Questions tagged [vacuum]

A region of space devoid of any fluid molecules resulting in a zero pressure in ideal cases. In practice, even space has a small but finite number of molecules. In QFT, it signifies the ground state devoid of excitations/particles.

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How did Wick's theorem work for Feynman propagator in Dirac Equation?

In David Tong's Quantum Field Theory Lecture Notes, Page 115 Eq. 5.34, the Feynman propagator was defined to be $$ S_F(x-y)=\langle 0|T\psi(x)\bar\psi (y)|0\rangle \newcommand{\normord}[1]{:\mathrel{#...
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I need help understanding the physics involved in the expansion rates of gases and/or dust (powdered solids) [closed]

I am writing a science-fiction/fantasy novel and I've come to a sci-fiesque part in my story where I am entertaining several options for a scene, one of which could involve some pretty serious science....
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Lasting gravity-free vacuum on the Earth [closed]

As the title says, Is it possible to create a lasting gravity-free vacuum here on Earth? sorry for my bad English
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Estimating how long for air inside spacecraft to escape from a hole [closed]

I'd like to know how long it would take for the air in a spacecraft to escape. I imagine this will be an iterative calculation, since as the air escapes into the vacuum of space the air pressure ...
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Diffusion vacuum pump plans [closed]

I found some plans of diffusion vacuum pump. I want to ask you if vacuum pump in this plans can work properly or thease plans are only some sketches from research which are not useable. I found one ...
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How do we know sound cannot travel in a quantum vacuum?

This is probably bad wording and I apologize. I mean the quantum vacuum in space that is made of a soup of emerging/vanishing pairs of particles. More generally, why sound (phonons) is assumed to not ...
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What is an automated vent valve?

I was inquiring a company about an air-cooled turbo-molecular pump, and the company asked me whether I used an automated vent valve. What does automated vent valve mean and do? How does it relate to ...
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Is their any proof that space is filled with virtual particles or can they only be emitted by atomic nuclei and electrons? [duplicate]

Is their any evidence for non zero energy in space? The Casimir effect for two plates separated by a small distance suggests that there is little energy in space.
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Will water in vacuum stop boiling?

Will water in vacuum chamber (low pressure chamber(around 0.02 atm)) stop boiling when the remaining air gets saturated? Or if the walls of the chamber are cold enough the water vapor condensates and ...
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Why does gas not do work when expanding in a vacuum?

Why does a gas do no work when expanding in a vacuum? I know it is true that there is no opposing force from other air molecules for the gas to overcome in a vacuum, so that gas molecules won't do ...
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Isn’t there suppose to be vacuum above the closed end of Mercury manometer?

I found this very old Mercury closed end manometer(I think so). Looking at the graduations on the left side it shows very low vacuum values and the right side values from 110-0-80. The reading is in ...
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Is the massless scalar's vacuum in flat space a non-normalizable state?

Let us not impose any IR cutoff on Minkowski space. The massive scalar's vacuum is given by a normalizable state. However, since there is a continuum of energies for the massless scalar starting from ...
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Can virtual particles interact with each other?

Virtual particles pop in and out of existence all the time. While they exist, can they interact with each other? Like repel or attract one another?
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Could gravitational waves have their origin in collision of true and false vacuum?

Could the gravitational waves the consequence of the collision between a true vacuum bubble and a false vacuum bubble, at the beginning of the universe? (as they try to explain there: https://www....
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Type I Vacuum fluctuations

Type one Parapositronium borrow energy from the vacuum to pop into existence, returning it after annihilation. Halfway through reading this eye opening paper about Vacuum fluctuations this one (...
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Fixed volume air flow to vacuum

I have a work project and am trying to wrap my head around the foundational aspects of the fluid dynamics before I attempt to take measurements. I want to have an idea of what to expect compared with ...
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For Hawking radiation, is the scalar field $\phi$ assumed to be in the Unruh vacuum state?

In Hawking's paper "Particle Creation by Black Holes" I'm not really able to pick apart what vacuum state Hawking is assuming the field $\phi$ to be in. The paper "Hawking radiation as ...
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Flow of virtual particles in the Casimir effect

In the Casimir effect experiment two plates are held near each other and in the edges of those plates a region of space with high virtual particle density meets with a region between the plates which ...
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Given an arbitrary electric field inside volume find generating charge distribution on the surface

This is somehow the inverse of the Poisson problem, which i could reformulate as follows: Given a volume in the empty space, bounded by a bidimensional surface, and an arbitrary electric field inside ...
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Does increasing water pressure change how high a column of water can be lifted in a vacuum?

If I take a 1 inch square pipe and submerge one end in water and at the other end I create a vacuum, does the height the column of water is lifted in the pipe vary with the depth of the submerged end? ...
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Normal ordering of operators

Just a quick question regarding normal ordering. To begin given a field $\phi(x)$ we can normal order it in respect to some state $|G\rangle$: $$:\phi(x):=\phi(x)-\langle \phi(x)\rangle $$ Typically ...
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How (or where) to look up vapor pressure of a material at ultra-high vacuum pressure?

Is there a way to look up the vapor pressure of a given material (usually binary compounds or simply elements) at ultra-high vacuum (usually near $10^{-9}$ Torr). For example, if I want to know the ...
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Can you used a tethered “boot” to move in space?

Preface: On Earth, with the help of gravity, I can easily tie a wrench to a rope, then spin it around, lasso-style, and let go at any time to send the wrench and rope flying away from me in the air. ...
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Hamiltonian positive definite and vacuum state

For the self-interating $\phi^4$ Lagrangian density $$\mathcal L=\frac{1}{2}\partial_\mu\phi \partial^\mu\phi-\frac{m^2}{2}\phi^2-\frac{\lambda}{4!}\phi^4,$$ the corresponding Hamiltonian is $$H=\int ...
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Field modes and canonical quantization in Schwarzschild spacetime

A scalar field can be quantized as $\phi(x) = \sum_k (\hat{a}_k u_k + \hat{a}^\dagger_k u_k^*)$, where $u_k$ are positive frequency modes satisfying the Klein-Gordon (K-G) equation $(\Box +m^2)u_k = 0....
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Normal-ordering with mass $m$ in sine-Gordon theory

I am new in PSE. I am studying the $1+1$ sine-Gordon theory from Sidney Coleman's article of 1975 (pdf). The Hamiltonian is \begin{align} H=\int dx\;\left(\mathcal{H}_0-\frac{\alpha_0^2}{\beta}\cos\...
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If the gravitational field contributes to the stress energy tensor, why is $T^{\mu\nu}=0$ in a vacuum solution?

I have read that the Einstein Field equations are non linear and gravitational fields can themselves be a source of curvature. Why do we then while solving for a vacuum solution take $T^{\mu\nu}=0$? ...
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Moving Water Creates a Vacuum?

I have a question about Bernoulli's principle as it pertains to water. A scuba diver instructor says that in order to back fin (swim backwards), you just need to displace water behind you and that ...
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Can vacuum breakdown occur from a positively charged surface?

Against a sufficiently large voltage, resistance is futile. Although the vacuum is a very good insulator, electrical breakdown can occur even in a perfect vacuum in the presence of a very strong ...
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Does Wightman's unitary $U(\Lambda)$ really exist for Lorentz boost?

This question is related to another question here. But I am asking a more fundamental question about the existence of Wightman's unitary $U(\Lambda)$ for Lorentz transformation. Let $\psi^\alpha$ be a ...
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Expansion of ideal gas into vacuum, connected to heat reservoir

I have a mono-atomic ideal gas, expanding from a smaller volume V1 to a larger volume V2, inside a piston. If the expansion is done slowly, so the process is reversible, I understand how to calculate ...
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How can zero-point energy have any measurable effect when it is just a constant offset to the Hamiltonian?

In classical (say Hamiltonian) mechanics, adding a constant energy offset has no effect on the dynamics of the physical system. One way to understand this might be to understand that Hamilton's ...
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Is the anomalous magnetic dipole moment due to interactions with the QED Vacuum?

I am pretty sure that it is, from what (little, so far) I understand, but... Most of what I have read about the anomalous magnetic dipole moment and it's contribution to the electron's $g$-factor do ...
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What means electrostatic in vacuum?

Can you explain what's the concept of electrostatic in vacuum? And exists electrostatic in no vacuum? If exists What's the difference between electrostatic in vacuum and electrostatic in no vacuum?
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What is a bubble from nothing?

Recently I was reading a collection of lectures on Swampland Conjecture and came across an interesting subtitle about a bubble from nothing. A bubble from nothing is a non-perturbative instability ...
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How to ease/reduce surface roughness caused by ion sputtering?

I want to investigate the electron emission of samples under electron bombardment. Experts will know that surface condition plays a huge role in the emission rate and some other properties (e.g. max ...
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Balloon in a container inside a vacuum chamber

The question I'm trying to understand is and getting a bit stuck with: Let's say we have a put a small balloon filled with air of volume, e.g. 1cm^3 inside a container. This container is not sealed i....
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What is the limitation on putting liquids into a vacuum chamber?

I am a student designing a physics vacuum and material science curriculum for my Senior Design project. It is for a week-long session, so we are attempting to make 1-day experiments. I say this to ...
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How does suppressing quantum vacuum fluctuations lead to positive and negative energy densities?

As mentioned in https://en.wikipedia.org/wiki/Negative_energy "It is possible to arrange multiple beams of laser light such that destructive quantum interference suppresses the vacuum ...
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Help with at home experiment for physics degree: how to suck water up a tube

I'm doing an at home experiment for my physics degree due to covid restrictions, and I need to suck water up a vertical tube. I would really appreciate any equipment recommendations or other advice ...
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Roughly measure vacuum pressure without sensor

How would you identify various levels of vacuum, without a calibrated, dedicated vacuum/pressure sensor? For instance, my understanding is that a Crooke's Radiometer only works in certain ranges of ...
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Particle interpretation for Fields and (non) vanishing VEV

I have some questions about the first part of the answer by Arnold Neumaier dealing with the interpretation of VEV (vacuum expectation value). Let me quote the parts I would like to understand better: ...
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Casimir energy in a circle for a scalar field with antiperiodic conditions

Following the section 2.3 of the book "Advances in the Casimir Effect" by M. Bordag, the Casimir energy is given, for a maseless field, by $$E(a) = E_0 (a) - E_{0M} (a)$$ where $E_0 (a)$ is ...
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What would happen if we use vacuum cleaner in space?

What would happen if we were to use a vacuum cleaner in space? Will the vacuum cleaner work? Would the vacuum cleaner be able to suck anything?
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Vacuum expectation values (VEV) and Spontaneous symmetry breaking

I have a basic question about spontaneous symmetry breaking for theory with one complex scalar field $\phi= \phi_1 +i \phi_2$ with Lagrangian $$ \mathcal{L}=\partial _\mu \phi ^*\partial ^\mu \phi +\...
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What is the expected energy density of the vacuum for QED Planck cutoff?

I would like to know the value of the expected energy density of vacuum in QED with Planck's energy cutoff in the units of kg/m^3 (mass density). I only find rough estimations in erg/cm^3 or joules ...
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Can you make a multistage roots vacuum pump quieter by putting something on the exhaust?

The multistage roots pump in our lab is really loud, currently, there is nothing on the exhaust, as we are just dealing with air. Does somebody know a way to make the pump quieter (i already proposed ...
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Behaviour of 2 resonant tuning forks in a vacuum

The scenario is the following. Two perfectly tuned resonant tuning forks A,B are placed in the same vacuum. [ Ideally the experiment is conducted when both A&B are in free fall]. Tuning fork A is ...
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Is it an assumption that Heisenberg's uncertainty principles applies to the vacuum or is there proof?

The Heisenberg uncertainty principle was found to apply to all particles in physics. Was it an assumption that it should also apply to the vacuum? One of the consequence of this extrapolation is that ...
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How to qualitatively imagine vacuum polarization by a photon?

The photon is constantly "dressed in a fur coat" of virtual pairs of particles (electrons and positrons, quarks and antiquarks). The lower the photon energy, the weaker the "coat". ...

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