Microscopic difference between gas and liquid

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Discussion Overview

The discussion revolves around the microscopic differences between gas and liquid phases, particularly in the context of phase transitions such as condensation and vaporization. Participants explore theoretical models and concepts, including the Ising model and renormalization techniques, to understand these phenomena.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant references the Ising model and questions if similar models can explain the microscopic differences between gas and liquid.
  • Another participant argues that there is no microscopic distinction between gas and liquid since one can transition continuously between the two, suggesting they are both fluids.
  • A participant corrects the previous mention of the triple point, indicating the critical point is more relevant to the discussion of phase transitions.
  • This same participant expresses frustration over the ambiguity in sources regarding the knowns and unknowns of microscopic models for phase changes, suggesting that the lack of a clear model presents a challenge.
  • Another participant provides an analogy comparing the gas-liquid transition to a wall with a gap, questioning whether it represents two distinct rooms or one continuous space.
  • It is noted that the renormalization group can be applied to understand universal behavior near the critical point.

Areas of Agreement / Disagreement

Participants express differing views on whether there is a clear microscopic distinction between gas and liquid phases, with some arguing for a lack of distinction and others suggesting that there must be differences due to the nature of phase transitions.

Contextual Notes

There are unresolved aspects regarding the definitions and assumptions related to phase transitions, particularly concerning the critical point and the nature of fluid states.

jostpuur
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I am familiar with Ising model, and the phase transition behavior the interacting "arrows" attached to lattice points exhibit. Now, I'm curious to know if similar theoretical models exist of more concrete examples. For example, what is the microscopic difference between gas and liquid? Can the condensation and vaporization be understood through the use of some renormalization techniques?
 
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jostpuur said:
For example, what is the microscopic difference between gas and liquid? Can the condensation and vaporization be understood through the use of some renormalization techniques?
Unfortunately no, as you can move continuously from liquid to gas (by going around the triple point on the phase diagram). Since there is no transition along this path, it suggests there is no way to distinguish them microscopically... they are just both fluids.
 
You probably meant the critical point, and not the triple point?

I see that it is possible to go from gas to liquid smoothly, but on the other hand, it is also possible to go from gas to liquid abruptly, so there must be some clear microscopical difference. This is a kind of thing, where it is frustrating that many sources merely mentions various things, leaving it ambiguous what is really known and what is not known. If it is the case that there is no microscopic theoretical model about the phase change between gas and liquid, it is of course very exciting, because one should consider it as a challenge :-p But I would prefer being more certain about it...
 
The best analogy I've hear is it's like a wall between 2 rooms, but the wall has a gap at the top. Is it 2 rooms or one room?

The renormalization group is applicable to universal behavior near the critical point.
 

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