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Straight out steal from CalMeacham post in the current thread Laws of Physics.
Too good a thread to start what would perhaps devolve into a hijack.
Which physicist said given the laws of matter he never would've thought of liquid? What did he mean?
Well, to begin with, there are only two liquid elements at standard pressure and temperature - Mercury and Bromine. Maybe conditions do not favor liquids? Seems hard to believe looking out the window right now.
Dennis
What is standard pressure and temperature? Does this refer to the universe or just our planet?
Probably the scientist referenced is Victor Weisskopf. In an article “About Liquids” (Transactions of the New York Academy of Sciences, Volume 38, Issue 1 Series II, November 1977, pages 202–218) he wrote
I don’t really understand quantum mechanics well enough to explain why he believed that.
It refers strictly to atmospheric conditions on Earth. See here Standard temperature and pressure - Wikipedia and Standard atmosphere - Wikipedia for more.
Back to the OP.
I’d suggest that it’s appropriate to think of liquids as a narrow transition region between solids and gasses. Some elements have fairly large areas of pressure/temperature space in their phase diagram (Phase diagram - Wikipedia) which can be liquid. Other elements have very little liquid space; they really want to be solid or gas, but not liquid.
The implication to me is that liquid state is a subtle and special thing. The vast majority of the conditions throughout the universe are incompatible with liquids, even exotic liquids. The fact we live in an environment conducive to liquid forms of common substances is yet another example of the Goldilocks phenomenon.
There are a variety of definitions depending on context, but standard temperature and pressure (STP) does essentially refer to a baseline for some terrestrial conditions. Most places in the universe, of course, experience conditions beyond the extremes of what we see on Earth, and there is no special chemistry that occurs just on our planet.
The liquid phase is a special class of fluid (a phase in which matter has zero shear modulus and therefore will flow) but has a defined boundary (liquid surface) and does not naturally expand or diffuse in the ambient atmosphere. That we use and consume what is likely the universe’s most common liquid–water–every day makes it seem prosaic but there is nothing obvious about its behavior. The behavior of individual molecules in a neutral gas or the overall mass can be simulated on various levels from basic quantum electrodynamics to statistical mechanics to classical thermodynamics with a high degree of fidelity. The behavior of water molecules, however, defies a comprehensive explanation, and depending on temperature distribution it may behave in very different ways. The anomolous properties of water are well characterized and described on various levels but not down to the point that we could deduce or simulate them using quantum field theory, and water is basically the most simple neutral multiple-element molecule except for hydrogen fluoride. More complex liquids act in even stranger ways, often behaving like amorphous or even crystalline solids under various ambient and charge conditions.
Stranger
I can see his point. Solids are fairly obvious, and so are gasses. Liquids aren’t. They only exist in goldilocks pressure/temperature conditions.
Not really. While the Earth is the only planet in the solar system which has free liquids on its surface (so does Titan, which, if it were in direct orbit of the Sun, would be considered a planet) we’ve now observed planets around other stars which should have temperature conditions favorable to for surface liquid, and of course there are other bodies in our solar system which have subsurface liquid (Europa, Ganymede, Enceladus, possibly Pluto) or intermittent surface liquid flows (Mars, possibly Ceres). The so-called ‘Goldilocks principle’ (in planetology, referring to the presumed narrow range of conditions which could sustain life) has essentially no evidence to support it since we have only one data point (the Earth) to extrapolate from. For all we know, the larger moons of Jupiter and Saturn may be teeming with subsurface life despite being far outside the supposed habitable range, supported by tidal energy and chemotrophic cycles.
Stranger
Of course, life (and the existence of physicists who can debate these questions) sort of depends on the existence of liquid medium. In our case, water.
Carbon dioxide and IIRC iodine, to take two common substances, go right from the solid phase to the gas phase at atmospheric pressure.
I’d seen an even more extreme statement (I think it was from Feynman) that at universal scales everything is a gas, and there is no such thing as a solid much less a liquid or more exotic state.
The universe is a bunch gas that has swirls and clumps in it due to the tenuous forces between the particles of the gas. The forces are too weak to form anything more than the tiniest clumps, and the idea that there is another phase of matter which sometimes forms on the surface of some of those tiny clumps is a small correction on top of a small correction.
I doubt this. With all the gas giants out there, I suspect liquid hydrogen is the most common liquid in the universe as hydrogen has everything else so outnumbered or outmassed whichever way you wish to compute most.
It’s worse than that, actually. At cosmological scales, matter is a dust, which is like a gas but with zero pressure. Galaxies interact gravitationally but collide so infrequently that they exert almost no “pressure” on each other. So the already simple gas laws become even simpler (of course, at these scales GR becomes a complicating factor).