| Caution Regarding Ultrascope View: The Ultrascope view is designed primarily to provide a QUALITATIVE insight into the small particle dynamics of gases, liquids and solids. They only provide a picture of the physics in the tiny area provided by the macroscopic view. In many cases, they will not "agree" with their macroscopic analogues. In the example below (taken from the Gas Diffusion simulator), the bottom half of the container contained a "medium" gas with medium-sized particles, and the upper half contained a gas with small particles. Ninety seconds after a membrane is exposed that is large enough for medium particles to pass through, the density of "medium" gas in the upper half is about 8% of the density of the "medium gas in the lower half. However, the Ultrascope view depicts exactly the same medium particle number density in both sides of the container near the membrane.

The physics depicted by the Ultrascope view is reasonably accurate, because, as the heavier gas leaks into the upper half of the container, it will first be concentrated near the membrane and spread out from there. The situation is analogous to water leaking out of a bucket through a small hole onto a floor. The water is first concentrated near the bucket, and then slowly spreads out across the floor from the pail. In the gas diffusion example, the gas density near the membrane should be higher than the average density in the upper half, which is what the figure above shows.