Yet another weird SF fan

I'm a mathematician, a libertarian, and a science-fiction fan. Common sense? What's that?

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Yet another weird SF fan

Wednesday, January 02, 2013

In Which I Disagree with XKCD

Duty calls.

The latest XKCD What-If discusses how to spin up the Earth:

If we wanted to get rid of leap seconds, we’d need to keep the Earth spinning at a more constant rate. This means speeding up the Earth and shortening each day by about 0.8 milliseconds.


In the end, there’s only one solution: Hitting the Earth with asteroids.

That isn't the only solution.

The Earth is slowing down as a result of tidal drag. As is well known, the rate at which the Earth is slowing can increase as a result of extracting energy from the tides (see The Last Judgment by J. B. S. Haldane). In the other direction, the slowing can decline or even reverse if energy is put into the tides. This will require enormous amounts of power … but far less than that present in the sunlight hitting the Earth.

The basic physics of this is simple enough. Pump enough water around the Earth's oceans to cause the tidal bulge to be ahead of the Moon instead of behind. The trivial engineering details can be left as an exercise for the reader.

In other news, I'm celebrating Isaac Asimov's birthday by posting something extremely nerdy on my blog.


Anonymous TJIC said...

We could put mass drivers on the moon and then mine the entire moon and shoot it far far away from the Earth, thus reducing the ongoing tidal drag.

Of course, by the time we succeeded, the Earth might already be tidally locked to the SUN...

5:44 PM  
Anonymous eddie said...

Or we could use said mass drivers as rockets to change the orbital speed of the moon. If we push the moon so that it's orbiting faster than the earth is rotating, then tidal forces will speed up the earth's rotation. [Note: we might need more energy and mass than the moon has, so that's where asteroid bombardment would come in handy.]

If we push it fast enough that it's in a resonant orbit, say 2:1, then the tidal forces will ensure a stable rotation speed from that point forward.

A 2:1 ratio would mean that the moon will still appear to cross the sky in a single day, but a) BACKWARDS from its current apparent direction, and b) going through all lunar phases every day (twice! once in daylight and once at night!) instead of once every month. But at least we'd still have a moon, and it would be interesting to see.

"And at least we could stop worrying about leap seconds."

12:03 PM  
Anonymous eddie said...

Also, having the moon orbit at the 20,000 km altitude required to get a twelve-hour orbital period (about 0.55 times the altitude of geosynchronous orbit, or about 5.8 times the diameter of the moon itself) would make for a GREAT view of the moon as it passes by overhead.

12:21 PM  

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