Diffusion? What powers diffusion? it seems to be hugely important for bodily functions as well as atomically and possibly astronomically
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Diffusion is powered by the thermal motion of molecules. They constantly fly around and collide with each other randomly, and this means that some of them are flying out all the time.
Similar to Brownian motion where the particle have their own movement energy and bounce off other things and naturally spread out.
Imagine a cup of water. While it looks still, the water molecules are actually moving around, bumping into each other, hitting the sides of the container, sometimes speeding up, sometimes slowing down. This movement is part of the reason you can dip your finger into the cup and the water will move out of the way (unlike ice, where the molecule are moving much less). The average speed at which the molecules are moving is related to the temperature. A higher temperature means they are moving faster (on average).
Now picture dripping a single drop of dye or food coloring into the water. Rather than stay as a single drop, it starts to spread out. This is diffusion. The dye molecules are also moving around, bouncing into each other and the water molecules. The dye will slowly diffuse and spread through the water in a largely random way.
This is the simplest form. You can also have things diffuse through a membrane – imagine putting a mesh screen in the cup and then only dropping the dye on one side. It will take a bit longer for it to diffuse to the other side, since the mesh interrupts or blocks some of the movement, but as long as the holes are big enough to allow molecules through, it will eventually spread throughout the cup.
Diffusion is a product of entropy.
Concentrated things have more potential energy than diffuse things, so their random motion is more likely to cause then to spread out than concentrate further.
There is a drive for things to become more disordered. Lots of things being on one side and less on the other is considered more ordered, compared to after things have diffused. The actual term for this type of disorder is entropy as mentioned by others.
Source: I am a physical chemist
Imaging a crowed of people in an otherwise empty field. Everybody has a sudden urge to go jogging. What you will likely see is that the people will not stick to the crowd but spread out to the whole field due to two factors: A) People would keep walking forward which eventually leads out of the crowd. B) People running towards a group are more likely to turn to avoid collision, them does running in the opposite direction.
With molecules this is the same. They move due to termal energy and push away from each other due to electromagnetic forces.
This process is known as diffusion.
Mathmatically this process means that structure gets lost (from the fairly localised crowd on the field to a constant level of people everywhere) which can be described by an increase in entropy.
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