tisdag 6 juli 2010
From Hot to Cold as Smoothing
In previous posts on backradiation comparing radiation to heat conduction/diffusion, the 2nd Law of Thermodynamics enters in the discussion as stating that without forcing heat flows from hot to cold, but not from cold to hot.
Another way of stating this principle is to say that diffusion acts to decrease differences by local averaging or smoothing, like softening an image in Photoshop. This is a stable process as shown by e.g. the Swedish tax system.
On the other hand, the reverse process of heat flowing from cold to hot increases differences as in sharpening an image in Photoshop. This is an unstable process, which is shown by the impossibility of restoring a smoothed image in Photoshop by sharpening.
The reason heat cannot by itself flow from cold to hot is thus that this process is unstable and thus impossible to observe and thus unphysical. Similarly backradiation is unstable and unphysical.
This connects to my treatise of why time has a forward direction:
which I hope you will have some time to look at. The central idea is that travel backward in time is unstable and thus unphysical. Instability is unphysical because it requires infinite precision which cannot be realized. When you smooth a picture in Photoshop, irreversibly small details are lost by blurring, and blurring is necessary because the precision is finite.
For a more mathematical presentation of the same idea as a version of the 2nd Law of Thermodynamics based on finite precision computation, see the upcoming book
In short: You have to throw old newspapers and clear the disc from old scientific reports, in order to not get drowned in useless information. Getting rid of information is the most basic instinct of life. Metabolism is destruction of information. Metabolism is necessary for the anabolism of growth.