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 Space Between Atoms And Sub-Atomic Particles And More [closed]

I was wondering what the space between atoms or electrons is called. Is it Vacuum ? And what is in there ? Is it really free or empty space ? And if so, how can nothing exist ? It is a bit of an odd ...
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Does anything exist in the intergalactic space?

I am a part time physics enthusiast and I seldom wonder about the intergalactic space. First, it is my perception that all(almost all) the objects in the universe are organized in the forms of ...
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141 views

Is space really empty? [duplicate]

This guy here says space is not empty.. It explains how space inside nucleus is Full of fields. Does it mean to say gluons are present everywhere, even outside nucleus? Consider a region without any ...
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25 views

What is meant by a “change in volume of a system”?

I keep getting confused when my professor talks about the change in volume of a system. Sometimes it seems as though he's talking about the volume of the gas and at other times he might be talking ...
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2answers
37 views

Does eq. of continuity hold in vacuum too?

When a streamlined flow of water flows down through an ordinary tap, it's cross-sectional area decreases according to eq. of continuity due to atmospheric pressure. If the same apparatus were to be ...
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4answers
451 views

Can I blow soap bubbles (of air) inside a vacuum chamber?

When I blow soap bubbles from a liquid dish soap mixed with distilled water at atmospheric pressure at ground level both internal and external air pressure nullify and the tension of the bubbles ...
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3answers
99 views

Thinking about the properties of 'nothing' [closed]

If a certain identifiable part of space that has no type of measurable energy fields manifesting 'in it' for a given duration ; is such a totally empty space the same as 'nothing'? Anything with any ...
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41 views

Imaginary part of the stress-energy tensor

I just encountered in an article of D. G. Boulware ("Quantum Field Theory in Schwarzschild and Rindler Spaces", Phys. Rev. D 11, 1404, 1975, in the last paragraph of the Introduction) the statement ...
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266 views

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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88 views

Vacuum has both zero four-momentum and nonzero vacuum energy?

I have heard that in QFT, the vacuum has zero four-momentum: $$P^\mu |\Omega \rangle = 0.$$ However, I also know that the vacuum has vacuum energy, i.e. $$ \langle \Omega | H | \Omega \rangle = E_0 ...
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52 views

How does water height in a vacuum chamber effect pressure

I am testing for package leaks in non-porous packages. Quick details are: 1) Package is sealed at atmospheric pressure. There is some headspace inside the package which is just air. 2) A small hole is ...
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Why is it impossible to have a perfect vacuum?

In another question someone mentioned that it couldn't happen. Why not? For example I asked about the speed an object would have to move at sea level to create a vacuum behind it; in the comments ...
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48 views

Balloon in a vacuum

What arrangement will a mixture of low density gas and high density gas take inside a balloon (in a vacuum chamber) in zero gravity? FYI: water boil then freeze's in a vacuum. which one will stick to ...
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31 views

Can we enhance a thermal gradient by combining a dark surface and a shiny surface with an external glass layer?

I refer to the article at this site: http://solarcooking.wikia.com/wiki/Solar_Kettle-Thermos_Flask As we know, dark surfaces absorb radiation (eg. solar water heater), while shiny surfaces reflect ...
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2answers
61 views

why is there no total vacuum condition on earth? [duplicate]

I know that Bell jars are often used in laboratories to form and contain a vacuum but not total vacuum like space.So i don't understand why can't human make vacuum bell jar a total vacuum state?
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41 views

what would happen to flowing electrons in a vacuum if they are not giving any exit point?

Lets say theoretically electron flow is captured in a vacuum and not allowed to exit then where would they go? I do not want to know the practical impossibilities of it. And also what would happen if ...
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1answer
20 views

HV Vacuum seals

I have a vacuum port that is 8.75" in diameter, it was attached to a block of aluminum. I am machining a piece of stainless steel to make a blank for it since it is a non-standard size. What are my ...
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168 views

Orbit in the vacuum

As the space is a vacuum and there is no friction in space, Can we assume that, if we place an object in gravity in exactly the right distance from a planet with gravity and in the right acceleration, ...
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3answers
86 views

Why would we freeze in space if there is no matter to conduct the heat away from us?

If a near perfect vacuum is assumed to be in space, how can heat leak around from our body for example? Although theoretically energy wishes to spread equally all around, it still needs a medium to ...
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3answers
50 views

Motion in vacuum [closed]

If we have a hollowed sphere in a vacuum, and its hallow space is filled with vacuum. In the center of the hollowed space inside the sphere is a ball. If we push the sphere does the ball move? (prior ...
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How is a vacuum able to propagate light?

We say that sound waves need a medium to propagate and we know that light doesn't need such a thing. But is that really how that works? There's no such thing as "nothing" according to Quantum ...
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1answer
47 views

Methods to solve a vapor pressure equilibrium question with water on the moon? [closed]

"Imagine a tall column of water on the Moon, maintained at a temperature of 50°C and left to the open vacuum at the top. Up to what depth will the water continue to boil? The Moon's radius is 0.273 ...
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738 views

Finding the vacuum which breaks a symmetry

I will start with an example. Consider a symmetry breaking pattern like $SU(4)\rightarrow Sp(4)$. We know that in $SU(4)$ there is the Standard Model (SM) symmetry $SU(2)_L\times U(1)_Y$ but depending ...
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96 views

Is the empty space really empty? [duplicate]

I've come across another article in "list verse" which says that the empty space is not actually empty at least for a while. I've tried to find about this, so I googled it .It also quotes a word ...
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302 views

Is false vacuum bubble nucleation possible in our universe?

Is it possible that a false vacuum bubble to nucleate into our universe rather than a true vacuum one ? If yes,it will expand at speed of light within our spacetime or what ?
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Could a perfect vacuum exist at the boundary of the universe?

Space is not truly a vacuum because of our observation of quantum foam, but if causality does not exist outside our universe, could that mean that quantum foam cannot exist outside our observable ...
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131 views

Atoms, Gravity and Electrostatic Charge [closed]

How close do 2 atoms of any type the have can be together before gravity with an electrostatic charge that repulses?
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29 views

acrylic vacuum chamber design

I want to build a vacuum chamber for experimentation from acrylic sheets, ideally a cube $60~\textrm{cm}$ on each side. Assume that the chamber can be pumped down to theoretical perfect vacuum. How ...
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905 views

A water balloon in vacuum: does it boil?

If I put water in a vacuum it will boil. But what if I put this water inside a balloon ? I searched for answers and fount this video: http://www.youtube.com/watch?v=9q8F3ClUuV0 It seams that the ...
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0answers
18 views

What result would I get from series-mounted vacuum assist? (hydraulic vacuum assist)

If I install two inline vacuum assist devices (such as VH44) on my clutch line, what will change in comparison to having a single boost? Will it decrease pedal travel? Tension? Both? Neither? Lest ...
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2answers
197 views

What happens with liquids in vacuum? [closed]

I am wondering what would happen in a situation where there is some liquid in a closed container A is vacuum and B is the liquid. I am also interested if there are any differences in behaviour ...
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87 views

Angular momentum of the vacuum

I'm studying quantum field theory from "An introduction to Quantum field theory" by Peskin and Schroeder and from "A modern introduction to quantum field theory" by Maggiore. I've read from "An ...
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4answers
2k views

Why is normal ordering a valid operation?

Why is normal ordering even a valid operation in the first place? I mean it can give us some nice results, but why can we do the ordering for the operators like that? Is its definition motivated by ...
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28 views

Baryonic operators in ${\cal N}=1$ $U(N)$ SQCD in four dimensions

Seiberg's duality is usually considered as a duality for $SU(N_c)$ theories with $N_f$ flavors. In his case, the vacuum for $N_f \geq N_c$ is parameterized by mesons $M$ and baryons ${\bar B}$ and ...
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Bell in a vacuum, where does the sound energy go?

I'm not educated in physics, but I learned that a bell struck in a small vacuum chamber will not be heard by people around it (in a school science lab). If it had been surrounded by air, there would ...
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557 views

Why does the QCD vacuum have zero momentum?

Today in the hadron physics tutorial we were talking about the Fabri-Picasso theorem where one step in the proof involves $\hat P |0\rangle$ which is the four-momentum operator on the vacuum. And from ...
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20 views

How to Calculate Pressure From Earth up to Space at Certain Height? [duplicate]

https://en.wikipedia.org/wiki/Vacuum#Measurements_relative_to_1_atm https://en.wikipedia.org/wiki/Pressure_measurement#Thermal_conductivity I wonder if there's a clear equation for this calculation. ...
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38 views

Cryogenic (LN2) gas vs liquid for cooling

For cooling, would you recommend using gas over liquid or vice-versa? What is the temperature differential between gas and liquid? In other words, at standard volumes and pressures from a gas ...
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7answers
1k views

Do all massive bodies emit Hawking radiation?

It is known that any accelerated observer is subject to a heat bath due to Unruh radiation. The principle of equivalence suggests that any stationary observer on the surface of a massive body should ...
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1answer
210 views

Can Impossible Vacuum balloon be possible with this idea?

As it is well known, a vacuum balloon using the materials we have at our disposal is not possible, because of the sheer force they have to resist from the air outside. I have an idea and I want to ...
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126 views

What happens to a sound wave going from air to vacuum?

Let's say you are in a space ship. The inside is filled with air, a medium in which sound waves can exist and travel. Then there's a wall, still a medium in which sound waves can exist and travel. And ...
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5answers
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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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1answer
34 views

What is the temperature of a vacuum? [duplicate]

what is the temperature of Vacuum since temperature of a system is related to the average of the molecular kinetic energy and there is no molecule in a vacuum? i know there could be radiations but i ...
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23 views

Can we lock electric charges in dielectric cells?

Suppose next. We using Wimshurst machine and gathering charges in dielectric cells such as mica .Before discharge we put whole machine in vacuum chamber.Question is next. Can we storage those charges ...
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26 views

possible x-ray production, low pressure discharge

What is the maximum pressure at which a high voltage discharge can produce x-ray radiation? I am experimenting with plasma in the form of ionized air in my vacuum chamber, maximum vacuum possible is ...
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1answer
39 views

Perfect vacuum in experiment [closed]

When conducting experiments to determine the speed of light in a perfect vacuum does that vacuum(?) replicate outer space?
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211 views

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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60 views

sound propagation at low pressure

I am curious about the properties of sound at low atmospheric pressure. Not the speed of sound, I want to know how lower pressure will affect the distance sound will carry and the frequency range. For ...
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649 views

What is “Energy” of a vacuum in the context of quantum theory?

I'm not a physicist or cosmologist, so I hope I am asking the right question with the right words here. My question regards the word "energy" as it pertains to quantum vacuum states, and to concepts ...
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Superheating Water Demonstration with a Vacuum

There are many Youtube videos which place a cup of water into a vacuum chamber and cause boiling around 0.020 atm, but I can't find any which show a vacuum-only "superheating" effect (to be clear, I ...