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. E

    Penrose equation for a vacuum spacetime

    Okay so for this one we can consider the Bianchi identity again$$\begin{align*} \nabla_{[\lambda}R_{\sigma \rho] \mu \nu} = 2 \nabla_{\lambda} R_{\sigma \rho \mu \nu} + 2\nabla_{\rho} R_{\lambda \sigma \mu \nu} + 2\nabla_{\sigma} R_{\rho \lambda \mu \nu} &= 0 \\ \nabla^{\lambda}...
  2. russ_watters

    What factors affect heat rejection in vacuum pump systems?

    I'm working on a project to replace a couple of vacuum pump skids for a lab campus. The existing pumps are water-cooled, liquid-ring pumps. Since they are water cooled, there is effectively no heat rejection into the mechanical room(s) except through un-insulated exhaust pipes. The new pumps...
  3. E

    Redshift & Total Energy Density

    1. If today vacuum and matter contribute 71 % and 29 % to the total energy density of the universe, at what redshift z were they contributing equally? 2. If today vacuum, matter, and radiation contribute 71 %, 29 %, and 0.01% to the total energy density of the universe, at what redshift z were...
  4. F

    Fresh air (vacuum) as media for electromagnetics, can it have losses?

    Recently I saw an exercise on electromagnetics (plane waves) in which it was said that a plane wave was traveling through vacuum (ε0 and μ0) BUT with losses, i.e, σ ≠0. Is that possible? I think I have read in the past that it's OK in some texbook, but now, I have searched for it in a couple of...
  5. A

    B Fundamental fields and vacuum energy

    Please forward to appropriate subforums as I wasn't sure where to post it.In the standard model there are the composite particles and elementary particles, for the elementary particles there is said to be an associated field and the particle is the excitation of that field. Apart from asking how...
  6. E

    I Entanglement and Regions of Space in Vacuum

    Sean Carroll (in a video) claims that regions of empty space (vacuum) that are near each other must be highly entangled. He appears to argue that if they were not, there would be "a lot of energy contained there" which - my conclusion - would not be consistent with these regions being low energy...
  7. R

    Understanding High Thrust of Vacuum Rocket Engines

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  8. The black vegetable

    A How to find the gamma function for a fermion vacuum energy calculation?

    Following the method by Peskin and Shroesder 11.4 Trying to calculate the vacuum energy of a fermion. If my method is correct so far the next step is to find gamma function , the formula I have for gamma fuctions doesn't match this equation. Can anyone help with the next step? Starting with the...
  9. I

    I About fundamental constants and vacuum

    Does it not raise question to be able to build two parameters with the same dimension and order of magnitude of two fundamental constants from five parameters (other fundamental constants and measured properties)? $$\sqrt{10\frac{\left(\varepsilon_0 e^{-2}\right)^3\left(k_B T\right)^4}{\rho_c}}...
  10. R

    Replacing bremsstrahlung tubes with solid-state alternatives?

    What are the reasons X-ray vacuum tubes could not be replaced by solid state alternatives?
  11. Q

    I Gerard 't Hooft's "Fast Vacuum Fluctuations"

    Gerard 't Hooft has been a renegade in Quantum Foundations for quite some time, insisting that there is natural order underlying the Quantum Mechanical mysteries. Essentially a local, deterministic hidden variable perspective. He has recently posted a new paper on arXiv where he lays out his...
  12. J

    I Deriving vacuum FRW equations directly from action

    Using the Einstein-Hilbert action for a Universe with just the cosmological constant ##\Lambda##: $$S=\int\Big[\frac{R}{2}-\Lambda\Big]\sqrt{-g}\ d^4x$$ I would like to derive the equations of motion: $$\Big(\frac{\dot a}{a}\Big)^2+\frac{k}{a^2}=\frac{\Lambda}{3}\tag{1}$$ $$2\frac{\ddot...
  13. Adams2020

    A Higgs particle and non-zero expected value in vacuum

    What does the phrase “Due to Lorentz invariance, only the Higgs particle can have a non-zero expected value in a vacuum” mean?
  14. Quantum23

    A What is gravity in the superfluid vacuum model of quantum gravity?

    It has been hypothesized by quantum field theory that the vacuum is not empty due to the energy time uncertainity relationship. Instead it is filled with a sea of virtual particles popping in and out of existence and renormalized to the observed value we see today in experiments like the casimir...
  15. S

    Vacuum Airships - would multi-skinning work?

    Vacuum airships are a scifi idea where you evacuate the air out of a chamber to achieve lighter-than-air lift. I put this in scifi as it's just a curiosity at the moment. The issue faced with these designs is the chamber buckling with the pressure of the atmosphere around it, which puts pay to...
  16. Haorong Wu

    I Does vacuum excitation violate the conservation of energy?

    Hi, there. I am reading the article Relativistic quantum optics: The relativistic invariance of the light-matter interaction models by Eduardo Martin-Martinez el al (2018). Here he calculate the transition probability of a vacuum excitation for a detector. Suppose there is a lab where the...
  17. R

    B Does the Torricelli Vacuum Experiment Prove the Strength of Vacuum Forces?

    If Evangelista Torricelli truly created a vacuum, then there would be nothing in it, yet you can see through it which means light is obviously still in there (and who knows what else), right? If there was truly nothing in it, and glass is a highly viscous fluid, and fluids conform to fill empty...
  18. T

    A Cosmic string and vacuum decay

    https://arxiv.org/abs/2002.04856 It's proposed that topological defects like cosmic string enhance vacuum decay. I do not quite believe it.
  19. N

    I Unconventional methods for pumping down a vacuum chamber?

    Hi all, I'm not sure if this is the correct space so please let me know if it belongs elsewhere. I've always been very interested in engineering. In my spare time, I tend to think about a lot of unconventional ways of doing stuff because I'm of the mindset that there's always new things to...
  20. D

    B Time dilation and the reference frame of the vacuum

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  21. D

    A Reference frame of the vacuum -- which forum?

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  22. wolfy

    B Has the Double Slit Experiment been Performed in a Near Vacuum?

    Where, When and Who has performed the Double Slit Experiment in a Near Vacuum Environment Cannot find it anywhere on Line Thank You
  23. R

    The RPM of Dyson DC04 vacuum motor and more....

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  24. G

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  25. mollwollfumble

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  26. Y

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  27. LaunyO

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  28. W

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  29. A

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  30. Replusz

    I Vacuum amplitudes in \phi^4 theory

  31. Q

    A Algebraic form of Klein Gordon ##\phi^4## vacuum and ladder operators

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  32. chito1

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  33. D

    Calculating the wall thickness of a vacuum chamber

    =
  34. A

    I Virtual particle content of the vacuum state....

    Hi all, One more virtual particle question (sorry all!): for individuals who would take virtual particles as being 'real' (but unobservable), what is their understanding then of the content of the vacuum? For example, if I place a electron all by itself in the vacuum (thus making it no longer...
  35. J

    I Is the Brans-Dicke Vacuum Cosmology Theory Still Relevant?

    Has anyone heard of papers describing Brans-Dicke vacuum cosmology solutions? I'd be interested to know if the following calculations make sense. I assumed a constant mass density vacuum with equation of state ##p=-\rho##. I then plugged this equation of state into the Brans-Dicke equations...
  36. DrInfinity

    A Effect of Spin on Vacuum Energy

    In equation (3) of this article https://arxiv.org/pdf/astro-ph/0605418.pdf , on page 3, you can see an expression for the vacuum energy density of a field as a function of its particle spin, particle mass and the wave number k. It is fairly straight forward to derive the integral portion of...
  37. cianfa72

    I Speed of Light in Vacuum in Non-Inertial Frame

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  38. J

    Influence of vacuum in the Conservation of energy

    I probably haven’t thought this through. A sideview of a closed container filled with air consisting of two vertical cylinders (with radius ##r_1## and ##r_2##) are connected by two horizontal tubes. The container is separated by a small and a large lid (red) that are circular and can move up...
  39. K

    Vacuum interrupter contacts and displacement current

    I’m self taught so I have a lot of holes in my understanding. I also have little to no mathematical understanding. Even though ironically, I tend to prefer to picture electricity as numbers rather than “water” in a pipe, etc. I’ve been studying displacement current recently and have a question...
  40. B

    I Everyone Measures Light in a Vacuum at the Same Speed

    I ran into something on a non-technical message board that is familiar to me - a poster, clearly without any scientific knowledge, saying that Relativity is wrong. Unfortunately, the point he used as a battering ram is one to which I don't know the answer. He suggested that the light...
  41. R

    I How air flows through a vacuum cleaner?

    Hello, Recently, I 'opened up' a Henry vacuum cleaner to trace the path the airflow takes - from inlet through to the outlet. The vacuum cleaner has 2 distinct sections: 1) A lower section with inlet pipe and the 'dust-bag' 2) and the upper section with the motor, fan and the outlet. Now, the...
  42. Auxirius

    Cyclotron - Vacuum Chamber Materials

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  43. currently

    Schrodinger's Equation in terms of vacuum permittivity?

    Summary:: How can Schrodinger's Equation be written relative to vacuum permittivity I am wondering why a particular problem uses this equation: It is stated to be Schrodinger's equation. Where does the potential come in, as well as the e^2/r ? An explanation would be greatly appreciated. Thanks.
  44. B

    Charging a magnetically levitating sphere to 1 gigavolt in a high vacuum

    What sort of limits would be encountered if you tried to charge a magnetically levitating sphere to as high a voltage as possible in an ultra high vacuum by using an electron beam aimed at the sphere? Assume the sphere is highly spherical and polished. If electrons have sufficient energy to...
  45. Philip Koeck

    A Dipoles on a clean surface in vacuum

    Assuming a completely clean and flat solid surface (metal and amorphous carbon as examples). The surrounding vacuum is contaminated with water vapour at very low pressure. In what orientation would the water molecules adsorb to the solid surface?
  46. D

    Electron gun in a vacuum -- How hard of a vacuum is needed?

    how high does a vacuum need to be for electron gun to work? for example, will 1 pascal work, will 1 tenth of a pascal work? is there a minimum vacuum for a electron gun to work?
  47. B

    Help with Building a Vacuum Chamber

    A client asked me to look into designing a vacuum chamber for drying out lumber. I am a decent fabricator but sadly not so great at the physics side of things. I know the chamber I'm building will need pretty thick material and a lot of reinforcement. He wants it to be roughly 10'x3'x3' inside...
  48. G

    A Vacuum energy density after spontaneous symmetry breaking

    If we start with the Lagrangian \begin{equation} \begin{split} \mathcal{L} = & \frac{1}{2}(\partial_\mu \phi)^2 + \frac{1}{2}\mu^2 \phi^2 - \frac{1}{4}\lambda^2 \phi^4\\ \end{split} \end{equation} and give the scalar field a VEV so that we can define the field ##\eta##, where $$\eta = \phi...
  49. S

    Periodic images of dipole line charge followed by a vacuum space

    Can I sum up the potential due to all positive line charges and all negative line charges separately, with the boundary condition being at the edge of my unit cell, the potential should be the same and inside the metal there is a contant potential?
  50. 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.
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