# 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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### 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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### Speed of sound in vacuum

I am not a scientist but I have a question about speed of sound in vacuum. All I know is that the speed of sound $v$ in a medium is given by formula $$v= \sqrt{\frac E\rho},$$ where $E$ is elasticity ...
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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 ...
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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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### 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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### 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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### Is empty space made of energy?

GR says that matter bends space around it, QM says even empty space must contain something. Is empty space a form of energy?
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### Virtual Particles real? Virtual particles create a universe?

I am reading the book of Lawrence Krauss "A universe out of nothing", where he explained that the vacuum is not empty. It is a boiling brew of virtual particles that come out of their existence. And ...
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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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### 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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### 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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### 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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### Vacuum to vacuum transition amplitude confusion

I keep seeing this for the vacuum to vacuum transition amplitude: $\langle 0,\infty|0,-\infty\rangle_J\,.$ What is $|0,-\infty\rangle_J?$ Am I to take the Hamiltonian with the source present, ie. \$H(t)...
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### Using reflective optics concepts to focus gas pressure in a vacuum

At very low vacuum pressures the bulk behaviour of molecules can be approximated by non interacting particles bouncing off of the chamber walls: For an monotonic molecule such as He with perfect ...
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### Partitioning a single vacuum chamber to isolate out-gassing components?

Planning a DIY vacuume chamber that would contain motors and electronics for manipulating in random experiments My thought is to section the chamber into two parts: clean and dirty - the dirty part ...
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### Locality, unitarity & vacuum energy

I've read in a set of lecture notes that the requirement of locality and unitarity in QFT imply that the vacuum must have a non-zero energy associated with it (http://arxiv.org/abs/1502.05296 , top of ...
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### Temperature of planets without atmosphere

I am wondering how come a planet without atmoshhere loses heat in space when the space around it is a vacuum. In my understanding for one object to lose heat it must have contact with another object/...
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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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### Forces of suction in WIllie Wonka's Chocolate Factory (filmed 2005 starring Johnny Depp) [closed]

Before I begin the question: I am in no way judging this movie, just happened to be casually watching it and saw the scene (referred to below) and thought to post this question. The scene: Boy falls ...
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### Pressure and humidity

Does pressure/vacuum affect water vapor differently than other gases and hence humidity? For example, imagine I have a vacuum bell at atmospheric (mean sea level) pressure and the air in it is 50% ...
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### Can a vacuum make a turbulent flow laminar?

When a vacuum is generated next to a turbulence, does the flow towards the vacuum become laminar? Imagine a vacuum cleaner tube is put next to turbulent air movement, does the "suction" change the ...
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### Are topological vacua of QCD Lorentz invariant?

Are topological vacua of QCD Lorentz invariant or they mix under boosts?
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### What happens to the total volume of a chunk of space that is being sucked into a black hole?

Does it increased, decrease, or stay the same? Maybe it explodes to infinity... Here is a similar question: Do black holes have infinite areas and volumes? But it's different because it asks how to ...
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### How abruptly would you have to brake to form an almost complete vacuum in the back seat? [duplicate]

Suppose you brake with a car (or any other moving object). As the air inside will rush forward, won't there be a relative dearth of air molecules in the back? So, how strong does the acceleration have ...
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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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### Do virtual particles actually physically exist?

I have heard virtual particles pop in and out of existence all the time, most notable being the pairs that pop out beside black holes and while one gets pulled away. But wouldn't this actually violate ...
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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 ...
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### Water in a vacuum sealed jar?

I recently purchased a Vacmaster VP215C chamber sealer, and have noticed that when I place a small container of water into the chamber, and pull a vacuum for just over 25 seconds, the water begins to ...
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### Why does Hauksbee orb or a similar device produce light?

This essentially fits well to the question asked earlier but had to placed as a separate question... An interesting and detailed answer was provided. However, there are few points, originating from my ...
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### If a bell is rung in a perfect vacuum and is suspended by opposing magnets will it ever stop ringing?

As far as I am aware a bell rung in a perfect vacuum would only lose energy and stop ringing due to friction between the bell and the hanging mechanism (due to the lack of air resistance). Therefore ...
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### Can electricity flow through vacuum?

People say yes, and give a wonderful example of vacuum tubes, CRTs. But can we really say that vacuum (..as in space) is a good conductor of electricity in a very basic sense?
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### Does gravity exist in a vacuum?

My understanding has always been that it does from conventional science courses, but really thinking about it, I was wondering if this is really the case. To my limited understanding there is a ...
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### If we go to space why isn't the temperature high? [duplicate]

We know that the temperature in space (which has vacuum) is low. If I go to space will I feel sweaty and hot or chilly? I think I will feel sweaty and hot because the radiation (UV, IR, etc) of the ...
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### Ground state for interacting field thoeries

Are there references where the ground state of an interacting quantum field theory is explicitly written in terms of states of the underlying free theory? For example, let us suppose to have a self ...
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### Why stars are white? According to Rayleigh Scattering

According to Rayleigh Scattering, the red waves are capable of travelling a long distance, so that only we are seeing the Sun as reddish during Sunset and Sunrise. If this was true then all other ...