[Havoc]

First, we need to know how the mass of Hell is changing in time.
So we need to know the rate that souls are moving into Hell and the rate they are leaving.

I think that we can safely assume that once a soul gets to Hell, it will not leave.
Therefore, no souls are leaving.

As for how many souls are entering Hell, lets look at the different religions that exist in the world today.
Some of these religions state that if you are not a member of their religion, you will go to Hell.

Since there are more than one of these religions and since people do not belong to more than one religion,
we can project that all souls go to Hell.

With birth and death rates as they are we can expect the number of souls in Hell to increase exponentially.

Now, we look at the rate of change of the volume in Hell because Boyle's Law states that in order for the temperature and pressure in Hell to stay the same, the volume of Hell has to expand proportionately as souls are added.

This gives two possibilities:

1. If Hell is expanding at a slower rate than the rate at which souls enter Hell, then the temperature and pressure in Hell will increase until all Hell breaks loose.

2. Of course, if Hell is expanding at a rate faster than the increase of souls in Hell, then the temperature and pressure will drop until Hell freezes over.

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You mean like that? :P

Sorry, just had to post that...