“The question is, ‘Can we make a passive cloak that makes human-scale objectsinvisible?’” said lead researcher Andrea Alù, an electrical and computerengineering professor at the University of Texas at Austin. “It turns out that thereare stringent constraints in coating an object with a passive material and making itlook as if the object were not there, for an arbitrary incoming wave and observationpoint.”

Those “passive materials” are things like metamaterials, which can bend or absorblight without drawing energy from an external power source. They’re the materialcloaks are made from. Researchers have been testing the cloaking properties ofmetamaterials since at least 2006 but no functional cloaking device exists — yet.

The problem is that the bigger the object to be hidden, the harder it is to “cloak” it.That’s because cloaking requires hiding the object from visible light waves, whichare much shorter than radio waves.

In other words, humans are too damn big to render invisible.

It may be possible, however, to create invisibility cloaks that can hide small objectsfor a specific electromagnetic wavelength — such as visible light or radiowaves. The shorter the wavelength, the easier it is to cover.

“For objects comparable in size to the wavelength that excites them (a typicalradio-wave antenna, for example, or the tip of some optical microscopy tools), thederived bounds show that you can do something useful,” said researcherFrancesco Monticone, a co-author on the paper.

Just last year, researchers announced they had developed an “ultrathin invisibilityskin cloak for visible light.” The cloak they created was able to cover an object and— by manipulating certain wavelengths of light — render it invisible,  according toTime.

The upside to the revelation that a human invisibility cloak is impossible is that theresearchers can now look into different ways to exceed the limits, now that they’veset them.

“Our group and others have been exploring active and nonlinear cloakingtechniques, for which these limits do not apply,” said Monticone.

“Alternatively, we can aim for looser forms of invisibility,” he said — for example,making objects harder to see or detect without necessarily blocking all visible lightwaves. That could involve “camouflaging techniques, or other optical tricks thatgive the impression of transparency, without actually reducing the overallscattering of light,” he said.

So they’re not saying, “The world is on its way to making its own Deathly Hallows,”but they’re also not saying, “Human invisibility will never happen.”

“Even with active cloaks, Einstein’s theory of relativity fundamentally limits theultimate performance for invisibility,” said Alù. “Yet, with new concepts anddesigns, such as active and nonlinear metamaterials, it is possible to move forwardin the quest for transparency and invisibility.”

Here’s hoping their future studies figure it all out. Think of all the things you coulddo while invisible!