d.w.rowlands [at] gmail.com
On occasion, I write short essays explaining scientific topics. The audience for these varies from non-scientists with fairly limited mathematical backgrounds to people familiar with calculus and an intermediate level of physics and chemistry. The topics also vary quite a bit, from posts on physics and chemistry topics that I have more direct experience with to discussions of things about biology and paleontology that I've learned from leisure reading. A number of these short essays are listed below:
In Fall 2015, I taught an introductory physics class at Anne Arundel Community College, where I am an adjunct professor. Unlike most adjunct teaching assignments, this one gave me the freedom to design the course materials from scratch. I prepared an eighty-page lecture handout in LaTeX, which I've posted online. If you are an instructor who would like to use some of this material for your own class, please let me know. I'm glad to share materials in general, and can provide the LaTeX source files.
This piece is part of the material I covered while helping substitute-teach a two-hour class for high school students as part of the MIT Educational Studies Program's Splash 2011 event. The teacher became seriously ill the day before the class was to be taught and he didn't leave a syllabus, only the course title "Faster-Than-Light Travel", so a physics grad student and I had twenty-four hours to come up with one from scratch. He ended up teaching an hour-long lecture on Special Relativity, while I put together an hour-long lecture on various things that are or look like ways to get around it. One part of this was a discussion of quantum entanglement that I wrote with a lot of input from a physicist friend. Writing this was hard, but I feel like I learned a good deal from it, because I never previously understood how we knew that hidden variables couldn't exist. I know I read a number of Scientific American articles on this topic when I was in elementary school, but I didn't really understand them, and this issue wasn't really covered in the quantum classes I did take in that much detail.
The following is a physics problem that came up as an example in the teaching class I took from the MIT Teaching and Learning Lab in spring 2014. I thought it was interestingly subtle and worth sharing. Suppose you have two long blocks of wood of the same length. The only difference between them is that one is twice the thickness of the other. If you hang them from the top and tap each one on the side to ring it, which produces the higher tone, and why?
It's probably due to my history of working with NMR, but I have a bit of an obsession with the concept of negative temperature, one of the consequences of thermodynamics that physicists and physical chemists tend to be vaguely aware of but not think about. An article in Science by a group that figured out a way to achieve negative temperature in the mechanical vibrational energy of a material brought the topic to my attention again and persuaded me to teach a class for high school students on the topic as part of the MIT Educational Studies Program. Secretly it's an introduction to statistical mechanics and the concepts of entropy and temperature, but I thought negative temperature would be a good way to make the material sound interesting.
The Ceyer Lab at MIT, where I did my graduate research, studies chemistry in "ultra-high vacuum." For us, this means that the base pressures of our vacuum chambers are around 5*10-11 torr (a couple of orders of magnitude better than Wikipedia thinks: we wouldn't count 5*10-9 as UHV at all). This is roughly four orders of magnitude higher vacuum than what the International Space Station experiences, a talking point that I like to use when describing my research to people who are unlikely to have a sense of what a milltorr is. I recently discovered that a lot of people are confused by the idea that there can be multiple "degrees of vacuumness," and are under the impression that outer space is a perfect vacuum. The following is a short explanation I wrote up for one such person, and am posting here in case other people find it useful or interesting.
In 2014, the Nobel Prize in Chemistry was won by a physicist and two physical chemists who were involved in the development of fluorescence microscopy techniques that allow optical imaging on a scale smaller than the "diffraction limit". While I was glad to see that the prize was for physical chemistry---albeit physical chemistry that's mostly of interest to biologists---instead of the all-too-frequent chemistry prizes that are really a second prize in biology, I was a bit embarrassed to admit that I didn't really understand how fluorescence spectroscopy works. I'd heard it mentioned in freshman biology at Caltech, but the professor didn't go into any detail about how it gets around the diffraction limit and the TAs didn't seem to know. And, since then, I hadn't really thought about it at all, since it's a technique that's really only of use in biology labs. However, the Nobel announcement made me decide that I needed to try to actually get a bit of an understanding. And, since I've been reading about it, I thought I'd write an essay to try to give a simple lay explanation of it.
One of the size limitations on single-celled organisms is that, the larger a cell gets, the larger the distance between the surface and the center. This makes it hard for nutrients to reach the interior of the cell and for waste products to be released. Being made of many small cells instead of one large one allows a much higher ratio of cell surface area to volume. However, when organisms get big enough, getting nutrients to cells in the interior itself starts to be a challenge. This is particularly challenging for metazoans---animals---since they tend to have relatively fast metabolisms to enable them to move around. Blood is a common solution to the problem that evolved separately in several metazoan lineages.
When I was in elementary school, the difference between plants and animals was explained to me as that "plants can make their own food from sunlight; animals have to eat other animals or plants for food." No one really bothered to define "food" very clearly, though, and I was always a bit confused by why plants needed fertilizer, or "plant food", if they made their own food. The answer is a bit more complicated and, unsurprisingly, it gets a lot more complicated once you start to consider bacteria.
A bioengineer friend recently recommended that I read Power, Sex, Suicide: Mitochondria and the Meaning of Life, by Nick Lane. It was indeed an incredibly neat book. While I somewhat suspect the author of having an agenda---wanting to prove that mitochondria are responsible for essentially everything---I certainly learned a lot about biology that I hadn't known.
This essay grew out of a conversation with some friends---a mix of scientists and historians---about sources of protein in the Medieval European diet. One of my friends argued that the introduction of potatoes in the 1500's couldn't have made a major difference because potatoes are of little nutritional value other than empty calories. This became a rather heated topic of debate and consideration of Wikipedia's chart of the nutritional value of the ten most-grown staple crops made me rather skeptical of the claim that potatoes are low in nutrients, so I decided it was worthwhile to make a more detailed comparison of all the major staple crops.
While gliding vertebrates appear to have evolved independently a couple of dozen times, true powered flight has only evolved in three vertebrate lineages: first among pterosaurs in the late Triassic about 230 million years ago, then among the theropod dinosaur ancestors of modern birds in the late Jurassic about 160 million years ago, and finally among bats in the Eocene about 50 million years ago. There are some basic similarities of the flight techniques that each group developed---in each case wings developed from forelimbs---but there are also significant differences that have affected what niches they are best adapted for.
Since cells are basically membranes filled with aqueous solution, it's generally assumed that life originated in water. When the first living things moved on land is not really clear, but the first land life presumably consisted of single-celled organisms. Multicellular life complex enough to invade land really only began around the start of the Phanerozoic Eon, 541 million years ago. During this eon, which continues to the present day, multicellular life developed from a few fairly simple forms to a wide variety of organisms that have spread into most environments on the planet. The first half of the Phanerozoic, the Paleozoic Era, saw life on land go from simple microbial mats to a variety of forms that we would largely recognize today, or at least are relatively familiar with even if they're now extinct.