Why Can't We Fly if Gravity Isn't Real?

Just read on the internet that a math genius scientist has arrived at the conclusion that gravity isn't real. He's also into string theory heavily, too, so I guess he additionally thinks time and space are illusions as well. It makes one think, exactly *what* is real? Something isn't real just because it's tangible, because in dreams, one often can feel items just as well as one can when one is awake. What if everything is just a collective illusion, like something out of the Matrix?