| The object or person is said to be invisible when it can not be see
for one reason or another. Invisibility is usually associated with the
science fiction and magic where the object can not be seen due to some
special powers cast upon it, or with the help of modern technology.
However the effect can be achieved in practice too in special cases.
To understand how the invisibility can be achieved one must first grab
the basic concept of what visibility is. We see objects by the means
of light photons reflecting off the surface of objects and getting into
our eyes where they hit retina, which triggers electromagnetic
impulses sent into our brain. Thus, if for some reason light photos do
not reflect off some object this object becomes invisible, and can not
be seen. This happens in substances and materials made which allow
light to pass through - feature known as transparency - which happens
in clear glass and air.
An object can be said to become invisible if it can not be seen for
reasons other than not reflecting off the light. Examples of such kind
include an object which is: located behind an obstacle, has the same
color as the background, is out of sight, or is positioned in the area
with little or not light.
Some objects with great mass create so strong gravity that any photons
of light can not escape this gravity field so they do not reflect off
the surface but stay there. These objects are known as black holes.
In folklore, literature, and science fiction invisibility is often one of
the favorite features. It is usually created by the means of spells
and powers, as well as special artifacts or technologies. |
In a recent campaign speech, Hillary Clinton was explaining how the economy
can be driven out of recession by so called "invisible hand" of the
market. Or, as Bill Clinton said, "the economy needs an invisible hand job."
