Hi everyone,

Just a little background context for those who aren't so familiar with thermodynamics:

The second law of thermodynamics expresses our experience that energy tends to dissipate with time, spreading out into forms that are less and less accessible for use to drive any particular process of interest.

According to the law of conservation of energy (the first law of thermodynamics), the total amount of energy is always conserved, so when you lose energy in one form, you always gain the same amount somewhere else, in another form. For example, a ball at rest at the top of a hill has no kinetic energy (the energy associated with motion) but it has gravitational potential energy because it's up on a hill. If it rolls down the hill it loses some of its gravitational potential energy, but exactly the amount it loses is converted into other forms -- in this case kinetic energy and a little heat due to the friction between the ball and the surface of the hill. No matter what complicated interactions might occur between the ball and its environment (it might hit something and emit sound waves, create a spark and give off light, etc), the total amount of energy always stays the same if you are careful to keep track and add it all up.

So a rough way to think of the second law is that it adds an additional constraint on energy transfer -- even though we never lose any energy, we *do* lose the ability to use it for things like powering lights or running a car. More and more of the energy goes into the form of heat which cannot be entirely transferred back into a mechanical process like lifting a weight or propelling a car. So for example in the case of a steam engine we start with energy in a "concentrated" and "useful" form -- ie energy stored in the chemical bonds of the coal or some other fossil fuel -- and at the end of the process we have some of that energy transferred into the energy of motion of the locomotive, and also some of it transferred into heat (in the air, the metal of the engine, etc.). The energy that is in the motion of the train we can fairly easily transfer into other forms (such as gravitational potential energy when the train goes up a hill). But we can only get a limited amount of the heat energy to go back into driving the train. No energy has been *lost* (it's still around in some form), but some of it is now unavailable to perform the work we want to use it for.

One of the very interesting topics in the foundations of physics for the last 150 years or so (and continuing today, as Pentcho is pointing out) has been the process of clarifying exactly what the second law says about nature and the conditions under which it applies. These ideas are important for our discussions of science integration because the second law plays a very dominant role in our everyday lives, and is closely tied to understanding the direction to time which is such an important part of our experience.

Also, more information about the San Diego conference on the second law this summer is available at http://www.sandiego.edu/secondlaw2002/ in case anyone else is interested.

Todd

> From: Pentcho Valev <pvalev@bas.bg>
> Reply-To: pvalev@bas.bg
> Date: Wed, 27 Feb 2002 18:06:49 +0100
> To: science@lists.pdx.edu
> Cc: pvalev@bas.bg
> Subject: two second laws?
>
> Hi. I am a Bulgarian researcher interested in the foundations of
> thermodynamics, and I wonder if this list would welcome challenges that
> usually meet hostility. There is a conference on the second law in San
> Diego this summer and I am going to participate, but why not an e-mail
> discussion as well. Please tell me if you see any difference between the
> following two Kelvin's versions:
>
> K1: No process is possible in which the only result is absorption of
> heat from a reservoir and its complete conversion into work.
>
> K2: No process is possible in which a system absorbs a heat from a
> reservoir, completely converts it into work and returns to its initial
> state.
>
> In order to find the difference, please think of a creature belonging to
> the surroundings (I call it "operator") that e.g. sets the heat engine
> on and off, switches to a different work production etc. and UNDERGOES
> CHANGES IN THE PROCESS. So, for isothermal conditions, the two versions
> take the forms:
>
> K1: In the absence of an operator, cyclical isothermal conversion of
> heat into work is impossible.
>
> K2: Even in the presence of an operator, cyclical isothermal conversion
> of heat into work is impossible.
>
> Clearly, K2 is more restrictive than K1, and it may turn out that K1 is
> correct whereas K 2 is not. At the San Diego conference, I am going to
> develop further the problem: K1 is related to "Entropy never decreases"
> whereas K2 is related to "Entropy is a state function".
>
> Is anybody interested in such problems?
>
> Best regards,
> Pentcho Valev