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Gauge verses Absolute Pressure Experiment.
The above gauge is a 'pressure/vacuum' gauge. It shows zero in any atmosphere even for atmospheric rounded off to,15 psi. Many pressure gauges measure their pressures relative to the atmosphere that they are in.

When put in a vacuum chamber and ported to the outside, they will read approximately 15 psi.

An absolute pressure gauge will read the pressure of the atmosphere it is in. A good example is a mercury collum barometer. They read 15 psi outside and zero inside. And if ported outside they again read 15 psi.

If the outside pressure is also a vacuum they will read zero. The above gauge has the potential to move negative, should it be possible to have a zero inside pressure, a vacuum, and a negative outside pressure. It's not. The following experiment would demonstrate that.

The above gauge, in a perfect vacuum chamber, now becomes an absolute pressure gauge, that can read both positive and negative pressures outside the chamber.

It can be hooked up to an outside displacer chamber. Th and Tc on either end of chamber. Moving the gas to ether end will give a reading of absolute pressure for, hot gas and cold gas.

I predict the outcome of this experiment will show a positive pressure for either, regardless of temperatures applied. The one point is that if the temperature used is below the liquefaction temperature the positive pressure will be so low as to read zero, from the crudeness of the meter. A more accurate meter would read slightly positive. Neither will go negative.

Another way to try it would be with a diaphragm that will bulge inward for positive pressure, and outward for negative pressure. Zero bulge for zero pressure.

This experiment should verify that with gasses, there is always a positive pressure. Experiment. See for yourself.

No fair using the inertia of the needle or diaphragm to momentarily pass the zero point.

Displacer chambers are positive pressure devices, always.

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If the Leonard -Jones Potential is used to model a substance, the following must be incorporated. From Wikipedia (bolding mine):

The mean intermolecular interaction of a Lennard-Jones particle strongly depends on the thermodynamic state, i.e., temperature and pressure (or density). For solid states, the attractive Lennard-Jones interaction plays a dominant role – especially at low temperatures. For liquid states, no ordered structure is present compared to solid states. The mean potential energy per particle is negative. For gaseous states, attractive interactions of the Lennard-Jones potential play a minor role – since they are far distanced. The main part of the internal energy is stored as kinetic energy for gaseous states. At supercritical states, the attractive Lennard-Jones interaction plays a minor role. With increasing temperature, the mean kinetic energy of the particles increases and exceeds the energy well of the Lennard-Jones potential. Hence, the particles mainly interact by the potentials' soft repulsive interactions and the mean potential energy per particle is accordingly positive.

"accordingly positive. ", means 'gasses always push'. They always push because, kinetic energy, (escape velocity), overcomes the LJ potential energy well. I.e., they completely break orbit around each other and go from vibrating to bouncing.

https://en.m.wikipedia.org/wiki/Lennard-Jones_potential


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https://skeptoid.com/episodes/4345

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