http://jfvrinfo.blogspot.ca/search?q=MIB
http://jfvrinfo.blogspot.ca/search?q=MIB