[chris (OP)]

This just in:

Hello, my name is Dylan Kirk, I was wondering what would happen if you had a cylinder magnet, and you take a ring basically that was also magnetic and repelled the cylinder, but on the top and bottom of the cylinder you had two more magnets blocking the ring from coming off and they also repelled the ring, would the ring float. And since the ring itself is not attached to anything, could you technically spin the ring forever, since wouldn't it technically not have any friction?

[PmbPhy]

This just in:

Hello, my name is Dylan Kirk, I was wondering what would happen if you had a cylinder magnet, and you take a ring basically that was also magnetic and repelled the cylinder, but on the top and bottom of the cylinder you had two more magnets blocking the ring from coming off and they also repelled the ring, would the ring float. And since the ring itself is not attached to anything, could you technically spin the ring forever, since wouldn't it technically not have any friction?

It's hard for me to picture this but there's nothing preventing a magnet from floating under the right conditions. But a magnet can't rotate forever in such a manner which causes a time-varying field. Such a field creates an electromagnetic wave and this in turn causes the rotation to eventually stop. One says that the field carries away energy and in order for energy to be conserved the rotation has to stop at some time.

[Kryptid]

It's hard for me to picture this but there's nothing preventing a magnet from floating under the right conditions. But a magnet can't rotate forever in such a manner which causes a time-varying field. Such a field creates an electromagnetic wave and this in turn causes the rotation to eventually stop. One says that the field carries away energy and in order for energy to be conserved the rotation has to stop at some time.

Would it ever completely stop rotating or would it just grow asymptotically closer to zero spin as time goes on?

[PmbPhy]

Would it ever completely stop rotating or would it just grow asymptotically closer to zero spin as time goes on?

Only ideally/mathematically would it rotate forever. In reality things are never like that. Eventually the rotation would slow to a point where it'd be impossible to detect rotation and that, quite literally, means it stops.

Observation/measurement is everything in science. You can't say that its "really" rotating but so slow that we can't detect it. That would have no physical meaning.

[Kryptid]

Only ideally/mathematically would it rotate forever. In reality things are never like that. Eventually the rotation would slow to a point where it'd be impossible to detect rotation and that, quite literally, means it stops.

Observation/measurement is everything in science. You can't say that its "really" rotating but so slow that we can't detect it. That would have no physical meaning.

Could it ever technically get too slow for detection? If we put a red spot on the ring, and had the ring suspended above a background colored half black and half white, then one could tell if the ring had moved by making repeated observations of what part of the background the red spot was over. If you record it as being over the the white part today when it was over the black part 100 years ago, wouldn't that imply that it was still rotating? What if it is still doing so after 1,000 years? Or a trillion? How long would it take before the red dot never leaves one part of the background and crosses over to the other?

I know it can't rotate literally forever because over insane periods of time you start to run into things like proton decay, false vacuum decay or quantum tunneling that would lead to the ring's destruction.

[PmbPhy]

Could it ever technically get too slow for detection?

Absolutely.

How long would it take before the red dot never leaves one part of the background and crosses over to the other?

I don't know. Calculations like that are extremely difficult to do. In physics forums we never make calculations this difficult. It's not a good use of time.

[SeanB]

Will never get to the Cavendish pitch drop speed, but will stop after a while, and essentially will be still, as vibration might move it randomly in either direction.

[Atomic-S]

I believe experiments of spinning magnetic objects in a vacuum have been done, and they do keep spinning for a very long time. The main limiting factors would be residual gases and field asymmetries, the latter being significant (at practical speeds) mainly in the way they would interact with hysteresis and conductivity of nearby objects.