(what is the lifetime of light?)
If there were no objects to absorb light, it would keep traveling forever. Light is made up of particles called photons that travel like waves. Unless they interact with other particles (objects), there is nothing to stop them. Unlike some types of particles, they do not decay, meaning that they do not spontaneously turn into other types of particles. With nothing to stop them and no chance of decaying, the will keep going forever.