Monthly Archives: June 2011

Holometer: Holographic Noise

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This summer I am working at [Fermi National Accelerator Laboratory](http://fnal.gov/) as a Teacher Research Associate as part of the [TRAC program](http://ed.fnal.gov/interns/programs/trac/). I plan on writing a series of posts about my experiences and, specifically, about the experiment with which I’m involved: [the holometer](http://holometer.fnal.gov/). Before describing my specific contributions to the experiment, I think I should start with the theory that led to holometer experiment. One of my goals this summer is to be able to explain this experiment and the theory that it is testing in a way that can be understood by my students. This will take several revisions and this post is my first draft.

The theorist involved with this experiment is [Craig Hogan](http://astro.fnal.gov/people/Hogan/) and the holometer is designed to test the the holographic principle. What is the holographic principle? Some describe this theory as claiming that the reality that we perceive is actually a three-dimensional projection from the two-dimensional reality at the edge of the universe. While that sounds cool and sci-fi, I have no idea what it means.

An analogy that I think helps explain the holographic principle is that of graphics on a computer screen. When you play Angry Birds, the bird flies across the screen in an apparently smooth path:

Angry Birds

However, if you zoom in and look more closely, you’ll see that the bird cannot follow an arbitrarily smooth path since the screen is made of pixels. As the bird flies across the screen, it must move in discrete intervals horizontally and vertically. That is, its location on the screen is quantized. What appears to be smooth movement, is actually the bird jumping from one pixel to the next. The minimum distance the bird can move is the width of one pixel. A pixel’s width is sufficiently small that we don’t notice these jumps as we play the game.

Angrybirdszoom

How does this analogy apply to the holographic principle? Space-time is the screen; we are the Angry Birds; and the Planck length is the width of a pixel. To elaborate, as we move through space-time, our movement is not perfectly smooth but, rather, jumpy because the smallest distance we can move is the Planck length (1.6 x 10-35 m)1. Similarly to how, if we zoom in on the computer screen, we can observe the jumpiness of the Angry Bird, through an analogous magnification we should be able to observe the jumpiness, or jitter, of our movement through space-time. This jitter is the focus of Hogan’s research and is called holographic noise. The holometer experiment is designed to measure this phenomenon. How can we build an apparatus that can measure this holographic noise when the Planck length is so incredibly small? Stay tuned for the next post in this series!

Does this make any sense? Feedback is most welcome!

This post is one in a series about The Holometer experiment and my work at Fermilab in the Summer of 2011:

* Holometer: Holographic Noise
* [Holometer: Interferometer](https://pedagoguepadawan.net/68/holometerinterferometer/)
* [Holometer: Spectral Analysis](https://pedagoguepadawan.net/81/holometerspectralanalysis/)
* [Holometer: Transverse Jitter](https://pedagoguepadawan.net/83/holometertransversejitter/)
* [Holometer: Correlated Interferometers](https://pedagoguepadawan.net/94/holometercorrelatedinterferometers/)
* [Holometer: Computer-Based Measurements](https://pedagoguepadawan.net/111/holometercomputerbasedmeasurements/)

1 The [Planck length](http://en.wikipedia.org/wiki/Planck_length) was derived from fundamental physical constants (speed of light, gravitational constant, and Planck constant) by Max Planck.

Nuclear Physics Project Reflections

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I have a few notes to share about the outcome of the [Nuclear Physics Project](https://pedagoguepadawan.net/45/nuclearphysicsproject/).

If you are interested in seeing the final projects, the entire [nnhsphysics wiki](http://nnhsphysics.wikispaces.com/) is available. If you don’t want to read every page, I created an [index that highlights](http://nnhsphysics.wikispaces.com/Sample+Projects) several project pages that cover a variety of topics in a variety of ways.

In terms of the quality of the projects, many students were very creative with their presentation methods. I strongly encouraged and pushed students to find creative ways to present their projects. I should have spent more effort encouraging students to have strong science, technology, and society-related content. In general, the content wasn’t as thorough, complete, and as accurate as I had hoped.

Overall, I think students learned a great deal about the history of nuclear weapons and nuclear power. I forget that events that I lived through (Three Mile Island, Chernobyl) are consigned to the last pages in my students’ U.S. History text that they never get to read.

In terms of technology, I was very impressed with [Wikispaces](http://wikispaces.com/). Wikispaces is ideal for classroom projects. I was able to easily create accounts for nearly 150 students very easily even though students don’t have school e-mail addresses. It is trivial to search by student name to see their recent edits to their pages and comments that they have made. The permissions model is sufficiently flexible to allow everyone to view content, yet only members to edit and comment on it.

I was also impressed with [Scribd](http://scribd.com/). It was very reliable and makes it easy to embed documents in Wikispaces. I found the ability to embed the document, either as individual pages to scroll through or as a slideshow, particularly useful.

A couple technologies were disappointing. [TeacherTube](http://teachertube.com/) was unreliable in terms of being accessible and successfully uploading videos. The 24-or-more-hour delay for approval, while understandable, was frustrating at times. The only reason I used it at all was that it wasn’t blocked by my school’s web filters.

Speaking of web filters, it goes without saying that they made these projects more cumbersome and frustrating than I would have liked. That said, the technology staff at my school was great about unblocking sites that were obstacles to students working on their projects.

Also disappointing was the wireless performance in my classroom. All students were able to connect via wireless but would frequently have difficulties logging into Wikispaces or posting comments on Wikispaces. They were particularly frustrated when they would compose a thoughtful comment only to lose it when the submission timed out. Reflecting back on this experience, I wonder if this was due to some sort of latency issue and Internet Explorer’s relatively short timeouts. I may try using Firefox to see if that mitigates the issue.

Overall, I would definitely try something similar to this again. Next time, I would like to plan a bit more ahead and have more time for the project so I could involve educators and students from other schools. If you have any tips for me for next time, please share!

Looking Back Before SBG

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Several weeks ago, I noticed a teacher grading some papers. I don’t remember where I was, but I wasn’t at school, and I didn’t know this teacher. As I watched more closely, I saw her writing “-1”, “-3”, “-2” in the margin and then, after finishing with the paper, adding up the deductions and writing a score on the top. At first, I was puzzled by this teacher’s actions, and then I realized that she was grading papers. This realization was quickly followed by the surprise that, just a few of years ago, I graded papers in the exact same manner.

My brain is wired such that I adapt to new situations pretty quickly and often forget things from the past, especially if those things have a negative connotation. So, while you may be skeptical that I actually forgot how to grade papers traditionally, I assure you that my initial confusion was genuine. Fortunately for my students and me, I now provide feedback in a different way and actually [enjoy doing so](https://pedagoguepadawan.net/10/ilikereadinglabreports/). This experience combined with the end of the school year has put me in a reflective mood.

I offer these reflections on how my approach to teaching has changed over the past few years not so much as a model of what should be done but more as a testament that it is possible to implement significant changes and, while these changes may seem daunting at first, in a relatively short period of time, they can become second nature.

Three years ago, everything that happened in my honors physics class was worth points. I checked homework almost every day and recorded points. I kept track of which students presented their solutions to problems to the rest of the class so I could record points. I stamped assignments that were submitted late so that I could calculate a late penalty when recording points. Every lab was collected and points recorded. There were opportunities to get extra points. I would pass back an exam so students could see how many points they lost and then we would begin the next unit. Students focused on collecting as many points as they could. Some played this game exceptionally well.

Two years ago, my colleague and I realized that these damn points were distracting our students from focusing on learning. We [wanted certain things for our students](https://pedagoguepadawan.net/37/whysbg/) and standards-based grading seemed like it could help.

It has. Two years ago we adapted a colleague’s implementation of SBG to our honors physics class. This past year, we [made some changes and adapted our approach](https://pedagoguepadawan.net/22/threerealizations/) to our regular physics class team-wide. Last semester, we made some [more tweaks](https://pedagoguepadawan.net/31/adjustmentsforsecondsemester/) to the implementation in regular physics. Now the [entire school is moving towards some form of SBG](https://pedagoguepadawan.net/23/growingsbarschoolwide/).

Two years ago when we embarked down this path, I had many concerns about the implementation of SBG. What helped me to put these in perspective was comparing this new approach with what would have been done in previous years. I asked myself, “Yes, it may not be ideal, but is it a step the right direction?” Some of my concerns were:

* Students won’t do labs if they aren’t graded. *If the labs are engaging (not cookbook) and you have established a classroom culture that values learning, they will. If they don’t, maybe you need to revise that lab.*
* Students won’t study for exams if they have multiple opportunities. *Some won’t. Some didn’t before. They get to prioritize and make choices. Learning to do that and the consequences of their choices in a valuable skill which is better practiced in high school than college.*
* Students will get behind and can’t catch up. *Some do and can’t. Some do and can. At least now they have the opportunity to catch up instead of being left behind as the class plows onward. Before SBG, I can remember only one student who would go back and study topics they still didn’t understand after the exam. Now almost every student does.*
* I will be overwhelmed creating multiple assessments. *It was work but not overwhelming since we split it. We limited reassessment opportunities and leveraged technology where feasible.*
* I will be overwhelmed with students assessing multiple times. *When a line formed out the door of my classroom the afternoon after our first exam, I realized I would have to set some boundaries. Reassessments are offered one day a week before and after school. Period.*
* I will be overwhelmed grading reassessments. *Grading reassessments is more grading, but checking for understanding is faster than deducting points. Overall, I do a lot less grading and provide a lot more useful feedback.*
* Parents will revolt. *Many were extremely supportive. Some couldn’t let go of the points game that their child had learned to play so well. Some couldn’t focus on anything other than the GPA that will be on a transcript for college. Patience, open house discussions, and phone calls help.*
* Students will revolt. *If you take the time to share the rationale for the structure of the class, discuss their concerns, and truly change your philosophy of education, [a strong majority of students prefer SBG](https://pedagoguepadawan.net/33/studentfeedbackonsbar/). After a career of playing the points game, some students are so frustrated that the rules of the game have changed, that they can’t adjust. I don’t give up on these students, but I’m not always successful in changing their perspective towards learning.*

The past two years haven’t been easy, and there have been some [challenges which could have been avoided](https://pedagoguepadawan.net/26/unfriendlygradebooks/). However, these past two years have been extremely rewarding. I feel that I spend my limited time in ways that benefit student learning. I feel that many students are once again focused on learning and understanding.

The best indication that I’m on the right track is that I can’t imagine teaching like I did two years ago.

Critical Thinking Assessment

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Those of us teaching physics have made a lot of changes this year. One major change is a focus on depth of understanding and critical thinking, which results in fewer topics covered. While I have qualitative evidence through formative assessments that students this year have developed stronger critical thinking and long-chains-of-reasoning skills, I’ve been bothered that I don’t have a summative assessment to measure this. Ideally, I would like an Force Concept Inventory pre-test/post-test equivalent for critical thinking. I’ve bookmarked the [College and Work Readiness Assessment (CWRA)](http://www.cae.org/content/pro_collegework.htm), but that isn’t an assessment that I can administer to my own class. If you know of another, please let me know!

Due to our crazy calendar and snow days, seniors graduated two weeks ago and I’ve had relatively few students in my regular physics classes since then. We’ve been investigating color, polarization, mirrors, and lenses. Since these students had already completed their final with the seniors, I decided to use the scheduled final exam time this week to try a critical thinking assessment. I wanted them to read a passage that describes a physics phenomenon with which they were unfamiliar, make several observations of a somewhat related physics phenomenon that they had never seen, and propose and defend an explanation for this observed phenomenon based on the prior knowledge. They read about diffraction, observed various wavelengths of light passing through various double slits, and tried to formulate an explanation. We had previously learned about interference of waves (slinkies and beats), but not in the context of light. This is quite a series of inferences and connections for students to make during a final exam; so, I prepared a series of guiding questions to help them make the connections. When a student said they were stuck or were off-track, I gave them one of the five guiding questions. Some students needed all five; one, amazingly, didn’t need any.

Here is my reading passage, observation procedure, and guiding questions:

Download (PDF, 231KB)

The students did quite well connecting what they read about diffraction to what they observed to what they already knew about interference. Here are some of my favorite student comments.

The black parts are shadows, I think we see them because the light is being destructed?

In order to have constructive interference, one ray must travel one wavelength further than the first.

The blue filter causes the lines to be closer than that of the red filer because blue has a shorter wavelength and when it travels to the plate, it forms more concentric circles. Thus, there are more intersection of circles and more lines formed.

and my favorite (written without any guiding questions):

… It’s like light beats.

I also had some really creative explanations of the interference pattern. Students mentioned internal reflection in our eyes as well as lens effects due to the slits.

Students commented that this was unlike any final exam they had previously taken. In fact, several students in one class didn’t want to leave until they were satisfied they had a complete explanation. It certainly seemed more worthwhile than giving students a list of equations and a set of problems with numbers for them to plug in on their calculator. I think there is a kernel of a good idea here, but I need to develop it more. In my largest class, it was hard to manage since I had to interact with each student during the assessment, read their explanations, and give them the appropriate guiding questions. Sometimes this required me asking my own clarification questions and the ensuing discussion could be overheard by other students. If you have tried anything like this, please share your experience!

Near-Space Balloon

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The Physics Club at my school recently completed our second-annual near-space balloon launch and recovery. Our goal was to launch the balloon payload to over 100,000 feet. We planned to record pressure, temperature, and radiation data; test the effects of altitude on biological samples; capture photos and video; and, ideally, recover the payload! While we didn’t achieve every goal, the launch and recovery was a resounding success.

An alumni of the Physics Club worked with Ken Walczak from the [Far Horizons project](http://www.adlerplanetarium.org/investigate/participate/farhorizons/?searchterm=horizons) at [Adler Planetarium](http://www.adlerplanetarium.org/) last summer and suggested that we contact Ken. The students contacted and met with Ken on their own, set the goals for the project, and designed and constructed almost every element of the balloon. (Ken provided the pressure and radiation sensors, while I provided the Arduino and temperature data logger.)

This project was a good excuse for me to buy a new Arduio Uno and the [Data Logger shield from Adafruit](http://www.adafruit.com/products/243). The data logger shield was easy to assemble, simple to interface with via the Arduino, and convenient to retrieve the data due to the SD card storage.

Armed with our supplies, we met up with Ken in El Paso, Illinois (selected due to its launch-friendly park and sufficient distance from Lake Michigan). With his experience, Ken provided many tips as well as the 1000-gram balloon!

We inflated the balloon:

IMG 5196

… assembled the payload and connected it to the parachute and balloon:

IMG 5201

.. and the president of Physics Club let go! (That process took over two hours!)

100 0316

The camera captured a great arial view of El Paso, Illinois:

IMG 1477

… and quickly rose above the clouds:

IMG 1567

While not definitive, based on our data, we estimate that the payload reached at least 105,000 feet:

IMG 2109

… before the balloon popped and the payload fell to earth:

IMG 2325

We used a cell phone that sent GPS coordinate to a web site to track the balloon. Unfortunately, the cell phone stopped sending coordinates immediately after launch. As a result, we had no idea where the balloon was until the payload landed back on the ground, two hours and forty minutes after launch. Fortunately, it landed in a vacant lot in a subdivision relatively close to the predicated location. We were able to retrieve the payload, recover all the data, and be home for dinner.

We had some issues with the data logging. The pressure data wasn’t valid (we were having issues before even launching; so, we weren’t too surprised). Also, the Arduino got too cold when falling and some of our temperature data may be suspect. Regardless, the graphs of temperature vs. time correlated with radiation counts will provide some authentic data for our freshman earth science class next year:

BalloonData

Next year, we plan on replacing our cell phone-GPS tracking system with a GPS receiver connected to a APRS transmitter. We don’t like losing contact with the payload during launch. We also hope to invite our district’s middle schools to design experiments to include in the payload. The students also expressed interest in adding a camera facing upward to capture a new perspective.

If you are interested in launching your own near-space balloon, feel free to contact me and, while limited, I’ll share our experiences!