Synthesia's new technology is impressive but raises big questions about a world where we increasingly can’t tell what’s real.In the not-too-distant future, Synthesia hopes to create full-body avatars that can walk and move around in a space that a person has generated.David Vintiner I’m stressed and running late, because what do you wear for the rest of eternity?  This makes it sound like I’m dying, but it’s the opposite. I am, in a way, about to live forever, thanks to the AI video startup Syn...