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Electron band structure in germanium, my ass (2001)

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Re: Electron band structure in germanium, my ass (2001)

#31
post #27

One of my Core Memories when it comes to science, science education, and education in general was in my high school physics class, where we had to do an experiment to determine the gravitational acceleration of Earth. This was done via the following mechanism: Roll a ball off of a standard classroom table. Use a 1990s wristwatch's stopwatch mechanism to start the clock when the ball rolls of the table. Stop the stopw…

I think if you showed not only the point estimate, but also some measure of uncertainty like standard deviation, it should have given you a passing grade. It's hard to say why an answer like 6.8 +- 5 is wrong. Even if you don't yet have formal statistical chops, it should be at least possible to show cumulative distribution function of results that will convey the story better than a single answer with overly optimis…

This is early high school. We didn't have error bars yet, we just took an average. I just used that as a convenient way to describe how erratic our numbers were. If 6.8 is the average you know we had some low numbers in there. And some nice high ones, too.

You're certainly correct that the true value would have been in our error bars, and one of those good teachers I acknowledge the existence of in my large paragraph, sarcastic as it may be, could conceivably have had us run such a garbage experiment and shown that as bad as it was, our error bars still did contain the correct value for probably all but one student or something like that. There's some valuable truth in that result too. Cutting edge science is often in some sense equivalently the result of bodging together a lot of results that in 30 year's hindsight will also be recognized as garbage methodology and experiments, not because the cutting edge researchers are bad people but because they were the ones pushing the frontier and building the very tools that later people would use to do those precision experiments with later. I always try to remember the context of early experiments when reading about them decades later.

It would also have been interesting to combine all the data together and see what happened. There's a decent chance that would have been at least reasonably close to the real value despite all the garbage data, which again would have been an interesting and vivid lesson.

This is part of the reason this is something that stuck with me. There were so many better things to do than just fail someone for not lying about having gotten the "correct" result. I'm not emotional about anything done to me over 30 years ago, but I'm annoyed in the here and now that this is still endemic to the field and the educational process, and this is some small effort to help push that along to being fixed.

Re: Electron band structure in germanium, my ass (2001)

#32
post #7

A thing of beauty is a joy forever - John Keats Honestly, physics is so full of pretension and hero worship. Even among seasoned lecturers there's a tendency to mythologise the progress of the art by making it sound like all the great results we rely on were birthed fully-formed by the giants who kindly lend us their divine shoulders. Ironically there's a kind of Gell-Mann amnesia here, working scientists know that m…

I feel like forgetting to multiply by sqrt(-g) must have been a pretty easy mistake to make back then. This stuff was new!

Re: Electron band structure in germanium, my ass (2001)

#33
post #27

One of my Core Memories when it comes to science, science education, and education in general was in my high school physics class, where we had to do an experiment to determine the gravitational acceleration of Earth. This was done via the following mechanism: Roll a ball off of a standard classroom table. Use a 1990s wristwatch's stopwatch mechanism to start the clock when the ball rolls of the table. Stop the stopw…

>Roll a ball off of a standard classroom table. Use a 1990s wristwatch's stopwatch mechanism to start the clock when the ball rolls of the table. Stop the stopwatch when the ball hits the floor.

Our class had some kind of device that would either punch a hole, or make a mark on paper at a regular time interval. We attached a narrow strip of paper to the ball, and let it pull through the marking device as it fell from the bench to the floor. We then measured the distance between each mark, noting that the distance increased with each interval, using this to calculate g. I don't recall anything more than that, or how I did on that lab. I received a 50 one marking period for lack of handing in labs, but had a 90+ average otherwise in the class.

Re: Electron band structure in germanium, my ass (2001)

#34
> (...) the apparent legitimacy is enhanced by the fact that I used a complicated computer program to make the fit. I understand this is the same process by which the top quark was discovered.

This is both hilarious and more common than you might think. In my field of expertise (ultrafast condensed matter physics), lots of noisy garbage was rationalized through "curve-fitting", without presenting the (I assume horrifyingly skewed) residuals, or any other goodness-of-fit test.

Re: Electron band structure in germanium, my ass (2001)

#35
post #27

One of my Core Memories when it comes to science, science education, and education in general was in my high school physics class, where we had to do an experiment to determine the gravitational acceleration of Earth. This was done via the following mechanism: Roll a ball off of a standard classroom table. Use a 1990s wristwatch's stopwatch mechanism to start the clock when the ball rolls of the table. Stop the stopw…

[deleted]

Re: Electron band structure in germanium, my ass (2001)

#36
post #27

One of my Core Memories when it comes to science, science education, and education in general was in my high school physics class, where we had to do an experiment to determine the gravitational acceleration of Earth. This was done via the following mechanism: Roll a ball off of a standard classroom table. Use a 1990s wristwatch's stopwatch mechanism to start the clock when the ball rolls of the table. Stop the stopw…

>Roll a ball off of a standard classroom table. Use a 1990s wristwatch's stopwatch mechanism to start the clock when the ball rolls of the table. Stop the stopwatch when the ball hits the floor. Our class had some kind of device that would either punch a hole, or make a mark on paper at a regular time interval. We attached a narrow strip of paper to the ball, and let it pull through the marking device as it fell from…

That's an interesting way to measure the passage of time -- just use something that produces a "regular distance" and derive a way from kinematics to calculate the acceleration from the change in the distance.

Re: Electron band structure in germanium, my ass (2001)

#38
post #22

hahaa, I love it! That's right there is engineering and true work and dedication. Can hear the frustration and it's 100% warranted. I wish universities were better equipped for what you pay. Where is all that money going anyways? Leaking like free electrons?

The gym, I think. Usually the brand new buildings, too.

[deleted]

Re: Electron band structure in germanium, my ass (2001)

#39
I read this in 1999 when entering university. It was so refreshing hearing a student provide a glimpse into the boots-on-the-ground reality of undergrad life at these world-renowned institution.

The closing sentence is also prescient; the author pivoted to CS, ultimately completing his doctorate at the University of Wisconsin at Madison

https://pages.cs.wisc.edu/~kovar/

Re: Electron band structure in germanium, my ass (2001)

#40
post #31

Earlier quoted context omitted.

I think if you showed not only the point estimate, but also some measure of uncertainty like standard deviation, it should have given you a passing grade. It's hard to say why an answer like 6.8 +- 5 is wrong. Even if you don't yet have formal statistical chops, it should be at least possible to show cumulative distribution function of results that will convey the story better than a single answer with overly optimis…

This is early high school. We didn't have error bars yet, we just took an average. I just used that as a convenient way to describe how erratic our numbers were. If 6.8 is the average you know we had some low numbers in there. And some nice high ones, too. You're certainly correct that the true value would have been in our error bars, and one of those good teachers I acknowledge the existence of in my large paragraph…

It's honestly kind of bullshit because the bedrock of a lot of my work is being realistic, and if I had such a piece of crap equipment I would have gladly reported the 6.8 meters per second squared and then turned around and identified all of the problems with my setup right down to characterizing the lag time on the stopwatch start.

In fact one of the trickiest problems I had to resolve once was to show that the reason a piece of equipment couldn't accurately accumulate a volume from a very small flow was because of the fixed-point decimal place they chose. And part of how I did that was by optimizing a measurement device for the compliance of a fixed tube until I got really good, consistent results. Because I knew that those numbers were actually really good it came down to how we were doing math in the computer and then I just had to do an analysis of all of the accumulation and other math to determine what the accumulated error was. It turned out to be in really good agreement with what the device was doing.

All of that came from our initial recognition that the measured quantity was wrong for some reason.

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