INVISIBILITY 23
If one could control the index of refraction inside a metamaterial
so that light passed around an object, then the object would become
invisible. To do this, this metamaterial must have a negative index of
refraction, which every optics textbook says is impossible. (Metamaterials were first theorized in a paper by Soviet physicist Victor Veselago
in 1967 and were shown to have weird optical properties, such as a
negative refractive index and reversed Doppler effect. Metamaterials
are so bizarre and preposterous that they were once thought to be impossible to construct. But in the last few years, metamaterials have
actually been manufactured in the laboratory, forcing reluctant physicists to rewrite all the textbooks on optics.)
Researchers in metamaterials are constantly pestered by journalists who wish to know when invisibility cloaks will hit the market. The
answer is: not anytime soon.
David Smith of Duke University says, "Reporters, they call up and
they just want you to say a number. Number of months, number of
years. They push and push and push and you finally say, well, maybe
fifteen years. Then you've got your headline, right? Fifteen years till
Harry Potter's cloak." That's why he now declines to give any specific
timetable. Fans of Harry Potter or Star Trek may have to wait. While a
true invisibility cloak is possible within the laws of physics, as most
physicists will agree, formidable technical hurdles remain before this
technology can be extended to work with visible light rather than just
microwave radiation.
In general, the internal structures implanted inside the metamaterial must be smaller than the wavelength of the radiation. For example, microwaves can have a wavelength of about 3 centimeters, so for
a metamaterial to bend the path of microwaves, it must have tiny implants embedded inside it that are smaller than 3 centimeters. But to
make an object invisible to green light, with a wavelength of 500
nanometers (nm), the metamaterial must have structures embedded
within it that are only about 50 nanometers long-and nanometers are
atomic-length scales requiring nanotechnology. (One nanometer is a
billionth of a meter in length. Approximately five atoms can fit within
a single nanometer.) This is perhaps the key problem we face in our
If one could control the index of refraction inside a metamaterial
so that light passed around an object, then the object would become
invisible. To do this, this metamaterial must have a negative index of
refraction, which every optics textbook says is impossible. (Metamaterials were first theorized in a paper by Soviet physicist Victor Veselago
in 1967 and were shown to have weird optical properties, such as a
negative refractive index and reversed Doppler effect. Metamaterials
are so bizarre and preposterous that they were once thought to be impossible to construct. But in the last few years, metamaterials have
actually been manufactured in the laboratory, forcing reluctant physicists to rewrite all the textbooks on optics.)
Researchers in metamaterials are constantly pestered by journalists who wish to know when invisibility cloaks will hit the market. The
answer is: not anytime soon.
David Smith of Duke University says, "Reporters, they call up and
they just want you to say a number. Number of months, number of
years. They push and push and push and you finally say, well, maybe
fifteen years. Then you've got your headline, right? Fifteen years till
Harry Potter's cloak." That's why he now declines to give any specific
timetable. Fans of Harry Potter or Star Trek may have to wait. While a
true invisibility cloak is possible within the laws of physics, as most
physicists will agree, formidable technical hurdles remain before this
technology can be extended to work with visible light rather than just
microwave radiation.
In general, the internal structures implanted inside the metamaterial must be smaller than the wavelength of the radiation. For example, microwaves can have a wavelength of about 3 centimeters, so for
a metamaterial to bend the path of microwaves, it must have tiny implants embedded inside it that are smaller than 3 centimeters. But to
make an object invisible to green light, with a wavelength of 500
nanometers (nm), the metamaterial must have structures embedded
within it that are only about 50 nanometers long-and nanometers are
atomic-length scales requiring nanotechnology. (One nanometer is a
billionth of a meter in length. Approximately five atoms can fit within
a single nanometer.) This is perhaps the key problem we face in our