Is there any theoretical reason to believe that gravity and not the other three forces should propagate into additional dimensions (should those dimensions, in fact, exist)?
I meant, of course, beyond the theoretical contribution to addressing the hierarchy problem...
In string theory, there exist extended objects, known as D-branes, on which open strings must end, while closed strings need not. The standard model particles can be described as open strings, while gravitons are closed. Hence, if one sets things up right, we could live on a 3-dimensional D-brane, with standard model particles confined there, while gravity propagates in all dimensions.
This is the general motivation. There are phenomenological constructions also, but this is perhaps the cleanest motivation.
Cheers,
Mark - That's very interesting and new to me. Thank you.
Commenting by HaloScan
