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In SI units, number density is measured in m −3, although cm −3 is often used. However, these units are not quite practical when dealing with atoms or molecules of gases, liquids or solids at room temperature and atmospheric pressure, because the resulting numbers are extremely large (on the order of 10 20).
The vacuum energy density of the Universe based on 2015 measurements by the Planck collaboration is ρ vac = 5.96 × 10 −27 kg/m 3 ≘ 5.3566 × 10 −10 J/m 3 = 3.35 GeV/m 3 [16] [note 1] or about 2.5 × 10 −47 GeV 4 in geometrized units.
The conversion between different SI units for one and the same physical quantity is always through a power of ten. This is why the SI (and metric systems more generally) are called decimal systems of measurement units. [10] The grouping formed by a prefix symbol attached to a unit symbol (e.g. ' km ', ' cm ') constitutes a new inseparable unit ...
If a given particle is taken to be at the origin O, and if = / is the average number density of particles, then the local time-averaged density at a distance from O is (). This simplified definition holds for a homogeneous and isotropic system. A more general case will be considered below.
This ratio of densities, and other ratios (using four fundamental constants: speed of light in vacuum c, Newtonian constant of gravity G, reduced Planck constant ℏ, and Hubble constant H) computes to an exact number, 32.8·10 120. This provides evidence of the Dirac large numbers hypothesis by connecting the macro-world and the micro-world.
Perhaps one of the hottest most recent SI models is Chrissy Teigen. And after being a cover star for the first time in 2014, she returned to the magazine this year again and looks hotter than ever.
Sports Illustrated is about to break down some serious stereotypes. The magazine's 2016 Swimsuit Edition will feature some fresh faces and some new body types, proving that the mag is about more ...
At the same time, gravity will attempt to contract the system even further, and will do so on a free-fall time = / /, where is the universal gravitational constant, is the gas density within the region, and = / is the gas number density for mean mass per particle (μ = 3.9 × 10 −24 g is appropriate for molecular hydrogen with 20% helium by ...