How Fast Can A Disc Spin?

[Eudoxus]

I wonder if it would be possible for rapidly rotating bodies where the rotational velocity exceeds c could give rise to quantum black holes, giving an alternate method of formation other than the big bang?

 

Now we just need to go and find some. ;)

Edited March 24, 2012 by Eudoxus

[CraigD]

I wonder if it would be possible for rapidly rotating bodies where the rotational velocity exceeds c could give rise to quantum black holes, giving an alternate method of formation other than the big bang?

According to special relativity, it’s not possible for a body with nonzero rest mass, in circular or any other motion, to reach or exceed the speed of light, so that part of your wondering most likely isn’t possible.

 

In principle, a body could be rotated fast enough for its relativistic mass to have an associated Schwarzschild radius greater than its radius, becoming a black hole. Practically, it’d take some hellacious engineering to realized, but is well established enough in the medium-hard SF genre to be something of a staple, and is a lot of fun to think about. :)

 

Though the engineering to make micro black holes this way so advanced it’s practically magic, there’s been lots of speculation in the past decade or so that it might be possible to make “quantum black holes” (a buzzphrase meaning simply black holes with Schwarzschild radii smaller than the classical radii of sub-atomic particles, AKA micro black holes) using the latest and greatest particle accelerators, especially the LHH (so much so that a few waggish pro and a much greater number of worry-prone armature physicists speculated that, if current theory were badly wrong and such tiny black holes didn’t vanish almost instantly in a shower of exotic particles, but rather gained mass, the LHC might cause the end of the world!). This isn’t possible with accelerators available now, including the LHC, if gravity follows classical physics law and General Relativity at very small radii (< 10^-19 m), but could be if it is much stronger at this scale, as some theories predict. So far, to the best of my knowledge, there’s no evidence the LHC has made any micro-black holes, refuting many of these theories.

[Eudoxus]

I misspoke, not for the rotational velocity to exceed c, but for it to approach c.

[Lancewen]

The maximum speed a solid disc(circular) can spin, is when the rim has a speed equal to that of light( the universal speed limit).

∴(therefore), the maximum number of rotations, a disc of radius R would be able to make is equal to, the speed of light © divided by 2πR.

 

However due to the relativistic mass involved the structural integrity of the disc would be compromised long before this speed was reached!

 

 

I was searching for fastest rotational speed of neutron stars and black holes and came across the following.

 

http://en.wikipedia.org/wiki/Stellar_rotation

 

A black hole is an object with a gravitational field that is sufficiently powerful that it can prevent light from escaping. When they are formed from the collapse of a rotating mass, they retain all of the angular momentum that is not shed in the form of ejected gas. This rotation causes the space within an oblate spheroid-shaped volume, called the "ergosphere", to be dragged around with the black hole. Mass falling into this volume gains energy by this process and some portion of the mass can then be ejected without falling into the black hole. When the mass is ejected, the black hole loses angular momentum (the "Penrose process"). The rotation rate of a black hole has been measured as high as 98.7% of the speed of light.

 

I'm not really sure how one goes about measuring the rotational speed of a black hole, but it seems to me that 98.7% of the speed of light is really pushing the limits of mass approaching the speed of light.

[Cyberia]

Every large object in space spins, even galaxies. It seems to be a property of gravity. So we have the event horizon of SMBH's spin at almost light speed because the central sphere of mass is spinning fast (we have no evidence that fundamental particles can be crushed to any smaller size). But I wonder if the core is held "solid" or do all the particles in it try and move at near light speed so despite the gravity, it is somewhat like a liquid sphere with particles near it's centre moving at the same speed as particles on the surface?

 

The fastest matter we have found so far (from space) has energies of 3x10^20 eV and in a race over 20 million light years, such protons would arrive less than one metre behind a photon.

[JonOne]

I know this is an old thread but this made me join scienceforums as it is a really interesting concept that until now i thought i was the only person who had questioned it.

The Nano carbon tube would probably need an ancor to attach the motor to, otherwise it would rotate the motor rather than the nano tube? Maybe the moon?

Another interesting implication would be how it would affect time.

The closer you get the the speed of light, the slower you travel through time. This would mean as the tip reached these massive speeds, it would start to become younger than the rest of the tube. Would this warp the tube into some kind of spiral?

This effect of time slowing for objects that go faster has me questioning another thing. Is the Land mass at the equator of our planet younger than the land mass at the pole's as it is spinnig faster and therefore traveling throug time slower?