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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Whether vacuum exists or not depends on the definition. One approach is to define a vacuum in a given volume, not a vacuum per se. There is a value called “mean free path”, that is an average distance that a particle can travel without colliding with another particles.
Based on this definition, there is vacuum in a given volume if the mean free path there is greater than the size of this volume. This leads to a paradox: there is vacuum in a vacuum tube, but not in the interstellar space, despite the fact that there are much more particles per cubic meter in the vacuum tube.
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