Physics Works Best if International

by Helena Reichlova

“Do you like to travel?” I have not met many young people who would answer “no” to that question. A much more interesting question is, “Why do you travel?” Although responses may vary, I might predict that they commonly contain words like “new” and “different.”   I imagine that’s because we like to interact with unfamiliar places, cultures, food, and people… simply because those interactions can be very refreshing and inspiring.

Conversely – when we travel – what is not different?  Almost anywhere in the world, with the exception of just two countries, you can buy a well known sweet drink called Coca-Cola.  But there much more common – often fancily called “global challenges.”  Although the interpretation of some of the global challenges depends upon your location on the planet, other interpretations are common for everybody.  Science, particularly physics, is for sure a universal source of such challenges.

But that is also one of the really cool things about physics.  In physics we have the freedom to travel everywhere and the problems that we are trying to solve at home remain the same.   In other words, the laws of physics don’t vary by location.  The only thing that might change (and most likely will) is how scientists approach the problems.  As a physicist who has experienced different cultures, I would like to share with you my experiences from several different countries and show that  international collaborations of scientists can, and do, achieve the best results.

My first experience with math and physics was in the Czech Republic, which is where I am from and where I did my bachelor’s degree in Physics. The classes that I took at Charles University were difficult, covering a lot of math formalism, and early on I felt like I knew more math than my colleagues from “real” math.  Some professors simply threw us into the middle of recent scientific problems; as a result we either sank (= approximately one third of the students did not finish their degree) or swam (=hours of studying at home were required to understand what he spoke about in class).


One of the buildings in the Department of Mathematics and Physics in Prague where we had lectures (left) and graduation ceremonies (that’s me on the right!) at Charles University. We had to promise to uphold the good reputation of the university.

To add some variety to my education, I decided to go to Strasbourg, France, to study for my master’s degree.  It was there that I experienced for the first time a different approach to physics. Compared to my fellow French students, I probably knew (or had at least heard of 🙂 ) more equations. But in Prague we were not taught to work in teams, or, more importantly, how to present our results. In Strasbourg, however, one entire class was dedicated to working in small teams to understand and present a recently published scientific paper that our professor had selected for us. Working in the lab, I also saw a new approach to physics. The official policy did not allow students to work past 7 pm, after which the building was locked and an alarm system was activated. If you combine this policy with generously long lunch times (in the best dining halls that I have ever seen), nice sunny afternoons on the cafeteria terrace, and at least five weeks of holidays, one would guess that the stereotypical “French laziness” was exactly correct. But I don’t think that’s true, and the experts would agree 🙂 ; instead they are just more efficient. They organize their time wisely and are taught to be independent, having productive discussions with colleagues during long lunches or coffee breaks. And they are not exhausted from long nights spent working in the lab.


Relaxed life in Strasbourg – a perfect network of bike routes, small cars, delicious food, and a beautiful historic city.

After one year in France, I went back to the Czech Republic and continued to work on another project toward my master’s degree. One way that I would describe experimental work in a Czech lab is that it’s like a hobby. I mean that I have the feeling that people working in science there usually love their work. It’s for sure not the best paid job, nor the most prestigious one (as being viewed as a ‘nerd’ by others doesn’t make people proud), but people work very hard and I am sure that they would oppose any policy that forced them to go home at 7 pm. The word hobby also reflects a homey atmosphere. Our “research center” looks more like someone’s house than an academic building and it is not long before you get a sense that everyone there knows everyone else.


Homey atmosphere of the Physics Research Building of the Czech Academy of Science in Prague where I am studying for my PhD.

It follows naturally that my PhD work is an international collaboration as well – my advisors are Czech, Catalan (Spanish), and American. This variety brings positive differences. My Czech supervisor has taught me a kind of flexibility and has also showed me that being modest can work in science. On the other hand, I have learnt from my Catalan advisor that science does not need to be formal at all. As he says, science is just like an expensive version of Facebook – having a lot of friends (collaborations) who eventually like (cite) your status updates (scientific publications). A fellowship called the Fulbright has brought me to Ohio. In Ohio I have seen that people work really hard and the environment of a big university made me feel science is here very serious (compared to the hobby-like atmosphere that I described in Prague). I took only one class at Ohio State and I liked that the professor was open and encouraged discussions instead of using the equations to say everything. What I really like here is that good presentation skills are equally as important as good results. And I am really impressed by the frequency of scientific meetings and talks here (compared to rare scheduled meetings in Prague). Apart from the science, I hope that this helps me learn to communicate my work often and to keep track of what others are doing as well.

I have tried to describe the differences in cultures, habits, and styles that I have seen in my scientific career. I believe that physics is one of the fields that can really profit from this variety. Let me mention at least one example from a project that I was involved with last year.  German colleagues prepared and characterized a specific sample. The precision that they achieved is unmatched, but to put their work in a broader context it was necessary to confirm their results by another method. Here the flexibility and speed of Prague scientists would be beneficial to the project, but first someone needs to make the connection between the two groups and create the story – the perfect job for my communicative Catalan advisor. One physics experiment approached from different perspectives. And I think the final product is perfect!

In sum, I hope that I have convinced you that different styles of work can bring together the best results.  So, if you decide to study physics one day, don’t forget to travel!


About Helena Reichlova

helenaI was born in the Czech Republic (Czechoslovakia at the time) and completed my undergraduate studies in physics at Charles University in Prague, the capital. I completed my MS degree in quantum optics and optoelectronics (in both the Czech Republic and in Strasbourg, France) and now I am working toward my PhD in the field of spintronics (which involves improving the present state of the art of electronics by including electron spin effects). Thanks to a Fulbright Fellowship, I have spent one year at OSU as a visiting researcher.  As a good experimentalist I really like exploring new things, including nonscientific activities like painting, snowboarding, and traveling to different places around the world.

Ponytail Physics

by Amy Connolly

I kept my hair pretty long as a kid, and I wore it in one or two ponytails most of the time (when it wasn’t in braids).  I have thick, thick hair, straight as can be.  Any curls needed to be strong enough that they would hold up to the weight of my hair.   My mom, who wanted her little girl to wear big, full curls, especially for pictures, would either fill my hair with curlers at night before bed so that I would have springy curls by morning, or devote time before school to working a curling iron through my hair.


Picture of me with curls in my hair.

My mom and I didn’t know about the competing effects of weight, elasticity, tension and “swelling pressure,” that together needed to reach the right balance in order for those curls to stay in place.  But a group of physicists in England has studied the interplay between these effects on bundles of hair, developed a mathematical theory that can predict the shape of a ponytail, and published these exciting results in a high-profile scientific journal.  Let’s look at that publication and see what we can learn about both ponytails and scientific papers!

The abstract of a paper is a short synopsis at the start where we hear about the most exciting parts of the paper.  We learn that they are going to reveal a “remarkably simple” equation describing the shape of a ponytail, and that they verified the validity of their equation with lab measurements.  That’s right, they carried out experiments on ponytails in a scientific laboratory.  Let’s read on.

Where does this study fit into the world’s body of knowledge on hair?  In the introduction, the authors provide us historical context, evoking Leonardo da Vinci (who opined on the best way to illustrate hair), as well as Brothers Grimm (authors of the storybook tale Repunzel).  Despite the influence of hair in both art and science throughout history, they argue, it is then surprising that the physics that determines the form taken by a ponytail remains an open question.   They tell us about a previous paper on a related topic: someone by the name of van Wyk studied the compressibility of wool way back in 1946.


Repunzel, from the Brothers Grimm fairytale collection,would let down her hair for the enchantress below (picture from

Next we learn all kinds of interesting facts about human hair.   The diameter of an individual hair can be anywhere from about 2/1000ths to 6/1000ths of an inch.  The “linear mass density” of human hair is about 6.5 grams/kilometer.  That means that a hair that is a half a mile long would only weigh as much as 5 paperclips.  From this, they find that the length over which gravity on earth should bend an individual hair is about 5 cm, or about 2 inches. (You can verify this by standing in front of a mirror, isolating a single hair and holding it sideways.  It will bend under the weight of gravity with a radius of curvature of about 2 inches.)  Therefore, 5 cm is a special length for human hair on earth, and they quote all ponytail lengths in this paper relative to this special length.  They name this ratio the “Repunzel number!”  Brilliant!  (Footnote:  Another storybook allusion in science:  in searches for earth-like planets, astronomers seek new worlds that exist in a “Goldilocks” region where the environment is not too hot, not too cold, but just right.)

Now that the authors have educated us in human hair properties, we know enough to tackle the rest of the paper.

Next the authors go through the steps to derive the “Ponytail Equation,” starting with a set of assumptions.   First, let’s imagine that in the middle of a thick ponytail, you could insert an imaginary bubble, and count how many hairs enter the bubble and how many leave the bubble.  If none of the hairs end inside the bubble, then the number entering and the number that leave should be the same.  This is analogous to the “continuity equation,” which is used in the study of the physics of liquids called “fluid dynamics,” and it is the first assumption in their ponytail derivation.  Next, the authors account for all of the energy in a ponytail bundle.  It includes the elastic energy, or springiness, of the hair, the gravitational potential energy, and a confinement energy, for example due to the hair being tied by a band.

In the next step of their derivation, they find the ponytail shape that makes the hair bundle contain the smallest amount of energy.  Any system wants to go to a state of least energy, for example when you put a ball at the top of a hill, it wants to roll down.

The ponytail equation is summarized nicely by the plot below.  There are four forces acting to balance a ponytail.  The horizontal axis tells you where you are along the length of a ponytail, with the hair restraint at s=2 cm.  The vertical scale tells you the strength of each force.  Near the hair restraint, the pressure due to the hair band is the same as the elastic force of the hair pushing back (the yellow and black curves are the same height).  For most of the ponytail length, however, the weight is the strongest competitor to the pressure.  The tension of the hair is small compared to the other forces (take a fallen hair and try and stretch it along its length – the tension force is what pulls back).


Results from the ponytail publication, showing the different forces acting along the length of the ponytail (the horizontal axis). On the vertical axis is the strength of the force.

The ponytail equation must be able to describe the ponytail data if it is to be regarded as a good theory.   In the figure below, the authors show that their ponytail equation (solid blue line) does agree with measurements of ponytail thicknesses at different lengths (solid black lines).  The new equation describes the data much better than the one derived by the van Wyk character who studied sheep hair (dashed red line).


The ponytail equation matches the experimental data!

Finally, the authors remind us that there is lots more work to be done on understanding hair.  Their work can be extended to study other hair and fur geometries.  Imagine the possibilities!  In addition, their theory can be used to understand hair motion.  They end with a tantalizing reference to a paper that investigates why a ponytail swings left and right while a runner bobs her head up and down.


About Amy Connolly

amyI grew up in Cincinnati, Ohio and went to college at Purdue University in Indiana where I found out that I love physics.  Since then I have lived Indiana, California, Chicago and England.  Now I am back in Ohio where I have been a physics professor at OSU for nearly 3 years.  I work on experiments that use radio antennas in Antarctic Ice to search for particle arriving here from deep in space called neutrinos.  I am so fortunate that learning new things about the universe is my job.  I also enjoy growing vegetables, and being really silly with my 3 year old.