Dimensions vs Universes: Understanding the Distinction and Connection

[thepopasmurf]

I always here talk of there being multiple universes or there being higher dimensions. When people use these terms are they referring to the same thing? If not, what's the difference?

 

[tiny-tim]

I always here talk of there being multiple universes or there being higher dimensions. When people use these terms are they referring to the same thing? If not, what's the difference?

Hi thepopasmurf!

Higher dimensions refers to either

i] spatial dimensions "outside" the universe, to "explain" how the universe is curved (for example, "the universe is like the surface of a balloon, and the universe expands the same way as a balloon expands, through an extra dimension") … these have no physical existence

ii] spatial dimensions "outside" "our" universe, in which "our" universe is a "brane" floating around, and maybe sometimes hitting other universes … these (if they exist) do have physical existence

iii] spatial dimensions "inside" the universe … these are "curled-up" dimensions, too small to see, in whch the strings of string theory vibrate

Multiple universes either refers to ii] above, or to some weird quantum theory idea which is basically like "different time-lines" in science fiction (but respectable! )