Still dreaming of being able to sneak into the restricted area of your local library? Harry Potter’s reasons for becoming invisible are pretty tame all told, but that doesn’t mean we can’t imagine what we would do if we had our very own invisibility cloak. Stop it.
But how close are scientists to actually creating ways of making people disappear? And is there any magic we could learn from the world around us?
How animals disappear
OK, let’s start with the basics: can anything in the natural world turn invisible, cloak or no cloak?
Plenty of animals use camouflage to keep themselves hidden. There’s a type of cuttlefish that can change its appearance depending on what’s around them. Cool. But not invisible.
There is another sea creature however that does something much, much more impressive.
Dr Helen Czerski, a physicist at UCL who is currently presenting a BBC4 series on the science of colour, tells us about the disappearing act of a crustacean called a sea sapphire, which is able to reflect light landing on it out of the visible spectrum.
“There is a brilliant little sea creature that can turn itself invisible,” Czerski explains. “It’s see-through effectively. What it has inside it are these layers which it can twist. You know when you shine a light at a CD, and you see all those colours as you tilt the CD? What this little sea creature can do is tilt its layers so it shows you whatever colours it wants.
“It can tilt its layers so far that the only colours it’s showing you are colours in the ultraviolet. Humans can’t see in ultraviolet, so it looks invisible. It then tilts back and looks blue. It is the most spectacular thing I’ve ever seen.”
Could humans turn invisible too?
The trouble is, it’s much trickier trying to ‘trick’ light when out of the water. Even with see-through objects like, say, a wine glass, we can still see the glass because the light is bent as it passes through.
As for humans, well, light bounces off us all the time, making us pretty trick to just hide away – although there is at least one person trying to make our bodies invisible.
Dr Mark Lythgoe is director of the Centre for Advanced Biomedical Imagining at UCL, where he is working on a project called, brilliantly, Invisible Man.
The process involves injecting a solution into the body which essentially makes it transparent. The solution has the same ‘refractive index’ as the what it’s injected into, meaning the light passes straight through without changing speed or bending.
Doctors can then look ‘through’ the tissue to examine tumours within the body.
By manipulating light, the cloak manages to make the object it is covering ‘disappear’. The cloak is made up of tiny gold blocks, which together act almost light a mirror, reflecting any light back without revealing what the object is. All you are seeing is a flat surface.
University of California, Berkeley scientist Xiang Zhang told CNBC, “The reason I can see you is that your face and body have different shapes and different heights — a nose, a chin, and they cast different shadows.
“But I can design the cloak so that it reflects light in such a way that it erases those differences in height and in shape. So what you see is a flat surface.”
The cloak is only 80 nanometers thick (in comparison, human hair is about 100,000 nanometers thick), and can cover any irregular-shaped object.
The catch? This “cloak” is currently about the size of a grain of sand.
There are many amazing ways people are playing with the idea of how we could hide in plain sight. But for now, we’ll just have to find other ways to manage mischief.