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Tuesday, December 28, 2004 CE

The second law of thermodynamics

I am not a physicist, but I will try to explain what I understand of it. If there is any scientist over there that wants to give me some help in explaining this he or she is welcomed.

This law states that thermal energy (heat), is special among the types of energies. All the forms of energy can be converted into heat, but in a way that is not reversible. It is not possible to convert the heat back fully in its original form. This essentially means that in each reaction, there is some energy that is going to be lost as heat without converting into another "more useful" form of energy. This unusable heat is characterized by the random motion of molecules. The second law says that the amount of random movement(entropy) can only increase in a closed system. Being the Universe a closed system, the law says that entropy will always increase in the Universe. This means that the random motion will only increase with time. After billions of years the possible scenario is the even distribution of heat (random motion) throughout the Universe.

Many people have tried to imply that the evolution contradicts the second law of thermodynamics. The Earth is an open system, receiving continuous new energy from the sun. The only way that life has been getting more complex in our planet as time passed is because the energy dissipated by the chemical reactions of life is replaced in excess by the sun' energy.

Links: The second Law of thermodynamics, Entropy


Blogger Daniel_T said...

I appreciated your post on this topic. I studied a lot of physics at university in Australia as part of an electrical engineering degree. I found the 2nd law of thermodynamics to be one of the most fascinating of natural laws - to me it defines the nature of life on earth - from a "simple" event like boiling the kettle to make some tea, to how humans function in social environments. In its basic essence it says to me that all entities, be they atoms, molecules, amoebas, carrots, lizards, cats, dogs, or humans all strive for maximum freedom. This is a law worth looking into!


6:41 PM  
Blogger Doctor Marco said...

It is indeed fascinating. This law actually predicts the end of the Universe as we know it.

11:31 PM  
Blogger Doctor Bean said...

Great post! Thermodynamics was my favorite undergraduate course. I'm a doctor by trade but a math/physics/engineering geek at heart.

I totally agree with your description of the 2nd law. One interesting thing about it is that it can not be derived from any other basic physical laws. That is, it can not be derived from Newton's Laws or even from General Relativity. It is purely empirical. We know it is true simply because it always agrees with our observations.

The other interesting thing about it is that unlike Newton's Laws or General Relativity the 2nd law is time asymmetric. That means that in Newtonian mechanics or even in General Relativity reversing the direction of time leaves the laws exactly as they are. Meaning if a certain process obeys GR, watching the process backwards would obey GR as well. The 2nd law breaks that symmetry and insists that time increases in the same direction as entropy. An egg cooking obeys the 2nd law. Watching a movie of an egg cooking backwards -- a cooked egg liquefying and cooling, thereby heating a pan which thereby heats a gas burner –- clearly violates the 2nd law which is how we can tell the movie is running backwards.

So some physicists believe that the 2nd law doesn’t really tell us something about entropy; it really tells us something about time. It gives us a law that lets us differentiate the “past” direction of the time axis from the “future” direction. The law simply states that the future is the time direction in which entropy increases.

I hope I'm making sense. Richard Hawking’s book A Brief History of Time has a wonderful discussion about this that is very readable by a non-physicist. From what I can tell from your blog we have similar reading tastes. So I think you’d like it.

Sorry for the long comment (but it’s not frequently I get to dust off my thermodynamics synapses). Good night.

3:33 AM  
Blogger Marrissa said...

I must admit, a physicist I'm not, so I struggle to understand this theory completely. I do understand that energy can neither be created nor destroyed. Under this "possible scenario" could this be why it's so hot in Austin in January? (I.E. global warming) Now I have to look this up. Your blog is taking more and more of my Sunday. :)

3:18 PM  
Blogger Doctor Marco said...

I do not think there is a direct link between the second law of thermodynamics and global warming, however, there is, I am sure, an indirect link.

10:51 PM  

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