Vacuum Definition and 1000 Threads

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. 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?
  2. 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?
  3. 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...
  4. 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...
  5. 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?
  6. 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.
  7. ravindrar

    Free Falling powder in a vacuum

    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...
  8. 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)...
  9. 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?
  10. B

    I Need advice on vacuum / suction experiment

    Summary: Vacuum pump help I need advice on what type of vacuum pump would create max negative pressure in a very small area ( a space no larger than your pinky finger I guess) ? Maybe some kinda high suction low cfm pump? I don't know enough about vacuum pumps to know which type to...
  11. A

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

    Hi all, Just had a look at the 2016 paper by Wang, Zhu, and Unruh, "How the huge energy of quantum vacuum gravitates to drive the slow accelerating expansion of the Universe," Qingdi Wang, Zhen Zhu, and William G. Unruh, Phys. Rev. D 95, 103504 – Published 11 May 2017 The paper states...
  12. gazaah

    Vacuum suspended fishtank: Why would this design work or not?

  13. N

    Negative pressure from vacuum to shunt a object upwards?

    Hi folks, I think a lot about aeronautics and physics for the purposes of helping people. I stumbled across the idea of vacuum airships as a cheap method of transporting food and water to places where it's unsafe for vehicles, or where there are no roads. We all know it's unconventional and...
  14. Cathr

    I On Hubble's constant, the expansion of the Universe and vacuum energy

    Recently I was thinking about the Hubble's constant (which, actually, is not Hubble's and not constant...) and wondering: if the universe is expanding at 70 km/s each Mpc, then there's possible to calculate some expansion of space, say from me to a person 1 meter away from me (theoretically)...
  15. Plat

    Radiometer rotation speed as function of pressure

    I am experimenting with using a radiometer as an approximate indicator of pressure in my homemade high vacuum system, running a small turbo pump. I am interested in the relationship between pressure and vane rotation speed, with light intensity being constant. I have only been able to find...
  16. F

    Pulling a vacuum on a heat pump with a recovery machine

    I am a student attending an HVAC program at a trade school. Today I recovered refrigerant out of a heat pump in order to debraze the compressor out of the heat pump. My instructor has taught me how to use a recovery machine to recover refrigerant out of an air-conditioner or heat pump before...
  17. H

    I Theoretical Torricelli Vacuum Test: Impurity Impact on Pressure

    Does the real vacuum pressure/underpressure depends only on the amount of impurities? In the case of theoretical Torricelli vacuum test, when no purities left in the vacuum: Is the vacuum 0Pa at 1m height (with 760mm of Hg) and also the same at 10m height (also with 760mm of Hg) of the test...
  18. M

    B Questions regarding expansion, the vacuum in space, and black holes

    Summary: Expansion of matter in the visible universe, total volume of space outside the visible universe, black hole mechanics, and general questions from an uneducated but extremely interested evolved monkey. Hello everyone! I do not know the rules of this forum, or any forum for that matter...
  19. M

    I Faster Than Light Particle: Could it Create the Universe?

    I've wondered what would happen to a particle if it could break through the 186,000 miles/second speed barrier and go faster than light. Would it go say 186,001 miles/second or would it go infinitely fast. I know Einsteins Special Relativity prohibits this but I have just wondered. Now if this...
  20. A

    B How Does Quantum Turbulence Affect Plasma in a Tokamak?

    Summary: I was reading that the most powerful gamma ray burst experienced a 'drag' due to quantum turbulence and wondered how this could effect a plasma. After reading this Wikipedia article https://en.wikipedia.org/wiki/GRB_080916C I noticed the part about how the light was slowed down by the...
  21. PGaccount

    A Why Is the Path Integral W[J] a Vacuum-to-Vacuum 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?
  22. J

    Choosing a heater band for vacuum system bakeout

    Hello, I'm trying to find the right wattage heater band for a cylindrical vacuum chamber that is stainless steel (304), ~2ft in length, ~0.5ft in diameter, and ~0.5 in thick. From a quick google search, I was able to calculate the required wattage for bring the chamber up to and constant at...
  23. epotratz

    I Does light consist of oscillating vacuum fluctuations?

    Hello, I've been studying electromagnetics, electromagnetic radiation, and bit of quantum electrodynamics for about 12 months, but I'm stumped on an issue.. This is what I understand so far: Charge consists of countless "vacuum fluctuations" (i.e., virtual particles). Accelerated charges...
  24. H

    Calculating Force on Springs in a Vacuum Chamber

    Hi, I have a bottom plate resting on a table (see figure in attachment). On top of this bottom plate is are series of springs and on top of it rests a top plate. Between the bottom and top plate (inside the springs) is a seal to create a vacuum chamber. Question: what is the total force acting...
  25. lovethepirk

    Vacuum bag vs bolt force (fabricating a carbon fiber wing)

    Hello, thanks in advance. I'm trying to make a near 100% solid carbon fiber wing. I'm vacuum bagging the top half of the wing and the bottom half of the wing separate. After making sure there is a thin 2mm gap b/w the center of both halves the goal is to put a very strong, thick epoxy between...
  26. W

    Unsteady filling of a vacuum tank

    I have a vacuum tank at work that I am trying to determine the flow rate and pressure curve of when I open up the tank and I just cannot figure these equations out. Environment: average office space Atmospheric pressure: 29.92 inHg (per weather information) Temperature: 72°F Tank info...
  27. K

    Need help in finalizing the vacuum pump to lift an object

    Hi, I have been asked to identify the right vacuum pump to lift the object having 500 grams weight with one suction cup. I am going through lot of materials to identify correct formulas to calculate the lifting force. and now I am able to calculate the theoretical lifting force. But seems, I am...
  28. O

    Speed of Light when not in a vacuum?

    In a vacuum the speed of light is a constant. What if its not in a vacuum? Okay, as always I'm confused. I'm very interested in physics but am a layman. Alright, so we know that time is relative to one's distance from a mass, so that as we go further from the Earth, let's say, time moves...
  29. S

    A Measuring Quantum Vacuum Fluctuations

    I have been reviewing potential methods for measuring Quantum Vacuum Fluctuations that I might be able to implement in a home hobbyist environment. Must be room temperature devices. I have seen that there are only a couple of possibilities: The Tunnel FET and the Single Electron Transistor. I...
  30. J

    I Vacuum energy length scale detectable by the Casimir effect?

    According to Sean Carroll's The Cosmological constant(https://arxiv.org/pdf/astro-ph/0004075.pdf) (Eqn.20) cosmological observations imply that the magnitude of the vacuum energy density in natural units is given by $$|\rho^{(obs)}_\Lambda|\le (10^{-12}\ \rm{GeV})^4.$$ Does this imply that the...
  31. J

    I Does the Friedmann vacuum equation have a linear solution?

    Does the Friedmann vacuum equation have a linear solution rather than an exponential one? Using natural units one can write Friedmann's equation for the vacuum as $$ \begin{eqnarray*} \left(\frac{\dot a}{a}\right)^2 &=& \frac{8\pi G}{3}\rho_{vac}\\\tag{1} &=& L^2 \left(\frac{\rho_0}{L^4}\right)...
  32. A

    I De Broglie-Bohm theory and Bohm-like models - how is vacuum treated?

    Hi all, I've been looking at de Broglie-Bohm theory and more recent attempts at Bohm-like models that are relativistic and attempt to reproduce QFT. What I'm not clear on (non-expert) is how the vacuum is modeled in these cases? If we have a set of infinite quantum harmonic oscillators...
  33. 1

    High dielectric strength, vacuum compatible glue

    Hi all, I would need an high dielectric strenght glue to fix PTFE or Hostaphan to the vacuum chamber wall in stainless steel, so the glue should be vacuum compatible. Force against the bonding direction would be 50N, so if the glue has already 100N it would be good but I don't think it is an...
  34. Plat

    Calculate the thickness of a plate to withstand a specified uniform pressure

    In exploring the feasibility of constructing a vacuum chamber, I am trying to calculate the thickness of rectangular polycarbonate sheet needed to withstand 100kPa of pressure, given dimensions of 30.5cm by 61cm (12 by 24 inches) and clamped edges. I have found some calculators that will tell...
  35. H

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

    If you calculate the uncertainty of a scalar field in the vacuum state, i.e. ##\langle0\left| \phi^2\right|0\rangle##, you get a divergent integral that comes out to something like $$\frac{1}{4\pi^2}\int_0^\Lambda \frac{k^2 dk}{\sqrt{{m^2}+{k^2}}}$$ Where ##\Lambda## is some momentum cutoff...
  36. A

    B Movement in a Vacuum: Does Acceleration Show Anything?

    A very basic level question. Two objects are floating in a vaccum, Object A and Object B. Then distance begins to grow between the two objects. Object A feels acceleration being exerted, Object B does not. What does this show? From a classical perspective, it would be my understanding...
  37. Y

    Molecular Seive for making vacuum tubes

    im trying to jog my memory back 30years when I worked with vacuum tubes. I worked with manufacturing of image tubes. I remember the vacuum systems used vac-ion pumps to achieve -12 power torr. I alsoo remember first using a molecular seive for roughing,pumping to 10 microns. The seive was a...
  38. D

    I Vacuum projection operator and normal ordering

    I've been reading this book, in which the author expresses the vacuum projection operator ##\vert 0\rangle\langle 0\vert## in terms of the number operator ##\hat{N}=\hat{a}^{\dagger}\hat{a}##, where ##\hat{a}^{\dagger}## and ##\hat{a}## are the usual creation and annihilation operators...
  39. F

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

    The Schwarzschild solution of the Einstein Equation of GR is said to be the only time-independent matter-free solution of that equation. In this usage, does “matter-free solution” mean without matter everywhere except at the singularity of the solution? I thought that the only solutions of the...
  40. Abimbola1987

    Measurement of vacuum diode electron flow

    Dear Sirs, After my theoretical post on vacuum diode electron flow, I decided to try and measure it physically. I didn't have a vacuum tube, so I improvised with some tungsten wire, aluminum sheets and some screws and the result was usable. Obviously the tungsten wire fails after some time due...
  41. 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...
  42. Abimbola1987

    Understanding Electron Flow in Vacuum Diodes

    Dear Sirs I have been going through the "radiotron designers handbook", but I can't seem to find the answer to the doubt I have about the electron flow of the source Vp. Kindly consider the below two circuits, the difference is the polarity of Vf. Question: In both circuits, the electrons...
  43. 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...
  44. K

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

    Hello all, as my final project to attain my bachelors, I have tasked myself with designing some sort of device to collect insects from the canopy of soybean plants that can be suspended under a UAS (quad copter/drone). What I am trying to do is essentially build some sort suction device. The...
  45. 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...
  46. 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 -...
  47. K

    Help me design a Vacuum Drying system

    Hello all, I've been entrusted a project of developing a Vacuum Drying System for my company. This system will be used for instant drying of automotive parts after washing. Needless to say the parts will be wet and at an elevated temperature (approx 50 degree C). The requirement is to dry the...
  48. C

    Geiger (or other ionizing ray) Probe for Vacuum Conditions

    I am planning a physical experiement under vacuum conditions. In this experiement, I want to detect ionizing rays, especially as broad band as possible, for instance including alpha radiation. Typically geiger tubes are filled with a certain gas, that gets ionized by the radiation to measure...
  49. M

    A Charge of the Vacuum in QED: Meaning & Implications

    Hello! When calculating the Hamiltonian operator in QED, in terms of creation and annihilation operators, we obtain an infinite term, which is considered irrelevant for most part (beside some renormalization problems) because we usually care about the difference in energies, so that would be...
  50. S

    Pressure differences in a leaking vacuum vessel

    Hello all, I'm new to this forum and I'm mucking about with some self-made physics conundrums, and I need some help! So, What I am aiming for is a roughly cylindrical vessel (it can, and I think probably has to, be tapered to achieve the effect) with the air being pumped out of one end, and a...
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