Light and gravity don't seem to have any mass like you would find with tangable matter. There seems to be other things but we are just beginning to detect.
Gravity is the bugaboo in Quantum Physics which you probably know bh. It is the one thing that cannot be enveloped/grasped/incorporated into Quantum Theory. YET. One day it will be but right now it is problematic. As for light all I know about it is that it travels a speed of 186,000 miles per second. I think. Is that right? Beyond that what is light? I'm gonna ask. Thank you for your reply! :)