Although numerous advancements in the field of cloaking technology have raised the hopes of creating a true invisibility cloak sometime in the future, a new study claims that this will never happen.
In the study, the team of researchers demonstrated that even the best cloaks can only hide an object from some observers, while others that are moving with respect to the first group will be able to notice the object due to visual distortions stemming from the limitations imposed by special relativity.
"In principle, what this paper shows is that invisibility cloaking is not possible for all observers," said Jad Halimeh, co-author of the paper. "Real invisibility cloaks will have to stay in the realm of fiction. Your cloak, if it is to be pragmatically broadband, will pretty much look like that of Predator, giving away what it hides via distortions when you move relative to it."
Invisibility cloaks typically work by diverting light around an object so that it continues to the other side as if it were not there, preventing the light from being reflected off of it and into the eyes of potential observers.
Previous research revealed that the straight path through a region of space is always shorter than the path that curves around the space. This means that when light travels around an object - as in the case of invisibility cloaks - it takes longer to make its way around the object it's concealing than to go straight through, creating a time delay that leads to visual distortions.
Some scientists have gotten around this limitation by cloaking objects with just one frequency of light, but this creates a new problem - single-frequency cloaks become visible at fast speeds due to a relativistic Doppler effect.
After taking these previous results into consideration and investigating the possibility of an invisibility cloak that could achieve full-spectrum frequency cloaking, as well as the ability to maintain invisibility while in motion, the team concluded that it is not possible.
"Although our results may be disappointing for would-be wizards, understanding the limitations of cloaking devices is actually important in real life," said Robert Thompson, who co-authored the study along with Halimeh. "New technologies are beginning to emerge from cloaking research, and we're looking for effects that could either compromise the functionality of these technologies, or which could be exploited for some new practical purpose in the future."
The findings were published in the March 10 issue of Physical Review A.
