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This would only work in deep space, where there are no
significant perturbations from the gravitational pulls of
other bodies.
A series of four identical rigid, elastic balls (depleted
uranium might be nice) are first arranged in a row, just
touching one another. A fifth, identical ball is
then placed
some distance from these four, but on the same line.
Gravity and the elasticity of the collisions will then do the
rest. The period of oscillation of the system will depend
on the mass of the balls but, for any reasonable mass, will
be quite considerable.
The long-term stability of this arrangement will depend on
the perfectness of the balls and on the precision of their
initial alignment; any imperfections will tend, over time,
to cause the arrangement to become unstable. However, a
pragmatic engineer might arrange for the contact points to
be very slightly flattened (so that contact is made over a
disc-shaped area, rather than at a point).
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[+] this should be our envoy to other worlds. |
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[+]. Because there are no strings it couldn't properly be called a 'cradle'. I would name it in honour of its inventor but as "Bucky Balls" is already taken and "Max Balls" sounds, well slightly salacious, I'll stick with "Newton's Balls". Of course, in space no one can see your strings. |
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[+] "We send this remarkable executive desk toy as an
example of our staggering engineering capabilities, and
hope that our two worlds can peacefully initiate economic
coitus. Please read operator's manual before use. Some
assembly required. Hecho en Mexico." |
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This is clearly what the Iranians are secretly building. |
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Newton's Five Body Problem ? |
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Hmm, 2 taking elements from the idea, namely; Uranium and Newton's Cradle, it occurs to me that it might be nifty to use a Newton's Cradle arrangement to manage the core of a nuclear reactor. Take 5 equal masses that together form a critical mass, and have them arranged into a Newton's Cradle. Only for instances when all 5 are in contact would the chain reaction occur, and as long as you could keep the cradle swinging, you'd be able to run a (relatively) low-intensity reactor, controlling the frequency of critical instants by lengthening and shortening the strings. |
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Lovely idea - however what, I wonder, is the probability that this, or an approximation to it, already exists? Let's say that there are a hundred billion small rocks floating in space in our solar system, a hundred billion similar stars in our galaxy and a hundred billion galaxies in the universe. This suggests that there are about 10^33 small rocks floating about - surely somewhere there must be five rocks arranged in a line? |
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//However, a pragmatic engineer might arrange for the contact points to be very slightly flattened (so that contact is made over a disc-shaped area, rather than at a point).// |
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This will happen anyway - the spheres will deform momentarily at the point of impact - this is how the force is transferred between them. |
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To keep them aligned, I wonder if you could put a charge on them and use some kind of scaled up variant of a Penning trap. |
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//the spheres will deform momentarily at the
point of impact// |
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True, but the deformation is what provides the
springing force. In other words, if the spheres are
even slightly imperfect (or imperfectly aligned),
the compression and rebound will throw them
progressively further "off" on each bounce. Small
flats machined onto the spheres would prevent
this. |
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Imagine dropping a bouncy ball onto (a) a flat floor
and (b) another bouncy ball. In (a), the ball will
bounce vertically; in (b), it will only do so if it is
aligned to hit the top dead centre of the other
ball. |
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Perhaps this could be run as a competition
between the advanced nations of the galaxy, to
see who could machine and align the balls
accurately enough to work for many bounces. |
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I'm not sure a flat portion would work, but maybe a cunningly shaped impact point could be designed, so that if the spheres hit each other slightly off-centre, the reaction force tends to restore the alignment rather than degrading it? |
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I think to work that the balls would have to be
incredibly massive (even without any
perturbations from anything else). Gravity is an
incredibly weak force, and likely that if displaced,
the 5th ball would sit at a distance for all eternity
(or at least until the second law of
thermodynamics has reduced the universe to an
entropically even, feezing grey soup).
Suggest carving them out of a neutron star rather
than using uranium. Impractical? Of course, but
not more so than setting up five balls of uranium
in deep space... |
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Would two lumps of neutron star rebound elastically, or would they merge? I'd suspect the latter. |
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Depleted uranium with a chewy neutronium centre... could that keep the N from uncollasping ? |
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If the neutronium centre was large enough to be stable then wouldn't it just crush the DU into more neutronium? |
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//but maybe a cunningly shaped impact point could be designed// - if the process is slow enough and the balls are sufficiently massive, the civilisations which live on them will have enough time to reshape the impact points between collisions. |
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Hmmm...Wrongfellow, you're probably right. If you
carved uranium balls big enough to have any
gravitational attraction, then they may also be too
massive to bounce anyway - just plough into each
other and deform and conjoin. It still sounds elegant
in theory though. |
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If you have enough compact stuff to produce 1g at its surface, then you have a shell of DU that is under the horrific stress of... 1g. |
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1g isn't enough to keep degenerate matter stable. If you could somehow magic up a lump like that, it would immediately explode. |
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Yes, it does, MUHWHAHAHA ! |
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// the spheres will deform momentarily at the point of impact // |
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Uranium is pretty soft ... it will deform considerably and absorb a lot of energy in the process. They will need a tough shell of steel or similar for this to work. |
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Also, the impact velocity of the incoming ball needs to be lower than the escape velocity of the system as a whole, otherwise the ball at the other end of the stack will continue in a straight line, and you'll have to wait for it to go all the way round the Universe and come back from the other side. |
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//the impact velocity ... lower than the escape velocity//
Well it would be, wouldn't it: that's how you start one of those things. |
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Think big. A solid Osmium sphere the size of the Moon would have 2/3 Earth's gravity. Of course I'm gonna go out on a limb and say you'd end up with a large pile of Osmium dust rather quickly, so something else: maximum bounce & maximum density. |
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Tetraneutronium n4 should have a decent specific gravity. |
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I was thinking to start with something more modest
than a moon, say a metre or ten in diameter. The
oscillation period would be quite long... |
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or cheat a bit: nuclear batteries charging internal electromagnets should help keep things lined up, as well as give a bit of an assist to gravity. |
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//I think to work that the balls would have to be incredibly massive// |
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Why? If you want truly elastic collisions, you're going to need to be in the tonnes-or-less scale, otherwise collisions will result in plastic deformation (inelastic collisions), and also I think you'll have problems with wave propagation and complete transfer of energy for large objects. |
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What [Custardguts] said. They tried a Newton's cradle using wrecking balls on "what would happen if". It didn't really work. |
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Most materials are, at best, close to linear and elastic within a range of stresses, which is a large part of the reason for the invention of theorbos and overwound strings in music. Very gentle collisions, and very large balls, are both problematic, and it's hard to see how you'll avoid both. |
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Yes, the long handle of a theorbo allows slower swings. Nutting someone with a lute tends to damage the bowl, or the soundboard, or both. |
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//Very gentle collisions, and very large balls, are both problematic,//
You know, Mrs AWOL commented that very same thing only last night. |
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