What is Vacuum: Definition and 1000 Discussions

A vacuum is a space devoid of matter. The word is derived from the Latin adjective vacuus for "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often discuss ideal test results that would occur in a perfect vacuum, which they sometimes simply call "vacuum" or free space, and use the term partial vacuum to refer to an actual imperfect vacuum as one might have in a laboratory or in space. In engineering and applied physics on the other hand, vacuum refers to any space in which the pressure is considerably lower than atmospheric pressure. The Latin term in vacuo is used to describe an object that is surrounded by a vacuum.
The quality of a partial vacuum refers to how closely it approaches a perfect vacuum. Other things equal, lower gas pressure means higher-quality vacuum. For example, a typical vacuum cleaner produces enough suction to reduce air pressure by around 20%. But higher-quality vacuums are possible. Ultra-high vacuum chambers, common in chemistry, physics, and engineering, operate below one trillionth (10−12) of atmospheric pressure (100 nPa), and can reach around 100 particles/cm3. Outer space is an even higher-quality vacuum, with the equivalent of just a few hydrogen atoms per cubic meter on average in intergalactic space.Vacuum has been a frequent topic of philosophical debate since ancient Greek times, but was not studied empirically until the 17th century. Evangelista Torricelli produced the first laboratory vacuum in 1643, and other experimental techniques were developed as a result of his theories of atmospheric pressure. A Torricellian vacuum is created by filling a tall glass container closed at one end with mercury, and then inverting it in a bowl to contain the mercury (see below).Vacuum became a valuable industrial tool in the 20th century with the introduction of incandescent light bulbs and vacuum tubes, and a wide array of vacuum technologies has since become available. The development of human spaceflight has raised interest in the impact of vacuum on human health, and on life forms in general.

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  1. jk22

    I Time Dilation: Relative to Medium or Vacuum?

    If a medium with speed of light ##c_1## is considered, shall the Lorentz transformation be considered relative to it or to speed of light in the vacuum ? I don't know if we could send particles like muons through water for example, to check this with their life time.
  2. ravindrar

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    I made experiment on "Free Fall". I made a conical hopper of 15 liter volume and a vacuum chamber of , installed hopper upon vacuum chamber of 65 liter volume. Fixed a 2.5" gate valve to discharge powder in vacuum chamber. Connected both, hopper and vacuum chamber to vacuum pump (63 cum/ hr) and...
  3. N

    Vector and scalar potentials for an EM plane wave in a vacuum

    Lorentz gauge: ∇⋅A = -μ0ε0∂V/∂t Gauss's law: -∇2V + μ0ε0∂2V/∂t2 = ρ/ε0 Ampere-Maxwell equation: -∇2A + μ0ε0∂2A/∂t2 = μ0J I started with the hint, E = -∇V - ∂A/∂t and set V = 0, and ended up with E0 ei(kz-ωt) x_hat = - ∂A/∂t mult. both sides by ∂t then integrate to get A = -i(E0/ω)ei(kz-ωt)...
  4. TheQuestionGuy14

    B Does a field's vacuum density violate conservation of energy?

    The vacuum density, or the zero point energy, of a field, doesn't change as space expands, it remains constant. But, aren't particles and virtual particles just fluctuations of these fields? Meaning as space expands, more and more particles are being created, violating conservation of energy?
  5. B

    I Need advice on vacuum / suction experiment

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  6. A

    A Confusion about 2016 Unruh paper - fluctuating vacuum energy density?

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  7. gazaah

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  8. N

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  9. Cathr

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  10. Plat

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  11. F

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  12. H

    I Theoretical Torricelli Vacuum Test: Impurity Impact on Pressure

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  13. M

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  14. M

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  15. A

    B How Does Quantum Turbulence Affect Plasma in a Tokamak?

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  16. PGaccount

    A Vacuum persistence amplitude

    In the functional integral approach to quantum field theory, we have W[J] = ⟨0+|0-⟩J = ∫ D[Φ] eiS + ∫ JΦ Can someone give me some insight into why this path integral is a vacuum-to-vacuum amplitude. How and also why does this path integral W[J] become a vev?
  17. J

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  18. epotratz

    I Does light consist of oscillating vacuum fluctuations?

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  19. H

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  20. lovethepirk

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  21. W

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  22. K

    Need help in finalizing the vacuum pump to lift an object

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  23. O

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  24. S

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  25. J

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  26. J

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  27. A

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  28. 1

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  29. Plat

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  30. H

    I Divergent vacuum uncertainty of fields in QFT, how to resolve?

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  31. A

    B Movement in a Vacuum: Does Acceleration Show Anything?

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  32. Y

    Molecular Seive for making vacuum tubes

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  33. D

    I Vacuum projection operator and normal ordering

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  34. F

    I Is there a zero-mass, vacuum Schwarzschild GR solution?

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  35. Abimbola1987

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  36. A

    I Einstein-Hilbert Action, Lagrangian Density & Vacuum Fields

    From the action ∫Ldt =∫ι√|g|d4x where |g| is the determinant of the metric .and ι the lagrangian density. For gravitational field why is this ι is replaced by the Ricci scaler R which yield field equations in vaccum.(Rij-1/2Rgij)=0 Is it that the lagrangian density corresponding to vacuum is the...
  37. Abimbola1987

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  38. A

    I Speed of Light in Materials: Explained

    It is commonly said that the speed of light when traveling inside materials is lower than that of light in vacuum, but I don't understand how this can be true. It is the same light traveling, so how can it act differently? Does light appear to be slower in materials because it is not following a...
  39. K

    Misc. Generating as much suction with as little weight as possible

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  40. S

    I Casimir force and the Vacuum Field

    The Casimir force is often explained in connection with the zero point energy of the quantized EM field, and the fact(?) that metal boundaries modify this spectrum in such a way that a force is created. However, other sources (including some discussions on this forum) say that this is not the...
  41. Cerenkov

    B The Spectral Gap and Quantum Vacuum Fluctuations

    Hello. Recently Scientific American magazine carried an article about the work of the authors of this paper. https://arxiv.org/abs/1502.04573 The Undecidability of the Spectral Gap. The SciAm article is linked to here -...
  42. K

    Help me design a Vacuum Drying system

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  43. C

    Geiger (or other ionizing ray) Probe for Vacuum Conditions

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  44. M

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  45. S

    Pressure differences in a leaking vacuum vessel

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  46. L

    How can I build a cost-effective DIY vacuum chamber for my experiment?

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  47. T

    Do vacuum Ironing boards cause negative pressure in my Space

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  48. D

    How do wet/dry vacuum cleaners work? What is the physics behind them?

    I have a problem designing and understanding Wet and Dry vacuum cleaners. I understand some of the basics behind pressure however things I need to know is: what pressure/ velocity is needed to suck up water? how to calculate the pressure and velocity generated by the fan? (some examples of...
  49. G

    B Waves in a medium versus waves in a vacuum (ie no medium)

    Famously em waves are an example of the latter case. The two cases (waves in a medium vs waves propagating without a medium) seem at first (to me) to be extremely different and perhaps only connected by their mathematical descriptions. I can think of two cases of waves without a medium...
  50. Javier Lopez

    I Ion sensor for 1e20 ions/m3 density

    What kind of ion sensor can I use in the range 1e19to 1e22 ions/m3? (corresponds to 0.1 to 5 pascals if non ionized) Does it exist any sensor based in the charge capacity?
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