"You cannot depend on your eyes when your imagination is out of focus."
Kaku separates scientific "impossibilities" into three classes: he describes Class I impossibilities as "technologies that are impossible today but that do not violate the known laws of physics." A primary (and very popular) example is invisibility.
(The idea of invisibility also showed up in Harry Potter. Here, Harry is seen to be wearing an "invisibility cloak," which turns anything it touches invisible.)
From ancient civilizations to current science fiction communities, the idea of invisibility has been very popular and well-known. Yet until just a few years ago, scientists had strongly believed that "metamaterials," which are substances that have unusual properties that have the potential to render objects invisible, cannot physically exist due to the laws of optics.
The process started in 1967, when Soviet physicist Victor Veselago theorized the inconsistent existence of these metamaterials. The ideas and consequences that these brought were so bizarre that they were thought to be impossible to construct.
This all changed in 2006, with groundbreaking research at Duke University and Imperial College.
Scientists there successfully defied conventional "knowledge" by creating an object invisible to microwave radiation. Although we cannot see the direct difference with the naked eye, it was nonetheless a crucial step toward an optical revolution.
Although many scientists initially held onto their theoretical laws of optics, arguing that a negative index of refraction (a number that describes how radiation propagates through a medium) is impossible and that metamaterials must have a negative value, they were reluctantly forced to rewrite all the textbooks on optics.
An even bigger step was taken in early 2007, when scientists in Germany and the U.S. Department of Energy anounced that they had formed metametrials that worked for red light as well as microwave radiation. Such creations foreshadow several drastic changes in optics, as well as the rise of true invisibility.
Kaku thus declares that, "The 'impossible' had been achieved."
It is important here to note how arguing and proposing inconsistent hypotheses-- those which contradicted "established" laws and theories-- were crucial in the making of the metamaterials; for instance, had Veselago not proposed his idea due to pressures by the previously-existing laws of optics, the idea of metamaterials might not have even been discovered now. We must remember that, especially in the realm of such Class I impossibilities, keeping an open and pluralistic mind is the only way to achieve the impossible.