limits of vacuum

Perhaps the OP is looking for an anti-matter solution.

The only way to have less than zero is to provide a substance of opposite existence which would conceivably cause a vacuum which would require the addition of matter to bring the state to zero.

That is the only way I can conceive of creating the stated state of less than minus one atmosphere at an external pressure of one atmosphere.

Actually I can think of a way of obtaining a gauge pressure of -several thousand atmospheres. It only requires taking the measurement within a chamber having an internal pressure of several thousand atmospheres. If one started with a vessel with only one atmosphere more or less and had a gauge fitted to it and then subjected the smaller vessel and gauge to a pressure of several thousand atmospheres within either a larger vessel or an environment having a high pressure, like for instance the surface of Saturn, the indicated pressure on the gauge would indeed show more than one atmosphere gauge pressure vacuum (assuming the smaller vessel and the gauge maintained integrity).

If I may ask, what possesses one to ask such a question?

Turbotroll III

you are quite a patient Guru Del!

:)

You need to read up a bit on vacuums, hydraulics and pneumatics. gases can be compressed and evacuated from a container - you will always be left with one molecule because of a half life effect and so a pure vacuum is not attainable in practice. (a Torricelli vacuum - see http://home.att.net/~cat4a/mechs_V.htm) The space "A" in the tube will be filled with water vapour (or whatever vapour related to the liquid used. You can decrease pressure only to nothing (1 atm) but you can go up as far as you like (or can before something busts).

Gases can be compressed and if pressure is high they can liquefy - (pneumatics). Liquids and solids cannot be compressed (hydraulics) so the pressure on their surface is what ever you apply.

Remember atm pressure relates to where you are on earth (altitude) and the climatic conditions (see weather reports) and is the starting point so you can only go down to nothing but you can go up to where you like (or can ! - mechanical restraints.)

Thankyou Turbotroll3 (Anti-matter), glad to hear someone else conceives that it is possible even if we havn't been able to reproduce it (to my knowledge) here on Earth.

Maybe when 'Black Holes' are better documented, we might be closer to replicating a more 'negative' atm.

Do a google search for "Magdeburg hemispheres".

Generally when we think of mechanically created vacuum we measure it in "gauge pressure" (atmg) meaning the difference between the pressure inside the vessel and the pressure outside the vessel (atmospheric pressure). So, to get a gauge to read -2 atmg you would need to set up your vacuum vessel inside a larger vessel that is pressurized to 2 atmg then draw vacuum on the inner vessel. Your gauge, if it is vented into the pressurized vessel will show the difference in pressure compared to 2 atmg which will be about -2 atmg (if you happen to have a gauge that can display -2 atmg; I have never seen one). Of course the pressure inside the vessel is still -1 atmg compared to air pressure at sea level on earth.

On the other hand, "absolute pressure" (atma) is the measure of force exerted on the pressure transducer by the molecules and particles that make up air. It is not possible to have less than zero matter inside the vessel - or anywhere else in the universe (that I know of); therefor the absolute pressure of the vessel can never be less than 0 atma.

Vacuum, like gauge pressure, is a relative value. The reference pressure will determine the attainable maximum vacuum. If the reference is standard pressure (1013.2 millibar), it is physically impossible to attain vacuum > -1 atm. However, if the reference is ambient pressure (which is nearly always the case in real world applications), a higher vacuum is easily achievable.

A high pressure weather system can easily provide an ambient pressure of 1045 millibar or more (the highest barometric pressure recorded was ~1082 millibar, nearly 7% above standard pressure). An evacuated container (such as in a lithium bromide absorption cooling system) in this environment would indeed experience vacuum > -1 atm.