Planet spin and relativity

Why do planets spin ? Where does the Relativity Theory come in ?

Here’s a good thread on this very question from a few months ago: The spinning planets

I searched the archives for “planets” in the subject only, in GQ only, for any date, and turned up about a dozen articles, two of which dealt with spinning planets :slight_smile:


Quite simply, because the cloud of dust and gas that the planets and stars were formed from was spinning, and that spinning was inherited by the planets. But what causes the cloud to spin you ask? Gravity from other objects,radiation pressure from starlight, and magnetic fields acting on the charged particles in the cloud would cause some degree of spin in the cloud. When the cloud contracts to form a planet, a physical principle called “Conservation of Angular Momentum” amplifies the minute spin and makes the new body as a whole spin.
This effect is sort of like water doing down a drain. In a sink, the water may appear to be motionless. The water has residual motion though, and when the plug is pulled, this motion is amplified as the water contracts going down the drain. Consequently, the water spins in a circle as it goes down, and doesn’t just slosh out.

Is there anything anywhere that doesn’t spin? Everything you see around you is spinning along with the Earth. Stars and planets and moons and galaxies and atoms are always spinning. The only things I can think of that might not be spinning are huge superclusters of galaxies, but their parts are all spinning.

Planets, stars and other heavy objects were formed by gravity causing a clapse of less dense material. any material that has some ‘spin’ will have a greater ‘spin’ if it’s mass moves closer to it’s center of gravity. So even the slightest spin will be amplified when the final planet is formed

You have to define spin relative to something else. No spin relative to the entire universe may not be possible for a physical object because the universe is not a static reference frame.

I’m not sure I get this. Surely I can definitely say that I’m spinning (if I turn around lots, not earthwise), because I can feel it, and…I was going to say otherwise everything would have to be orbiting around me, but I guess that’s relative to other things…hmm…there are always other things…I’m confused; is that all you meant?

Taking that approach, though, you couldn’t achieve no spin relative to your whole house (darn spiders), nevermind the universe.

If I can treat my house as a static reference frame (I do, mostly), then I can do it for the universe.