Conservation

This week in physics lab my students are testing the principle of conservation of energy by dropping a marble through a photogate and comparing the kinetic energy the marble gained with the gravitational potential energy it gave up as it fell. In a perfect world, these quantities would be equal, and thus total energy conserved. Since we don’t live in a perfect world, energy is continually dissipated by insidious forces like air resistance et al. Regarding this points, I had Serendipitously just read the following comic from xkcd.com and asked my students to write about it:

SOURCE: XKCD.com

What I wanted them to think about is the divergence between the tools, powerful and useful they may be, that we use to describe the world (total energy always stays the same) and what is really practical to do. According to the principle of conservation of energy (also known as the first law of thermodynamics for those keeping track at home) the scheme shown in the comic should be a perfectly acceptable way to “transport wind,” with no loss of intensity. Of course, this comes with the proviso that the turbine must capture all of the wind energy and be perfectly efficient. The power cable must have zero electrical resistance, and the fan must also have a 100% efficiency rating.

However, we know intuitively (or at least, we should) that, in the real world, nothing is perfectly efficient, and the actions of the cartoon’s protagonist will inevitably lead to a colossal waste,  since each step of converting from wind to electricity and electricity to wind entails a loss of energy.

In case you think that the whole discussion is silly, and that no one in their right would convert so profligately from one form of power to another, consider the case of back-up power for server farms. Google has a patent on a method that saves energy by reducing the number of times electricity has be to converted between AC and DC. Evidently, this was an innovation, and existing server farms were build with inefficiency wired-in:

From Google’s “Story of Send.” Click for video

Now, there are limits, even in principle, to the efficiency of some processes. Once you get past the idyllic world of the 1st law, the second law of thermodynamics puts some upper bounds on what you can do even if you try your hardest to squeeze every last bit of efficiency out of certain ways of converting energy between various forms. However, as one of my students pointed out, there is no reason why you couldn’t drive forever in a “perfect” hybrid car that recaptured all of the energy from braking (and going up hills).

 

Physics Nobel

Peter Higgs is going to have to wait at least one more year (although he might be used to waiting by now, since it took researchers almost half a century to find his boson in the first place).  The 2012 Nobel Prize in physics is going to Serge Haroche and David Wineland for their work on observing the quantum state of individual atoms. For my fellow Americans who like to keep track of US Nobel winners as a quantifiable metric of our awesomeness at science,  not only is Dr. Wineland an American, he works for us taxpayers as an employee of NIST. Lest you think that tax dollars should not be frittered on basic science, consider some of the important applications to come from government research, as in: “The next time a GPS keeps you from getting lost, thank a fed”  Now, this current research promises to point the way towards the next generation of quantum computers and optical clocks. More importantly, this work helps us make sense of how, as far as well can tell, the Universe actually works. Far from being a weird curiosity, the paradoxes of quantum mechanics are how things really behave when you peel back all the layers. It’s our everyday experience, where things aren’t (or a least seem to act like they are not) in multiple places at once, that needs explaining.

Continue reading “Physics Nobel”

Rewinding History

Some of the most interesting history thought-experiments consider the question of the inevitability of important world events. Was the South destined to lose the US Civil war due to its inherent disadvantages, or could some strategic blunder have turned the tide? The question of contingent history has a parallel in biological evolution. The difference is that science is now beginning to give us the tools to draw actual conclusions about what would happen if we could “rewind” the clock of evolution and play it again. We can start to identify the contingent calf-paths in our ancestry, and distinguish them from the traits, like flying and vision, which have evolved separately multiple times different lineages. The similarity between  marsupials and placentals is commonly cited as strong evidence that not everything is by accident. However, the amplifying effects of the “rich-get-richer” is a hallmark of network behavior. Just as the choice, possibly based on minor considerations existing centuries ago, of whether a tiny settlement might be built on bank of the river or the other can dictate the location of a modern metropolis, small, accidental changes may get locked-in by evolution.

We now have the opportunity to watch history play out again, either by doing it ourselves and growing 20 years of bacterial generations, as in the Lenski lab, or by resurrecting ancient genes from 500 million years ago and inserting them into modern specimens. The picture that is forming from these experiments is, as in history, a mix or randomness and inevitability that shows the importance of individual mutation events that can “potentialize” or “actualize” a given adaptation. There is likely to be a crucial, revolutionary advance hit upon by evolution that, by itself, does not totally provide for the trait, but is close enough so that some among the population of its descendants are, under the right external conditions, strongly favored to have a large advantage when they perfect the trait. So the response to our question should be “how far back do you want to rewind?” 

Poor Power

That the Gettysburg Address is among the most famous speeches in the American consciousness is one of history’s great ironies. If you actually read the words, Lincoln discusses the powerlessness of words, and that no one will care about what said that day:

 “…we can not dedicate, we can not consecrate, we can not hallow this ground. The brave men, living and dead, who struggled here, have consecrated it, far above our poor power to add or detract. The world will little note, nor long remember what we say here, but it can never forget what they did here.”

Perhaps this is why he spoke for only 2 minutes, while others droned on for several hours at the same dedication. In any case, the role of an observer, who notes but does not alter the situation, can to my mind today as I was teaching physics lab. In my class, overwhelmingly pre-med students, 12 of 15 were female. This might seem surprising for subject matter that had been seen as the Provence of men, but I was not so surprised.  I just started reading The End of Men: And the Rise of Women by Hanna Rosin. She is aware that the purpose of her book is not to set forth an argument, but rather to mark a  momentous shift in the course of the human experience. For the first time since ever, females are overtaking their chromosomal mismatched counterparts. Rosin points out that the rise of automation has dealt a heavy blow to traditionally “male” occupations, like construction and manufacturing. When given a level playing field, where brawn is not an issue, women are thriving and men are getting left behind. At Nova Southeastern University, where I teach, about 70% of the student body is of the female persuasion, and nationally the figure is around 2/3. In this new connected world, where a machine (or third-world laborer) can do most taxing and menial tasks, the value of education has never been greater. Women are seeing the larger divergence in life- paths between unskilled workers and trained professionals and choosing their education levels accordingly.

Revenge of Discarded Ideas

The webcomic xkcd has many gems, but one my all-time favorites pokes fun at how teachers have a pechant for over-emphasizing the wrong-ness of a “misconception.” In an usually admirable but misguided effort to move students from a naive way of thinking, “overzealous” instructors salt the Earth so that no further thinking can occur in the “wrong” tracts. However, sometimes the most seemingly incorrect views reappear when least expected. One of the famous scientific controversies middle school biology students are taught regards the theory of Lamarckism, which essentially states that evolution occurs because offspring inherit changes that occurred to their ancestors. The classic example is of a giraffe, which is said to acquire a long neck from stretching for the leaves at the top of trees. According to Lamarck, this useful trait (long neck) is then inherited by its children. Ask any elementary school teacher about the “heritability of acquired characteristics” today, and you are overwhelming likely to hear stories involving mice getting their tails hacked off, but going on to give birth to normally-tailed offspring. Students get drilled into them the concept that only germ cells can carry heritable information, and that what happens to a organism during its lifetime has no bearing on the “book of life” it gifts to its offspring. But what if that book can have annotations? The growing field of epigenetics is showing almost daily that just a copy of the “instruction manual” is not enough to get through the business of living. Genes can be turned on or off, in way we are only beginning to fully appreciate. For example, all the cells in your body, whether nerve, muscle, lymphocyte or whatever, carry around a full copy of your DNA sequence. The assignment to become a certain cell type requires changes that “mark-up” the genes needed or not needed, depending on the jobs. This may be done with chemical tags; for example, adding a methyl group to a nucleotide base to change how its gene it encodes is expressed. We are finding that some changes, like the difference between worker bees as nurses or foragers, are reversible, or even heritable from your parents experiences.

While it may be important to replace naive conceptions of giraffes with more sophisticated ones, teachers often do a disservice to their students by “overselling” certain concepts. Because nature is (and must be) more complex than that.