Tag Archives: vacuum

The speed of light!

The speed of light stays the same—186,282 miles per second in a vacuum. It doesn’t change relative to other objects. If you switch on a light in your rocketship while cruising along at 12 parsecs, the light doesn’t travel at 186,282 miles per second plus 12 parsecs. It stays at 186,282 miles per second. This is because light is an electromagnetic wave and has no mass. Signals from a radio station are electromagnetic waves, too. They wouldn’t speed up or slow down if the radio station were moving.

I say ‘in a vacuum’ because outside of a vacuum light’s going to be slowed down by atmosphere: dust particles, car exhaust, hairspray from actors in 1970s sci-fi movies, bird poop, cigar smoke, &c, &c. Beyond Earth’s atmosphere, in outer space, it’s a vacuum.

My vacuum seems to have a lot of dust particles and dog fur in it, so that slows the light down somewhat.

A lightyear is the distance light can travel in a vacuum—at 186,282 miles per second—in one year. Earth-year, that is!


Back to the beginning of The Western Civ User’s Guide to Time & Space

Cæsium steam

Cesium, like every element, is made up of only one kind of atom. There are only cesium atoms in cesium.

I just had this information tattooed on my forehead in mirror writing, so I don’t forget.

Here’s how you get cesium atoms to float around: you boil the cesium. Cesium melts at room temperature, like an ice cube melts into water. So all you need to do to get cesium atoms is boil cesium until it turns into cesium steam. Then you funnel the cesium steam down a tube which is a vacuum—nothing else in there, no air, just cesium atoms and that’s it. Then you expose those atoms to radio waves. When the radio waves hit the exact same frequency as the atoms’ own oscillations—9,192,631,770 times per second—the atoms change to a different energy state.


I guess I need to research radio waves now. Great merciful Zeus, I’m never getting to the end of this. Thanks for holding while I go look up radio waves.


Wow—that hold music is awful. Back to the beginning of The Western Civ User’s Guide to Time & Space