Explosions producing strange outcomes

[Laura]

I noticed that exploding a normal density object results in objects of a high density. Example: Exploding the moon in the Earth/Moon example simulation into 500 fragments results in some fragments with a density as high as almost 50g/cm^3 (suggesting elements that do not occur naturally in planets or moons). Every single fragment ends up with a higher density than the original object, though most are only 4 times as dense (at the level of Americium).
How does the simulation arrive at these figures?

[deoxy99]

Each piece should be 500 times the original object.
I think.

[atomic7732]

No, cause when it collides, then you would have 500x the normal mass. It should have 1/500 of the orignal mass. I don't think the mass is the problem, I think the size is too small for the object, thus making a VERY high density.

[deoxy99]

No, cause when it collides, then you would have 500x the normal mass. It should have 1/500 of the orignal mass. I don't think the mass is the problem, I think the size is too small for the object, thus making a VERY high density.

Cause ain't a zword, NeutronStar.
Haha.
NeutronStar est le maƮtre de l'Univers Sandbox.

[Laura]

No, cause when it collides, then you would have 500x the normal mass. It should have 1/500 of the orignal mass. I don't think the mass is the problem, I think the size is too small for the object, thus making a VERY high density.

The sizes seem more plausible than the densities, actually. In fact, if the decimal point of the density of explosion fragments was moved one step to the left, things would look pretty plausible.
I.e. The original moon has a density of about 3.4g/cm^3. Fragments come out between 13g/cm^3 and 46g/cm^3.
Moving the decimal point would mean 1.3g and 4.6g respectively, putting them in the ballpark of Magnesium and Titanium. I realize that no fragment would be a pure element, of course, but it does seem to look better. Even a pure core fragment should be no more than 7.87g/cm^3 (Iron).

Anyway, I can only speculate. I'd love a word from Dan on this

[Dan Dixon]

Exploding a sphere divides it into 13 smaller spheres that all fit within the original sphere. The original mass is divided among the resulting spheres and the high density results because the mass is the same, but the total volume is less.

You're right that this is unrealistic. Feel free to share your thoughts on how this could be improved. I look forward to improving the explosion code in the next few months.

Thanks for pointing out this problem.

[deoxy99]

Exploding a sphere divides it into 13 smaller spheres that all fit within the original sphere. The original mass is divided among the resulting spheres and the high density results because the mass is the same, but the total volume is less.

You're right that this is unrealistic. Feel free to share your thoughts on how this could be improved. I look forward to improving the explosion code in the next few months.

Thanks for pointing out this problem.

I don't know how that's unrealistic.

[Bla]

Exploding a sphere divides it into 13 smaller spheres that all fit within the original sphere. The original mass is divided among the resulting spheres and the high density results because the mass is the same, but the total volume is less.

You're right that this is unrealistic. Feel free to share your thoughts on how this could be improved. I look forward to improving the explosion code in the next few months.

Thanks for pointing out this problem.

Maybe if they didn't have to fit within the original sphere, but instead had to have the same total volume as the volume of the object that was being exploded?

[Laura]

Exploding a sphere divides it into 13 smaller spheres that all fit within the original sphere. The original mass is divided among the resulting spheres and the high density results because the mass is the same, but the total volume is less.

You're right that this is unrealistic. Feel free to share your thoughts on how this could be improved. I look forward to improving the explosion code in the next few months.

Thanks for pointing out this problem.

That explains it
Especially when specifying 500 fragments.
Perhaps collision code could be modified in such a way that, following an explosion, objects are allowed to overlap until they no longer do so, at which time the standard collision code would re-enable. This would allow fragments of proper volume and density to temporarily coexist inside the volume of the original object until the force of the explosion drives them sufficiently apart.

[Laura]

I don't know how that's unrealistic.

It's unrealistic because it isn't what would happen in reality 
Matter with a density of 46g/cm^3 should not exist anywhere, except under the influence of extreme gravitation/pressure/temperature, such as in the cores of large gas giants, in white dwarf stars, in neutron stars, etc.

[deoxy99]

I don't know how that's unrealistic.

It's unrealistic because it isn't what would happen in reality 
Matter with a density of 46g/cm^3 should not exist anywhere, except under the influence of extreme gravitation/pressure/temperature, such as in the cores of large gas giants, in white dwarf stars, in neutron stars, etc.

46g/cm³ doesn't sound that dense.

[Sanduleak]

I don't know how that's unrealistic.

It's unrealistic because it isn't what would happen in reality 
Matter with a density of 46g/cm^3 should not exist anywhere, except under the influence of extreme gravitation/pressure/temperature, such as in the cores of large gas giants, in white dwarf stars, in neutron stars, etc.

46g/cm³ doesn't sound that dense.

That's 46000kg/m3, nearly 4 times the density of the center of earth. (Also 4 times the density of lead)

[deoxy99]

I don't know how that's unrealistic.

It's unrealistic because it isn't what would happen in reality 
Matter with a density of 46g/cm^3 should not exist anywhere, except under the influence of extreme gravitation/pressure/temperature, such as in the cores of large gas giants, in white dwarf stars, in neutron stars, etc.

46g/cm³ doesn't sound that dense.

That's 46000kg/m3, nearly 4 times the density of the center of earth. (Also 4 times the density of lead)

Well, I didn't know that.

[Laura]

I don't know how that's unrealistic.

It's unrealistic because it isn't what would happen in reality 
Matter with a density of 46g/cm^3 should not exist anywhere, except under the influence of extreme gravitation/pressure/temperature, such as in the cores of large gas giants, in white dwarf stars, in neutron stars, etc.

46g/cm³ doesn't sound that dense.

That's 46000kg/m3, nearly 4 times the density of the center of earth. (Also 4 times the density of lead)

Well, I didn't know that.

Have a look at this list of elements sorted by density:
http://en.wikipedia.org/wiki/List_of_elements_by_density
46g/cm³ is above the range of naturally occurring elements.

[deoxy99]

Oh. It's above Osmium. Yikes.

[Laura]

Oh. It's above Osmium. Yikes.

Indeed 

[Maccara]

Glad I found this topic. Was going to make a bug report...

Exploding a sphere divides it into 13 smaller spheres that all fit within the original sphere. The original mass is divided among the resulting spheres and the high density results because the mass is the same, but the total volume is less.

You're right that this is unrealistic. Feel free to share your thoughts on how this could be improved. I look forward to improving the explosion code in the next few months.

Thanks for pointing out this problem.

Why are you doing it like this? is there a technical limitation in US why you can't use a better approximation (there are several)?

Some simple methods that come to mind, which at least would be better approximations than the current:

First expand the original body radius and only after that divide to spheres. That's actually how it would "approximately" happen in reality (considering something blowing up due to internal pressure, for example). The math for this is simple (since you already have the part down of dividing to spheres contained in equal volume, you can even use that for derivation of the required fraction) and this would be infinitely better approximation of reality.

Or first transform the body to a cube with equal mass and density and then divide that to cubes of required number. Dunno how your engine would cope with cubes, but since there are dice in the catalog, I suspect this would be simple too.

I guess using conic sections would be pushing it.

[Dan Dixon]

Why are you doing it like this? is there a technical limitation in US why you can't use a better approximation (there are several)?

I haven't prioritized improving this feature is the reason. I got it working 'well enough' and moved on to other features. I will be improving explosions in a future 2.x release.

That's a good idea to expand the original body and then divide into spheres. Thanks for that.

[Maccara]

I haven't prioritized improving this feature is the reason. I got it working 'well enough' and moved on to other features. I will be improving explosions in a future 2.x release.

Just realized my original question came out a little accusatory. Sorry about that (was a bit tired when I wrote that). Thanks for confirming "it's on the table".

That's a good idea to expand the original body and then divide into spheres. Thanks for that.

Yeah, I thought about how I would program it myself and that seemed like a trivial solution to the issue, without creating too much additional issues (sphere packing algorithm is the "hard part", and you have that implemented sufficiently already). Glad it gave you some ideas!

[Darvince]

I haven't prioritized improving this feature is the reason. I got it working 'well enough' and moved on to other features. I will be improving explosions in a future 2.x release.

Just realized my original question came out a little accusatory. Sorry about that (was a bit tired when I wrote that). Thanks for confirming "it's on the table".

That's a good idea to expand the original body and then divide into spheres. Thanks for that.

Yeah, I thought about how I would program it myself and that seemed like a trivial solution to the issue, without creating too much additional issues (sphere packing algorithm is the "hard part", and you have that implemented sufficiently already). Glad it gave you some ideas!

Well, I think the best solution to the problem would be to convert the planet/moon/star or whatever you happen to be exploding into a cube with the same radius as the sphere. A sphere might have 2000 polygons or more, and a cube only has six. Plus, changing the object into a cube would nearly double the volume and result in a much lower density than we're getting now.