Skeptophilia (skep-to-fil-i-a) (n.) - the love of logical thought, skepticism, and thinking critically. Being an exploration of the applications of skeptical thinking to the world at large, with periodic excursions into linguistics, music, politics, cryptozoology, and why people keep seeing the face of Jesus on grilled cheese sandwiches.

Thursday, September 13, 2018

Light speed

There's a claim I've now seen three times on social media that claims the ancient Egyptians knew the speed of light.

This is a pretty outlandish claim right from the get-go, as there is no evidence the Egyptians had invented, or even had access to, any kind of advanced technology.  Plus, even with (relatively) modern technology, the first reasonably decent estimate of the speed of light wasn't made until 1676, when Danish astronomer Olaus Roemer used the difference in the timing of the eclipses of the moons of Jupiter when the Earth was moving toward them as compared to when the Earth was moving away from them, and came up with an estimate of 225,300,000 meters per second -- not too shabby given the limited technology of the time (the actual answer is just shy of 300,000,000 meters per second).

But there's something about those ancient Egyptians, isn't there?  There have been "secrets of the Pyramids" claims around for years, mostly of the form that if you take the area of the base of the Pyramid of Khufu in square furlongs and divide it by the height in smoots, and multiply times four, and add King Solomon's shoe size in inches, you get the mass of the Earth in troy ounces.

Okay, I made all that up, because when I read stuff about the "secrets of the Pyramids" it makes me want to take Ockham's razor and slit my wrists with it.  But I was forced to look at the topic at least a little bit when the aforementioned post about the speed of light started popping up on social media, especially when a loyal reader of Skeptophilia said, "You have got to deal with this."

The gist is that the speed of light in meters per second (299,792,458) is the same sequence of numbers as the location of the Pyramid of Khufu (29.9792458 degrees north latitude).  Which, if true, is actually a little weird.  But let's look at it a tad closer, shall we?

[Image licensed under the Creative Commons Jerome Bon from Paris, France, Great Pyramid of Giza (2427530661), CC BY 2.0]

29.9792458 degrees of latitude is really specific.  One degree is approximately 111 kilometers, so getting a measurement of location down to seven decimal places is pretty impressive.  That last decimal place -- the ten-millionths place -- corresponds to a distance of 0.0111 meters, or a little over a centimeter.

So are they sure that last digit is an 8?  Measuring the position of the Great Pyramid to the nearest centimeter is a little dicey, given that the Great Pyramid is big (thus the name).  Even if the claim is that they're measuring the position of the top -- which is unclear -- the location of the top has some wiggle room, as it doesn't come to a perfect point.

But if you're just saying "somewhere on the Great Pyramid," there's a lot of wiggle room.  The base of the Pyramid of Khufu is about 230 meters on an edge, so that means that one-centimeter accuracy turns into "somewhere within 23,000 centimeters."

Not so impressive, really.

There's a second problem, however, which is that the second wasn't adopted as a unit of time until the invention of the pendulum clock in 1656.  The meter as a unit of length wasn't proposed until 1668, and was not adopted until 1790.  (And some countries still don't use the metric system.  I'm lookin' at you, fellow Americans.)  So why would the ancient Egyptians have measured the speed of light -- even assuming they could -- in meters per second, and not cubits per sidereal year, or whatever the fuck crazy units of measurement they used?

So as expected, this claim is pretty ridiculous, and not even vaguely plausible if you take it apart logically.  Not that there was any doubt of that.  The bottom line is that the ancient Egyptians were  cool people, and the pyramids are really impressive, but they weren't magical or advanced or (heaven help us) being assisted by aliens.

No matter what you may have learned from the historical documentary Stargate.

Oh, and for the record, I didn't invent the unit of "smoot" for length.  A smoot is 1.70 meters, which was the height of Harvard student Oliver R. Smoot, who in 1958 got drunk with his fraternity buddies and decided to measure the length of Harvard Bridge in Smoot-heights.  It turned out to be 364.4 smoots long, plus or minus the length of Oliver R. Smoot's ear.

And considering they were drunk at the time, it's pretty impressive that they thought of including error bars in their measurement.  Better than the damn Egyptian-speed-of-light people, who couldn't even get their measurement to within plus or minus 230 meters.


This week's Skeptophilia book recommendation is a charming inquiry into a realm that scares a lot of people -- mathematics.  In The Universe and the Teacup, K. C. Cole investigates the beauty and wonder of that most abstract of disciplines, and even for -- especially for -- non-mathematical types, gives a window into a subject that is too often taught as an arbitrary set of rules for manipulating symbols.  Cole, in a lyrical and not-too-technical way, demonstrates brilliantly the truth of the words of Galileo -- "Mathematics is the language with which God has written the universe."

1 comment:

  1. I did an intermediate physics lab back in my third year of university where the goal was to calculate the speed of light using two different methods. You know all this, but let me explain for some of your readers who may not.

    The first method we used was the Foucault method. We failed miserably. I forget how accurate (or inaccurate we were) but it was off by a lot. Granted, we were in the physics building after hours in relative darkness quite enjoying fucking around with stupid expensive oscilloscopes and spinning mirrors and whatnot. The second method we used was the Michelson–Morley experiment. For this one we got to have a lot of fun. As you know, the original experiment essentially disproved the notion of "aether wind". What we did, however, was to make one path of light go a really short distance (but still far enough that the time it took to get there and back was measurable using our ancient equipment) and make the other path of light go really far (we bounced it down the halls, up stairs, and even tried to get it into our lab TA Rohan's office. Of course, we couldn't get it out of his office because it was locked so we had to abandon that idea). Now, insomuch as light is concerned 15 centimeters or 150 meters is practically the same thing, but it is a measurable difference. Figure out the difference, figure out the speed of light (using what I think is some wonderfully elegant math). With this second method we were able to calculate the speed of light to within an amazing 99.something percent accuracy. A right proper bulls eye when you factor in the margin of error.

    Even though we got the wrong number the first time we outlined what we thought were the flaws and how they might account for the discrepancy. We handed in the lab and received a 19.5 out of 20 on it. I asked Rohan where we lost the half mark and his response was, "Andrew, perfection is reserved for but one entity in the Universe... and you are not He."

    Oh, and for what it's worth I took the Google location of the pyramid and looked at it's north latitude and it was listed as 29.9792345. So I punched in the speed of light latitude and got this. Close, but no cigar. Not even within 230 meters and definitely not worth 19.5 out of 20 from Rohan.