By David Siegel Bernstein, PhD
What do you think about people seeing through you (optically—not because you are a shallow person, as you most certainly are not!)? Or, how about cloaking your starship as you sneak past an enemy armada? If you have thought about it, then read on. But beware: the methods of invisibility I’m going to describe are more Klingon than Harry Potter.
The goal of S4F, as always, is to help you understand the science behind plot devices you might use in writing science fiction. There are two scientific ways to render an object invisible—spatial cloaking (space) and temporal cloaking (time). These theories are straightforward and easy to understand; however, the methods of their application are very complex. In science fiction, the opposite is usually true: the application is simple, e.g., we could push a button, or drink a formula (or, gulp wave a magic wand that is sometimes called a sonic screwdriver) and, voila, you’re invisible.
As you may have guessed, the key to invisibility is light manipulation. As light reflects off an object, it carries information about the object such as its size and shape to our eyes or mechanical detectors. So, the goal of invisibility is to prevent tattletale light from passing on these details.
1. Spatial Cloaking
This is where light flows around the object and recombines on the other side—leaving no evidence of its detour. If you were to look at the object, you would only see what’s on the other side. The physics behind this isn’t much different than how refraction makes a straw appear bent in water.
As usual, the difficulty (not so difficult in science fiction) is in the how of building such a cloak. It all comes down to the construction of metamaterials: materials that have properties not found in nature. In spatial cloaking, you need optical metamaterials made from nanotechnology to surround the object. Nanotechnology and metamaterials will be topics in future posts of S4F.
2. Temporal cloaking
Instead of cloaking an object, why not cloak an event? Whenever light illuminates an event, it marks it in time. However, if an event occurred and it somehow managed to leave light unperturbed, then the event is hidden.
How can this be done? Easily—by exploiting a characteristic of light: speed.
Here is how it could work: as light passes through a time lens, it will split, i.e., light scattering—some of the light will speed up and some will slow down—creating a zone of darkness. These separate pieces pass through a second lens, recombining the light streams back together. Then there is no record of the hole or that anything had happened. This is a time gap.
The best thing about temporal cloaking is that you get to use cool phrases like: manipulating the perception of time, time lens, and time gap. All of these are actual concepts in real science.
Now for the difficult question: how can we get it to work? Once again, this isn’t as difficult for a writer as it would be for a physicist. Temporal cloaking requires special lasers and optical fiber metamaterials to disperse and reconstitute light.
See you in time and space… and S4F.
Comments: No Comments »