Vacuum Definition and 1000 Threads

  1. B

    Flow of gas into a vacuum system through an orifice

    Hello, I'm sorry if this is in the wrong section but I recently took real interest in physics, particularly fluid mechanics, so this is my first post. Consider the following: A glass system has a pump pulling gas out of the system, which has an orifice to the atmosphere at the opposite end...
  2. V

    Comparing Vacuum Capability of Pump Models WELCH 1375 & PFEIFFER DUO65

    Dear All, Appreciate if you can guide me on understanding the ultimate pressure of vacuum pump. I have two models for review. One has ultimate pressure of 1 x 10^-4Torr the other has 2 x 10^-3Torr. From this can it be said that the vacuum capability of the first pump (1 x 10^-4)...
  3. A

    Is Vacuum Energy of a Free Scalar Field Zero?

    Homework Statement I have the following task: In quantum free scalar field theory find commutators of creation and anihilation operators with total four-momentum operator, starting with commutators for fields and canonical momenta. Show that vacuum energy is zero. Homework Equations...
  4. L

    Vacuum Polarization: Dielectric Possibility?

    Could the vacuum ever be polarized to become a dielectric? Has this ever been done? http://en.wikipedia.org/wiki/Vacuum_polarization
  5. B

    Exploring the Constancy of Light in Vacuum: Einstein vs Maxwell's Equations

    Einstein postulated that the speed of light in vacuum is constant and is the same for all observers. It this related to the fact that in Maxwell's equations for electromagnetic waves in a vacuum, c = \frac {1} {\sqrt{\mu_0 \epsilon_0}} ? The electric and magnetic constants, which are...
  6. K

    THF evaporation under partial vacuum

    Long story short I'm making some nanoparticles and one of the steps require me to evaporate THF(tetrahydrofluran) out of an aqueous solution containing the NP's. This needs to be done under a partial vacuum with only one intake valve(I know, it sucks but I have no other option). I'm looking more...
  7. C

    The Effectiveness of Nuclear Weapons in a Vacuum

    Much to my surprise, there is substantially less information on this topic on the internet than I initially thought there would be. Wikipedia has very little to go on, and I can't find any papers or serious discussions of this topic. There are many people asking similar questions on websites...
  8. T

    Number of weighted vacuum Feynman diagrams

    I didn't know where to put this, because it isn't a homework or coursework I have to do but just a thing I'm trying to understand. Anyway, I have attached the problem as an image. We have a scalar quartic lagrangian in d dimensions. It says that the number of vacuum Feynman diagrams, at a...
  9. m4r35n357

    Confused about curvature of vacuum solutions

    When I first started learning about GR, I understood that a vacuum solution is one where the Einstein tensor vanishes, for the simple reason that the stress-energy tensor, T, vanishes. I have since read many times that the Ricci tensor vanishes for a vacuum solution. I am confused because to...
  10. Y

    What is the average radius of a betatron vacuum chamber?

    My friend and I were discussing particle accelerators (betatrons to be exact) and we began to argue about the size of the core magnets and vacuum chamber. He said that an average torodial vacuum chamber is 0.5m. I have seen old photos of them and said that's more likely to be the diameter. I...
  11. K

    Question about momentum in vacuum of space

    If you were, say a person moving forward in space and threw something, would you still go backwards? I know that fuel would push you forward (like a rocket's propulsion system) and a fire extinguisher would also propel you in the opposite direction, but do you need a source of fuel for that to...
  12. A

    Is vacuum having any temperature.?

    if vacuum has virtual particles it should have temperature right.? If a perfect vacuum exists ie without any virtual particles..whats temperature of this .is it zero.?
  13. B

    A free electron in a total vacuum

    If you were to release a free electron in a total vacuum what would its behavior be? Say you released it from the center of a sphere with a surface capable of detecting the electron when it comes in contact. Wouldn't you be able to calculate the speed and direction of the electron by the...
  14. S

    Connecting a glass dewar flask to a vacuum system

    I'm wondering how a glass dewar flask connects to a vacuum system, i.e. how is it vacuum sealed? Once it is sealed, I see how you can use appropriate flanges to pump out the, say, He gas, but how is a glask flask connected to this vacuum system? Thanks.
  15. D

    Is Dark Energy the Same as Vacuum Energy?

    Dark energy = Vacuum energy? I am working on giving a presentation on dark energy and its possible relation to vacuum energy (i.e. one and the same). I have complied information from a couple of books, as well as websites (Scientific American, NASA, Astrophysical Journal). As i understand...
  16. L

    Vacuum in qft, what are we refering to?

    When we talk about the vacuum in qft, what are we referring to? The lowest state vector of the Fock space or the lowest energy field configuration that minimize the Lagrangian? Also related, when we sandwich the free field between two vacuum states, we get zero plus quantum fluctuations. But...
  17. S

    What is the interpretation of the vacuum correlation function in QFT

    I'm currently trying to make some intuitive sense out of Quantum field theory, but I'm not really understanding the vacuum. Consider a real (or complex, with + in the right places) scalar particle (a Klein-Gordon field). Now consider the propagator (or correlation function) G(x-y)=...
  18. H

    Rotation of free solid object in vacuum, location of axis of rotation

    Hi, I would be happy if you could solve and explain following problem: Imagine some solid long object (wooden plank for example) being just like that in vacuum, free, without being fixed to any point of space. Then, imagine only one forse pushing this object in a certain point of object...
  19. I

    Conformal Field Theory: Evaluating the Vertex Operator on the Vacuum

    Homework Statement Evaluate \lim_{z \to 0}:e^{ik \cdot X(z)}:|0\rangle where X(z) is a free chiral scalar field in the complex plane. Homework Equations In Conformal Field Theory, the free chiral scalar field in the complex plane is given by: \begin{array}{rcl} X(z) &=& \frac{1}{2}q -...
  20. A

    The Unruh effect and vacuum states

    Hi all, I've recently been reading about the Unruh effect, and there are a few things that I'm not very clear on: 1) An accelerating observer will see a vacuum filled with particles in thermal equilibrium (a warm gas) where an inertial observer would see zone. I'd originally read that...
  21. james.goetz

    Will space always expand when the space has vacuum energy and zero mass?

    I am examining various models of eternal inflation and I want to double check one of my assumptions, which is that space always expands when the space has vacuum energy and zero mass. Is this correct? Will space always expand when the space has vacuum energy and zero mass? Thank you.
  22. M

    Water held in straw by vacuum. Is this possible on grand scale?

    We all know the trick of holding water in a drinking straw by holding your thumb over the top creating a vacuum I know its also to do with air pressure below. I managed this on a bigger scale using a 2inch pipe, a water pump and a valve i could close at the top of the pipe to replicate the...
  23. E

    Vacuum energy and principle of uncertainty

    Let us assume that harmonic oscilator has the lowest energy level equals 0, (and next one \hbar \omega and so on). Does this harmonic oscilator violates the principle of uncertainty? Let us assume that energy of vacuum equals 0 and not \hbar \omega/2. Does such vacuum violates the principle...
  24. M

    How Does a High-Frequency, High-Power Electron Beam Affect a Vacuum?

    What happens when we send in a vacuum pulsed electron beam with a frequency 1e9Hz and power 1e6MeV? Thanks.
  25. R

    Protecting an LM324 Op-Amp in a Vacuum Tube Deflection Amplifier

    Hello. Here joined is the schematic of a small deflection amplifier. Outputs H0 & H1 are connected to electrodes placed in a vacuum volume. These outputs are protected by varistors. High voltage to collectors is 200 V DC. Sometimes, not very often, the head Op-Amp (LM324) is burnt. The only...
  26. A

    Varying Fine Structure Constant and Vacuum Energy Density

    Hi all, I have a bit of a variation of a question I asked some time ago. Webb et al. continue to publish results which suggest that the fine structure constant may vary over space and time. I realize the results are controversial - what I'm wondering: If the fine structure constant...
  27. F

    Going uphill with no friction (vacuum)

    Going uphill with no friction, think maglev, what forces would the mass/vehicle only have to overcome its weight... and gravity? I used the 'search' function but yielded no results. Please feel free to discuss or to simply put me in the right direction. Just to put things in context, I am...
  28. N

    Design Vacuum Vessel for Training Stand

    Hello, This is my first post, so I believe, that you understand and help for me. So I have a task to design vacuum vessel, precisely, my task names "Training stand to measure the height of the flight fuel pump". Height will be simulated by vacuum in fuel tank, which will create a vacuum pump...
  29. N

    The 'nothingness' of the vacuum.

    How is this for a perhaps unconventional, but I think accurate, description of the 'empty' vacuum: Without the vacuum we would be nothing...it contributes to everything around us, our very existence:The 'empty' vacuum has: ...spacetime, from which curvature arises and gives us gravity...
  30. B

    What holds conducting electrons from flying off into vacuum

    In a conductor suspended in an external electric field, in a vacuum, what holds the conducting electrons inside the conductor? Why don't they just fly off into space, under the influence of the field? If they are free enough to move between the atoms of the conductor, this means the force from...
  31. P

    Is a perfect vacuum truly achievable in reality?

    Let's say there is a chamber with 1000 O2 molecules. According to wikipedia, a perfect vacuum is an arbitrary space in which there is an absence of matter. Of course, the space that consists of the entire volume inside the chamber isn't a vacuum because of those 1000 molecules, but then isn't it...
  32. A

    How permittivity arises in vacuum?

    I've read that permittivity is resistance offered to flow of field lines,But vacuum does not have anything in it to resist or alternatively to get polarized.but we've seen that vacuum has permittivity constant..How's this possible??
  33. E

    Can a Balloon be Filled with Vacuum in a Vacuum?

    Could a balloon be filled with vacuum - in a vacuum? And if a balloon was filled with any other gas and put in a vacuum, it would just expand until it popped, no doubt?
  34. G

    Gas in tank exposed to a vacuum

    Homework Statement A tank is equally divided into two equal halves, one a vacuum and one filled with argon gas at 298K and 700 bar. The divider bursts and the gas equally disperses throughout the tank. What is the new T and P of the gas assuming argon is an ideal gas? Homework Equations...
  35. J

    Alternative methods to reach given level of vacuum

    I am currently collaborating in a student team to develop a CubeSat. One of the requirements provided by our launch contractor is to perform a bakeout test at system level. The given requirements for that tests are a duration of 24 hours, at a temperature of 50 degrees Celcius at a vacuum level...
  36. S

    What is Vacuum Level? - Explained in Detail

    Hi, What is vacuum level? I browsed internet and came across different definitions like 1. Threshold energy with which electron leave the atom. 2. Energy of electron outside the crystal. Can you please explain in detail what is vacuum level? At the same time, pls clarify why and how...
  37. E

    How Does a Black Body Balloon Behave in a Vacuum?

    Homework Statement There is a perfectly spherical balloon with surface painted black. It is placed in a perfect vacuum. It is gently inflated with an ideal mono-atomic gas at Kelvin temperature Ti, slowly enough so that it reaches thermal equilibrium with the gas, and then it is sealed off. It...
  38. C

    Pressure vessel in a (near) vacuum

    I don't know if its daylight savings or what, but I just can't seem to wrap my head around this analysis. There is a polycarbonate hemispherical head with 8 psi in a near vacuum environment (2.8 torr) Im trying to figure out what the minimum thickness is for the head. The shell is super...
  39. L

    Time for Gravity to force two objects in a vacuum together

    If I have two, 10 kg objects, 10 meters apart, in a vacuum, How long will it take for the gravitational force between them to pull them together so that there is no room between? Please help I have been trying to figure how to do this math forever! I know the physics formula for the...
  40. L

    Inflation and electroweak and GUT vacuum

    Before Higgs symmetry breaking of SU(2)xU(1) electroweak unified force or even before that, when strong and electroweak were unified as GUT theories propose, the vacuum was different from today's universe. What effects had these different vacua on the evolution of the universe? thanks
  41. I

    Basic Thermodynamics: Gas expansion against a vacuum

    Homework Statement Okay, so the problem given is that there is a rigid tank with a partition down the middle. For partition A, the specific volume, the temperature, and therefore the pressure is known. The mass, or total volume is not known. Partition B is a vacuum for which the total volume is...
  42. W

    Infinite Energy beneath Quantum Vacuum?

    In the thread https://www.physicsforums.com/showthread.php?t=343049 Science Advisor Born2bwire mentioned: "Since the vacuum state has infinite energy, it has infinite photons. Everytime we add energy into the electromagnetic fields, we just pull a photon out of the vacuum state." How many...
  43. D

    Can Kinetic Energy in Electromagnetic Waves Explain Their Speed in a Vacuum?

    Does anyone have an explanation for why kinetic energy carried by electromagnetic radiation travels at the speed of light? My understanding of the speed of sound is that the denser the medium, the faster the wave velocity. Since this is just kinetic energy propagating through a medium, how is...
  44. E

    Behavior of water in a vacuum?

    I've been reading about what happens to water when exposed to vacuum, but can't seem to find a definitive answer concerning a few details in the step-by-step process. I read that water will quickly boil in the vacuum of space due to very low pressure, and then freeze. But roughly how long does...
  45. O

    QCD vacuum contribution to W/Z masses

    The QCD vacuum condensate which breaks chiral symmetry in qcd, also break the SU(2) electoweak gauge symmtery, right? The operator which gets a vacuum expectation value isn't SU(2) invariant since it is built out of left handed quarks and right handed quarks which are in different...
  46. D

    Making a vacuum seal with a screw?

    I apologize for my lack of mechanical term knowledge. I'm looking for a type of screw I could use in a project. Sorry if the thing is unrealistic or if the part is obvious. I attached a sketch of what I'm looking for. The screw would never be completely out of the hole like the sketch...
  47. Y

    Is there vacuum tube models for LTspice?

    I know the default library of LTspice don't have vacuum tube model. Does anyone know where I can get one. If not, any other free spice program have vacuum tube models? The only one I find so far is: http://www.duncanamps.com/technical/ltspice.html I tried to follow the instruction and...
  48. A

    Does electricity travel through vacuum?

    Does electricity travel through vacuum?If so ,is it a good conductor?What is its resistance.
  49. R

    Bullet Acceleration in Vacuum: Why Does It Stop After Exit?

    If a bullet is fired from a gun in vacuum(assume no gravity, no resistance). why is it that the bullet accelerates 0 to v inside the barrel but as it exit the muzzle it stop accelerating. Isn't when the bullet exit , it exit with some force which give it a initial velocity v.
  50. B

    Building a flat rectangular vacuum chamber

    I'm uneducated in Physics so I'm not sure where to begin with this. I want to build a vacuum chamber that is rectangular and fairly flat. It will measure 48"X96"X8" I plan on constructing it from clear polycarbonate sheet on one face (would clear acrylic be a better choice?) and aluminum sheet...
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