Prepare to Have Your Mind Blown

I'll apologize in advance to those who were enjoying my recent rash of silly posts. This one is much more thoughtful, even intelligent. But I promise I'll soon return to the potty humor and pointless quotes from my five year old.

I love physics. I don't have the math background to understand it beyond a basic, conceptual level, but I like studying it and thinking about it. I think about it all the time. Here's something for you to chew on, and if you're like me, it will make you go, "Whoooa, dude!"

Bill, strange things are afoot at the Circle-K.

Do you realize you've never been in the same place twice? That place where you're sitting right now? Yeah, it's the first time you (or probably anyone else) has ever been there. And it's probably the last time anyone will be there. I'm not talking about your seat in front of the computer in the upstairs bedroom. I mean your place in the universe. Let me explain... (Pay attention! This might be on the test.)

Earth is spinning, no? So at this moment you're in a different spot than where you were a few seconds ago. You keep blazing forward (along a circular path) to new places!

"Oh," you say, "but I'll come back around 24 hours from now, right back to the same place." Not so fast, genius... Earth is also revolving around the sun, so tomorrow the whole place will be in a new spot, about two and half million kilometers from where it is right now.

Imagine a wheel. Like a ferris wheel, or the wheel of a bicycle that is suspended off the ground. Now imagine a point on it, like one ferris wheel seat, or the bike tire's valve stem. As the wheel spins, that point will move into the same place over and over again every time it comes around, right?

Imagine if you were to move that wheel sideways as it spins. The path that valve stem follows through space will be shaped like a corkscrew. The slower the wheel is spinning (or the faster it moves sideways), the more elongated the corkscrew shape.

Now, think of the bicycle tire rolling across the ground. The wheel is spinning, but it is also moving forward, as shown by these two arrows:

The valve stem follows a path that looks like this:

You'll just have to trust me. I may be no good at math, but I'm okay with geometry. (And drawing bikes!)

Still with me? Okay, so think of this big ball we're all standing on. It's spinning, sort of like a bicycle wheel turned on its side, except it's spherical. (If you hold with those who still insist the earth is flat, that's okay; the visualization will be even easier for you. Just ignore the following drawing and substitute a land-and-sea-colored pizza.)

Can you find your house?

Add to that rotation another movement, as the Earth revolves around the sun: (If you still think Earth is in the center, with the sun moving around it, I'm going to ask you to leave now, because the rest of my little demonstration will not work for you.)

This is not exactly drawn to scale, but you get the idea.

The result, or path through space taken by somebody standing on the Earth, looks something like this:

Here, we're viewing the whole thing from above, looking down on the North Pole.

I know what you're thinking... you're thinking that with each year there will be another path, like a pretty Spirograph pattern. Eventually, two of those paths will overlap exactly, so if you stay on your couch every day for years, you will eventually come back to the same place where you were before, right? Guess again! Not only is Earth moving around the sun, but the sun and all the planets are moving within the Milky Way galaxy. That's right, there are more movements going on than we can even keep track of.

On the galactic scale, this motion might be too slow for us to perceive; it takes millions of years for anything to move far enough for us to notice the change. But we're talking about a really ginormous space... you may have moved a thousand kilometers in the time it took to read this sentence--that's nothing on a galactic scale, but it's far enough to support my claim: you will never be in the same place twice.

Thoughts? Please leave a comment. If I get lots of remarks along the lines of, "Couldn't you just share some knock-knock jokes or something?" I'll make this my last physics lesson on U by C. If there's some positive feedback, maybe I'll write more of this kind of stuff in the future. It's all on you, folks.