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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Particles in a box simulation of vacuum system; how to treat scattering from walls?

note: I expect that a microscopic treatment of the rate of heat transfer between gases and solid surfaces will likely need to address this as well and so I'm looking in to that today, but if someone ...
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Vacuum energy density with respect to what reference frame?

Wikipedia quotes the observed vacuum energy density to be around $10^{-9}\frac{J}{m^3}$. Whatever the real energy density is, my question is, with respect to what reference frame is this being quoted?
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Does the speed at which a chain is pulled in vacuum of space, matter? [closed]

If I pull a very long chain attached to a 50 pound dumbbell at $1000 \; mph$ in the vacuum of space (assuming we are uninfluenced by gravity), will the chain break? Take a steel chain for example. The ...
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Do electrons in a vacuum exist in a probability wave or do they have a definite point?

Quantum mechanics says that electrons orbiting an atom cannot be described as having a definite location, but instead exist in a probability function of where they are most likely to be. But, if an ...
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Resources to study quantum fluctuation of zero point energy

What are some good resources to study quantum fluctuation of zero point energy for example the virtual particle antiparticle creation and annihilation?
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Is the quantum vacuum common across the many-worlds?

I don't have the physics to elaborate on this in anything but a hand-waving manner, but this is my conjecture: In the MWI when the universe splits A/B at a collapse event, both A and B originated in ...
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Why in spontaneous symmetry breaking do we only look at the scalar fields? [duplicate]

In all the examples of SSB in our course/the books (even in our SUSY course) we have just looked at minima of the scalar potential. Why do we restrict ourselves to the scalars, why not also minimise ...
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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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Hawking-Page Phase Transition for Charged AdS Black Holes

My question is concerned with the vacuum state of charged black holes in a Hawking-Page type phase transition. Is the vacuum of a charged AdS$_d$ black hole a pure AdS$_d$ spacetime or an AdS$_d$ ...
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How close can refractive index be to one? Classical vs Quantum calculation?

How close can the refraction index of a gas be to one such that it can still be used in classical calculations? For example imagine we have $n-1=10^{-22}$. In [1] I find $n-1=\frac{\gamma_{mol}P}{2 ...
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A simplistic question about virtual particles

Please understand, I am not a scientist. My understanding of "nothing" is that virtual particles are constantly springing into existence on borrowed time and borrowed energy. Almost instantly ...
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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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Is there an exact solution to the Vacuum Einstein Equations for a universe with a single massless particle?

One can think of the Kerr metric as a solution to the EE's with an empty universe and a single non-charged, rotating, massive particle. The stress energy tensor is 0 because we remove the world line ...
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In spontaneous symmetry breaking, can we define quanta of $\phi$ field?

A simple Lagrangian where spontaneous symmetry breaking is possible is that of a real scalar field $\phi$ with quartic interaction $$\mathcal{L}=\frac{1}{2}(\partial\phi)^2-\frac{\mu^2}{2}\phi^2-\...
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Confusion about vacuum fluctuation and the Big Bang

I usually hear physicists say that the Big Bang was probably caused by vacuum fluctuations. However, as I understand from answers here (this one for example), what we refer to by vacuum fluctuations ...
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What is the property of sound that Allows it not to travel in vacuum?

What is the property of sound that makes it does not travel in a vacuum.
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Are impacts in outer space more powerful than on Earth? [duplicate]

Is an impact less destructive on Earth than on other planets with no atmosphere, given that the momenta, factors like the line of impact are identical in both cases? If yes, then is it because there ...
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How can an EM wave create fields in a vacuum?

I know there are a number of questions asking how EM waves can travel through a vacuum. My question is specifically about the oscillating electric and magnetic fields. To my understanding, magnetic ...
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How to calculate the heat energy lost to two steel electrodes in contact with a piece of heated Titanium in a Vacuum

Say within a vacuum chamber I have two steel electrodes in contact with 0.0006 m^2 of Titanium heated to a temperature of 1,800 degrees Kelvin. How would I calculate the heat energy lost via contact ...
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Vacuum energy cancellation

The quantum field theory predicts that vacuum energy should manifest as a repulsive field. At the same time, vacuum energy should be gravitationally attractive. So, attraction and repulsion should ...
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Continuity of $\phi(f)\vert\Omega\rangle$ in Wightman QFT

I have to prove the following statement: $f\mapsto \phi(f)\vert\Omega\rangle$ is continuous, where $\phi$ is a scalar Wightman quantum field, $\Omega$ the vacuum state of the theory and $f$ a ...
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What is the difference between the quantum fluctuation, the zero point energy and the cosmological constant?

I have difficulty to understand the real difference between those three concepts of the energy of the vacuum it's self.( Quantum fluctuation, the zero point energy and the cosmological constant.) I ...
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Why hasn't the false vacuum collapsed yet?

The Standard Model, and current measurements of the Higgs mass, suggest that our universe is in a metastable state, which may catastrophically collapse into a false vacuum. https://en.wikipedia.org/...
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Vacuum energy and cosmic graviton background

What is the best way to show that vacuum energy (the cosmological constant) cannot be the same as a cosmic graviton background (or cosmic gravitational radiation background)?
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Why can we minimize the potential as just a function of a single numeric variable in spontaneous symmetry breaking?

In the discussion of spontaneous symmetry breaking one starts with considerations about the classical vacuum, defined as the field configuration $\Phi(x)$ which minimizes the energy encoded in the ...
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Is there a vacuum for Majorana fermions?

I know this question sounds somewhat odd. But if $\psi = \psi^\dagger$ is the Majorana operator, what would $\psi |0\rangle$ be? Is it the zero state or a Majorana fermion? This is confusing, because $...
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What is the density of Higgs Boson at different places

I understand that the Higgs Field is everywhere, but I don't have a feel for the density, or number, of Higgs Bosons in an area - say 1 cubic metre. Is there 1 mole of HB for every mole of quark in a ...
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What is the physical meaning of $W[J]=\frac{\hbar}{i}\ln Z[J]$?

The quantity $Z[J]$ (which is the generating functional for all Green functions) physically represents the probability amplitude for a system to remain in the vacuum state. Can we find a similar ...
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In a vacuum is there a way of converting the gravitational potential energy between two objects into electrical energy?

I was just pondering something before work started. Could a satellite convert the gravitational pull it experiences as it gets closer to a moon or asteroid into electrical energy? or Could an ...
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Superconducting hoop balloon calculation

A vacuum airship is an airship which uses vacuum as a "lifting gas" instead of helium or hydrogen. The main problem one faces when attempting to design such a vacuum airship is that no practical ...
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Assumption in isolating ground state of the interacting theory in Peskin & Schroesder

In QFT (specifically Peskin & Schroesder), when developing an expression for the ground state of the interacting theory $|\Omega\rangle$, the following expression $$e^{-iHt}|0\rangle=e^{-iE_0t}|\...
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When the EM vector field is given a mass by Higgs mechanism, why isn't this equivalent to a massive photon?

In chapter 6 of Classical Theory of Gauge Fields (Rubakov), we are presented with a scalar field $\phi$ coupled to the electromagnetic vector potential $A_\mu$. In this Lagrangian there is a quartic ...
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How is mass-energy conserved during false vacuum decay?

If we live in the false vacuum, there is a probability that spontaneous vacuum decay could occur: quantum fluctuations could result in a bubble of true vacuum that expands at the speed of light. In ...
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Vacuum energy conversion (to heat)

Two metal plates placed close together in vacuum will collide due to more and more vacuum (electromagnetic) energy being converted from quantum EM modes to kinetic energy of the plates because of the ...
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Does atmospheric pressure determine gravity

If all the air were removed from a room creating a vacuum, would an object be weightless?
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Definition of vacua in QFT in generic spacetimes

I have been learning QFT in curved spaces from various sources (Birrell/Davies, Tom/Parker, some papers), and one thing that confuses me the most is the choice of vacua in various spacetimes, and the ...
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Discrete spacetime: what does it mean for spacetime fields and vacuum?

Suppose we imagine that the space-time continuum is really a discrete stuff of something. This something could be some kind of particles or "substance"/matter/energy field. Then, I see two conceptual ...
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How would you explain that the buoyancy in/on water is influenced by the pressure of the air above the water?

I have difficulties explaining this experience: Principe d'Archimède dans le vide. An object in water does not float. We remove the air on top of the water with a pump, and when the air reached a ...
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Why can the masses of the Higgs and top quark determine whether we live in a false vacuum?

I read in the paper linked below that the ground state of the universe depends on the potential of the Higgs field, particularly the graph of the Higgs potential with its minima and maxima. I think I ...
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Why are perpetual motion machines impossible?

Is the reason we don't have any perpetual motion machines because of the first law of thermodynamics? Would it be possible to create one if (for example) there was a wheel, and it had a push– if it ...
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What is the speed of electricity in a vacuum? [duplicate]

I was looking up the difference of the speed of electricity versus the speed of light online and I found that the speed of electricity can approach (up to 90% of) the speed of light at 186,000 miles ...
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Do QFT Fields Constitute an Ether? [closed]

As all pervasive, stationary fields, do the QFT fields (various Quark, electron, EM, etc.) constitute the modern equivalent of the traditional ether concept?
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Does this paper falsify the vacuum energy? [duplicate]

If Dark Energy is falsified by this paper, https://arxiv.org/abs/1808.04597, does that mean the vacuum energy is also falsified?
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Why isn't current carried through a vacuum?

The empty vacuum of space shouldn't offer any resistance to a travelling electron, and so a large collection of electrons should similarly travel through a vacuum without resistance. As a result, the ...
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Shouldn't quantum fluctuations break thermodynamics?

I learned that particles and antiparticles are constantly popping into existence and out through annihilation. But I also learned that annihilation gives off energy. If this is the case, aren't ...
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Can QFT be constructed without using vacuum?

So my question is simple when doing QFT in classical curved spacetime we found out that we have different sets of complete functions which leads to different vacuum states. And these different vacuum ...
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Vacuum Birefringence with alternating EM waves

I read [1] that in the presence of strong static electric or magnetic fields in vacuum the refractive index changes in such a way that there is a difference of refractive index between parallel and ...
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How did the Atmospheric Steam Engine do work?

Hello everyone and happy thanksgiving! The first workable steam engine was the Newcomen Atmospheric Engine (https://en.wikipedia.org/wiki/Newcomen_atmospheric_engine). It worked through the ...
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Scattering cross-section of a nano-particle with background gas in high vacuum

Let's say I have a Silica nano-particle trapped with an optical tweezer in high vacuum (pressure ~ $10^{-6} \mathrm{mbar}$). I know the molar mass of the background gas and its temperature. How would ...
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Is the cosmological constant problem real?

The cosmological constant problem assumes that the cosmological constant (determined experimentally) can be identified with the vacuum energy density. Theroretical arguments from quantum gravity ...

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