What are its chemical properties? I know it’s some the densest material in existance. Have scientists found any practical applications for it?
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Please disregard the second post. That’s supposed to be an entirely seperate entity. That resulted from a posting error.
Neutronium is a hypothesized material that supposedly makes up neutron stars. Physicists are pretty sure it’s there — they’ve observed some objects out there that could only be neutron stars given their rate of spin and mass — but since there aren’t any neutron stars on (or anywhere near) Earth, and it’s currently impossible to make it in a lab, there hasn’t been a chance to test its physical properties. Sorry to disappoint you.
You’re not the first here to ask about this.
Some properties of neutronium that I’ve picked up over the years, simply from being fascinated by physcis’ oddities:
-'Tis superfluid… if you could get a magically stable sample, it’d flow like there’s no tomorrow. Why not? It’s just a bunch of neutrons. Imagine if you were a thousand miles tall, and someone handed you a mile-high cup full of normal-sized steel ball bearings.
-'Twouldn’t last very long. If I recall correctly, neutrons have a half-life of ten hours, and outside a stabilizing environment (an atom, or a neutron star’s intense gravity), they’d degenerate.
-You wouldn’t be able to hold it. I believe it was Chronos that told me that a ball of neutronium would fall right through the planet like a bowling ball falling through a cloud. This lead me to think of neutronium’s use as a weapon… get a few dozen (magically stabilized… we’re assuming science fiction here) balls of neutronium and drop 'em on a planet from orbit. After a few days of criss-crossing through the planet’s mass, it should be pretty well swiss-cheesed…
-The only hypothetical matter that I’ve seen suggested as being denser than neutronium would be strangelets. I don’t know what recent conclusions/discoveries/theories about strange matter have come to light, however.
Er… I’m pretty sure neutrons don’t have a half-life. Particularly not one of ten hours. If they did, wouldn’t all elements therefore have a half-life of ten hours, since half their neutrons would disappear in that time?
Spoofe is correct. Free neutrons have a halflife about about 636 seconds. When they’re in a stabilizing environment, such as in an atom or a very strong gravity field, then they’re stable.
This PDF file is a bit basic, but explains it nicely.
Chronos, do you have any input?
I’ve read that hypothetically, if the military were to caot their tanks with a super-dense caoting of neutronium armor, the tanks would be so heavy and cumbersome, they would sink to the center of the Earth.
Please excuse those typos, that should read “coat” and “coating”.
You could build one of these with it.
duh-duh, duh-duh, duh-duh, DUH-duh. . .
I think what you’ve read on the topic is probably a bunch of sci-fi pseudoscience. You can’t take a layer of neutronium and coat something with it. Neutronium only exists in that superdense state because it’s being acted on by the gravity of a neutron star.
Of course, if life were like Star Trek, you could build a Doomsday Machine. 
(see Earl Snake-Hips Tucker’s post, above.)
In this thread, it was said that a sample of neutronium under Earth conditions would fly aparts once the gravity wan’t there to counter balance the pressure. My question is, where is this pressure coming from? I don’t see what wouold compel the neutrons to fly apart.
After all, they have no charge, so there is no electromagnetic repulsion. They interact via the strong nuclear force, which is very attractive. And there would be gravity, which is also attractive, but peanuts compared to the strong force. Therefore, all the forces between all the neutrons are trying to keep them together.
So where is all this pressure coming from?
I’m guessing it’s a quantum mechanical effect. Neutrons are fermions, meaning that you can only have one in a given state. As a result of this, one can calculate that it is energetically favorable for them to be somewhat spread out. So there is an effective pressure (sometimes called degeneracy pressure) acting to push them apart. If my understanding is correct, this is not a true pressure and doesn’t correspond to any of the four forces.
Not sure if this covers it but astronomers think they may have found Quark Stars (I think also sometimes called “Strange Stars”).
The material in these stars would be far more dense than that in a Neutron Star.
IIRC a teaspoon of neutron star material (neutronium if you like) would weigh more than Mt. Everest. How you could ever make practical use of it is beyond me (assuming you could even keep it stable).
tim314 has it and what he is talking about is the Pauli Exclusion Principle. After electron degeneracy you get to neutron degeneracy and as mentioned it basically says no two neutrons can occupy identical states. So, in a star some neutrons fill up the lowest energy levels then some fill up the next lowest and so on. There are of course a lot of neutrons there so you have a lot (most) with rather high energy states that they would rather not have but are forced to hold by the star’s gravitation. Now go scoop up your teaspoon full of neutronium and take it away from the star’s gravitational field. All those neutrons are now free to give up all that energy. Whether that means a hefty BOOM or they just all go whizzing off I do not know but bottom line you won’t have your neutronium for long without something to keep forcing them together (ala a spectacularly strong gravitational field you can carry with you).
Wouldn’t it actually go the other way around? Wouldn’t the earth be yanked by the neutronium ball into a status of concentricity?
They would both be yanked towards each other. The body that would experience the bigger yank (i.e. the larger acceleration) would be the body with the smaller mass. Which could be either the earth or the neutronium ball, depending on its size.