I am endebted to Anders Sandberg for this idea.
The air we breathe consists of about 0.2 atmospheres
of oxygen and about 0.8 atmospheres nitrogen. Divers
have shown that helium can be substituted for the nitrogen,
since the body does not use either substance. Helium
actually works better for high pressure applications, since it is
a noble gas, and so does not react with or dissolve in the
bloodstream like nitrogen will do under sufficient pressure.
In a diving bell, oxygen can be held at .2 atmospheres and
helium added with no apparent harm or discomfort to the
divers.
The noble gas xenon is chemically similar to helium,
except for being nearly 33 times denser. If a person
were to be placed in a pressure chamber with oxygen held at
0.2 atmospheres, then xenon added until the total pressure came
up to about 190 atmospheres, the density of the gas mixture
in the chamber would be about equal to that of water. The
person would then float. It would simulate weightlessness
better than being in water, since the xenonaut could breathe the
medium in which she was floating.
The partial pressure of oxygen would need to be increased
somewhat to counteract the tendency of the oxygen to
float to the top, however there is no reason to doubt that
humans could swim in xenon. The experience would not
be exactly the same as floating in your living room however,
for the pitch of the voice varies as the inverse square root
of the density of the medium. The xenon swimmer's voice
would be lowered by nearly 4 octaves, causing her to talk
like Lurch the butler.
It would take no extraordinary engineering of pressure vessels
to accommodate 190 atmospheres. In fact even a relatively
thin walled container would do fine, if one could arrange to lower
it into the sea as the pressure is raised. Alternately, the chamber
could be placed at the bottom of a mile-deep shaft and water could
be allowed to flow in as the pressure is raised, then drained
as the pressure is lowered. Even if the pressure needed to be
dropped quickly, this should not present a problem, since it has
been pointed out that the solubility of xenon is negligible. The worst
possible effect would be the expanding xenon would escape from
the bodily orifices into which it has been forced during the
pressurization, perhaps creating embarrassing noises.
The one killer app for weightlessness that eeeeveryone wants
to try might not work out either, since one likely could not
breathe fast enough. The dense column of xenon would resist
changing direction quickly, so the participants could scarcely
get their breathing rate much above 1 Hz, insuffient for this
kind of activity. Then there's the problem of sounding like
Jabba the Hut and Mrs. Hut on their honeymoon, which might
in itself spoil the mood. Other than that, one could put together
a really cool sensory deprivation chamber. spike
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