My high school chemistry teacher said that there is no such thing as a “vacuum,” it’s just a difference in air pressure. But you always hear about the “vacuum” of space, or when something is “vacuum-sealed.” I am not scientifically inclined, so I don’t even know where to begin. Im also not sure if “physics” is the correct flair lol. I was wondering if it could be explained from either side of the argument.
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I think of vacuum and pressure as a spectrum, sort of like temperature (I’ll get there give me a second). If high pressure is a lot of gas molecules in specific volume, then vacuum is zero molecules in a specific volume. Getting a true vacuum (ie, no gas at all) is actually surprisingly difficult. But I digress.
Pressure and temperature both have a zero point – absolute zero for temp, hard vacuum for pressure. As the temperature or pressure increase, there is basically no limit on the top end of the scale.
The difference between pressure and vacuum on earth is defined relative to atmospheric pressure. In fact, there’s different pressure scales based on this concept. Ambient pressure is 0 PSIG (gauge) or 14.7PSIA (absolute) vacuum can be 0 to -14.7PSIG, pressure is any positive value of PSIG. Defined relative to absolute pressure, vacuum is 0-14.7PSIA, pressure is anything greater than 14.7PSIA. The reference is atmospheric pressure – useful on earth, less useful elsewhere in the solar system.
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