Re: 2nd law clarifications

MarkE <me22over7@gmail.com> wrote:

Are these statements correct? Could they be better expressed?
 
 
Local entropy can decrease in an open system with an input of free energy.
 
Free energy alone is not sufficient to maintain or further decrease low
local entropy: an energy capture and transformation mechanism is also
needed.

Not necessarily. A rotating planet around a star is bathed in
low-entropy photons during the day and radiates high-entropy photons
during the night.

Extant life *maintains* low local entropy through its organisation and
processes.

That's not it. Extant life *uses* a source of low entropy. The sun's
energy is high-frequency low-entropy (visible light), allowing life to
consume that and give off waste energy as heat, which is radiated away
as infra-red.

There's a nice quote from Discover magazine:

https://www.discovermagazine.com/the-sciences/evolution-and-the-second-law

"The energy we get from the Sun is of a low-entropy, useful form,
while the energy we radiate back out into space has a much higher
entropy. The temperature of the Sun is about twenty times the average
temperature of the Earth. The temperature of radiation is just the
average energy of the photons of which it is made, so the Earth needs
to radiate twenty low-energy (long-wavelength, infrared) photons for
every one high-energy (short-wavelength, visible) photon it receives.
It turns out, after a bit of math, that twenty times as many photons
directly translates into twenty times the entropy. The Earth emits the
same amount of energy as it receives, but with twenty times higher
entropy."

Andrew.