Thinking of a pyramid, you have three condos on bottom and one on top. If the middle condo on the bottom is a non-smoking condo and the other three are smoking condos, whose smoke goes into the non-smoking condo? Does smoke go down as a rule? If not, is there a theory that proves this?

My opinion is that this situation is primarily dependent upon the air flow between the condo units. Smoke is airborne particles and gaseous compounds - it goes with the flow, up, down, or sideways. I would expect the middle condo is enjoying the smoke of all the other condos.

An uneducated guess would be smoke or warm arises. If cold out, smoke should go up?
If the air is warmer, it would go down? The direction of wind would be a factor. Any ot the smokers could be the cause, depending on wind direction.
I would wait for an educated answer.
I am having a problem visualizing 4 apartments at the bottom of a pyramid, one of them in the center.
I would knock out some walls, and make 4 equal shaped apartments.
Or if you need a middle apartment, then build 5 apt's. Middle one would have no windows and should be Cheap rent.

Cigarette smoke doesn't just go up - it wafts about on air currents pretty easily. So it would depend on which way the wind blows, how tight the building is, who has or has not opened windows, how the ventiation system or A/C works, which room the smoker is standing in, etc etc etc. Bottom line - there's a good chance that the non-smoker in the middle condo could smell cigarette smoke from any of the other condos.

Thinking of a pyramid, you have three condos on bottom and one on top. If the middle condo on the bottom is a non-smoking condo and the other three are smoking condos, whose smoke goes into the non-smoking condo? Does smoke go down as a rule? If not, is there a theory that proves this?
This can be explained by the science of fluid dynamics. Everything relies on the situation, temperature of the air, the AC, leaks in the rooms...