Friday, August 08, 2008

Thermodynamics is like a parent!


An old McSweeny's list compared different physical theories to women in a man's life. For example,

0. Newtonian gravity is your high-school girlfriend. As your first encounter with physics, she's amazing. You will never forget Newtonian gravity, even if you're not in touch very much anymore.

In a spirited response, Jennifer Oullette offers us -- "in the interests of fair play, the women should have their own version while we're having fun with the battle of the sexes." -- physical theories as men [Thanks to Guru for both the links]. Here's the same Newtonian gravity as a man:

0. Newtonian gravity is that guy you had a crush on in high school. You never really dated, but you spent a lot of time together, and once you even made out in the science lab after school over a partially dissected fetal pig. It didn't go well. Things were kinda awkward after that, but you remained friendly from a distance. Or so you thought. Years later, you find out he told everyone you were a frigid lesbian -- even though he was the one who wouldn't go past second base because he "respected" you too much. To paraphrase Whistler, the helpful demon from Buffy (Season 2): "Newtonian gravity is like dating a nun. You're never gonna get the good stuff." You suspect he may have been gay.

Both the pieces are fun and interesting, and all. But neither of them had anything to say about thermodynamics.

I was glad to see a few comments on Oullette's blog filling this crucial gap:

Tom: Thermodynamics is the guy you're never really into, who helps you move into a new apartment/dorm, even while you're dating Electrodynamics or Special Relativity. By the time Quantum comes along, he realizes it's hopeless.

Matt: Tom is too generous. Thermodynamics is your dad. [see also the Footnote]

Ouch!

* * *

But I think Matt is onto something. Like a good parent, thermo lays down very few laws. They are laws that can never be violated (Even Homer Simpson got it right when he said "In this house, we OBEY the LAWS of THERMODYNAMICS!"). And they are laws that are full of wonderful insights about all kinds of things, and make us see the connections among them.

* * *

Why am I posting this stuff? Well, I start teaching this subject today.

* * *

[Footnote] Here's Lab Lemming on who thermo is really like:

Thermo isn't your dad, it's your daughter.

7 Comments:

  1. Poonkuzhali said...

    I think you're wrong when you say that the laws of thermodynamics can NEVER be violated. Size apparently does seem to matter and a new framework may have to be developed that generalizes thermodynamics (something that could tie non-equilibrium thermodynamics to equilibrium thermodynamics, perhaps?) The second law can be violated, stat mechanically speaking ie. Surprised you didn't know about this...

  2. Abi said...

    Poonkuzhali: Oops! Just to clarify: I teach thermodynamics of materials at the macroscopic scale, where the thermodynamic laws continue to retain their inviolable status. It is only when the systems shrink to tiny sizes -- about a few nanometers -- one gets interesting results that point to limits of applicability of the second law.

    But your broader point is valid (and I thank you for making it): I should have been clearer about the macroscopic viewpoint.

  3. Chuck said...

    If your students want a historical introduction, perhaps you should teach them about the thermodynamics of hot chicks.

  4. Animesh said...

    Good luck teaching thermodynamics. Don't forget the zero'th law! [still not sure why they had to make a law abt something so obvious :)]

  5. Rahul Siddharthan said...

    abi, poonkuzhali: Yes, the second law doesn't apply to small systems. It's a statistical law. And that's exactly why it's inviolable in large systems.

    Eddington on the second law: "If someone points out to you that your pet theory of the universe is in disagreement with Maxwell's equations—then so much the worse for Maxwell's equations. If it is found to be contradicted by observation—well these experimentalists do bungle things sometimes. But if your theory is found to be against the second law of thermodynamics I can give you no hope; there is nothing for it but to collapse in deepest humiliation."

    Though historically statistical mechanics came first and information theory came later, I think it makes more sense to think of statistical mechanics as an application of information theory (cf. Jaynes).

  6. Anonymous said...

    In the guise of teaching thermodynamics, you asre bringing in hot Babes.
    Now for some thing coolNow That's Cool




    Abstract:
    "Ye canna change the laws of physics!" Scotty warned Captain Kirk on "Star Trek." But engineers and physicists at the University of Maryland may rewrite one of them.

    The Third Law of Thermodynamics is on the minds of John Cumings, assistant professor of materials science and engineering at the University of Maryland's A. James Clark School of Engineering, and his research group as they examine the crystal lattice structure of ice and seek to define exactly what happens when it freezes.

    Now That's Cool
    COLLEGE PARK, MD | Posted on August 6th, 2008
    "Developing an accurate model of ice would help architects, civil engineers, and environmental engineers understand what happens to structures and systems exposed to freezing conditions," Cumings said. "It could also help us understand and better predict the movement of glaciers."

    Understanding the freezing process is not as straightforward as it may seem. The team had to develop a type of pseudo-ice, rather than using real ice, in order to do it.

    Despite being one of the most abundant materials on Earth, water, particularly how it freezes, is not completely understood. Most people learn that as temperatures fall, water molecules move more slowly, and that at temperatures below 32º F/0º C, they lock into position, creating a solid—ice. What's going on at a molecular level, says Cumings, is far more complicated and problematic. For one thing, it seems to be in conflict with a fundamental law of physics.

    The Third Law of Thermodynamics states that as the temperature of a pure substance moves toward absolute zero (the mathematically lowest temperature possible) its entropy, or the disorderly behavior of its molecules, also approaches zero. The molecules should line up in an orderly fashion.

    Ice seems to be the exception to that rule. While the oxygen atoms in ice freeze into an ordered crystalline structure, its hydrogen atoms do not.

    "The hydrogen atoms stop moving," Cumings explains, "but they just stop where they happen to lie, in different configurations throughout the crystal with no correlation between them, and no single one lowers the energy enough to take over and reduce the entropy to zero."

    So is the Third Law truly a law, or more of a guideline?

    "It's a big fundamental question," says Cumings. "If there's an exception, it's a rule of thumb."

    Materials that violated the Third Law as originally written were found in the 1930s, mainly non-crystalline substances such as glasses and polymers. The Third Law was rewritten to say that all pure crystalline materials' entropy moves toward zero as their temperatures move toward absolute zero. Ice is crystalline—but it seems only its oxygen atoms obey the Law. Over extremely long periods of time and at extremely low temperatures, however, ice may fully order itself, but this is something scientists have yet to prove.

    Creating an accurate model of ice to study has been difficult. The study of ice's crystal lattice requires precise maintenance of temperatures below that of liquid nitrogen (-321 °F/-196 °C), and also a lot of time: no one knows how long it takes for ice to ultimately reach an ordered state—or if it does at all. Experiments have shown that if potassium hydroxide is added to water, it will crystallize in an ordered way—but researchers don't know why, and the addition shouldn't be necessary due to the Third Law's assertion that pure substances should be ordered as they freeze.

    To overcome these problems, scientists have designed meta-materials, which attempt to mimic the behavior of ice, but are created out of completely different substances. A previous material, spin ice, was designed from rare earth elements and had a molecular structure resembling ice, with magnetic atoms (spins) representing the position of hydrogen atoms. However, it did not always behave like ice.

    The Cumings group is refining a successor to spin ice called artificial spin ice, which was originally pioneered by researchers at Penn State. The newer meta-material takes the idea a step further.

    "The original spin ice research went from one part of the periodic table to a more flexible one," said Cumings. "But artificial spin ice goes off the periodic table altogether."

    Artificial spin ice is a collection of "pseudo-atoms" made of a nickel-iron alloy. Each pseudo-atom is a large-scale model made out of millions of atoms whose collective behavior mimics that of a single one.

    As with the original spin ice, magnetic fields are stand-ins for hydrogen atoms. Working at this "large" scale—each pseudo-atom is 100x30 nanometers in size (100 nanometers is 1000 times smaller than the width of a human hair)—gives the researchers control over the material and freedom to explore how real atoms behave.

    "It mimics the behavior of real ice but is completely designable with specific properties," Cumings said. "We can change the strength of the spin or reformulate the alloy to change the magnetic properties, which creates new bulk properties that we either couldn't get from normal materials, or couldn't control at the atomic level."

    The team is also able to image the behavior of the pseudo hydrogen atoms using an electron microscope—such direct observation is not possible with the original spin ice or real ice.

    "This is the first time the rules of ice behavior have ever been rigorously confirmed by directly counting pseudo hydrogen atoms," explained group member and postdoctoral research associate Todd Brintlinger. "We can track the position and movement of each pseudo atom in our model, see where defects occur in the lattice, and simulate what happens over much longer periods of time."

    The ultimate impact of the research may go beyond civil engineering and the environment. "Although we're mimicking the behavior of ice," Cumings explained, "our meta-material is very similar to patterned hard-disk media. Magnetic 'bits' used in hard drives are usually placed at random, but memory density could be increased if they were in a tight, regular pattern instead.

    "We've found that both hydrogen in ice and the pseudo-hydrogen in our artificial spin ice also behave as bits, can carry information, and interact with each other. Perhaps in the future, engineers will be inspired by this in their hard drive designs. The formal patterning and bit interactions may actually help to stabilize information, ultimately leading to drives with much higher capacities."



    Anon

  7. Anonymous said...

    As I am begining to teach periodic Table, Iam inpired by your approach to thermodynamics.
    Look what I found:Mendeleev's table, a celebrated example of the visual display of quantitative information, transformed chemistry (and triggered imitations cataloguing everything from breakfast cereals to sex positions to neo-nerds). The table inspired thinkers including Primo Levi and C.P. Snow. "I could scarcely sleep for excitement the night after seeing the periodic table," Oliver Sacks wrote in his 2001 memoir Uncle Tungsten.

    Eka-nanopolitan