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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The total energy in the Casimir effect
In the usual derivation of the Casimir effect between two large conducting plates, one finds that the energy in the empty space (relative to the ground state energy one has when the plates are ...
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Objects in a perfect Vacuum
Suppose An isolated room. I somehow created a perfect vacuum (0 atm) inside the room, and placed an object inside it, will the object explode and all its molecules will be scattered throughout the ...
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Is it possible to produce protons from vacuum polarization?
Is it possible, according to the standard model, to create proton-antiproton pairs from the vacuum? I know it is possible to do it with photons and electrons, but is it theoretically possible in the ...
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Why aren't there in vacuum any charges nor currents?
In this video (MIT $8.02$ course titled "Electricity and Magnetism", video number $214$, taught by Pr. Krishna Rajagopal), professor considers Maxwell's equations in the special case of the ...
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Vacuum Energy Versus Fundamental Force Higgs Field Unification State
The Hubble constant H = ~70km/s/Mpc +/- 5% has not changed since the period of recombination, t ~ 379,000 years after the Big Bang, which follows the separation of the Higgs field unified fundamental ...
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Inflationary Expansion and Vacuum Energy
During inflationary expansion, the spatial dimensions of the spacetime metric each expand by a factor of $10^{26}$ in $10^{-32}$ seconds. This super-luminal expansion from a universe radius of $3\...
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Zero-point connected correlator $\langle 1 \rangle_C$ is not 1?
This is so confusing: books are saying that connected correlator is given by
$$\langle \phi(x_1) \phi(x_2) ... \phi(x_n) \rangle_C = \left.(-i)^{n-1}\frac{\delta }{\delta J(x_1)} \frac{\delta}{\delta ...
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Why can we set $\Phi_{fv} = 0$ as the limit when $\rho$ tends to infinity?
On Pg.14 of Dine, Leigh, et al's Towards The Theory Of The Electro-Weak Phase Transition, they reduce the 3-dimensional instanton equation to: $$\frac{d^2 \phi}{d \rho^2} + \frac{2}{\rho}\frac{d\phi}{...
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Can the Casimir force produce a non-zero force component in the 𝑦 y-direction when acting on plates arranged at an angle?
The Casimir force is typically considered between two parallel plates, where it results in an attractive force perpendicular to the plates. However, I came across an article in which the author ...
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The path integral representation of the transition amplitude between the vacua of two field theories
The background of the question: PhysRevLett.115.261602.
$
\newcommand\ket[1]{| #1 \rangle}
\newcommand\braket[1]{\left\langle{#1}\right\rangle}
\newcommand\dif{\mathrm{d}}
\newcommand\E{\mathrm{e}}
$...
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Could our Universe have a insanely small 'drag coefficient' that results in a non-infinite speed of light [closed]
Could our universe have some way of having a insanely small 'force' that slows down objects an incredibly small amount, but at relativistic speeds, it would restrict massless particles to a specific ...
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Can anything have permittivity and permeability less than that of vacuum? [duplicate]
Is it possible for something to have permittivity and permeability less than that of free space? Because space is not really truly empty as annihilation and formation of matter and antimatter ...
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Reeh-Schlieder theorem: what's the matter with the Taj Mahal?
I'm currently struggling to understand the implications of the Reeh-Schlieder theorem - having little mastery of QFT formlism, let alone AQFT.
Its connection with vacuum state entanglement, although I ...
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Vacuum entanglement: between what and what, exactly?
I sometimes read that the entanglement of the vacuum state of a field -- maximal and ubiquitous -- is an inescapable axiom of QFT. In articles often oriented towards AQFT, but also in this ...
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Smoothing Pump Pressure Spikes with a Helmholtz or Pipe Resonator?
When a roots blower runs, it has some oscillation in the flow rate (and consequently pressure) due to lobe geometry. The pattern occurs $4$ times per rotation, so for a direct drive $1800 \ \text{rpm}$...
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Why can't a vehicle (in a vacuum) propel itself by accelerating and decelerating a rotating mass?
I understand that a vehicle cannot change velocity by accelerating a mass from the front to the back, as it will need to decelerate the mass (and return it to the front), which cancels out any change ...
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Are there any special vacuum cases of quantum gravity theories like there is for the General Theory of Relativity?
General Relativity has Special Relativity as a special case of the general theory in vacuo. Do theories of quantum gravity have general and special cases for in vacuo limits as well, or is this not ...
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How are continuous wavevector components dealt with in vacuum energy calculation?
I'm currently working on calculations relating to the Casimir effect, the first and foremost of which is solving for the energy content of a vacuum (I'm starting with the simple two-conducting-plates ...
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Vacua in holography?
I was reading some papers* on celestial holography which aims to apply the holographic principle to a flat spacetime, making a duality between a celestial sphere and a celestial conformal field theory ...
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Working of Siphon in Vacuum
I have just studied about working principle of a siphon, I read that atmospheric pressure is one of the main agent in its working principle, but I was amazed to know that it could also work in vacuum ...
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What exactly does one mean by a "vacuum sector" in a Hilbert space?
I was going through a rather unique but interesting paper (arXiv) by Chiribella on an extension of Quantun Shannon theory to include even quantum trajectories.
In his paper, when a system corresponds ...
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In vacuum decay, why must the bounce solution be a stationary point, but not necessarily a minimum of the Euclidean action?
In Chapter 12 of Weinberg's Classical solutions in QFT the author discusses vacuum decay and in particular the thin wall approximation. Eq.12.32 describes the action of the solution as a function of ...
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How vacuum tube diode works?
I am on journey to learn about world of electricity and all around it.
I have come to the topic of vacuum tube diodes and having hard time to understand what is going on.
I will start with how I ...
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Does vacuum polarization strengthen or weaken the electric field emitted from a proton?
I’m currently reading Rafelski and Muller’s The Structured Vacuum, and I’m a little confused by something they’re saying. I wouldn’t exactly call this a pop-physics book, but it’s pop-ish, so it’s ...
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Can there be decoherence of quantum fluctuations in Minkowski spacetime?
I was reading a paper (https://arxiv.org/abs/1008.0808) on whether observers (like Boltzmann Brains) arising from vacuum fluctuations could occur in a Minkowski vacuum. I had a a question on this:
The ...
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Does air filling a vacuum produce a force?
Imagine you have a vacuum chamber set at a complete vacuum, and there is a valve to let air in.
If you open this valve, the air molecules will start moving into this empty area, eventually filling it.
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If virtual particles are a convenient way of unpacking the maths of quantum field theory, isn’t it possible that THAT’S what’s real? [closed]
If virtual particles don’t exist, then what are, for example, the electron positron pairs that appear and disappear? One drifts beyond the event horizon, and one becomes a real particle.
This stuff ...
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How dense exactly is a vacuum in space (because of quantum fluctuations)?
You hear all the time that quantum fluctuations take up a given amount of energy in a vacuum, and this is how experiments such as The Casimir Effect gets the results that they do.
Have we actually ...
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What does stable/meta-stable vacuua actually mean in theories with spontaneously broken symmetries?
In SSB, there exists a scalar field has non-zero VEV. So we redefine the fields to have zero VEV for several reasons. But what is the vacuum used in calculation of the correlators in this field and ...
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Can there be a progressive and slow vacuum transition event instead of a sudden one?
I have a question on transition events between vacua, and what do our models predict that would happen:
Could there be a transition between vacua without involving a sudden event like a bubble ...
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How can the future of the universe and heat death be affected by fluctuations?
I got this question after reading a bit into heat death (https://en.wikipedia.org/wiki/Heat_death_of_the_universe#Time_frame_for_heat_death)
In that section, it is indicated that:
It is suggested ...
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Can a vacuum reverse rusting of iron?
In this answer, by appeal to Le Chatelier's principle, it is predicted that increased pressure would accelerate the process of rusting iron. Symmetrically, Le Chatelier's principle suggests that ...
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Higgs VEV and the Minkowski metric
The empty spacetime is described by the Minkowski metric. However, does the Higgs VEV has any effect on the Minkowski metric? If so, how?
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Why does the imaginary time Euler-Lagrange equation imply the potential goes to zero at infinite imaginary time?
On reading up about the bounce solution for false vacuum decay in S. Coleman's The Fate of the False Vacuum I it was stated that the equation
$$0 = \frac{1}{2} \frac{\partial q}{\partial \tau} . \frac{...
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How can a non-derivative interaction involve the derivative of a scalar field?
I was reading up on the paper "The Fate of the False Vacuum" by Sidney Coleman and the claim is made that a scalar field with standard Lagrangian density:
$$
L = \frac{1}{2} \delta_{\mu} \...
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Could a single gamma ray photon break the Schwinger limit? If so, at what energy?
Is it possible for a ray of light, or even a single photon, to 'break' the vacuum of space?
If so, at what energies (in eV, e.g.) would this happen?
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Calculate number of air particles going through a hole in high vacuum at molecular flow
I have a vacuum chamber, connected to a vacuum pump with a pipe of diameter 50mm and need to create a high (0.0001mBar) vacuum.
I need to calculate the total suction time, and since I was not in the ...
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Vacuum flucutuations = local entanglement between quantum fields?
I'm puzzled by this statement by Dieter Zeh: "Various types of quantum fluctuations (in particular vacuum fluctuations, often visualized in terms of 'virtual particles') are used to describe ...
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Static Patch Decomposition of Bunch-Davies Vacuum
In the Jerusalem Lectures on Black Holes section 3.3 the author considers a QFT in Minkowski space. He then picks out a space coordiante, say $x$, and divides the Hilbert space $H$ of the QFT in two ...
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Is it possible to lower the energy of the vacuum?
The energy of the vacuum is given by $$\sum_k \frac{1}{2}\hbar\omega_k.$$ However the frequency $\omega_k$ depends on the wavevector $k$ and some constants like the speed of light $c$, which in turn ...
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Could cosmic rays induce a vacuum decay in the future?
I've been told that very energetic cosmic rays could cause a vacuum phase transition or vacuum decay (and even could cause a true vacuum level to go "uphill" to a false vacuum) due to their ...
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Bogoliubov transformation of Bunch-Davies vacuum
Let $\left|0\right>$ be the Bunch-Davies vacuum state of a QFT, for example a free scalar field, in de Sitter space. The creation and annihilation operators w.r.t. this state is a vacuum, i.e. $a^...
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How does gravity overpower a vacuum?
While watching experiments with vacuum chambers, I had a thought.
If you put a sealed box at normal atmospheric pressure inside a vacuum chamber, pumped out the air and pierced the pressurized box I'd ...
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Theoretically, can perfectly flat space exist in the universe?
According to general relativity, mass and energy cause the curvature of space. To have perfectly flat space, there must be a completely empty vacuum state with no mass or energy.
Theoretically, is it ...
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Do all quantum fields fluctuate in interstellar space?
For a while now I have heard that the explanation behind the non-zero energy of vacuum space is due to quantum fluctuations. Sometimes this phenomenon has been described with virtual particles, where ...
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Radial reparametrization ansatz in Schwarzschild metric derivation
The standard derivation of Schwarzschild solution (and Birkhoff's theorem) seem to begin with the most general spherically symmetric static metric
$$ds^2 = -U(\rho) dt^2 + V(\rho) d\rho^2 + W(\rho) \...
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What does it mean for particles to be created?
I am right now studying scalar (semi) quantum electrodynamics, i.e. a charged Klein Gordon field coupled to a background classical electric field in 1+1 spacetime dimensions.
The setup is as follows:
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Is there a formula for calculating the strength of a suction? [closed]
Let’s say I have a plunger and I know the area of where it suctions, the volume of the vacuum, and assuming it had been completely sealed and has 100% vacuum (not likely!)
Could I figure out how much ...
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Can absolute silence exist and how are thermal and quantum noise a limit? [closed]
For my exam, I must answer the question: can absolute silence exist? While doing research, I obviously heard about noises internal to our body and noises external to our environment but I also heard ...
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Vacuum solutions in presence of mass?
Here is the page I will be referencing: Vacuum solution (general relativity) - Wikipedia
My point is: if $T_{\mu\nu}=0$ implies that there is no mass, how can Schwarzschild vacuum be a solution, if ...
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