Saturday, January 17, 2015

Stopping The Earth

The short answer: It can't be done. Not no way, not no how. But first, some background...

I saw this item on Andrew Sullivan's site, a link to an article by Aatish Bhatia about what would happen if the Earth were to somehow stop orbiting around the Sun. Well, the obvious answer is that if it stopped orbiting, it's fall into the Sun. What Bhatia tells us, though, is specifically what would happen, on a day-to-day basis, during the sixty-four and a half days it'd take to get there.

I had no beef with that ... except for one sentence, early on in the article:

"What would happen to us if a giant space finger were to gently stop the Earth in its orbit?"

It didn't hit me right away. It set off a kind of slow-burn ... I don't want to call it annoyance, it doesn't rise to that level, but there's no other word that quite describes the sensation. Something was just not right with that sentence.



Before I reacted any further, I needed figures. What was Earth's mass, and its orbital speed? That will tell us the magnitude of kinetic energy we're talking about. And, once the numbers are crunched, we're talking about 2.685 x 10^33 Joules.

That's a totally nonsensical number. Once numbers get sufficiently large, they cease to have any real meaning. I can't relate that immensity to anything within my, or anyone else's experience. So, we go to find something else sufficiently gigantic that we might be able to use as a yardstick. For this purpose the Sun's total power output might serve. The Sun's power output is, on average, 3.846 x 10^26 Watts.

OK, that's another stupidly big number. But we can divide energy by power to get time. Which is ... 80.8 days.

And, friends, when you collect the Sun's entire power output for eighty freaking days, there is NO WAY to apply that much energy gently. That's like using a atom bomb to gently crack an egg. Or using a 120mm smoothbore tank gun to gently drive a finishing nail. It just ... no. You can't get there from here.

The same thing applies to stopping the Earth's rotation around its axis, which appears to be another popular Google search. People really seem to be afraid that this is a real thing ... which they shouldn't. Stopping the Earth from spinning isn't near as hard as stopping it in its tracks, but it's still so damn hard that it'll take totally stupid amounts of energy to do it. The Earth's rotational energy is 2.138 x 10^29 Joules ... yet again another ridiculously huge number. But we can divide that by the Sun's power output to get an idea of how it relates. It works out to 9 hours, 16 seconds.

And again, the after-effects of such stoppage become irrelevant. The friction of so much energy applied all at once would melt the crust to magma. (Which goes back to the point that there's no way to apply such a stupendous amount of energy gently.) What comes after is kind of beside the point. The rock under your feet suddenly becoming liquid is a much more immediate problem than anything that might happen afterwards.

Besides, no one's ever going to have that much energy all in one place to begin with. You can rest easy now, and stop worrying about this ever happening.

Now, all this reminds me of one of my favorite cheesy '70s sci-fi series ... Space: 1999. The premise, if you'll recall, was that the Moon got blasted out of Earth's orbit.

It was a different time.

So, we'll need some numbers. First, the Moon's mass: 7.348 x 10^22 kilograms. And its orbital speed: 1.022 kilometers per second. The escape velocity at that distance is 1.414 times the orbital velocity, so the escape velocity is 1.445 km/sec. Now, we can compute the kinetic energy before and after the event, and see how much additional energy is required. That works out to be 3.834 x 10^28 Joules. Again, an unbelievably stupendous meaningless number. But we link it back to the Sun's power output, and we get about a minute and a half.

Yeah. No way in Hell is a nuclear waste dump generating that kind of kaboom.

Not that I care. That show is still one of my guilty pleasures.

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