MOTION MOUNTAIN

the description of electromagnetic field evolution 91
F I G U R E 48 Typing a letter and playing video tennis using thought alone (© Fraunhofer FIRST).
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Challenge 97 s
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computer commands by an electronic device. The system, based on neural networkalgorithms,worksafter
only 20 minutes of training with a particular person. In this way,
thesystemallowspeoplewhoarefullyparalysedtocommunicatewithothersagain.The
systemissofastthatitallowsplaying ‘mental video tennis’ on a computer screen.
Typing with thought alone is possible because the brain region responsible for the
hand is near the skull, so that signals for hand rotation can be read out with sufficient
spatial resolution by the electrodes on the cap. Researchers know that resolution limitationsdonotallowreadingoutthecommandsforsinglefingersinthisway.Forsuchhigh
resolution tasks, electrodes still need to be implanted inside the relevant brain region.
However, at present the functional lifetime for such electrodes is only a few months, so
that the dream of controlling machines or even artificial limbs in this way is still distant.
Recent research with brain–computer interfaces suggests that in a not-toodistantfuture
a computer might be able to read out a secret number, such as a credit card PIN,
thatapersonisthinkingabout. Thecomingdecadeswillsurelyyieldmoresuchresearch
results.
Challenges and fun curiosities about electrodynamics
Notonly animals, alsoplants can feel electricandmagneticfields.At leastformagnetic
fields, the sensors seem to use very similar mechanisms to those used by animals and
bacteria.
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For everyday size – and larger – systems, electromagnetic motors are most effective. For
microscopic sizes, electrostatic motors are more effective. They are used in sensors and
small actuators. In contrast, large power systems use alternating current instead of direct
current.
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If you calculate the Poynting vector for a charged magnet – or simpler, a point charge
near a magnet – you get a surprising result: the electromagnetic energy flows in circles
around the magnet. How is this possible? Where does this angular momentum come
from?
Worse, any atom is an example of such a system – actually of two such systems. Why
is this effect not taken into account in calculations in quantum theory?
Motion Mountain – The Adventure of Physics copyright © Christoph Schiller June 1990–November 2015 free pdf file available at www.motionmountain.net