Hi Vincent,
Not really. In an explosion, a material either burns very rapidly,
as is the case with conventional explosives, or undergoes nuclear
reactions, as you mention. Both kinds of reactions make the material of
the bomb very very hot. At high temperatures, materials vaporize --
they turn into gases which take up more space than their solid
versions. Hot gases take up even more space than cold ones. The "Ideal
Gas Law" says that
Pressure*Volume = (number of molecules)*Temperature*(a universal constant).
If the number of molecules doen't change but they suddenly get
really hot, then the pressure times the volume goes way up. Instead of
a void, one has in the center of an explosion, a region with very hot,
high-pressure gas, which isn't very dense. It is this gas which presses
on other stuff nearby and which causes damage. Damage also comes from
fires ignited by the explosion, and in the case of nuclear explosions,
also by radiation and contamination.
As the explosion progresses, the hot, expanding gases push on the
surrounding gases, piling up a shock front in front of it. The
expansion slows as the expanding gas cools off, and the shock front
will separate and travel on its own as a wave when the speed of the
expanding gases falls below the speed of sound in the air. Supersonic
shock fronts are possible in very strong explosions, such as nucear
explosions.
The hot ball of gas released by the explosion is not dense but
takes up a lot of space, and so it floats upwards. Explosions often
result in a fireball floating upwards over the explosion site. There
may be an inward draft of cooler air after the initial shock front has
passed as air replaces the hot gases that float away.
In the Big Bang, we think that no part of space was much different
from any other part, since the left-over radiation seems about the same
in every direction. So there would have been no particular place to
have a 'void'. It's not to picture the Big Bang as a bunch of stuff
exploding into a pre-existing space, but rather as the space itself
blowing up carrying stuff with it.
Tom and Mike
(published on 10/22/2007)
