Since we are all bragging about our special knowledge (scuba, aerospace) let me add that I have built powerful multi-stage vacuum pump systems (using different kinds of pumps at each stage) strong enough that the remaining air barely conducts electricity and glows when it does. I used a 9000v neon sign transformer as a poor mans pressure gage. When the pressure got low enough the 9000V would make it glow, sometimes in strange ways, bars and bands and things that I never really understood. When the vacuum got really good the glow went away, probably because there weren’t enough ionized air molecules left to conduct electricity. I was trying to get enough air out that electrons could travel freely, i.e. very fast. In there somewhere I also studied advanced thermodynamics which is where the gas laws describing this behavior comes from. Trust me! The gas laws are a better guide than intuition or gut feel when trying to predict what differences in air pressure will do, in a bag or elsewhere. And practical experience with extreme low pressure is even better.