What is vacuum?

  1. What is vaccum? Many say its "empty" space. But what does "empty" mean? Does it mean that there are no atoms (or protons/electrons, or quarks, or strings)?

    Can anyone explain this?
  2. jcsd
  3. Andrew Mason

    Andrew Mason 6,833
    Science Advisor
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    Vacuum is not a precisely defined term. A perfect vacuum could mean a space where the air pressure is 0 (That does not necessarily mean that it is empty of matter - just that there is no pressure (matter could have solidified, for example) - or it could mean a space devoid of all matter, although a better term would be "free space".

  4. classical idea of vacuum was that of a region in space that are devoid of any matter.. up to the late 19th century, an atom was considered to be the most fundamental particle that constitute the universe, so in classical term, the defination of vacuum was pretty clear and straight forward. But with the advent of quantum theories in early 20th century, the concept of a particle as a point like localised entity in space has been replaced by a more fussy picture of probability distribution in space.. so in essence a particle can no longer be thought of as a localised object in space, which means you cannot pin down the precise location of a particle, which by the was is also consistent with the uncertainty principle. so if you can't pin down a particle to a point how do you talk of a space without particle? and moreover from the field theory, there is always a field fluctuation in space, again thanks to uncertainity principle, which implies that you cannot pin down an energy at a given precise instant of time. so theoretically even if we take the classical case of vacuum there is always a field fluctuation which can lead to matter-antimatter pair production. thus vacuum in its real sense in not possible physically..
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