Because no substantive evidence for the existence of ghosts is universally accepted by science, arguments for their existence are more insinuations of likelihood or probability than they are concrete proofs. Some of the commonly evoked ideas related to the possibility of ghosts' existence involve multidimensional and many-world theories.
With respect to the theory of multiple dimensions – an idea endorsed by modern physics – proponents for the existence of ghosts argue that such an idea suggests that persons can move across unseen barriers, and perhaps back again. The many-worlds theory offers a similar notion, with the possibility of realms where alternative histories and lives are playing out in real time. Others, following the work of Einstein, Stapps, Hameroff and Penrose, have suggested that the ghostly element expelled by a dying body is actually quantum energy being released by the brain into the atmosphere.
Another popular support for the existence of ghosts is instances where paranormal activity, particularly the image of a ghost itself, is captured on camera, either photographically or as a moving image. Numbers of these cases abound. However, detractors of these examples claim that such evidence is easily manufactured, especially with modern media tools such as Photoshop.
Ultimately, there is also the weight of testified experience. For example, there are many significant, documented cases where the alleged haunting of properties has affected resale values, and where sellers have actually been sued by previous owners for not revealing to buyers that a residence was haunted before the sale. Similarly, there are documented cases of people fleeing locations, even their own homes, in terror, citing paranormal activities that science had no capacity to otherwise explain. While not empirical, these instances supply ample evidence to a great many for the existence of ghosts.