When we see an object, it means that light left
that object and traveled to our eye. And, light
travels in an ALMOST perfectly straight line. This
means that, in order for you to see something,
you need to be able to draw a straight line from
the object to your eye (or have a mirror to
reflect the light). However, light doesn’t travel
in a truly straight line.
Einstein’s general theory of
relativity, which describes gravity, predicts
that light is affected by gravity, and that the
path light follows can be measurably bent by
massive objects, like black holes. This has
been observed by astronomers, who have seen the
light from the same supernova (an exploding star)
multiple times, since the light traveling in
different directions was bent toward earth. So,
over really, really big distances, it is
possible to see around corners!
Interesting question. You can hear around
corners because sound waves have a wavelength of
typically a few feet. The wavelength of
visible light is 450-700 nanometers, which is a
million times smaller. Around a corner, waves
will diffract. The amount by which a wave can
diffract is roughly the same as its wavelength.
Therefore, sound waves can diffract around corners
(on the order of a few feet) whereas light will
not diffract enough (nanometers).
read more here
The military is actually very interested in
this problem. Certain solutions have been
realized. There exists technology where the
presence of objects in a room can be determined
using radio frquency signals, not light. For
"seeing" around corners, one has to be very clever
about how to overcome this problem. Preliminary
research shows that by using very very fast lasers
and ultra-fast imaging, one can reconstruct an
image of what's around a corner by using light
diffracting off of known surfaces. However, it
takes a while and is not perfect.
This video explains it best: video
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