Tag Archives: HistoryOfScience

Why Didn’t Copernicus Figure Out Kepler’s Third Law Decades Earlier?

Kepler’s third law is so simple to state that (as shown last time) it is something that any grade school kid, armed with Copernicus’s data and a calculator, can verify. Yet it was 75 years from Copernicus’s publication til Kepler discovered this formula! Why did it take Kepler until 1618, nearly 50 years of age, to recognize such a simple relationship? Were people just dumber than high-school students back then?

Here’s a clue. We take all sorts of math for granted that didn’t exist four hundred years ago, and calculations which take an instant now could easily take an hour or even all day. (Imagine computing the cube root of 4972.64 to part-per-million accuracy by hand.) In particular, one thing that did not exist in Copernicus’ time, and not even through much of Kepler’s, was the modern notion of a logarithm.

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The Best Proof that the Earth Spins

In my last post I gave you a way to check for yourself, using observations that are easy but were unavailable to ancient scientists, that the Earth is rotating from west to east. The clue comes from the artificial satellites and space junk overhead. You can look for them next time you have an hour or so under a dark night sky, and if you watch carefully, you’ll see none of them are heading west. Why is that? Because of the Earth’s rotation. It is much more expensive to launch rockets westward than eastward, so both government agencies and private companies avoid it.

In this post I want to describe the best proof I know of that the Earth rotates daily, using something else our ancestors didn’t have. Unlike the demonstration furnished by a Foucault pendulum, this proof is clear and intuitive, involving no trigonometry, no complicated diagrams, and no mind-bending arguments.

The Magic Star-Pointing Wand

Let’s start by imagining we owned something perfect (almost) for demonstrating that the Earth is spinning daily. Suppose we are given a magic wand, with an amazing occult power: if you point it at a distant star, any star (excepting the Sun), from any location on the Earth, it will forever stay pointed at that star. Just think of all the wonderful things you could do with this device!

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Einstein, History and Science

On Saturday I gave a lecture, newly minted, on how Einstein is perceived in the public eye, and on how the numerous misconceptions about Einstein affect the way many non-experts believe that science is actually carried out.  Doing the research for the lecture involved, among other things, going back to some original sources I’d never read or had only read a long time ago, looking a bit at Einstein’s notebook from the period around 1912 (online here), and re-reading large portions of a wonderful biography of Einstein that I’m afraid was written by a physicist for physicists — and consequently largely unreadable without technical background, but a must-read for anyone who has that background.  I refer here to Abram Pais’s famous biography: “Subtle is the Lord…”, whose title refers to Einstein’s famous quip: “Subtle is the Lord, but malicious He is not.”  (You can read about the origin of this quip in Pais’s book.)

I also enjoyed tracking down some videos online of various physical effects that Einstein explained, or that he predicted in advance.  These included videos (linked below) of Continue reading