Monday, July 25, 2011

Physicists Are Not Afraid to Get Their Hands Dirty

I am continually forced to rethink my definition of "most exciting class ever" with Bill's physics course. You'd think roller coasters would prove hard to beat, but literally every class brings something new to get excited about. Today, it was more than something; it was everything. Even just the set up for the lab we are going to perform tomorrow to measure the speed of light got my blood pumping.

Admittedly, the first hour of class was incredibly hard to follow. Despite Bill's exceptional ability to eloquently explain complicated topics, describing how to build a circuit with a light-sensing diode or a laser controlled by a transistor and connected to function generator is no easy task.

Consequently, it wasn't until we broke up into our new lab groups and got to fiddle with the wires and the circuit boards that the diagrams we were given (on the left) started making any kind of sense.

At first it was confusing and slightly frustrating, especially because Bill specifically told us that he had it all set up last night so everything was working perfectly, but disassembled it just so we would have to put it back together. Once we transformed the diagrams and mess of wires and banana plugs into the mechanisms we would be using to perform our experiment, I understood why he did it. Even before the experiment began, I already felt a sense of pride and ownership regarding the data we are going to collect with the gadgets that we built ourselves. Not only that, but we have a much deeper understanding of how our tools work and therefore what the numbers that come up actually mean.
Each week it seems we delve even deeper into the realm of what experimental physics actually feels like. In this further step, not only are we collecting our own data, but we are building our own tools with which to do it and it feels amazing. If this ends up being what I do for a living, I will have no objections.

After the lab setup, guest speaker Phil Nelson spoke about the physics of human and superhuman color vision. He began with a puzzling paradox about yellow light. First he showed us pure yellow light, visible in a spectrum created by shining white light through a prism. Next he showed us a square of yellow light made by a projector. When he diffracted this yellow light with the prism, he did not get yellow light, instead he got red and green. The question that he posed was why our eyes were unable to distinguish between the two (true yellow light versus the red/green mixture).

To explain this phenomenon, he described to us the way our eyes perceive color. Specifically, that the photo receptors in our eyes are capable of distinguishing between blue, green and red wavelengths. These can be expressed as curves showing how many photons of each particular color are sensed. The reason we are unable to distinguish true yellow from the mixture now becomes clear: our eyes can only measure the relative presence of green and red light. Therefore, because yellow neighbors both green and red on the spectrum, true yellow light contains traces of wavelengths from both red and green and so is indistinguishable to our tri-color sensitive eyes.

He went on to suggest that if we create a machine with the ability to detect more than three discrete wavelengths, it proves useful in a number of fields. Spectral karyotyping, for instance, uses such machines to detect subtle differences in stain colors of chromosomes, allowing scientists to conduct studies regarding genetic mutation, cancerous cells, and the genetic history of evolution. Superhuman color detection also allows scientists to maps the connectomes of mouse brains. When Nelson mentioned this, it really got my attention because I had seen the images he had displayed before on a podcast - the very podcast that got me interested in neuroscience in the first place. I was not aware when I watched it however, how interdisciplinary the sciences that were used in developing the method were. In fact, it is remarkable how often the guest lectures tie into my prior knowledge, and also to each other. I am slowly realizing as the weeks progress that it is very difficult to find scientific research that is independent from a network of other fields, which to me is what makes science truly spectacular.

We took a long break for lunch today so that the Non-Newtonian Fluids group could set up their "demonstration". Really, it was more like two hours of the entire class playing with the vats of "oobleck" that they brewed up. The stuff is surprisingly entertaining. We ran our fingers through it, slowly at first sow that it flowed like a liquid, then quickly so it ripped like a solid. If you moved fast enough, you could form it into a ball, but once you stopped applying pressure and just let it sit in your hand, it would melt away and slide through your fingers. Needless to say, it wasn't long before we were all covered with the corn-starch/water mixture. To demonstrate the unique principle of more applied force creating a larger resists to that force, we punched it and slapped it and threw stuff at it, and then we started to get really creative. Bill dropped a bowling ball into one of the vats and the effect was counter intuitive (as non-Newtonian fluids often are). Instead of the six pound ball creating a splash in the tub of liquid, it almost bounced off the surface before slowly sinking in.

Of course, the next step was to line the three containers up and have people run across it. The different techniques that people used to stay on the surface varied greatly. Some students hopped from tub to tub like hopscotch. This worked for some people, but when I tried it I found that the time between jumps was so long that I started to sink in as I prepared for the next jump. The easier thing to do was to continuously stomp on it, as if you were smashing grapes while running across. A surprising amount of students chose to walk through it to see what it felt like. The trick to walking is to move as slowly as possible, because as hard as it is to get something to move quickly into the mixture, it proved even more difficult to yank a foot out.
Bill wrapped the day up nicely with a demonstration of how a pro does it:

When the excitement was over, I returned to the quad and rested for a while before going out to famous cheese steak restaurant Pat's King of Steak, for Emily, the Texan on our floor's birthday. I have to say I was disappointed with the quality of food they served there. For such a famous place, the sandwiches were just not tasty. I much preferred the random little shop we found in our first couple days in the city. But we ate cake, sang happy birthday, and got to see more of the city it was an altogether pleasant experience.

As we walked off the bus, we were surprised to see it had started raining in the time it took us to make the trip home. Instead of retreating into the dorms, I took of my sneakers and played some Frisbee in the wet grass. Even though I got soaked, the air was warm enough that I didn't freeze to death like I would have back at home.

Once I got myself dried off and cozy, I relaxed in my room for the rest of the night.

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