As a self-confessed and hopeless geek, I am, of course,
obsessed with the incomparable Sir Isaac Newton. If you have visited this blog before you may have
read about Isaac Newton and the Cat Flap, a tongue-in-cheek but nonetheless
respectful homage to the great man. I was therefore extremely interested to
hear about the recent award of the Institute
of Physics ’ prestigious Newton
The human race has always been fascinated
by the idea of invisibility, and our literature
is full of it. Probably the first and most interesting instance occurred
in 1897 in HG Wells' science fiction novella (or, as Wells styles it,
‘grotesque romance’) The Invisible Man. In this story Griffin
Other famous invisibility plot devices
occur in Star Trek, in which the Starship
Enterprise protects itself from attack by means of a ‘cloaking device’ using technology stolen by Captain Kirk from a Romulan ship, and Harry Potter, where the ‘invisibility
cloak’ is a magical garment which renders the wearer invisible. For all those of you who would not classify Star Trek and Harry Potter as literature, I can only apologise for mentioning them
in the same breath as the great HG Wells, who is another one of my personal
heroes.
In the 21st Century real scientific
knowledge is starting to catch up with the predictions of science fiction. How
close is current scientific knowledge to achieving true invisibility? In HG Wells' story, invisibility was achieved
chemically, with the use of 'special pigments'. Nevertheless his ideas are
uncannily similar to Sir John Pendrys’s metamaterial discoveries. In chapter 19 of The Invisible Man, CERTAIN FIRST PRINCIPLES, Wells offers this scientific explanation:
But consider,
visibility depends on the action of the visible bodies on light. Either a body
absorbs light, or it reflects or refracts it, or does all these things. If it
neither reflects nor refracts nor absorbs light, it cannot of itself be
visible. You see an opaque red box, for instance, because the colour absorbs
some of the light and reflects the rest, all the red part of the light, to you.
If it did not absorb any particular part of the light, but reflected it all,
then it would be a shining white box. Silver! A diamond box would neither
absorb much of the light nor reflect much from the general surface, but just
here and there where the surfaces were favourable the light would be reflected
and refracted, so that you would get a brilliant appearance of flashing
reflections and translucencies—a sort of skeleton of light. A glass box would not
be so brilliant, nor so clearly visible, as a diamond box, because there would
be less refraction and reflection. See that? From certain points of view you
would see quite clearly through it. Some kinds of glass would be more visible
than others, a box of flint glass would be brighter than a box of ordinary
window glass. A box of very thin common glass would be hard to see in a bad
light, because it would absorb hardly any light and refract and reflect very
little. And if you put a sheet of common white glass in water, still more if
you put it in some denser liquid than water, it would vanish almost altogether,
because light passing from water to glass is only slightly refracted or
reflected or indeed affected in any way. It is almost as invisible as a jet of
coal gas or hydrogen is in air. And for precisely the same reason!
Compare this with Sir
John’s proposal for creating an ‘invisibility cloak’ by using
metamaterials. These are substances defined not by their chemical constitution, but by their internal
structures on the smallest scale, which allow them to guide light around
objects and render them invisible to the human eye. Altering the nano-scale
structure of a metamaterial causes directional changes in its electromagnetic
waves. Light waves flow around objects
covered in metamaterial and – hey presto – they are invisible!
I must admit that I am only a geek with no real scientific credentials, and I apologise for the inadequacy of my technical explanation. For a fuller explanation of the properties of metamaterials, why not have a look at
Professor Pendry’s website? http://www.cmth.ph.ic.ac.uk/photonics/Newphotonics/
This year's Newton award will be presented at a
ceremony in London
From the website of the Institute of Physics:
