It looks like Harry Potter fans and RPGers might receive a bit of bad news with this one. A study conducted by researchers at the Ludwig Maximilian University of Munich have concluded that an invisibility cloak like the one featured in J.K. Rowling's beloved series is most likely a physical impossibility.
In a paper published in Physical Review A, the scientific team stated that, although invisibility cloaks in the version we're accustomed to — actual shrouds like the ones Harry Potter espouses — would be able to partially work, they wouldn't be able to do so fully.
According to the study, there are certain "devices" that could achieve the same effect of invisibility, but the shape and form of a cloak doesn't have the capacity to do it:
"... only an invisibility device that perfectly cloaks both the amplitude and the phase of light in its own inertial frame will also (perfectly) cloak this light in any other inertial frame. The same conclusion lends itself to invisible objects that are not cloaks, such as the invisible sphere."
In other words, because the shape of the cloak shifts, and because light can't directly pass through the material, it's more or less defective. The scientists went on to describe what an invisibility cloak, if worn, would effectively look like:
"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."
To create an invisibility cloak that properly works, the design would be more of what the researchers termed as an "amplitude cloak." This particular iteration would "[discard] information about the phase of light" in the environment at hand, instead creating a fully-detailed rendering of the surrounding environment, and "introduce a time delay," as Gizmodo reports.
Essentially, someone wearing an invisibility cloak would look a lot like this:
If it's any solace, even though we probably won't ever see a proper invisibility cloak in our lifetime — if at all — at least we can take comfort in Universal's Harry Potter-themed Wizarding World, and a nice glass of butterbeer.
Source: Physical Review A