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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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How does the Torricelli barometer create a vacuum at the top of the tube?

Hi everyone! Can someone explain to me how does the Torricelli barometer creates a vacuum at the top of the tube? And how does it work?
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Volume of dark energy in space [duplicate]

As I understand it, Dark Energy is believed to reside in empty space. As the Universe exapnds, more empty space exists inside the Universe and so the small energy per unit of empty space adds up to a ...
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In a spinning tube, how low can the vacuum in the center be?

If you put a gas in a tube, and spin the tube [edit: along the axis of the cylinder], you will get a centrifuge. What's the maximum pressure differential between edge and centre? Asked another way: ...
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Lightning in space, would it be a perfectly straight line?

I have read this question: Can lightning happen in a vacuum? I do understand that here on Earth lightning consists of electrons moving in space and some of these electrons are tracing path, and ...
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Are 40 Kelvin interstellar gas clouds evidence of virtual positron and real electron annihilation

Given that Hawking radiation includes separation of a virtual electron-positron pair, then why cannot it be the case that in the vicinity of a real electron it annihilates with the virtual positron? ...
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Propagation of mechanical waves in vacuum

It is known that, while electromagnetic waves can propagate in vacuum as they do not need a medium, mechanical waves (e.g. sound waves) cannot. However, vacuum has vacuum fluctuations, where (virtual)...
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Pressure Difference in a vacuum environment

We all know pressure is relative, and the pressure of a containment changes with change in its surrounding pressure. Now comes the obvious question: If I have a water balloon half filled in a ...
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Can an electron inside an atom annihilate? [duplicate]

We know that in QFT, all particles are being created and annihilated, and because of the conservation laws, on average the number of particles remains constant. Suppose we have an electron in an atom....
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Are there any real ways at least in theory to manipulate quantum vacuum for propulsion or energy generation? [duplicate]

https://patents.google.com/patent/US10144532B2/en US Navy was granted a patent for polarised vacuum propulsion using microwave radiation and high em energy resonating cavities. It seems to be a ...
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Realistic vacuum boundary conditions in fluid mechanics?

What are some realistic boundary conditions between a fluid and vacuum? Is there an interface or does the fluid kind of spray out into the vacuum?
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Is it possible to create an ongoing vacuum?

This is a crazy thought but here goes. We all know about creating a vacuum in a jar but it is feasible to create a continuous vacuum or low pressure to reduce drag by dispelling or otherwise creating ...
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Will sound be generated by the capture of air from a vacume?

I have a thought experiment. If I had a box sized vacuum sitting on the floor in front of me and I were to instantaneously remove all the walls of my box. Would the capturing of air from that vacuum ...
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What happens when a the volume of a perfect vacuum (0 psi) is increased?

I'm an engineer working on a design in which a "plunger" will be pulled out of a sealed vessel, where the starting volume of the vessel is essentially zero and I need to know what will happen to the ...
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QFT must vacuum states have non zero energy?

Vacuum states of different quantum fields corresponds to different energy levels. Some sources say they are mostly zero, some other says that it is a limit imposed by heisenberg uncertainty principle, ...
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Casimir effect: where did the pressure come from?

From my understanding of Casimir effect, there exists a difference in energy between plates and that of the outside environment. How did this translate to a pressure difference and eventually where ...
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Why are single mode vacuum fluctuations important in Quantum Optics?

There answer here by @ACuriousMind explains that the vacuum fluctuations of a quantum field, free or interacting, always diverge irrespective of spin of the field. But in quantum optics, people ...
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Variance of an interacting quantum field in its vacuum state

A non-interacting quantum field $\hat{\phi}(x)$ can be decomposed into $a_{\textbf{k}}$ and $a_{\textbf{k}}^\dagger$. This enables us to calculate the variance of a free field. For example, the ...
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Empty space inside of atoms [duplicate]

Since most of the space between the nucleus and electron is empty space is that space in a vacuum? I’ve not seen any info on this online or in textbooks does anyone have anything on this?
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Vacuum energy length scale detectable by Casimir effect?

According to Sean Carroll's The Cosmological constant (Eqn.20) cosmological observations imply that the magnitude of the vacuum energy density in natural units is given by $$|\rho^{(obs)}_\Lambda|\le (...
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Friedmann vacuum solution linear rather than exponential?

Does the Friedmann vacuum equation have a linear solution rather than an exponential one? Using natural units one can write Friedmann's equation for the vacuum as $$ \begin{eqnarray} \left(\frac{\dot ...
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Virtual pair of particle-antiparticles trajectory [duplicate]

Is it possible to do heuristic calculations on virtual pair of particle-antiparticle trajectories that appear in a vacuum? For example, what is the maximum distance between them during virtual process?...
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Symmetry and symmetric vacuum in Quantum Field theory

In the start of section 28.2 of Schwartz's Quantum Field theory and the Standard Model, Schwartz states that for a conserved charge, $\hat{Q}$, which generates the corresponding symmetry ...
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Does a vacuum solution to the Einstein equation imply flat spacetime?

I have read that a solution to the vacuum Einstein equation has a vanishing Einstein tensor, and therefore a vanishing stress-energy tensor. This means that there is no matter to generate spacetime ...
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How fast will air travel to fill a vacuum?

Suppose I have a sealed glass cylindrical vessel of radius r and length l that is evacuated. I smash one end. How long will it take for air to (a) reach the end of the cylinder (b) fill the vacuum ...
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Strong empirical falsification of quantum mechanics based on vacuum energy density

It is well known that the observed energy density of the vacuum is many orders of magnitude less than the value calculated by quantum field theory. Published values range between 60 and 120 orders of ...
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Why do people think that rockets can thrust in the vacuum of space? [duplicate]

A force is required to change the momentum of the rocket exhaust which consists mainly gas moving out of the rocket chamber. People think that it is the rocket that pushes the gas out. If this were ...
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Can our universe be a true vacuum bubble?

The paper "Spontaneous creation of the universe from nothing" by Dongshan He, Dongfeng Gao and Qing-yu Cai claims that our universe was created by the quantum fluctuations in the metastable false ...
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Are wave equations equivalent to Maxwell's equations in free space?

In free space, do Maxwell's equations contain the same amount of information regarding electric and magnetic fields as is contained in the wave equations derived from them? If so, how?
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Divergent integral problem

When expanding the scalar field vacuum energy $$\sum_k \frac{1}{2} \omega_k = \frac{1}{2} (L/2\pi)^{n-1} \int \omega(k) d^{n-1}k = \frac{(L^2/4\pi)^{(n-1)/2}}{\Gamma(\frac{n-1}{2})} \int_0^\infty (k^...
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Could the cosmological constant be due to vacuum fluctuations in a box, i.e., in a finite universe?

Assumption: If the universe were a finite box whose boundary is the cosmological horizon, then there would be a zero-point energy inside that box. Consequence 1: This zero-point energy would be given ...
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Why can't we superpose two quantum vacuum states?

i read in this paper (Spontaneous Symmetry Breaking as the Mechanism of Quantum Measurement by Michael Grady) that we are not allowed to consider the superposition of two vacuum states. i do not ...
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Is there only one vacuum solution of the Einstein equations?

I am thinking about this: A vacuum solution means vanishing Ricci tensor. The Ricci tensor is a contraction of the Riemann, which itself involves contains second derivatives of the metric. Thus they ...
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Expressing the vacuum projection operator in terms of number operator

I've been reading this book, in which the author expresses the vacuum projection operator $\vert 0\rangle\langle 0\vert$ in terms of the number operator $\hat{N}=\hat{a}^{\dagger}\hat{a}$, where $\hat{...
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Vacuum energy in continuous phase transitions

In a first-order cosmological phase transition, the tunneling from the false to the true vacuum (see left picture below) releases false vacuum energy corresponding to the potential difference $\Delta ...
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Layperson wondering about The power within one protium atom (1H) or H

Within 1 hydrogen atom (1H) protium we have 1 electron the half life of this stable isotope is 10 to the 34th power years. It can fuse into Helium if 4 atoms fuse when the Coulomb force is overcome ...
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How to calculate vacuum energy density? Do we need to sum up the zero-point energy of all kinds of fields in the vacuum?

If we are not sure whether the Standard Model has already included all the fields in the nature, then how can we calculate vacuum energy?
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Could pressure differentials be used to produce power?

There is potential energy between something like a vacuum in a container and a gas on the outside of it, or vice-versa. Could this energy be harvested in a vacuum, or close to vacuum situation like on ...
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Harnessing molecule vibration energy

Disclaimer: I am learning physics for fun, please dont kill me but explain where I am wrong. As I understand all molecules have a lowest energy state in which they posses some amount of momentum even ...
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Einstein-Hilbert action and Lagrangian density for vacuum Ricci scalar

From the action, $$\int L\,\mathrm dt=\int R \sqrt{|g|}\,\mathrm d^4x,$$ why is the Lagrangian density for the gravitational field replaced by the Ricci scalar, which yield field equations in vacuum $$...
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Is it possible to slow down the speed of light in a vaccum? [duplicate]

Is it possible to slow down the speed of light in a vaccum?
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Speed of waves in vacuum

All electromagnetic waves travel at speed of light in vacuum. Gravitional waves also travel at speed of light. I am having this vague notion that all waves in vacuum must travel at speed of light. Is ...
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Is the quantum harmonic oscillator energy $E = n\hbar\omega$ or $E = (n + 1/2)\hbar\omega$? (Feynman Lectures)

Please, read the whole question. I've discussed a few contradictions and so far have not found an explanation for them. I was reading The Feynman Lectures on Physics (vol. 1), the part where he talks ...
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Can there be charges in free space without it being on some particle?

We see leptons and quarks possessing charges. Can there be charge in free space devoid of matter(neither leptons nor quarks or anything else)?
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Questioning whether gravity is strictly attractive. Is there a possibility for repulsion?

My teacher wanted to test our understanding before starting a new topic. The question he gave goes something like this “There are 2 vacuums present here about which there is an abundance of mass ...
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Why accelerating observer can see Unruh radiation?

I read that uncertainty principle allows a pair of virtual particles to spawn in a vacuum as long as time is $h/E$ and nature forbid negative energy to exist, a accelerating person will see the photon ...
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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)...