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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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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Are we living in a false vacuum? Is there any way to tell?

I was thinking of the noted 1980 paper by Sidney Coleman and Frank de Luccia--"Gravitational effects of and on vacuum decay"-- about metastable vacuum states that could tunnel to a lower energy "true ...
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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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Vacuum movement over time from Big Bang [closed]

If I simulate the universe from the bigbang to see the movement of energy and vacuum, I put a red color for energy and green for vacuum. I would also see that the green color is moving. and I am ...
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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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How does the interacting vacuum $|\Omega \rangle$ enter the theory?

To calculate scattering amplitudes, we consider $$ A(i\to f) = \langle{f | \hat S|i} \rangle = \langle{f |\mathrm{e}^{ -\frac{i}{\hbar} \int_{-\infty}^{\infty} dt' H_{\mathrm{i}}(t')} |i}\rangle$$ $...
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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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In Higgs context, do false vacuum hypothesis imply that true vacuum is *higher* (not lower)?

In theories of false vacuum for Higgs potential, the Higgs field would be currently in an instable false vacuum and would later evolve in a true vacuum, with a lower potential value. Would this true ...
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Virtual Particles? [duplicate]

Plain "empty space" or vacuum is not empty after all. It contains small quantum fluctuations. Virtual Particles pop in and out of existence all around us. In this system, an electron and a ...
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How do we define a pure vacuum?

How do we define a pure vacuum? Is the definition limited by our own capability of what we understand or know how to measure?
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Why is the speed of light in vacuum frequency-independent?

I recently came across this paper: Mainland & Mulligan, Foundations of Physics 50(5), 457–480, "Polarization of Vacuum Fluctuations: Source of the Vacuum Permittivity and Speed of Light" ...
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At what speed will a gas exit a vacuum?

I have limited knowledge about vacuums and fluid dynamics. Question: Let's say that I have some hydrogen inside of a fully sealed container at low pressure and I unseal it. At what speed will the ...
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Cosmological constant, electron mass

I'm doing an essay on the cosmological constant problem. I understand that fluctuations in the vacuum have an energy of the order $(TeV)^4$, This is because it's proportional to $m^4 $where m is the ...
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How to fully ionize plasma

How would I fully ionize plasma in a vacuum chamber? How would I know that it is fully ionized? Could I even come close? How could I measure how would I know how ionized the plasma is.
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Vacuum in string theory

How is vacuum described in string theory? The same as in the QFT? Does string theory have quantum fluctuations of the vacuum, are the processes of creation and destruction of virtual strings ...
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About an expression of Peskin and Schroeder

On page 83 of Peskin and Schroeder, they expand an interacting field $\phi(x)$ at a fixed time $t_0$ in terms of the ladder operators as $$\phi(t_0,\vec{x})=\int\frac{d^3p}{(2\pi)^3\sqrt{2E_{\vec{p}}}}...
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What is meant by “vacuum polarization”?

When we talk about vacuum polarization in effects like the Lamb Shift, what is actually being polarized? What effects does it have?
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How to distinguish between no state and the state with zero photon?

This question comes from my consideration of the superposition of coherent states such as $(|\alpha\rangle+|0\rangle)/\sqrt{N}$. I know the annihilation operator has $\hat{a}|\alpha\rangle=\alpha|\...
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How many different vacuums are there in the string theory landscape? [closed]

Different sources give different estimates, from $10 ^{100}$, $10 ^{500}$, $10 ^ {20,000}$, while others write that there are infinitely many of them.
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$\phi^4$-theory, S-matrix Feynman diagram to first order from Peskin and Schroeder

This relates to page 111 in Peskin and Schroeder. We have the $\phi^4$ S-matrix for a 2-particle to 2-particle scattering reaction: $$-i\frac{\lambda}{4!}\int d^4x \langle p_1p_2|\mathcal T\left(\phi(...
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Cooling down a container in outer space

If I have two containers filled with very hot water(~210F) with one in outer space and one on earth, which one has a higher rate of cooling initially? Imagine the containers are single wall metal ...
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Scattering, Perturbation and asymptotic states in LSZ reduction formula

I was following Schwarz's book on quantum field theory. There he defines the asymptotic momentum eigenstates $|i\rangle\equiv |k_1 k_2\rangle$ and $|f\rangle\equiv |k_3 k_4\rangle$ in the S-matrix ...
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Can you define a vacuum state on a Cauchy surface?

In the functional approach, one can define a vacuum state of a scalar field at a point in time as: $$\Psi_0[\phi] \propto e^{-\int \int \phi(x) G(x-y) \phi(y) dx^3 dy^3 }$$ Where $G$ is some specified ...
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Is there any possibility of manipulating the Higgs field, and if so, what effects would we see?

These are questions asked from a perspective of "what if" according to current theory. If the Higgs field is the source of mass for (most) elementary particles, and the unique property of ...
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Dirac fields: Do particle and antiparticle creation operators act differently on the vacuum?

Given a Dirac field $$\Psi(x):=\int\frac{d^4k}{(2\pi)^4}\delta\left(p_0-\omega(\mathbf{k})\right)\sum_s\left(a_s(k)u_s(k)e^{-ikx}+b^\dagger_s(k)v_s(k)e^{ikx}\right)$$ with the creation operators $a^\...
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Why is Permittivity of free space or vacuum not Zero 0?

Permittivity is the measure determining the electric field produced by charge in a particular medium. Now electric field, $E$ increases as ε (permittivity) decrease, and E decreases as ε increases, ...
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Phase Transitions and Bubble Nucleation

The potential for a first order phase transition is shown below The phase transition occurs from the spontaneous formation of bubbles. Inside the bubbles the field value is at the "true vacuum" and ...
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Vacuum space has mass/energy?

It is said that vacuum spaces contain particles and antiparticles, my question is if so whether empty space has mass/energy?
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Is the QFT vacuum $T$-invariant?

A quantum vacuum corresponds to closed loops of particle-antiparticle pairs, in the language of Feynman diagrams. There is no relation between $E$ and $p$ for these particles, i.e., they are not on ...
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Does following relation holds for an interacting vacuum of QFT [duplicate]

For a non-interacting vacuum of QFT we have $$\hat{P}^\mu|0\rangle=0$$ where $\hat{P}^\mu$ is the $4$- vector momentum operator having eigenvalue and eigenvector given by $$\hat{P}^\mu|p\rangle=p^\mu|...
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Vacuum fluctuations of quantum scalar field

Consider a free scalar quantum field $$ H = \int d^3 x \left( \, \Pi(x)^2+(\nabla\phi(x))^2 \right). $$ Introducing the creation and annihilation operators we find the "vacuum catastrophe" $$...
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Prevent aluminium vapour condensing on a surface

I have a situation where aluminium vapour is created in a vacuum chamber ($10^{-6}\ \mathrm{mbar}$). I would like a window to look into the chamber; however, the aluminium vapour produced condenses on ...
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Zero-point energy? (D-branes C.Johnson's book)

In Johnson's Book about D-branes (11.2) gives the zero point energy. This is given using (2.80) \begin{equation} +\frac12\omega: \text{for boson and}\;\; -\frac12\omega: \text{for fermion}. \end{...
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Thermodynamics - Superheated vapor expanding into vacuum

When I have a gas in one vessel which is expanding into another vessel in vacuum, I know the work done will be $0$. My question is, what if that gas is not ideal, and it's a superheated vapor, is ...
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Why does blending hot food in the Nutribullet blender create a “pressure seal”?

I have noticed that when blending cold foods in the Nutribullet, it is easy to unscrew the blender once the blending process is finished. When I blend something hot (i.e, boiled tomatoes, to create a ...
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Which vacuum do I use for the path-integral?

In Weinberg, vol. 1, Section 9.2, Weinberg defines the in and out vacua as states with no particles (9.2.4): $$a_{\rm in}|{\rm VAC,in}\rangle=0$$ $$a_{\rm out}|{\rm VAC,out}\rangle=0$$ He does this ...
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Lorentz Transformation of ladder operators

Hello I am a beginner of QFT. I have some questions about the behavior of the momentum ladder operators under Lorentz Transformation. For simplicity, let's consider the momentum ladder operators of a ...
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About the steps in a book about Quantum Field Theory [duplicate]

I have a question about the steps in the book "An Introduction To Quantum Field Theory" By Peskin & Schroeder. In page 213, i don't understand why the $e^{iPx}$ before the $<\Omega|$ ...
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Could some kind of vacuum decay modify the most fundamental laws of physics?

A false vacuum is a hypothetical vacuum that is not actively decaying, but somewhat yet not entirely stable ("metastable"). It may last for a very long time in that state, and might ...
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Why field expansion into positive and negative frequency Fourier components becomes ambiguous in curved spacetime?

Why is the expansion of a relativistic field into positive and negative frequency components $$\phi({\vec x},t)=\int\frac{d^3{k}}{~~(2\pi)^{3/2}}\left[A\left({\vec k}\right)e^{-i\omega_{\vec k}t}+A^*\...

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