# Thursday Throughput: Io Edition

Michael Siegel

Michael Siegel is an astronomer living in Pennsylvania. He blogs at his own site, and has written a novel.

### 10 Responses

1. Jaybird says:

The experiment that I heard about that, now that I’m thinking about it, must not have worked.

Imagine, if you will, an octogon mirror box. In the style of a cylinder.

Now imagine two mirrors, at a 90 degree angle, a mile away. These mirrors are set up in such a way that if you shoot a laser at the cylinder at a 90 degree angle to it, offset by a few inches, the light travels a mile to hit the angle bounces 90 degrees to hit the other mirror, then bounces back and hits the cylinder again on one of the other mirrors two sides away and go in the exact same spot as if you were shining the laser without the cylinder there in the first place. That same exact spot is where you have the measuring device. It just needs to be something that says “yep, I’m being hit with a laser!”

With me?

Then start rotating the cylinder. When you find the speed at which the cylinder can turn and the initial flash of light bounces off of the first mirror and goes two miles, comes back, and hits the mirror only one side away (instead of two) and you’ve got the speed of light.

As a kid, I thought that that was elegant.

And *NOW* I’m thinking “that requires a level of precision that makes sense in comic books but they’d never be able to pull that off in real life.”

And the planet example is elegant as hell. And it predates Watt’s steam engine.Report

• Michael Siegel in reply to Jaybird says:

That experiment works just fine. We did it as undergraduates. You shine a laser onto a spinning mirror. The beam goes to a second mirror and comes back, at which point the mirror has moved slightly and creates a dot offset from the original. That was done in the late 19th century to try to characterize the ether.Report

• Jaybird in reply to Michael Siegel says:

No one is a bigger supporter of ether characterization than I, but I’m questioning the whole “0 degrees of shift over two miles using 4 mirrors” thing.Report

• Oscar Gordon in reply to Jaybird says:

I don’t think the spinning mirror method is two miles.Report

• Jaybird in reply to Oscar Gordon says:

I’d hope not! But my high school physics teacher explained the experiment talking about one guy on one mountain and another guy on another mountain and then did the math for us and we all sat agape at how brilliant it was.Report

• Michael Siegel in reply to Jaybird says:

Michelson-Morley Experiment. That was the word I was looking for:

• Jaybird in reply to Michael Siegel says:

That is an awesome page. Thank you!Report

• Asimov once suggested repeating Michelson-Morley on the Moon. Just in case we’d misunderstood the results all these years and the earth really was the fixed point of the universe.Report

• George Turner in reply to Mike Schilling says:

Michelson served as an officer aboard the USS Constitution (the three-masted frigate launched in 1797), when she was still an active warship in the US Navy. Later in life, long after he disproved aether theory by measuring the speed of light, he met with Einstein and Edwin Hubble at Mt Wilson to discuss relativity, red-shifts, other galaxies, and the big bang.

Nobody would ever write that as a character arc in a novel, except perhaps the old “Outlander” series about immortal beings. It’s like taking a character straight out of Pirates of the Caribbean and making him a science officer on Star Trek.Report

• rexknobus in reply to Michael Siegel says:

Trivia I am almost ashamed to know: The Cartwrights on “Bonanza” back in 1962, helped Michelson with his speed-of-light experiment.Report