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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What vacuum should be defined for a observer in Kerr spacetime?
A scalar field in Kerr spacetime can have two kinds of modes, one labeled by "in", and the other by "up". The "in" modes originate from the past null infinity, while the &...
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If you put some air onto the moon, is it possible to talk within the region that the air is present in?
So uhhh lets say there is some air, you've just put it onto the surface of the moon. Question being, if you are present within the mass of the air, can you listen to others and talk to them within the ...
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How do Lockheed Skunk Works extract energy from the zero point vacuum field? [closed]
Lockheed-Martin Skunk Works Vacuum Energy
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What mathematics indicate that the vacuum of the universe is metastable?
As I understand it, the meta stability of the universe's vacuum depends on the electroweak force, which depends on the mass of the top quark and the Higgs boson. But I don't understand this fully. Can ...
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What would the universe look like if it had undergone a false vacuum decay in the past?
Inspired by "if a metastable de Sitter space lasting for cosmological durations really is impossible in string theory, then dark energy needs to be explained in some other way, e.g. via ...
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How to justify the vacuum energy density without creation/annihilation operators?
In classical field theory, a well known calculation (pretty involved) gives the following expression for the total energy of the free electromagnetic field in empty space (I'm not writing the MKSA ...
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Can a black hole absorb vacuum energy?
Can a macroscopic black hole absorb vacuum energy from the surroundings, and thereby increase its mass?
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Question about semiclassical approach to QCD
I'm struggling to understand the usefulness of the semiclassical approach to QCD. In particular, by using this approach, we can analyze the vacuum structure of QCD, including theta-vacua, $n$-vacua, ...
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Why vacuum state is an exception from the general rule of quantum theory?
Based on the double slit experiment we know that in the case of a single particle system the wave function or state vector of position is in a superposition of possibilities before measurement.
But ...
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Do topological solitons allow modeling non-degenerate multiple vacua?
I am not well-versed in the research on topological solitons but am interested to make a good sense of its implication.
The highly interesting point in this new talk by Nick Manton was where he is ...
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What is meant by the term “borrowing energy from the vacuum” in quantum physics?
What is meant by “borrowing energy from the vacuum” seems like a totally illogical statement and a violation of conservation of energy
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Is the vacuum state in superposition before measurement of its gravity effect?
In the case of a particle system the wave function or state vector is in a superposition of possibilities before measurement.
But does this rule apply in the case of vacuum state?
Is it in a ...
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Cosmological Constant Problem calculations involving energy densities
I am following Timo Weigand lecutre notes on QFT, on page 28, he breifly touches on the Cosmological Constant Problem.
But I am a little confused.
He begins with a Lagrangian and include a nonzero $V_{...
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Calculation about fermions via quantum field theory
I want to ask a specific question occurred in my current learning about neutrinos.
What I want to calculate is an amplititude:
\begin{equation}
\langle\Omega|a_{\bf k m}a_{\bf pj}a_{\bf qi}^{\dagger}...
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QFT Fields or Energy Mesh
I'm not a mathematician, but I've read alot about QFT theory. The way it is visualized are different levels of energy and the fields interacting with one another. Am I correct that these fields ...
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Calculating the vacuum in an $O(2)$ spontaneous symmetry breaking
Consider the Lagrangian (we ignore the quantum correction here)
$$\mathcal{L}=-\frac{1}{2} \partial_\mu \phi_1 \partial^\mu \phi_1-\frac{1}{2} \partial_\mu \phi_2 \partial^\mu \phi_2-\frac{\mu^2}{2} \...
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What is the state of matter-energy inside Black Holes? [closed]
Do we know absolutely nothing about what might be the state of matter-energy inside the black hole?
Are there existing theories or research that explore the possibility of a metastable vacuum inside ...
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Behaviour of weightless objects (objects in a state of zero gravity) in a vacuum
SCENARIO 1: So lets say there is a room with no air in it, meaning the room is a vacuum. Now lets say there is a single metal cube (the metal cube is 5kg) in the room, of course gravity still exists ...
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What is the formalism for calculating the vacuum energy density from the observed data of the expansion of the universe?
Wikipedia states here the calculated effective vacuum energy density value of free space from the observed and collected cosmological constant data of the 2015 Planck telescope satellite mission. But ...
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Is this formula, other than (2.38) in peskin's quantum field theory, also true?
This is soft interlude question. I am rereading the Peskin & Schroeder's Quantum field theory, p.23, (2.38) and some question arises.
First, let's refer to Lorentz transformations for scalar ...
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Poincare invariance of the vacuum
When quantizing the free scalar field, we define positive frequency modes according to
$$\frac{\partial}{\partial t} \phi_{\omega}=-i \omega \phi_{\omega}. $$
In the mode expansion we then separate ...
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Are Feynman Diagrams Concealing the True Nature of Particle Scattering? [closed]
I've recently delved back into some alternative interpretations of quantum field theory.
While Richard Feynman often emphasized that calculations were sufficient and discouraged fixation on the "...
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Are intermediate states just mathematical constructs?
In the vacuum state, particles and antiparticles can spontaneously emerge as virtual pairs due to the uncertainty principle. These virtual particles have a brief existence before they annihilate each ...
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Can real particles be created from a false vacuum spontaneously through decay?
Consider false vacuum decay.
Given the energy difference between the false to true,
Can this process lead to the creation of real particles as well as the vacuum bubbles?
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Permittivity of free space [closed]
Free space is a region in which there is no matter and no electromagnetic or gravitational field. Which means that the resistance in free space is zero, because there is no resisting force and as far ...
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Spontaneous increase of vacuum energy?
If the vacuum energy of the universe is not at its minimum, that is, the universe is at a false/metastable vacuum state, then it could decay into the true vacuum state.
However, if our universe is ...
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Adiabatic free expansion into vacuum
Consider an adiabatic vessel with a partition and a plug in the partition wall. On one side of the partition, there is gas at certain pressure and on the other side of partition there is perfect ...
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In relation to Newtonian physics, can an object's movement still be affected by extreme temperature when in a vacuum?
I'll try to keep it short:
Can an object (such as a ship or shuttle) be slowed by extreme temperature when in the vacuum of space, or is temperature irrelevant at that point due to the nature of a ...
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Doubt about the derivation of Casimir Effect
I was reading about Casimir effect from David Tong's QFT notes and I was struggling to understand one thing.
At page 27, equation (2.33) describes the energy in between the plates, then why does the ...
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Whether vacuum energy gravitate?
What is the relationship between vacuum energy and gravity, particularly in terms of gravitational effects and its contribution to the overall cosmological constant? Does vacuum energy possess ...
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Is Vacuum Expectation Value equivalent to the sum of Tadpole Diagram in the QFT?
I am recently learning Spontaneously Symmetry Breaking in the QFT. For example let us just focus on the potential $V[\Phi]=a\Phi^2 + b\Phi^4$ where $a<0,b>0$ and denote the vacuum expectation ...
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The vanishing of vacuum expectation value
I have some difficulty understanding why the vacuum expectation value vanishes. As illustrated in my notes, we can split the field into two parts:
$$
\phi(x) = \phi^+(x) + \phi^-(x),
$$
where $\phi^+(...
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States created by local unitaries in QFT
In quantum field theory, consider acting on the vacuum with a local unitary operator that belongs to the local operator algebra associated with a region. In such a way, can we obtain a state that is ...
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How to "naively" calculate the vacuum energy density in a $4 + d$ spacetime?
The "naive" calculation of the vacuum energy density in flat 4D spacetime is resumed by the following divergent integral (I'm considering only free massless fields):
$$\tag{1}
\rho_{\text{...
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Why do strings select vacuum solutions of Einstein Field Equations as their natural backgrounds?
I have a conceptual issue here. The action of a bosonic string in some curved metric $g_{\mu\nu}(X)$ is given by
$$S[X] = -\frac{1}{4\pi \alpha'} \int d\sigma d\tau \: g_{\mu\nu}(X)\: \partial^\alpha ...
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What path will air take to leave the space station?
Hi everyone,
lets say we have a circle shaped space station and there was an accident where we got a hole (hole A on the picture) on a station and now most of the station is vacuum except for one ...
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Relation between RG flow and space of vacua
When studying supersymmetric QFT's, it is very common to compute the moduli space of the theory by solving all F-term equation (derivatives of the superpotential). More precisely, one should also ...
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How can we describe the attenuation of sound in an expanding gas cloud in a vacuum?
For example, suppose a spaceship explodes. The sound of the explosion will travel in the expanding cloud of escaping gas. I gather that it should rapidly weaken and the pitch should drop, but I'd like ...
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UHV chamber starts oscillating once the pressure gets down to $2.5 \times 10^{-5}$, Why?
Using a new Edwards nXDS15iC scroll pump as a roughing pump for a new Kurt Lesker EMT3304 turbo pump. Chamber is a cylinder about $100{\textrm{ ft}^3}$. We have identified leaks and corrected using a ...
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Creating vacuum in a rubber hose by replacing air with helium which escapes through osmosis?
Yesterday I heard this: suppose you have a rubber hose, in which you inject helium, which replaces the air which was there before. Now, because there is no helium in air, so the partial pressure is ...
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Why use infinite energy to change a vacuum to the another in usual SSB?
I am reading Strominger's Lecture in the IR triangle, there is a short argument about differences between the usual Higgs case and Large Gauge Symmetry (LGS) one in P38. Strominger says:
In the usual ...
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What is meant by the speed of light in a vacuum if a true vacuum cannot exist?
Because of quantum mechanics doesn't allow for a perfect vacuum, what does it mean to say the speed of light in something that cannot exist is a constant?
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Can matter and light exist without the free space absolute vacuum?
According to the standard model of particle physics, is matter and light possible to exist without the existence of the omnipresent vacuum?
By "vacuum" here I mean the ideal perfect vacuum ...
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Proof that asymptotic particle states are free
In quantum field theory, It’s often said that the interacting annihilation operator (defined by the Klein Gordon inner product between the interacting field and a plane wave) behaves like the free ...
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Ground eigenstate of the quantum harmonic oscillator with the interacting vacuum $| \Omega \rangle$
According to this video (at the timestamp), the professor writes down the derivation of the ground state of the 1D quantum harmonic oscillator.
Here is the screenshot from the slides of where she does ...
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How the EM energy-momentum tensor of vacuum state could be proportional to the metric?
We read "everywhere" that, because of Lorentz invariance, the energy-momentum tensor of any field in the vacuum state should reduce to a constant multiplying the metric tensor (I'm using the ...
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Existence and uniqueness of vacuum of fermion or boson operators
Suppose I have a set of boson (or fermion) annihilation operators $\{a_i\}$ defined on a Hilbert space. These operators satisfy the canonical (anti-)commutation rules
$$
\text{boson:} \quad [a_i, a^\...
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Calculating the second-order correlation function for a 2-mode squeezed vacuum state
I am trying to calculate the second order correlation function $g^2(τ)$ at τ (delay) equal to zero, for a 2 modes squeezed vacuum state that is given by:
According to the following paper https://www....
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Does a real vacuum exist actually? [duplicate]
Recently I read some article about vacuum and negative pressure, and the reasoning was like this:
Assume you have a vacuum in a cylinder, and then you move the top of the cylinder (like a piston) up ...
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Field operators on vacuum
What do the field operators $\psi$ and $\pi$ produce when they act on vacuum $|0>$ state?
Here,
$$\psi(\vec{x}) = \int \frac{d^3p}{(2\pi)^{3}}\frac{1}{\sqrt{2E_p}}\left(a_p e^{i\vec{p}\cdot \vec x} ...
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