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. A

    Vacuum energy and harmonic oscillator

    Hi everyone I was wondering, why is vacuum energy related to the zero point energy of an harmonic oscillator? The hamiltonian of an harmonic oscillator is $H= \frac{p^{2}}{2m} + \frac{1}{2} \omega x^{2}$. Where does the harmonic potential term come from in the vacuum?
  2. S

    B I heard a spin-top in a perfect vacuum would stay spinning

    Ok I heard that a very fast spinning top, in a perfect vacuum, on Earth, would stay spinning forever, and I suppose it would in the middle of the vacuum without falling, because spinning at lightspeed means it can't move 1 down, so if the speed in this top stays in it, then it could avoid...
  3. J

    Will a metal vacuum mug beat a cooler bar with 300mL Ice?

    I guess the question is also when. If you have some food or liquid to store. If you use a low quality cooler bag with 200mL to 300mL Ice pack at what point will a Vacuum seal with no Ice beat the cooler bag? I guess at the 10 hour mark or 24 hour mark or at some very long period of time.
  4. Brakwa

    Is my air ejector condenser causing vacuum issues?

    Having trouble at a plant where the vacuum has increased to the point where a pump has been put on the end of the air ejector condenser to maintain vacuum, without it the limits would be too high and trip the Steam Turbine. The question is, does the air ejector condenser continuously drain...
  5. S

    Can charge be held in a vacuum?

    It's my understanding that matter holds charge on Earth from the insulation of the atmosphere, since the atmosphere is a bad conductor and essentially blocks current due to the gaseous molecules' atomic structure and their covalent bonds. Does this mean it's impossible for matter to hold charge...
  6. C

    Continuity vacuum level at interface

    Hi, I am studying the Metal-Semiconductor junction. I cannot find any clear explanation of the continuity of the vacuum level at the interface. Can someone help me? My reference book provides me with the following: When two different materials are brought into contact, they must share the...
  7. S

    Divergence of integral over vacuum energies (Free field)

    Hi, The Hamiltonian for the free scalar field, expressed in terms of the creation/annihilation operators, is H = \int d^{3}p [\omega_p a^{\dagger}_p a_p + \frac{1}{2}\omega_p \delta^{3}(0)] \hspace{3mm} I thought: \omega_p is a function of p as \omega^{2}_p = |p|^{2} + m^2 and so the...
  8. G

    Blocking Back Of Fan Creates Vacuum In Front?

    Hi there, I have recently observed a strange effect regarding a fan and was wondering if someone could explain what's going on. I have a 22cm computer case fan which I am using in a project. For my purposes, I had to partially tape over the back of the fan. I also put a large plastic jar lid...
  9. H

    Vacuum fluctions and the Casimir Effect

    I don't recall where I saw this...but the author said that the Casimir effect experimentally proved that vacuum fluctuations exist. Does the Casimir effect really prove that or is it consistent with vacuum fluctuations? Thanks for any comments you care to make.
  10. D

    Why is QFT insensitive to absolute energies?

    In the canonical formulation of QFT (to which I've been exposed), it is always argued that only differences in energy are physically observable and so we can deal with the fact that the vacuum energy is infinite by redefining the vacuum such that its energy is zero and we subsequently measure...
  11. D

    Why is Gravity Sensitive to Absolute Energy?

    As far as I understand it gravity is sensitive to absolute energies, as seen directly through Einstein's equation G_{\mu\nu}=8\pi GT_{\mu\nu} Thus the local geometry of spacetime is directly affected by the local energy density (and not just differences in energy). So whenever gravity is taken...
  12. M

    B Does Space Really Contain Nothing?

    Is space actually a vacuum or it is so large that any matter is negligible?
  13. P

    Why Kink can not tunnel to vacuum, and is topologically stable

    Why the kink (\phi(x)=tanh(\frac{x}{\xi})), can not tunnel into vacuum +v or -v (Spontaneous symmetry breaking vacuum). From the boundary condition(x\rightarrow \pm\infty, \phi(x)\rightarrow \pm v), it is self-evident. but the book states: Due to the infinite high energy barrier, the kink...
  14. 6

    Is vacuum acceleration directly proportional to distance?

    Do we know if the instantaneous/observed acceleration due to the vacuum is directly proportional to distance or possibly? (ignore any gravitational effects) A~D ? A~D^2 ? A~D^(1/2) ? A~D^(-2) A~D^(Other) ? OR A= constant (edited as I forgot this one) If not, is there a best guess/fit or...
  15. G

    Interacting Quantum Field Theory: Ground State

    Hi all, I have a question about the ground state of an interacting quantum field theory. The state space in non-interacting QFT is a space where each field mode (with specified momentum p) has some occupation number n. These modes are interpreted as n particles with momentum p. The vacuum is...
  16. H

    Classical/QFT Vacuum Fluctuations

    I want to ask a question about the Quantum Vacuum, but I want to make a few statements about my understanding of the Classical concept of a vacuum to act as a background. 1.)As I understand it, the classical vacuum is a place where there is nothing. 2.)Two attributes of the classical vacuum are...
  17. BiGyElLoWhAt

    Exploiting time varying B field to employ vacuum acceleratio

    So I've been wanting to build a particle accelerator for a while, and have kind of been brain storming ideas to make it work. I've been recently trying to figure out how to get the actual acceleration to happen. I have a few ideas, but the one that I like (assuming it's possible) is using a...
  18. R

    Can a Perfect Vacuum be Created & Stretch Space? Answers Here!

    I have no qualifications in science but find it fascinating in general. Could anyone answer the following for me? Imagine an immensely strong pipe closed at one end with an airtight piston pressed tightly against the closed end. (a) Is it possible to pull the piston any distance along the...
  19. P

    Strength of container for vacuum freeze drying

    I have read that freeze drying is the best way to salvage wet books (http://www.ccaha.org/uploads/media_items/technical-bulletin-salvaging-books.original.pdf). However, freeze dryers run in the thousands of dollars, and I don't know anyone who has one I can borrow. Solution: make my own! I...
  20. fluidistic

    Plane wave passing from vacuum to conductor

    Homework Statement A monochromatic plane wave with frequency ##\omega## and real amplitude ##E_0## passes from medium 1 to medium 2 orthogonally with the surface between the 2 media. Both media are semi-infinite; the indices of refraction are ##n_1=\sqrt{\mu_0 \varepsilon _0}## and...
  21. quantumfunction

    How different can quantum vacuums be?

    For instance our quantum vacuum has a certain Cosmological constant and the question is can there be other vacuums with different values and if so where's the evidence for this I would like to read it. How do you derive the Cosmological Constant through something like Quantum field theory or...
  22. M

    Primordial black holes refute Higgs vacuum decay?

    http://arxiv.org/abs/1507.05760 Higgs boson cosmology Ian G. Moss (Submitted on 21 Jul 2015) The discovery of the Standard Model Higgs boson opens up a range of speculative cosmological scenarios, from the formation of structure in the early universe immediately after the big bang, to relics...
  23. S

    Electrical Can I Use JB Weld to Build DIY High Voltage Vacuum Feedthroughs?

    I want to build high voltage feedthroughs (vacuum) from epoxying pieces of alumina together, and then epoxying alumina strips on the outside to cover the spaces between. Can I use JB weld, as far as things go electrically? People have reported that JB weld is unexpectedly wonderful for vacuum...
  24. norlesh

    Surface treating mild steel for hard vacuum

    I understand mild steel is very bad at out gassing so is never usually considered for hard vacuum applications. But if the decision was constrained by other factors would it be possible to apply a surface treatment or coating to the internal walls of the vessel - am I correct in assuming that as...
  25. R

    Best Way to Control Vacuum Level in a series of Tanks

    I have two tanks next to each other, first needs to be kept at 200 mmHg vacuum & the second at 500 mmHg. Both are attached to a vacuum header which can achieve a 600 mmHg vacuum by means of a water jet ejector. What is the best way to maintain the vacuum levels? Would a set of globe valves...
  26. P

    Is speed of light in vacuum an axiom in relativity?

    The speed of light is constant in all frame of reference... So the relative motion of the source of light and the frame of reference from which you are making measurement does not matter... Is it an Axiom in relativity ? I understand that they are experimentally proved concepts... But is it an...
  27. Gvido_Anselmi

    Vacuum state Lorentz invariance

    Hi everybody! Why we don't have to prove Lorentz invariance of the Vacuum state in QFT? This fact is quite obvious in QED and follows from Lorentz invariance of electric charges. But in general case? I don't know, but it seems to me this fact is not so obvious as it treated.
  28. LarryS

    Does classical vacuum permittivity have a QM analog?

    According to Maxwell's Equations, the classical vacuum permittivity and permeability have a very important role: They determine the speed of light. But it seems like these two important concepts are not as precisely defined in the quantum world. Are there rigorous analogs of these two...
  29. D

    Locality, unitarity & vacuum energy

    I've read in a set of lecture notes that the requirement of locality and unitarity in QFT imply that the vacuum must have a non-zero energy associated with it (http://arxiv.org/pdf/1502.05296v1.pdf , top of page 3 under heading "What is the problem?"). My question is, why does the locality and...
  30. firin81

    Can Space Aircraft Reach Speed of Light in Vacuum?

    As we known, the force applied to the plane that fly in the atmosphere is to keep plane moving forward. The force given is to against the pressure of the air. If a space aircraft flies in the vacuum, the force given to it will accelerate aircraft because there is no friction caused by air...
  31. J

    Determine equivalent vacuum for water depth

    Hello, I need to figure out the max water depth a motor will operate without water ingress. The plan is to use a vacuum pump to create differential pressure and correlate that to water depth. My issue is the correlation between the vacuum and pressure. Can someone please provide a formula for...
  32. wolram

    Dark matter, Mach's ether and the QCD vacuum

    I have found this paper, it seems interesting although i haven't read it all yet arXiv:1507.00460 [pdf] Dark matter, Mach's ether and the QCD vacuum Gilles Cohen-Tannoudji Subjects: History and Philosophy of Physics (physics.hist-ph); Cosmology and Nongalactic Astrophysics (astro-ph.CO)
  33. S

    Can I Connect a Smaller Valve to a Varian M4 Diffusion Pump for Lower Costs?

    Hello all, I have a Varian M4 diffusion pump that has a 6 inch diameter opening at the top, is it okay for me to connect that to a reduced size opening like just 2 or 3 inches diameter so that I can use a smaller valve? I am only trying to pump down a cubic foot or two sized chamber. I am...
  34. JG1009

    Zero-point energy and QED vacuum state

    I'm relatively new to QFT and was wondering how the QED vacuum has a dormant zero average-field condition if there is a zero-point energy of the field as well? How is there a zero average and a zero point energy?
  35. Z

    What is the derivation for the vacuum density of states in the Purcell effect?

    The Purcell effect is when an atom placed inside a high finesse cavity with a very small mode volume gets an increase in the spontaneous emission rate. I've tried to find correct explanation for this effect, but it seems hard to find, except that it comes from an increase in the vacuum density...
  36. N

    How is work measured in a vacuum?

    I've just learned that work is done when a force moves something, and it's measured in joules. I've also learned that work = force x distance, but what significance does distance have? The force itself is what's being measured. In other words, if an object weighing 1kg was accelerated to...
  37. V

    Forever boiling water in vacuum

    Hello my first post :) I was wondering if it could be possible to achieve forever boiling of water in room temperature in vacuum. I understand that as water evaporates pressure increase and when equilibrium is reached, water stops boiling. But could it be possible to do that vapor in vacuum...
  38. eftrsd

    Understanding the Vacuum Debye Screening Length: Importance and Calculation

    What is the correct value for the vacuum Debye screening length?
  39. ShayanJ

    Integral kernel in vacuum wave functional

    I'm trying to solve the exercise below in a book I'm reading. I inverted equation 1.3 to get ## \phi_{\mathbf k}(t)=\int \frac{e^{-i \mathbf k \cdot \mathbf x}}{(2\pi)^{\frac 3 2}} \phi(\mathbf x,t) d^3 \mathbf x ##. Then I put it in I to get: ## I=\int \int d^3 \mathbf x d^3 \mathbf y...
  40. J

    Vacuum tubes and electronic oscillators

    I've been reading up about vacuum tubes and (more specifically) the Audion, and how they were used for instruments/amplifiers. This isn't anything I'm learning about on my degree, just things I'm reading up on myself so forgive me if I'm a little slow to grasp some parts. I understand how the...
  41. wabbit

    De Sitter Vacuum: Is it the Only Positive CC Solution?

    Assuming a spacetime with zero Weyl curvature and an Einstein tensor proportional to the metric, is it true that in a finite neighborhood of any point, that spacetime must be isometric to a de Sitter vacuum, or are there other possible solutions, and if so how are they classified? Thanks
  42. R

    Air Conditioner commissioned without a vacuum pump & N2?

    I bought a new home AC (split; 1.5 ton) and the tech the company sent to install it didn't seem to have neither a vacuum pump nor a N2 cylinder in his kit. I am leery. Is it really possible to install an AC without these items? Can he do a reasonable job evacuating the lines & leak testing any...
  43. B

    How does vacuum polarization conserve energy?

    So just to clear things up before we start, does vacuum polarization occur randomly, or does it just occur when an electromagnetic field is present? Also, how would vacuum polarization conserve energy - does it take energy from the field or does it emit negative energy gravity waves or...
  44. D

    Black hole seeding vacuum decay

    Hello all, please forgive me if I seem somewhat unaccustomed to this site, I have just registered. I suffer from an illness called catastrophic thinking syndrome, simply put this means that I turn everything I read into a disaster until I become ill due to anxiety / depression . I recently...
  45. F

    Local measurement of the Vacuum Energy?

    Is it possible to measure the vacuum energy locally? I wonder if it might change with gravity? I'm told that we can measure the vacuum energy globally by measuring the acceleration of the universe's expansion. But can we measure it locally? Or are all local measurements independent of the vacuum...
  46. F

    I Inflation and the false vacuum

    I'm trying to understand more about how our present universe is supposed to be the result of a false vacuum falling to the present vacuum energy. I've been told (correct this if it's wrong), the universe initially underwent a kind of hyperinflation, expanding exponentially due to a much higher...
  47. Biscuit

    Can Objects Continue Traveling Forever in a Vacuum?

    So a couple of days ago I ran into someone who said that an object traveling forever in a vacuum will eventually come to a stop due to deformation. After a little research I wasn't able to find much on the topic can someone explain it to me, and is it true that he object will eventually stop...
  48. LHCSafetyReview

    A hole in the LHC's vacuum bubble safety argument

    A hole in the LHC's vacuum bubble safety argument One of the four specific risks considered in the most recent official safety review for the Large Hadron Collider (LHC) is the possibility that LHC collisions could trigger a transition to a lower-energy vacuum state. The current review by the...
  49. R

    Barometric Leg to drain a slurry from a system under vacuum

    Often to drain liquids from a vacuum a tall (32 feet) barometric leg is used. Can I use such a leg to drain a slurry? The vacuum is approx. 200 mm Hg abs & the slurry has 5% to 10% hard crystalline solids in water. In particular how do I design the liquid seal at the bottom of the barometric...
  50. S.Daedalus

    A firewall confusion related to disentangling the vacuum

    So while reading some old threads/blog posts on the black hole firewall paradox, it occurred to me that I had some residual confusion regarding why firewalls (supposedly) form at all. IIUC, the argument is that usually, the vacuum is a highly entangled state, and that disentangling it (in order...
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