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A few clarifications on this thread in case anyone is reading in the future and is getting confused. I know however, that the temperature did in fact change, hence it's not an adiabatic process. That isn't really how an adiabatic process is defined. The temperature can change within a system (and often does) and it still be adiabatic. An adiabatic ...

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I provide below a rough guess of what might be influenced or influence it, and possible cosmological effects. It is by no means an answer you can take to the bank. But it is based on some of the relevant physics. I'm probably missing other relevant issues, and I hope others chime in, if only as an exercise in non-factual what ifs. It's pretty hypothetical ...

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The equations for the density of air are available on the engineering toolbox site. The density of dry air is approximately given by: $$\rho_{dry} = \frac{0.0035\,P_0}{T}$$ where $P_0$ is the pressure and $T$ is the temperature. The density of moist air is approaximately given by: $$\rho_{wet} = \rho_{dry}\,\frac{1 + x}{1 + 1.609 x}$$ where $x$ is ...

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It's because the centre of buoyancy and centre of gravity don't necessarily lie on the same point. This creates two types of mechanical equilibrium: stable and unstable. It turns out that when a human body is floating with its face inside the water, the body is in stable equilibrium. That is because in that position, the centre of gravity lies below centre ...

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Bob Bee's answer already covers a lot of extra detail, so I just want to give the very concise answer to your specific question. One form of one of the Friedmann equations is: $$H(t) = \sqrt{\frac{8\pi G}{3}\rho(t) - \frac{kc^2}{(a(t))^2}}$$ In a universe with zero global spatial curvature ($k=0$), like ours is thought to be, then the expansion rate $H(t)$ ...

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The Standard cosmology model, the $\Lambda$CDM model, rearranged from the Friedmann equations, looks like, $H = H_0 {\sqrt{L_m a^{-3} + L_r a^{-4} + L_{de}}}$ This assumes zero curvature space, pretty well measured now (note, not zero spacetime curvature, just the spatial slices). H is the Hubble parameter as function of time, from the Big Bang. $H_0$...

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If I understand you correctly you are concerned that a black hole somehow manages to become less dense than the matter that made it, as if it somehow expands against its own gravity to increase its volume. However a black hole event horizon is not an object - it is just a place in spacetime. Although we can calculate a density by calculating the volume ...

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There is nothing wrong in having something more dense than a black hole, large black holes can have densities less than water. If you put a lot of iron together it might or not become a black hole. An object of any density can be large enough to fall within its own Schwarzschild radius. The larger the black hole the lower the density, so you iron ball will ...

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You can calculate the volume from the information given about the radius, assuming the planet to be spherical of course.

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There's a type of alloy called interstitial alloy, which might increase the density of the metal, while perhaps not expanding its volume, by introducing small atoms that can fit

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Copper is quite a dense metal at 8.96. Both the stable copper oxides are lower density. I do not believe any surface treatment could increase the bulk density of pure copper, unless there are cavities in the material. The only way apparent density might increase is if the volume is assumed constant and the treatment causes the surface to adsorb external ...

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The density of water (and other fluids) depends both on the pressure and the temperature. A graph for water is here: You may see that at 1 bar (1 atmosphere), the density is highest around 4 °C. That's the conditions where the density reaches the nice 1,000 kilograms per cubic meter. Water contracts when it gets warmer than that, but also when it gets ...

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Please study Ned Wright's Cosmology FAQ: How do Astronomer's Measure the Density of the Universe? There it is pointed out that the local density varies from region to region; the scale of the region surveyed determines the granularity. The answer is clear and obvious: the density of the universe is NOT uniform at all distance and time scales.

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