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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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Is it possible to drain all oceans' water to space? [duplicate]

Assuming: That I have an ideal straw (a very long pipe) from the ocean to space; That the straw (pipe) is ideal (will not break); That i can pump all the air from the pipe creating vacuum inside the ...
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How does entanglement create empty space?

It is claimed that empty space is full of quantum fields which their waves perfectly cancel out each other, but this can only happens when all the waves are entangled. Is this claim valid because I ...
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What does the 'cosmological constant' represent?

Newtons theory of gravity involves a gravitational constant $G$, however one does not refer to it directly, we speak instead of gravity or the force of gravity. Now Einsteins introduced a ...
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3's a crowd. Particle me but may i have this dance? [closed]

In a particle accelerator (built for 3 particles), could we smash them into a vacuum with only enough space for 2 particles?(electrons, protons, neutrons) what would be the result?
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Scattering of light in Quantum Vacuum

The quantum mechanical vacuum (i.e. the vacuum of a typical QFT) viewed as the zero-point state of the system has an energy (of course, here enters the Vacuum Catastrophe and all the mess that follows)...
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SUSY vacuum has 0 energy?

This is related to Modern Supersymmetry: Dynamics and Duality by Terning. Consider $N=1$ SUSY. $\{Q_a,\bar{Q}_{\dot{a}}\}=2\sigma_{a\dot{a}}^\mu P_\mu$. Sum over $a=\dot{a}=1,2$ and this yields $4P^...
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Stable bubbles in a vacuum

I want to make space bubbles that hold some gaseous stuff - at very low pressure - for a long time and through nothing but surface tension. I can't use soap water as the water will evaporate quickly. ...
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Trying to make some sense of the cosmological constant

The question is simple: Does the naive reasoning below have some physical sense, or is it pure gibberish junk? (I use $c = 1$ and metric signature $\eta = (1, -1, -1, -1)$) I suppose that the ...
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What kind of average could give a Lorentz invariant energy-momentum tensor?

The electromagnetic (EM) radiation energy-momentum tensor is of the following shape, in the case of incoherent superposition of EM plane waves (I'm using $c = 1$ to simplify things, and metric ...
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Natural classification of fundamental constants of Nature

I was wondering about the fundamental constants of Nature since several years, and still pondering on them. Of course, I have read a lot of papers on them, but never found any satisfying ...
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Could false quantum vacuum decay change fundamental laws of physics? [closed]

It is often said that low energy/effective physical laws (i.e fundamental physical constants) could possibly change if a quantum false vacuum decays into a true (stable) level of quantum vacuum. But, ...
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Virtual particles

I use Wikipedia to learn physics. In a recent search I found an ample description of virtual particles in terms of a discontinuous (in the present) and asymptotic distribution of these particles from -...
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Why should vacuum energy be zero for LSZ formalism?

Can anyone explain why vacuum energy must be zero if we are to use LSZ formalism?
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How can zero point energy vacuum be Lorentz invariant?

What distribution of electromagnetic radiation is Lorentz invariant? How can radiation look the same regardless of inertial frame? According to Marshall and Boyer a cubic distribution like $ \rho(\...
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Gauge transformation on vacuum

Suppose we have two electromagnetic vector potential operator that differ by a gauge transformation in free field theory. $A'_{\mu}= A_{\mu}-\partial_{\mu}\alpha$ is the state $A_{\mu}|0\rangle$ ...
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Normalization for the overlap $\langle \phi_a | 0 \rangle$

This question is related to my previous post here. According to Wienberg's Volume I (9.2.9), we have the result $$ \langle \phi_a | 0 \rangle = \mathcal{N} \mathrm{exp}\left( - \frac{1}{2} \int d^{3}\...
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Will Vacuum Energy persist at the Heat Death of the Universe?

By "vacuum energy" I mean the underlying background energy that exists in space throughout the entire Universe, codified in Heisenberg's energy–time uncertainty principle, a special case of zero-point ...
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Question regarding the degeneracy of vacuum state in various spacetimes

In a talk, it was mentioned that if one attempts to do quantum gravity in the following spacetimes (of any dimension), then the vacuum state has the following degeneracy. In $AdS$ - There is a ...
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Is this how vacuum works?

Vacuum exerts a net zero force, or i guess pressure? on what's inside it, right? So if the universe is expanding at an accelerating rate, is the vacuum of outer space is growing? Like space is ...
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Einstein equation outside of the source

When solving Einstein equation outside the source it is assumed that we have $R=0$ where $R$ is Ricci tensor. But if we have as a source Earth and for example, a black hole, how can this equation ...
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What are the “basic things” we need in physics to define any kind of energy, including “mass”?

After having commented an answer there: Relative potential energy vs Absolute potential energy, I realised that the energy concept may be much more subtle than what we usually believe, even if we ...
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Electron interaction with vacuum fluctuations

The cause of Lamb shift is interaction between vacuum fluctuations and electron in the atom. Will electron (or photon) in free space interact with vacuum fluctuations? How momentum will transfer ...
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Absorbing the Cosmological “Constant” in the standard Energy-Stress Tensor

Recently I found some publications on Cosmologies with variable cosmological constant. The Bianchi Identity then implies that the divergence of the modified Energy Stress: Tensor $$\hat{T}_{ab}=T_{ab}...
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Energy/mass of Quantum Vacuum

So far as we have measured the volume of the universe, has anyone calculated the virtual energy/mass of the Quantum Vacuum? If so, what? Or if not, a local volume such as 1 sq. meter? This relates to ...
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Inner product in QFT

When we write inner product in QM for example $\langle\psi\rvert x \psi\rangle$it means (in position space) $\int\psi^*(x,t)x\psi(x,t)dx$. But when we write, in QFT, $\langle0\rvert0\rangle=1$ what ...
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What is in space?

I was recently on a chat server having a random discussion about science stuff and someone I was talking to then made the comment that "space is not a complete vacuum and it's full of plasma / matter"....
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Is the term “quantum fluctuation” an aide to understanding? [closed]

I would like to ask if anyone has found a tight enough way to define the term "quantum fluctuation" so that it can become a useful rather than a misleading piece of physics terminology. Terminology ...
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Must the electromagnetic 2-form be harmonic in vacuum?

The Maxwell equations in vacuum are $dF=0$ and $d*F=0$. Is this not the same as saying $F$ is both closed and co-closed, and hence harmonic? But Hodge's theorem says the space of harmonic $p$-forms on ...
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Can space be compressed in an empty bottle?

On a spacewalk, in a vacuum, if an open empty water bottle were capped and squeezed, would it pressurize or collapse as if it were not capped?
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QFT and vacuum energy [duplicate]

According to Quantum Field Theory, all 'particles' are oscillations in their own fields. And according to Vacuum Zero Point Energy and the Heisenberg Uncertainty Principle, these fields have ...
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vacuum chamber and impact on various liquids

I am hoping to do an experiment on "the impact of a vacuum chamber on various liquids". What liquids would be the most interesting? Water, coffee, soda, gatorade? Would carbonated versus non ...
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Does a symmetry operator $U$ and its generator $Q$ acting on a vacuum $|0\rangle$ both represent new degenerate vacuum?

After the spontaneous breakdown of a symmetry characterized by $$\hat{U}=e^{i\hat{Q}\theta},$$ the commutation relation $[H,Q]=0$ continues to hold. Let us consider two states after this symmetry ...
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Why does the vacuum even have permeability and permittivity?

The vacuum is empty, yet it seems to have 2 properties: it's absolute permeability and absolute permittivity, which have specific, finite, non-zero values. Why? Why are the vacuum permeability and ...
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What is the cause of the vacuum of space?

It seems logical that if space is expanding and also being dragged into black holes throughout the universe, the result would be a vacuum in the universe. Is that a satisfactory explanation of why ...
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Is there a medium less dense than vacuum, in which light can travel faster than $c$? [closed]

Is there a medium less dense than vacuum, in which light can travel faster than $c$? If not, can we make it?
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Can someone explain why there is water in this vacuum chamber?

I work at a water treatment plant that uses a vacuum system to pull the water into the filters and backwash the filters. In the middle of the vacuum system there is the vacuum chamber. What I don't ...
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In terms of energy, are virtual particles an intermeidiate state between real particles and a vacuum?

What exactly is the difference between real and virtual particles? Are virtual particles just fluctuations in their quantum field? If so, how is that different to real particles?
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Eigenstates in QFT and amplitude of a field operator

I've seen in different posts (such as here) that given a field $\hat{\phi}(x)$, its eigenstates $|\phi\rangle$ are of the form: $$|\phi\rangle\ = e^{\int dx\phi(x)\hat{\phi}(x)}|0\rangle\tag1$$ I ...
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Do electrical arcs in vacuums have voltage drops?

I have looked for a long time online but have found no answer to this question. I have however found two things: Vacuums are neither conductors nor resistors, it takes a fairly large voltage for arc ...
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Perfect Vacuum Beneath an Object

Recently I became interested in how suction cups work by creating a region of space with lower pressure than their surroundings, thus sealing the suction cup to the contact surface. Extrapolating this ...
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Simplification using Wick's theorem

I was reading Tom Lancaster, Stephen J. Blundell - Quantum field theory for the gifted amateur. I came up to this exercise problem ...
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Why the vacuum expectation value?

I am reading "QFT in a Nutshell", and the beginning of the book progresses like this: Show how $\langle q_F|e^{-iHt}|q_I\rangle=\int Dq\ e^{iS}$ Says that we are more interested in $\langle F|e^{-iHt}...
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Derivation of the formula for the electrostatic force with a dielectric in the middle

In the answer by user JohnRennie on the post "What is the force in the presence of a dielectric?", it says: If the dielectric constant is $K$ and the thickness of the dielectric is $t$, then for ...
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Amplifying stress at near perfect vacuum?

So, I've got a vacuum chamber as part of a home freeze drying project. It is a cylindrical steel pot with a 1.5in acrylic lid. The manual is poorly translated from Chinese, so some of it is seemingly ...
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Vacuum Energy Calculation using Path Integral

I am currently reading Zee's book on quantum field theory, and I am in the chapter where he is introducing Grassmann integrals. He re-introduces the path integral evaluated for the vacuum, i.e. no ...
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How does the global $G^2G'$ anomaly make all the $\theta$-vacua associated to the gauge group $G$ physically equivalent?

Consider a gauge group $G$ and suppose that there is a $\theta$-term associated to it. According to this answer, the existence of a global anomalous symmetry $G'$ which rotates the $\theta$-term, ...
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What does $B+L$ anomaly have to do with a phase redefinition of the left-handed quark field?

According to this answer, the reason why $SU(2)_L$ weak theory does not have a theta vacuum is because any theta term can be reabsorbed with a phase redefinition of the left-handed quark field. ...
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Quantum Fluctuations of the vacuum

In this video we see a visualization of quantum fluctuations. What equations underlie this visualization? And how exactly is it related to quantum field theory? And what is the open problem he talks ...
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If it was heated up enough, could water-soaked wood in a vacuum catch on fire? [closed]

Obviously you can set a damp piece of wood on fire- not exactly revolutionary. I specifically mean if the wood was in a perfect vacuum. It doesn't matter where the heat comes from-just say the amount ...
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Since water boils at room temperature in a near vacuum, is it possible to use this to generate electricity in some way?

This may be a blatantly obvious question but I've never heard about such a thing happening. Could this be possible in some way using a vacuum chamber to boil the water and spin a turbine?