Monday, July 25, 2011


Maximizing the amount of sleep I get lately has been one of my top goals. Last night I got plenty of sleep and felt energetic and ready to head to class. I grabbed a quick breakfast to eat on my way/in class and then walked over to our class with Alex because Julia had already left. Alex and I were a little early today, so I had time to say hello to my friend Mikael before class began. Today was unique because Bill tied together many of the ideas we have been studying in the last few weeks into one large goal for the next couple of days – measuring the speed of light-.

To be a bit more specific, over the last several weeks, we have studied mechanics, optics, learned to use oscilloscopes and many other neat things. These topics are being united in a way because measuring the speed of light we will need to use our knowledge that we gained here to put together a device that is essentially a laser that sends out a beam of light that we split, reflect, and carefully time how long the pulse takes to return to our oscilloscope which we learned how to use last week.

To be honest, actually walking into the lab and seeing the dozens of wires and pieces of equipment that we had to hook together I felt like we wouldn’t be able to actually create the device that we needed to. With some excellent teamwork we actually managed to put together several of the circuits before we asked for help. Our teachers all have a nice approach to helping us where they try to steer us in the right direction and only interfering if we’re totally stuck. Today, Mary helped us several times when the wiring diagrams got a little overwhelming or we otherwise got stuck. I was very grateful for her help as well as Bill and Ryan’s and sooner than we expected we had constructed our light-speed measuring apparatus.

Next up, we were lucky to get to hear from another one of Penn’s faculty, Dr. Phil Nelson. Something that I’ve found great about the UPenn faculty we’ve gotten to listen to is that while they are very well educated and deeply into very specific research, they have all been excellent speakers as well. Phil spoke today about light and color. The first thing that he did was demonstrate how our eyes combine colors to make other colors. He showed us a pure yellow slide (which he proved was only yellow by shining it through a prism) and then showed us how he could overlap a red slide and a green slide to create an identical looking yellow. However, the mixed yellow could be separated back out into red and green. Then Phil began to throw some questions at us, why do our brains combine these colors instead of sorting them out? Can electronics make superior vision? And what are the applications of this knowledge?

Phil began to answer his first question by speaking about a man named Thomas Young. Young made many very accurate predictions about color and our eyes almost 200 years before his hypotheses could be confirmed. Perhaps the most consequential hypothesis that Young made is that the response of the photoreceptors in our eyes to light is equal to the Intensity times the Sensitivity. Thus our photoreceptors must sacrifice some clarity in order to be sensitive to a wider range of colors. For evolutionary reasons, humans have evolved to have three different types of photoreceptor cells that each specialize in decoding what we call red, green, and blue light. Because these photoreceptors are tuned to these colors, our brains must guess when something is in between these colors and that is where the red and green look yellow. Our brains see that the red and green photorecetors are reporting the same amount of light and ‘average it’ to yellow. Phil then talked about the many applications of this knowledge. Perhaps the most obvious is that LCD and Plasma screens each use different combinations of red, green, and blue light to make every color they display. The other applications are countless, and once again I was impressed by how articulate and relevant Phil was.

In the afternoon, it was time for my group to present what we have been working on for the last several days. As a brief synopsis, we have been experimenting (playing) with a mixture of cornstarch and water called oobleck. Oobleck is classified as a non-Newtonian fluid because it behaves as a fluid when you move something slowly through it, but it behaves as a solid when you quickly try to move through it. This has some interesting results, because you can slowly sink your hand into it and it’ll get wet and covered in oobleck, but if you punch it as hard as you can you’ll probably end up breaking your knuckles. Today, my group displayed these properties by making four huge tubs of oobleck and then having the entire class run across the surface. Watching them do this was a bit of a cruel natural selection process because the faster students made it out unscathed while those who hesitated sank in and then had to struggle to get out.

Overall, today was a lot of fun because I worked hard with my group in the morning and overcame obstacles, I enjoyed hearing another incredible lecture, and I had fun making a mess in the afternoon.

Oh, and my favorite thing that Bill said today was about how earning a PhD is beneficial, “By learning everything about something, you learn something about everything.” I don’t know if my educational interests will take me in the direction of a PhD, but I thought that quote really summed the idea of a PhD up nicely.

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