# Tagged Questions

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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### Suction from flowing water

My memory from physics says yes but I want to check. Our pool is dirty and our vacuum is broken. If I were to stick the vacuum hose into the pool drain, would the flow of water going into the drain ...
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### Is the vacuum empty? Are virtual particles in the vacuum? Is the vacuum non-zero? [duplicate]

I have read a lot about this stuff. Is the vacuum empty? How is it not-empty? But nobody can it explain serious and simple that I can fully understand it. Some physicists tell may that virtual ...
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### Can you record sound through vacuum? Like this: (object)(vacuum)(object)

There are these videos on youtube that play sound of Jupiter for example: http://www.youtube.com/watch?v=e3fqE01YYWs Does anyone know if this is real at all? How can you record sound through vacuum ...
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### Why vacuuming an air chamber is much slower than vacuuming an argon chamber?

When pumping a chamber full of air down to a certain level of vacuum, it takes a while. However, when that same chamber is full with argon, reaching the same level of vacuum is much faster. What makes ...
232 views

### How to calculate planar window's buckling pressure in vacuum chamber wall

I can't find the formula, I can see some formulas for circular windows are given here [1] (thanks CERN!). For example with a circular (flat/dome?) window, buckling pressure ($p_\text{CL}$) and max ...
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### Difference between vacuum and pseudovacuum vector?

What exactly is the difference between the vacuum and pseudovacuum vector? In my case the ground state of a system is the vacuum vector and by letting operators act on that vacuum vector magnons are ...
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### Does the density of virtual particles decrease when space expands due to dark energy? [closed]

I understand that vacuum (i.e. QED vacuum) is theorized to contain spontaneously appearing and annihilating pairs of virtual particles. Suppose the average density of those particles at a given moment ...
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### Pressure - How much fluid can void support?

Please refer to the attached (terrible) drawing while reading the post ! After watching some videos about the U-tube effect in drilling, a question came to me. Imagine one fluid of heavy density ...
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### Does it take infinite energy to create a perfect vacuum?

Question is inspired by a recent burst of perpetuum mobile-type questions. It would be nice if one could simply discard them all (or at least the huge class that assumes some kind of perfect vacuum to ...
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### How does the fluid's vapor pressure in aspirator (pump) relate to strength of vacuum?

From wikipedia: If a liquid is used as the working fluid, the strength of the vacuum produced is limited by the vapor pressure of the liquid (for water, 3.2 kPa or 32mbar at 25 °C). https://en....
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### What exists in the Space between quarks

Apologies to all if this has been asked before, I searched but was unable to find one similar. This is a question that has been bugging me for a while that i haven't really been able to find a ...
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### Does string theory have a notion of vacuum?

Does string theory have a notion of vacuum? If yes, what is known about it?
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### Why does very cold water in a thermos cause there to be strong suction on the cap?

After putting ice-cold water in a thermos, the cap is strongly held on by what feels like suction. I assume the cold water condenses the air, thus lowers the pressure inside, but can someone explain ...
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### Can I say that the two-body problem is also a vacuum solution for the special case of two orbiting black holes?

A two body system is one where two bodies orbit each other. In the case of two orbiting black holes, since an individual black hole is described by a vacuum solution, can I say that the two-body ...
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### Can you stop an electron in vacuum?

If we shoot an electron in vacuum tube, then stop it with electromagnetic field, and switch off the field, what will happen with electron? Will it continue its movement? If there is a gravitational ...
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### Why is space a vacuum? Also, why doesn't air from the Earth escape into space? [duplicate]

Why is space a vacuum? Also, why isn't the air from the Earth escaping due to the vacuum in space? The ozone layer is only gas and a magnetic field, so why doesn't the air escape from Earth into space?...
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### Resonance and natural vibrations in vacuum

In my Physics textbook, it says that if two pendulums of the same natural frequency are placed next to each other and if one is set into vibration, the other starts resonating and when the first one ...
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### What's the difference between vacuum particle-antiparticle annhiliation and regular annihilation?

Why does vacuum particle-antiparticle creation and annihilation result in nothing rather than photons? What is the difference between that and regular annihilation that does result in photons.
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### Infinite Accelatation

Before I ask my question, let me just say, I know very little about particle physics and general relativity, so I may ask a obvious question or a question that makes little or no sense. Now, what ...
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### Can a pure vacuum with 0% gas be created? [duplicate]

If we were to create a vacuum room with no air in it to avoid air resistance can it be done?
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### Vacuum pressure equivalent in a siphon hose filled with water?

So, I was thinking about how siphons worked today, and no matter how high or low the tube goes, as long as the end is lower than the start, water will flow. So, if you took a hose, ran it up 50 feet,...
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### Is it easy to create a vacuum in space?

Say for example you have a closed, empty, and air-tight plastic bag, then you can't grip it from each side and pull the sides apart because for that to work a vacuum would need to be created inside ...
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### Cosmological constant in General Relativity [duplicate]

According to my GR notes the cosmological constant can be thought of as a vacuum energy much in the same way as the ground state of the harmonic oscillator. The notes claim that the regularised energy ...
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### How do EM waves travel in a vacuum? [duplicate]

Apart from that electric and magnetic field variation thing, is there any other explanation? Can photons simply pass through vacuum?
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### Quantum gravity- Vacuum catastrophe

Why does the predicted mass of the quantum vacuum have a very little effect on the expansion of the universe?
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### Difference between Cosmologial Constant and Quantum Vacuum State

Hello I am very new to cosmology and quantum physics. I need some basic understanding (in Layman's term) of the Difference between Cosmological Constant and Quantum Vacuum. Cosmological Constant is, ...
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### Can high speed moving hydrogen atoms drive turbines?

We know that hydrogen is a part of air so if we accelerate hydrogen atoms in a circular vacuum tube as done in a particle accelerator, can the high speed moving atoms of hydrogen drive a turbine if we ...
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### If you brought a hollow one-inch cube of steel filled with air into space, would the air exert a pressure of 14.7 psi on the cube?

In my thought experiment, since air exerts $14.7$ psi at sea level, the air within the cube of steel should exert the same pressure outward, $14.7$ psi. Right? The whole thing about balanced air ...
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### Could a vacuum airship be possible? [duplicate]

According to Wikipedia, a vacuum airship is a hypothetical airship that is evacuated instead of using a lighter gas. Really, once I first saw this, I thought, "Why did I never think about this before?!...
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### Are dark energy and zero-point energy the same thing?

According to Quantum Mechanics is it possible that the famous "dark energy" and "zero-point energy" are the same thing that drives the accelerated expansion of the universe or maybe related to each ...
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### Can we spin a top in vacuum?

What happens to a top if we spin it in vacuum. Will it have any difference to rotating in a normal surface to a surface in vacuum.
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### Propagation speed of photons when taking higher-order QFT corrections into account

In our group of experimental physicist who have nothing to do with and know very little about quantum field theory, we recently had a question concerning the propagation speed of photons in vacuum: ...
14k views

### How can a black hole produce sound?

I was reading this article from NASA -- it's NASA -- and literally found myself perplexed. The article describes the discovery that black holes emit a "note" that has physical ramifications on the ...
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### Speculative experiment: A golf ball at the frontier of the universe

Consider a golf ball in the center of an empty sphere (maybe a GR vacuum, I'm not so sure). Consider this empty sphere as being the only space available to the golf ball, it is surrounded by nether. ...
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### How is possible to hear mechanical sounds in space?

In the footage taken by U.S. astronaut Terry Virts during spacewalk (EVA) on the International Space Station on 25.02.2015, sounds can be heard while in space. I can understand "shaking" sounds while ...