# In mathematics, you don’t understand things. You just get used to them.April 21, 2015 6:42 AM   Subscribe

Calculating the Speed of Light Using a Microwave and PEEPS (or other melty things) from National Geographic's Education Blog and NPR's Skunk Bear videos (showing some history of calculating the speed of light... with peeps as historical scientists, of course)
posted by oneswellfoop (16 comments total) 12 users marked this as a favorite

This is the speed of light in a microwave oven, not the usually quoted number which is the speed of light in a vacuum.
I like this demonstration. It sounds like fun. I would try it if I had the peeps.
posted by MtDewd at 8:06 AM on April 21, 2015

In mathematics, you don’t understand things. You just get used to them.
NOVA's The Great Math Mystery ponders whether we as humans invented Math as a way of understanding the Nature of things or if we discovered Math as a fundamental construct of the Nature of things.
posted by Emor at 8:35 AM on April 21, 2015 [2 favorites]

These days the speed of light is defined to be exactly 299,792,458 m/s, so what this experiment is actually estimating is the length of the meter.
posted by Pyry at 8:36 AM on April 21, 2015 [5 favorites]

Something bothers me about this experiment. They didn't calculate for the effect of the stirrer. I don't know how this affects the result, since they do get the final result of c. I think it has something to do with the stirrer being tuned to the magnetron and the oven cavity.
posted by charlie don't surf at 9:07 AM on April 21, 2015

Are you sure they're not estimating how long a second is?
posted by benito.strauss at 9:14 AM on April 21, 2015

...and how do you estimate the length of second using a household appliance and a holiday-themed-product? That's NEXT week's video. (Hint: just in time for Mother's Day)
posted by oneswellfoop at 10:49 AM on April 21, 2015

In mathematics, you don’t understand things. You just get used to them.

...and that's the story of how I got through Calc II.
posted by TrialByMedia at 12:40 PM on April 21, 2015 [2 favorites]

We have two microwaves in the Nat Geo Education office, and had to look on the back of one and the inside panel of the other to find the frequency info. Like most modern microwaves, they have the same frequency as the microwave in the video—2,450 MHz, or 2.45GHz."
I'm in favor of both kitchen science demonstrations and destroying peeps, and I can see the appeal of pitching it as a way to measure the speed of light. . . but, there's something a little silly about reading off the frequency printed on the oven in order to turn a wavelength into a speed. If I were a student doing this as a class assignment, I'd be really annoyed.

Sure, chances are that an identical oven actually was measured against a frequency standard by someone, and that's not an easy thing to do using items found in the typical kitchen. But, it's also true the people who designed the magnetron in the first place had a pretty accurate value for c in hand. Turning this into a quest to "measure the speed of light" is pretty artificial. They could have at least talked about how one could independently measure frequencies, instead of pulling it out of thin air.

I assume the goal is to present a mystery to be solved, rather than just demonstrating some neat properties of electromagnetic waves. However, a much less hokey approach would be to assume c is known (and ignore the oven cavity details) and then ask, "without knowing anything about what's inside of a microwave oven, how can you estimate its frequency?" That could lead to an interesting discussion of why that's a good frequency to use for heating water, why the metal grill on the microwave door has holes of a particular size, the dimensions of antennas in daily life, etc. And, it's the sort of puzzle someone might actually have to solve in the real world.

While we're at it, handing out the statement "The average distance between these areas is about half a wavelength" without taking the opportunity to explain why seems like a wasted opportunity.

Finally, "in mathematics, you don’t understand things. You just get used to them," is a wacky quote to lead with. This isn't math, it's physics; and, except for the specific value of one constant, everything described is pretty easy to understand. What's more, "don't bother trying to understand things" isn't exactly a great pitch when engaging people in experimental science.

Why, yes, I do spend my days trying to ruin fun things for other people. Why do you ask?
posted by eotvos at 12:59 PM on April 21, 2015 [3 favorites]

To be clear, my complaint about the quote was directed at the National Geographic blogger who picked it in the first place, not oneswellfoop. It's a great title for the post.
posted by eotvos at 1:05 PM on April 21, 2015

I don't know that it's so bad, eotvos. I don't see much difference between using a 9 GHz frequency reference from a cesium clock and using a 2 GHz frequency reference from a commercial magnetron, except that the magnetron frequency is only good to about three significant figures. I do agree that what's technically being measured is the length of the experimenter's meter stick, since c is a defined constant.
posted by fantabulous timewaster at 1:38 PM on April 21, 2015

> If I were a student doing this as a class assignment, I'd be really annoyed.

And there's the key. This is not for students, but for people who could just as easily switch over to watch a bunch of cat vids I think it works well. They will have a least heard that c = λ ν, and have an actual real-world reference to what a "wavelength" is. If, because of this video, their minds don't automatically turn off the next time they hear "gigahertz" it will have been a win.
posted by benito.strauss at 1:55 PM on April 21, 2015

"NOVA's The Great Math Mystery ponders whether we as humans invented Math as a way of understanding the Nature of things or if we discovered Math as a fundamental construct of the Nature of things."

A mathematician I read once said that all mathematicians these days are nominally formalists but secretly platonists, which seems exactly right to me. It's also the philosophical position I take with regard to scientific realism (strictly speaking, not, but practically and intuitively, of course).
posted by Ivan Fyodorovich at 3:15 PM on April 21, 2015

Didn't you get the schedule, IF?
posted by benito.strauss at 3:24 PM on April 21, 2015 [1 favorite]

I once calculated the speed of light in my head from the knowledge of the distance between the earth and sun and the time it takes for light to travel the distance. I was having trouble falling asleep.
posted by Gadgetenvy at 5:05 AM on April 23, 2015

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