From: Hal Finney (hal@finney.org)
Date: Wed Jul 09 2003 - 19:28:19 MDT
Wired is doing a series on super-powers, based on the August issue of
the magazine.
http://www.wired.com/wired/archive/11.08/pwr_invisible.html is about an
invisibility cloak, and
http://www.wired.com/wired/archive/11.08/pwr_antigravity.html discusses
so-called anti-gravity devices, actually lifters powered by ion wind.
Tomorrow there should be an article on time travel, and the next day
one on "8 super powers".
The anti-gravity lifters don't amount to much, IMO; I played with
ion wind powered pinwheels when I was a boy, and these just aim the
propulsion downwards. You can't get any significant lifting power
without using voltages that would be unsafe.
But the invisibility cloak article is quite interesting. They mention
an amusing party trick I haven't seen: putting a webcam on your back and
holding a laptop screen in front of you, allowing people to see right
through you. Seems it would work even better with a tablet PC, make
a Halloween costume of a guy with a hole through his chest.
Unfortunately doing "real" invisibility requires producing a view valid
from all directions, for which they propose using a 10 megapixel per
square centimeter display, with fish-eye lenses in front of each 180x180
pixel block, so that each pixel gets aimed in a different direction.
The only problem is that computing power to generate 4 square meters of
such imagery amounts to 10 billion GHz, which is rather far away even
with Moore's Law helping out. Still, a cruder and smaller version could
work as a proof of concept.
The author doesn't consider the possibility of interleaving light sensors
among the pixels, using the fisheye lenses to focus light coming from
different directions. That might reduce the computing power requirements
and make the logic of what to display much simpler; just mimic what is
being received at the corresponding position and angle on the other side
of the cloak.
One thing I liked is that the article discussed the alien's invisibility
suit in the movie Predator, which I have always thought was a well
done effect. It seemed realistic in that there was a certain amount of
lag or distortion when the alien moved, which was not only a dramatic
visual effect (and probably pretty easy to do) but also realistic for
the way you'd imagine a suit like that would work.
Hal
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