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Statements like "with the current record of 0.9 mg/cm3 being the lowest value for any solid yet discovered" don't make much sense to me without a rigorous definition of "solid". If you allow voids in a "solid", then you could just make a big empty box with very thin sides. What's the difference? 18.104.22.168 (talk) 01:12, 24 November 2011 (UTC)
It seems that it's the "by convention" which provides the "definition" which allows this to be called a solid. I tagged that phrase for a reference at one stage, but that was removed because the Science article included that. However, the Science article was written by one of the HRL guysm which hardly seems impartial. Surely if there's some convention out there then should be a reference to the fact that wasn't written by one of the researchers spruiking this new metamaterial? — Preceding unsigned comment added by 22.214.171.124 (talk) 05:26, 25 November 2011 (UTC)
It was I who removed it. I am looking for good reference on "conventions". The Science article doesn't offer one, but I note that air density is 1.2 mg/cc, and the past records  were 1.0-1.2 mg/cc, i.e. they were measured (by other groups: LNL and Sandia) with air excluded. Anyway. those materials are >99% air, and thus with or without is just a matter of adding 1.2. Materialscientist (talk) 06:05, 25 November 2011 (UTC)
Excuse me if I got this totally wrong, but... if the density of metallic microlattice is 0,9 mg/cc and air is 1,2 mg/cc - Shouldn't this stuff float then? — Preceding unsigned comment added by D-Frame (talk • contribs) 15:33, 25 November 2011 (UTC)
It probably crosses the line on "original research" to include this, but I think a fair comparison is with the Eiffel Tower. A guy on Yahoo Answers estimates the area the Eiffel Tower encloses to be 3,290,250 cubic meters, and according to the article it weighs 10,000 tonnes; thus it has a density of 1E13 mg/3.3E12cm^3 = 3 mg/cc. It would be 2 if all you counted was the metal frame. So we should avoid getting wrapped up in hype and bear in mind that this is simply a very, very small metal construction. (Though I doubt the Eiffel Tower is quite so elastic!) Wnt (talk) 15:40, 25 November 2011 (UTC)
The stuff that is lighter than air makes only some 0.01% of the microlattice; 99.99% of it is air. Thus, residual forces (adhesion, electrostatics on some dust and organics that got stuck to it, etc) should keep it in place, but I guess any minor draft will blow it away. Materialscientist (talk) 00:15, 26 November 2011 (UTC)
Actually, as the article (at least now) explains, the quoted density is the one it would have in vacuum; when put in normal air, some air seems to "fill holes" in the material, doubling its actual density to substantially above pure air's density. --Roentgenium111 (talk) 20:23, 13 July 2012 (UTC)
This seems impossible to me. How can the overall density rise above air's density just by adding air? It would just get closer and closer to air's density, but never above. --D-Frame (talk) 14:34, 10 December 2012 (UTC)
Sure it can - add air density to material density in vacuum, and the total density will exceed the air density - this is what is described above. Materialscientist (talk) 23:46, 10 December 2012 (UTC)
Please forgive my stubbornness, but I really would like to understand how that can be possible. Let's say we have 10 cc of microlattice, which would weigh 9 mg. Now even if we add a huge amount of air - let's say a hundred cubic metres - the overall density of the "mix" would only be 120,000,009 mg / 100,000,010 cc = 1,19999997 mg/cc. You can keep adding and adding and adding air, but it will only get closer to - and never exceed - 1,2 mg/cc. --D-Frame (talk) 14:55, 17 December 2012 (UTC)
Final density = (Mmicrollatice+Mair)/Volume would always be larger than Mair/Volume = Air density. Your mistake is adding volumes, whereas air fills in the vacuum inside the microlattice (further, we neglect the tiny volume of metal when calculating the final volume and take it as volume of air). Materialscientist (talk) 22:58, 17 December 2012 (UTC)
A new material with an even lower density of 0.2mg/cm3 has been discovered by German scientists (see phys.org, , or many other German-language sources), made of carbon nanotubes and called "Aerographit" ("aerographite" in English). --Roentgenium111 (talk) 20:20, 13 July 2012 (UTC)