When I was a kid my neighbor little Billy did just that. He put his eye out.
I think I may be able to take a stab at translating the OP’s friend:
I think “absolute space” just means a total vacuum, and by “no exterior forces” he means no other forces except that spinning the coin. I think this is just a version of “as speed apporoaches that of light, mass approaches infinity”. I reckon the friend thinks that anything accelerted to close the speed of light will gain enough mass to collapse under it’s own gravity, and form a black hole.
As I understand it (not very well), the idea of mass increase as objects approach the speed of light is misleading, and the OP’s friend is completely wrong.
But is it possible for an object to spin so fast that it creates a gravitational field strong enough to collapse into a black hole?
That link has nothing to do with frame-dragging, you can see they use the Schwarzchild metric instead of the general Kerr metric. The precission effect described is a different effect to Lense-Thirring precission.
Again this is not frame-dragging, this is measuring gravitational red-shift.
This an experiment to specifically measure frame-dragging, but at the moment the results are not accurate enough that I would say frame dragging has been experimentally verified
This test is to measure the equiavlence principle, something that is independent of frame-dragging.
The physics community in regards to experimental evidence for frame-dragging is still waiting on the results of Gravity Probe B which so far is the only test conducted that could possibly provide conclusive experimental evidence for frame-dragging.
The special theory of relatvity is like quantum mechanics and it’s quantum field theory cousins in that the experimental evidence for it is absolutely overwhelming and the kind of limitations that the experimental evidnece places on alternative theories is that they must be pretty much identical within large regimes.
General relativity has nowhere near this kind of evidence and this is mainly due to the difficulties in testing it’s predictions. It certainly is not one of the most throughly verified theories in physics.
This is my point though, in reading the popular science press, etc, you may very well get the impression it is on par with SR, QM etc in terms of experimental evidence, which is just not true.
No. In fact, there is a limit to the amount of angular momentum a specified mass can have to even form a black hole.
Stranger
If you started with a coin with mass density just a hair below what is necessary to form a black hole, then spinning it could push it over the threshold without centrifugal effects destroying the black hole, no?
Another truly interesting thread created by a simple question.
I love the Dope.
In principle, yes. But in practice, almost anything in the Universe that’s spinning (which is to say, almost anything in the Universe) will have to shed significant amounts of angular momentum to be able to collapse to a black hole.
And impressive as Gravity Probe B is, everything it can do has already been done better by precise measurements of the GPS satellites. It’s an example of a project that would have been a really great idea when it was proposed, but which got caught up in red tape for so long that by the time it launched, it was obsolete.
How accurate would you require? The measured value of the east-west drift rate from GP-B is R[sub]EW[/sub] = -80.4 +/- 5.4 marcsec/yr. Subtracting off the expected non-frame-dragging component of -36 +/- 1 marcsec/yr leaves an observed excess drift of R=-44.4 +/- 5.5 marcsec/yr. The GP-B collaboration hasn’t given official systematic error estimates yet, but they claim that they expect them to be around the 1 marcsec/yr or so level. Even if they creep up to, say, 5 marcsec/yr, the excess drift would be R=-44.4 +/- 7.4 marcsec/yr, which would still be a 6-sigma indication of a new source of drift that lines up perfectly with the GR frame-dragging prediction of -39 marcsec/yr.
For the geodetic effect, perhaps. But I don’t think GPS satellites have observed frame dragging. (I could believe they put frame dragging terms into their calculations – why not – but that’s a far cry from measuring the effect in any meaningful way.)
More accurate in order to say that frame dragging has been experimentally verified!
I’[m not saying there is no frame dragging effect or that GR is wrong, just that the amount of experimental evidence for GR isn’t quite as great (i.e. on a par with other major theories in physics) as the general public realize.
In terms of gravitational redshift, yes. GPS satellites don’t correct for frame-shifting, though, because the difference between frame effects on the ground and in orbit are too small to create a significant difference between synchronization cycles.
GP-B was disappointing in the “noisiness” of the data despite the revolutionary use of SQUIDs; the development of the mission lagged the development of technology. The funds would have been better used to support other experiments, but that’s politics in science.
Stranger
I think in the simplest model of collapse rotation actually makes on object harder to collapse here’s my reasonsing:
Collapse is very difficult to model, even more so when rotation is a major factor. However a non-rotating object will collapse in to a black hole if all it’s mass is within it’s Scwarzchild radius. IIRC with a Kerr black hole the radius of the event horizon actually decreases as it’s angualr momentum increases, so therefore spinning the coin will actually make it harder to collapse.
The random angualr momentum of objects in a system will contribute to that objects mass, but the effect of a systems total angualr momentum should not be seen to contribute directly to a system’s mass for reasons of symmetry. Instead it’s effects are more subtle (e.g. frame dragging).
Now I msut admit this is more in WAG territory, rather than soemthing I have tkane the time to work out properly.
You can ask where your freakin’ car keys are and you’d get the same result.
Wouldn’t a spinning coin actually be losing energy due to gravitational radiation? After all each atom of the coin except those right on the spin axis are accelerating. This would be a tiny effect, but if the coin had no other forces acting on it, it would be the only effect, right? So if it didn’t start with a mass-energy density high enough to form a black hole, it never would have such. (I guess unless some constants of the laws of physics where changing over time.)
A question that occurred to me while reading this (hope it is not too much a hijack):
If I get in my never-runs-out-of-fuel-but-no-bigger-than-a-car-impossible-rocket and accelerate continually my mass increases right?
Will I eventually collapse into a black hole or is there something about my reference frame (the scale in my rocket accelerating at a constant 1g claims I still weigh 70 kilos) that means no black hole?
I think the answer to that is it depends which axis it is spinning on (relative to it’s axes of symmetry).
Not so sure.
IIRC (forgot where I read it) the Earth is losing energy via gravity waves (akin to a cork bobbing in water loses energy).
In the case of the Earth that is not very much. Again IIRC somewhere around the energy sufficient to operate an electric toaster. Given the size of the Earth that is insanely small but, given enough time (long after our sun snuffs out), it’ll do the trick.
The amount of graviational radiation given off by the Sun-Earth system is of approximately the same order as would be needed to power an electric toaster. So it’s not just the Earth we’re considering but the Sun and Earth together!
The amount of gravitional radaiton that would be produced by a spinning Earth in isolation is much, much, MUCH smaller than that (what it does radiate will be a function of the tiny assymetries in it’s shape and in it’s rotation)
The gravtiational raditiation produced by a roating coin sysetm will depend on the assymetries in the system.
This is all true, but then with no forces acting on the spinning coin per the OP, this is the only thing going on, so the coin does not gain energy, it loses (an incredibly minuscule amount of) energy rather than gaining energy so it “moves” further from collapsing into a black hole not closer to it.
Good heavens no Whack-a-Mole. We’ve been over this a thousand times on this board. Relativistic mass is a bad concept for this very reason; it causes too much of this type of confusion. Let’s say someone else is going as fast as you. Will he think you’ve gained mass?
Of course not. Mass is equal to the energy of a system that cannot be transformed away.