J.K. Rowling has created one of the most interesting and deep-rooted fictional universes in history - the Harry Potter series. These books are mostly based along the lines of magic, but it might be possible to explain the basis of Harry Potter's invisibility cloak using actual science. As Arthur C. Clarke once said:
Any sufficiently advanced technology is indistinguishable from magic.
A team of researchers in Montreal has successfully rendered an object invisible to broadband light, using a new technique dubbed "spectral cloaking".
Researchers shone the laser light through a cloaking device that changed the light’s frequency so it would pass through the target object, rather than interacting with it to make it visible. Another filter behind the object returned the light to its original frequency. They reconstructed the light wave exactly as it was before, so it’s exactly as if there were no object at all.
Most light sources in the world, including the sun, emit a broad range of visible light waves. This broadband light typically appears white, but shining it through a prism reveals that it’s actually made up of a range of individually-coloured waves. Objects in everyday life are visible to the naked eye when they reflect and absorb a portion of this broadband light.
For example, a blue object reflects blue light waves and absorbs everything else. The object looks blue to the human eye because that’s the colour of light that is bouncing off of it.
Spectral cloaking effectively bumps light waves into a frequency that will pass through the target object, then returns those light waves to their original state.
In other words, you could shine a flashlight through a “cloaked” basket of blueberries and it would shine directly onto the wall on the other side, without reflecting any light from the blueberries in between. You’d just need to program the filter to cloak blue light.
Previous attempts at achieving invisibility have only succeeded in narrow ways, either by concealing an object (e.g. a stealth jet) from radar, distorting light waves to move around an object or rendering the object invisible under a single colour of light.
The latter form of cloaking is practically useless, because the real world is filled with different colours of light that would ruin the effect.
The spectral cloaking experiment didn’t hide anything as complicated as a jet or a human, but it did demonstrate that light can be shifted to completely pass through an object, rather than being reflected or absorbed.
The cloak is dependent on knowing the exact colours need to be filtered out. However, one could theoretically program a cloaking device to ignore the full visible spectrum, effectively rendering an object invisible to the naked eye.
The study demonstrated that a one-dimensional object can be rendered invisible. The next step is to apply that same concept to two- and three-dimensional objects.
This experiment, at the very least, proves that an invisibility cloak is indeed possible in real life. It has a long way to go though, so don't expect invisible people to be stalking you anytime soon. Of course, if all else fails, you'll still have the fond memories of the Harry Potter Universe to ponder upon.